Treatment with enalapril modifies the pain perception pattern in hypertensive patients

Impact of homeostatic body hydration status, evaluated by hemodynamic measures, on different pain sensitization paths to a chronic pain syndrome

Contrasting findings on the mechanisms of chronic pain and hypertension development render the current conventional evidence of a negative relationship between blood pressure (BP) and pain severity insufficient for developing personalized treatments. In this interdisciplinary study, patients with fibromyalgia (FM) exhibiting clinically normal or elevated BP, alongside healthy participants were assessed. Different pain sensitization responses were evaluated using a dynamic 'slowly repeated evoked pain' (SREP) measure, as well as static pain pressure threshold and tolerance measures. Cardiovascular responses to clino-orthostatic (lying-standing) challenges were also examined as acute re- and de-hydration events, challenging cardiovascular and cerebrovascular homeostasis. These challenges involve compensating effects from various cardiac preload or afterload mechanisms associated with different homeostatic body hydration statuses. Additionally, hair cortisol concentration was considered as a factor with an impact on chronic hydration statuses. Pain windup (SREP) and lower pain threshold in FM patients were found to be related to BP rise during clinostatic (lying) rehydration or orthostatic (standing) dehydration events, respectively. These events were determined by acute systemic vasoconstriction (i.e., cardiac afterload response) overcompensating for clinostatic or orthostatic cardiac preload under-responses (low cardiac output or stroke volume). Lower pain tolerance was associated with tonic blood pressure reduction, determined by permanent hypovolemia (low stroke volume) decompensated by permanent systemic vasodilation. In conclusion, the body hydration status profiles assessed by (re)activity of systemic vascular resistance and effective blood volume-related measures can help predict the risk and intensity of different pain sensitization components in chronic pain syndrome, facilitating a more personalized management approach.

Low- and high-frequency spinal cord stimulation and arterial blood pressure in patients with chronic pain and hypertension: a retrospective study

PURPOSE

Evidence suggests that traditional low-frequency spinal cord stimulation (LF-SCS) reduces arterial blood pressure (BP) in patients with chronic pain and hypertension independent of improved pain symptoms. However, it remains unclear whether high-frequency spinal cord stimulation (HF-SCS) also lowers BP in chronic pain patients with hypertension. Therefore, in a retrospective study design, we tested the hypothesis that clinic BP would be significantly reduced following implantation of HF-SCS in patients with chronic pain and hypertension.

METHODS

Clinic BP within 3 months before and after surgical implantation of either a LF-SCS or HF-SCS device between 2010 and 2020 were collected from electronic medical records at The University of Kansas Health System (TUKHS).

RESULTS

A total of 132 patients had available records of clinic BP (64 ± 13 years of age). Patients with hypertension (n = 32) demonstrated a significantly greater reduction in systolic BP (-8 ± 12 versus 2 ± 9 mmHg, P < 0.001) following implantation compared with normotensive patients (n = 100). Importantly, the change in BP was inversely related to baseline BP independent of age and sex following implantation of HF-SCS (n = 70, R =  -0.50, P < 0.001) or LF-SCS (n = 62, R =  -0.42, P = 0.001). Higher pain scores before implantation were not associated with reduction in systolic BP (R = 0.10, P = 0.43) or diastolic BP (R =  -0.08, P = 0.53) (n = 69) after implantation.

CONCLUSION

These findings confirm previous studies showing reduced BP following implantation of LF-SCS in patients with chronic pain and hypertension and provide novel data regarding reduced BP following implantation of newer generation HF-SCS devices.

