An ROC analysis of pain reactions in dysmenorrheic and nondysmenorrheic women

Dysmenorrhea subtypes exhibit differential quantitative sensory assessment profiles

Women who develop bladder pain syndrome (BPS), irritable bowel syndrome, or dyspareunia frequently have an antecedent history of dysmenorrhea. Despite the high prevalence of menstrual pain, its role in chronic pelvic pain emergence remains understudied. We systematically characterized bladder, body, and vaginal mechanical sensitivity with quantitative sensory testing in women with dysmenorrhea (DYS, n = 147), healthy controls (HCs) (n = 37), and women with BPS (n = 25). Previously, we have shown that a noninvasive, bladder-filling task identified a subset of women with both dysmenorrhea and silent bladder pain hypersensitivity, and we repeated this to subtype dysmenorrhea sufferers in this study (DYSB; n = 49). DYS, DYSB, and BPS participants had lower vaginal mechanical thresholds and reported more pain to a cold stimulus during a conditioned pain modulation task and greater pelvic examination after-pain than HCs (P's < 0.05). DYSB participants also had reduced body mechanical thresholds and less conditioned pain modulation compared to HCs and DYS participants (P's < 0.05). Comparing quantitative sensory testing results among the DYS and HC groups only, provoked bladder pain was the only significant predictor of self-reported menstrual pain (r = 0.26), bladder pain (r = 0.57), dyspareunia (r = 0.39), and bowel pain (r = 0.45). Our findings of widespread sensory sensitivity in women with dysmenorrhea and provoked bladder pain, much like that observed in chronic pain, suggest a need to study the trajectory of altered mechanisms of pain processing in preclinical silent visceral pain phenotypes to understand which features convey inexorable vs modifiable risk.

Detectability and Bias Indices of Pneumatic Corneal Stimuli Using Signal Detection Theory

Purpose

To evaluate the feasibility of using signal detection theory (SDT) in estimating criterion and detectability indices for corneal pneumatic stimuli and test corneal psychophysical data against linking hypotheses from nonprimate physiology using Bayesian analysis.

Methods

Corneal pneumatic stimuli were delivered using the Waterloo Belmonte esthesiometer. Corneal thresholds were estimated in 30 asymptomatic participants and 1.5× threshold stimuli were used as signals (with 0.4 probability). There were 100-trial mechanical and cold stimulus experiments and 50-trial chemical experiments. Trials were demarcated auditorily and “yes” or “no” recorded after each trial. Cold stimulus experiments were conducted with 0.6 signal probability. Criterion (c), likelihood ratio (lnβ), and d′ were calculated from the yes-no responses.

Results

Average d′ was 0.59 ± 0.1, 1.65 ± 0.37, and 1.14 ± 0.3 units for cold, mechanical, and chemical stimuli, respectively. Bayes factors obtained using Bayesian analysis of variance mildly favored (BF₁₀ = 1.55) differences between d′s of the stimulus types, with no support for differences in criteria between stimulus types. Multiple comparisons of d′ supported linking hypotheses based on nociception and nerve conductance theories.

Conclusions

Our experiments are the first to demonstrate the feasibility of estimating SDT indices and test different hypotheses. The conservative strategy (reporting “no” more often) chosen by participants was anticipated due to relatively large proportion of catch trials.

Translational Relevance

SDT when using pneumatic esthesiometry is vital to evaluate bias in responses of participants. Considering the varied forms of inherent noise in the corneal sensory system, SDT is critical to understand the sensory and decisional characteristics.

Experimental evaluation of central pain processes in young women with primary dysmenorrhea

Primary dysmenorrhea (PD; menstrual pain without an underlying medical condition) is associated with enhanced pain sensitivity and temporal summation (TS) in adult women, which may reflect the presence of central pain processes. Research in this area has been limited by focusing on only adult populations and incomplete assessments of central sensitization. The current study explored both excitatory and inhibitory measures of pain processing in girls and young adult women with and without PD. Thirty-two young women with PD and 34 healthy controls underwent laboratory pain testing during each of 3 menstrual cycle phases (menstrual, ovulatory, and midluteal), which included measures of pain tolerance and threshold, TS, and conditioned pain modulation. Results indicated enhanced pain sensitivity in young women with PD as measured by heat pain tolerance and Average Pain50 (P50), compared with healthy controls. These group differences were evident at all phases of the menstrual cycle. No group differences in cold pain tolerance, TS, or conditioned pain modulation were evident at any phase of the menstrual cycle. These data suggest some evidence of central sensitization in young women with PD, although no evidence of enhanced excitatory or deficient inhibitory mechanisms were observed. Future research should focus on identifying other potential phenotypes for PD to determine those at risk of developing other pain problems.

