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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. [ABSTRACT FROM AUTHOR]

Objective. To conduct a systematic review of the possible effects of passive heating protocols on cardiovascular autonomic control in healthy individuals. Approach. The studies were obtained from MEDLINE (PubMed), LILACS (BVS), EUROPE PMC (PMC), and SCOPUS databases, simultaneously. Studies were considered eligible if they employed passive heating protocols and investigated cardiovascular autonomic control by spontaneous methods, such as heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreflex sensitivity (BRS), in healthy adults. The revised Cochrane risk-of-bias tool (RoB-2) was used to assess the risk of bias in each study. Main results. Twenty-seven studies were included in the qualitative synthesis. Whole-body heating protocols caused a reduction in cardiac vagal modulation in 14 studies, and two studies reported both increased sympathetic modulation and vagal withdrawal. Contrariwise, local-heating protocols and sauna bathing seem to increase cardiac vagal modulation. A reduction of BRS was reported in most of the studies that used whole-body heating protocols. However, heating effects on BRS remain controversial due to methodological differences among baroreflex analysis and heating protocols. Significance. Whole-body heat stress may increase sympathetic and reduce vagal modulation to the heart in healthy adults. On the other hand, local-heating therapy and sauna bathing seem to increase cardiac vagal modulation, opposing sympathetic modulation. Nonetheless, further studies should investigate acute and chronic effects of thermal therapy on cardiovascular autonomic control. [ABSTRACT FROM AUTHOR]

Fighter pilots (FP) are exposed to flight accelerations and stressful situations that defy cardiovascular control during and after flight. FP presents a smaller adjustment in sympatho‐vagal balance during tilt test after flight compared to baseline, suggesting a huge impact of flight on autonomic modulation to the heart. We undertake to test the hypothesis that FP will have a smaller vagal reentrance and lower sympathetic withdrawal during the recovery at the supine position after a prolonged active standing test that mimics flight hemodynamic demands. Twenty‐one military personnel (20–34 years old), composed of 9 FP and 12 non‐pilots (NP) matched by age, V̉O2max and body mass index were enroled in the experimental protocol. R‐R intervals were continuously recorded in the supine position for 15 min (SUPbaseline), during the prolonged active standing test (45 min) windowed in six 5 min time frames (from ORT1 to ORT6), and a recovery period in the supine position for 15 min (SUPrecovery). Heart rate variability was performed by spectral analysis to obtain the normalized low (LFn) and high (HFn) frequency components. The variation (Δ) from baseline (Δ = ORT6 − SUPbaseline) and from recovery (Δ = SUPrecovery–ORT6) periods were calculated. FP had a smaller ΔLFn (sympathetic mediated) and ΔHFn (vagal meditated) during recovery after active standing as compared to NP. Both groups showed similar changes in ΔLFn and ΔHFn during orthostatic stress compared to baseline, with no differences over time. Therefore, FP show a smaller vagal reentrance and a lower sympathetic reduction during recovery at supine following active standing compared to NP. [ABSTRACT FROM AUTHOR]

Systemic sclerosis (SSc) patients often present cardiovascular autonomic dysfunction, which is associated with the risk of arrhythmic complications and mortality. However, little is known regarding the progression of cardiac autonomic impairment over time. We aimed to evaluate the cardiac autonomic modulation among SSc with limited cutaneous (lcSSc), diffuse cutaneous (dcSSc) subset, and age-matched healthy control (HC) at baseline (t0) and five-year follow-up (t1). In this follow-up study, ECG was recorded at t0 and t1 in twenty-four SSc patients (dcSSc; n = 11 and lcSSc; n = 13) and 11 HC. The heart rate variability (HRV) analysis was conducted. The spectral analysis identified two oscillatory components, low frequency (LF) and high frequency (HF), and the sympatho-vagal balance was assessed by the LF/HF ratio. The LF/HF increased (p = 0.03), and HF reduced at t1 compared to t0 in dcSSc (p = 0.03), which did not occur in the lcSSc and HC groups. Otherwise, both lcSSc and dcSSc groups presented augmented LF/HF at t0 and t1 compared to HC (p < 0.01). In conclusion, a worsening of cardiac autonomic dysfunction is related to the dcSSc subset, in which a more extent of skin fibrosis and internal organs fibrosis is present. [ABSTRACT FROM AUTHOR]

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The article focuses on a study conducted to determine the effect of the changes of heart rate variability (HRV) at rest corresponding to orthostatic (ORT) positions, maximal oxygen uptake, physical activity level and quality of life (QoL). It also suggests that HRV at rest decreases with aging process and vagus nerve activity is connected to the increased level of physical activity, capacity and quality of life.

