Mechanisms of cutaneous vasodilation during the postmenopausal hot flash

Hot flashes and sleep disruption in a randomized trial in menopausal women

BACKGROUND

Hot flashes, common during menopause, affect up to 80% of the Western menopausal women and are reported to contribute to sleep disturbances in midlife. Few prospective data are available to confirm the specific role of hot flashes in disrupting sleep in midlife women, however, or confirm whether changes in hot flashes in response to clinical therapies result in improvement in sleep.

OBJECTIVE

To examine the effects of continuous nitroglycerin therapy on sleep quality in perimenopausal and postmenopausal women with frequent hot flashes (pre-specified secondary trial endpoint) and to examine prospective associations between hot flashes and sleep disruption in this population.

STUDY DESIGN

Sleep data were analyzed from a randomized, double-blinded, placebo-controlled trial of continuous transdermal nitroglycerin (NTG) therapy to suppress nitric oxide-mediated vasodilation in perimenopausal or postmenopausal women with hot flashes. Participants were randomized to uninterrupted use of transdermal NTG (0.2-0.6 mg/hour) or placebo for 12 weeks. Nocturnal hot flashes awakening participants from sleep were evaluated using 7-day symptom diaries at baseline, 5 weeks, and 12 weeks. Sleep disruption (wakefulness after sleep onset, WASO) was assessed using validated sleep diaries, and global sleep quality was assessed by the validated Pittsburgh Sleep Quality Index (PSQI: range 0 [best] 21 [worst]) questionnaire. Mixed linear models examined changes in sleep quality and disruption, as well as the strength of associations between nocturnal hot flash frequency and sleep outcomes, over 5 and 12 weeks, adjusting for baseline values, age, race, and ethnicity.

RESULTS

Among the 141 participants (70 to NTG and 71 to placebo, mean age 54.6 [±3.9] years), the mean baseline hot flash frequency was 10.8 (±3.5) per day, including 2.6 (±1.7) nocturnal hot flashes awakening participants. At baseline, hot flashes were the most commonly reported reason for nocturnal awakening, with 62.6% of participants reporting waking due to hot flashes at least twice nightly. Over 5 and 12 weeks, mean frequency of nocturnal hot flashes causing awakenings decreased in both groups (NTG: -0.9 episodes/night, placebo: -1.0 episodes/night). Sleep disruption as measured by average nightly WASO also decreased (NTG: -10.1 minutes, placebo: -7.3 minutes), and mean PSQI score improved (NTG: -1.3 points, placebo: -1.2 points). No significant between-group differences in change in sleep outcomes were detected from baseline to 5 and 12 weeks, including PSQI sleep quality score as a prespecified secondary trial endpoint (P≥.05 for all). Greater improvement in nocturnal hot flash frequency over 5 and 12 weeks was associated with greater improvement in PSQI sleep quality score (β= -0.30, P=.01) and sleep disruption reflected by WASO (β= -1.88, P=.02) in the combined sample.

CONCLUSION

Among menopausal women in a randomized trial of continuous NTG therapy for hot flashes, hot flashes were the most frequently reported cause of nocturnal awakenings. Compared to placebo, continuous NTG therapy did not result in greater improvements in sleep quality from baseline to 5 and 12 weeks. Based on night-by-night symptom diaries and questionnaires, however, greater improvement in nocturnal hot flash frequency in both groups was associated with greater improvement in sleep quality and disruption.

The influence of habitual physical activity and sedentary behavior on objective and subjective hot flashes at midlife

OBJECTIVE

The purpose of this study was to evaluate relationships between physical activity, sedentary time, and hot flashes during both waking and sleeping periods using concurrent objective and subjective measures of hot flashes in midlife women.

METHODS

Women aged 45 to 55 years (n = 196) provided self-reported data on physical activity and underwent 24 hours of hot flash monitoring using sternal skin conductance. Participants used event marking and logs to indicate when hot flashes were perceived. Wake and sleep periods were defined by actigraphy. Mean ambient temperature and humidity were recorded during the study period. Generalized linear regression modeling was used to evaluate the effect of physical activity types and sedentary time on hot flash outcomes. Isotemporal substitution modeling was used to study the effect of replacing sedentary time with activity variables on hot flash frequency.

