Differences in Psychosocial Factors and Experimental Pain Sensitivity Between Hispanics and Non-Hispanic Whites from the U.S.-Mexico Border

Abstract

Purpose

Research suggests that ethnicity is a predictor of pain-related outcomes; however, studies comparing the differences in experimental pain sensitivity between Hispanics and non-Hispanic Whites (NHW) are scarce. This study investigated these differences between Hispanics and NHW from the U.S.- Mexico border.

Methods

Fifty-eight healthy participants completed the survey packet, which included a demographic and a psychosocial factors questionnaire. Participants underwent quantitative sensory testing, which included heat pain threshold, heat pain tolerance, Suprathreshold Heat Pain Response (SHPR), and Conditioned Pain Modulation (CPM). SHPR was induced by repeated thermal stimuli in both thenar eminences. CPM was assessed using SHPR as the experimental stimulus and cold pressor task as the conditioning stimulus.

Results

Analyses showed significant differences in experimental pain measures believed to be representative of facilitatory pain processing including SHPR and heat pain threshold, where Hispanics reported significantly higher pain ratings than NHW. Hispanics also reported higher levels of ethnic identity and acculturation. However, these factors were not significantly associated with experimental pain sensitivity.

Conclusion

The experimental pain sensitivity and psychosocial factors included in this study differed by ethnic group, where Hispanics reported significantly higher pain ratings, when compared with NHW. However, ethnic identity and acculturation were not associated with these pain-related outcomes. Overall, enhanced understanding by clinicians of pain sensitivity and disparities in the pain experience between ethnic groups allows for increased cultural sensitivity and can be used to optimize pain treatment on an individual-by-individual basis.

Introduction

The conditions and social context in which persons live might explain, in part, why certain groups of people experience pain differently than others. Ethnic differences have been reported for many pain-related responses. Chronic pain states are commonly associated with alterations in the central nervous system, specifically in central processing of noxious stimuli [1–7]. Recent evidence highlights the importance of examining pain in the context of a broader social environment [8].

Ethnicity refers to a social group of people who share a common ancestral origin, language, physiology, and culture or social background that provides a sense of identity [9]. Conversely, ethnic identity is part of a person’s self-concept that is socially constructed and derived from one’s knowledge or membership in a social group [10, 11]. Ethnicity has been proven as a predictor of health-related outcomes, beliefs, and behaviors [9]. In addition, ethnicity has been associated with pain sensitivity in ethnic minority groups and has been reported as a potential mediator for group differences in pain perception [12–15].

For example, adults of ethnic minorities experience pain more frequently, are more pain sensitive [12], and suffer from more severe pain compared with non-Hispanic Whites (NHW). In fact, several investigators have reported ethnic differences in clinical pain as well [13, 15–17]. Moreover, ethnicity is intercorrelated with acculturation, the degree to which one has adopted the norms (beliefs and behaviors) of the dominate group, which may also reveal potentially meaningful health disparities between and within ethnic groups. To date, studies on the impacts of the multidimensions of acculturation (practices, values, and identifications) regarding health and illness of Hispanics have produced mixed results. Acculturation tends to be both protective and harmful depending on the condition of interest and type of measurement [18–20].

On the other side of the acculturation scale is ethnic retention, in which retaining cultural norms and behaviors rather than acculturating to mainstream U.S. culture is associated with a range of favorable health and social outcomes. In such situations, acculturating to U.S. cultural norms is associated with downward assimilation. Indeed, the ethnic retention-acculturation continuum is in part used to explain the Hispanic Health Paradox, where Hispanics have more favorable mortality and other health outcomes than Whites.

Some commonalities of neural pathways connecting the experience of physical and social pain also have been reported suggesting a considerable overlap or underlying construct between these two mechanisms [21–23]. Some studies have reported a dynamic interaction between physiological, psychological, and sociocultural factors, where the pain experience is shaped and modulated [24]. An example of this includes how personality traits such as optimism and resilience might engage the endogenous pain inhibitory system (assessed by conditioned pain modulation) [24, 25] or exacerbate the central pain facilitatory system (suprathreshold heat pain response) [26, 27], alter pain sensitivity, and subsequently produce disparities in the perception of pain. Therefore, it may be that psychosocial factors may influence pain responses by altering endogenous pain processing. Additionally, emerging literature supports the protective nature that resilience has on chronic pain, which has been defined as a dynamic process promoting adaptation to adversity or severe stress [28, 29].