Experimental and procedural pain responses in primary dysmenorrhea: a systematic review

Primary dysmenorrhea (PD) has been the focus of a number of experimental pain studies. Although a number of reviews exist, few have critically evaluated the existing body of research on PD and experimental and procedural pain. Data from 19 published research articles that include women with PD and responses to an experimental or procedural pain stimulus (or stimuli) suggest that women with PD may have elevated pain reactivity, as compared to women without PD. This pattern appears to be true across different phases of the menstrual cycle. However, there is an abundance of conflicting findings, which may be due to significant methodological issues such as inconsistent definitions of PD, wide variation in experimental pain methodologies, and inaccurate assessment of the menstrual cycle. Future research should focus on identifying specific symptoms (i.e., pain threshold ratings) to more clearly define what constitutes PD, establish reliable and valid laboratory testing protocols, and assess the menstrual cycle with greater precision.

Towards an Objective Psychophysics of Pain

The limits of most sensory systems can now be routinely determined by objective detection-theory methods. The threshold of pain, however, is often thought to require more traditional methods that rely on a subject providing some estimate or description of what is perceived. The subject makes a measurement that cannot be contested and, in this sense, the methods are subjective. An experimental study of electrocutaneous stimuli showed how it is possible to interpret a traditional identification method and a category method in detection-theory terms. On this interpretation, these traditional methods yield results similar to a rating method of detection theory, a method that measures sensory resolution. However, the traditional methods give rise to additional judgmental variance not involved in standard detection-theory methods. They therefore do not provide a special insight into the experience of pain, and the extra variance they produce serves only to degrade, rather than to enhance, their usefulness.

Association of trauma, posttraumatic stress disorder, and experimental pain response in healthy young women

BACKGROUND

Evidence of pain alterations in trauma-exposed individuals has been found. The presence of posttraumatic stress disorder (PTSD) may be explaining these alterations, as some of the psychological characteristics of PTSD are hypothesized to increase pain response.

OBJECTIVES

To examine differences in pain response and in certain psychological variables between trauma-exposed women (TEW) with PTSD, TEW without PTSD, and non-trauma-exposed women (NTEW) and to explore the role of these psychological variables in the differences in pain response between the groups.

METHODS

A total of 122 female students completed a cold pressor task (42 TEW with PTSD, 40 TEW without PTSD, and 40 NTEW). Anxiety sensitivity, experiential avoidance, trait and state dissociation, depressive symptoms, state anxiety, catastrophizing, and arousal were assessed.

RESULTS

TEW with PTSD reported significantly higher pain unpleasantness than NTEW, but not more than that of TEW without PTSD. They also presented higher trait dissociation, state anxiety, depressive symptoms, and skin conductance than the other 2 groups and higher anxiety sensitivity than TEW without PTSD. TEW without PTSD reported more pain unpleasantness than NTEW, but they recovered faster from pain. However, these differences were not explained by any psychological variable.

CONCLUSIONS

The results suggest that although trauma-exposed individuals are not more sensitive to painful stimulation, they evaluate pain in a more negative way. Exposure to trauma itself, but not to PTSD, may explain the differences found in pain unpleasantness.

Comparing pain sensitivity and the nociceptive flexion reflex threshold across the mid-follicular and late-luteal menstrual phases in healthy women

OBJECTIVES

Understanding the relationship between the menstrual cycle and pain can contribute significantly to our knowledge of pain processing in women. Many early studies suggested that pain sensitivity was enhanced during the luteal phase of the menstrual cycle relative to the follicular phase; however, these studies were often limited by small sample sizes, lack of ovulation verification, focus on a single pain modality, inadequate assessment of menstrual cycle regularity, and low-powered statistical methods. The current study was designed to address these limitations and examine the difference in pain processing between the mid-follicular (days 5 to 8) and late-luteal (days 1 to 6 preceding menses) phases.

