Sex differences in perceptual and cardiovascular responses to pain: the influence of a perceived ability manipulation

The gender context of pain

Pain is a major source of global suffering, with women bearing the greatest burden. Alongside biology, psychological and social factors, including gender, help explain these differences. However, there has been no direct attempt to develop a unified social psychological model of men and women's pain. By drawing on approaches to both gender and pain, a gender context model of pain is presented. It proposes that pain is partly influenced by the gender context in which it occurs, which operates at both individual and interpersonal levels. The model is used to structure an appraisal of the existing evidence around gender and pain, and explore whether the model helps explain why such variation occurs. It is argued that despite evidence for an association between gender and pain, there are empirical gaps that need to be addressed. Implications and directions for future investigations into sex, gender and pain are considered.

Circadian mismatch and cardiovascular response to a performance challenge: Larks in morning and evening work sessions

We presented morning chronotype ("Lark") university undergraduate volunteers a more or less difficult Sternberg-type recognition memory task either in the morning (8-11 am) or in the evening (5-8 pm) with instructions that they could win a prize if they were 85% successful. We established morning chronotype using the Composite Scale for Morningness (Smith et al., 1989), employing a tertile split on a pool of scale scores that ranged from 13 (extreme eveningness) to 55 (extreme morningness). Participants had scores above 37, with most participants identifying as White/Caucasian, Hispanic/Latino, or Black/African-American. Among women (final sample n = 81), systolic blood pressure and mean arterial pressure responses assessed during work formed a crossover pattern, being positively correspondent to difficulty in the morning but negatively correspondent to difficulty in the evening. Heart rate and heart pre-ejection period responses ran parallel in the morning but not the evening. Among men (final sample n = 41), cardiovascular responses differed neither with difficulty nor with time. Findings for women support the extension of a recent analysis of fatigue influence on effort and associated cardiovascular responses to the phenomenon of circadian mismatch. Findings for men do not support the extension but should be interpreted guardedly in light of prohibitively low cell ns and unexpected findings on key subjective measures.

How Stereotypes Affect Pain

Stereotypes are abundant in everyday life – and whereas their influence on cognitive and motor performance is well documented, a causal role in pain processing is still elusive. Nevertheless, previous studies have implicated gender-related stereotype effects in pain perception as potential mediators partly accounting for sex effects on pain. An influence of stereotypes on pain seems indeed likely as pain measures have proven especially susceptible to expectancy effects such as placebo effects. However, so far empirical approaches to stereotype effects on pain are correlational rather than experimental. In this study, we aimed at documenting gender-related stereotypes on pain perception and processing by actively manipulating the participants’ awareness of common stereotypical expectations. We discovered that gender-related stereotypes can significantly modulate pain perception which was mirrored by activity levels in pain-associated brain areas.

Rethinking Explicit Expectations: Connecting Placebos, Social Cognition, and Contextual Perception

Expectancy effects are a widespread phenomenon, and they come with a lasting influence on cognitive operations, from basic stimulus processing to higher cognitive functions. Their impact is often profound and behaviorally significant, as evidenced by an enormous body of literature investigating the characteristics and possible processes underlying expectancy effects. The literature on this topic spans diverse fields, from clinical psychology to cognitive neuroscience, and from social psychology to behavioral biology. We present an emerging perspective on these diverse phenomena and show how this perspective stimulates new toeholds for investigation, provides insight in underlying mechanisms, improves awareness of methodological confounds, and can lead to a deeper understanding of the effects of expectations on a broad spectrum of cognitive processes.

Relationship between adaptation and cardiovascular response to tonic cold and heat pain Adaptability to tonic pain and cardiovascular responses

BACKGROUND

The mechanisms of adaptation to tonic pain are not elucidated. We hypothesized that the adaptability to tonic pain is related to the cardiovascular system.

METHODS

Twenty-six subjects received over two sessions in a random order: tonic cold (7 ± 0.2 °C) and heat pain (47.5 ± 0.5 °C) on the hand for 5 min. Pain intensity, blood pressure (BP), and heart rate (HR) were continuously monitored.

