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ETHNIC DIFFERENCES IN RESPONSES TO MULTIPLE EXPERIMENTAL PAIN STIMULI By CLAUDIA M. CAMPBELL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004
Copyright 2004 by Claudia M. Campbell
iii ACKNOWLEDGMENTS This material is the result of work suppor ted with resources and the use of facilities at the Malcom Randall Veterans Affairs Medica l Center, Gainesville, FL. This work was also supported by National Institute of H ealth/National Institute of Neurological Disorders and Stroke, grant NS42754.
iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES...............................................................................................................v ABSTRACT....................................................................................................................... vi CHAPTER 1 INTRODUCTION........................................................................................................1 2 METHODS...................................................................................................................4 Participants................................................................................................................... 4 Psychophysical Measures.............................................................................................5 Thermal Pain Procedures.......................................................................................5 Ischemic-pain Procedure.......................................................................................6 Cold Pressor Pain Procedure.................................................................................7 Psychological Measures................................................................................................8 3 RESULTS...................................................................................................................10 4 DISCUSSION.............................................................................................................15 LIST OF REFERENCES...................................................................................................20 BIOGRAPHICAL SKETCH.............................................................................................25
v LIST OF TABLES Table page 1 Demographic Variables for African Americans and Whites.....................................4 2 Means (SD) for Experimental Pain Meas ures for African Americans and Whites, Including Sample Size, E ffect Sizes, and F-Values.................................................11 3 Means (SD) for Psychological Measures for African Americans and Whites.........12 4 Correlations of Experimental Pain Measures for African Americans......................13 5 Correlations of Experimental Pain Measures for Whites.........................................14
vi Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ETHNIC DIFFERENCES IN RESPONSES TO MULTIPLE EXPERIMENTAL PAIN STIMULI By Claudia M. Campbell May 2004 Chair: Roger B. Fillingim Major Department: Clini cal and Health Psychology A growing body of literature s uggests that the experience of clinical pain differs across ethnocultural groups. Additionally, some evidence indicates greater sensitivity to experimentally induced pain among African Americans; however, most studies have included only one pain modality. This study ex amined ethnic differences in responses to multiple experimental pain stimuli, including heat-pain, cold pressor pain, and ischemicpain. Subjects included 120 (62 African Am erican, 58 white) healthy young adults. Heatpain threshold and tolerance a nd ratings of repetitive suprat hreshold heat we re obtained. Also, ischemic and cold pressor pain thre shold and tolerance were determined, and several psychological instruments were admi nistered. Findings i ndicated no ethnic group differences on threshold measures, but that African Americans had lower tolerances for heat-pain, cold pressor pain, and ischemic-pai n compared to whites. Ratings of both the intensity and the unpleasantness of repeti tive suprathreshold heat stimuli were significantly higher among African Americans. No differences in mood appeared, but
vii African Americans reported greater use of passive pain -coping strategies and higher levels of hypervigilance. Use of pain-coping st rategies as a covariate did not account for group differences in pain responses, while use of hypervigilance rendered group differences in heat-pain tolerance and is chemic-pain tolerance nonsignificant. These findings demonstrate that differences in la boratory pain responses between African Americans and whites occur across multiple stimulus modalities; and effect sizes for these differences in pain tolerance were mode rate to large. Thus, ethnic differences in experimental pain responses a ppear to be largest for supr athreshold measures, and these differences were consistent across stimul us modalities and were relatively robust. Additional research to determine the mechanis ms underlying these effects is warranted.