METHODS

Forty-one healthy, regularly cycling women attended testing sessions that measured pain sensitivity from mechanical pain threshold, electrocutaneous pain threshold/tolerance, and ischemia pain threshold/tolerance, as well as McGill Pain Questionnaire qsensory and affective ratings of electric and ischemic stimuli. Electrocutaneous stimulation was also used to assess nociceptive flexion reflex threshold, a physiological measure of spinal nociception.

RESULTS

When analyses were limited to data collected only in the targeted menstrual phases (N=30), results indicated no menstrual phase effect on any pain outcome (all P's>0.05), with the exception of lower electrocutaneous pain thresholds during the late-luteal phase. No outcomes differed by menstrual phase in the full sample (N=41). This indicates nociceptive responding varies little between the mid-follicular and late-luteal phases.

DISCUSSION

The present study suggests that experimental pain processing does not significantly differ between the mid-follicular and late-luteal phases of the menstrual cycle in healthy women. This implies hormonal variation across these 2 phases (ie, progesterone) has a minimal effect on subjective and physiological responses to pain.

Gender role expectations of pain mediate sex differences in cold pain responses in healthy Libyans

Previous studies found a relationship between response to experimentally-induced pain and scores for the gender role expectations of pain (GREP) questionnaire. Findings were similar in individuals from America, Portugal and Israel suggesting that gender role expectations may be universal. The aim of this study was to translate and validate Arabic GREP using Factor Analysis and to investigate if sex differences to cold-pressor pain in healthy Libyan men and women are mediated through stereotypical social constructs of gender role expectations and/or pain-related anxiety. One hundred fourteen university students (58 women) underwent two cycles of cold pressor pain test to measure pain threshold, tolerance, intensity, and unpleasantness. Participants also completed the Arabic GREP questionnaire and the Pain Anxiety Symptom Scale-Short form (PASS-20). It was found that Libyan men had higher pain thresholds and tolerances than women (mean difference, 95% CI: threshold = 4.69 (s), -0.72 to 10.1, p = 0.005; tolerance = 13.46 (s), 0.5-26.4, p = 0.018). There were significant differences between sexes in 6 out of 12 GREP items (p < 0.004 after Bonferonni adjustment). The results of mediational analysis showed that GREP factors were the mediators of the effects of sex on pain threshold (z = -2.452, p = 0.014 for Self Sensitivity); (z = -2.563, p = 0.01, for Self Endurance) and on pain tolerance (z = -2.538, p = 0.01 for Self Endurance). In conclusion, sex differences in response to pain were mediated by gender role expectations of pain but not pain-related anxiety.

Effect of the menstrual cycle phase on post-operative pain perception and analgesic requirements

BACKGROUND

Research has shown that menstrual cycle phase may affect pain sensitivity. There is a lack of studies evaluating this effect on post-operative pain and analgesic needs.

METHODS

In this prospective cohort study, we determined the effect of menstrual cycle phase on pain perception and analgesic requirements following total abdominal hysterectomy. Sixty women with regular menstrual cycles undergoing elective surgery were recruited and divided into 'follicular' and 'luteal' groups according to their menstrual history. Post-operative pain was managed with intravenous patient-controlled analgesia using tramadol. Intravenous morphine was used for rescue analgesia, and pain was assessed for 24 h.

RESULTS

Pain scores in the recovery room and ward six and 24 h post-operatively were similar in the groups at rest and on coughing. Pain scores at rest 12 h post-operatively were significantly higher in the luteal group (P = 0.043), while they were similar on coughing. There was no significant difference in the total tramadol requirement. Number of patients requiring rescue analgesia and the amount of morphine used was also similar.

CONCLUSION

There was no difference in pain scores or analgesic requirements between the two groups except for rest pain at 12 h, which was significantly higher in the luteal group. As pain was assessed at 13 different time points, a significant difference seen only at one point could be due to random chance. We suggest that future research should concentrate on studying this issue in patients of relatively younger age groups with more pronounced hormonal variations during the cycle.

Influence of the menstrual cycle on the pressure pain threshold of masticatory muscles in patients with masticatory myofascial pain

OBJECTIVE

The aim of this study was to investigate the influence of the menstrual cycle and oral contraceptive (OC) intake on the pressure pain threshold (PPT) of masticatory muscles in patients with masticatory myofascial pain (MFP).

