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1 EFFECTS OF NEUROMUSCULAR ELECTRICAL STIMULATION INTENSITY AND BOLUS SIZE ON HYOID MOVEMENT By CHRISTINE M. CARMICHAEL A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORI DA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008
2 2008 Christine M. Carmichael
3 To my father who is watching over me always
4 ACKNOWLEDGMENTS I would like to thank Sandy for her support, commitm ent, and sacrifice throughout my prolonged educational years, and for ultimatel y making me a better person. Thank you to my mom for emphasizing the value of education, for be lieving in me, and for constantly encouraging me to persevere. I would like to thank my committee members for their intellectual advice throughout my doctoral program. I would also like to thank Christine Sapienza, Ph.D., for her invaluable mentorship and friendship.
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES.........................................................................................................................8 ABSTRACT.....................................................................................................................................9 CHAP TER 1 INTRODUCTION AND REVIEW OF THE LITERATURE ............................................... 11 Anatomy and Physiology of Normal Swallowing.................................................................. 11 Evaluation of Swallowing.......................................................................................................14 Hyoid Bone Movement and Effect on Swallow Function......................................................16 Swallowing Rehabilitation...................................................................................................... 18 Traditional Swallow Therapies........................................................................................ 19 Neuromuscular Electrical Stimulation............................................................................ 19 Statement of the Problem....................................................................................................... .25 Purpose............................................................................................................................25 Aims and Hypotheses......................................................................................................26 2 METHODS.............................................................................................................................27 Participants.............................................................................................................................27 Description of the VitalStim Unit...........................................................................................28 Procedures..................................................................................................................... ..........28 Data Analysis..........................................................................................................................30 Penetration-Aspiration Measures.................................................................................... 30 Hyoid Angle and Displacement Measures...................................................................... 31 Statistical Analysis........................................................................................................... .......34 3 RESULTS...............................................................................................................................40 Discomfort Ratings at Ma xim um Intensity Levels................................................................. 40 Angle and Displacement Differences between Intensity Levels............................................ 40 Penetration Aspiration Scores................................................................................................. 41 4 DISCUSSION.........................................................................................................................46 NMES and Bolus Size............................................................................................................48 NMES Intensity Level............................................................................................................48 Other NMES Parameters........................................................................................................ 51 Hyoid Movement....................................................................................................................52
6 Penetration Events............................................................................................................. .....54 Other Swallowing Events.......................................................................................................56 Summary and Conclusions.....................................................................................................57 APPENDIX A HEALTH HISTORY QUESTIONNAIRE............................................................................. 62 B INTENSITY SCALE..............................................................................................................63 C PENETRATION-ASPIRATION SCALE..............................................................................64 D DATA FOR ANGLE OF HYOID DISPLACEMENT AT INTENSITY LEVELS.............. 65 E DATA FOR HYOID DISPLACEMENT AT INTENSITY L EVELS................................... 68 LIST OF REFERENCES...............................................................................................................71 BIOGRAPHICAL SKETCH.........................................................................................................82
7 LIST OF TABLES Table page 2-1 Participant demographics................................................................................................... 36 3-1 Means and standard deviations for bolus size of 5ml........................................................ 42 3-2 Means and standard deviati ons for bolus size of 20m l......................................................42 3-3 Results of multivariate re peated m easures and ANOVAS................................................ 43 3-4 Post-hoc results of angle and displace m ent measures between intensity levels................ 44 3-5 Means and standard deviations associat ed with th e Penetration-Aspiration Scale scores at each intensity level.............................................................................................. 44
8 LIST OF FIGURES Figure page 2-1 VitalStim unit used in the study......................................................................................... 37 2-2 Channel 1 and Channel 2 electrode placements................................................................ 37 2-3 Points and distances for angle measure............................................................................. 38 2-4 Angle and displacement of hyoid bone.............................................................................. 38 2-5 Example of hyoid displacement......................................................................................... 39 3-1 Hyoid movement measures including A 1, A2, D1, and D3 across intensity levels (collapsed across bolus size). ............................................................................................. 45 4-1 Sample hyoid displacement (a ) as a com bination of anteri or and superior movement..... 60 4-2 Penetration, as denoted by the arrow................................................................................. 60 4-3 Cricopharyngeal prominence (at arrow)........................................................................... 61
9 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EFFECTS OF NEUROMUSCULAR ELECTR ICAL STIMULATION INTENSITY AND BOLUS SIZE ON HYOID MOVEMENT By Christine M. Carmichael May 2008 Chair: Christine M. Sapienza Major: Communication Sciences and Disorders Dysphagia, a movement disorder in whic h swallowing is difficult, uncomfortable or painful, is caused by problems with movement sensation, or physical difficulties, and can disrupt nutritional status and quality of life. The study of healthy anatomy and physiology required for normal swallowing has contributed to a greater understa nding of disordered swallowing and its rehabilitati on. Traditional swallow therap ies include diet alterations, positional changes, oral strengthening exercise s and swallowing maneuvers. An emerging and controversial area for treatment of dysphagia th at targets muscles for swallow is the clinical application of surface neuromuscular electrical stimulation (NMES), marketed as VitalStim Therapy, which is expanding de spite only six empirical studies on NMES swallow outcomes. NMES uses electrical impulse to activate muscles through direct s timulation of the muscle belly to achieve maximal hyolaryngeal excursion in an effort to reduce or eliminate aspiration or penetration events for a safer sw allow. It was the goal of this investigation to examine NMES for swallow with 5ml and 20ml thin liquid bolu s sizes in order to assess its effects on hyoid movement and to determine swallowing safety of NMES therapy as measured by penetration and aspiration in a h ealthy population.
10 Results revealed significant differences in maximum displacement and maximum angle of the hyoid bone at three tested intensity levels (maximum tole rance threshold = 100%, 75% of maximum tolerance, and 50% of maximum toleran ce). Significant differences were also found between the lowest (50%) and mi d (75%) intensity levels and between the lowest and highest (100%) intensity levels across NMES swallows. However, the mid-intensity level (75%) was not significantly different from the highest level. Penetration-Aspiration Scale scores revealed 17 penetration events during NMES swallows with 64% occurring during the highest intensity level. These results suggest that NMES may pose risk for penetration as presently utilized at maximum intensity levels. Fu rther, NMES intensities lo wer than the recommended high threshold may provide a similar effect on hyol aryngeal excursion while increasing swallowing safety and decreasing discomfort. No influe nce of bolus size during NMES swallow on hyoid movement was found in the present study.
11 CHAPTER 1 INTRODUCTION AND REVIEW OF THE LITERATURE Dysphagia, or difficulty swa llowing, is a prevalent m oveme nt disorder of swallowing structures and can impact an individuals qua lity of life (Chen et al., 2001; Grill, Craggs, Foreman, Ludlow & Buller, 2001; Gillespie, Br odsky, Day, Lee, & Martin-Harris, 2004). The different etiologies of dysphagi a include infection, ir ritation of oral and/or pharyngeal mucosa, anatomical anomaly, head and neck cancer, tr aumatic brain injury, stroke, and progressive neurologic disease as well as other diseases a nd disorders. Dysphagia may disrupt nutritional status, potentially leadin g to respiratory infection from aspiration of foods and liquids and/or causing aspiration pneumonia and even death (C roghan, Burke, Caplan, & Denman, 1994; Marik & Kaplan, 2003; Petroianni, Ceccarelli, Cont i, Terzano, 2006; Singh & Hamdy, 2006). Hence, successful swallowing therapy may be essential to improve health status and quality of life in persons with dysphagia. Anatomy and Physiology of Normal Swallowing Swallowing is a com plex process involving co ntraction and relaxation of muscles located in the mouth, pharynx, larynx and esophagus (E rtekin & Aydogdu, 2003). Twenty-six muscles and five cranial nerves work t ogether in order to move food from the mouth to the stomach (Vaiman, 2007). The swallowing process incorp orates three phases: oral prepatory/oral, pharyngeal, and esophageal (Dodds, Stewar t, & Logemann, 1990; Ertekin & Aydogdu, 2003; Logemann, 1998). The oral preparat ory/oral stage consists of ma stication, bolus formation, and bolus transport from the oral cavity to the phary nx. During the pharyngeal stage, the epiglottis inverts over the laryngeal vesti bule and the larynx and hyoid bone are pulled anteriorly and superiorly to open the pharynx, re lax the cricopharyngeus (upper es ophageal sphincter, or UES) muscle, and assist the vocal folds in closi ng off the glottis (Cook, Dodds, & Dantas, 1989;
12 Dodds, Stewart, & Logemann, 1990; Jacob, Kahr ilas, Logemann, Shah, & Ha, 1989; Leonard, Kendall, McKenzie, Goncalves, & Walker, 2000). The bolus is then propelled through the pharynx toward the esophagus by action of the ph aryngeal constrictors. Th e oral and pharyngeal phases, or oropharyngeal stage, are mainly under vo litional control and play an important role in protecting the airway (Dodds et al., 1990; Langmore & Miller, 1994; Logemann et al., 1992). The esophageal phase involves bolus flow through the esophagus via peristaltic contractions of striated and smooth muscle al ong the esophageal wall. Relaxation of the lower esophageal sphincter allows the bolus to flow into the stomach. The duration of the oropharyngeal swallow is typically rapid within a range of 0.6 1.0 seconds (Ertekin et al., 1 995; Ertekin, 1996; Ertekin & Aydogdu, 2003; Jean, 2001). The esophageal phase of swallowing is slower than the oropharyngeal phase with the entire stage lasting approximating 10 seconds (Ertekin & Aydogdu, 2003; Jean, 2001; Miller, 1999). Although the combined oropharyngeal swallow take s approximately one second, the oral phase can vary in duration depending on taste, environment, hunger and motivation. The primary muscle working within the oral phase is the tongue, which is responsible for pressing the bolus against the soft and hard palate and initiating movement of the bolus to the posterior tongue. Contraction of the lips (orbicularis oris muscle ) and cheeks (buccinator muscles) are crucial in this stage to prevent bolus escape during masti cation of solids and containment of liquids. Intrinsic lingual muscles (superior longitudinal, tr ansverse, and vertical muscles) and extrinsic lingual muscles (genioglossus, styloglossus, pala toglossus, and mylohyoid muscles) elevate the tongue, beginning with the tongue tip and continui ng to the posterior tongue while squeezing the bolus towards the oropharynx. Positi ve pressure from lingual contac t with the faucial pillars and contraction of the palatoglossus and palatopharyngeus muscles propel the bolus into the pharynx.