1 CHAPTER 1 INTRODUCTION Pain is one of todays most expensive pub lic health issues, co sting in excess of 125 billion dollars annually (Turk et al., 1999). Each year, more than 35 million new office visits to physicians are caused by pain symptoms (Knapp and Koch, 1984), accounting for 80% of all office visits to physicians annually in the United States (Koch, 1986). Pains prevalence, severity, and impact on functioning may vary according to an individuals ethnicity (Ril ey, 2002). To improve pain diagnosis and treatment for individuals from diverse ethnic backgrounds relationships amongh race, ethnicity and pain must be better understood. In recent years, an expanding body of research has focused on discerning the particular contri butions of race and ethnicity to pain responding. Considerable evidence shows that the e xperience of clinical pain differs among ethnic groups (Edwards et al., 2001; Green et al., 2003). For instance, African Americans report higher levels of pain in clinical conditions such as glaucoma (Sherwood et al., 1998), AIDS (Breitbart et al., 1996 ), migraine headache (Stewa rt et al., 1996), jaw pain (Widmalm et al., 1995), postoperative pain (Faucett et al., 1994; White et al., 1999), myofascial pain (Lawlis et al., 1984; Nelson et al., 1996), angi na pectoris (Sheffield et al., 1999), joint pain (Rantane n et al., 1998), nonspecific daily pain (Edwards and Fillingim, 1999), and arthritis (Anders on and Felson, 1987; Creamer et al., 1999), compared to whites. In contrast, others have reported no significant ethnic differences in clinical pain severity (Todd et al., 1994; Jordan, 1999). Wh ile research suggests greater
2 severity and prevalence of temporomandibul ar disorder (TMD) in African Americans (Widmalm et al., 1995), a recent study by Ples h et al. (2002) indicat es higher frequency, earlier onset, and greater symptom severity among whites. More recently, several investigators noted ethnic differences in pain-related symptoms among patients with chronic non-cancer pain. Edwards and collea gues (2001) found higher levels of pain and disability among African Ameri cans relative to white patients seen in a multidisciplinary pain center. Other African Americans studi ed in a chronic pain center reported higher levels of pain unpleasantness, emotional res ponse to pain, and increased pain behaviors relative to whites (Riley et al ., 2002; Green et al., 2003). B ecause ethnic differences in clinical pain responses can be influenced by factors such as disease severity and disparities in pain treatment, it is importa nt to examine ethnic differences in pain perception among healthy indivi duals (Stewart et al., 1996; Todd, 1996; Cleeland et al., 1997; McCracken et al., 2001). Early labor atory studies, reviewed by Zatzick and Dimsdale, suggested increased experimental pain sensitivity among African Americans as compared to whites (1990). For instance, lower heat-pain thres holds and tolerances were reported decades ago among African Am erican subjects compared to whites by Chapman and Jones (1944). Similarly, cold pressor pain tolerances were lower in a combined group of African Americans and Hisp anics in comparison to whites (Walsh et al., 1989). Two recent studies demonstrated greater sensitivity to heat-pain among African Americans compared to whites, especially fo r measures of pain unpleasantness (Edwards and Fillingim, 1999; Sheffield et al., 2000). T hus, ethnic differences in responses to both clinical and experimental pa in have been reported; howev er, most previous studies
3 included only one form of experimental pai n, and varied considerably in their paininduction methods (Zatzick & Dimsdale, 1990) Therefore, the pattern of ethnic differences across different stimulus modaliti es has not previously been evaluated. Moreover, few investigators have examined the contribution of ps ychological factors to ethnic differences in pain perception, though multiple authors have noted the importance of evaluating the influence of these vari ables (Zatzick and Dimsdale, 1990; Rollman, 1998; Edwards et al., 2001; Green et al., 2003). This study was designed to further elucidate the nature of ethnic differences in pain perception by investigating responses to multiple experimental pain modalities, and assessing psychosocial variables that may contribute to group differences in pain sensitivity.