STUDY DESIGN

The sample was composed of 36 women, divided into 4 groups, according to the presence of MFP and the intake of OC (15 patients had MFP [7 taking OC] and 21 were pain-free controls [8 taking OC]). The algometer-based PPT of masseter and temporalis, and the record of subjective pain by visual analog scale (VAS) were determined during 2 consecutives menstrual cycles at 4 phases (menstrual, follicular, periovulatory, and luteal). A 3-way ANOVA for repeated measurements, Kruskal-Wallis, Friedman, and Dunn tests, with a 5% significant level analyzed the data.

RESULTS

PPT was significantly lower in MFP patients when compared with controls throughout the experiment (P < .001). The menstrual phases did not influence PPT (P > .05), while the intake of OC seems to raise PPT levels for the left temporalis (P = .01) and right masseter (P = .04). VAS was, in general, higher at the menstrual phase

CONCLUSIONS

Different phases of the menstrual cycle have no influence on PPT values, regardless of the presence of a previous condition, as masticatory myofascial pain, while the intake of OC is associated with decreased levels of reported pain.

Does experimental pain response vary across the menstrual cycle? A methodological review

The findings on sex differences in human experimental pain research are inconsistent. One possible factor contributing to the inconsistent findings is the female hormonal cycle, as hormone levels may affect pain sensitivity. A number of studies suggest that women's responses to experimentally evoked pain vary across the menstrual cycle. However, at least an equal number of studies suggest a lack of variability. The purpose of this article is to review the literature with emphasis on what we believe could be the reasons for the inconsistent findings, namely, differences in populations sampled, timing of experimental sessions across the menstrual cycle, and nomenclature used to identify the time (phases) in the cycle when measurements were done, nature of the pain stimuli chosen, and outcomes measured. These inconsistencies and other methodological problems associated with most experimental pain studies make it difficult to draw inferences from this literature. For the science to improve, replication of significant findings using standardized timing of sessions, pain stimulus procedures, outcomes, and hormonal assessment is necessary.

Effects of Experimentally Induced Pain on Mismatch Negativity

Abstract: Previous research has found that pain can exert a disruptive effect on cognitive processing. This experiment was conducted to extend previous research with participants with chronic pain. This report examines pain's effects on early processing of auditory stimulus differences using the Mismatch Negativity (MMN) in healthy participants while they experienced experimentally induced pain. Event-related potentials (ERPs) were recorded using target and standard tones whose pitch differences were easy- or difficult-to-detect in conditions where participants attended to (active attention) or ignored (passive attention) the stimuli. Both attention manipulations were conducted in no pain and pain conditions. Experimentally induced ischemic pain did not disrupt the MMN. However, MMN amplitudes were larger to difficult-to-detect deviant tones during painful stimulation when they were attended than when they were ignored. Also, MMN amplitudes were larger to the difficult- than to the easy-to-detect tones in the active attention condition regardless of pain condition. It appears that rather than exerting a disruptive effect, the presence of experimentally induced pain enhanced early processing of small stimulus differences in these healthy participants.

A comparison of modality-specific somatosensory changes during menstruation in dysmenorrheic and nondysmenorrheic women

OBJECTIVE

The objective was to evaluate somatosensory thresholds to a multimodality stimulation regimen applied both within and outside areas of referred menstrual pain in dysmenorrheic women, over four phases of confirmed ovulatory cycles, and to compare them with thresholds in nondysmenorrheic women during menstruation.

DESIGN

Twenty dysmenorrheic women with menstrual pain scoring 5.45 +/- 0.39 cm (mean +/- standard error of mean) on a visual analog scale (10 cm) participated. Fifteen nondysmenorrheic women with a menstrual pain score of 0.4 +/- 0.2 cm participated as controls. Ovulation was confirmed by an enzyme-multiplied immunoassay technique. Menstrual pain was described with the McGill Pain Questionnaire. Areas within menstrual pain referral were two abdominal sites and the midline of the low back, and the arm and thigh were the control areas. The pressure pain threshold (PPT) and pinch pain threshold were determined by a hand-held electronic pressure algometer, the heat pain threshold (HPT) by a contact thermode, and the tactile threshold with von Frey hairs.