Though numerous factors are suggested to contribute to these disparities [28, 30–33], and in fact, several investigators have reported ethnic differences in clinical pain [12–16, 21, 34], research addressing the contribution of psychosocial constructs, on experimental pain sensitivity, and how this alters the pain response in the Hispanic population is limited. Therefore, this study aimed to examine ethnic differences in experimental pain sensitivity and the potential influences of ethnic identity, resilience, and acculturation on experimental pain sensitivity between Hispanics and NHW from the U.S.-Mexico Border.

Materials and Methods

Procedure and Participants

The University of Texas at El Paso institutional review board for human participants approved this study. This cross-sectional design included healthy pain-free Hispanic and NHW subjects. Investigators recruited participants through multiple mechanisms from The University of Texas at El Paso and its vast surrounding areas along the U.S.-Mexico border. Recruitment mechanisms included posted advertisements and local print media. Participants helped with recruitment through word of mouth. Some participants inevitably knew potential future participants; therefore, to reduce confounding factors, investigators requested that participants not discuss the nature of the study with prospective participants.

The inclusion criteria for being a participant in the study consisted of being healthy subjects 18 years or older and Hispanic or NHW. Exclusion criteria included participants who 1) had a current fracture, tumor, or infections; 2) were pregnant; 3) were participating in current psychiatric management (from self-report of patient history or self-report of medication usage involving multiple psychiatric drugs); 4) and presented rheumatoid arthritis that had been treated with injectable cortisone medications within the past 6 months. Subjects were included in the study on a volunteer basis as long as they met the inclusion criteria. After researchers ensured that the inclusion criteria were met, all participants provided informed consent before participating in this study that consists of a demographic survey, a psychosocial survey, and experimental pain sensitivity measurements (see Figure 1). All assessments were performed by evaluators trained in the assessment protocol. Evaluators who performed the experimental pain sensitivity assessment were blinded to both psychological and demographic data.

Measures

Demographic Information

Study participants completed a standard intake information form. Demographic data collected at initial evaluation included gender, age, race, ethnicity (self-identification of ethnicity), employment status, marital status, educational level, and any currently prescribed medications.

Experimental Pain Sensitivity

Heat Pain Threshold and Heat Pain Tolerance. Heat pain threshold and heat pain tolerance was tested at the forearm of both arms using a thermode 27 mm in surface area by a Neuro Sensory Analyzer (Medoc Advanced Medical Systems TSA-II, Ramat Yishai, Israel). This apparatus is composed of an HP-thermode that provides fast heating and cooling rate of up to 8°C per second. Participants received a continuously ascending heat stimulus applied to the forearm of both arms. The stimulus started at 35°C and increased at a rate of 0.5°C per second. Participants were asked to indicate when the sensation first changed from heat to pain and were immediately instructed to rate their level of pain using a numerical rating scale with 0 (no pain) to 100 (worst pain imaginable). Two different trials were performed, and the average of the two temperatures were calculated as the participant’s heat pain threshold. In a separate trial, subjects were asked to indicate when the heat “became so painful that they wished it would stop.” Two separate tolerance trials were performed, and the average temperature was recorded as the participant’s heat pain tolerance.