RESULTS

Modeled results indicated that increasing sitting by 1 hour was associated with a 7% increase in the rate of objectively measured but not subjectively reported hot flashes during sleep. Replacing 1 hour of sitting with 1 hour of vigorous activity was associated with a 100% increase in subjectively reported but not objectively measured waking hot flashes. There was little evidence for an effect of temperature or humidity on any hot flash outcome.

CONCLUSIONS

These data provide support for relations between sedentary time, physical activity, and hot flashes and highlight the importance of using objective and subjective assessments to better understand the 24-hour hot flash experience.

Efficacy of Continuous Transdermal Nitroglycerin for Treating Hot Flashes by Inducing Nitrate Cross-tolerance in Perimenopausal and Postmenopausal Women: A Randomized Clinical Trial

Importance

Due to the potential risks of long-term systemic estrogen therapy, many menopausal women are interested in nonhormonal treatments for vasomotor symptoms. Physiologic studies indicate that nitric oxide plays a key role in mediating hot flash-related vasodilation, suggesting that nonhormonal medications that induce nitrate tolerance in the vasculature may offer therapeutic benefit for vasomotor symptoms.

Objective

To determine whether uninterrupted administration of transdermal nitroglycerin (NTG) to induce nitrate cross-tolerance decreased the frequency or severity of menopause-related hot flashes.

Design, Setting, and Participants

This randomized, double-blinded, placebo-controlled clinical trial included perimenopausal or postmenopausal women reporting 7 or more hot flashes per day who were recruited from northern California by study personnel at a single academic center. Patients were randomized between July 2017 and December 2021, and the trial ended in April 2022 when the last randomized participant completed follow-up.

Interventions

Uninterrupted daily use of transdermal NTG (participant-directed dose titration from 0.2-0.6 mg/h) or identical placebo patches.

Main Outcome Measures

Validated symptom diaries assessing changes in any hot flash frequency (primary outcome) and moderate-to-severe hot flash frequency over 5 and 12 weeks.

Results

Among the 141 randomized participants (70 NTG [49.6%], 71 placebo [50.4%]; 12 [85.8%] Asian, 16 [11.3%] Black or African American, 15 [10.6%] Hispanic or Latina, 3 [2.1%] multiracial, 1 [0.7%] Native Hawaiian or Pacific Islander, and 100 [70.9%] White or Caucasian individuals), a mean (SD) of 10.8 (3.5) hot flashes and 8.4 (3.6) moderate-to-severe hot flashes daily was reported at baseline. Sixty-five participants assigned to NTG (92.9%) and 69 assigned to placebo (97.2%) completed 12-week follow-up (P = .27). Over 5 weeks, the estimated change in any hot flash frequency associated with NTG vs placebo was -0.9 (95% CI, -2.1 to 0.3) episodes per day (P = .10), and change in moderate-to-severe hot flash frequency with NTG vs placebo was -1.1 (95% CI, -2.2 to 0) episodes per day (P = .05). At 12 weeks, treatment with NTG did not significantly decrease the frequency of any hot flashes (-0.1 episodes per day; 95% CI, -1.2 to 0.4) or moderate-to-severe hot flashes (-0.5 episodes per day; 95% CI, -1.6 to 0.7) relative to placebo. In analyses combining 5-week and 12-week data, no significant differences in change in the frequency of any hot flashes (-0.5 episodes per day; 95% CI, -1.6 to 0.6; P = .25) or moderate-to-severe hot flashes (-0.8 episodes per day; 95% CI, -1.9 to 0.2; P = .12) were detected with NTG vs placebo. At 1 week, 47 NTG (67.1%) and 4 placebo participants (5.6%) reported headache (P < .001), but only 1 participant in each group reported headache at 12 weeks.

Conclusions and Relevance

This randomized clinical trial found that continuous use of NTG did not result in sustained improvements in hot flash frequency or severity relative to placebo and was associated with more early but not persistent headache.

Trial Registration

Clinicaltrials.gov Identifier: NCT02714205.

Physical activity and exercise for hot flashes: trigger or treatment?