RESULTS

In dysmenorrheic women the McGill Pain Questionnaire showed a larger sensory and affective component of pain than the evaluative and miscellaneous groups. The HPT and PPT were lower in the menstrual phase than in the ovulatory, luteal, and premenstrual phases, both within and outside areas of referred menstrual pain (p <0.01), with a more pronounced decrease at the referral pain areas. The pinch pain threshold was lower in the menstrual phase than in the ovulatory phase (p <0.02), and the tactile threshold did not differ significantly across the menstrual phases or within any site. Dysmenorrheic women had a lower HPT at the control sites and a lower PPT at the abdomen, back, and control sites, than in those of nondysmenorrheic women in the menstrual phase.

CONCLUSIONS

The results show reduced somatosensory pain thresholds during menstruation to heat and pressure stimulation, both within and outside areas of referred menstrual pain in dysmenorrheic women. Dysmenorrheic women showed a lower HPT at the control sites and a lower PPT at all the sites than those for nondysmenorrheic women in the menstrual phase. The altered somatosensory thresholds may be dependent on a spinal mechanism of central hyperexcitability, induced by recurrent moderate to severe menstrual pain.

Sex-related hormonal influences on pain and analgesic responses

Considerable evidence indicates sex-related differences in pain responses and in the effectiveness of various analgesic agents. Specifically, females are at greater risk for experiencing many forms of clinical pain and are more sensitive to experimentally induced pain relative to males. Regarding analgesic responses, nonhuman animal studies indicate greater opioid analgesia for males, while a limited human literature suggests the opposite. Though the mechanisms underlying these effects remain unclear, the influence of gonadal hormones on nociceptive processing represents one plausible pathway whereby such sex differences could emerge. The present article reviews the complex literature concerning sex steroid effects on pain responses and analgesia. First, nonhuman animal research related to hormonal effects on nociceptive sensitivity and analgesic responses is presented. Next, human studies regarding gonadal hormonal influences on experimental pain responses are reviewed. Several potential mechanisms underlying hormonal effects on nociceptive processing are discussed, including hormonal effects to both peripheral and central nervous system pathways involved in pain transmission. Finally, based on these findings we draw several conclusions and make specific recommendations that will guide future research as it attempts to elucidate the magnitude and importance of sex-related hormonal effects on the experience of pain.

Pain perception to the cold pressor test during the menstrual cycle in relation to estrogen levels and a comparison with men

Animal and human research has shown that pain sensitivity changes during the menstrual cycle. This has sometimes been ascribed to hormonal variations. The aim of the present study was to examine how perception of pain, induced by the cold pressor test to the dominant hand, was related to gender and phases of the menstrual cycle. A repeated-measures design was used, where twenty-two female students participated at two different phases of the menstrual cycle (days 2-4 and days 20-24). A control group of nineteen male students participated on two occasions, separated by a three week period. The cycle phase during which each woman began her participation was randomized. Pain was induced using the cold pressor test. Pain threshold was determined as the duration of time between when the subject first reported pain and exposure to the painful stimulus. Pain tolerance was determined as the duration of time until the subject withdraw her/his hand from the test water because the pain was too intensive. The results showed that men tolerated significantly greater pain than women. Women's pain threshold was significantly higher during the second phase of the menstrual cycle. Systolic pressure was higher in men than women, increasing more in men in response to cold pressor testing than women. Further research, including measurements of plasma hormone levels during the menstrual cycle, is needed to clarify the role played by estrogens in pain perception.

Menstrual cycle, blood pressure and ischemic pain sensitivity in women: a preliminary investigation

Eleven women were tested twice for ischemic pain sensitivity; once during their follicular phase (Days 4-9) and once during their mid-late luteal phase (5-10 days after ovulation) of a confirmed ovulatory cycle. Additionally, in order to examine blood pressure-related hypoalgesic effects, each had 3-4 clinic blood pressures determined during an initial screening interview and each also completed a daily symptom calendar for one complete menstrual cycle prior to testing in order to investigate relationships between 'real life' symptomatology and laboratory-induced pain sensitivity. Results revealed significantly shorter pain tolerance times and marginally shorter pain threshold times in the luteal vs. follicular phase, while verbal descriptors of pain intensity (sensory) and pain unpleasantness (affective) did not vary with cycle phase. Clinic blood pressures were positively correlated with pain threshold and tolerance times assessed during both cycle phases. Real-life physical symptom ratings were predictive of laboratory pain intensity ratings during the follicular phase and tended to predict unpleasantness ratings during both phases. These results not only confirm recent reports of greater sensitivity to ischemic pain in women during the luteal phase of their cycle, but extend the literature by demonstrating pressure-related hypoalgesic effects in women during both cycle phases.