Suprathreshold Heat Pain Response (SHPR). Evidence supports enhanced SHPR for involvement in a variety of chronic pain disorders [2, 3, 6, 7] via altered central pain processing. SHPR results in the perception of increased pain despite constant or even reduced peripheral afferent input. This study tested SHPR at the thenar eminence of both hands with a thermode 27 mm in surface area by a Neuro Sensory Analyzer (Medoc Advanced Medical Systems TSA-II). The TSA-II is an apparatus composed of an HP-thermode that provides fast heating and cooling rates of up to 8°C per second. The TSA-II was programmed to deliver 5 consecutive heat pulses that rose rapidly from an adapting temperature to a peak temperature of 48°C and 50°C at a rate of 8°C per second and remained at this level for 0.5 seconds and then returned to baseline at a rate of 8°C per second with an interpulse interval of 2.5 seconds [27]. Participants were instructed to verbally rate the intensity of each thermal pulse using a numerical rating scale from 0 (no pain) to 100 (the worst pain imaginable). This procedure was performed two times; the first trial using 48°C and the second trial using 50°C as a thermal stimulus. Performing this testing procedure twice allowed the researchers to determine the participant’s moderate level of pain to be used during the following assessment (for specifics, see conditioned pain modulation [CPM] assessment below). This study utilized the “fifth pain rating,” which is the fifth pain rating from the fifth pulse of each trial [35, 36], which is considered to represent a simple measure of SHPR assessment [7]. In addition, this was included in the current study because our previous study indicated that the fifth pain rating of a SHPR train accounted for a significant proportion of variance in clinical pain intensity [37].

Conditioned Pain Modulation. CPM is a type of endogenous modulation of pain [38, 39], which is typically induced by a painful stimulus applied to a remote area of the body (conditioning stimulus), thus causing inhibition of pain in response to a different painful stimulus (test stimulus). A reduction in the magnitude of the test stimulus in response to the conditioning stimulus is considered as CPM [40]. This measure is believed to be an indication of the potential for endogenous pain inhibition.

Test Stimulus (SHPR). SHPR was tested at the thenar eminence of the participant’s left hand, using the TSA-II (described above). Sequences of five consecutive heat pulses with interpulse intervals of 2.5 seconds were delivered. The temperature used for the test stimulus (SHPR) was determined from the participant’s previous SHPR assessment and was the temperature that reached a moderate level of pain, as indicated previously by the participants (pain rating of 50 or closer to 50 from the 0 to 100 numerical rating scale) using an average of five heat pulses. Participant’s verbally rated the intensity of each thermal pulse using a numerical rating scale from 0 (no pain) to 100 (the worst pain imaginable).

Conditioning Stimulus (Cold-Pressor Pain). Participants were instructed to submerge their right hand up to the wrist into a cold-water bath for up to 1 minute. The water was maintained at a constant temperature of 8°C and was constantly circulated to prevent warming of the hand.

Conditioned Pain Modulation Procedure. CPM assessment consisted of the application of the test stimulus (described above) on the left hand. Thirty seconds after the last heat stimulus, participants were instructed to submerge their right hand into the cold-water bath (conditioning stimulus). Thirty seconds after hand submersion, participants were instructed to rate the pain from the submerged hand and were instructed to maintain their hand in the cold-water bath for as long as tolerable for a maximum duration of 1 minute. One minute after the submersion of the right hand, a new test stimulus was delivered to the left hand (see Figure 1).

Psychosocial Factors

Ethnic Identity. Ethnic identity was measured using the Multigroup Ethnic Identity Measure (MEIM) [41]. The MEIM was designed to meet the need for a general measure that can assess ethnic identity across diverse ethnic groups. The MEIM consists of 15 items that assess the core components of ethnic identity, which are assumed as common across all ethnic groups. One example question is, “I have a lot of pride in my ethnic group.” The MEIM uses a four-point rating scale, from 1 (strongly disagree) to 4 (strongly agree) that rates the ethnic identity search and affirmation. The MEIM mean for descriptions was calculated for items 1, 2, 4, 8, and 10, with a higher score indicating higher ethnic identity. The mean for affirmation on the subject’s ethnic identity was calculated with items 3, 5, 6, 7, 9, 11, and 12, with a higher score indicating a higher level of affirmation. The MEIM has shown adequate reliability and validity and has been used to assess ethnic identity across multiple ethnic groups [41, 42].

Resilience. Resilience was measured from the Brief Resilience Scale (BRS) [43]. The BRS is a 6-item survey composed of statements gauging the subject’s self-reported resilience. Examples of BRS questions include “I have a hard time making it through stressful events” and “I tend to take a long time to get over set-backs in my life.” The interpretation of the scores range from low resilience (1.00–2.99), normal resilience (3.00–4.30), and high resilience (4.31–5.00). The BRS is reported to be a reliable and valid measure of resilience [43].