13 Concurrently, the palate contacts the posterior pharyngeal wall, sealing off the nasopharynx and increasing positive pressure for bolus transport (Dodds et al., 1990; Kahrilas, Lin, Logemann, Ergun, Facchini, 1993; Logemann, 1988). Normally, the oral and pharyngeal phases of swallowing are coupled tightly together in sequence but they can temporally overlap with each other an d occur almost simultaneously (Dodds et al., 1990; Ertekin & Palmer, 2000; Lo gemann, 1998). The pharyngeal phase involves airway protection and bolus flow into the esophagus. This phase includes a variety of subtle actions triggered by cranial nerves V (Trigemi nal), IX (Glossopharyngeal ), X (Vagus) and XII (Hypoglossal), and involves many musc les with distinct functions su ch as the suprahyoid muscle group, intrinsic laryngeal muscles, infrahyoid muscles and the cricopharyngeus muscle. Anatomical structures involved in the pharyngeal phase include the tongue base, epiglottis, hyoid bone, larynx, and pharyngeal wall. The task of airway protection during the pharyngeal phase is a complex, multi-mechanism process essential for healthy, safe swallowing (Bacon & Smith, 1994; Cook et al., 1989; Dodds et al., 1990; Ertekin & Aydogdu, 2003; Le onard et al., 2000; Shaker, Dodds, Dantas, Hogan, & Arndorfer, 1990). Airway protection begins when the bolus enters the oropharynx and flows into valleculae, which direct the bolus away from the laryngeal vestibule. The epiglottis inverts to provide the first line of defense agai nst penetration, or bolus entry into the laryngeal vestibul e at the level of the vocal fold s. The suprahyoid and thyrohyoid muscles are superficial and are involved in the oral and phary ngeal phases of swallow (Vaiman, 2007). Contraction of the suprahyoid muscle group, which consists of the paired mylohyoid, paired geniohyoid, and anterior belly of the digastri c, results in superior (elevation) and anterior (protraction) movement of the hyoid bone. Thyr ohyoid muscles connect the thyroid cartilage of the larynx to the hyoid bone and shorten the distance between the thyroid and hyoid bone,
14 essentially elevating and prot racting the larynx during swallo w. The thyrohyoid muscles can also act to depress the hyoid. Intrinsic laryngeal adductor mu scles (interarytenoids, lateral cricoarytenoids, and thyrovocalis muscles) contract to adduct the vocal folds, resulting in glottal closure (Dodds et al., 1990; Ishida, Palmer & Hiiemae, 2002; Shaker et al., 1990). Hyolaryngeal elevation is a vi tal component of airway prot ection because in addition to facilitating laryngeal vestibule closure, it al so repositions the larynx under the tongue base (Ertekin & Aydogdu, 2003). The bolus then fl ows through the hypopharynx into the pyriform sinuses. Infrahyoid muscles connect the hyoid to the anterior UES and aid in UES opening during swallow via hyoid traction, primarily anteri or hyoid movement. In addition, the bolus head acts as a force that c ontributes to UES opening (Dodds, Stewart, & Logemann, 1990). The diameter of sphincter opening, typically 1.5 cm for a 20ml swallow (Kahrilas, Dodds, Logemann, & Shaker, 1988) depend s on the volume of the bolus (D odds et al., 1990). Following UES relaxation, the bolus is allowed to flow into the esophagus. The UES then returns to its resting state of contract ion. When not engaged in the act of swallowing, the UES remains in a tonic state of contraction in order to prevent backflow and to block air from entering the esophagus (Kirchner, 1958; Logemann, 1998; Parrish, 1968). Evaluation of Swallowing Several m odalities have been used to exam ine the process of oropharyngeal swallowing including fiberoptic endoscopic evaluation of swallowi ng (FEES) to directly observe preand post-swallow function via flexible nasoendosco py, measurement of oral, pharyngeal and/or esophageal pressures via manome try, electromyography recordings of submental and infrahyoid muscle groups to measure muscle activity, and th e bedside swallow exam which allows for brief screening of swallow function through subjective report of dyspha gic symptoms and observation of swallowing trials (Maddock & Gilbert, 1993; Ohmae, Logemann, Kaiser, Hanson, & Kahrilas,
15 1995; Shaker et al., 1990; Vaiman, 2007). A lthough informative, these methods are not comprehensive enough for visualization and measure of the entire oropharyngeal swallow in order to evaluate anatomical structures and physiologic co mponents during bolus flow. In the clinical setting, FEES a nd the bedside swallow exam are widely used for swallowing assessment. While FEES allows for examina tion of anatomy and physiology of the pharynx and the larynx (via a superior view) before and after the swallow, the oral and esophageal phases of swallow cannot be visualized, and there is a whiteout period during the swallow when the pharynx closes around the scope, blocking the image (Logemann, 1998). Although a bedside swallow exam yields important subjective (p atient and caregiver report) and objective information (when observing the patient swallow) it does not provide visualization of the physiologic aspects during the swallow and only a llows for anatomical assessment of the oral cavity and a superior view of the larynx (if a mi rror exam is tolerated). Because treatment for pharyngeal swallowing disorders is based largel y on motor activity duri ng the swallow, FEES and bedside exam make it difficult to define the exact physiologic na ture of a swallowing disorder as well as to gauge the effectiven ess of clinical treatment (Logemann, 1998). Videoflouroscopy is a dynamic x-ray techni que with superior spatial and temporal resolution useful in evaluating swallow function. It is the preferred method for evaluating swallowing function (depending on the purpose for ev aluation) and includes video recording of the complete x-rayed swallow with simultaneous timing information related to bolus movement. When barium contrast is used in combination with different bolus sizes and consistencies, videofluoroscopy allows for the examination of oral, pharyngeal, laryngeal, and upper esophageal anatomy and swallow physiology of bolus flow events (Gates, Hartnell, & Gramigna, 2006; Logemann, 1996; Marik & Kaplan, 2003).
16 There is no consensus as to the amount of bolus volume or method of food delivery (spoon, cup, straw) that should be used in videofluoroscopic swallowing studies (Kuhlemeier, Palmer, & Rosenberg, 2001; Logemann, 1983; Pa lmer, Kuhlemeier, Tippit, & Lynch, 1993; Robbins, Sufit, Rosenbek, & Levine, 1987). It is known that bolus volume alters oropharyngeal swallow physiology even in healthy participan ts (Bisch, Logemann, Rademaker, Kahrilas, & Lazarus, 1994; Dantas et al., 1990; Kahrilas et al., 1993; Logemann et al., 1992). Airway closure duration and cricopharyngeal opening increase as bolus volume increases, whereas tongue base movement is delayed with an increase in bolus size. In reference to bolus delivery method selected for the current study, support from Kuhlemeier and colleagues (2001) found liquid delivery by cup or spoon to be consistent with safer swallowing. Straw delivery, especially sequential swallows, is not recommended due to the possibility of premature swallow, loss of bolus control and penetration in patients with dysphagia, in older adults, and in healthy young adults ( Daniels & Foundas, 2001; Daniels, Corey, Hadskey, Legendre, Priestly, Rosenbek, & Foundas, 2004; Yilmaz, Basar, & Gisel, 2004). Regardless of bolus type or delivery me thod, swallow function can be assessed during videofluoroscopy by measuring movement or timing of the swallow. Black and white radiographic imaging, as used in fluoroscopy, allows for identification of dense tissue, such as bone. Therefore, many measures regarding move ment and timing of swallow have focused on the hyoid bone. Hyoid Bone Movement and E ffect on Sw allow Function The hyoid bone moves superiorly and ante riorly during swallowing as a result of submental muscle contractions (Cook et al., 1989; Dantas et al., 1990; Maddock & Gilbert, 1993). Both superior and anterior hyoid bone movements create a trajectory of movement. Hyoid kinematics during swallowing have been well-studied. Specifically, amplitudes,
17 distances, peak velocities and movement durations of the hyoid during swallowing have been investigated across factors of bolus volume and viscosity, age, and sex (Chi-Fishman & Sonies, 2002; Jacob et al., 1989; Kendall & Leonard, 200 1; Leonard et al., 2000; Logemann, 1988). Chi-Fishman and Sonies (2002) found longer move ment durations of the hyoid in spoon-thick swallows; greater maximum amplitude, forward p eak velocity, and total anterior distance in larger volume swallows; greater maximum amplitude, longer durations, longer distances, and higher peak velocities in males than in females; and greater anterior am plitude, longer anterior distance, and greater backward peak velocity in older subjec ts. Kendall & Leonards (2001) study of an elderly population with no obvious cause for their dyspha gia revealed longer durations of hyoid elevation a nd shorter durations of maximu m hyoid elevation. Increased amplitude in both superior and anterior displ acements (distances) of hyoid movement has been reported to occur with increased bolus size (Leo nard et al., 2000) and with different bolus viscosities (Jacob et al., 1989). Bolus size affects hyoid movement and its subse quent measurement. Increasing bolus size increases duration of maximum hyoid elevation (J acob et al., 1989), the amplitude of suprahyoid EMG activation (Ertekin, Aydogdu, Yuceyar, Peh livan, Ertas, Uludag, & Celebi, 1997; Jacob, Kahrilas, Logemann, Tracy, Lazarus, & McLaugh lin, 1988), and the overall amplitude of hyoid movement superiorly and ante riorly (Cook et al., 1989; Dantas & Dodds, 1990; Jacob et al., 1990; Kendall & Leonard, 2001; Leonar d et al., 2000). Ishida et al. (2002) reported greater superior hyoid movement with larger volume li quid swallows (10 and 20 mL) than with small volume liquid swallows (1 mL). Introduction of different bolus si zes during videofluoroscopic exam allows the clinician to observe changes in swallowing physiology and identify the size(s) which elicit the most
18 movement characteristic of a normal oropha ryngeal swallow (Logemann, 1998). Therefore, bolus size should be a consideration when perf orming clinical videofluoroscopic studies based on the desired rehabilitation targets. As previously stated, movement of th e hyoid bone during the pharyngeal stage of swallowing is dependent upon contraction of the submental muscle group (mylohyoid, geniohyoid, and anterior belly of the digastri c muscles). Airway closure via hyolaryngeal movement, epiglottal positioning, and vocal fold a dduction must occur to prevent the bolus from entering the airway. If excursion of the hyoid and larynx is diminished or decreased during swallowing, individuals risk penetration or aspiration (L undy, Smith, Colangelo, Sullivan, Logemann, Lazarus, Newman, Murry, Lombard, & G aziano, 1999). Dysphagia involves slowed or decreased range of hyoid movement, likely resulting from submental muscle weakness (Easterling et al., 2000; Kendall & Leonard, 2001; Schultz, Perlman, & VanDaele, 1994). Thus, hyolaryngeal movement has been a focus of swallowing rehabilitation. Swallowing Rehabilitation Evaluation of dysphagia is unique in that there is opportuni ty to study the effects of treatm ent during diagnostic procedures, sp ecifically during videofluoroscopy (Logemann, Kahrilas, Kobara, & Vakil, 1989; Martin-Harris, Logemann, McMahon, Schleicher, & Sandidge, 2000). Generally, treatment methods are c hosen based on the pathophysiology of the swallowing impairment, observed symptoms, and functional needs of th e patient. Introduction of rehabilitation stra tegies during videofluoroscopy such as swallow maneuvers, postural techniques, or bolus alterations provides good information on the immediate effectiveness and short-term evidence of the treatment (Logemann, 2006). Rehabilitative strategies for swallowing have been a major focus of research (Bar tolome & Neumann, 1993; Lazarus, Logemann, & Gibbons, 1993; Logemann et al., 1989; Neumann, 1993; Ohmae, Ogura, Kitahara, Karaho, &
19 Inouye, 1998; Shanahan, Logemann, Rademaker, Paulowski, & Kahrilas 1993; Shaker et al., 1997; Shaker et al., 2002; Veis, Logemann, & Colange lo, 2000) as the goals of therapy include improvement in swallow function in order to increase swallowing safety, improvement in quality of life, and prevention of respiratory infec tion that could cause aspiration pneumonia. Traditional Swallow Therapies Although slower and weaker m uscle move ments can alter the timing, force and coordination of the swallow in patients with dysph agia, few techniques that specifically activate the swallow musculature have been proposed. Mo re so, rehabilitation techniques have focused on changing swallowing physiology and improvi ng swallow safety (Clark, 2003; Logemann, 1998). Traditionally, dysphagia treatments have included diet alterations (Bulow, Olsson, & Ekberg, 2005), positional changes of the head and neck such as chin tuck (Logemann, 1993; Robbins, Hind, & Logemann, 2004; Zuydam, R ogers, Brown, Vaughaqn, & Magennis, 2000) and head turn (Logemann, 1993), oral and neck strengthening exercises (Shaker et al., 1997; Veis et al., 2000), and swallowing maneuvers such as the effortful swallow, Mendelsohn maneuver, supraglottic swallow and super-sup raglottic swallow (Clark, 2003; Langmore & Miller, 1994; Lazarus, Logemann, Song, Rade maker, & Kahrilas, 2002; Logemann, 1993; Logemann, Pauloski, Rademaker, & Colangelo, 1997; Zuydam et al., 2000). Diet modifications and positional changes have been the most clinically utilized of all traditio nal swallow strategies. While these compensatory techniques addre ss swallow safety, they are not designed to rehabilitate weak swallowing muscles or recover lost motor control. Neuromuscular Electrical Stimulation An e merging and controversial area for treatm ent of dysphagia that targets muscles for swallow is the clinical application of surface neuromuscular electrical stimulation (NMES), marketed as VitalStim Therapy. VitalStim was introduced in 2001 along with the first published
20 study using it as a treatment modality for dysphagia (Freed et al., 2001). To date, more than 9,000 speech pathologists in the U.S. have take n the VitalStim certification course (CarnabyMann & Crary, 2007) and thousands of devices and considerably more patented one-time use disposable electrodes have been sold (Shaw, Sechtem, Searl, Keller, Rawi, & Dowdy, 2007). Many clinical investigators and cl inicians question the VitalStim procedure for the treatment of dysphagia due to only a few studi es supporting the efficacy of V italStim and a poorly defined neurophysiologic basis for using the procedure (Humbert et al., 2006; Kiger et al., 2006; Logemann, 2007; Ludlow et al., 2007; Suiter et al., 2006). However, more experimental questions needed to be tested on NMES in order to reach definitive conclusions about its validity and use. NMES is defined as the use of electrical stim ulation for activation of muscles by directly stimulating the belly of the targeted muscle(s). Major reported treatment goals of NMES are to activate weak muscles and aid in recovery of motor control. Functional NMES is the use of NMES to promote, maximize and sustain f unctional activities (P eckham & Knutson, 2005; Ogino et al., 2002), e.g. stimula ting ankle dorsiflexors during walk ing, or stimulating submental muscles while swallowing. In more than 40 years of physical therapy re search, greatest gains using NMES have been achieved when electrically elicited muscle contractions are coordi nated with functional movement (Langzam, Isakov, Nemirovsky, & Mizrahi, 2005; Peckham & Knutson, 2005; Vanderthommen, Depresseux, Dauchat, Degueldre, Croisier, & Crie laard, 2000). Based on this evidence, it might be assumed that the most functional gain for swallowing is achieved by applying NMES while a patient is swallowing. F unctional gain of swallowing is an important goal of VitalStim.