Ischemic but not thermal pain sensitivity varies across the menstrual cycle

OBJECTIVE AND METHOD

Findings from both animal and human research suggest that pain sensitivity changes across the menstrual cycle; however, among humans the nature of these menstrual cycle effects remains unclear. The present study used a repeated-measures design to evaluate changes in thermal and ischemic pain responses during three phases of the menstrual cycle, midfollicular (postmenstrual), ovulatory, and mid-to-late luteal (premenstrual), in 11 healthy women. The cycle phase during which subjects began their participation was determined randomly. Plasma levels of estrogen, progesterone, luteinizing hormone (LH), testosterone, and beta-endorphin were determined at each experimental session. Participants also completed a daily diary of physical and emotional symptoms for two complete menstrual cycles before the experimental sessions.

RESULTS

The results indicated that women showed less ischemic pain sensitivity during the midfollicular compared with the ovulatory and mid-to-late luteal phases, but thermal pain responses did not vary significantly across menstrual cycle phases. Physical and emotional symptoms were minimal and did not change significantly across the menstrual cycle.

CONCLUSIONS

These findings indicate greater ischemic but not thermal pain sensitivity among women after the midcycle LH surge. The practical relevance and potential mechanisms of these findings are discussed.

The "plantar test" apparatus (Ugo Basile Biological Apparatus), a controlled infrared noxious radiant heat stimulus for precise withdrawal latency measurement in the rat, as a tool for humans?

In the present study, we precisely and automatically measured the withdrawal latency to noxious radiant heat application in unrestrained male rats and in human subjects of both sexes, by means of the "plantar test" apparatus (Ugo Basile Biological Apparatus). The infrared light stimulus of this tool was applied underneath the hindpaws of rats and the middle fingers of human subjects. With one right and one left stimulation every 10 min, we observed a decrease in latency over a 40-min testing period in rats; the latency reached a mean value of 5.08 +/- 0.25 sec after 40 min with a 36-W stimulus, which corresponded to 46.5 degrees C. In pilot experiments, also performed on rats, we showed that the opiate morphine (10 mg/kg, i.p.) produced remarkable increases of the withdrawal latency only in "naive" animals (i.e., ones that had never experienced the plantar test stimulus) and not in animals "habituated" to it. Among humans, we noted gender differences, such as less sensitivity to the infrared noxious radiant heat for women, particularly during the menstrual period. A difference from rats was that there was no significant latency modification along the 40-min testing period for either women or men, with a mean latency of 5.61 +/- 0.18 sec (47.5 degrees C) for the women and 4.39 +/- 0.10 sec (45.5 degrees C) for the men. These data confirm the reliability of the plantar test in rats, and demonstrate the possible use of an infrared source in human subjects as a noxious heat stimulus; the withdrawal reaction to this stimulus is emphasized as a good index of nociception in humans.

Discriminability of electrocutaneous stimuli after topical anesthesia: detection-theory measurement of sensitivity to painful stimuli

In three experiments on the psychophysical measurement of pain, electrocutaneous currents were applied to the volar surface of the forearm. In the first experiment, a conventional category scaling method was compared with the rating method of signal detection. The results of both methods were analyzed in detection-theory terms to derive receiver operating characteristic curves and measures of the discriminability of adjacent currents. The rating method yielded larger discriminability values than the category scale did, and that method was therefore used in the subsequent experiments to examine the effect of a topical anesthetic on discriminability. When the stimuli were applied through surface electrodes, no effect of the topical anesthetic on discriminability was found, but when the stimuli were applied to a more localized area by intradermal needle electrodes, a dose-dependent effect of the anesthetic on discriminability occurred. For this experiment, the slope of the cumulative sensitivity function increased with increasing elapsed time since the removal of the anesthetic. This result is congruent with the theory that discriminability can serve as a measure of sensitivity to painful stimuli.

