Blood pressure but not parental history for hypertension predicts pain perception in women

Chronic Pain-Associated Cardiovascular Disease: The Role of Sympathetic Nerve Activity

Chronic pain affects many people world-wide, and this number is continuously increasing. There is a clear link between chronic pain and the development of cardiovascular disease through activation of the sympathetic nervous system. The purpose of this review is to provide evidence from the literature that highlights the direct relationship between sympathetic nervous system dysfunction and chronic pain. We hypothesize that maladaptive changes within a common neural network regulating the sympathetic nervous system and pain perception contribute to sympathetic overactivation and cardiovascular disease in the setting of chronic pain. We review clinical evidence and highlight the basic neurocircuitry linking the sympathetic and nociceptive networks and the overlap between the neural networks controlling the two.

Exploring the Association of Hypertension With Risk for Depression: Evidence for Tamed Neurobehavioral Arousal Versus Central Emotional Dysregulation

Depression is an established predictor of adverse cardiovascular disease outcomes. Less is known about cardiovascular risk factors as predictors of depression. In this issue of Psychosomatic Medicine (2018;80:508-514), Patel et al. report data indicating that pre-existing hypertension may be inversely associated with the atypical but not typical form of depression. We highlight here the strengths and limitations of the article and discuss the findings in light of research linking blood pressure and emotion regulation. In general, evidence suggests that higher blood pressure is associated with reduced expression of negative emotions and pain. Two prominent models of interaction have been proposed and supported by epidemiological and experimental research: one assumes that elevations in blood pressure lead to reduced arousal and pain sensitivity through baroreceptor activation and possibly additional afferent mechanisms. Operant conditioning may then result in (chronic) hypertension. The other one posits that impaired emotion processing as indicated by dampened emotion recognition may lead to disinhibition of hypothalamic centers and thereby result in sustained increases in blood pressure. These models are described in context of the current literature and open research questions are formulated.

Racial/ethnic differences in experimental pain sensitivity and associated factors - Cardiovascular responsiveness and psychological status

This study evaluated the contributions of psychological status and cardiovascular responsiveness to racial/ethnic differences in experimental pain sensitivity. The baseline measures of 3,159 healthy individuals-non-Hispanic white (NHW): 1,637, African-American (AA): 1,012, Asian: 299, and Hispanic: 211-from the OPPERA prospective cohort study were used. Cardiovascular responsiveness measures and psychological status were included in structural equation modeling based mediation analyses. Pain catastrophizing was a significant mediator for the associations between race/ethnicity and heat pain tolerance, heat pain ratings, heat pain aftersensations, mechanical cutaneous pain ratings and aftersensations, and mechanical cutaneous pain temporal summation for both Asians and AAs compared to NHWs. HR/MAP index showed a significant inconsistent (mitigating) mediating effect on the association between race/ethnicity (AAs vs. NHWs) and heat pain tolerance. Similarly, coping inconsistently mediated the association between race/ethnicity and mechanical cutaneous pain temporal summation in both AAs and Asians, compared to NHWs. The factor encompassing depression, anxiety, and stress was a significant mediator for the associations between race/ethnicity (Asians vs. NHWs) and heat pain aftersensations. Thus, while pain catastrophizing mediated racial/ethnic differences in many of the QST measures, the psychological and cardiovascular mediators were distinctly restrictive, signifying multiple independent mechanisms in racial/ethnic differences in pain.

Acute analgesic effects of nicotine and tobacco in humans: a meta-analysis

Although animal models have consistently demonstrated acute pain inhibitory effects of nicotine and tobacco, human experimental studies have yielded mixed results. The main goal of this meta-analysis was to quantify the effects of nicotine/tobacco administration on human experimental pain threshold and tolerance ratings. A search of PubMed and PsycINFO online databases identified 13 eligible articles, including k = 21 tests of pain tolerance (N = 393) and k = 15 tests of pain threshold (N = 339). Meta-analytic integration for both threshold and tolerance outcomes revealed that nicotine administered through tobacco smoke and other delivery systems (eg, patch, nasal spray) produced acute analgesic effects that may be characterized as small to medium in magnitude (Hedges g = 0.35, 95% confidence interval = 0.21-0.50). Publication bias-corrected estimates remained significant and indicated that these effects may be closer to small. Sex composition was observed to be a significant moderator, such that pain threshold effects were more robust among samples that included more men than women. These results help to clarify a mixed literature and may ultimately help to inform the treatment of both pain and nicotine dependence. Pain and tobacco smoking are both highly prevalent and comorbid conditions. Current smoking has been associated with more severe chronic pain and physical impairment. Acute nicotine-induced analgesia could make smoking more rewarding and harder to give up. Future research should use dynamic measures of experimental pain reactivity and further explore biopsychosocial mechanisms of action.

Nicotine withdrawal and stress-induced changes in pain sensitivity: a cross-sectional investigation between abstinent smokers and nonsmokers

Chronic smoking has been linked with alterations in endogenous pain regulation. These alterations may be pronounced when individuals quit smoking because nicotine withdrawal produces a variety of psychological and physiological symptoms. Smokers interested in quitting (n = 98) and nonsmokers (n = 37) completed a laboratory session including cold pressor test (CPT) and heat thermal pain. Smokers set a quit date and completed the session after 48 h of abstinence. Participants completed the pain assessments once after rest and once after stress. Cardiovascular and nicotine withdrawal measures were collected. Smokers showed blunted cardiovascular responses to stress relative to nonsmokers. Only nonsmokers had greater pain tolerance to CPT after stress than after rest. Lower systolic blood pressure was related to lower pain tolerance. These findings suggest that smoking withdrawal is associated with blunted stress response and increased pain sensitivity.