21 Use of VitalStim for swallowing therapy attempts to achieve maximal anterosuperior hyolaryngeal excursion in order to reduce or elim inate aspiration or penetration events (Wijting & Freed, 2003). This can be accomplished by stimulating suprahyoid muscles and thyrohyoid muscles via surface electrodes in order to improve muscle act ivation and promote hyolaryngeal movement. VitalStim delivers an electrical curr ent that causes a depolariz ation of the peripheral motor nerve, reportedly at the neuromuscular juncti on or motor end plate. This in turn elicits muscle contraction (Wijting & Freed, 2003). Muscle contraction, specifically the recruitment order of moto r units during stimulation is different from voluntary activati on of muscle. The recruitment order of voluntary muscle contraction involves asynchronous firing of type I fibers (small, slow, low power) followed by type II (large, fast, high power) only with increased effort, such as ri gorous exercise. In contrast, NMES evokes immediate, synchronous recruitmen t of type II fibers (Hainaut & Duchateau, 1992; Lake, 1992; Trimble & Enoka, 1991). Type II fibers dominate type I fibers in the swallowing musculature and partic ipate in high speed, forceful c ontractions of muscles involved in swallowing (Korfage, Schueler, Brugman, & Va n Eijden, 2001; Stal, 1994). Because type II fibers have a higher specific force than type I, selective augmentation of type II will increase the force generation of the muscle c ontraction and overall muscle f unction (Lake, 1992; Sinacore et al., 1990). Traditional swallowing therapies would most likely activ ate only type I fibers unless vigorous exercise were applied. However, a modality such as NMES that favors recruitment of type II muscle fibers may discourage disuse atrophy and enhance muscle performance for swallowing (Shaw et al., 2007). The idea to use electrical stimulation to improve muscle function is not new. Electrical stimulation is currently being used by numerous disciplines to control pain, enhance muscle
22 performance, augment range of motion, stimul ate wound healing, treat xerostomia, enhance sensorimotor recovery, and increase circulation while controlli ng edema (Baker & Parker, 1986; Bauer, 1983; Boswell, 1989; Lake, 1992; Li eber & Kelly, 1991; Peckham & Knutson, 2005; Pekindil, Sarikaya, Birtane, Pekindil, & Salan, 20 01). Low intensity electrical stimulation increases endurance of human skeletal muscle (Nuhr et al., 2004; Theriault, Boulay, Theriault, & Simoneau, 1996). There is evidence to show the effectiveness of this modality for improvement of muscle function in the physical therapy litera ture for healthy athletes (Maffiuletti, Dugnani, Folz, DiPierno, & Mauro, 2002; Pichon, Chatar d, Martin, & Cometti, 1995), deconditioned patients (Valli, Boldrini, Bianchedi, Brizzi, & Miserocchi, 2002), patients with progressive neuromuscular disease (Handa et al., 1995; Milner-Brown & Miller 1988; Zupan, Gregoric, Valencic, & Vandot, 1993; Zupan, 1992) and patients with paraplegia or quadriplegia (Handa et al. 1996). Clinical utilization of NMES for dysphagia is expanding despite very few controlled research studies. The literature contains publishe d studies on the use of electrical stimulation to improve swallowing function. Some researchers have used surface electrodes (Freed, Freed, Chatburn, & Christian, 2001; Humb ert et al., 2006; Kiger, Brown, & Watkins, 2006; Leelamanit, Limsakul, & Geater, 2002; Ludlow et al., 2006; Su iter, Leder, & Ruark, 2 006), some have used needle (hooked-wire) electrodes (Burnett, Mann, Cornell, & Ludlow, 2003 ), and others have implanted electrodes (Broniatowski et al., 2001 ; Ludlow et al., 2000). While hooked-wire and implanted electrodes have yielded fair results, surface electrodes are much less invasive and offer similar effects. Other advantages of surface electrodes include less time to apply, no risk of infection, and no need for topical anesthesia or additional necessary medical personnel (physician). To date, only six pr ospective experimental studies have been published on the use
23 of surface electrical stim ulation for the swallowing musculatur e. Freed et al. (2001) compared therapeutic effects of NM ES to thermal sensory stimulation in patients with dysphagia secondary to stroke. Results indicated greater and longer-lasting improvement of swallow function with NMES than with thermal stimulation. Howeve r, participant groups were not randomized, and patients were accepted into the study if they ha d a history of swallowing disorders caused by stroke, several of which underwent cricopharyngeal myotomy. Leel amanit and colleagues (2002) used surface stimulation w ith sEMG to the laryngeal region in patients with dysphagia and found positive results with activation of the thyrohyoid muscles resulting in laryngeal elevation. Contradicting result s were found by Suiter and colleague s (2006) when NMES to the submental muscles of 10 healthy volunteers failed to produce significant increases in muscle activity as measured by sEMG. Kiger et al (2006) found no significant difference in NMES treatment versus traditional dysphagia treatment in 22 patients with dysphagia. In addition to mixed reports of muscle recruitment activity and overall effects of NMES, many variables remain unstudied regarding NMES for swallow such as the intensity (amplitude of the current), timing, and duration of the stimulation, electrod e placement, and effects of bolus size and consistency on swallow outcomes. One recent study tested different surface elect rode placements during NMES for swallow of a 5ml liquid bolus in 29 h ealthy individuals (Humbert et al., 2006). Contraindicative movement (hyoid depression via hypothesized omohyoid and sternohyoid muscle activation) occurred and the risk for swallowing safety wo rsened with 7 out of 10 electrode placements tested. However, only one electrode placement was tested during swallowing ; with the other nine placements strictly tested at rest, and only one bolus size of 5ml (approximately half the size of a normal swallow) was used. Another research protocol manipulated intensity (amplitude)
24 levels of the VitalStim Therapy unit in eight i ndividuals with dysphagia during swallows of 5ml and 10ml liquid (Ludlow et al., 2007). Ludlow and colleagues used two intensity (amplitude) levels, a low sensory level and a maximal mot or level during NMES. Aspiration events at rest were reduced at the low amplitude level but not at the maximum level. No significant change was noted in swallowing safety at either level during swallow. Although they hypothesized that stimulation w ould lower the hyoid when a pplied, the greatest hyolaryngeal elevation occurred at the maxi mal motor level during swallow. This indicates greater recruitment in the suprahyoid muscle group with possible thyroid activati on (raising the larynx) at maximal amplitude during swallow, c onfirming the goals of VitalStim Therapy. Maximum amplitude levels for NMES, defined as a stimulus reaching a maximal stimulation that is not painful to the patient have been recommended in the physical therapy field for stimulation of skeletal limb muscle (Bax, Staes, & Verhagen, 2005; de Ruiter & de Haan, 2003) to increase muscle activation and m u scle strength. VitalStim Therapy has adopted this physical therapy rationale and recommends maximal NMES tolerance levels for the swallowing musculature to promote muscle recru itment. However, appropriate amplitude levels for NMES promoting maximal hyolaryngeal excurs ion without penetration or aspiration during swallow (for swallowing therapy) ha ve not been thoroughly researched. As discussed above, during swallowing, musc le activity and movement timing can be modified by bolus size and consistency (Danta s & Dodds, 1990; Dantas et al., 1990; Kendall et al., 2001). Bisch et al. (1994) f ound prolonged airway closure and cricopharyngeal opening with an increase in bolus size in individuals with dysphagia. Bulow and colleagues (2003) found reduced penetration/aspiration and reduced phary ngeal retention with carbonated and thickened liquids versus thin liquid swallows in individu als with and without dysph agia. Reimers-Neils et
25 al. (1994) revealed significant EM G muscle activity with thicker liquid swallows, whereas thin liquids showed less muscle activity during swal lowing. It is recommended by Logemann (1998) that various bolus sizes or c onsistencies be examined during a swallowing exam to guide recommendations for swallowing therapy. Howeve r, no published data exists regarding the effects of bolus size or bolus consistency as a function of NMES stimulus intensity as an indication or contraindica tion for VitalStim Therapy. Statement of the Problem Hyoid bone move ment during NMES of submental and thyrohyoid muscles during swallowing has not been sufficiently re ported. Neither has the effect of different amplitudes of stimulation been examined in relation to mu scle recruitment response (as measured by hyoid movement). The recommended amplitude level of maximum tolerable muscle activation is based on physical therapy protocol s rather than on specific swa llow-related research. As well, the effect of bolus size on hyoid movement dur ing NMES swallow is no t well-studied. Safe swallowing in any population during NMES has not been proven. Acquiring hyoid measures during NMES swallow at different device amplitude s using different bolus sizes would allow for examination of these effects on hyoid movement. In addition, rating of penetration/aspiration events would provide further assessment of NMES by addressing a component of swallowing safety. Purpose This study investigated the effects of varying N MES amplitude levels on hyoid bone movement during swallow of differ ent bolus sizes (5ml and 20ml thin liquid) as measured from videofluorographic images in he althy volunteers of ages 18 to 50 years. This allowed for assessment of biomechanical properties of hyoi d bone movement of NMES for swallowing and contribution to the present literature base on NMES swallow.