IMPORTANCE AND OBJECTIVE

Hot flashes (HFs) are a prevalent feature of menopause. Hot flashes can be bothersome and affect quality of life. However, HFs have also been associated with the risk for cardiovascular disease. Therefore, providing current evidence on the effect of therapies to reduce HFs can help patients and providers with decision making. This review provides details on the scientific evidence to date related to the effect of physical activity (PA) and exercise to alter the HF experience in women.

METHODS

The PubMed database was searched between June 2020 and June 2022 for currently available evidence regarding the relation between PA and exercise and HFs. Our analysis included randomized control trials on exercise training, epidemiological studies, and studies evaluating acute exercise on the self-reported and objectively measured HF experience in addition to systematic reviews on the topic published as of June 2022.

DISCUSSION AND CONCLUSIONS

The majority of evidence from randomized control trials indicates that aerobic and resistance exercise training lead to a decrease in subjectively experienced HFs. The limited available studies on acute exercise indicate that a bout of moderate-intensity exercise may decrease objectively measured and self-reported HFs but acute increases in PA intensity above accustomed levels may influence subjective HF experience. Some evidence suggests that for those with depression, habitual PA may be an effective way to reduce HF symptoms. Weighing the available evidence, for people who experience HFs, engaging in regular moderate-intensity PA, including aerobic and resistance exercise, may be an effective therapy to reduce HFs and women should be counseled on the benefits of regular, moderate exercise. However, significant gaps in knowledge remain about the optimal exercise prescription, effectiveness for a diverse population, meaning of differences between objective and subjective experience, and mechanisms that lead to changes in HFs.

Vasomotor symptoms of menopause, autonomic dysfunction, and cardiovascular disease

Cardiovascular disease (CVD), the leading cause of death among US adults, is more prevalent in menopausal females compared with age-matched males. Vasomotor symptoms of menopause (VMS; hot flashes/flushes and night sweats) are common among females undergoing menopausal transition and have been associated with elevated blood pressure (BP) and increased CVD risk. Autonomic dysregulation of BP has been posited as a contributing factor to the elevated CVD risk in menopausal females with VMS. This review includes 1) a brief overview of the relationship between VMS and CVD, 2) mechanisms of hot flushes and their potential impact on short- and long-term BP regulation, and 3) how the disruption of autonomic function associated with VMS might provide a mechanistic pathway to CVD development. Finally, this review will highlight knowledge gaps and future directions toward better understanding of hot flush physiology and VMS contributions to CVD.

Decreased Frequency of Mental Workload-Induced Subjective Hot Flashes Through Gum Massage: An Open-Label, Self-Controlled Crossover Trial

Objective:

Hot flashes, a symptom of menopause, can decrease women's quality of life. Sympathetic nervous system activation has been identified as an important factor in the occurrence of hot flashes. Given that somatosensory stimulation of the oral cavity can affect autonomic nervous activity, we aimed to investigate the possibility that somatosensory stimulation of the gums (i.e., gum massage) could improve hot flashes.

Materials and Methods:

Nineteen women experiencing at least one hot flash per day were instructed to perform a gum massage on themselves before undertaking mental workload, using arithmetic task, and the frequency of hot flashes experienced during this task was measured. Changes in autonomic nervous activity were assessed based on heart rate variability.

Results:

Massage conditions promoted a significantly lower arithmetic task-induced hot flash frequency compared with nonmassage conditions (p < 0.05). During gum massage, the ratio between low and high frequency (LF/HF) values decreased significantly under massage conditions compared with nonmassage conditions (p < 0.01). During the arithmetic task, the gum massage-induced reduction in LF/HF, which changed from baseline, was significantly correlated with the gum massage-induced reduction in hot flash frequency.

Conclusions:

The results of this study indicate that gum massage can reduce the subjective frequency of hot flashes over a certain period under mental workload. Our study also indicates that gum massage can potentially decrease sympathetic nerve activity, which is known to be involved in the occurrence of hot flashes.

Clinical Trial Registration number 328 (the institutional review board of Lion Corporation).