4 CHAPTER 2 METHODS Participants The total study sample consisted of 120 healthy young adults (62 African American, 58 white) recruited from a southeas tern university. Subj ects received course credit for their participati on in the study. Participants demographic information is presented in Table 1. The University of Alabama at Birminghams Institutional Review Board approved all study procedures. Table 1. Demographic Variables for African Americans and Whites. Variable African Americans (n=62) Whites (n=58) Age (SD) 20.1 (2.6) 22.1 (5.8) Sex (% female) 67.6 47.1 All subject participated in a single expe rimental session involving psychophysical testing. The data reported below represen t information collected in two different experiments, and not all experiments included every pain task. Ther efore, the number of subjects differs across pain tasks; howe ver, the two ethnic groups were equally distributed across experiments. For all studies, verbal and written informed consent were obtained on arrival; after whic h, participants completed a h ealth history questionnaire, which indicated that all were in good health and had no prior history of pain problems. Ethnicity was determined using self-report. Subjects who described themselves as either African American or non-Hisp anic white were included in the analyses. Participants from other ethnic groups were not included in the analysis. This included 11 Asians, 1
5 Hispanic, 1 Native American, and 4 who e ndorsed the other et hnic category. Next, subjects completed several psychol ogical measures (see below). After the questionnaires, the laborato ry pain-induction procedures were administered. In one experiment, 3 pain procedures were conducted: thermal pain, ischemic-pain, and cold pressor pain. In th e other experiment, each of these procedures except for cold pressor pain was conducted. The thermal procedure was conducted first, followed by ischemic and cold pressor pr ocedures (when applicable), and also administered in counterbalanced order. A 15-minute rest period was allowed between pain-induction procedures. Psychophysical Measures Thermal Pain Procedures Threshold/tolerance. Contact heat stimuli were delivered using a computercontrolled Medoc Thermal Sensory Analy zer (TSA-2001, Ramat Yishai, Israel), a peltier-element-based stimulator with a 30 x 30 mm surface area. Heat-pain threshold (HPTh) and heat-pain toleran ce (HPTo) were assessed on th e ventral forearm using an ascending method of limits. The temperat ure increased from a baseline of 32 C with a 0.5 C/sec rate of rise, until the subject res ponded by pressing a button. Between trials, the positioning of the thermode was moved up the arm slightly, to avoid overlapping the testing sites, and a 30-second interstimulu s interval was maintained. The cutoff temperature (to avoid tissue damage) for all trials was 52 C. Heat-pain threshold was determined first. Subjects were instructed to press a button on a hand-held device when the thermode first produced a painful sensation. Each time the button was pressed, the temperature of the thermode was recorded. Four trials
6 were conducted in order to obtain consiste nt results; the heat-pain threshold was determined as the average of these trials. Heat-pain tolerance was then determined by instructing the subjects to press a button when the pain from the thermode became intolerable. The temperature of the thermode at the time the button was pressed was recorded. Four trials were conducted and heat-pain to lerance was determined by averaging these trials. Temporal summation. After a 5-minute rest, the th ermode described above was placed on the dorsal forearm. A series of brie f, repetitive, noxious thermal stimuli were administered twice in ascending order. The two inter-trial intensities were 38 C and 41 C, and the target temperatures were 49 C and 52 C, respectively. The target temperature was delivered for a 1.5-second durat ion, with a 3-second in ter-pulse interval at the inter-trial intensity. Subjects provide d either intensity or unpleasantness ratings of each stimulus using 0-20 box scales (Coghill a nd Gracely, 1996). Both series of stimuli were delivered twice, once for intensity ratings, and once for unpleasantness, in counterbalanced order. Subjects were inst ructed regarding the distinction between intensity and unpleasantness using a standardized script (Price et al., 1983). The trial was terminated if the subject said, stop at a ny point or if they provided a rating of 20. Numerical ratings of each pulse were recorded. Ischemic-pain Procedure Ischemic-pain was induced using a modi fied submaximal effort tourniquet procedure (Moore et al., 1979). The left arm was exsanguinated by elevating it above heart level for 30 seconds. The arm was th en occluded using a 10 cm wide straight segmental blood pressure cuff (model SC-10) inflated to 240 mm Hg using a Hokanson
7 cuff inflator and air source (Bellevue, WA). Subjects performed 20-handgrip exercises of 2-second duration at 4-second intervals at 50% of their maximum grip strength. Subjects were instructed to say pain when they firs t felt pain and to c ontinue until the pain became intolerable. The time to pain threshold and pain tolerance were recorded. Every 60 seconds, subjects were prompted, to rate the unpleasantness and intensity of their lower arm and hand pain using the 0 to 20 box s cales. The test was terminated when the subjects indicated they wanted to stop by saying, stop, when they reached 20 on either the intensity or unpleasantness scales, or wh en they reached an uninformed time limit of 15-minutes. Cold Pressor Pain Procedure Cold pressor pain was assessed by having the subjects immerse their left hand up to the wrist in 5C water. The water temperature was maintained (+ 0.1C) by a refrigeration unit (Neslab, Portsmouth, NH), a nd was constantly circulated to prevent local warming around the submerged hand. The subject was instructed to keep his/her hand in the water for as long as possible, however if the pain became intolerable, participants were told that they could rem ove their hand at any time. Cold-pressor pain threshold was determined to be the time when the participant said, pain and tolerance was recorded when the hand was withdrawn from the water. Subjects were prompted to rate the unpleasantness and inte nsity of the cold-pressor pain using the 0 to 20 box scales at 30-second intervals. Subjects continued until they reported intolerable pain or until a 5-minute uninformed time limit was reached.