Acculturation. Acculturation among Hispanics and NHW was measured using the Short Acculturation Scale for Hispanics (SASH) [44]. The SASH is a 12-item scale consisting of three subscales: language use, media, and ethnic social relations. The scale measures each item given on a five-point bipolar scale; scores ranged from 1 (only Spanish) to 5 (only English) with a midpoint of 3 (both equally). Scores above the cut point (2.99) represented higher acculturation levels, and scores below the cut point represented lower acculturation levels. This instrument can benefit clinicians and researchers in further understanding the “immigrant paradox” among relationships and individual function [18]. The SASH was originally developed for Hispanics [44], and it has been used in diverse populations, including in patients with breast cancer, with oversampling of Latinas and African Americans [45], as well as in Korean immigrants [46] and NHW [47].

Data Reduction and Analysis

Data analyses were conducted using SPSS, Version 23. Bonferroni correction was used to reduce the risk of type 1 error, where significance levels (α) were adjusted (α/number of tests). Significance levels were adjusted at P < 0.005 for all t test comparisons. Descriptive statistics (mean and standard deviation) were calculated for all variables. The distributions of variables were tested for normality by visual examination and using the Kolmogorov-Smirnov test before being used in the analysis. For analysis purposes, measurements from both arms were averaged into one score, because paired t tests showed non-significant differences (P > 0.05) between measures in the participant’s right side versus left side, which is consistent with findings from an earlier shoulder pain cohort [48].

For analysis purposes on CPM, we followed recommendations [38] on presenting results and calculating CPM by using the absolute difference for CPM and the percent change [38]. The absolute difference for CPM was calculated using the difference between the test stimulus before the application of conditioning stimulus (pre-CPM), minus the test stimulus after the application of conditioning stimulus (post-CPM). The percent change for CPM was calculated as follows: [(post-CPM—pre-CPM)/pre-CPM] * 100.

Independent samples t test were used to determine differences on experimental pain sensitivity (heat pain threshold and tolerance, SHPR, and CPM), as well as psychosocial factors (ethnic identity, resilience, and acculturation between ethnic groups [Hispanics and NHW]). Stratification into the two ethnic groups was based on participant’s self-identification of ethnicity. Differences in proportion of race, employment, education, and income by groups (Hispanics and NHW) were assessed using χ² analyses as these were categorical measures.

Correlation analyses and regression models were conducted to assess associations between experimental pain sensitivity measurements and psychosocial factors and to determine which psychosocial factor(s) accounted for a significant amount of variance in experimental pain sensitivity. Regression models included age, gender 1 (male), and ethnic group 1 (Hispanic) in the first step to control for these potentially confounding factors, and psychosocial factors in the second step of the regression model in a simultaneous method of entry. Variance inflation factor was reported for the final model to investigate potential multicollinearity among the independent variables.

Results

Subject Characteristics

This study included 58 healthy participants (mean age = 25.34 [SD = 10.24] years, 36 Hispanics and 22 NHW). Post hoc power analysis with an effect size of 0.5, alpha level of 0.05, and a sample size of 58 (36 Hispanics and 22 NHW) reached a power of 0.57 [49]. Self-identification of ethnicity revealed that 62% of the participants were Hispanic. The distribution of gender across ethnicity was 52.8% Hispanic females and 63.6% NHW females. The mean age was 24.4 years for Hispanics and 26.2 years for NHW. Descriptive statistics for the demographics from the sample are summarized in Table 1. No ethnic group differences were found among participants in employment. However, differences were found on the level of education and income between ethnic groups (Table 1). There was a significant difference on the question, “Do you come from an immigrant family?” where 52.8% of Hispanics responded “yes” and 86.4% of NHW responded “no.” No differences were found in the number of years participants have resided in the United States (Table 1).

All continuous dependent variables were found to approximate a normal distribution by visual examination and were appropriate for the planned independent samples t test and multiple regression analyses.

As the fifth pain rating at 48°C and 50°C were highly correlated (r’s between 0.89 and 0.95), the fifth pain rating at 50°C was only used in subsequent analyses.

