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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., (© 2023 Institute of Physics and Engineering in Medicine.)

The current study was undertaken to test the hypothesis that the high physical capacity of rowing athletes may not reverse the influence of age on cardiac autonomic control decline estimated by heart rate variability (HRV). Forty-four male subjects divided in four groups: 11 young athletes (YA; 18 ±1 year), 11 young non-athletes (YNA; 20 ±1 year), 11 middle age athletes (MAA; 43 ±6 years) and 11 middle age non-athletes (MNA; 44 ±8 years) participated in the study. Heart rate (HR) was recorded beat-by-beat for 10 minutes in supine (SUP) and 10 min in orthostatic (ORT) positions. HRV was analyzed in the frequency domain to obtain the spectral power in the high (HF) and low frequency (LF) bands, and the changes to ORT (%∆HRV) were calculated (ORT - SUP / SUP). During SUP, HF was lower in MNA and MA compared to YA and YNA, while LF was lower in MNA than YA. For %ΔHRV, %ΔHF was higher in YA than YNA, MA and MNA. The %ΔLF was not different among groups. In conclusion, aging seems to overcome the influence of physical fitness on neural regulation of the heart, as highlighted by the HRV response to active standing.

Objective. To investigate the interplay between active standing and heat stress on cardiovascular autonomic modulation in healthy individuals. Approach. Blood pressure (BP) and ECG were continuously recorded during 30 min in supine (SUP) and 6 min in orthostatic position (ORT) under thermal reference (TC; ∼24 °C) or heated environment (HOT; ∼36 °C) conditions, in a randomized order. All data collection was performed during the winter and spring seasons when typical outdoor temperatures are ∼23 °C. Spectral analysis was employed by the autoregressive model of R-R and systolic blood pressure (SBP) time series and defined, within each band, in low (LF, 0.04 to 0.15 Hz) and high (0.15-0.40 Hz) frequencies. The indices of cardiac sympathetic (LF) and cardiac parasympathetic (HF) were normalized (nu) dividing each band power by the total power subtracted the very-low component (<0.04 Hz), obtaining the cardiac autonomic balance (LF/HF) modulation. The gain of the relationship between SBP and R-R variabilities within the LF band was utilized for analysis of spontaneous baroreflex sensitivity (alpha index; α LF). Nonlinear analysis was employed through symbolic dynamics of R-R, which provided the percentage of sequences of three heart periods without changes in R-R interval (0V%; cardiac sympathetic modulation) and two significant variations (2UV% and 2LV%; cardiac vagal modulation). Main results. HOT increased 0V% and HR, and decreased α LF and 2UV% during SUP compared to TC. During ORT, HOT provokes a greater increment on HR, LF/HF and 0V%, indexes compared to ORT under TC. Significance. At rest, heat stress influences both autonomic branches, increasing sympathetic and decreasing vagal modulation and spontaneous baroreflex sensitivity. The augmented HR during active standing under heat stress seems to be mediated by a greater increment in cardiac sympathetic modulation, showing an interplay between gravitational and thermal stimulus., (© 2021 Institute of Physics and Engineering in Medicine.)

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., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Objective: 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., Methods: 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., Results: 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., Conclusion: 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., (Copyright © 2019 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.)

Purpose: Aging impairs the autonomic balance reducing the vagal and increasing the sympathetic components of heart rate variability (HRV) and this could be associated with a decline in physical capacity. Inspiratory muscle training (IMT) is a possible tool to attenuate this physical capacity decline in older women. The aim of this study was to investigate the influence of IMT in the older women on physical capacity and autonomic cardiac modulation at rest and post exercise., Methods: 20 female participants 60-72 years old were randomly allocated in two groups. One group underwent IMT set at 50% of maximum inspiratory pressure (MIP), every day for 4 weeks (IMT-group). The placebo group performed the same training procedure but with a minimal resistance (5% MIP; PLA-group). Every week, the IMT load was readjusted and the HRV evaluated at rest. The six-minute walk test (6MWT) was performed once pre and post IMT-intervention. The IMT-group and PLA-group performed the same test and intervention procedures., Results: After a 5 weeks intervention, the MIP had significantly improved in the IMT-group but not in the PLA-group (p < 0.01; es = 1.17). The high frequency power of the HRV spectrum had already improved by the second week (p < 0.01; es = 1.13) and remained elevated until the last week of intervention (p < 0.01; es = 1.43). The same positive results were described in 6MWT distance (p = 0.04; es = 0.39) and the change (∆) of heart rate recovery (HRR) from 1 min (p = 0.02; es = 0.68)., Conclusion: IMT increases HRV, improves 6MWT distance and HRR.

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 (HF(log)) increased (P<0.01) and the sympathetic activity (LF(log)) and sympatho-vagal balance (LF/HF(log)) 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., (Published by Elsevier Ireland Ltd.)

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.