Gender differences in blood pressure-related hypoalgesia in a general population: the Tromsø Study

An inverse association between resting blood pressure (BP) and acute pain sensitivity is well documented. Whether BP-related hypoalgesia differs by gender is unclear from prior work. Whether it increases proportionally with BP throughout the full BP range is also unknown. We examined BP-related hypoalgesia in a general population sample (n = 10,371, aged 30-87) of equal gender distribution reflecting the extremely low through hypertensive BP range. Resting BP was assessed and individuals participated in a standardized cold pressor test, providing pain ratings every 9 seconds. For systolic BP (SBP), a significant SBP × Gender interaction was observed on mean pain ratings (P < .001). Females displayed significant BP-related hypoalgesia (P < .001), with males showing a 38% smaller effect (P < .001). A similar DBP × Gender interaction was also observed (P < .05). Spline regression indicated a significant (P < .001) change in slope of the SBP-pain association at 140 mmHg. Among individuals with lower resting SBP (<140/90), increasing hypoalgesia with increasing SBP levels was observed (P < .001), with no further increases in those with higher BP (≥140/90; P > .10). This is the first large-scale study to confirm past results suggesting that BP-related hypoalgesia differs by gender; that is, females exhibited greater hypoalgesia. BP-related hypoalgesia appears subject to ceiling effects in the hypertensive BP range.

PERSPECTIVE

Females show greater BP-related hypoalgesia than males, highlighting gender differences in endogenous antinociceptive systems. Extent of BP-related hypoalgesia does not increase further once resting pressures reach the hypertensive range, suggesting persistent maximal demands on these antinociceptive systems among hypertensive individuals.

Beep tones attenuate pain following Pavlovian conditioning of an endogenous pain control mechanism

Heterotopic noxious counter-stimulation (HNCS) is commonly used to study endogenous pain control systems. The resulting pain inhibition is primarily based on spinal cord-brainstem loops. Recently, functional imaging studies have shown that limbic structures like the anterior cingulate cortex and amygdala are also implicated. Since these structures are involved in learning processes, it is possible that the HNCS-induced pain inhibition may depend on specific cues from the environment that have been associated with pain reduction through associative learning. We investigated the influence of Pavlovian conditioning on HNCS-induced pain inhibition in 32 healthy subjects by using a differential conditioning paradigm in which two different acoustic stimuli were either repeatedly paired or unpaired with HNCS. Series of noxious electrical pulse trains delivered to the non-dominant foot served as test stimuli. Diffuse noxious inhibitory control (DNIC)-like effects were induced by concurrent application of tonic HNCS (immersion of the contralateral hand in ice water). Subjective pain intensity and pain unpleasantness ratings and electromyographic recordings of the facial corrugator muscle and the nocifensive RIII flexion reflex were used to measure changes in pain sensitivity. HNCS induced significant pain and reflex inhibitions. In the post-conditioning phase, only the paired auditory cue was able to significantly reduce pain perceptions and corrugator muscle activity. No conditioned effect could be observed in RIII reflex responses. Our results indicate that the functional state of endogenous pain control systems may depend on associative learning processes that, like in the present study, may lead to an attenuation of pain perception. Similar albeit opposite conditioning of pain control mechanisms may significantly be involved in the exacerbation and chronification of pain states.

Stress response dysregulation and stress-induced analgesia in nicotine dependent men and women

Alterations in the stress response and endogenous pain regulation mechanisms may contribute directly and indirectly to maintenance of nicotine dependence and relapse. We examined the extent to which nicotine dependence alters endogenous pain regulatory systems, including the hypothalamic-pituitary-adrenocortical axis, cardiovascular activity, and stress-induced analgesia. Smokers and nonsmokers attended a laboratory session that included assessment of hormonal and cardiovascular responses to stress. Smokers smoked at their regular rate prior to the session. The hand cold pressor and heat thermal pain tests were completed twice, once after acute stress (public speaking and math tasks) and the other after rest. While smokers and nonsmokers exhibited significant hormonal and cardiovascular responses to stress, smokers exhibited blunted stress responses relative to nonsmokers. They also exhibited diminished stress-induced analgesia. Results demonstrate altered stress response and diminished stress-induced analgesia among chronic smokers, and suggest that these dysregulated physiological responding may contribute to altered endogenous pain regulation.

Hypertension prevalence and diminished blood pressure-related hypoalgesia in individuals reporting chronic pain in a general population: the Tromsø study

Resting blood pressure (BP) is inversely related to pain sensitivity in individuals free of chronic pain, reflecting homeostatic interactions between cardiovascular and pain modulatory systems. Several laboratory studies indicate that BP-related hypoalgesia is diminished in chronic pain patients, suggesting dysfunction in these interacting systems. Separate epidemiological findings reveal elevated hypertension prevalence in the chronic pain population. This study for the first time simultaneously evaluated both hypertension prevalence and BP-related hypoalgesia as they relate to chronic pain in the same sample. Resting BP and pain sensitivity were evaluated in a large general population sample (n=10,135, aged 30-87years). Subjects participated in a standardized 106s cold pressor test, providing pain ratings at 9s intervals. Self-reported presence of chronic pain and history of hypertension and use of antihypertensive medication were assessed. Significant interactions between chronic pain status and resting systolic (P<.001) and diastolic BP (P<.001) on mean pain ratings were observed. These interactions were due to significant (P<.001) BP-related hypoalgesia in individuals free of chronic pain that was twice the magnitude of the hypoalgesia observed in the group reporting chronic pain. Presence of chronic pain was associated with significantly increased odds of comorbid hypertension (P<.001). Within the chronic pain group, higher chronic pain intensity was a significant predictor of positive hypertension status beyond the effects of traditional demographic risk factors (P<.05). Results are consistent with the hypothesis that increased hypertension risk in the chronic pain population might be linked in part to chronic pain-related dysfunction in interacting cardiovascular-pain modulatory systems.