Experimental Pain Sensitivity and Psychosocial Factors Differences

Independent samples t test showed no differences in the absolute difference of CPM [t(56) = -0.11; P = 0.91] or in the percent change of CPM [t(56) = 1.08; P = 0.28]. However, differences in the fifth pain rating at 50°C [t(53) = 3.58; P = 0.001] and the pain threshold [t(55) = 2.93; P = 0.005] were found between Hispanics and NHW, with Hispanics experiencing significant greater pain ratings (Table 2) (Figure 2). The heat pain tolerance was not significant [t(55) = 2.25; P = 0.02] after the Bonferroni correction.

Psychosocial factors analyses showed significant differences in ethnic identity (MEIM) [t(56) = 3.57; P = 0.001], resilience (BRS) [t(56) = -2.90; P = 0.005], and acculturation (SASH) [t(56) = 3.45; P = 0.001] between Hispanics and NHW, with Hispanics experiencing significant greater levels of ethnic identity and acculturation (Table 2) (Figure 3).

Associations Between Psychosocial Factors and Experimental Pain Sensitivity

The fifth pain rating at 50°C was positively associated with ethnic identity (MEIM) (r = 0.29; P = 0.03). Heat pain threshold was positively associated with acculturation (SASH). In addition, a negative association between resilience (BRS) and acculturation (SASH) (r = −0.38; P = 0.003) was found (Table 3).

Using a simultaneous method of entry, hierarchical regression analyses were conducted to determine the contribution of psychosocial factors to experimental pain sensitivity (SHPR, CPM, heat pain threshold, and heat pain tolerance). As resilience was not associated with experimental pain sensitivity, only ethnic identity and acculturation were included in the models.

The models explaining CPM, heat pain threshold, and heat pain tolerance were not significant and did not have significant psychosocial factors as predictors, even after controlling for demographics. The model explaining the fifth pain rating at 50°C explained 17% of the variance (P = 0.02), where ethnic group (beta = 0.40; P = 0.003) was the unique significant predictor. When ethnic identity and acculturation were included into the model, ethnic group was still a significant factor (Table 4). These results did not change after controlling for education and income. Variance inflation factor showed minimal multicollinearity concerns among the independent variables in all regression models.

Discussion

This study aimed to investigate the differences in experimental pain sensitivity between Hispanics and NHWs and the influences of ethnic identity, resilience, and acculturation in pain perception. The present study contributes to the growing body of literature by providing evidence that measures of central sensitization and psychosocial factors may play a differential role in determining pain sensitivity when comparing Hispanics and NHWs. Specifically, differences were consistently found between Hispanics and NHWs in several measures believed to be representative of facilitatory central pain processing including SHPR and heat pain threshold. For all of these measures, Hispanics reported enhanced responses indicative of greater pain sensitivity. In contrast, a measure believed to be representative of inhibitory central pain processing, CPM, did not differ between these ethnic groups. Hispanics also reported higher levels of ethnic identity and acculturation and overall lower levels of resilience compared with NHWs. These factors, however, did not have a significant association with experimental pain sensitivity, even after controlling for ethnic group, education, and income.

The present study offers novel data that extend our previous work [7, 37] and the work of others [16, 24, 25, 32, 50–52] in several ways. Firstly, while several studies provide evidence for an association between ethnicity and pain or the potential role of acculturation and pain, most are comparisons between African Americans and NHWs, and only a few investigations have examined ethnic differences in response to experimental pain stimuli in the Hispanic-American community. The present study provides novel evidence for an association between ethnicity and facilitatory pain processing in Hispanics living on the U.S.-Mexico border, where Hispanics showed an enhanced response indicative of greater pain sensitivity when compared with NHWs. Secondly, because this study further extends the literature investigating the differences in experimental pain sensitivity between Hispanics and NHWs living on the U.S.-Mexico border, our results can provide insight as to how increased cultural sensitivity can lead to pain treatments tailored for a specific demographic and optimized on an individual-by-individual basis.