RESULTS

Pain experience during the heat (HIT) and cold (CIT) immersion tests exhibited different average time courses, being approximated with a linear and cubic function, respectively. In each test, two groups of participants could be identified based on the time course of their tonic thermal pain: one-third of participants were pain adaptive and two-thirds non adaptive. The adaptive group exhibited higher initial pain, lower last pain, and shorter latency to peak pain than the non-adaptive one. Interestingly, some participants were adaptive to both pain stimuli, most were not. HIT as well as CIT produced a stable elevation of BP. However, BP was higher during CIT than HIT (p = 0.034). HR was also increased during CIT and HIT, but the two tests differed with respect to the time course of responses. Finally, the intensity and time course of pain rating to both HIT and CIT correlated with neither BP nor HR responses.

CONCLUSIONS

These results suggest that individual sensitivity and adaptability to tonic thermal pain is related to the intensity of initial pain rating and the latency to peak pain but not to cardiovascular responses.

Sex differences in pain: a brief review of clinical and experimental findings

Recent years have witnessed substantially increased research regarding sex differences in pain. The expansive body of literature in this area clearly suggests that men and women differ in their responses to pain, with increased pain sensitivity and risk for clinical pain commonly being observed among women. Also, differences in responsivity to pharmacological and non-pharmacological pain interventions have been observed; however, these effects are not always consistent and appear dependent on treatment type and characteristics of both the pain and the provider. Although the specific aetiological basis underlying these sex differences is unknown, it seems inevitable that multiple biological and psychosocial processes are contributing factors. For instance, emerging evidence suggests that genotype and endogenous opioid functioning play a causal role in these disparities, and considerable literature implicates sex hormones as factors influencing pain sensitivity. However, the specific modulatory effect of sex hormones on pain among men and women requires further exploration. Psychosocial processes such as pain coping and early-life exposure to stress may also explain sex differences in pain, in addition to stereotypical gender roles that may contribute to differences in pain expression. Therefore, this review will provide a brief overview of the extant literature examining sex-related differences in clinical and experimental pain, and highlights several biopsychosocial mechanisms implicated in these male-female differences. The future directions of this field of research are discussed with an emphasis aimed towards further elucidation of mechanisms which may inform future efforts to develop sex-specific treatments.

Sex differences in pain and pain inhibition: multiple explanations of a controversial phenomenon

A clear majority of patients with chronic pain are women; however, it has been surprisingly difficult to determine whether this sex bias corresponds to actual sex differences in pain sensitivity. A survey of the currently available epidemiological and laboratory data indicates that the evidence for clinical and experimental sex differences in pain is overwhelming. Various explanations for this phenomenon have been given, ranging from experiential and sociocultural differences in pain experience between men and women to hormonally and genetically driven sex differences in brain neurochemistry.

Gender role affects experimental pain responses: a systematic review with meta-analysis

Gender role refers to the culturally and socially constructed meanings that describe how women and men should behave in certain situations according to feminine and masculine roles learned throughout life. The aim of this meta-analysis was to evaluate the relationship between gender role and experimental pain responses in healthy human participants. We searched computerized databases for studies published between January 1950 and May 2011 that had measured gender role in healthy human adults and pain response to noxious stimuli. Studies were entered into a meta-analysis if they calculated a correlation coefficient (r) for gender role and experimental pain. Searches yielded 4465 'hits' and 13 studies were eligible for review. Sample sizes were 67-235 participants and the proportion of female participants was 45-67%. Eight types of gender role instrument were used. Meta-analysis of six studies (406 men and 539 women) found a significant positive correlation between masculine and feminine personality traits and pain threshold and tolerance, with a small effect size (r = 0.17, p = 0.01). Meta-analysis of four studies (263 men and 297 women) found a significant negative correlation between gender stereotypes specific to pain and pain threshold and tolerance, with a moderate effect size (r = -0.41, p < 0.001). In conclusion, individuals who considered themselves more masculine and less sensitive to pain than the typical man showed higher pain thresholds and tolerances. Gender stereotypes specific to pain scales showed stronger associations with sex differences in pain sensitivity response than masculine and feminine personality trait scales.