Effect of sensory blockade and rate of sensory stimulation on local heating induced axon reflex response in facial skin

Local neuronal circuits in non-glabrous skin drive the initial increase of the biphasic cutaneous vasodilation response to fast non-noxious heating. Voltage-sensitive Na⁺ (NaV) channel inhibition blocks the afferent limb of the non-glabrous forearm cutaneous axon reflex. Slow local heating does not engage this response. These mechanisms have not been adequately investigated or extended into areas associated with flushing pathology. We hypothesized that despite regional differences in sensory afferents, both sensory blockade and slowing the heating rate would abate the cutaneous axon reflex-mediated vasodilator responses in facial skin. We measured skin blood flow responses (laser-Doppler flowmetry) of 6 healthy subjects (5 female) to non-noxious forearm, cheek, and forehead local heating, expressed as a percentage of cutaneous vascular conductance at plateau (CVC = flux/mean arterial pressure). We assessed CVC during fast (1 °C/30s) and slow (1 °C/10 min) local heating to 43 °C in both NaV inhibition (topical 2.5% lidocaine/prilocaine) and control conditions. NaV inhibition decreased forearm (control: 84 ± 4, block: 34 ± 9%plateau, p < 0.001) and trended toward decreased forehead (control: 90 ± 3, block: 68 ± 3%plateau, p = 0.057) initial CVC peaks but did not alter cheek responses (control: 90 ± 3, block: 92 ± 13%plateau, p = 0.862) to fast heating. Slow heating eliminated the initial CVC peak incidence for all locations, and we observed similar results with combined slow heating and NaV inhibition. Slower sensory afferent activation rate eliminated the axon reflex response in facial and non-glabrous skin, but topical sensory blockade did not block axon reflex responses in flushing-prone cheek skin. Thus, slower heating protocols are needed to abate facial, particularly cheek, axon reflex responses.

The influence of habitual endurance exercise on carotid artery strain and strain rate in young and middle-aged men

NEW FINDINGS

What is the central question of this study? Carotid artery peak circumferential strain (PCS) and strain rate attenuate with age, but appear to be modulated by cardiorespiratory fitness status in young males. However, the relationship between habitual endurance exercise (running) and these parameters has not been studied in young and middle-aged men. What is the main finding and its importance? Young and middle-aged runners exhibited elevated PCS and systolic strain rate (S-SR) compared with non-runners, but habitual running did not influence diastolic strain rate (D-SR). Habitual exercise is associated with comparable improvements in carotid strain parameters in young and middle-aged men, but the age-related decline in PCS and S-SR might be more amenable to habitual endurance exercise than D-SR.

ABSTRACT

Central arterial stiffness is an independent predictor of cardiovascular risk that can be modified by exercise training. However, conventional local measures of carotid artery stiffness display conflicting responses to habitual endurance exercise in young and older adults. Two-dimensional (2D)-Strain imaging of the common carotid artery (CCA) quantifies circumferential deformation (strain) of the arterial wall across the cardiac cycle, which is more sensitive at detecting age-related alterations in CCA stiffness than conventional methods. Therefore, the study was designed to examine the relationship between habitual endurance exercise (running) and CCA 2D-Strain parameters in young and middle-aged men. Short-axis ultrasound images of the CCA were obtained from 13 young non-runners [23 years of age (95% confidence interval: 21, 26 years of age)], 19 young runners [24 (22, 26) years of age], 13 middle-aged non-runners [54 (52, 56) years of age] and 19 middle-aged runners [56 (54, 58) years of age]. Images were analysed for peak circumferential strain (PCS; magnitude of deformation) and systolic and diastolic strain rates (S-SR and D-SR; deformation velocity), and group differences were examined via two-way ANOVA. PCS, S-SR and D-SR were attenuated in middle-aged men compared with young men (all P ≤ 0.001). PCS and S-SR were elevated in young and middle-aged runners when compared with non-runners (P = 0.002 and P = 0.009, respectively), but no age × training status interaction was observed. In contrast, there was no influence of habitual running on D-SR. Habitual exercise is associated with comparable improvements in CCA 2D-Strain parameters in young and middle-aged men, but the age-related decline in PCS and S-SR might be more amenable to habitual endurance exercise than D-SR.

