tVNS acutely improves cBRS and autonomic modulation in healthy young men.

Acute IHG exercise increases cBRS and cardiac vagal activity in healthy young subjects, but the magnitude and the time course of changes in cBRS differ between men and women.

BackgroundRecent studies have shown that isometric handgrip (IHG) training reduces resting arterial blood pressure (BP) in both normotensive and hypertensive populations, but the mechanisms underlying these adaptations remain unclear. Furthermore, little is known regarding the effects of a single bout of IHG on the neural control of BP in humans. This becomes important given the fact that chronic adaptations may result from temporal summation of acute responses. In addition, the majority of studies regarding cardiovascular effects of IHG are performed in men and the possible sex differences in this context are unknown.AimTo test the hypothesis that neural control of BP following a single bout of IHG exercise are different between men and women.MethodsEight healthy men (24 ± 3 years) and 10 healthy women (23 ± 4 years) randomly performed a single bout (four 2‐min static contractions) of experimental (30% MVC) or sham (3% MVC) bilateral IHG exercise. All women are non‐oral contraceptives users and performed experiments in the early follicular phase of the menstrual cycle. Beat‐to‐beat heart rate (HR) and arterial BP was continuously monitored using finger photoplethysmography (Human NIBP, AD instruments) before and following IHG exercise (5–10 and 25–30 min of recovery). Spontaneous cardiac baroreflex sensitivity (cBRS) was assessed via sequence technique (CardioSeries v2.4, Brazil). Power spectral analysis of HR variability (HRV) was employed (CardioSeries v2.4, Brazil) and the ratio between low and high frequency of HRV (LF/HF) was used as a surrogate of sympathovagal balance.ResultsBaseline HR was greater while arterial BP and cBRS gain were lower in women compared with men (P<0.05). Following IHG exercise, SBP increased in men (Δ7 ± 1 mmHg, 10‐min vs. rest, P<0.05), but was unchanged in women (Δ2 ± 1 mmHg, 10‐min vs. rest, P>0.05). At 10‐min following IHG exercise, HR significantly decreased (Δ‐7 ± 1 bpm, P<0.01) and remained attenuated at 30‐min time point (Δ−3 ± 1 bpm, P<0.05) in women, but was unchanged in men (10‐min: Δ−2 ± 1 bpm, and 30‐min: Δ1 ± 2 bpm, P>0.05). In women, cBRS gain significantly increased from rest at 10‐min following IHG (Δ23.7 ± 7%, P=0.01) and returned to baseline values at 30‐min of recovery (14.9 ± 2.0 ms/mmHg, P>0.05). In contrast, no differences were found in cBRS gain in men following IHG (P>0.05). In addition, RMSSD and HF components of HRV, a proxy of cardiac vagal activity, were increased at 10‐min following IHG in women while no differences were found in men. LF/HF ratio was not affected by IHG trials. All physiological variables were unaffected by the sham protocol in both groups.ConclusionThese results allow us to conclude that the acute effects of IHG exercise on neural control of BP is sex dependent and baseline sex differences in spontaneous cBRS were acutely abolished after a single bout of IHG exercise.Support or Funding InformationCAPES, CNPq and FAPDF.

BackgroundDespite positive outcomes across a variety of disease states, invasive vagus nerve stimulation (VNS) has been associated with adverse side‐effects. Given this, non‐invasive VNS (tVNS) via the auricular branch of the vagus nerve (ABVN) has been proposed as an alternative approach. However, the mechanisms underlying these positive outcomes remain unclear. Therefore, we controlled the sensory effects (placebo) to investigate if tVNS acutely improves blood pressure (BP) control.MethodsThirteen healthy men (23±1yrs) were randomized across three experimental visits in a random order. In active tVNS, electrodes were placed on the tragus of the ear and electrical current was applied by using a Transcutaneous Electrical Nerve Stimulation device. A time‐ control visit was performed with the electrodes placed on tragus, but no current was applied (sham‐T). Additionally, to avoid a confounding sensory effect, another sham protocol was performed with same electrical current of the active visit, but the electrodes were placed on the ear lobe (an area without cutaneous nerve endings from the vagus – sham‐L). Before interventions were applied, we inform to subjects that both active tVNS and sham‐L would not cause any harm. Beat‐to‐beat heart rate (HR) and BP were monitored at rest, during tVNS (active, sham‐T and sham‐L) and recovery. Spontaneous cardiac baroreflex sensitivity (cBRS) was measured via sequence technique. Both HR (LF/HF) and BP variability (BPV) were also measured.ResultsArterial BP and BPV were not affected by any active or sham protocols (P>0.05). HR and LF/HF ratio decreased (Δ–3.4±1% and Δ–17±10%, P<0.05, respectively) and cBRS increased (Δ20±7%, P<0.05) only during active tVNS, but were unchanged during both sham protocols (P>0.05).ConclusionThe results of the present study provide evidence that tVNS acutely improves neural control of BP in healthy young men. These findings allow us to suggest that spontaneous cBRS and cardiac sympathovagal balance could play a role in the mechanisms involved in previously reported beneficial outcomes caused by tVNS. Future studies are needed to confirm these findings in older and diseased populations.Support or Funding InformationJ.L.S., A.L.T., P.M.M. have been supported by scholarships from Coordination for the Improvement of Higher Education Personnel (CAPES).