A systematic literature review of 10 years of research on sex/gender and pain perception - part 2: do biopsychosocial factors alter pain sensitivity differently in women and men?

This systematic review summarizes the results of 10 years of laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian to access multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The second set of results presented in this review (129 articles) examined various biopsychosocial factors that may contribute to differences in pain sensitivity between healthy women and men. The results revealed that the involvement of hormonal and physiological factors is either inconsistent or absent. Some studies suggest that temporal summation, allodynia, and secondary hyperalgesia may be more pronounced in women than in men. The evidence to support less efficient endogenous pain inhibitory systems in women is mixed and does not necessarily apply to all pain modalities. With regard to psychological factors, depression may not mediate sex differences in pain perception, while the role of anxiety is ambiguous. Cognitive and social factors appear to partly explain some sex-related differences. Finally, past individual history may be influential in female pain responses. However, these conclusions must be treated with much circumspection for various methodological reasons. Furthermore, some factors/mechanisms remain understudied in the field. There is also a need to assess and improve the ecological validity of findings from laboratory studies on healthy subjects, and perhaps a change of paradigm needs to be considered at this point in time to better understand the factors that influence the experience of women and men who suffer from acute or chronic pain.

Concept priming and pain: an experimental approach to understanding gender roles in sex-related pain differences

Prior research has found that sex differences in pain are partially due to individual variations in gender roles. In a laboratory study, we tested the hypothesis that the presence of covert gender role cues can also moderate the extent to which women and men experience pain. Specifically, we varied gender role cues by asking male and female participants to write about instances in which they behaved in a stereotypically feminine, masculine, or neutral manner. Pain and cardiovascular reactivity to the cold pressor task were then assessed. Results revealed that, when primed with femininity, men reported less pain and anxiety from the cold pressor task than women. However, no differences existed between the sexes in the masculine or neutral prime conditions. The results indicate that covert gender cues can alter pain reports. Further, at least in some situations, feminine role cues may be more influential on pain reports than masculine role cues.

Sex, gender, and pain: a review of recent clinical and experimental findings

Sex-related influences on pain and analgesia have become a topic of tremendous scientific and clinical interest, especially in the last 10 to 15 years. Members of our research group published reviews of this literature more than a decade ago, and the intervening time period has witnessed robust growth in research regarding sex, gender, and pain. Therefore, it seems timely to revisit this literature. Abundant evidence from recent epidemiologic studies clearly demonstrates that women are at substantially greater risk for many clinical pain conditions, and there is some suggestion that postoperative and procedural pain may be more severe among women than men. Consistent with our previous reviews, current human findings regarding sex differences in experimental pain indicate greater pain sensitivity among females compared with males for most pain modalities, including more recently implemented clinically relevant pain models such as temporal summation of pain and intramuscular injection of algesic substances. The evidence regarding sex differences in laboratory measures of endogenous pain modulation is mixed, as are findings from studies using functional brain imaging to ascertain sex differences in pain-related cerebral activation. Also inconsistent are findings regarding sex differences in responses to pharmacologic and non-pharmacologic pain treatments. The article concludes with a discussion of potential biopsychosocial mechanisms that may underlie sex differences in pain, and considerations for future research are discussed.

PERSPECTIVE

This article reviews the recent literature regarding sex, gender, and pain. The growing body of evidence that has accumulated in the past 10 to 15 years continues to indicate substantial sex differences in clinical and experimental pain responses, and some evidence suggests that pain treatment responses may differ for women versus men.

Prevalence of oral pain and barriers to use of emergency oral care facilities among adult Tanzanians

Background

Oral pain has been the major cause of the attendances in the dental clinics in Tanzania. Some patients postpone seeing the dentist for as long as two to five days. This study determines the prevalence of oral pain and barriers to use of emergency oral care in Tanzania.

Methods

Questionnaire data were collected from 1,759 adult respondents aged 18 years and above. The study area covered six urban and eight rural study clusters, which had been selected using the WHO Pathfinder methodology. Chi-square tests and logistic regression analyses were performed to identify associations.