EFFECT OF HYPERTENSION ON PAIN THRESHOLD IN PATIENTS WITH CHRONIC PAIN

Introduction: Little is known about the relationship between pain and hypertension (HT). This study aimed to analyze the effect of HT on pain sensitivity in patients with chronic musculoskeletal pain complaints. Methods: This analytical, cross-sectional study included 45 patients aged 29–75 years with HT. The control group comprised 44 normo/hypotensive patients aged 19–66 (P = 0.107). Education status, age, gender, height, weight, smoking, presence of diabetes mellitus, physical activity level, blood pressure measurement, anti-HT drug use, vital parameters, including heart rate, respiratory rate, and body temperature, were recorded for all participants. Results: The pain score was significantly higher in the HT group, with a mean of 72.1 ± 30.2 points (P = 0.008). Also, the HT group’s systolic blood pressure and pain score were significantly positively correlated (rho = 0.245, P = 0.02). The pulse rate was found to be significantly related to the pain score and pain threshold (P < 0.001); it was negatively correlated with algometer values (rho = –0.286, P = 0.015). Systolic pressure (P = 0.033) and BMI ( P < 0.001) were significantly different among the groups according to physical activity level. The Spearman correlation analysis showed a positive correlation of diastolic blood pressure with the body mass index (rho = 0.224, P = 0.036) and pain score (rho = 0.456, P < 0.001).  Conclusion: The present study showed that the pain complaint increases as the blood pressure and weight increase. Also, the pain threshold decreases as the heart rate increases. The pain threshold was lower in women than in men, independent of tension.

Associated risk factors of postoperative pain after glaucoma surgery: a prospective study

PURPOSE

This study aimed to determine degree of postoperative pain and the incidence of serious postoperative pain after glaucoma surgery and further to identify the associated risk factors.

METHODS

A total of 194 consecutive patients who were diagnosed with glaucoma and underwent glaucoma surgery were enrolled in this study. The intensity of postoperative pain was evaluated using numerical rating scale (NRS) within 24 h after surgery; NRS ≥ 5 was considered as clinically significant postoperative pain. Risk factors associated with the development of postoperative pain were analyzed by multivariate logistic regression analysis.

RESULTS

Clinically significant postoperative pain was experienced at any time after glaucoma surgery in 41.75% of the patients, which peak at 2 h. 27.8% of the patients requested analgesic medication within 24 h after surgery. According to multivariate logistic regression analysis, preoperative anxiety (OR = 4.13 [1.29-13.2], p = 0.017), cyclophotocoagulation (OR = 30.9 [3.47-375.1], p = 0.002), and phacotrabeculectomy combined with or without intraocular lens implantation (OR = 30.0 [2.69-335.6], p = 0.006) were associated with increased clinically significant postoperative pain. Interestingly, patients with diabetes and/or hypertension were associated with less postoperative pain after glaucoma surgery (OR = 0.23 [0.08-0.64], p = 0.005).

CONCLUSION

Patients undergoing glaucoma surgery tend to experience postoperative pain in the early postoperative period. Anxiety level and surgery types of cyclophotocoagulation and phacotrabeculectomy are risk factors for postoperative pain. Patients with diabetes and/or hypertension are less likely to develop postoperative pain.

Blood pressure-related hypoalgesia: a systematic review and meta-analysis

OBJECTIVE

Spontaneous or experimentally induced high blood pressure (BP) is associated with reduced pain perception, known as BP-related hypoalgesia. Despite its clinical implications, such as the interference with early detection of myocardial infarction in 'at risk' groups, the size of the association between high BP and pain has not yet been quantified. Moreover, the distinct association between high BP and physiological or psychological components of pain has not yet been considered so far. The aim of this study was to overcome this gap by performing separate meta-analyses on nociceptive response versus quantifiable perceptual measures of pain in relation to high BP.

METHODS

PubMed and Web of Knowledge databases were searched for English language studies conducted in humans. Fifty-nine studies were eligible for the analyses. Pooled effect sizes (Hedges' g) were compared. Random effect models were used. Results show that higher BP is significantly associated with lower nociceptive response (g = 0.38; k = 6) and reduced pain perception, assessed by quantifiable measures (g = 0.48; k = 59).

RESULTS

The association between BP and pain perception, derived from highly heterogeneous studies, was characterized by significant publication bias. BP assessment, pain assessment, site of pain stimulation, percentage of female participants in the sample, and control for potential confounders were significant moderators.

CONCLUSION

Current meta-analytic results confirm the presence of BP-related hypoalgesia and point towards the need for a better understanding of its underlying mechanisms.

Impact of antihypertensive treatment on resiliency to clinical pain

OBJECTIVES

Although progress has been made in the regulation of hypertension over the past decades, the USA and some other countries have faced a significant rise in incidence of chronic pain management cases during the same period. Studies of the relationship between pain and blood pressure (BP) regulations propose that these two processes may be interconnected. Studies of effects of antihypertensive treatment on pain in general and its chronification have never been reviewed.

METHODS

A narrative review of respective studies with analysis of credibility of the findings was conducted.