Ethnicity has proven to be a powerful predictor of health-related outcomes [9], beliefs, and behaviors. In fact, ethnic differences in pain perception have been documented in a variety of clinical pain conditions [13, 15, 16]. Ostrom et al. [12] used controlled laboratory-evoked pain stimuli to provide evidence for ethnic differences in pain perception among African American, Asian, Hispanic, and NHW populations, where African Americans, Asians, and Hispanics all reported higher heat pain sensitivity than NHWs. In a similar study, Cruz-Alameida and colleagues [53] examined the patterns of interindividual variability in experimental pain responses in a racially and ethnically diverse sample. The results showed differences in experimental pain phenotype profiles.

The present study’s findings are consistent with previous findings, where differences were found between Hispanics and NHWs. Hispanics reported greater facilitatory central pain processing responses than NHWs and significantly greater pain ratings on pain threshold than NHWs. Interestingly, these differences in pain threshold were noted for pain rating, but not for the pain stimuli (temperature), meaning that the pain perception differed for the same pain stimuli between groups. The present study also demonstrated that ethnicity is associated with facilitatory central pain processing (SHPR). However, no significant differences in the inhibitory process (CPM) were found. Perhaps it can be inferred that significantly greater acculturation and ethnic identity levels are not considered protective factors for pain experience, where individuals with greater acculturation and ethnic identity may be more likely to present greater facilitatory pain responses.

Psychosocial characteristics have been extensively examined in relation to pain perception, clinical outcomes, and disparities in the pain experience and have become an accepted factor in the development of chronic pain [54–56]. Considerable evidence has also demonstrated substantial ethnic disparities in the prevalence, treatment, progression, and outcomes of pain-related conditions [50]. Past studies have implied that the relationship individuals may share with depression can play a role in the development of chronic pain and other serious health issues [57]. Other studies suggest the need for pain treatments that take into account the educational and cultural context of pain. These include comparing educational disparities across ethnicities, limitations in accessing health care and pain specialists, and patient and provider attitudes, as well as knowledge and cultural beliefs [58]. These combined factors can contribute to a patient’s coping mechanisms and level of disability [59].

Ethnic identity has been associated with pain sensitivity in ethnic minority groups and has been reported as a potential mediator for group differences in pain perception [15]. Rahim-Williams et al. determined that ethnic identity was associated with pain range only when observing African American and Hispanic groups [15]. The present study’s results show significant greater ethnic identity in Hispanic population in affirmation, search, and overall ethnic identity, when compared with NHW, which is consistent with previous evidence [15]. In the present study, even though ethnic identity was significantly correlated to the fifth pain rating, ethnic identity was not a significant predictor of experimental pain sensitivity. These findings indicate that ethnic identity is associated with pain sensitivity in ethnic minority groups and may potentially mediate ethnic group differences in pain perception.

Another way to examine potentially meaningful health disparities within an ethnic group is through acculturation. Studies have reported that higher degrees of acculturation are associated with problematic health outcomes, a phenomenon known as the “Immigrant Paradox” [60], specifically regarding one of the present study’s populations of interest, Hispanics. The “Hispanic Health Paradox” shows that Hispanics from low socioeconomic status can experience better health-related outcomes if they are less acculturated. This could be explained by Hispanics not adopting some or all of the health-compromising behaviors of the host country (the Unites States, in this case). Alternatively, Hispanics have experienced lower levels of stress by belonging to an ethnic enclave [61]. This study’s results have shown that the Hispanic population experiences higher levels of acculturation when compared with the NHW population and that acculturation is associated with pain threshold. However, acculturation was not proven as a significant predictor of experimental pain sensitivity. This study’s results are consistent with previous evidence in showing that the impact of acculturation on health and illness in the Hispanic population has shown mixed results. Acculturation tends to be both protective and harmful depending on the condition of interest and type of measurement [18, 62]. Bui Q et al. reported that chronic back and neck pain was higher among more acculturated Hispanic-Americans [63]. Evidence has also shown that Hispanics whose primary language is Spanish experienced higher pain intensity and prevalence of pain than NHWs [62]. In addition, researchers have found mixed results of acculturation in NHW immigrants, where they experienced higher rates of suicide, cancers, and cardiovascular disease in relation to their host-country-born counterparts [64–66]. Interestingly, these health disparities diminished up to 90% in second generation of host-country-born immigrants [64, 65].