Changes in skin temperature of ovariectomized rats under different incubation temperatures

AIM

This study aimed to investigate changes in skin temperature in the main body regions of ovariectomized rats under different incubation temperatures to identify regions that are similar to hot flashes experienced by menopausal women.

METHODS

A total of 96 adult female Sprague-Dawley rats were randomly divided into sham, ovariectomized and ovariectomized with estrogen treatment groups, with treatment lasting for 4 weeks. After 3 weeks of treatment, each group was randomly divided into five subgroups and placed in separate incubators set at 4, 15, 25, and 37°C. Changes in the skin temperature in seven main regions (head, neck, chest, abdomen, back, tail, and paws) for four time intervals (0-3 min, 3-5 min, 5-10 min and 10-15 min) were monitored using infrared thermography.

RESULTS

All rats showed rapid changes in skin temperature followed by a gradual slowdown under different incubation temperatures. However, changes in ovariectomized rats were significantly different from that in normal rats, and changes on the back, tail and paws were more rapid and lasted longer. Estrogen treatment effectively controlled these abnormalities of ovariectomized rats.

CONCLUSIONS

Temperature responses in the back, tail and paws in ovariectomized rats might be similar to the face, neck and upper chest in menopausal women, where the symptoms of hot flashes are most obvious, which suggests that the back, tail and paws could be regarded as the focus of research on hot flashes, and offer theoretical foundations for mechanisms behind the occurrence of hot flashes in specific regions. Geriatr Gerontol Int 2020; ••: ••-••.

Oxybutynin vs Placebo for Hot Flashes in Women With or Without Breast Cancer: A Randomized, Double-Blind Clinical Trial (ACCRU SC-1603)

BACKGROUND

Hot flashes (HFs) negatively affect quality of life among perimenopausal and postmenopausal women. This study investigated the efficacy of oxybutynin vs placebo in decreasing HFs.

METHODS

In this randomized, multicenter, double-blind study, women with and without breast cancer with 28 or more HFs per week, lasting longer than 30 days, who were not candidates for estrogen-based therapy, were assigned to oral oxybutynin (2.5 mg twice a day or 5 mg twice a day) or placebo for 6 weeks. The primary endpoint was the intrapatient change from baseline in weekly HF score between each oxybutynin dose and placebo using a repeated-measures mixed model. Secondary endpoints included changes in weekly HF frequency, HF-related daily interference scale questionnaires, and self-reported symptoms.

RESULTS

We enrolled 150 women. Baseline characteristics were well balanced. Mean (SD) age was 57 (8.2) years. Two-thirds (65%) were taking tamoxifen or an aromatase inhibitor. Patients on both oxybutynin doses reported greater reductions in the weekly HF score (5 mg twice a day: -16.9 [SD 15.6], 2.5 mg twice a day: -10.6 [SD 7.7]), placebo -5.7 (SD 10.2); P < .005 for both oxybutynin doses vs placebo), HF frequency (5 mg twice a day: -7.5 [SD 6.6], 2.5 mg twice a day: -4.8 [SD 3.2], placebo: -2.6 [SD 4.3]; P < .003 for both oxybutynin doses vs placebo), and improvement in most HF-related daily interference scale measures and in overall quality of life. Patients on both oxybutynin arms reported more side effects than patients on placebo, particularly dry mouth, difficulty urinating, and abdominal pain. Most side effects were grade 1 or 2. There were no differences in study discontinuation because of adverse effects.

CONCLUSION

Oxybutynin is an effective and relatively well-tolerated treatment option for women with HFs.

Changes in heart rate and blood pressure during nocturnal hot flashes associated with and without awakenings