RESULTS

Some studies have suggested that aggressive reduction of high BP may contribute to a return in pain symptoms and may require more aggressive, long-term pain management. Other studies propose that long-term antihypertensive medication could also increase the risk for new cases of chronic pain. Pain initiates a central neuroplastic resetting of the baroreceptor activation accounting for sustained increase of BP with an adaptive 'pain-killing' or maladaptive 'pain-complication' effect associated with pain chronification, and these mechanisms may be moderated by antihypertensive medications. However, different antihypertensive drugs and nondrug treatments may diversely affect pain mechanisms at different stages of treatments.

CONCLUSION

Uncontrollable reduction of high BP in some patients with hypertension could increase the risk for chronic pain incidence and its severity. Practical recommendations in BP control should be reconsidered to take into account patients' chronic pain. Further research is needed of moderation effects of different antihypertensive manipulations on pain to improve pain management in these patients.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Hypertension and Postoperative Pain: A Prospective Observational Study

Objectives

The relationship between pain and hypertension is of great pathophysiological and clinical interest in the pain field, but the mechanism is poorly understood. This study used the postoperative patient-controlled analgesia (PCA) dose and the visual analysis scale (VAS) score to assess the relationship between pain and hypertension.

Methods

In this prospective study in a single-center hospital, 200 participants were enrolled and divided into three groups: normotensive group, hypertension without treatment group, and hypertension with treatment group. The participants scheduled for elective inhalational general anesthesia were interviewed at hospital admission.

Results

A significant difference was observed in analgesic dosage on postoperative days 1, 2, and 3 between the female normotensive group and female hypertension with treatment group (independent-samples, one-way analysis of covariance, age, and weight as covariates:P=0.021, 0.014, 0.032). No significant differences in the VAS scores and PCA dosages were observed between the male normotensive group and any one of the male hypertensive groups.

Conclusion

We agree that hypertensive hypoanalgesia exists in some experimental settings. The mechanism linking postoperative pain and hypertension is far more complex than we initially believed. Therefore, more studies are required to investigate the roles that antihypertensive drugs, sex, and psychological stress play. Antihypertensive drugs may play a crucial role in mediating the relationship between pain and hypertension. Psychosocial factors were discussed but were not examined.

Adverse Drug Reactions in the Orofacial Region

A wide spectrum of drugs can sometimes give rise to numerous adverse orofacial manifestations, particularly dry mouth, taste disturbances, oral mucosal ulceration, and/or gingival swelling. There are few relevant randomized double-blind controlled studies in this field, and therefore this paper reviews the data from case reports, small series, and non-peer-reviewed reports of adverse drug reactions affecting the orofacial region (available from a MEDLINE search to April, 2003). The more common and significant adverse orofacial consequences of drug therapy are discussed.

An Observation of the Correlation Between ACEI and ARB Medications and Chronic Pain Medication Utilization in a Community Pharmacy

Background. Bradykinin has shown to affect pain hypersensitivity via reducing the pain threshold when it binds to bradykinin B1 receptors. Bradykinin B1 receptors are upregulated following tissue injury. Thus, any mechanism causing an increase in bradykinin could escalate pain perception. Angiotensin-converting enzyme inhibitors (ACEIs) increase bradykinin by blocking the ACE enzyme from inactivating bradykinin. Angiotensin receptor blockers (ARBs) do not increase bradykinin as much and may not make patients as susceptible to chronic pain by the described expected mechanism. Objective. This analysis observed retrospective data from a single community pharmacy to determine if there was a difference between patient groups who chronically used ACEIs and ARBs regarding their use of chronic pain medications. Methods. Reports were generated containing all prescription fills of ACEIs and ARBs during the 18-month period and length of therapy was determined from that report per patient. The patients meeting the length of therapy requirements were assessed for pain medication usage to determine presence and length of pain medication therapy. Results. The percentage of patients filling chronic pain medications among chronic ACEI patients was 3.99% higher than chronic ARB patients. This was not statistically different. Other evaluated group differences were not statistically significant.

