Fluid Loss during Exercise-Heat Stress Reduces Cardiac Vagal Autonomic Modulation
- 30 August 2019
- journal article
- research article
- Published by Ovid Technologies (Wolters Kluwer Health) in Medicine & Science in Sports & Exercise
- Vol. 52 (2), 362-369
- https://doi.org/10.1249/mss.0000000000002136
Abstract
Purpose Sweat-induced fluid loss during prolonged exercise-heat stress can compromise cardiovascular and thermoregulatory function, although its effects on cardiac autonomic modulation remain unclear. We therefore examined heart rate variability (HRV) and recovery (HRRec), as surrogates of cardiac autonomic modulation, during and after prolonged exercise in the heat with and without fluid replacement. Methods Eleven young and healthy men performed 90 min of semi-recumbent cycling in dry heat (40°C; 20% relative humidity) at a fixed rate of metabolic heat production (600 W; ~46% V˙O2peak) followed by 40-min resting recovery without fluid replacement (No-FR; ~3.4% reduction in body mass). On a separate day, participants completed the same protocol with fluid replacement (FR; 500–700 mL timed boluses) to offset sweat losses. Esophageal temperature and ECG were recorded throughout, with measurements analyzed over 10-min averaged epochs during baseline, each 30-min interval during exercise and 20-min interval during recovery. Results Esophageal temperature and heart rate were elevated in No-FR relative to FR throughout exercise (all P ≤ 0.02). The HRV indices reflecting vagal influence of heart rate including the cardiac vagal index (CVI = log10[16 × SD1 × SD2]) and root-mean-square of successive differences were attenuated throughout exercise relative to baseline in both conditions (all P < 0.05), with the magnitude of the reduction greater in the No-FR condition (all P < 0.05). Further, sample entropy was reduced throughout all time points measured during exercise in the No-FR relative to FR condition (all P ≤ 0.03). Conclusions Our unique observations indicate that while prolonged exercise heat stress attenuates the vagal influence and complexity of cardiac rhythms, that reduction is further exacerbated by fluid loss, highlighting the importance of fluid replacement in such conditions.This publication has 38 references indexed in Scilit:
- Effects of an isotonic beverage on autonomic regulation during and after exerciseJournal of the International Society of Sports Nutrition, 2013
- Cardiac Arrest during Long-Distance Running RacesThe New England Journal of Medicine, 2012
- Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysisBritish Journal of Sports Medicine, 2011
- Review and classification of variability analysis techniques with clinical applicationsBioMedical Engineering OnLine, 2011
- Human thermoregulation: separating thermal and nonthermal effects on heat lossFrontiers in Bioscience-Landmark, 2010
- Fluid replacement and heat stress during exercise alter post‐exercise cardiac haemodynamics in endurance exercise‐trained menJournal Of Physiology-London, 2009
- The influence of hydration status on heart rate variability after exercise heat stressJournal of Thermal Biology, 2005
- Heart-Rate Recovery Immediately after Exercise as a Predictor of MortalityThe New England Journal of Medicine, 1999
- Heart Rate VariabilityCirculation, 1996
- Vagally mediated heart rate recovery after exercise is accelerated in athletes but blunted in patients with chronic heart failureJournal of the American College of Cardiology, 1994