26 Aims and Hypotheses Aim 1: Determ ine the effects of bolus size on the angle and displacement of hyoid movement during NMES swallow. Hypothesis 1 : It was hypothesized that there sign ificant increases in hyoid angle and displacement would exist duri ng NMES swallow as a function of increased bolus size. Aim 2: Determine the effects of unit amplitude on the angle and displacement of hyoid movement during NMES swallow. Hypothesis 2a: It was hypothesized that significant di fferences in hyoid angle and displacement would exist between 75% and 100% maximum amplitude levels of NMES swallow. Hypothesis 2b: It was hypothesized that significant differences in hyoid angle and displacement would exist between 50% and 100% maximum amplitude levels of NMES swallow. Hypothesis 2c: It was hypothesized that significant di fferences in hyoid angle and displacement would exist between 50% and 75% maximum amplitude levels of NMES swallow. Aim 3: Determine the effects of bolus size and am plitude level on penetration or aspiration events during NMES swallow. Hypothesis 3 : It was hypothesized that no change in penetration or aspi ration events would occur during NMES swallow as a function of varying amplitude or bolus size.
27 CHAPTER 2 METHODS Participants A power analysis was perform ed based on a balanced two-way ANOVA model. Without effect size information from previous studies, the sample size was calculated for testing the difference in the outcome (hyoid movement) across three intensity levels and two bolus sizes. Type I error (two-sided) was a ttained at 0.05, and power was a ttained around 80%. SAS macro fpower.sas (Friendly, 1995) was used to perform the sample size calculation of n = 18 to detect an effect size of 0.25. An n of 20 was determined to meet these criteria. Twenty healthy volunteers par ticipated in this prospectiv e experimental study with one participant group. Ten female and 10 male participan ts were recruited in the age range of 20 to 48 years from the local Gainesville, Florida and University of Fl orida community. All participants completed a questi onnaire regarding their genera l health and medical history (Appendix A). None had a history of rheumatic fever, mitral valve prolapse or other cardiac problems, pulmonary, neurological otolaryngological, psychiatric, untreated gastroesophageal problems or speech or swallowing problems. The principal investigator confirmed symmetrical head and neck anatomy for all participants from the visual display obtained from videofluoroscopy that was used in the evalua tion of swallow function. No females were pregnant or breastfeeding at the time of the study (pregnancy or breastfeeding would exclude participants due to radiation exposure during videofluoroscopic proce dures). Study protocol approval was obtained from the University of Florida Institutional Review Board as well as the Malcom Randall VA Medical Center Radiat ion Safety Committee and Research and Development Committee.
28 Description of the VitalStim Unit The handheld VitalStim Dual Channel Unit (Cha ttanooga Group) was used in this study to provide electrical stimulation to the submental muscle group and the thyrohyoid muscle. The unit is comprised of two channels with two 2.1 cm round surface electrodes for each channel, connected to the unit by lead wi res (Figure 2-1). Each electric ally conductive electrode has a water-resistant adhesive and is size-specific for th e throat area. Electrode adhesive material for fixating the electrodes to the skin of the neck consists of latex-free, woven polyurethane. The conductive substrate material of the electrodes is carbon-silver de signed for low impedance. The configuration of the V italStim unit provides a biphasic, continuous dual channel current with a fixed pulse duration (pulsed curr ent) at 700 microseconds and a fixed frequency of 80 Hertz. Amplitude, or intensity of the current, is adjustable from 0 to 14 milliamperes. Procedures Af ter participants gave their informed consent, they were asked to fill out a brief health history questionnaire to c onfirm some of the inclusionary/exclusionary criter ia listed above. For each participant, the skin on the neck was thoro ughly cleansed with skin wipes included in the VitalStim electrode package. Male participants were required to be cl ean-shaven. Measures of adipose tissue thickness in the suprahyoid and laryngeal regions were obtained using a skin caliper. The skin thickness measures were compiled into a database to help establish future guidelines documenting the influence of neck adi pose tissue as resistance of electrical current during stimulation. Presently, no skin caliper measurements of neck adipose tissue thickness exist for reference purposes. The principal investigator fit each partic ipant with the NMES electrodes prior to videofluoroscopy in a separate area of the swa llow suite. Channel 1 electrodes were adhered to the skin lateral to each other over the submental muscle group targeting mylohyoids,
29 geniohyoids, and the anterior belly of the digastric. Channel 2 electrodes we re placed on the skin overlying each side of the thyrohyoid muscle, superior to the thyroid cart ilage and below the hyoid bone (Figure 2-2). Intensity of both channels was slowly incr eased simultaneously to maximum stimulation tolerance, according to particip ant verbal feedback. Particip ants were shown a diagram of increasing intensity levels and related sensations (Appendix B). As stimulation intensity was increased, participants were instructed to provide verbal feedback as they began to feel a tingling sensation on the front of the neck, then a vibratory sensation, and finally a tensing sensation of the front neck muscles. Maximum stimulation tolerance was defined as the level of motor contraction of the muscles reported as a tensing sensation by the participant (Wijting & Freed, 2003). Maximum tolerance (100% intensity) was documented for each participant, and 50% and 75% intensity levels were also computed and re corded. After intensity levels were obtained, participants were asked to rate their discomfort at the 100% intensity le vel on a scale of 0 to 10, with 0 being no pain or discomfort to 10 signify ing the worst pain or discomfort possible. Following the discomfort rating, participants we re escorted to the videofluoroscopy room. Participants underwent the videofluoroscopy study performed by a radiologist in the radiology suite at the Malcom Randall VAMC. A certified and licensed speech language pathologist was present for bolus delivery. Videofluoroscopic st udies of each swallow were recorded with a resolution of 30 frames pe r second using the Kay Digital Swallowing Workstation, model 7100 (Lincoln Park, NJ). Partic ipants were seated and an anterior view was obtained to verify anatomical symmetry of swallowing structures. A lateral view was obtained for each self-administered cup swallow of wate r with barium contrast. The third cervical
30 vertebra (C3) was denoted as a landmark by adhere nce of a penny to the sk in lateral to C3 for later data analysis. During the experimental protocol participants were instructed to relax the tongue and jaw at rest, while keeping their lips loosely sealed in order to avoi d extraneous submental muscle movements. To establish baseline swallows, pa rticipants swallowed two bolus sizes, 5ml and 20ml thin barium contrast solution per graded medicine cup, with no elect rical stimulation. The liquid contrast material was th e manufacturer preparation EZ-E M (Varibar contrast agents, EZEM, Inc., Lake Success, NY). Participants then swallowed the two bolus sizes, 5ml and 20ml thin liquid barium, three times each with stim ulation set on amplitudes of 100%, 75% and 50% of maximum tolerable intensity while being recorded with videofluoroscopy. The 18 amplitude and bolus trials (2 bolus sizes x 3 stimulation inte nsities x 3 trials) with electrical stimulation on were completed in random order. During the vi deoflourographic examination, participants were instructed to take and hold the material in thei r mouth, stabilize the head (to prevent neck flexion and to minimize movement artifact), and swallow when prompted by the speech pathologist. Participants were instructed to swallow each bolus in one swallow. The VitalStim unit intensity was slowly ramped up to the appropriate level and the fluoroscope was activated prior to the selfadministration of the contrast material into the mouth. Both remained activated for two seconds after the bolus tail exited th e upper esophageal sphincter to al low for reliable measurement of hyoid movement and penetration or aspiration events. The reco rded videofluoroscopic images were integrated into the Kay Digital Swallowi ng Workstation for later analysis of the data. Data Analysis Penetration-Aspiration Measures Scores from the Penetration-Aspiration Scal e (PAS) (Rosenbek, Robbins, Roecker, Coyle & Wood, 1996) served as a primary dependent va riable. The PAS is an 8-point scale that
31 quantifies penetration, aspirati on, and residue during videofluor oscopic swallowing evaluations (Appendix C). A speech pathologist with at least ten years experience interpreted the videofluoroscopic swallow studies and was blinded to the experi mental conditions. The speech pathologist rated all swallows using the PAS to quantify penetr ation, aspiration, and residue by examining all trials of the fl uorographic images obtained from the participants. Interrater reliability was tested by a second speech path ologist with at least ten years experience interpreting 50% of the videofluoroscopic swallow studies, also blinded to the experimental conditions, using the PAS. Hyoid Angle and Displacement Measures Our laboratory developed a MATLAB routine to analyze the biom echanical characteristics of the oropharyngeal swallow and track the m ovement of the hyoid bone during swallow. Individual JPEG images of swallows were extracted from the Kay recording device using ImagePro Plus (Media Cybernetics, Silver Spring, MD). Image se quences of swallows containing all frames from hyoid onset (initiation of hyoid moveme nt at the beginning of the swallow) to hyoid rest (at the end of the swallo w) were identified and extracted from the Kay Swallow Station. After extrac tion, the files were transferred to a computer set up with MATLAB, version 7.0.1 (T he MathWorks Inc.). The MATLAB swallow routine was designed to track hyoid bone movement using C3 as a reference. The program is organized as three se parate programs for ease of analysis. The first section displays the series of images in a ra ndom manner, the second is a sequential display, and the third provides plots of the hyoid trajectory. The random display of the swallow images ensu res that there is no bias involved in the selection of points on each frame. The user is required to select two points on each frame, one corresponding to the position of the hyoid and the other a chosen reference (C3). In the first
32 frame of the random image display, the user is required to select two diametrically opposite points on a reference (example: penny) which will set the pixel to millimeter conversion. In all other images, the user is required to select two points, one corresponding to the C3 reference at its most anteroinferior point and other to the hyoid bone at its most antero superior point. When all the images have been displayed, dimension of the reference in millimeter is entered. All the images with the hyoid bone are highlighted and displayed. These images have the position of the hyoid bone, as selected by the user in each frame, hi ghlighted as a red circle. Then trajectory of the hyoid bone is generated, considering every imag e frame. There is an option to generate the trajectories of hyoid bone in increments other th an unity (every third and every fifth frame considered), to obtain smoother trajectories and reduce the number of images needed for data analysis. After all frames are measured, the program calculates angle of change and displacement (excursion) of the hyoid from the initial resting position. The angle is measured in degrees, with respec t to the base line (the line that connects the C3 reference point and the hyoid bone at rest, i.e. the initial positio n) and the displacement as the magnitude of the connecting lines (the lines c onnecting the hyoid bone a nd C3 reference point) in millimeters, in each frame. Three angle measures were calculated: the angle at maximum displacement (A1), the maximum angle (A2), and the ending angle (A3). Three displacement measures were calculated: the maximum displ acement (D1), the displacement at the maximum angle (D2), and the endi ng displacement (D3). Formulae used to calculate the displacement and angle measures: Displacement measure: To calculate the dist ance between the points in the image, the Euclidean distance formula is used. For example: Consider a line AB, connecting th e points A and B, as shown in the figure. B (X2, Y2) A (X1, Y1)
33 The distance between the point s A and B in an image ha ving the co-ordinates (X1, Y1) and (X2, Y2) respectively can be com puted using the Euclidean formula: Distance = [(X1-Y1)2 +(X2-Y2)2] 0.5 Angle measure: The baseline has two points. One of them is the fixed reference (C3 vertebra); call this point X. This is a fixed point and its co-ordinates are used for the calculation of the angle measure in all image fram es of the swallow. The other point is the initial position of the hyoid bone (i.e. the hyoid b one point selected in the first frame, when the hyoid is at rest); let us call this point Y. The Euclidean distance between X and Y is computed; call this distance of the baseline b The hyoid bone in all other frames has a vertical and horizontal displacement from the baseline. The moving hyoid point in each frame is Z. The Euclidean distance between X and Z is computed; call this distance c. Also compute the distance between Y and Z; call this distance a. The points and distance values are as shown in Figure 2-3. Points X, Y, Z form a triangle. Using the di stance values a, b, and c, the angle measures are computed using the Cosine rule. The angle opposite to the line a is to be computed. Using the Cosine rule, the angle form ed by the lines XY and XZ can be calculated in degrees as follows: a2 = [b2 + c2 (2bc x Cosine (a))] Cosine (a) = (a2 b2 c2) / (2bc) By taking the inverse cosine of the above, the angle measure is found. The angle computed thus gives the vertical displacement of the hyoid bone with respect to the baseline. The program outputs the following plots: Angle vs. frame number: Angle of the hyoid bone in degrees, as measured with respect to its initial position and C3 reference, plotted as a function of frame number. Displacement vs. frame number: Displacement of the hyoid bone in pixels and millimeters, as measured with respect to the C3 reference, plotted as a function of frame number. The swallow process is captured as a series of images at a frame rate of almost 30 frames per second. The time taken for each swallow can be calculated by knowing the number of frames present for that particular swallow, as:
34 Time taken for swallow = (Number of frames in the swallow process) (Frame rate) Thus, by changing the X-axis in the previous pl ots, from frame number to time in seconds, the following plots can be generate d as illustrated in Figure 2-4: Angle vs. time: Angle of the hyoid bone in degree s, is measured with respect to its initial position and C3 reference, and plotted as a function of time in milliseconds. Displacement vs. time: Displacement of the hyoid bone in millimeters, is measured with respect to the C3 reference, and plotted as a function of time in milliseconds. An example of hyoid displacement (as measured with respect to the C3 reference and the starting displacement the C3 reference and the maximum displacement) illustrated by the program is shown in Figure 2-5. These calculati ons were generated in Excel (Microsoft, Inc.) within the program thus allowing for easy data re duction and importing into st atistical packages. Dividing the displacement (D1, D2, or D3) by th e starting displacement in order to control for sex or individual differences normalized disp lacement. Normalization was completed on all displacement measures. Statistical Analysis Statis tical analysis of the data was completed using SAS software version 9 (SAS Institute, Inc.). The statistical analys is compared outcomes for hyoid movement across three intensity levels (100%, 75%, and 50% of maximum tolera nce) and across two bolus sizes (5 ml and 20ml). Interaction effects betw een sex, intensity and bolus size were determined. A three-way analysis of variance (ANOVA) with repeated meas ures (3 intensity levels by 2 bolus sizes by 2 sexes) was used with a probability setting of p > 0.05. Significant interactions were analyzed post-hoc using pair-wise comparisons. A one-way ANOVA was used to determine gender effect across skin caliper measures (SM and TH), 100% intensity level, and discomfort rating at the 100% level. Intrarater and inte rrater reliability were measured on 20% of the movement data
35 using Intraclass Correlation Coefficients (ICCs). Th e ICCs for intrarater and interrater reliability were .98 and .99, respectively, indicating high reliability on these measures. Interrater reliability for the penetration/aspira tion scores was measured on 50% of the PAS data using ICCs. The ICC was .95, indicating high reliability for PAS scores across raters.