Cortical and autonomic responses to noxious stimulation during anesthesia in cardiac surgery patients are moderated by preanesthetic blood pressure levels

Evidence has revealed that elevated blood pressure is associated with reduced sensitivity to noxious stimulation. The current study investigated the association between resting blood pressure and nociception during anesthesia in 32 patients undergoing cardiac surgery. Pain-related middle latency cortical somatosensory evoked potentials (MLCEPs) elicited by noxious 50 mA median nerve stimulation were used to assess intraoperative nociception and algesia. Noxious stimulation elicited MLCEPs in 18 (56%) patients. Resting blood pressure was significantly higher in patients without MLCEP than those with MLCEP. Moreover, systolic blood pressure responses to intraoperative electrical stimulation of median nerve were blunted in the group without MLCEP compared to those with MLCEP. The current findings extend the hypertensive hypoalgesia phenomenon to the operating theatre.

Does chronic pain alter the normal interaction between cardiovascular and pain regulatory systems? Pain modulation in the hypertensive-monoarthritic rat

Hypertension-associated hypoalgesia is widely recognized in acute pain conditions. In chronic pain states, however, the relationship between blood pressure and pain sensitivity is still ill-defined, with different authors reporting negative, positive, or even no relationship at all. This work addresses this issue, using complete Freund's adjuvant (CFA)-induced monoarthritis in different models of hypertension: Spontaneous (spontaneously hypertensive rats, SHR), induced by infusion of angiotensin II (ANG) or 1,3-dipropyl-8-sulfophenylxanthine (DPSPX, an adenosine receptors' antagonist), and renal artery ligation (RAL). Nociceptive responses associated with monoarthritis were evaluated by different behavioral tests (von Frey, ankle-bend and CatWalk) and by quantification of Fos expression at the dorsal horn upon noxious stimulation. In all hypertension models, higher von Frey thresholds and lower Fos expression were detected in hypertensive rats with chronic inflammatory pain, as compared to normotensive monoarthritic rats. In SHR and DPSPX, but not ANG or RAL models, hypertensive animals displayed lower inflammation than normotensives. Ankle-bend and CatWalk results indicated lower pain sensitivity in hypertensive rats only in SHR and DPSPX models. The present study shows the importance of using multiple models of hypertension, and evaluating pain responses by various methods, to better understand the complexity of the interactions between pain and cardiovascular regulatory systems.

PERSPECTIVE

This study used different models of hypertension to investigate whether chronic pain alters the normal integration of cardiovascular and pain regulatory systems. A complete understanding of the mechanisms underlying the complex interactions between these systems may disclose future therapeutic approaches to treat hypertension/chronic pain comorbidity states.

Examination of the dose-response relationship between pain perception and blood pressure elevations induced by isometric exercise in men and women

The purpose of this study was to examine exercise-induced hypoalgesia (EIH) in men and women, and whether different magnitudes of BP elevations induced by isometric exercise systematically influenced pain perception. Twenty-five men and 25 women performed isometric exercise at 25% MVC for 1-min, 3-min, and 5-min while BP and pain perception were assessed. Results indicated that BP was significantly elevated (p<0.05) by isometric exercise in a dose-response manner. Pain thresholds were found to be elevated while pain ratings were lower (p<0.05) immediately following isometric exercise but not in a dose-response manner. It was concluded that isometric exercise produced EIH in men and women, and there was not a dose-response relationship between BP and EIH.

Reinventing the ACE inhibitors: some old and new implications of ACE inhibition

Since their inception, angiotensin-converting enzyme (ACE) inhibitors have been used as first-line therapy for the treatment of cardiovascular and renal diseases. They restore the balance between the vasoconstrictive salt-retentive and hypertrophy-causing peptide angiotensin II (Ang II) and bradykinin, a vasodilatory and natriuretic peptide. As ACE is a promiscuous enzyme, ACE inhibitors alter the metabolism of a number of other vasoactive substances. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have been proven effective in the treatment of hypertension, and reduce mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction. They inhibit ischemic events and stabilize plaques. Furthermore, they delay the progression of diabetic nephropathy and neuropathy and act as antioxidants. Ongoing studies have elucidated protective roles for them in both memory-related disorders and cancer. Lastly, N- and C-domain selective ACE inhibitors have led to new uses for ACE inhibitors.