Responsiveness to laboratory pain in women as a function of age and childbirth pain experience

Pain responsiveness was investigated experimentally as a function of age and childbirth pain experience. Sensitivity to cold pressor-induced pain was assessed through threshold, tolerance, and visual analog pain ratings. It was hypothesized that childbirth pain experience would mostly modify experimental pain judgment, in accordance with the adaptation-levels model. That is, childbirth pain would be used as an "anchor" in evaluating other painful events. Fifteen parous women were compared to 12 nulliparous women of the same age (mean age: 35 years) as well as to 15 nulliparous younger women (mean age: 24 years). This comparison was undertaken in order to distinguish the effects of age, which was found to correlate with pain threshold. Analysis of variance comparing the three groups of women was performed on each of the three cold pressor measures. A significant effect was found for pain threshold. Multiple comparisons indicated that parous women had a higher pain threshold than both groups of nulliparous women which did not differ from one another. Thus, painful childbirth experience is sufficient to raise cold pressor pain threshold. This finding has never before been reported in the pain literature. It is consistent with anecdotal reports from parous women who, when providing cold pressor pain judgments, say that "nothing compares to labor pain."

Sex differences in the perception of noxious heat stimuli

This study compared pain perception in young male and female subjects, using experimental noxious heat stimuli. During 2 sessions, each of 40 subjects rated the magnitude of 120 heat stimuli, ranging from 45 degrees C to 50 degrees C. The study included a comparison of visual analogue and magnitude matching rating procedures, as well as a test of simulated analgesia, in which the range of stimuli presented during the 2 experimental sessions was shifted by 1 degree C. We found that females rated noxious heat stimuli as more intense than did males, independent of the gender of the experimenter or the type of rating scale. In addition, the data suggest that females discriminate among the painful heat intensities better than males. For example, female subjects showed significant between-session discrimination of noxious heat stimuli, while male subjects did not, and females produced steeper within-session stimulus-response functions than did males. These observed differences in nociceptive discrimination between males and females indicate that the sex-related variation in pain perception is probably related to sensory factors rather than differences in attitude or emotional response.

Reactions of dysmenorrheic and nondysmenorrheic women to experimentally induced pain throughout the menstrual cycle

It has been proposed that dysmenorrheic women have a heightened pain sensitivity compared to nondysmenorrheic women, although previous studies investigating this hypothesis have yielded conflicting results. This study investigated the pain sensitivity of nondysmenorrheic women and of women suffering from spasmodic, congestive, and combined dysmenorrhea, across three phases of the menstrual cycle: premenstrual, menstrual, and intermenstrual. No interaction between type of dysmenorrhea and menstrual phase was found for either pain threshold or pain tolerance, using three procedures of experimentally induced pain. On a self-report measure of pain, however, the congestive and combined dysmenorrheics reported the highest degree of pain and distress, especially during the premenstrual and menstrual phases; nonsufferers reported the lowest degree and were stable across phases.

Sensitivity to cold pressor pain in dysmenorrheic and non-dysmenorrheic women as a function of menstrual cycle phase

Pain responses (threshold, tolerance, and visual analog ratings) to the cold pressor task were studied in 46 normally menstruating dysmenorrheic and non-dysmenorrheic women during 2 phases of the menstrual cycle. Twenty-six women provided measurements during the follicular (days 8-14) and 20 during the luteal (days 15-21) phases of the menstrual cycle. A significantly lower pain threshold was obtained during the luteal as compared to the follicular phase. Pain tolerance showed a similar but non-significant trend. Visual analog ratings were significantly lower in dysmenorrheic women during the follicular than the luteal phase. Also, these ratings were lower than those of non-dysmenorrheic women in the follicular phase. This finding may support an adaptation-levels model, in that dysmenorrheic women report less pain than do non-dysmenorrheic women because they compare cold pressor pain with internal menstrual pain.

Pain reactions in pregnant women

Reactions to radiant heat stimuli were measured in pregnant women and in a control group of non-pregnant women matched in age. Receiver operating characteristic curve parameters were computed for each of the stages of pregnancy from the 6th month until the postpartum period. When painful stimuli were used, a group by stage of pregnancy interaction was found in the analysis on the response criterion for reporting pain. Pregnant women were found to be significantly more willing to label radiant heat stimuli as painful during the last 2 weeks of pregnancy than during any of the other stages of pregnancy. The control women tested during the same time sequence as the pregnant women showed stable response criteria across the 6 month testing period. There were no group or stage of pregnancy effects evident when the discrimination accuracy measures were analyzed; nor were any effects found with responses to thermal stimuli. The results suggest that the changes in pain reaction associated with pregnancy are based on non-sensory factors that influence the subject's willingness to report pain.