36 Table 2-1. Participant demographics Subject Age Sex SM TH 100% Pain rating 16 20 F 5 5 3.0 4 8 20 F 10 5 9.5 1 1 22 F 8 9 2.5 3 15 22 F 19 13 6.0 2 2 26 F 13 8 5.5 2 3 26 F 15 12 6.5 1 12 27 F 13 11 8.5 0 9 30 F 11 6 4.5 1 13 37 F 15 12 4.0 1 4 43 F 10 11 4.5 5 M 27.3 11.9 9.2 5.45 2 (SD) (7.56) (3.98) (3.05) (2.25) (1.56) 14 20 M 5 3 12.0 0 10 21 M 5 3 6.5 1 19 22 M 8 7 5.5 3 20 22 M 9 5 10.0 3 6 23 M 7 6 11.0 3 7 23 M 8 4 6.0 0 18 23 M 10 5 9.0 2 17 28 M 4 4 5.5 3 11 38 M 9 8 11.5 0 5 48 M 16 19 8.5 1 M 26.8 8.1 6.4 8.55 1.6 (SD) (9.10) (3.41) (4.72) (2.54) (1.35) Total M 27.05 10 7.8 7.0 1.8 Total (SD) (10.01) (3.88) (4.16) (2.92) (1.33) Neck skin thickness measurem ents, maximum NMES intensity level with pain rating. Note: SM=skin caliper measurement of submental ar ea; TH=skin caliper measurement of thyrohyoid area; 100%=maximum tolerabl e NMES intensity level; M =mean; SD =standard deviation.
37 Figure 2-1. VitalStim unit used in the study. Figure 2-2. Channel 1 and Ch annel 2 electrode placements. Channel 1 Channel 2
38 Figure 2-3. Points and dist ances for angle measure. Figure 2-4. Angle and displacement of hyoid bone. C3 Angle Displacement a c b (Base Line) Z Y X
39 Figure 2-5. Example of hyoid displacement.
40 CHAPTER 3 RESULTS Discomfort Ratings at Maximum Intensity Levels Table 2-1 shows the m aximum tolerable NM ES intensity levels (100%) and related pain/discomfort ratings. A ll participants were able to tolerate a 100% intensity level. In general, participants indicated mild discom fort at the 100% intensity level. Males tolerated an average of 3.10mA more than females, and reported sligh tly lower discomfort ratings on average. The minimum tolerance level was rated by a 22-year old female participant at 2.5mA with a discomfort rating of 3. The maximum tolera nce level was rated by a 20-year old male participant at 12mA with a discomfort rating of 0. One participant, a 43-year old female reported anxiety at her 100% intensity le vel, and tolerated 4.5mA with the highest reported discomfort rating of 5. Angle and Displacement Differences between Intensity Levels Means and standard deviations for each of the hyoid angle and displacement m easures across the three intensity levels for 5ml and 20ml bolus sizes are in Tables 2A and 2B. Average maximum hyoid displacement (D1) for the 5ml bolus was highest at the 75% intensity level (16.32 mm) and lowest at the 100% intensity le vel (13.86 mm). For the 20ml bolus, D1 was comparable at the 100% level (14.10mm) as at the 75% level (13.96 mm). Although differences in gender was not a sp ecific aim of this study, a one-way ANOVA was completed on gender across skin caliper measures (SM= submental area and TH=thyrohyoid area), 100% intensity level, and discomfort rating at the 100% le vel. Significant differences between males and females were found for SM measures [ F (1, 19) = 5.245, p = .034] and 100% intensity levels [ F (1, 19) = 8.32, p = .010] but not for TH measures [ F (1, 19) = 2.485, p = .132] or discomfort ratings [ F (1, 19) = .375, p = .548]. Males had a significantly lower SM skin
41 caliper measures (less adipose tissue in the submental area) than females, and males tolerated significantly higher intensity levels than did females in the study. To test the hypotheses set forth in Aims 1 and 2, a repeated measures analysis of variance (ANOVA) was completed. For angle and displa cement measures A1, A2, A3, D1, D2, and D3, significance was set at p = .05. Results of the analysis reveal ed that the factors of age and bolus size were not significant across hyoid measures. Th ere was no main effect for sex. There were significant differences in hyoid measures among inte nsity levels except D2 (displacement at the maximum angle) and A3 (ending angle) (Table 3-3). Post-hoc analysis revealed si gnificant differences between th e 50% intensity level and the 75% level and between the 50% level and the 10 0% level (see Table 3-4 and Figure 3-1). However, the 75% level was not signifi cantly different from the 100% level. Penetration Aspiration Scores Table 3-5 shows the m eans and standard devia tions for the penetra tion/aspiration scores across the three intensity levels for 5ml and 20ml bolus sizes. Scores were highest on average (indicating more penetration even ts including residues or vocal fold contact) at the 100% intensity level for both 5ml and 20ml. Overall, 17 events of penetra tion were reported, 11 of which were at the 100% intensity level; 6 of th e 11 were with 20ml. The worst level of penetration, a score of 5 (material enters the airway, contacts the vo cal folds, and is not ejected) occurred twice with two differe nt participants when swallo wing the 20ml bolus at the 100% intensity level. No events of aspiration were found. All baseline swallows with no stimulation scored a 1 (material does not enter the airway) with the exception of one participant where penetration occurred during the 20ml baseline swallow. That same participant had one other penetration event on a 20ml swallo w at the 100% intensity level.
42 Table 3-1. Means and standard devi ations for bolus size of 5ml. Measure Intensity 0 50 75 100 Trajectory A1 8.42 (6.49) 8.83 (6.57) 9.15 (6.99) 10.88 (7.30) D1 15.75 (4.72) 15.18 (4.41) 16.32 (5.00) 13.86 (5.71) A2 13.53 (5.32) 13.89 (5.66) 15.06 (5.08) 15.98 (6.28) D2 8.68 (6.03) 8.70 (6.84) 8.89 (6.18) 8.25 (5.49) A3 1.78 (6.28) 2.36 (1.90) 2.33 (1.65) 2.53 (2.10) D3 1.22 (1.76) 2.42 (1.81) 3.48 (2.30) 2.31 (1.32) Note: A1=angle associated with maximum displacement; D1=maximum displacement; A2=maximum angle; D2=displacement associat ed with maximum angle; A3=angle at end of task; D3=displacement at end of task. Displacements were normalized for each participant. Angles were measured in degrees; displacements were measured in mm. Table 3-2. Means and standard devi ations for bolus size of 20ml. Measure Intensity 0 50 75 100 Trajectory A1 8.91 (4.34) 10.25 (6.73) 10.29 (5.41) 11.99 (8.05) D1 16.87 (4.98) 15.00 (5.09) 13.96 (4.49) 14.10 (4.11) A2 12.70 (3.65) 13.75 (6.13) 15.79 (4.95) 16.22 (6.30) D2 9.17 (7.85) 8.92 (5.78) 10.18 (4.85) 8.47 (4.84) A3 1.76 (1.95) 2.70 (2.26) 2.92 (2.23) 3.63 (4.02) D3 1.67 (1.46) 1.73 (1.33) 2.31 (1.69) 1.88 (1.66) Note: A1=angle associated with maximum displacement; D1=maximum displacement; A2=maximum angle; D2=displacement associated with maximum angle; A3=angle at end of task; D3=displacement at end of task. Displacem ents were normalized for each participant. Angles were measured in degrees; displacements were measured in mm.
43 Table 3-3. Results of multivariate repeated measures and ANOVAS. df F p A1 Between Age (1, 129) 1.18 0.28 Sex (1, 129) 1.22 0.27 Within Intensity (3, 129) 2.74 0.04* A2 Between Age (1, 129) 2.33 0.13 Sex (1, 129) 0.00 1.00 Within Intensity (3, 129) 5.09 0.002* A3 Between Age (1, 129) 0.19 0.66 Sex (1, 129) 2.16 0.14 Within Intensity (3, 129) 2.20 0.09 D1 Between Age (1, 129) 0.02 0.90 Sex (1, 129) 0.15 0.70 Within Intensity (3, 129) 2.52 0.006* D2 Between Age (1, 129) 0.00 0.95 Sex (1, 129) 0.29 0.59 Within Intensity (3, 129) 0.39 0.76 D3 Between Age (1, 129) 0.83 0.36 Sex (1, 129) 2.34 0.13 Within Intensity (3, 129) 8.29 <.0001* p <.05
44 Table 3-4. Post-hoc results of angle and displacement measur es between intensity levels. t p Intensity A1 50 vs. 75 -2.71 0.50 50 vs. 100 -1.92 0.045* 75 vs. 100 -1.37 0.17 A2 50 vs. 75 -3.21 0.002* 50 vs. 100 -2.45 0.01* 75 vs. 100 -0.80 0.42 D1 50 vs. 75 2.65 0.26 50 vs. 100 1.14 0.04* 75 vs. 100 1.67 0.09 D3 50 vs. 75 -2.41 0.02* 50 vs. 100 1.99 0.96 75 vs. 100 -0.04 0.049* *p <.05 Table 3-5. Means and standard deviations associated with the Penetration-Aspiration Scale scores at each intensity level. Intensity 0 50 75 100 5ml 1.00 (0.00) 1.00 (0.00) 1.20 (0.62) 1.50 (0.89) Bolus size 20ml 1.10 (0.45) 1.15 (0.49) 1.10 (0.45) 1.65 (1.27)
45 A10 5 10 15 20 05075100 Intensity LevelAngle (degrees) Bolus A20 5 10 15 20 25 05075100 Intensity LevelAngle (degrees) Bolus D10 5 10 15 20 25 05075100 Intensity LevelDisplacement (mm) Bolus D30 1 2 3 4 5 05075100 Intensity LevelDisplacement (mm) Bolus Figure 3-1. Hyoid movement measures including A1, A2, D1, and D3 across intensity levels (collapsed across bolus size).