Results

Forty two percent of the respondents had utilized the oral health care facilities sometimes in their lifetime. About 59% of the respondents revealed that they had suffered from oral pain and/or discomfort within the twelve months that preceded the study, but only 26.5% of these had sought treatment from oral health care facilities. The reasons for not seeking emergency care were: lack of money to pay for treatment (27.9%); self medication (17.6%); respondents thinking that pain would disappear with time (15.7%); and lack of money to pay for transport to the dental clinic (15.0%). Older adults were more likely to report that they had experienced oral pain during the last 12 months than the younger adults (OR = 1.57, CI 1.07–1.57, P < 0.001). Respondents from rural areas were more likely report dental clinics far from home (OR = 5.31, CI = 2.09–13.54, P < 0.001); self medication at home (OR = 3.65, CI = 2.25–5.94, P < 0.001); and being treated by traditional healer (OR = 5.31, CI = 2.25–12.49, P < 0.001) as reasons for not seeking emergency care from the oral health care facilities than their counterparts from urban areas.

Conclusion

Oral pain and discomfort were prevalent among adult Tanzanians. Only a quarter of those who experienced oral pain or discomfort sought emergency oral care from oral health care facilities. Self medication was used as an alternative to using oral care facilities mainly by rural residents. Establishing oral care facilities in rural areas is recommended.

Sex differences in thermal pain sensitivity and sympathetic reactivity for two strains of rat

Human females are more sensitive than males to brief nociceptive stimuli such as heat and cold. However, a more pronounced peripheral vasoconstriction by females than by males during prolonged nociceptive stimulation predicts that females would be more sensitive to prolonged cold but not heat stimulation. We tested this possibility with reflex (lick/guard) and operant escape and preference tests of sensitivity to prolonged stimulation of Long-Evans and Sprague-Dawley rats. Escape responses to cold stimulation revealed a greater sensitivity of females. In contrast, males were more sensitive to nociceptive heat stimulation. An operant preference test of relative sensitivity to cold or heat stimulation confirmed these results. Cold was more aversive than heat for females, but heat was more aversive than cold for males. Recordings of skin temperature during nociceptive heat stimulation were consistent with the results of operant testing. A reduction in skin temperature (peripheral vasoconstriction) during nociceptive stimulation should increase cold sensitivity as observed for females relative to males. Lick/guard testing did not confirm the results of operant testing. Lick/guard (L/G) responding to nociceptive heat stimulation was greater for females than for males. Female escape responses to heat were more variable than males, but L/G responding of males to the same stimulus was more variable than for females.

PERSPECTIVE

A variety of chronic pain conditions are more prevalent for females, and psychological stress (with attendant sympathetic activation) is implicated in development and maintenance of these conditions. Therefore, understanding relationships between gender differences in pain sensitivity and sympathetic activation could shed light on mechanisms for some varieties of chronic pain.

Male--female differences in the impact of beta-adrenoceptor stimulation on resistance to experimental metastasis: exploring the effects of age and gonadal hormone involvement

We studied the development of sexual dimorphism in resistance to NK-sensitive experimental metastasis under baseline conditions and following adrenoceptor stimulation. With increasing age, baseline resistance to MADB106 lung tumor retention (LTR) increased in both sexes, but also the susceptibility to the tumor-enhancing effects of a beta-adrenergic agonist, metaproterenol. Beginning at 13 weeks, males exhibited a 2- to 3-fold greater increase in LTR than females following adrenoceptor stimulation. This adult dimorphism was robust to ovariectomy, and questionably related to androgens. The findings are consistent with reduced female responsiveness to sympathetic activation, and substantiate the importance of including both sexes when studying neuroimmunomodulation.

Emotion and Pain: A Functional Cerebral Systems Integration

Emotion and pain are psychological constructs that have received extensive attention in neuropsychological research. However, neuropsychological models of emotional processing have made more progress in describing how brain regions interact to process emotion. Theories of emotional processing can describe inter-hemispheric and intra-hemispheric interactions during emotional processing. Due to similarities between emotion and pain, it is thought that emotional models can be applied to pain. The following review examines the neuropsychology of emotion and pain using a functional cerebral systems approach. Specific comparisons are made between pain and anger. Attention is given to differences in cerebral function and physiology that may contribute to the processing of emotion and pain. Suggestions for future research in emotion and pain are given.