Effects of naltrexone on electrocutaneous pain in patients with hypertension compared to normotensive individuals

An opioid mechanism may help explain hypertensive hypoalgesia. A double-blind placebo-controlled design compared the effects of opioid blockade (naltrexone) and placebo on electrocutaneous pain threshold, pain tolerance, and retrospective McGill Pain Questionnaire ratings in 35 unmedicated patients with essential hypertension and 28 normotensive individuals. The hypertensives experienced less pain than normotensives during the assessment of their pain tolerance; however, this manifestation of hypertensive hypoalgesia was not moderated by naltrexone. These findings fail to support the hypothesis that essential hypertension is characterised by relative opioid insensitivity.

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.

Pain perception, blood pressure levels, and peripheral benzodiazepine receptors in patients followed for differentiated thyroid carcinoma: a longitudinal study in hypothyroidism and during hormone treatment

BACKGROUND

Elevated blood pressure levels that are associated with hypalgesia and hypothyroidism have major influences on the cardiovascular system. The potential modulation of pain sensitivity by thyroid hormones is largely undetermined. Moreover, a few experimental studies show that peripheral benzodiazepine receptors (PBRs), which may be altered in hypothyroidism, seem to be related with pain perception.

METHODS

Dental pain threshold and tolerance were evaluated in 19 patients followed for differentiated thyroid carcinoma (1) in severe short-term hypothyroidism (phase 1) and (2) during thyroid stimulating hormone-suppressive LT4 treatment (phase 2). PBR expression (cytofluorimetric evaluation) on peripheral blood mononuclear cells was also investigated in the 2 phases.

RESULTS

Pain perception differed throughout the study, the dental pain threshold was higher in phase 1 (P<0.05) whereas pain tolerance was higher but not significantly (P=0.07). Although the systolic blood pressure was higher during hypothyroidism (P<0.01), no relationship was found between blood pressure changes and pain sensitivity variations. Moreover, the multiple regression analysis showed an independent association of the clinical phase with pain sensitivity (r=-2.61, P=0.029), while accounting for systolic blood pressure. The intensity of PBRs was significantly higher in the first phase of the study (P=0.047) whereas the ratio did not significantly differ. However, no relationship was observed between pain sensitivity and PBRs.

DISCUSSION

In conclusion, in athyreotic patients, the pain sensitivity is related to the thyroid status and is independent of the increase in blood pressure induced by thyroid hormone deprivation. The PBRs do not seem to have major influence on pain sensitivity changes in hypothyroidism.

Chest pain is inversely associated with blood pressure during exercise among individuals being assessed for coronary heart disease

Acute and chronic increases in blood pressure have been related to decreases in pain perception. This phenomenon has been studied primarily using acute experimental pain stimuli. To extend the literature to naturalistic pain and in particular the problem of silent cardiac ischemia, this study examined the relationship between blood pressure and chest pain during exercise stress testing. Nine hundred seven (425 men, 482 women) individuals undergoing exercise stress testing for diagnosis of possible myocardial ischemia completed the McGill Pain Questionnaire (MPQ) immediately afterward and other questionnaires before and after testing. Blood pressure was measured before, during, and after exercise. Systolic blood pressure at the end of exercise was inversely related to a number of measures of pain such as total score on the MPQ. The relationship could not be explained by individual differences in exercise duration, medication use, sex, or other measured variable. In sum, the inverse relationship between blood pressure and sensitivity to pain that has been observed in other populations in experimental and naturalistic conditions was observed for chest pain during exercise. Blood pressure may contribute to episodes of silent ischemia.

Inhibition of nociceptive responses of spinal cord neurones during hypertension involves the spinal GABAergic system and a pain modulatory center located at the caudal ventrolateral medulla

The mechanisms of hypertension-induced hypoalgesia were studied in a model of hypertension induced by adenosine receptors blockade with the non-selective antagonist 1,3-dipropyl-8-sulfophenylxanthine (DPSPX) during 7 days. Based on the positive correlation between pain thresholds and noxious-evoked expression of the c-fos protooncogene in spinal cord neurones, we used this marker of nociceptive activation of spinal neurones to evaluate the involvement of the spinal GABAergic system and the caudal ventrolateral medulla (VLM), an important inhibitory component of the supraspinal endogenous pain modulatory system. In DPSPX-treated animals, a 20% increase in blood pressure was achieved along with a decrease in Fos expression in the superficial (laminae I-II) and deep (laminae III-VII) dorsal horn. In these animals, lower percentages of neurones labeled for GABAB receptors that expressed Fos were obtained in the superficial dorsal horn. Lesioning the VLMlat with quinolinic acid prevented the decrease in Fos expression at the spinal cord of DPSPX-hypertensive rats whereas in normotensive animals, no changes in Fos expression were detected. The present results support previous findings that hypertension is associated with a decrease of nociceptive activation of spinal cord neurones, through descending inhibition exerted by the VLMlat. This study further shows that during hypertension a decrease in the expression of GABAB receptors in nociceptive spinal neurones occurs, probably due to changes in the local GABAergic inhibitory system.