Pain, nicotine, and smoking: research findings and mechanistic considerations

Tobacco addiction and chronic pain represent 2 highly prevalent and comorbid conditions that engender substantial burdens upon individuals and systems. Interrelations between pain and smoking have been of clinical and empirical interest for decades, and research in this area has increased dramatically over the past 5 years. We conceptualize the interaction of pain and smoking as a prototypical example of the biopsychosocial model. Accordingly, we extrapolated from behavioral, cognitive, affective, biomedical, and social perspectives to propose causal mechanisms that may contribute to the observed comorbidity between these 2 conditions. The extant literature was 1st dichotomized into investigations of either effects of smoking on pain or effects of pain on smoking. We then integrated these findings to present a reciprocal model of pain and smoking that is hypothesized to interact in the manner of a positive feedback loop, resulting in greater pain and increased smoking. Finally, we proposed directions for future research and discussed clinical implications for smokers with comorbid pain disorders. We observed modest evidence that smoking may be a risk factor in the multifactorial etiology of some chronically painful conditions and that pain may come to serve as a potent motivator of smoking. We also found that whereas animal studies yielded consistent support for direct pain-inhibitory effects of nicotine and tobacco, results from human studies were much less consistent. Future research in the emerging area of pain and smoking has the potential to inform theoretical and clinical applications with respect to tobacco smoking, chronic pain, and their comorbid presentation. (PsycINFO Database Record (c) 2011 APA, all rights reserved).

Relationship between resting blood pressure and laboratory-induced pain among healthy children

BACKGROUND

Adult studies have demonstrated that increased resting blood pressure (BP) levels correlate with decreased pain sensitivity. However, few studies have examined the relationship between BP and experimental pain sensitivity among children.

OBJECTIVES

This study investigated the association between resting BP levels and experimental pain tolerance, intensity, and unpleasantness in healthy children. We also explored whether these BP-pain relationships were age and gender dependent.

METHODS

Participants underwent separate 4-trial blocks of cutaneous pressure and thermal pain stimuli, and 1 trial of a cold pain stimulus in counterbalanced order.

RESULTS

A total of 235 healthy children (49.6% female; mean age 12.7 [2.9] years; age range 8-18 years) participated. The study revealed specific gender-based BP-pain relationships. Girls with higher resting systolic BP levels were found to have lower thermal intensity ratings than girls with lower resting systolic BP levels; this relationship was stronger among adolescent girls than among younger girls. Among young girls (8-11 years), those with higher resting diastolic BP (DBP) levels were found to have lower cold intensity and unpleasantness as well as lower thermal intensity ratings than did young girls with lower resting DBP levels; these DBP-pain response relationships were not seen among adolescent girls.

CONCLUSIONS

Age, rather than resting BP, was predictive of laboratory pain ratings in boys. The findings suggest that the relationship between BP and experimental pain is age and gender dependent. These aspects of cardiovascular relationships to pain in males and females need further attention to understand their clinical importance.

Anger suppression predicts pain, emotional, and cardiovascular responses to the cold pressor

BACKGROUND

Manipulated anger suppression has been shown to heighten pain and anger responses to pain.

PURPOSE

We examined whether individual differences in self-reported anger suppression predicted pain, anger, and blood pressure responses to acute pain.

METHODS

Healthy participants (N = 47) underwent an anger-provoking speech task followed by a cold pressor pain task. Participants reported their degree of suppression of thoughts and feelings related to the speech. Pain intensity ratings were obtained throughout the cold pressor. Self-reported anger, anxiety and positive emotion, as well as ratings of sensory, general distress, and anger-specific elements of pain were obtained following the cold pressor. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were recorded throughout.

RESULTS

Self-reported suppression predicted greater pain intensity ratings, perception of sensory and anger-specific elements of pain, and self-reported anger in response to the cold pressor. Associations between self-reported suppression and pain intensity and ratings of anger-specific elements of pain were statistically mediated by pain-induced changes in self-reported anger, whereas the effect of suppression on sensory pain ratings was not. Self-reported suppression was also correlated inversely with SBP responses to the cold pressor.

CONCLUSIONS

Consistent with an ironic process model and prior studies involving experimental manipulation of suppression, self-reported suppression of anger predicted greater pain intensity and perception of the anger-specific element of pain. Findings also suggest that suppression might attenuate homeostatic pressor responses to acute pain.