8 Psychological Measures To determine the contribution of psychos ocial factors to group differences in experimental pain responses, all subj ects completed the following psychological questionnaires. The Coping Strategies Questionnaire (CSQ) (Rosenstiel and Keefe, 1983) consists of 44 items relating to how individuals cope w ith pain. It yields seven subscales based on the pain-coping strategies that individuals report us ing: diverting attention, catastrophizing, praying and hoping, ignoring pain sensati ons, reinterpreting pain sensations, increasing behavioral activity, and coping self-statements. It has been widely used with various pain populat ions (Keefe et al. 1987; Parker et al. 1989) as well as with healthy young adults (Lefebvre et al., 1995). The Kohn Reactivity Scale (KRS) consists of 24 items that assess an individuals level of reactivity or central nervous system ar ousability. It has been recently used as a measure of the construct of hypervigilance (McDermid et al., 1996). This measure has been shown to correlate ne gatively with pain toleran ce (Dubreuil and Kohn, 1986) and has been reported to have adequate intern al consistency, ranging from alpha of 0.73 to 0.83 (Kohn, 1985). The Pennebaker Inventory of Limbic Languidness (PILL) assesses the frequency of occurrence of 54 common physical symptoms a nd sensations and appears related to the construct of somatization or to the general tendency to endorse physical symptoms. It has been reported to have high internal cons istency (alpha = 0.88) a nd adequate test-retest reliability (0.70 over two months) (Pennebaker, 1982). Recently it has been used as a measure of hypervigilance in fibromyalgia pa tients. These patients demonstrated lower
9 pressure pain thresholds and tolerances and higher scores on the PILL compared to arthritis patients and pain-free c ontrols (McDermid et al., 1996). The Profile of Mood StatesBi-Polar (POMS-Bi) consists of 72 mood-related items, and subjects indicate the extent to whic h each item describes their current mood. This questionnaire assesses both positive and negative affective dimensions. The POMS has been well validated with ot her mood measures and is sensitive to subtle differences in affective state (Lorr and McNair, 1988). T hough the POMS yields a variety of subscale scores, only the global indices of positive affect and negativ e affect were used in our study.
10 CHAPTER 3 RESULTS A total of 120 participants were stud ied, including 62 African Americans (41 female, with a mean age of 20.1 + 2.6 years) and 58 whites (24 female, having a mean age of 22.1 + 5.8 years). Age and sex differed between ethnic groups (ps < 0.05); therefore, they were used as covariates in subsequent analyses. An alyses of covariance (ANCOVAs) revealed no signifi cant differences in measures of HPTh, IPTh, or CPTh. However, significant group differences emerge d for HPTo, IPTo, and CPTo (ps < 0.05), with African Americans displaying lower tolera nces than whites. Significant differences also appeared for ratings of intensity a nd unpleasantness during the temporal summation procedure at both 49 Celsius (ps < .005), with African Americans reporting greater pain compared to whites. Data for each of the experimental pain tasks are presented in Table 2. In addition, effect sizes and