A longitudinal study of pain sensitivity and blood pressure in adolescent boys: results from a 5-year follow-up

A growing literature has observed a significant reduction in pain sensitivity among hypertensive animals and humans. It is uncertain whether a reduced sensitivity to pain can be observed in nonnotensive individuals who go on to develop high blood pressure. Blood pressure (BP) was reassessed in one hundred fifteen 19-year-old boys initially tested at age 14, when they were also presented with a pain stimulus (mechanical finger pressure). Hierarchical regression analyses indicated that information regarding pain tolerance improved prediction of changes in systolic and diastolic blood pressure beyond that afforded by differences in BP at age 14, parental history of hypertension, and body mass index. These analyses suggest that pain sensitivity may be associated with physiological processes involved in the development of sustained high blood pressure.

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.

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

Previous work has suggested an attenuated sensitivity to painful stimulation in hypertensive men. We recently reported that, compared with persons with negative parental history, men, but not women, with a positive history for hypertension showed attenuated pain perception. This study specifically addressed factors that predict pain perception in women, including blood pressure, parental history and mood states. Fifty-four normotensive women with positive (PH+; n = 20) or negative parental history (PH-; n = 34) for hypertension and high or low casual systolic blood pressure (BP) performed the cold pressor (CP) test. Participants rated their pain every 15 s during a 90-s hand CP (0-4 degrees C) and a 90-s post-CP rest period. Detailed mood ratings were obtained immediately before the CP test. Data were evaluated using multivariate repeated measure analyses of variance and regression analyses. PH+ and PH- women did not differ in age, height, weight, education, resting BP, or heart rate. PH+ and PH- women did not differ in pain ratings during or after the CP, or pain ratings using the McGill Pain Questionnaire (MPQ), and they did not differ in their cardiovascular responses to the CP, confirming our earlier study in a separate sample. Women with high casual systolic BP reported significantly less pain, especially after the CP (P < 0.01). MPQ total scores confirmed this finding with high BP women reporting less pain than low BP women (P < 0.05). Regression analyses confirmed these effects. Controlling for potential confounding variables did not alter these relationships. These findings suggest that in women, phenotype systolic BP may be a better predictor of hypoalgesia than parental history of hypertension.

The current perception thresholds vary between horizontal and 70 degrees tilt-up positions

We investigated the influence of posture on current perception threshold (CPT). The subjects consisted of 20 healthy male volunteers (23-31 yr old). At both the horizontal and the 70 degrees tilt-up position (TUP), the CPTs (5, 250, and 2000 Hz) of the middle finger were determined by using the Neurometer CPT/C (Neuropteran, Baltimore, MD). Autonomic nervous activities were evaluated by heart rate variability (HRV) analysis and spontaneous baroreflex sensitivity analysis at the two postures previously mentioned. The three CPTs at the 70 degrees TUP were significantly lower than those at the horizontal posture (5 Hz, P < 0.05; 250 Hz, P < 0.001; 2000 Hz, P < 0.05). The changes in HRV and spontaneous baroreflex sensitivity at the 70 degrees TUP indicated decreasing parasympathetic tone. The CPTs of 5 and 250 Hz were significantly correlated with mean systolic blood pressure at the 70 degrees TUP. The CPT of 2000 Hz was significantly correlated with the 0.15-0.4 Hz component in HRV at both postures. The regression analysis of the difference of 5 Hz CPT with that of the mean systolic blood pressure showed a significant correlation (P < 0.001). To evaluate the clinical course of peripheral nerve disorders, the comparison of CPTs measured during the same posture is important. This suggests that CPTs must be measured at the horizontal posture.

IMPLICATIONS

Current perception thresholds at the 70 degrees tilt-up posture were significantly lower than those at the horizontal posture. When the compensatory mechanism for preserving blood pressure was emphasized, the current perception thresholds would have a relational connection to mean systolic blood pressure, similar to the concept of hypertension-induced hypoalgesia.