Ethnic differences in cardiovascular-somatosensory interactions and in the central processing of noxious stimuli

Ethnic differences in central sensitization of pain processing and stress-relevant endogenous pain regulatory mechanisms were examined. Forty-four African Americans (AAs; 50% women) and 44 non-Hispanic Whites (nHWs; 50% women) matched for socioeconomic status, were tested for pain responses to the temporal summation of heat pulses and ischemic and cold pain. Resting and stress blood pressure (BP) and norepinephrine (NE) were assessed. AAs had heightened pain responses to all 3 pain tasks relative to nHWs. In nHWs, higher BP and NE were related to reduced pain. In AAs, there was no relationship between BP and pain, but higher NE was related to increased pain. This study provides evidence for ethnic differences in centrally mediated pain and extends prior research demonstrating ethnic differences in endogenous pain regulatory mechanisms. These results have implications for understanding biobehavioral factors contributing to ethnic disparities in clinical pain.

Hypoalgesia related to elevated resting blood pressure is absent in adolescents and young adults with a history of functional abdominal pain

Elevated resting blood pressure (BP) is hypoalgesic in healthy individuals, but this effect is absent in adults with chronic somatic pain. This study tested whether BP-related hypoalgesia is similarly altered in individuals with a history of chronic visceral pain in childhood. Resting BP was assessed in 94 adolescents and young adults with a known history of childhood functional abdominal pain (FAP) and 55 comparable healthy controls. Responses to an acute heat pain stimulus were then evaluated following exposure to two laboratory stressors. A significant participant type x systolic BP (SBP) interaction (p<.005) revealed that elevated resting SBP was associated with significantly higher heat pain threshold (p<.001) in healthy controls, but was unrelated to pain threshold in the FAP group. A similar pattern was observed for heat pain tolerance, with elevated SBP linked to significantly higher pain tolerance (p<.05) in healthy controls, but unrelated to tolerance in the FAP group. Dysfunction in BP-related hypoalgesia associated with FAP was evident regardless of whether childhood FAP had resolved or still persisted at the time of laboratory testing. Subgroup analyses indicated that BP-related hypoalgesia (in healthy controls) and FAP-linked absence of this hypoalgesia was observed only among females. Result suggest that childhood visceral chronic pain may be associated with relatively long-lasting dysfunction in overlapping systems modulating pain and BP that persists even after FAP resolves. Potential implications for later hypertension risk are discussed.

Hypoalgesia associated with elevated resting blood pressure: evidence for endogenous opioid involvement

This study used a placebo-controlled, between-subjects opioid blockade design to evaluate endogenous opioid involvement in the hypoalgesia associated with elevated resting blood pressure (BP) in 163 healthy individuals. Participants were randomly assigned to Drug condition (placebo, naltrexone) and Task Order (computerized maze task with harassment followed by an ischemic pain task or vice versa). Resting BP was assessed, followed by drug administration, and then the pain and maze tasks. A significant Drug x Systolic BP (SBP) interaction was observed on McGill Pain Questionnaire-Affective pain ratings (P < .01), indicating that BP-related hypoalgesia observed under placebo was absent under opioid blockade. A significant Gender x Drug x SBP x Task Order interaction was observed for VAS pain intensity (P < .02). Examination of simple effects comprising this interaction suggested that BP-related hypoalgesia occurred only in male participants who experienced the pain task in the absence of emotional arousal, and indicated that this hypoalgesia occurred under placebo but not under opioid-blockade. Results suggest that under some circumstance, BP-related hypoalgesia may have an endogenous opioid-mediated component in healthy individuals, particularly men.

Anemia-related hemogram, uterine artery pulsatility index, and blood pressure for the effects of Four-Agents-Decoction (Si Wu Tang) in the treatment of primary dysmenorrhea

OBJECTIVES

We previously reported pain intensity as the primary outcome of Four-Agents-Decoction (Si Wu Tang) for treating primary dysmenorrhea. We further explored other effects of this formula in accordance with the theory of Traditional Chinese Medicine on anemia-related hemogram parameters for "nourishing blood" and uterine artery pulsatility index (PI) for "blood stagnation."

DESIGN

Data were assessed for post-hoc analysis from 76 young women from the Taipei metropolitan area of Taiwan who participated in the randomized double-blind clinical trial. Analysis of variance and t test were used to examine the treatment effect between and within the Four-Agents-Decoction and placebo groups.

OUTCOME MEASURES

In addition to pain intensity, anemia-related hemogram parameters, uterine artery PI, menstruation characteristics, and blood pressure were compared.

RESULTS

Compared to placebo, biochemical indicators for anemic status did not change differently after the treatment with Four-Agents-Decoction (Si Wu Tang). The changes in uterine artery PI, menstrual pain intensity, and blood pressure were statistically greater in the active treatment group than in the placebo group. In the 25 women receiving ultrasound examination on the same menstruation day, the directions of the changes in both PI and in visual analog scale (VAS) pain intensity aligned well. The changes in the left PI, right PI, and VAS pain intensity in the Four-Agents-Decoction group were -0.391 +/- 0.861, -0.344 +/- 1.03, and -0.251 +/- 2.02 cm; those in the placebo group were 0.208 +/- 1.10, 0.372 +/- 1.06, and 0.438 +/- 2.98 cm, respectively. Inversely, the changes in blood pressure were 11.4 +/- 10.5 mm Hg for systolic blood pressure and 8.36 +/- 8.65 mm Hg for diastolic pressure for the Four-Agents-Decoction group and 6.36 +/- 8.66 and 2.91 +/- 11.2 mm Hg, respectively, for the placebo group. The directions of the changes did not shift, nor did the values change drastically, after adjusting for the level at screening cycle.