46 CHAPTER 4 DISCUSSION Traditionally, dysphagia treatm ents have incl uded diet alterations, positional changes of the head and neck, oral and neck strengthening exercises, and swallowing maneuvers (Bulow, Olsson, & Ekberg, 2005; Clark, 2003; Langmore & Miller, 1994; Lazarus, Logemann, Song, Rademaker, & Kahrilas, 2002; Logemann, 1993; L ogemann, Pauloski, Rademaker, & Colangelo, 1997; Robbins, Hind, & Logemann, 2004; Shaker et al., 1997; Veis et al., 2000; Zuydam, Rogers, Brown, Vaughaqn, & Magennis, 2000). While outcomes of these techniques have increased swallow safety (e.g. chin tuck and swallowing maneuvers) and some have addressed the effect of bolus size on swallowing (e .g. diet modifications), none have measured physiological change in swallow via hyoid movement Airway closure via anterosuperior hyoid movement along with laryngeal elevation, epiglo ttal positioning, and vocal fold adduction is essential in order to prevent the bolus from ente ring the airway. If excu rsion of the hyoid is diminished or decreased during swallowing, indivi duals risk penetration or aspiration (Lundy et al., 1999). Therefore, determining risk of penetr ation or aspiration via airway closure may be gained by measuring hyoid movement. An emerging and controversial area for treatm ent of dysphagia which targets muscles for swallow is the clinical application of surf ace neuromuscular electrical stimulation (NMES), marketed as VitalStim Therapy. NMES uses electr ical stimulation in an attempt to activate weak muscles and aid in recovery of motor control (Bax et al., 2005; Daly et al., 1996; Hainaut & Duchateau, 1992; Lake, 1992; Parker et al., 2003) to achieve ma ximal hyolaryngeal excursion for reduction or elimination of aspiration or penetration events (Wijting & Freed, 2003) enabling a safer swallow.
47 Clinical utilization of NMES for dysphagia is expanding at a rapid rate despite limited research studies. Lack of empirical study threat ens evidenced-based practic e and related clinical practice guidelines. The effects of different am plitudes of stimulation have not been thoroughly examined in relation to hyoid movement. This is important to examine because amplitude level affects the magnitude of stimulated muscle c ontractions (to move the hyoid), which in turn reflects clinical benefit and swallowing safe ty of NMES. Moreover, the recommended maximum tolerable NMES amplitude level for swallowing therapy is based on physical therapy protocols rather than on specific swallow-related research for application to small, specialized swallowing muscles. As well, the effect of bolus size on hyoid movement during NMES swallow has only been studied at boluses of 3ml and 5ml, both of which are smaller than a typical swallow. Safe swallowing during NMES has not been thoroughly studied Therefore, the aims of this project were to determine the effects of NMES on the angle and displacement of hyoid bone movement during swallow and to further determine the effects of various amplitude levels of NMES intensity in order to assess NM ES tolerability, its effect on hyoid movement and its effect on swallow safety as measured by pe netration and aspiration events. Accomplishment of these aims is important for expanding unders tanding of surface electr ical stimulation as a swallowing therapy. Findings of this study supported the hypotheses that discrete differe nces do exist with regards to hyoid bone movement (as measur ed by displacement and angle) during NMES swallow at varying intensity levels Further analysis of intensity levels indicated differences in hyoid angles and displacements between 50% and 75%, and 50% and 100% in tensity levels. No significant difference was found in hyoid angles and displacements between the 75% and 100% intensity levels, suggesting that these two leve ls of intensity produce similar hyoid movement.
48 This finding may be clinically useful in determining which inte nsity level is more appropriate (and more tolerable) for NMES swallowing rehab ilitation. If a 75% level is comparable to a 100% level of intensity, discomfort for the patient could be spared or lessened with a lower intensity. This finding refutes current interpre tation of NMES which adheres to the philosophy that maximum intensity as tolerated by the pa tient is necessary to achieve maximum motor movement (muscle contraction). NMES and Bolus Size It was an objective of this study to m easure NMES swallow with a small liquid bolus (5ml) and a more challenging liquid bolus (20ml) approximating a natural swallow size. Other studies report penetration in a smaller bolus size of 5ml thin liquid using NMES in healthy participants (Humbert et al., 2006) and in pa tients with dysphagia (Ludlow et al., 2007). Although bolus size was not found to be significantly different with regard to intensity leve l in this study, 39% of penetration events occurred on a 5ml bolus while the majority of penetration events (61%) occurred with the 20ml bolus. No controlled experimental studies exist for comparison using a 20ml bolus during NMES swallow. In other studies, bolus size has been shown to change oropharyngeal swallow physiology in healthy pa rticipants (Bisch, Logemann, Rademaker, Kahrilas, & Lazarus, 1994; Dantas et al., 1990 ; Kahrilas et al., 1993; Logemann et al., 1992). However, none of these studies used NMES as a modality when measuring physiological changes during swallow. Therefore, results of the current study are novel in that a large bolus size was tested during NMES swallow. NMES Intensity Level Muscle recruitm ent patterns using NMES are universal in that type II fibers are synchronously activated before type I fibers, pr oducing high speed, forcef ul contractions of muscles (Korfage, Schueler, Brugman, & Van Eijd en, 2001; Stal, 1994). Th is type of muscle
49 recruitment is engaged at the maximum intensit y level for NMES in physical therapy. The maximum intensity level has been successful in ph ysical therapy to activate targeted muscles or muscle groups and restore function. VitalStim ha s adopted this treatment modality and intensity rationale for NMES in swallowing therapy. It is l ogical to think that striated muscle response in one part of the body might work in the same way in the swallowing muscles. However, swallowing muscles are much smaller than any ot her muscles rehabilitated in physical therapy, and collectively have a different anatomical organization and speci alized function than any other area of the body. Swallowing is a complex neuromuscular pro cess involving 31 paired striated muscles innervated by five cranial nerv es (Dodds et al., 1990). Swallowi ng muscles particip ate in a large variety of motor tasks, including mastication, tongue propulsion, velopharyngeal closure, epiglottic inversion, hyoid excursion, laryngeal elevation, peristaltic contractions and UES opening. In addition to swallowing, some of th ese same muscles have dual roles for speech articulation, voice production, cough production and other respirat ory-related ac tivity. These activities require neuromuscular specializati on and a diversity of forces which must be maintained under various contra ction velocities (Kor fage, Koolstra, Langenbach, & Eijden, 2005). To be able to perform the vast array of different tasks, the system contains many different muscles. The fact that not one muscle or muscle fiber type can perform all activities effectively explains why the swallowing muscles contain many fiber types. When a musc le is composed of one particular fiber type, it is optimized to perform one t ype of activity. However, this reduces its ability to perform another type of activity. The mo re variation in fiber-type composition of a muscle the larger its potential role in different motor tasks. To achieve a wider repertoire of movement velocities, and to sustain different durations of activation, swallowing muscles use
50 different fiber types (Mu & Sanders, 1998; Mu & Sanders, 2000; Mu & Sanders, 2007; Ren & Mu, 2005; Slaughter, Li & Sokoloff, 2005). In neuromuscular junctions, the size of th e presynaptic nerve terminal, the area of postsynaptic specialization, and the duration of synaptic currents are relative to the size of muscle fibers (Slater, Lyons, Walls, Fawcett, & Young, 1992). Due to the relatively small fiber size of swallowing muscles, presynaptic terminals are small and synaptic currents are long in duration. These properties enable swallowing musc les to require less stimulation amplitude for neuromuscular transmission and muscle contraction. Therefore, swallowing muscles may respond differently at various leve ls of intensity, specifically at a maximum level of stimulation than do other muscles. With regard to stimulation intensity level, this study showed significant differences in hyoid angles and displacements between the low (50%) intensity level and the mid-intensity level (75%), and between 50% and the high (100 %) levels. A novel finding was that there were no differences in hyoid angle and displacement measures between the 75% and 100% levels. This result suggests that a higher intensity or amplitude of electrical stimulation during swallowing that is aimed at maximum motor recruitment may not be better than a slightly lower one, and that limited frequency, phase width an d phase duration parameters (as with the VitalStim unit) are not sufficient to change hyoid angle and displacement. In fact, most penetration events during this study took place at the 100% intensity level, suggesting that the highest level of stimulation to lerance may not be safe for sw allowing therapy. Also, 100% of tolerance produced some level of discomfort for most participants. This discomfort may be lessened or eliminated by lowering the intensity to the 75% level while achieving comparable or better hyoid movement (more superior a nd anterior) than the 100% level.