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]

Purpose: Resting cardiac vagal modulation (RCVM) and postexercise vagal reactivation (PEVR) are markers of parasympathetic activity. We investigated whether adaptations in these markers to aerobic training are influenced by baseline autonomic control. Methods: Forty healthy men (19.2 ± 0.8 yr) of similar cardiorespiratory fitness (...O2peak = 50.4 ± 5.7 mL⋅kg-1⋅min-1) completed the study, being matched for autonomic activity and randomized into four groups: training low-RCVM (TL; n = 11, high-frequency power component [HF] = 48.1 ± 8.2 normalized units [n.u.]) and high-RCVM (TH; n = 11, HF = 63.1 ± 5.9 n.u.) and nonexercise control low-RCVM (CL; n = 9, HF = 47.1 ± 7.5 n.u) and high-RCVM (CH; n = 9, HF = 65.5 ± 8.3 n.u.). Aerobic training groups exercised 3 d⋅wk-1 for 40 min at 75%-85% HR reserve for 12 wk. Before and after the training period, sequences of 5-min R-R intervals were recorded at rest and immediately after maximal treadmill test to estimate (a) RCVM (HF) and (b) PEVR (root mean square of successive R-R differences--rMSSD3-5min = mean value from 3 to 5 min of recovery). Results: Training improved ...O2peak in TL (11.7% ± 5.4%, P < 0.01) and TH (7.0% ± 2.9%,P < 0.01), with no difference between groups (P = 0.70), but not in CL (0.8% ± 3.9%) and CH (1.8% ± 6.2%, P = 0.90). Only TL increased RCVM (56.6 ± 13.3 n.u., P = 0.03), approaching TH level (58.9 ± 12.3 n.u.; P = 0.60); rMSSD3-5min increased in both training groups (P < 0.01) but not in controls (P = 0.99). Relative changes in RCVM (ΔHF%) and PEVR (ΔrMSSD3-5min%) were significantly correlated in TL (r = 0.61, P = 0.04). Conclusions: PEVR after exercise increased in both exercise training groups, whereas RCVM increased only in the group with low vagal activity at baseline. Vagal reactivation may be improved by aerobic training, even when basal activity remains unaltered. [ABSTRACT FROM AUTHOR]

Introduction: Diabetic autonomic neuropathy is a complication of diabetes mellitus (DM) that can cause cardiovascular and respiratory abnormalities. The association between respiratory muscle weakness and autonomic cardiovascular neuropathy has not yet been studied. The aims of the present study were to assess respiratory muscle strength, pulmonary function, and heart rate (HR) variability in diabetic patients with and without diabetic autonomic neuropathy. Materials and methods: Twenty-four patients with type 2 DM were divided into two groups: those without diabetic autonomic neuropathy (C group, n = 12); and those with diabetic autonomic neuropathy (DAN group, n = 12). We evaluated pulmonary function, maximum static inspiratory pressure (PImax), maximum static expiratory pressure (PEmax), and HR variability. Results: The results of the pulmonary function tests were similar in both the groups. PImax was lower in the DAN group (80 ± 24 vs. 102 ± 24 cmHO, p = 0.03), but PEmax was similar in both the groups. RR intervals (878 ± 122 vs. 743 ± 88 ms; p < 0.01), standard deviation of RR intervals (28 ± 11 vs. 14 ± 4 ms; p < 0.01) and squared root of the sum of successive differences of squared RR intervals (15 ± 6 vs. 8 ± 5 ms; p < 0.01) were higher in the C group. In the DAN group, resting HR was higher (82 ± 10 vs. 69 ± 9 bpm; p = 0.01) than in the C group. There was a positive correlation between PImax and RR intervals ( r = 0.452, p = 0.02) and a negative correlation between PImax and resting HR ( r = −0.482, p = 0.01), and PImax and DM duration ( r = −0.463, p = 0.02). Conclusion: Patients with type 2 DM and autonomic neuropathy showed reduced respiratory muscle strength and less HR variability. Respiratory muscle weakness may be associated with autonomic dysfunction in these patients. [ABSTRACT FROM AUTHOR]

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 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]

Abstract: This study explored physiological mechanisms of diabetic dysfunction in baroreceptors and chemoreceptors-mediated hemodynamic responses, and cholinergic neurotransmission in 30-day diabetic rats (n =14) and controls (n =14). Basal hemodynamic data and vagal response to electrical stimulation and methacholine injection were also evaluated. Muscarinic receptors were characterized using a radioligand receptor binding assay ([3H]N methylscopolamine). Experimental diabetes (50mg/kg of STZ, i.v.) decreased systolic, diastolic, and mean arterial pressure and basal heart rate. Heart rate (HR) responses to vagal electrical stimulation (16, 32, and 64Hz) were 15%, 11%, and 14% higher in diabetics vs non-diabetics, as were HR responses to methacholine injection (−130±24, −172±18, −206±15bpm vs. −48±15, −116±12, −151±18bpm, P <0.05). Muscarinic receptor density was higher (267.4±11 vs 193.5±22fmol/mg/prot, P <0.05) in the atria of diabetic rats than in those of controls; the affinity was similar between groups. Diabetes-induced reduction of reflex responses to baro- (reflex bradycardia: −3.4±0.3 and −2.7±0.2bpm/mm Hg; reflex tachycardia: −1.6±0.1 and −1.4±0.07bpm/mm Hg, in control and diabetics, P <0.05) and chemoreceptor stimulation, enhancement of HR responsiveness to cardiac vagal electrical stimulation and methacholine stimulation, plus an increase in the number of atrial muscarinic receptors indicates reduced parasympathetic activity, which is probably derived from central nervous system derangement. [Copyright &y& Elsevier]