CONCLUSIONS

The anemia status evaluated in conventional medicine does not readily explain the effect of "nourishing blood" by Four-Agents-Decoction (Si Wu Tang) from this exploratory study. Although we did not find strong statistical significance of treatment effect, the decreased PI and extra blood pressure elevation may indicate an improvement of "blood stagnation" in the Four-Agents-Decoction group. The added information warrants a further larger clinical trial with an increased power to enhance our understanding of the efficacy, the dose-response relationship, and the mode of action of this ancient formula for treating primary dysmenorrhea.

Naltrexone effect on physiological and subjective response to a cold pressor task

In this double-blind, cross-over study physiological (i.e. blood pressure, heart rate, plasma catecholamine concentrations, plasma cortisol concentrations) and subjective (i.e. McGill Pain Questionnaire, positive affect, distress) response to a cold pressor task was assessed in 19 subjects 1 h after the administration of 50 mg naltrexone and after placebo. Significant differences in plasma catecholamine concentrations were found. Plasma epinephrine concentrations increased during the 1 h period after naltrexone administration but remained largely unchanged after placebo administration. A significant treatment x period effect was also found for plasma norepinephrine concentrations. No significant differences were found for other measures assessed. Further research is necessary to determine the subpopulations in which these effects are of greatest magnitude and the long term safety implications of these effects.

Nociceptive flexion reflex thresholds and pain during rest and computer game play in patients with hypertension and individuals at risk for hypertension

Supraspinal pain modulation may explain hypertensive hypoalgesia. We compared nociceptive flexion reflex (NFR) thresholds and pain during rest and computer game play in hypertensives and normotensives (Experiment 1) and normotensives with and without hypertensive parents (Experiment 2). The game was selected to modulate activity in pain pathways. NFR thresholds did not differ between groups during rest or game play. Pain ratings never differed between hypertensives and normotensives, whereas individuals with hypertensive parents reported less pain during the first two NFR assessments, compared to those without. NFR thresholds and pain were reduced by game play compared to rest. The failure of game play to differentially modulate NFR thresholds or associated pain reports between groups argues against enhanced supraspinal modulation of nociception and pain in hypertensives and those at increased risk for hypertension.

Adverse events of blood-pressure-lowering drugs: evidence of high incidence in a clinical setting

OBJECTIVES

Our primary objective was to determine the incidence of AEs of antihypertensive drugs in a cohort of outpatients attending a specialized clinic. The secondary objectives were to determine the incidence of AEs by classes of blood-pressure-lowering drugs used in monotherapy and to identify risk factors for the occurrence of AEs.

METHODS

In a prospectively planned cohort study, patients attending a hypertension outpatient clinic were systematically interrogated about the occurrence of AEs of blood-pressure-lowering drugs. We compared the incidence of AEs by classes of drugs employed in monotherapy and identified risk factors for the occurrence of AEs in a logistic regression model.

RESULTS

Participants were followed for 12.3 +/- 12.2 months. In total, 534 (35.4%) of 1,366 patients treated with blood pressure drugs complained of at least one AE during the follow-up, corresponding to an incidence of 31.3 AEs per 1,000 patients/month [95% confidence interval (CI) 28.6-33.9). The systolic blood pressure in the initial evaluation (P = 0.002) and use of two or more drugs (P < 0.001) were associated with higher incidence of AEs. The incidence of AEs was higher among patients treated with calcium channel blockers in monotherapy than in patients treated with diuretics (47.2 vs. 7.6%, P < 0.001).

CONCLUSION

Adverse events of blood-pressure-lowering drugs are quite frequent in a clinical context, and may influence the adherence to treatment. Patients under treatment with diuretics in monotherapy have the lower incidence of AEs.

Nociception and baroreceptor stimulation in hypertension-prone men and women

We examined the effects of baroreceptor stimulation on nociceptive responding in men and women with a positive or negative parental history of hypertension. The effects of three baroreceptor conditions (stimulation, inhibition, and control) on subjective pain and nociceptive responding were evaluated during electrocutaneous sural nerve stimulation. Pain ratings were lower in men with positive parental history relative to men with negative parental history, but this difference was not found in women. Both stimulatory and inhibitory baroreceptor conditions were associated with reduced pain reports compared to the control condition. There were no significant differences in nociceptive responding as a function of parental history of hypertension. Although this study confirms a link between hypoalgesia and risk for hypertension in men, it does not support the hypothesis that this attenuated pain perception is due to enhanced baroreceptor activity.

Prevalence of Clinical Hypertension in Patients With Chronic Pain Compared to Nonpain General Medical Patients

OBJECTIVES

In healthy individuals, elevated blood pressure is associated with diminished acute pain sensitivity. These cardiovascular/pain regulatory system interactions appear altered in patients with chronic pain; elevated blood pressure is associated with increased acute and chronic pain responsiveness. If these alterations reflect failure of overlapping systems modulating pain and blood pressure, it was expected that prevalence of clinical hypertension would be increased in the chronic pain population.

METHODS

A retrospective review was conducted on randomly selected records of 300 patients with chronic pain (Pain) evaluated at a tertiary care pain center and 300 nonpain internal medicine (Medicine) patients seen at the same institution.

RESULTS

Results revealed that 39% of the Pain group was diagnosed with clinical hypertension, compared with 21% of the Medicine group (P < 0.001). Analyses by sex revealed similar group differences in males (P < 0.05) and females (P < 0.001), although the difference in females was double in magnitude compared with males. In contrast to more frequent male hypertension in the general population and the Medicine sample, females were more often diagnosed with hypertension (41.2%) than males (35.6%) in the Pain group. Similar group differences were obtained for antihypertensive use (P < 0.001). Stepwise logistic regression in the Pain group revealed that chronic pain intensity was a significant predictor of hypertensive status independent of the effects of age, race/ethnicity, and parental hypertension (P < 0.05).