F-values for group differences on each pain measure are indicated. Figure 1 shows these data graphica lly, after standardizi ng the variables such that each pain measure had a mean of 50 and a standard deviation of 10. ANCOVAs, controlling for sex and age, were also conducted on psychological variables in order to determine the reliab ility of between-group differences. These analyses revealed no group difference on th e POMS, the PILL, or the Active Coping subscale of the CSQ. However, significan t group differences emerged on the Passive Coping subscale of the CSQ (p = 0.0001) and the KRS scale (p = 0.003), with African Americans scoring higher than whites (Tab le 2). To determine whether these
11 Table 2. Means (SD) for Experimental Pa in Measures for African Americans and Whites, Including Sample Size, Eff ect Sizes, and F-Values Variable N (AA/W) African Americans Mean (Std Dev) Whites Mean (Std Dev) Effect Size F-value HPTh 120 (62/58) 41.89 (4.02) 43.42 (3.91) 0.39 (1,115) 1.03 HPTo* 120 (62/58) 46.17 (3.56) 48.44 (2.86) 0.70 (1,115) 7.16 IPTh 114 (58/56) 150.9 (160.15) 119.05 (78.23) 0.27 (1,109) 1.59 IPTo* 114(58/56) 362.93 (253.28) 462.95 (268.4) 0.38 (1,109) 4.9 CPTh 64 (40/24) 11 (7.6) 12.7 (7.3) 0.23 (1,60) 0.52 CPTo* 64 (40/24) 25.7 (54.4) 77.1 (55.4) 0.94 (1,60) 11.31 Unpleas. Rating @ 49 C* 119 (61/58) 12.4 (5.04) 8.95 (3.37) 0.82 (1,114) 9.91 Unpleas. Rating @ 52 C* 118(60/58) 15.79 (4.39) 12 (5.49) 0.77 (1,113) 12.19 Intensity Rating @ 49 C* 119(61/58) 13.66 (4.43) 10.61 (5.01) 0.65 (1,114) 8.25 Intensity Rating @ 52 C* 118(60/58) 16.91 (3.42) 13.14 (5.41) 0.86 (1,113) 14.76 *p < 0.05 44 46 48 50 52 54 56 HPThHPToIPThIPToCPThCPTounp totint tot Pain MeasuresStandardized Scores African Americans Whites Figure 1. Standardized Means (Mean=50) for a ll Experimental Pain Measures in African Americans and Whites
12 psychological variables contri buted to ethnic group differe nces in pain responses, ANCOVAs were performed. Group differences remained significant for all variables after adjusting for the Passive Coping subscal e. However, controlling for KRS scores, both HPTo and IPTo became nonsignificant, while all other measures remain unchanged. Thus, KRS scores may have contributed to the group differences in heat-pain tolerance and ischemic-pain tolerance. Table 3. Means (SD) for Psychological Me asures for African Americans and Whites Variable N (AA/W) African Americans Mean (Std. Dev.) Whites Mean (Std. Dev.) Effect Size F-Value Coping, Active 114 (58,56) 7.82 (3.41) 8.5 (4.15) 0.18 (1,110) 0.88 Coping, Passive* 114(58,56) 3.86 (1.94) 1.99 (1.61) 1.05 (1,110) 25.34 POMS, Positive Mood 113 (58,55) 49.41 (13.94) 52.85 (14.95) 0.24 (1,109) 0.73 POMS, Negative Mood 113(58,55) 29.4 (17.58) 29.78 (17) 0.02 (1,109) 0.05 PILL 100 (50,50) 103.12 (24.95) 104.34 (21.16) 0.05 (1,96) 0.12 KRS* 105 (53,52) 77.85 (10.36) 68.73 (12.42) 0.80 (1,101) 9.17 *p < 0.05 Correlations were calculated in order to characterize the associations across stimulus modalities, and to determine wh ether inter-task correla tions differed across ethnic groups. Results are shown in Tables 4 and 5. Modest correlations emerged across stimulus modalities, with stronger relations hips within modalities. Additionally, the intraand inter-task correlations were similar across ethnic groups.