Relationship between dental pain perception and 24 hour ambulatory blood pressure: a study on 181 subjects

OBJECTIVE

To investigate dental pain perception in a large group of essential hypertensive subjects.

METHODS

A total of 130 hypertensive patients together with 51 normotensive subjects were submitted to tooth-electrical stimulation to determine the dental pain threshold (occurrence of pulp sensation) and tolerance (time when the subject asked for the test to be stopped). Blood pressure was measured at rest, before pain perception evaluation, and during a 24 h period by ambulatory monitoring.

RESULTS

The normotensive and hypertensive subjects differed with regard to pain threshold (P = 0.002) and tolerance (P = 0.01). Pain perception variables were significantly correlated with both resting blood pressure and 24 h, diurnal and nocturnal arterial pressures, the correlation between pain threshold and 24 h systolic blood pressure being the most significant (r = 0.31, P < 0.0001). By contrast, parameters indicating 24 h blood pressure variability (percentage of nocturnal blood pressure reduction and 24 h blood pressure variation coefficients) were not associated with pain perception. Moreover, among the hypertensives only, a significant relationship was observed between pain sensitivity and both baseline and 24 h pressures. No association was found when pain perception and blood pressure were correlated in the normotensive group.

CONCLUSIONS

The correlation between both baseline and 24 h blood pressure and pain perception has been confirmed in a large group study of normotensive and hypertensive subjects. Moreover, even among the hypertensive range of blood pressure, the higher the blood pressure is, the lower the sensitivity to pain is. These findings strengthen the hypothesis of a role of the degree of blood pressure elevation in modulating pain sensitivity.

Sex differences in pain perception and cardiovascular responses in persons with parental history for hypertension

We investigated gender differences in cardiovascular and pain responses to the cold pressor (CP) test in persons with positive (PH+) or negative parental history (PH-) for hypertension. Previous work has suggested an attenuated sensitivity to painful stimulation in hypertensive men and more recently in men with parental disposition for hypertension. It is not known whether this hypoalgesic effect is present in PH+ women. In this study, we evaluated differences in pain perception between men and women with PH+ or PH- using an assessment method to measure current as well as delayed pain. Participants rated their pain every 15 s during a 90-s hand CP (0-4 degrees C) and a 90-s post-CP rest period. Systolic and diastolic blood pressures (SBP, DBP) and heart rate (HR) were measured before, during, and after the CP. PH+ and PH- groups did not differ in age, height, weight, education, resting SBP, DBP, or HR. PH+ men showed greater DBP responses to the CP than PH- men, while female groups did not differ in cardiovascular responses to the CP. Although pain ratings during the CP did not differ between groups, post-CP reported pain receded faster in the PH+ men than in the PH- men. PH+ women, on the other hand, tended to report greater pain than PH- women. These findings question the generalizability of the hypoalgesic effects in hypertension-prone women.

Hyperactivity caused by a nitric oxide synthase inhibitor is countered by ultra-wideband pulses

Potential action of ultra-wideband (UWB) electromagnetic field pulses on effects of N(G)-nitro- L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), on nociception and locomotor activity was investigated in CF-1 mice. Animals were injected IP with saline or 50 mg/kg L-NAME and exposed for 30 min to no pulses (sham exposure) or UWB pulses with electric field parameters of 102+/-1 kV/m peak amplitude, 0.90+/-0.05 ns duration, and 160+/-5 ps rise time (mean+/-S.D.) at 600/s. Animals were tested for thermal nociceptive responses on a 50 degrees C surface and for spontaneous locomotor activity for 5 min. L-NAME by itself increased mean first-response (paw lift, shake, or lick; jump) and back-paw-lick response latencies and mean locomotor activity. Exposure to UWB pulses reduced the L-NAME-induced increase in back-paw-lick latency by 22%, but this change was not statistically significant. The L-NAME-induced hyperactivity was not present after UWB exposure. Reduction and cancellation of effects of L-NAME suggest activation of opposing mechanism(s) by the UWB pulses, possibly including increase of nitric oxide production by NOS. The action, or actions, of UWB pulses appears to be more effective on locomotor activity than on thermal nociception in CF-1 mice.