DISCUSSION

These results suggest that chronic pain may be associated with increased risk of hypertension. Factors that may underlie this association are discussed.

Increased sensitivity to acute and persistent pain in neuron-specific endothelin-1 knockout mice

Endothelin-1 (ET-1) exists in endothelial cells as well as a variety of other cell types. The presence of ET-1 and its receptors in neurons suggests its possible role as a neurotransmitter and/or neuromodulator. Studies utilizing exogenous ET-1 have suggested that ET-1 affects pain transmission. This study was designed to examine the possible role(s) of neuronal ET-1 in pain processing. We produced neuron-specific ET-1 knockout mice using the Cre/loxP system with a synapsin I promoter and examined the effects produced by the lack of neuronal ET-1 on pain behavior using common pain models and a model of stress-induced analgesia. In acute nociceptive pain models, paw withdrawal thresholds to radiant heat and mechanical stimuli applied with von Frey hairs were significantly lower in the knockout mice compared with control. This indicated that the absence of neuronal ET-1 leads to greater sensitivity to acute nociceptive stimuli. After inflammation was produced by intraplantar injection of carrageenan, there was a significantly greater degree of thermal hyperalgesia and mechanical allodynia in the knockout mice even after the difference in baseline values was compensated. Furthermore, in a neuropathic pain model produced by spinal nerve ligation, there was also a greater degree of mechanical allodynia in the knockout mice. Finally, in a swim-stress model, the magnitude of stress-induced analgesia was less in the knockout mice, indicating the involvement of neuronal ET-1 in stress-induced analgesia. The results suggest that there is a basal release of ET-1 from neurons that affect baseline pain thresholds as well as an additional release during persistent pain states that acts to suppress the pain. The involvement of neuronal ET-1 in stress-induced analgesia further suggests its role in endogenous pain inhibitory systems. To confirm that ET-1 is released in persistent pain states and to determine which part of the CNS is involved, we measured the concentrations of ET-1 before and after inducing peripheral inflammation in different parts of the CNS involved in endogenous pain inhibitory systems in normal mice. We found that ET-1 was increased in the hypothalamus while no significant increase was observed in the midbrain, medulla and spinal cord. The results of the present study suggest that neuronal ET-1 is involved in endogenous pain inhibitory control likely via pathways through the hypothalamus.

Cardiovascular reactivity and family history of hypertension: A meta-analysis

A regression-based meta-analysis examined the degree to which the effects of a family history of hypertension on cardiovascular reactivity are moderated by the magnitude of cardiovascular responses elicited in challenge/task conditions. Mean change scores for negative family history groups were regressed on mean change scores for positive family history groups. The slopes of separate regression lines obtained for systolic and diastolic blood pressure and heart rate were significantly less than 1.0 and the y-intercepts for these regression lines were significantly greater than zero. This pattern indicates that family history differences in cardiovascular reactivity to stress are greatest in situations that elicit the smallest baseline-stressor change scores in non-family-history groups.

An evaluation of sex differences in psychological and physiological responses to experimentally-induced pain: a path analytic description

A cold pressor task (CPT) was used with 203 college students (112 women and 91 men) in a study of sex differences in pain response. Physiological measures were taken before and after pain induction, and sex-differentiating personality traits were assessed with the Personal Attributes Questionnaire (PAQ). The Pain Catastrophizing Scale (PCS) was given with standard instructions prior to the CPT, and it was re-administered after the CPT with modified instructions to assess catastrophic thinking during the CPT. Hypotheses were formulated into an explanatory model that was evaluated by path analysis. Pain induction elevated blood pressures and cortisol levels for both sexes, but systolic blood pressure reactivity and cortisol response were greater in men, even with sex differences in CPT tolerance times controlled statistically. Post-CPT PCS scores were positively related to pain ratings and negatively related to tolerance, but baseline PCS scores did not predict tolerance or pain ratings. Pre-PCS scores were not well correlated with post-PCS scores (r=0.46) and underestimated post-PCS scores, particularly for women. The Sex difference on the post-CPT PCS was largely attributable to the PAQ personality trait of Emotional Vulnerability. The differential results obtained from assessing catastrophizing before and after the CPT emphasized the importance of specifying the context in which catastrophizing is assessed (both timing and instructions). Theoretical considerations in the construct of catastrophizing are also highlighted, including, but not limited to, the confounding of variables such as pain intensity and unpleasantness.

Interactions between the cardiovascular and pain regulatory systems: an updated review of mechanisms and possible alterations in chronic pain

Endogenous pain regulatory system dysfunction appears to play a role in the maintenance of chronic pain. An important component of the pain regulatory process is the functional interaction between the cardiovascular and pain regulatory systems, which results in an association between elevated resting blood pressure (BP) and diminished acute pain sensitivity. This BP/pain sensitivity relationship is proposed to reflect a homeostatic feedback loop helping restore arousal levels in the presence of painful stimuli. Evidence is emerging that this normally adaptive BP/pain sensitivity relationship is significantly altered in chronic pain conditions, affecting responsiveness to both acute and chronic pain stimuli. Several mechanisms that may underlie this adaptive relationship in healthy individuals are overviewed, including endogenous opioid, noradrenergic, and baroreceptor-related mechanisms. Theoretical models are presented regarding how chronic pain-related alterations in the mechanisms above and increased pain facilatory system activity (central sensitization) may contribute to altered BP/pain sensitivity interactions in chronic pain. Clinical implications are discussed.