Objective: Impaired parasympathetic modulation increases the risk for sudden death in patients with heart diseases. Therefore, cholinergic stimulation may have a potential protective role. The aim of this study was to verify the effects of pyridostigmine bromide, a reversible cholinesterase inhibitor, on heart rate (HR), blood pressure (BP), HR and BP variability, and baroreflex sensitivity (BS). Methods: Male Wistar rats were divided in two groups: (1) treated with pyridostigmine in drinking water (7 days, n=10; PYR) and (2) a control group (n=12; CTR). BP was recorded in freely moving rats, and HR and BP variability were quantified by the standard deviation (S.D.) of the mean values during a 30-min period and by spectral analysis. BS was assessed by the ratio between pulse interval and BP power spectra (spontaneous BS) and also by the changes on HR produced by phenylephrine and sodium nitroprusside-induced BP changes. Results: Treated rats had a PYR intake of 7.91±1.90 mg/day (≈31 mg/kg/day). There were no differences between groups concerning resting HR (P=0.158), systolic BP (P=0.481), and BP variability (P=0.201). On the other hand, treatment with PYR increased HR variability on the time domain (S.D.—PYR: 13.5±5.3 ms vs. CTR: 9.9±3.6 ms; P=0.034) and frequency domain (Total power—PYR: 208.3±157.7 ms2 vs. CTR: 109.2±65.6 ms2; P=0.030). BS was also augmented with PYR for both the spontaneous method (High frequency band—PYR: 2.55±1.06 ms/mm Hg vs. CTR: 1.85±0.60 ms/mm Hg; P=0.033) and the drug-induced reflex bradycardia (PYR: 2.48±1.02 bpm/mm Hg vs. CTR: 1.54±0.58 bpm/mm Hg; P=0.024) and reflex tachycardia (PYR: 4.08±1.04 bpm/mm Hg vs. CTR: 2.95±1.30 bpm/mm Hg; P=0.037). Conclusions: In conclusion, treatment with pyridostigmine increased HR variability and BS in normal rats with no modifications on basal hemodynamic parameters. Considering that reduced HR variability and baroreflex sensitivity are independent risk factors in heart disease, the present results support the concept that cholinergic stimulation with pyridostigmine may become a therapeutic option for vagal dysfunction. [Copyright &y& Elsevier]

Although the literature demonstrates that cardiac autonomic control (CAC) might be impaired in patients with chronic pulmonary diseases, the interplay between CAC and disease severity in end-stage lung disease has not been studied yet. We investigated the effects of end-stage lung disease on CAC through the analysis of heart rate variability (HRV) among patients awaiting lung transplantation. Forty-nine patients on the waiting list for lung transplantation (LTx; 19 men, age 38 ± 15 years) and 49 healthy non-smoking controls (HC; 22 men, age 40 ± 16 years) were enrolled in a case–control study at Policlinico Hospital in Milan, Italy. LTx patients were divided into two groups, according to disease severity evaluated by the Lung Allocation Score (LAS). To assess CAC, electrocardiogram (ECG) and respiration were recorded at rest for 10 min in supine position and for 10 min during active standing. Spectral analysis identified low and high frequencies (LF, sympathetic, and HF, vagal). Symbolic analysis identified three patterns, i.e., 0V% (sympathetic) and 2UV% and 2LV% (vagal). Compared to HCs, LTx patients showed higher markers of sympathetic modulation and lower markers of vagal modulation. However, more severely affected LTx patients, compared to less severely affected ones, showed an autonomic profile characterized by loss of sympathetic modulation and predominant vagal modulation. This pattern can be due to a loss of sympathetic rhythmic oscillation and a subsequent prevalent respiratory modulation of heart rate in severely affected patients. [ABSTRACT FROM AUTHOR]

• Inspiratory muscle training improves neural control of the heart but not the baroreflex sensitivity in older women. • Breathing pattern is a putative mechanism underlying improved cardiac vagal modulation after inspiratory muscle training. • Inspiratory muscle training is a feasible method to enhance inspiratory muscle strength, respiratory and cardiac control. Even though recent studies reported a positive inspiratory muscle training (IMT) effect on cardiovascular autonomic modulation, its underlying mechanisms as the breathing pattern remain unclear. The study aimed to investigate the IMT effects on resting heart rate variability (HRV), spontaneous baroreflex sensitivity (BRS), and spontaneous breathing pattern in older women. Fourteen healthy older women participated in this study, allocated in IMT (50 % MIP; n = 8) or Sham (5% MIP; n = 6) protocols for four weeks. Blood pressure, heart rate, and ventilatory data were continuously recorded before and after interventions. After four weeks, IMT-group increased maximal inspiratory pressure and vagal-mediated HRV, following by the reduction of sympatho-mediated HRV and the inspiratory time during the spontaneous breathing cycle compared to Sham-group, but did not change BRS. Therefore, the shorter inspiratory time suggests a putative mechanism behind improved vagal-mediated HRV post-IMT in older women. [ABSTRACT FROM AUTHOR]