Hot flashes (HFs) are a hallmark of menopause in midlife women. They are beyond bothersome symptoms, having a profound impact on quality of life and wellbeing, and are a potential marker of cardiovascular (CV) disease risk. Here, we investigated the impact on CV functioning of single nocturnal HFs, considering whether or not they were accompanied by arousals or awakenings. We investigated changes in heart rate (HR, 542 HFs), blood pressure (BP, 261 HFs), and pre-ejection period (PEP, 168 HFs) across individual nocturnal physiological HF events in women in the menopausal transition or post-menopause (age: 50.7 ± 3.6 years) (n = 86 for HR, 45 for BP, 27 for PEP). HFs associated with arousals/awakenings (51.1%), were accompanied by an increase in systolic (SBP; ~6 mmHg) and diastolic (DBP; ~5 mmHg) BP and HR (~20% increase), sustained for several minutes. In contrast, HFs occurring in undisturbed sleep (28.6%) were accompanied by a drop in SBP and a marginal increase in HR, likely components of the heat dissipation response. All HFs were accompanied by decreased PEP, suggesting increased cardiac sympathetic activity, with a prolonged increase for HFs associated with sleep disruption. Older age predicted greater likelihood of HF-related sleep disturbance. HFs were less likely to wake a woman in rapid-eye-movement and slow-wave sleep. Findings show that HFs associated with sleep disruption, which are in the majority and more likely in older women, lead to increases in HR and BP, which could have long-term impact on nocturnal CV restoration in women with multiple HFs.

Is core temperature the trigger of a menopausal hot flush?

OBJECTIVE

Menopausal hot flushes negatively impact quality of life and may be a biomarker of cardiovascular and metabolic disease risk; therefore understanding the physiology of hot flushes is important. Current thinking is that a small elevation (∼0.03-0.05C) in core temperature surpasses a sweating threshold (that is reduced in the menopause), sweating is activated, and a hot flush ensues. Nevertheless, more recent studies examining thermoregulatory control question whether core temperature per se can explain the trigger for a hot flush. The primary aim of this study was to assess the contribution of increases in core temperature on the occurrence of menopausal hot flushes.

METHODS

For this purpose, 108 hot flushes were objectively assessed in a laboratory setting in 72 symptomatic postmenopausal women (aged 45.8 ± 5.1 years; body mass index 25.9 ± 4.5 kg/m) from five previously reported studies. Women rested, wearing a tube-lined suit (or trousers), which was perfused with 34C water. A subset then underwent mild heat stress (48°C water). Sweat rate, skin blood flow, blood pressure, heart rate, skin, and core temperature were measured continuously throughout. A hot flush was objectively identified during rest (spontaneous hot flush) or mild heating as an abrupt increase in sternal sweat rate. Further, a subset of symptomatic postmenopausal women (n = 22) underwent whole-body passive heating for 60 minutes to identify core temperature thresholds and sensitivities for sweat rate and cutaneous vasodilation, which were compared to a subset of premenopausal women (n = 18). Data were analyzed using t tests and/or general linear modeling, and are presented as mean (95% confidence interval).

RESULTS

In the 20 minutes before a spontaneous hot flush, core temperature increased by 0.03 ± 0.12C (P < 0.05), but only 51% of hot flushes were preceded by an increase in core temperature. During mild heating, 76% of hot flushes were preceded by an increase in core temperature. The temperature thresholds for sweating were similar, but the vasodilatory threshold was higher in postmenopausal compared with premenopausal women (37.1 ± 0.2 vs 36.8 ± 0.3°C; P = 0.06).

CONCLUSION

We provide new evidence that menopausal hot flushes are unlikely triggered by an increase in core temperature. These findings provide important information about the physiology of hot flushes that have implications for treatment and management options for menopausal hot flushes.

What's in a name: are menopausal "hot flashes" a symptom of menopause or a manifestation of neurovascular dysregulation?

Hot flashes have typically been classified as "symptoms of menopause" that should be tolerated or treated until they resolve. However, mounting evidence points to hot flashes as a manifestation of one or several underlying pathophysiological processes. Associations exist between the presence, timing of onset, severity, and duration of hot flashes, and the risk of several neurological (affecting sleep, mood, and cognition) and cardiovascular conditions. In addition, four consistent patterns of vasomotor disturbances have been identified across different countries, making it unlikely that these patterns are solely explained by socioeconomic or cultural factors. The changing hormonal environment of menopause may unmask differences in the autonomic neurovascular control mechanisms that put an individual woman at risk for chronic conditions of aging. These differences may have a genetic basis or may be acquired across the life span and are consistent with the variability of the clinical manifestations of aging observed in women after bilateral oophorectomy. It is time to investigate the pathophysiological mechanisms underlying the four patterns of vasomotor symptoms more closely, and to shift from describing hot flashes as symptoms to be tolerated to manifestations of an underlying autonomic neurovascular dysregulation that need to be addressed.