13Table 4. Correlations of Experimental Pain Measures for African Americans Variable HPTh HPTo IPTh IPTo CPTh CPTo Int. Total Unp. Total HPTh 1.0 0.80230*** 0.22646 0.33577* 0.08386 0.16139 -0.37384** -0.44604*** HPTo 1.0 0.28203* 0.39278** 0.21553 0.41301** -0.65205*** -0.63236*** IPTh 1.0 .67882*** 0.34831* 0.02470 -0.05682 -0.00919 IPTo 1.0 0.08821 0.20864 -0.23472 -0.19284 CPTh 1.0 0.53908*** -0.01728 -0.01738 CPTo 1.0 -0.37967 -0.38268 Int. Total 1.0 0.76679*** Unp. Total 1.0 *p < 0.05, **p < 0.01, ***p < 0.001
14Table 5. Correlations of Experimental Pain Measures for Whites Variable HPTh HPTo IPTh IPTo CPTh CPTo Int. Total Unp. Total HPTh 1.0 0.71941*** 0.05783 0.16456 0.42628* 0.44495* 0.50641*** -0.51893*** HPTo 1.0 0.20722 0.42432** 0.52871** 0.51050* -0.56487*** -0.64823*** IPTh 1.0 0.0273* -0.9614 0.11579 -0.17650 -0.24719 IPTo 1.0 0.30961 0.62946** -0.39577** -0.50531*** CPTh 1.0 0.48479* -0.09374 -0.13788 CPTo 1.0 -0.54830** -0.39260 Int. Total 1.0 0.79769*** Unp. Total 1.0 *p < 0.05, **p < 0.01, ***p < 0.001
15 CHAPTER 4 DISCUSSION The findings of this study provide evidence of ethnic differences in laboratory pain responses across multiple stimulus modalities. While African Americans did not differ from whites on threshold measures of heat-p ain, ischemic-pain, and cold pressor pain, they exhibited significantly lower tolerances for each of the stimulus modalities. Group differences also emerged for ratings of the intensity and unpleasantness of suprathreshold heat-pain, with African Americans providing hi gher ratings compared to whites. The effect sizes for these group differences in pain responses ranged from small to large, with the average effect size being moderate. Thus, ethnic differences in tolerance measures of experimental pain responses appear to be consistent ac ross pain tasks and relatively robust. That the largest effects were found on supra-threshold measures may be important, as these procedures have been f ound to be among the most clinically relevant experimental pain-induction tasks (Edwards et al., 2001; Petersen-Felix and ArendtNielsen, 2002). Pain tolerance and suprathreshold rati ngs of pain unpleasantness may primarily reflect the affective-motivational dimens ion of pain, while pain threshold and suprathreshold ratings of pain intensity may be more str ongly associated with sensorydiscriminative aspects of the experience (Price, 1994). It has been theorized that ethnic differences in pain responses may be most apparent for the affective-motivational dimension of pain (Edwards and Fillingim, 1999; Sheffield et al., 2000; Riley et al., 2002). However, in the present study African Americans reported suprathreshold heat
16 pulses to be more intens e and unpleasant at both 49 and 52 Celsius when compared to whites. These findings suggest group differenc es in the sensory-discriminative aspects as well as the affective-motivational dimensions of pain perception. Taken together, these results are generally consistent with prev ious findings of ethnic differences in experimental pain (Chapman and Jones, 1944; Woodrow et al., 1972; Walsh et al., 1989; Zatzick and Dimsdale, 1990; Edwards and Fi llingim, 1999; Sheffi eld et al., 2000) and chronic pain (Lawlis et al., 1984; Nelson et al., 1996). Differences in pain sensitivity across ethnic groups are often attributed to psychological factors such as anxiet y, depression, and hypervig ilance (Zatzick and Dimsdale, 1990; Jordan et al., 1998; Rollm an, 1998; Edwards and Fillingim, 1999; Edwards et al., 2001; Green et al., 2003). In the current study, no differences were observed in mood measures or in somatic complaints between groups. African Americans did, however, score higher on a measure of hypervigilance, the Kohn Reactivity Scale (KRS), than whites; and th is psychological factor was correlated with pain perception. Statistically controlling for KRS scores rendered group differences in HPTo and IPTo nonsignificant, while CPTo a nd heat-pain ratings remained significantly different. This measure previously has been shown to negatively correlate with pain tolerance (Dubreuil & Kohn, 1986). One po ssible explanation for the change in significance of HPTo and IPTo could be that KRS data were missing for several subjects (5 African Americans, and 4 whites); therefor e, introducing this variable into the model reduced the power of the anal ysis. Although the mechanisms underlying this effect are unclear, heightened attention to painful stim uli may contribute to ethnic differences in pain responding.