Personality factors in the explanation of sex differences in pain catastrophizing and response to experimental pain

OBJECTIVE

To examine the effects of personality and pain catastrophizing upon pain tolerance and pain ratings and to examine the impact of an experimental pain induction on subsequent ratings of catastrophizing.

METHOD

Two hundred nineteen college students participated in a cold pressor task. Sex-differentiating personality constructs were measured by the Extended Personal Attributes Questionnaire. The Pain Catastrophizing Scale was given before and after the cold pressor task.

RESULTS

A path-analytic model fit the data well and permitted tests of explanatory relationships. Mediational analyses demonstrated that sex differences in catastrophizing were explained by the Personal Attributes Questionnaire Masculinity-Femininity and Verbal Passive-Aggressiveness scales. Pain tolerance and pain ratings differed significantly between men and women, but Masculinity-Femininity partially mediated those sex-pain relationships. Additionally, higher pain ratings and lower pain tolerance were independently associated with increased catastrophizing after the cold pressor task.

CONCLUSIONS

The results suggest that sex differences in catastrophizing and pain responsivity are partially accounted for by the dispositional tendency to describe oneself as emotionally vulnerable. The findings also suggest that pain catastrophizing may be situational as well as dispositional.

Primary and secondary vulvar vestibulitis syndrome: systemic pain perception and psychophysical characteristics

OBJECTIVE

Women with primary and secondary vulvar vestibulitis syndrome (VVS) report similar vulvar pain symptoms; however, it is not clear whether these subsets have similar pain and psychophysical characteristics. This study evaluated systemic pain perception, cardiovascular measures, and anxiety level in women with primary and secondary VVS.

STUDY DESIGN

Eighty-nine women were enrolled in the study: 44 had primary vulvar vestibulitis, 45 had secondary vulvar vestibulitis. Their anxiety level was first assessed. Then, heat pain stimuli were applied to the forearm, and pain threshold and pain scores for suprathreshold phasic (44 degrees C-48 degrees C) and tonic (46 degrees C) stimuli were assessed by visual analog scale. Finally, blood pressure was recorded using a volume clamp method before, during, and after a tonic stimulus of 1 minute at 46 degrees C.

RESULTS

Women with primary vulvar vestibulitis had higher visual analog scale scores for pain perception at 46 degrees C to 48 degrees C, a higher level of trait anxiety 43.3 +/- 1.5 versus 37.8 +/- 1.5 (P=.010), an increased incidence of dysmenorrhea (chi(2) 8.9, P=.003), and lower resting blood pressure: systolic (108.6 +/- 2.1 vs 118.9 +/- 2.0 mm Hg) (P>.001) and diastolic (59.3 +/- 1.6 vs 64.2 +/- 1.5 mm Hg) (P=.038). Logistic regression revealed that dysmenorrhea and lower systolic blood pressure are associated with primary VVS.

CONCLUSION

Women with primary and secondary VVS differ in their systemic pain perception and psychophysical characteristics. The impact of these findings on treatment modalities should be further evaluated.

Association between quantitative sensory testing, treatment choice, and subsequent pain reduction in vulvar vestibulitis syndrome

The chronic pain syndrome of vulvar vestibulitis is a major cause of sexual dysfunction, and complete cure is not always achieved. The aim of the study was to determine whether the psychophysical characteristics of systemic pain perception predict treatment choice and outcome. Ninety women with vulvar vestibulitis syndrome were evaluated by using quantitative sensory testing with heat pain threshold measurements and pain scores for suprathreshold stimuli applied to the forearm, blood pressure measurements, and an assessment of the number of other pain disorders. Women were free to choose a surgical procedure (ie, vestibulectomy), one of the possible nonsurgical treatments (eg, biofeedback, cognitive-behavioral therapy, or hypoallergic agents), or to avoid treatment entirely. Eight months later, women reported the success of the treatment on the basis of reduction in the level of vulvar pain. Vestibulectomy demonstrated the best therapeutic effectiveness (chi2, 26.4; P <.0001). Women who chose this type of treatment had lower pain scores (P =.038) and fewer pain syndromes other than the vulvar pain (P =.025). Logistic regression analysis, controlling for the effect of vestibulectomy, indicated that lower experimental pain scores (P =.044), fewer pain disorders (P =.023), and higher systolic blood pressure (P =.039) are predictive variables for reduction of vulvar pain. An assessment of systemic pain perception might be helpful in choosing the optimal treatment and in predicting its success.

PERSPECTIVE

The present study suggests that pain perception variables might be of value in the prediction of treatment choice and outcome among women with vulvar vestibulitis.

