Women have a greater cardiac vagal withdrawal to heat stress compared to men.

The heated environment shifts the sympatho-vagal balance toward sympathetic predominance and vagal withdrawal. Women's heart is more reliant on vagal autonomic control, while men's heart is more dependent on sympathetic control. However, sex differences in cardiovascular autonomic responses to heat stress remain unknown. We aimed to investigate the cardiovascular autonomic regulation under heat stress between sexes. Thirty-two young participants (27 ± 4 years old; 16 women) were enrolled in a single visit, resting for 30min at baseline (thermal reference condition TC; ∼24°C) and 30min under a heated environment (HOT; ∼38°C). Blood pressure (BP), skin temperature, electrocardiogram, and respiratory oscillations were continuously recorded. The heart rate variability (HRV) was assessed by spectral analysis (low-frequency [LFnu; sympathetic and vagal] and high-frequency [HFnu; vagal]), and symbolic analysis (0 V% [sympathetic] and 2UV%, and 2LV% [vagal]). The spontaneous baroreflex sensitivity (BRS) was calculated by the gain between BP and R-R within the LF band (αLF). The estimated maximal aerobic capacity and body surface area were employed as covariates in sex comparisons. The effects of HOT were the following: 1) Women have a greater cardiac vagal withdrawal to heat stress compared to men; 2) Sex differences on cardiac autonomic response to heat stress exist after controlling for the effect of estimated physical fitness and body surface area. Therefore, heat stress provokes a higher vagal withdrawal to the heart in women compared to men. It could be attributed to sex per se since significant differences between men and women were not modified after covariate analysis.

Sex differences in blood pressure regulation during the isometric exercise under heated environment.

In the absence of heat stress, females increase blood pressure (BP) during isometric handgrip exercise due to cardiac output more than total peripheral resistance (TPR) compared to men. Although heat stress seems to blunt BP responses at rest and during handgrip, possible sex differences remained unknown. We hypothesized that BP responses during handgrip under a heated environment (HOT) will be different between men and women. Eight healthy men (29 ± 6 years) and eight women (26 ± 4 years) participated in this study. The experimental protocol was separated into two environmental conditions: HOT (~ 36 °C) and thermoneutral (TC; ~ 24 °C). In both conditions, participants rested for 30 min and performed the handgrip for 3 min. BP, heart rate (HR) stroke volume and cardiac output were continuously recorded, and TPR was calculated (TPR = mean blood pressure (MBP)/cardiac output). HOT reduced BP and TPR at baseline and during handgrip in females as compared to TC, while males showed similar responses in both thermal conditions. HR was higher under HOT in both groups. Cardiac output and stroke volume were not different under HOT compared to TC for females. In males, cardiac output increased at the last minute of handgrip under HOT through augmented HR, because stroke volume was unchanged. In conclusion, the main effect of HOT was to shift downwards BP and total peripheral resistance at rest and during isometric exercise in females. In males, the combination of handgrip and HOT increased cardiac output by augmented HR, whereas BP presented similar responses between thermal conditions during handgrip.

Assessment of vascular function in HIV-infected patients.

PURPOSE: The vascular function in HIV-infected persons under HAART and non-HIV-infected persons was investigated. METHOD: 18 HIV-positive patients and 23 HIV-negative subjects (14 younger group and 9 older group) were evaluated for microvascular vasodilatation during postocclusive reactive hyperemia (PORH) and during prolonged local thermal hyperemia; overall microvascular flux increase induced by iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) and large artery stiffness (SI(DVP)). RESULTS: Cutaneous vascular conductance (CVC) responses to ACh were lower in HIV patients compared to both HIV-negative groups (mean [SEM]) (HIV positive: 878.2 [99.5]; older HIV negative: 1129.3 [231.6]; younger HIV negative: 1366.5 [172.6] % baseline). Regarding SNP iontophoresis, HIV-positive and older HIV-negative groups showed lower CVC responses than younger HIV-negative group (HIV positive: 1043.0 [164.6]; older HIV-negative: 980.8 [108.3]; younger HIV-negative: 1757.3 [245.1] % baseline). Vasodilatation induced by thermal hyperemia (HIV positive: 1.63 [0.11]; older HIV negative: 1.48 [0.08]; younger HIV negative: 1.85 [0.27] perfusion units/mm Hg) and PORH (HIV positive: 0.374 [0.025]; older HIV negative: 0.326 [0.025]; younger HIV negative: 0.326 [0.037] PU/mm Hg) were similar between all groups. SIDVP was greater in HIV and older healthy groups than younger healthy group (HIV positive: 9.17 [0.42]; older HIV negative: 8.19 [0.43]; younger HIV negative: 6.42 [0.22] m/s). CONCLUSION: HIV-infected patients under HAART exhibited slight but nonsignificant lower microvascular reactivity to pharmacological stimuli and increased arterial stiffness compared to age-matched HIV-negative subjects. Comparison of both HIV-positive and older HIV-negative groups with younger HIV-negative subjects suggests that age plays a major role in microvascular reactivity regardless the HIV-infection.

Coronary artery bypass surgery and longitudinal evaluation of the autonomic cardiovascular function.

INTRODUCTION: Imbalance in autonomic cardiovascular function increases the risk for sudden death in patients with coronary artery disease (CAD), but the time course of the impact of coronary artery bypass grafting (CABG) on autonomic function has been little studied. Thus, the purpose of the present study was to determine the effects of the CABG on the cardiovascular autonomic function. METHODS: Patients undergoing CABG (n = 13) and two matched control groups (patients with CAD who refused surgical treatment [n = 9], and healthy volunteers [n = 9]) underwent a prospective longitudinal study consisting of autonomic evaluation before and after (3, 6, 15, 30, 60, and 90 days) surgery, including measurement of heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and Valsalva maneuver. RESULTS: After CABG there was a decrease in, and a later recovery of, (1) the HRV in the time domain and in the frequency domain, (2) RSA, and (3) Valsalva maneuver. CONCLUSIONS: CABG caused an impairment, reversible after 60 days, of cardiovascular autonomic function, with a maximal decrease on about the sixth day after surgery.