The Effects and Action Mechanisms of Phytoestrogens on Vasomotor Symptoms During Menopausal Transition: Thermoregulatory Mechanism

Background:

Phytoestrogens have recently been claimed to positively influence menopausal discomforts, including hot flashes. However, little is known about the influence of phytoestrogens on core body temperature during oestrogen fluctuation at menopause.

Objective:

Previously published findings showed that phytoestrogens could relieve menopausal complaints, thus, the present review was aimed at assessing the effects of phytoestrogens on thermoregulatory mechanism during menopausal transition.

Results:

The molecular mechanisms underlying hot flashes are complex. Oestrogen fluctuations cause hypothalamic thermoregulatory centre dysfunction, which leads to hot flashes during menopause. The phytoestrogens of interest, in relation to human health, include isoflavones, lignans, coumestans, and stilbenes, which are widely distributed in nature. The phytoestrogens are capable of reducing hot flashes via their oestrogen-like hormone actions. The potential effects of phytoestrogens on hot flashes and their molecular mechanisms of action on thermoregulatory centre are discussed in this review.

Conclusion:

The effects of phytoestrogens on these mechanisms may help explain their beneficial effects in alleviating hot flashes and other menopausal discomforts.

Thermoregulation and age

The thermoregulatory functions may vary with age. Thermosensitivity is active in neonates and children; both heat production and heat loss effector mechanisms are functional but easily exhaustable. Proportional and lasting defense against thermal challenges is difficult, and both hypothermia and hyperthermia may easily develop. Febrile or hypothermic responses to infections or endotoxin can also develop, together with confusion. In small children febrile convulsions may be dangerous. In old age the resting body temperature may be lower than in young adults. Further, thermosensitivity decreases, the thresholds for activating skin vasomotor and evaporative responses or metabolism are shifted, and responses to thermal challenges are delayed or insufficient: both hypothermia and hyperthermia may develop easily. Infection-induced fevers are often limited or absent, or replaced by hypothermia. Various types of brain damage may induce special forms of hypothermia, hyperthermia, or severe fever. Impaired mental state often accompanies hypothermia and hyperthermia, and may occasionally be a dominant feature of infection (instead of the most commonly observed fever). Aging brings about a turning point in women's life: the menopause. The well-known influence of regular hormonal cycles on the thermoregulation of a woman of fertile age gives way to menopausal hot flushes caused by estrogen withdrawal. Not all details of this thermoregulatory anomaly are fully understood yet.

Continuous transdermal nitroglycerin therapy for menopausal hot flashes: a single-arm, dose-escalation trial

OBJECTIVE

To describe the efficacy and tolerability of continuous nitroglycerin for treatment of hot flashes.

METHODS

Perimenopausal and postmenopausal women reporting at least seven hot flashes per day were recruited into a single-arm, dose-escalation trial of continuous transdermal nitroglycerin. Participants were started on a generic 0.1 mg/hour nitroglycerin patch applied daily without patch-free periods. During 4 weeks, participants escalated dosage weekly to 0.2, 0.4, or 0.6 mg/hour as tolerated, then discontinued nitroglycerin during the final week. Changes in hot flash frequency and severity were assessed using symptom diaries. Paired t tests examined change in outcomes between baseline and maximal-dose therapy and after discontinuation of nitroglycerin.

RESULTS

Of the 19 participants, mean age was 51.4 (±4.3) years. Women reported an average 10.6 (±3.0) hot flashes and 7.1 (±3.8) moderate-to-severe hot flashes per day at baseline. Eleven women escalated to 0.6 mg/hour, three to 0.4 mg/hour, two to 0.2 mg/hour, and one remained on 0.1 mg/hour nitroglycerin. Two discontinued nitroglycerin before the first outcomes assessment. Among the remaining 17 women, the average daily frequency of hot flashes decreased by 54% and the average frequency of moderate-to-severe hot flashes decreased by 69% from baseline to maximum-dose therapy (P < 0.001 for both). After discontinuing nitroglycerin, participants reported an average 23% increase in frequency of any hot flashes (P = 0.041) and 96% increase in moderate-to-severe hot flashes (P < 0.001).