Muscle pain during exercise in normotensive african american women: effect of parental hypertension history

The purpose of the present investigation was to determine the influence of parental hypertension history on leg muscle pain ratings during cycling exercise in African American women. Eighteen women (age, 19 +/- 2 years) with a positive family history (+PH) of hypertension and 16 (age, 19 +/- 1 years) with a negative family history (-PH) underwent maximal exercise and cold pressor testing. Maximal exercise was conducted on a cycle ergometer. Quadriceps muscle pain intensity ratings were obtained each minute during the maximal exercise test by using a category-ratio scale. The hand cold pressor test was used to determine cardiovascular reactivity. Repeated measures analysis of variance showed significantly lower pain ratings during exercise for the +PH group compared to the -PH group. Psychophysical power functions indicated that the +PH participants had significantly lower exponents for pain throughout exercise. Systolic blood pressure reactivity did not significantly predict pain ratings during exercise. Normotensive African American women with +PH of hypertension experienced less muscle pain during exercise compared to normotensive African American women with a -PH of hypertension. The results are consistent with data demonstrating reduced sensitivity to experimental pain stimuli in individuals at risk for developing hypertension and extend them to naturally occurring muscle pain produced by exercise.

PERSPECTIVE

African American women, a sedentary group with an elevated risk for developing hypertension and chronic pain, show the same negative relationship between +PH and pain perception as men, suggesting that central nervous system mechanisms of pain modulation are more related to family history than gender. Acute exercise provides an experimental model for manipulating naturally occurring pain in studies concerned with the association between pain and hypertension.

Blood pressure but not cortisol mediates stress effects on subsequent pain perception in healthy men and women

Research has demonstrated that exposure to acute stress may attenuate pain perception. Mechanisms of this effect in humans have not been determined. This study was conducted to determine the extent to which psychophysiological and adrenocortical responses to acute stress predict subsequent pain perception. One hundred and fifty-two healthy participants (80 women) were assigned to one of two conditions: rest followed by the cold pressor test (CPT; N=76) or stress followed by CPT (N=76). The stress protocol consisted of a public-speaking challenge. Participants rated their pain every 15 s during a 90-s hand CPT (0-4 degrees C), and they completed the short form of the McGill Pain Questionnaire. Salivary cortisol, mood, blood pressure (BP), and impedance cardiography measures were collected in both conditions. Women had lower BP and reported greater pain than men in both conditions (ps<0.01). Participants in the stress condition reported less pain during CPT than those in the rest condition (p=0.02). Regression analyses demonstrated that the stress effect on pain ratings was mediated by systolic BP level during stress; however, cortisol responses did not affect this relationship. Mood changes were independent predictors of pain. The study demonstrates that BP changes in response to stress mediate the stress-induced attenuation of pain perception.

Adrenocortical and hemodynamic predictors of pain perception in men and women

Research has demonstrated that women report more pain than men, and clinical observations suggest that attenuated adrenocortical activity is associated with high pain sensitivity. The extent to which cortisol concentrations and hemodynamics contribute to gender differences in pain sensitivity has not been investigated. Thirty-four women and 31 men performed the hand cold pressor test (CPT). Participants rated their pain every 15 s during a 90-s CPT and a 90-s post-CPT recovery period and reported pain using the McGill Pain Questionnaire (MPQ). Salivary cortisol samples and cardiovascular measures were collected prior to, during, and after the CPT. Women reported greater pain than men during and after the CPT and on the MPQ (Ps<0.01). CPT disrupted the expected diurnal decline in cortisol, as shown by a significant increase in cortisol concentration post-CPT (P<0.01) in men and women. Regression analyses revealed that pre-CPT cortisol concentrations predicted lower pain reports during and after CPT in men only (P<0.01). Systolic blood pressure (BP) and stroke volume correlated negatively with pain reports only in women (Ps<0.05). Controlling for potential confounding variables did not alter these relationships. The negative association between pre-CPT cortisol and pain perception in men and the association between BP and pain in women demonstrate different physiological predictors of pain perception in men and women.

Changes in pain perception during treatment with angiotensin converting enzyme-inhibitors and angiotensin II type 1 receptor blockade

OBJECTIVES

Besides the well-known role of the angiotensin system in blood pressure control, an interaction of angiotensin and pain perception has been suggested. This study sought to investigate whether an angiotensin converting enzyme inhibitor, which facilitates bradykinins, algesic peptides, and/or an AT1 receptor antagonist may modify hypertension-related hypoalgesia in humans. The study was approved by the ethical committee of our Department.

METHODS

A total of 22 hypertensive patients were submitted to dental pulp stimulation to obtain the dental pain threshold and tolerance, and to 24 h blood pressure monitoring together with a control group of 55 normotensives. Then the hypertensives were randomized to enalapril or losartan treatment and were re-evaluated (dental pain perception and ambulatory monitoring) after 8 weeks of the first treatment and after an additional 8 weeks of the second treatment.

RESULTS

Untreated hypertensives showed a reduced perception to painful stimuli when compared with normotensives. A significant reduction of both pain threshold and tolerance was observed during the anti-hypertensive treatments (Friedman test: P = 0.007 and P = 0.006, respectively). Pain sensitivity was similar during the two treatments and it did not differ from pain sensitivity values of normotensive controls. ANCOVAs were computed to evaluate the relationship between anti-hypertensive agents and pain sensitivity, after controlling for blood pressure. A 24 h mean pressure served as covariate, removing any effect of blood pressure; a significant difference was observed entering both pain threshold and tolerance as dependent variables (F = 5.28, P = 0.0076; F = 8.16, P = 0.0007, respectively).

CONCLUSIONS

Both the angiotensin converting enzyme inhibitor enalapril and the AT1 receptor blocking agent losartan acted similarly on pain threshold and tolerance, pain sensitivity being increased during the two anti-hypertensive treatments. The blood pressure reduction during drug assumption could not account for the pain sensitivity changes observed. The latter may be due to a specific pharmacodynamic mechanism mediated through angiotensin II AT1 receptors.