The Role of Mood States Underlying Sex Differences in the Perception and Tolerance of Pain

While sex differences in pain reporting are frequently observed, the reasons underlying these differences remain unclear. The present study examined sex differences in self-report and physiological measures of pain threshold and tolerance following the administration of two laboratory pain-induction tasks. The primary study aim centered on determining whether repeated exposure to such tasks would yield sex differences in terms of pain threshold and tolerance. In addition, it was hypothesized that if such differences did exist, negative mood states might account for changes in pain ratings, threshold, and/or tolerance in subsequent exposure to noxious stimuli. Recruited from a convenience sample, 66 participants (44 female and 22 male) were exposed to both thermal and cold noxious stimuli at three separate times, while psychophysiological and self-report data were collected. Because women outnumbered men 2:1, Fisher z transformations were performed to determine whether the observed associations between mood states and pain ratings differed. We found stronger associations between fatigue and thermal-heat pain ratings for men at their first and third exposure to the pain task compared to women (z = 2.11, P < 0.05; z = 3.14, P < 0.001, respectively). Results indicated that women evidenced greater pain tolerance than men on both a behavioral and physiological level; however, they reported greater pain severity than men. Fatigue was also found to be particularly important to reports of pain severity in men and pain tolerance in response to noxious stimuli for women. Possible pathways in which mood states influenced these endpoints are discussed.

Sex differences in regional brain response to aversive pelvic visceral stimuli

To explore sex differences in the response of seven brain regions to an aversive pelvic visceral stimulus, functional magnetic resonance images were acquired from 13 healthy adults (6 women) during 15 s of cued rectal distension at two pressures: 25 mmHg (uncomfortable), and 45 mmHg (mild pain), as well as during an expectation condition (no distension). Random-effects analyses combining subject data voxelwise found 45-mmHg pressure significantly activated the insular and anterior cingulate cortices in both sexes. In men only, the left thalamus and ventral striatum were also activated. Although all activations appeared more extensive in men, no sex difference attained significance. To explore the presence of deactivations, which are generally cancelled by more numerous activations when subjects are combined for each voxel, the number of activated voxels, number of deactivated voxels, and ratio of deactivated voxels to total voxels affected were assessed via random-effects, mixed-model analyses combining subject data at the region level. Greater insula activation in men compared with women was seen during the expectation condition and during the 25-mmHg distension. Greater deactivations in women were seen in the amygdala (25-mmHg distension) and midcingulate (45-mmHg distension). Women had a significantly higher proportion of deactivated voxels than men in all four subcortical structures during 25-mmHg distension. Greater familiarity of females with physiological pelvic visceral discomfort may have enhanced brain systems that dampen arousal networks during lower levels of discomfort.

Sex differences in cardiac and autonomic response to clinical and experimental pain in LBP patients

Rehabilitation professionals are currently using heart rate (HR) in order to assess the sincerity of effort in certain evaluations. It has been shown that a relation exists between HR and pain but no study has measured cardiac response during both clinical and experimental pain among a patient population using an intra-subject design. Thirty patients with low back pain (LBP) participated in this study including 16 men. Clinical pain was induced by applying a postero-anterior pressure (PA) on a painful lumbar segment for 15 and 30s in order to reproduce the patient's typical LBP at an intensity ranging between 50 and 70/100. Experimental pain was induced with a 15s thermal stimulus at a temperature which reproduced the same pain intensity as the 15s PA. For both reproduced clinical pain durations, we observed a rise in HR ranging between 8.5% and 12.67%. However, unlike men, women's cardiac response failed to show a constant rise in HR during the 30s PA. For all subjects, the rise in HR was much lower during the experimental pain condition (p<0.001), reaching only 5%. On the other hand, galvanic skin responses were significantly higher during the experimental pain condition (p<0.001). During this same condition, women also had a greater rise in galvanic skin responses than men (p=0.04). Finally, a significant correlation was found between both types of pain. These results suggest that pain induced during a clinical evaluation will produce a significant HR augmentation. However, heart rate variability analysis showed greater sympathetic cardiac regulation for men. The sex differences observed in this study call for caution when interpreting HR during pain assessment.