51 Other NMES Parameters Effects of electrical st imulation (pr imarily targeted mu scle activation) are dependent on muscle depth, intensity of stimulation and othe r parameter settings, and subcutaneous adipose tissue at the electrode site. In addition to intensity, other mechanic al unit settings involved in the application of electrical stimul ation need further study for NM ES in swallowing. Presently, pulse width, pulse duration and frequency of th e VitalStim unit are fixed at 700 ms, 59 seconds, and 80 Hz, respectively. VitalStim amplitude (int ensity) has a ceiling of 14 mA. These chosen parameters are not specific to swallow musculat ure nor have they been empirically manipulated or studied. Pulse width is required to be high enough in or der to recruit motor axons over sensory axons (Baldwin, Klakowicz, & Collins, 2006). Pulse duration variation allows for control of isometric torque and activated muscle cross-sectional area. Manipulating frequency parameters changes specific muscle tension. Cha nges in intensity affect torque and the area of activated muscle proportionally (Gorgey, Mahoney, Kendall, & Dudley, 2006) and may be the most effective parameter that can be used to enhance NMES effects (Han, Kim, Lim, & Lee, 2007). The manipulation of these parameters fo r NMES as a swallowing therapy modality may yield more desirable physiologic changes (e.g. in creased hyolaryngeal elevation), safer swallow and less stimulation discomfort for patients with dysphagia. It is essential to determine optimal parameters of stimulation for targeted muscles in order to maintain appropriate muscle force during NM ES. Protocols that use variable frequency, double-pulse stimulation and submax imal intensity have been eff ective in maintaining muscle contraction and prolonging force output over time (Doucet & Griffin, 2008). In physical therapy, the trained therapist is able to select NMES parameters based on the specific muscle(s) of interest (composition, size, a nd depth), functional objectives, and patient tolerance. The magnitude of swallowing muscle adaptations in regards to pulse width and duration, frequency,
52 and intensity are matters of debate and require much more study and extensive training for the clinical speech pathologist. For example, if the VitalStim unit allowed for variable frequency with submaximal intensity, physiological propertie s (torque, fatigue, contractile potential) of the suprahyoid muscle group may change to reflec t increased hyoid movement and prolonged hyoid elevation. Hyoid Movement Movem ent of the hyoid bone during the phar yngeal stage of swallowing is dependent upon collective contraction of the submental muscle group (myloh yoid, geniohyoid, and anterior belly of the digastric muscles) and c ontraction of the thyrohyoid muscle which in turn elevates the larynx (or pulls the hyoid downward toward the larynx). Airway closure via hyolaryngeal movement, epiglottal positioning, and vocal fold adduction has to occur to prevent the bolus from entering the airway. Penetration can result if excursion of the hyoid and larynx is diminished or decreased during swallowing. In addition to penetration events which occurred during this study, a decrease in maximum hyoid displacement (as compar ed to initial hyoid displacement) was found in 28 of 40 participant swallowing trials at the 100% intensity level. Whereas the angle of hyoid movement is indica tive of mostly superior movement, hyoid displacement involves a combination of anteri or and superior move ment (Figure 4-1). Therefore, it is suspected that at the 100% le vel, muscles responsible for lowering the larynx (e.g. sternohyoid and omohyoid) were engaged by el ectrical stimulation, preventing and actually reversing normal hyoid excursion during swallo w. Given that the sternohyoid and omohyoid muscles are large and overlie the deeper thyrohy oid muscle responsible for elevating the larynx to the hyoid, it could be hypothesized that high leve ls of NMES over the t hyroid region, as tested in this study, could pull the hyoid downward b ecause of stimulation of the sternohyoid and omohyoid muscles and a lack of stimulation to the deeper thyrohyoid muscle. It is also
53 suspected with electrodes placed over the submental area that the 100% level was able to stimulate the anterior belly of the digastric muscles to pull the hyoid upward but unlikely to have reached much deeper muscles, such as the mylohyoid and geniohyoid muscles. Hence with possible sternohyoid and omohyoid activation causing la ryngeal descent plus stimulation of only potentially one of the three submental muscles responsible for hyoid movement, hyoid excursion was collectively reduced at the 100% intensit y level. These deductions were proposed by Ludlow et al. (2007) when hyoid depression occu rred in participants with dysphagia during NMES. Ludlow hypothesized that at lower intensities, surface NM ES merely activates sensory nerve endings in the skins surface layers. Se nsory stimulation is thought to possibly improve swallow as a result of sensory facilitation and increased awareness rather than actual muscle activation, evident in results from Ludlows study when aspiration was significantly reduced in participants with dysphagia only at the low sens ory levels of stimulation. Findings from the present study support this theory with increased hyoid displacement at the lower intensity (sensory) level of 50%. The decrease in hyoid displacement at the 100% intensity level can also be explained by a ceiling effect of muscle contrac tion. When a muscle is electrical ly stimulated, the steady state force of the muscle increases, thus increasi ng muscle tone and stiffness (Oskouei & Herzog, 2005). This steady state force ha s been observed in single muscle fibers, isolated muscles and muscle groups during electrical stimulation (Abbott & Aubert, 1952; deRuiter, Didden, Jones, & de Haan, 2000; Lee & Herzog, 2002). It is possibl e that muscle tone and stiffness reached a maximum during the 100% intensity level of stimu lation. The addition of the functional task of swallowing during 100% stimulation intensity could not increase mu scle stiffness of suprahyoid or thyrohyoid muscles because it was at its maximum. Therefore, muscle contraction at the
54 100% level during swallowing exhi bited a plateau effect, and hyoi d movement was arrested at the point of maximum stiffness of the stimulated muscles. Hyoid depression with NMES at rest (while not swallowing) was found in healthy adults tested at maximum tolerance intensity levels (Humbert et al., 2006). Stimulation-induced hyolaryngeal descent at rest co uld not be overcome by the healthy participants as NMES swallows were rated as unsafe (penetration into the laryngeal vestibule). Although resting NMES hyoid movement was not measured in th is study, inability to overcome a possible hyoid descent at rest could be an additional explanation of the d ecreased hyoid displacements during NMES swallows at the 100% intensity level. Penetration Events Rating scales have been created in an effort to quantitatively describe patterns of deficits in videofluoroscopic swallowing studies, with som e lending to errors of misinterpretation (Robbins, Coyle, Rosenbek, Roecker, & Wood, 1999). Rosenbe k et al. (1996) developed the PAS, an 8point scale to quantify penetrati on and aspiration events determined by scores rating material depth in the airway and expulsion of material (Appendix C). Othe r quantitative scales have been created and utilized to further describe and ra te swallowing events during videofluoroscopy such as pooling of residues in pyriform sinuses or in valleculae and backflow or regurgitation events (e.g. NIH Swallowing Safety Scale). However, these additional events were merely more descriptive, or qual itative, and were not found to impact pe netration or aspiration (Ludlow et al., 2007). Penetration and aspiration ev ents with additional aspects of the depth to which material passes into the airway and whet her or not it is expelled appear to hold important clinical relevance (Robbins, Coyle, Rosenbek, Roecker, & Wood, 1999). In addition, reliability and validity of other tools have not been confirmed. The PAS has high reliability and validity and its ordinality has also been established (McCu llough, Rosenbek, Robbins, Coyle, & Wood, 1998).
55 As stated previously, there were 17 events of penetrati on as rated with the PAS in this study of healthy participants during swallows of both bolus sizes. An example of penetration is shown in Figure 4-2. Four penetration events were rated as a : material entered the airway above the vocal folds and was ejected. Three of those four were during 20ml swallows at 100% intensity. Eleven penetration events rated a : material entered the airway above the vocal folds but was not ejected, with six out of the 11 at 100% intensity. The remaining two penetration events scored a (material entere d the airway, contacted the vocal folds, and was not ejected) with 20ml at 100% intensity. Overall, the rate of penetrat ion in the current study of healthy participants was 4.25% during NMES swallow, occurring in 50% of the pa rticipants, with the highest (worst) penetration score of a Robbins and colleagues (1999) reported a 2% rate of penetration in 21% of healthy participants, with no penetration scores exceeding a The 17 penetration events in this study of healthy participants with otherw ise safe swallow that occurred following the methods as recommended by VitalStim guidelines, suggests that maximum intensity levels of NMES aimed at increasing hyolaryn geal excursion to promote safe r swallow may increase risk of penetration during swallow in healthy persons. Furthermore, these guidelines, if used with persons with dysphagia could resu lt in even greater risk of pe netration or possible aspiration during swallow. Because radiation exposure was administered in this study in healthy volunteers for research purposes only and was not necessary for medical care, the Radiation Safety Committee limited the exposure time per participant for th e total study. Therefore, depending on exposure time for each participant, some swallows were not filmed for a complete 2 seconds after the bolus passed through the UES as is recommended for PAS rating (Rosenbek et al., 1996). The
56 PAS raters did not have sufficient information to score five out of the 400 swallows of the study, and these five were excluded from PAS analysis. Other Swallowing Events Additiona l events occurred th at were not captured in PAS ratings and did not influence swallowing safety but are deservi ng of mention. One 22-year old female participant exhibited a cricopharyngeal prominence in all twenty sw allows as displayed in Figure 4-3. A cricopharyngeal prominence is characterized by an obstruction of the lumen of less than 50% at the level of the cricoid cartilage. This makes an indentation in the barium column that persists throughout the swallow. Cricophary ngeal achalasia, or persistent spasm of the CP can cause failure of the CP to relax ad equately, contributing to a CP prominence and symptoms of dysphagia, including penetrati on (Logemann, 1998). However, although a CP prominence was present in all swallows including baseline swallows all swallows of this individual were scored as a (material did not enter the airway), exhi biting no penetration. In another case, a 26-year old female participant encounter ed backflow of bolus at the level of the cricopharyngeus in several NMES swallows. Functionally, the CP act s as the upper esophageal sphincter relaxing to allow bolus passage into the esophagus during swa llowing, and remaining toni c at rest to prevent reflux of gastric contents and air from enteri ng the esophagus. Although one swallow of this participant yielded a penetration event (with a PAS of ), no CP dysfunction was present on this particular swallow. All other swallows were rated normal. CP dysfunction can be accompanied by other abnormal swallowing events such as laryngeal spillover, aspiration, nasopharyngeal regurgitation, and ph aryngeal stasis. CP achalasia may or may not be a predictor for penetration or aspiration depending on the le vel of dysfunction (Baredes, Shah, & Kaufman, 1997).
57 Aryepiglottic residue, or resi due at the level of the aryepi glottic folds of the larynx was observed in two NMES swallows of another 26-year old female participant. Valleculae filling with overflow reaching the aryepiglottic folds oc curred before the pharyngeal stage of swallow was triggered, signifying delayed pharyngeal swal low. Both abnormal swallows were given a penetration rating of indicating that material had entere d the laryngeal vestibule and remained above the true vocal folds. All other swallows were rated as normal. Three events of penetration in the NMES sw allows of a 48-year old male participant involved premature spillage of the bolus into th e valleculae before the pharyngeal swallow was triggered. All three penetration swallows were rated a (bolus entered the airway above the level of the true vocal folds and was ejected). The other 17 swallows by this individual also involved premature spillage but th e material did not enter the ai rway, scoring on the PAS. The variation in swallow latency among flow rate s has been found directly related to the duration of liquid containment within the vallecul ae (Pouderoux, Logemann, & Kahrilas, 1996). This suggests that the valleculae may act to contai n secretions and resi due and prevent overt aspiration by diverting contents around the larynx before swa llowing. Healthy populations with intact vocal fold closure would not experience aspirati on from this deficit. However, patients with dysphagia involving decrea sed laryngeal elevation and in complete vocal fold adduction could aspirate on material around the larynx. Summary and Conclusions In conclusion, four of the six hyoid move ment measures examined in this study were found to be discretely different from one another acro ss tested intensity levels of 50%, 75%, and 100%. In addition, congruency was found in the 75% a nd 100% levels for hyoid movement. As well, penetration occurred in several swallows at the 100% level which placed healthy participants at risk for unsafe swallowing. These results lend insi ght into effects of maximum intensity levels
58 and overall safety issues during NMES swallow as measured by penetration, and imply cautious utility of NMES and careful profiling of patients with dysphagia by clinicians. In addition to mixed reports of muscle recr uitment activity and overall effects of NMES, many more variables need additional study re garding NMES swallow therapy such as appropriate amplitude, timing and duration of th e stimulation, frequency and pulse patterns, electrode placement, and effects of bolus consis tency on swallow outcomes. This study did not address whether or not NMES aids dysphagia ther apy in patients at risk for penetration or aspiration. However, because this study yielded penetration with NMES in healthy volunteers with typically intact swallow, safety of NMES for swallowing therapy remains questionable for patients with dysphagia. Outcomes from this study help to direct future research on the safety of NMES for swallowing and contribute to the present lite rature base. Generally, there is a strong neurophysiologic rationale for a procedures application to a particular patient population, followed by small studies that define efficacy, then larger group studies involving several patient populations, and finally randomized clinical trials to determine efficacy (Robey, 2004). VitalStim inventors neglected clinic al research responsibility, clin ician ethics and patient safety by not taking these steps before marketing the product. Patients with dysphagia who are anxious for additional treatment to improve swallowing f unction and quality of life seek the opportunity to try even experimental techniqu es. Clearly, more work needs to be done in larger double-blind studies and other clinical trials to reevaluate NMES swallow rationales, to demonstrate VitalStim Therapy's effectiveness and reliability, and to evaluate long-term results. Future studies using NMES for swallowing will con tinue to assist patients and clinicians in determining if the use of NMES is an effective treatment for dysphagia. First, NMES swallow in
59 healthy populations needs continued study in order to understand neurophysiology of the application. As well, experimentation with unit parameters (int ensity, pulse duration and width, and frequency) is necessary to determine which settings will elicit desi red physiological changes (e.g. increased hyoid elevation) and preven t unsafe events (e.g. hyoid depression and penetration). Secondly, controlle d studies directed specifically toward patient populations with dysphagia are needed to confirm appropriate pa rameters for NMES swallow, and to further examine hyoid movement and swallowing safety in order to esta blish NMES swallow effectiveness and efficacy data. Specifically, futu re studies will entail manipulation of VitalStim frequency and phase parameters as well as ex tended study of intensity levels to determine appropriate stimulation settings for NMES swallow through measures of hyoid movement, muscle activity and recruitmen t (via electromyography), and penetration/aspiration ratings, further addressing swallowing safety of NMES. Effects of varying bolus consistencies on hyoid movement and muscle activation during NMES swa llow will also be investigated. In addition, future research will address immediate and long-t erm effects of VitalStim Therapy (via treatment paradigms) involving larger hea lthy participant groups and define d populations with dysphagia.