17 Coping styles and strategies may also m oderate the relationship between ethnicity and pain; and have been found to vary by culture (Jordan et al., 1998; Moore and Brodsgaard, 1999). Catastrophizi ng, an aspect of passive coping, has been associated with pain responses in both experimental (Sullivan et al., 1995; Sullivan et al., 1997; Sullivan and Neish, 1998) and clinical populatio ns (Keefe et al, 1989; Tan et al, 2001). Catastrophizing is theorized to increase the attentional focu s and/or increase emotional reactivity to pain, thereby amplifying its experience (Sullivan et al., 2001). Although African American participants reported greater use of passi ve pain-coping strategies, including catastrophizing, this factor did not account for di fferences in pain responses between groups. However, it is important to note that the coping m easure used in this study queried subjects as to their typical method of pain-coping, and it is possible that subjects used different strategi es to cope specifically with th e experimental pain stimuli. Moreover, psychological factors not assessed in the present study could have influenced the current findings. For example, sociocultu ral or environmental influences may play a role in a persons perception and response to pain and thos e factors were not directly assessed in this study. Given the consistenc y of ethnic differences in pain perception across stimulus modalities, these findings demonstrate the need for future research to address psychological variables and factors effecting pain-cop ing and pain responses. Results of the correlational analysis, perf ormed on the experimental pain tasks, indicated that partic ipants responses were moderate ly correlated across stimulus modalities, and these relationships were co mparable across ethnic groups. This is consistent with previous reports (Janal, et al. 1994; Lautenbacher et al., 1993). These
18 results illustrate the potential importance of using multiple stimulus modalities when assessing pain perception a nd the differences therein. Several limitations of our study should be noted when interpreting the results. First, all of the tasks were acute, controlled painful experiences. Given the artificial nature of the experimental procedures, the outcomes may have limite d practical utility. However, several studies have shown the re levance of using expe rimental pain-induction procedures in order to predict clinical pain (Langemark et al., 1989; Fillingim et al., 1996; Clauw et al., 1999; Edward s, et al. 2003a; 2003b; Granot, et al. 2003). In addition, because all participants we re healthy college students recruited from a homogenous population, the degree to which these findings generalize to other populations, including older and more poorly educated samples, is unknown. Another limitation is the relatively small sample size for the cold pres sor procedure, which may have reduced our ability to detect group differences on this ta sk. Another issue is th at the considerable heterogeneity within the broader category of African American and white was not investigated in the present study. Differenc es in experimental pain responses among subgroups within larger Ethnic ca tegories have been reported (Chapman and Jones, 1944; Sternbach and Tursky; 1965); how ever, others have reported no significant intra-ethnic differences in pain responding (Lipto n and Marbach, 1984; Greenwald, 1991). These limitations notwithstanding, these fi ndings indicate rela tively consistent ethnic differences in responses to multiple e xperimental pain modalities, and the effects are generally moderate in magnitude. Also, the largest ethnic differences emerged for suprathreshold pain measures. Some group differences in psychological measures, such as coping and hypervigilance, were observed ; however, these variables did not fully
19 account for the ethnic differences in pain re sponses. Current findings provide further evidence for the existence of ethnic differen ces in experimental pain perception, and additional research to elucidate the mechanisms and clinical relevance of these effects is warranted.
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25 BIOGRAPHICAL SKETCH Claudia M. Campbell received her Bachelor of Science degree in psychology with a minor in womens studies from the Universi ty of Florida in 2001. As a result of her interdisciplinary background, she developed an interest in the psyc hological aspects of diversity, specifically in the field of pain research. U pon completion of her Bachelor degree, Ms. Campbell accepted a research a ssistant position in the sensory testing laboratory of Dr. Roger Fillingim. Thus, she has been able to pursue her research endeavors investigating sex and ethnic differences in pain perception. She continues her work through the pursuit of a doctoral degree in Clinical and H ealth Psychology at the University of Florida. Ms. Campbell has also been the recipien t of several awards from the American Pain Society, which include a Citation Awa rd and two Young Investigator Awards, the later of which facilitated travel to the nati onal meetings. Current memberships include the American Pain Society, American Psychologi cal Association, and Florida Psychological Association.