Establishing a link between heart rate and pain in healthy subjects: a gender effect

Heart rate (HR) is currently used by rehabilitation clinicians as a complementary objective measure of pain. The premise is that, as pain increases, HR should also increase. However, this relationship is not clearly established. The goal of this study was to verify the relationship between HR and pain perception. Thirty-nine healthy volunteers participated in this experimental study. Painful stimuli were induced by a 2-minute immersion of the hand in hot water (47 degrees C). HR was recorded before and during the stimulation and was matched to a pain rating. We observed a rise of 11% in HR after 2 minutes of immersion. There was a significant intrasubject correlation between HR and pain intensity (r = 0.50, P < .001) and pain unpleasantness (r = 0.55, P < .001). Furthermore, there was a strong gender effect in the intersubject correlations. Men presented a strong correlation between mean HR and mean pain perception (intensity: r = 0.77, unpleasantness: r = 0.86), whereas this relationship was absent in women (intensity: r = -0.2, unpleasantness: r = 0.001). In conclusion, results show that, for healthy volunteers, experimental pain can elicit a rise in HR up to 11%. Moreover, the relationship between HR response and pain is gender related. Considering that a positive relationship between HR and pain perception was only found in men, these results do not support a clinical significance of the use of HR for pain evaluation in women. Clinical implications need to be further evaluated with patients before clinicians can use HR as a complementary tool in pain assessment.

PERSPECTIVE

A positive correlation between HR and pain was observed for men but not for women. These differences underline the importance of taking into account gender differences in the development of complementary pain assessment. Further research should be conducted to verify the role of sex hormones on heart rate and pain.

Psychophysical evidence of hypersensitivity in subjects with interstitial cystitis

PURPOSE

We quantified differences in somatic and visceral sensation in healthy subjects and subjects with interstitial cystitis (IC).

MATERIALS AND METHODS

A total of 13 subjects with IC and 13 healthy subjects answered psychological questionnaires and underwent psychophysical testing of thermal and pressure thresholds for sensation as well as the ischemic forearm test of pain tolerance. A subset of subjects also underwent bladder sensory testing with the determination of 3 consecutive cystometrograms. Ratings of intensity and unpleasantness were determined.

RESULTS

Subjects with IC were significantly more sensitive to deep tissue measures of sensation related to pressure, ischemia and bladder than healthy subjects. Cutaneous thermal pain measures were similar in the 2 groups. Psychological measures indicated higher reactivity in subjects with IC.

CONCLUSIONS

Similar to other visceral pain disorders, such as irritable bowel syndrome, hypersensitivity to somatic stimuli was noted in subjects with IC. This suggests altered central mechanisms in the processing of sensory events from the bladder.

Hypothalamic–Pituitary–Adrenal and Autonomic Nervous System Functioning in Fibromyalgia

In general, there seems to be a reduction in some neuroendocrine and autonomic nervous system (ANS) responses to applied stresses in individuals who have fibromyalgia. This article presents an overview and discussion of these findings with respect to the role of the ANS and the neuroendocrine system in the response to stress, with emphasis on the hypothalamic-pituitary-adrenal axis and the possible implication to fibromyalgia.

Exercise lowers pain threshold in chronic fatigue syndrome

Post-exertional muscle pain is an important reason for disability in patients who are diagnosed to have Chronic Fatigue Syndrome (CFS). We compared changes in pain threshold in five CFS patients with five age and sex matched controls following graded exercise. Pain thresholds, measured in the skin web between thumb and index finger, increased in control subjects with exercise while it decreased in the CFS subjects. Increased perception of pain and/or fatigue after exercise may be indicative of a dysfunction of the central anti-nociceptive mechanism in CFS patients.