It has been theorized that meaningful social ties may predict lower levels of pain intensity and increase positive psychological responses under stressful or painful stimuli [22]. The present study’s results show that higher levels of acculturation are not a significant factor in determining greater facilitatory pain responses or lower inhibitory pain responses. This is an important finding for Hispanics living on the U.S.-Mexico border, where higher comorbidities exist (obesity, heart disease, and asthma) [67–69].

Resilience has been associated with enhanced CPM for individuals with low levels of optimism but not intermediate or high levels of optimism [29]. In addition, greater pain-specific resilience has been associated with less pain interference, pain catastrophizing, and more effective coping strategies [70]. This present study’s results are consistent with previous research findings where minority populations reported greater pain ratings and lower levels of resilience than their NHW counterparts. It can be inferred that individuals who possess greater positive psychological factors, such as resilience, may be less likely to present greater facilitatory pain responses or exhibit maladaptive pain responses. The present study’s results have shown that resilience is not associated with experimental pain sensitivity. However, these results may vary in patients experiencing chronic pain, where perhaps resilience may potentiate endogenous pain inhibition.

Some limitations of this study will need to be addressed by further research. Firstly, SHPR, CPM, heat pain threshold, and tolerance were the only experimental pain sensitivity measures reported in this study. Future studies should include additional measures, such as pressure pain threshold, to facilitate a more comprehensive experimental pain sensitivity assessment assessment. Secondly, a study with a larger sample size might provide a better model to study differences in pain sensitivity associated with psychosocial factors. Additionally, a larger sample size with a wider age range may provide future researchers the potential to examine the influences of ethnic identity, resilience, and acculturation on experimental pain sensitivity separate by ethnic groups and the ability to generalize the findings. Third, even though conducting studies in healthy participants is of a great value, further studies should explore the relationships between experimental pain sensitivity and different psychosocial factors (including negative personality traits) using experimental and controlled pain testing in individuals with chronic pain to better elucidate potential differences between ethnicities living on the U.S.-Mexico border, where higher comorbidities exist.

The ethnic retention-acculturation continuum is in part used to explain the Hispanic Health Paradox, where Hispanics have more favorable mortality and other health-related outcomes than NHWs. Examining the intra-ethnic differences and ethnic retention are of relative importance, given the considerable heterogeneity within the broader category of Hispanics, especially along the U.S.-Mexico border. Further examination of intra-ethnic differences has the potential to better elucidate the factors and mechanisms that may contribute to pain disparities among ethnic groups living on the U.S.-Mexico border. In addition, the city of El Paso, Texas, is one of the few cities in the United States in which the Hispanic population is not considered the ethnic minority. The University of Texas at El Paso is also located in one of the largest binational communities in the United States. Even though these unique characteristics are extremely important to study pain disparities among ethnic groups living on the U.S.-Mexico border, they may add a threat to external validity to this study.

Conclusion

The present study provides novel evidence for an association between ethnicity and experimental pain sensitivity in Hispanics living on the U.S.-Mexico border. Specifically, differences were found between Hispanics and NHWs on SHPR and heat pain threshold where Hispanics from the U.S.-Mexico border reported a greater level of facilitatory pain processing (SHPR) than NHWs and significantly greater pain ratings on pain threshold. Additionally, psychosocial factors may play a significant role when assessing disparities in the pain experience between ethnic groups. Examination of intra-ethnic differences when measuring pain sensitivity is of critical importance in potentially reducing and eliminating disparities in the pain experience [16, 51, 71].This will allow clinicians to practice increased cultural sensitivity in understanding the differences in pain processing for Hispanics and NHWs living on the U.S.-Mexico border, thus optimizing pain treatment on an individual-by-individual basis.

Disclosure: The authors have no financial relationships that might lead to a conflict of interest in this work.

Acknowledgments

This work was supported by the Charles H. and Shirley T. Leavell Endowed Chair Faculty Fellowship from the College of Health Sciences at The University of Texas at El Paso.

References