CONCLUSIONS

Continuous nitroglycerin may substantially and reversibly decrease hot flash frequency and severity. If confirmed in a randomized blinded trial, it may offer a novel nonhormonal hot flash treatment.

The scientific legacy of Stephen Rothman

The year 2014 marks the centennial of events that led to the First World War ("the war to end all wars") following the assassination of Archduke Ferdinand of the crumbling Austro-Hungarian Empire. It also marks the 120th anniversary of the birth of Stephen Rothman and the 60th anniversary of the publication of his epic textbook The Physiology and Biochemistry of the Skin. In this review, we document our belief that Rothman had a seismic impact on moving investigative dermatology from a medical backwater to a scientific discipline that can hold its own with any other specialty.

Relationship between sympathetic nerve activity and aortic wave reflection characteristics in postmenopausal women

OBJECTIVE

Aortic wave reflection characteristics, such as augmentation index, are positively related to muscle sympathetic nerve activity in young men. In young women, there is an inverse relationship. We investigated whether this inverse relationship persisted in postmenopausal women.

METHODS

Muscle sympathetic nerve activity (peroneal microneurography) and arterial pressure (brachial catheter) were measured in 16 postmenopausal women (mean [SEM] age, 60 [2] y). Aortic blood pressure and wave form characteristics were synthesized from radial arterial pressure waves (applanation tonometry). Specifically, augmentation index, wave reflection amplitude, and estimated wasted left ventricular energy were calculated. These data were compared with our previously published work from an identical protocol in 23 young women (mean [SEM] age, 25 [1] y).

RESULTS

Tonic sympathetic activity was higher in postmenopausal women than in young women (64 [3] vs 24 [4] bursts/100 heartbeats). All indices of aortic wave reflection were higher in postmenopausal women than in young women (P < 0.05). Baseline sympathetic activity was inversely related to augmentation index (r = -0.63, P < 0.05), augmented pressure (r = -0.62, P < 0.05), and wasted left ventricular energy (r = -0.61, P < 0.05) in young women. Conversely, baseline sympathetic activity was positively related to augmentation index (r = 0.63, P = 0.09), augmented pressure (r = 0.69, P < 0.05), and wasted left ventricular energy (r = 0.79, P < 0.05) in postmenopausal women.

CONCLUSIONS

High levels of sympathetic activity are associated with higher indices of aortic wave reflection in postmenopausal women. Consequently, postmenopausal women with high sympathetic activity may be more at risk for developing cardiovascular diseases or experiencing adverse cardiovascular system-related events.

Miniature ambulatory skin conductance monitor and algorithm for investigating hot flash events

A skin conductance monitoring system was developed and shown to reliably acquire and record hot flash events in both supervised laboratory and unsupervised ambulatory conditions. The 7.2 × 3.8 × 1.2 cm(3) monitor consists of a disposable adhesive patch supporting two hydrogel electrodes and a reusable, miniaturized, enclosed electronic circuit board that snaps onto the electrodes. The monitor measures and records the skin conductance for seven days without external wires or telemetry and has an event marker that the subject can press whenever a hot flash is experienced. The accuracy of the system was demonstrated by comparing the number of hot flashes detected by algorithms developed during this research with the number identified by experts in hot flash studies. Three methods of detecting hot flash events were evaluated, but only two were fully developed. The two that were developed were an artificial neural network and a matched filter technique with multiple kernels implemented as a sliding form of the Pearson product-moment correlation coefficient. Both algorithms were trained on a 'development' cohort of 17 women and then validated using a second similar 'validation' cohort of 20. All subjects were between the ages of 40 and 60 and self-reported ten or more hot flashes per day over a three day period. The matched filter was the most accurate with a mean sensitivity of 0.92 and a mean specificity of 0.90 using the data from the development cohort and a mean sensitivity of 0.92 and a mean specificity of 0.87 using the data from the validation cohort. The matched filter was the method implemented in our processing software.