Inspiratory muscle training improved maximal inspiratory pressure (MIP) and vagal-mediated heart rate variability (HRV) in older women. However, it is unknown what occurs if the training is discontinued (detraining protocol). The aim of this study was to investigate the IMT and detraining effects on resting HRV in older women. Twelve healthy older women (60–72 yrs) enrolled in home-based IMT at 50% MIP (IMT-group) or placebo at 5% MIP (Sham-group) protocol for 4 weeks using a mechanical pressure threshold loading device. The participants were not engaged in any other exercise protocol at that time. During IMT and Sham interventions, the inspiratory load was adjusted weekly by the actual MIP and resting heart rate variability (HRV) evaluated. After training cessation (4 weeks of detraining), participants returned to the lab for HRV and MIP recordings. Adherence to IMT was superior to 95%. IMT increased MIP (23 ± 8 cmH 2 O) and vagal-mediated HRV (normalized HF; 37 ± 8%), following by the reduction of sympatho-vagal balance (LF/HF), from the second week to the end of the protocol compared to sham-group. After detraining, IMT-group reduced MIP (−23 ± 8 cmH 2 O) and vagal-mediated HRV (normalized HF; −38 ± 14%) returning to baseline values. In conclusion, MIP and vagal-HRV improvements induced by IMT were reversed by four weeks of detraining. • IMT provided an early improvement in cardiac vagal modulation in older women. • Detraining reversed improvements in cardiac autonomic modulation provided by IMT. • Respiratory muscle strength increased by IMT, but it was reversed by the detraining. [ABSTRACT FROM AUTHOR]

To compare autonomic heart rate variability (HRV) parameters at rest and during active stand in a population of SSc patients, taking into account SSc subsets age-matched to healthy control subjects. Sixty-nine consecutive SSc patients were enrolled in study; these included 12 subjects with early SSc, 39 with limited cutaneous (lcSSc) and 18 with diffuse cutaneous SSc (dcSSc) along with 36 age- and sex-matched healthy controls (HC). ECG and respiration were recorded in supine position and in orthostatism (ORT). HRV analysis was performed on samples of 300 beats. Spectral analysis identified two oscillatory components, low frequency (LFnu, sympathetic) and high frequency (HFnu, vagal). Symbolic analysis identified three patterns, 0 V%, (sympathetic) and 2UV% and 2LV%, (vagal). The %∆ORT was calculated from the differences between HRV in ORT and SUP, normalized (%) by the HRV values at rest. SSc as a whole had higher markers of sympathetic (LF, 0 V%) and lower markers of vagal modulation (HR, 2UV%, 2LV%) compared to HCs. In addition, %∆LFnu, %∆HFnu, %∆0 V, %∆2UV and %∆2LV were lower in SSc than HC. dcSSc and lcSSc were dissimilar to HC as far as rest indexes were concerned (↑LF/HF, ↑LFnu, ↓HFnu, ↑0 V% and ↓2UV%) while no differences could be detected between HC and EaSSc. SSc showed a reduced vagal and increased sympathetic modulation at rest and a blunted autonomic response to ORT in comparison to HC. These alterations were mostly detectable in the advanced and fibrotic forms of SSc (dcSSc and lcSSc), while EaSSc were similar to HC. • Linear and nonlinear heart rate variability is impaired in Systemic Sclerosis. • Systemic Sclerosis patients have a blunted autonomic response to orthostatic stress. • Autonomic impairment occurs during the fibro-vascular progression of the disease. • Heart rate variability is not an early maker of dysfunction in this population. [ABSTRACT FROM AUTHOR]

Abstract: To investigate whether the manipulation of brain excitability by transcranial direct current stimulation (tDCS) modulates the heart rate variability (HRV), the effect of tDCS applied at rest on the left temporal lobe in athletes (AG) and non-athletes (NAG) was evaluated. The HRV parameters (natural logarithms of LF, HF, and LF/HF) was assessed in 20 healthy men before, and immediately after tDCS and sham stimulation. After anodal tDCS in AG the parasympathetic activity (HFlog) increased (P <0.01) and the sympathetic activity (LFlog) and sympatho-vagal balance (LF/HFlog) decreased (P <0.01), whereas no significant effects were detected in NAG (P >0.05). No significant changes in HRV indexes were provoked by sham stimulation in both AG and NAG (P >0.05). In conclusion, tDCS applied on the left temporal lobe significantly increased the overall HRV in AG, enhancing the parasympathetic and decreasing the sympathetic modulation of heart rate. Consequently the sympatho-vagal balance decreased at rest in AG but not in NAG. Releasing a weak electric current to stimulate selected brain areas may induce favorable effects on the autonomic control to the heart in highly fit subjects. [Copyright &y& Elsevier]

• Acute inspiratory resistive loading provoked an acute improvement of cardiac autonomic modulation in older women. • The respiratory adjustments induced by acute inspiratory resistive load may relate to the improvement of cardiac vagal modulation in older women. We tested the hypothesis that inspiratory resistive loading (IRL) increases vagal-mediated complexity of heart rate variability (HRV) in older women. We recorded heart rate continually during 30 breaths with Sham or IRL (30 % of maximal inspiratory pressure) in sitting position. The normalized spectral power in the low (LFn) and high (HFn) frequency bands and the symbolic dynamics measures for 0 V, 2UV and 2 L V were obtained. HFn was higher and LFn was lower during IRL than Sham (p < 0.05). During IRL, 2UV component increased more than Sham (p < 0.05) while 0 V index remained unchanged (p> 0.05). In conclusion, acute IRL improved vagal modulation index of both linear (spectral analysis) and non-linear analysis (symbolic dynamics) in older women. [ABSTRACT FROM AUTHOR]