60 Figure 4-1. Sample hyoid displacem ent (a) as a combination of an terior and superior movement. Figure 4-2. Penetration, as denoted by the arrow. a
61 Figure 4-3. Cricopharyngeal prominence (at arrow).
62 APPENDIX A HEALTH HISTORY QUESTIONNAIRE Subject # __ __-__ __ Age: __ __ Gender (M/F): ___ Have you ever had significant di fficulty swallowing? (Y/N): ___ Have you ever been told you have/had dyspha gia (a swallowing diso rder)? (Y/N): ___ Do you have a history of any of the following conditions? (Y/N): ___Rheumatic fever ___Mitral valve prolapse or other cardiac problems, including a pacemaker ___Pulmonary disease ___Neurological problems ___Otolaryngological problems ___Psychiatric disorder ___Gastroesophageal disease ___Head and neck cancer ___Speech or swallowing problems If yes to any, please explain: ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________
63 APPENDIX B INTENSITY SCALE
64 APPENDIX C PENETRATION-ASPIRATION SCALE ( Rosenbek et al., 1996) 1 Material does not enter the airway 2 Material enters the airway, rem ains above th e vocal folds, and is ejected from the airway. 3 Material enters the airway, remains above the vocal folds, and is not ejected from the airway. 4 Material enters the airway, contacts the vocal folds, and is ej ected from the airway. 5 Material enters the airway, contacts the vo cal folds, and is not ejected from the airway. 6 Material enters the airway, pa sses below the vocal folds, and is ej ected into the larynx or out of the airway. 7 Material enters the airwa y, passes below the vocal folds, and is not ejected from the trachea despite effort. 8 Material enters the airwa y, passes below the vocal folds, and no effort is made to eject.
65 APPENDIX D DATA FOR ANGLE OF HYOID DISPLACEMENT AT INTENSITY LEVELS
66 Note: A1=angle associated with maximum displacement; A2=maximum angle; A3=angle at end of task; 50=50% intensity level; 75=75% intensity level; 100=100% intensity level. Subject Sex Bolus (ml) A1 0 A1 50 A 1 75 A1 100 A 2 0 A 2 50 A 2 75 A2 100 A3 0 A 3 50 A 3 75 A3 100 1 F 5 3.18 5.165.0312.877. 117.639.5413.61 3.040.543.441.85 1 F 20 4.60 17.255.858.7211. 5217.739.2812.13 0.793.051.361.22 2 F 5 3.17 7.230.969.2215. 79.016.579.83 0.133.790.500.33 2 F 20 16.14 12.7713.5419.7116.64 12.9417.2221.17 0.6220.127.116.11 3 F 5 14.57 0.805.297.7816. 058.368.9910.51 0.654.052.990.50 3 F 20 9.85 8.3114.8610.1111.83 13.4514.8611.91 0.711.214.050.48 4 F 5 3.10 11.103.350.1914. 3815.5212.627.33 0.812.012.151.96 4 F 20 4.17 1.0610.194.529.49 7.299.1612.20 0.337.295.672.25 5 M 5 7.90 21.082.9413.7515. 8321.0811.8716.74 0.960.420.152.04 5 M 20 6.36 5.961.348.738.40 11.7816.4014.59 0.286.961.504.48 6 M 5 6.03 14.991.5516.838. 3716.1516.4216.83 0.370.720.881.37 6 M 20 5.46 7.862.389.977.87 12.0016.5113.87 0.874.421.472.88 7 M 5 13.24 16.7619.6610.3414. 0823.9124.1815.57 2.610.420.021.94 7 M 20 14.65 28.3911.5924.4817.04 30.2823.8326.85 0.171.584.494.46 8 F 5 5.05 5.215.284.6013. 0710.1218.9121.02 0.911.661.711.06 8 F 20 9.18 1.479.891.1313.53 6.6712.665.46 0.300.200.291.31 9 F 5 6.58 2.105.3417.508. 872.568.5517.50 0.931.002.942.13 9 F 20 6.42 0.038.094.4712.68 3.5710.729.29 4.042.141.683.97 10 M 5 6.22 6.677.008.327.37 21.1315.5611.80 0.240.201.569.84 10 M 20 3.29 7.407.522.5810.7610. 216.2319.64 0.740.748.0519.3 11 M 5 7.19 12.449.922.3110.54 16.5717.5810.80 3.291.353.841.81 11 M 20 8.52 8.4313.876.7012.1211. 3216.4014.29 0.271.810.913.86 12 F 5 17.01 0.7318.549.0217.01 14.3918.5427.25 2.962.161.622.14 12 F 20 12.88 16.528.7115.2515.5516. 5217.7215.77 3.492.003.535.64 13 F 5 13.29 7.2614.4619.3214.78 13.9717.3623.21 1.763.450.793.93 13 F 20 6.55 10.156.4619.819.8411. 757.4424.49 4.830.524.621.92 14 M 5 26.84 21.5223.9429.3631.02 23.2525.6329.36 1.835.671.905.32 14 M 20 9.77 16.6326.1630.4116.1923. 0029.0630.52 6.230.001.562.75 15 F 5 2.92 0.323.774.0116.26 11.2912.1818.99 1.366.965.831.23 15 F 20 3.76 7.0910.7813.199.5210. 6714.4117.67 0.975.636.591.74 16 F 5 13.43 11.108.3520.2315.07 13.7214.0222.38 2.164.464.851.54 16 F 20 17.84 15.2712.5513.3722.3817. 7816.2915.42 1.785.975.431.09
67Subject Sex Bolus (ml) A1 0 A1 50 A 1 75 A1 100 A 2 0 A 2 50 A 2 75 A2 100 A3 0 A 3 50 A 3 75 A3 100 17 M 5 8.62 14.1312.6314.4113.44 17.7212.6316.25 4.321.872.843.57 17 M 20 13.44 15.9116.9816.5314.7419. 1819.4616.84 1.341.982.005.66 18 M 5 0.16 3.2521.404.726.23 8.8121.406.69 3.782.753.962.91 18 M 20 12.06 6.709.655.9214.708. 4817.1713.48 5.672.022.061.72 19 M 5 0.21 3.033.952.3612.44 9.8113.7712.09 1.440.540.561.57 19 M 20 4.93 6.908.642.749.3012. 0913.417.72 0.400.020.352.09 20 M 5 9.63 11.779.6710.5312.94 12.8614.8511.75 2.043.174.103.60 20 M 20 8.38 10.886.7421.0210.0118. 2717.4921.02 1.383.161.464.82
68 APPENDIX E DATA FOR HYOID DISPLACEMENT AT INTENSITY L EVELS
69Note: D1=maximum displacement; D2=displacem ent associated with maximum angle; D3 =displacement at end of task; 50=50% intensity level; 75=75% intensity level; 100=100% intensity level. Displacements have been normalized for each participant. Subject Sex Bolus (ml) D1 0 D1 50 D1 75 D1 100 D2 0 D2 50 D2 75 D2 100 D3 0 D3 50 D3 75 D3 100 1 F 5 10.93 19.7920.2616.523.327.0110.9913.54 1.314.754.551.22 1 F 20 13.37 15.1416.5717.334.01 14.8013.9114.52 1.372.463.251.24 2 F 5 9.65 12.498.3911.785. 342.020.1513.98 2.795.443.273.66 2 F 20 15.94 18.5312.4315.3315.94 12.9611.9415.16 0.693.250.350.56 3 F 5 11.94 14.8013.709.4111.795.601.902.83 0.022.504.500.54 3 F 20 13.59 12.1617.6710.321.81 5.4917.671.01 1.700.382.464.18 4 F 5 15.55 14.7713.889.775. 962.972.903.80 0.692.360.620.74 4 F 20 12.16 17.3911.1811.006.94 6.133.055.33 0.418.104.22.168 5 M 5 13.80 13.1417.7520.961. 2213.145.8310.24 0.200.593.440.26 5 M 20 16.08 16.9715.2018.476.03 10.978.454.74 3.110.791.000.11 6 M 5 17.74 9.6915.109.1717. 747.140.489.17 0.235.202.641.31 6 M 20 9.52 15.6513.9811.679.52 11.582.297.43 3.681.632.821.35 7 M 5 18.33 17.0519.1512.3117. 3215.8312.132.23 1.433.933.281.68 7 M 20 22.46 22.5413.5613.9017.53 22.057.7511.04 2.193.061.480.67 8 F 5 16.54 17.797.0911.652. 770.6014.514.40 3.770.7010.33.38 8 F 20 20.89 18.8418.9719.454.61 2.6516.477.71 1.610.491.822.12 9 F 5 12.77 11.3513.7011.171.899.835.0311.17 0.300.560.051.57 9 F 20 27.23 13.4513.0412.510.06 4.2511.3115.30 1.432.504.041.95 10 M 5 18.34 22.9118.8317.9011.61 8.915.754.32 22.214.171.1243.06 10 M 20 23.11 18.7520.4617.68.583.8 89.546.48 3.571.871.443.37 11 M 5 4.08 14.2316.4210.722.02 5.184.332.68 3.120.563.202.68 11 M 20 13.16 3.4318.1621.480.920. 543.0516.35 0.011.810.006.00 12 F 5 12.83 12.5118.658.2712.83 4.9118.656.83 0.852.614.863.08 12 F 20 13.83 11.636.787.3413.7211. 636.763.22 1.870.802.142.65 13 F 5 18.68 18.5421.4326.9518.48 16.5516.2922.63 0.423.195.983.07 13 F 20 15.98 22.5218.0717.6710.2617. 8316.9912.46 1.172.552.310.94 14 M 5 22.06 18.9024.9911.0214.03 11.0116.3011.02 0.860.930.740.99 14 M 20 21.21 19.4515.5712.4416.0612. 3012.068.95 0.550.030.383.00 15 F 5 21.95 18.2124.0121.722.26 0.634.131.73 0.561.643.431.26 15 F 20 26.65 18.7120.8519.8133.159. 1918.912.21 0.491.051.530.36 16 F 5 13.14 15.1011.4611.628.49 12.145.809.89 0.230.224.603.57
70Subject Sex Bolus (ml) D1 0 D1 50 D1 75 D1 100 D2 0 D2 50 D2 75 D2 100 D3 0 D3 50 D3 75 D3 100 16 F 20 15.47 12.5912.3112.3912.197. 9910.499.77 5.605.102.694.23 17 M 5 15.17 10.1510.344.274.77 1.4210.343.72 1.744.394.643.51 17 M 20 15.68 11.7210.818.281.550. 778.727.22 2.770.697.841.24 18 M 5 22.46 5.0618.6822.097.93 23.5918.6816.12 0.500.691.354.23 18 M 20 13.32 4.314.2314.566.821. 837.709.51 0.250.003.410.25 19 M 5 17.70 14.6911.6311.986.14 3.237.269.09 0.145.183.811.64 19 M 20 12.43 13.518.889.511.3711. 066.540.07 0.840.543.370.06 20 M 5 21.32 22.420.9917.9817.78 22.2316.375.71 2.121.900.614.66 20 M 20 15.26 12.6210.3810.9512.4010. 5410.0010.95 0.052.511.790.27
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BIOGRAPHICAL SKETCH Christine M. Carm ichael received both her bachelors and masters degrees from the University of Central Florida in 2001 and 2003, respectively. Following completion of her Ph.D., she will begin a position as assistant pr ofessor at Our Lady of the Lake University, Department of Communication Disorders, in San Antonio, Texas. Her research plans for the future include the study of rehabilitation for dysphag ia and voice disorders. Her interests outside of academics include landscaping and gardening, drawing, cooking, and Florida Gator sports.