Autonomic regulation of the heart and arrhythmogenesis in trained breath‐hold divers

Breath‐hold divers are known to develop cardiac autonomic changes and brady‐arrthymias during prolonged breath‐holding (BH). The effects of BH‐induced hypoxemia were investigated upon both cardiac autonomic status and arrhythmogenesis by comparing breath‐hold divers (BHDs) to non‐divers (NDs). Eighteen participants (9 BHDs, 9 NDs) performed a maximal voluntary BH with face immersion. BHDs were asked to perform an additional BH at water surface to increase the degree of hypoxemia. Beat‐to‐beat changes in heart rate (HR), short‐term fractal scaling exponent (DFAα1), the number of arrhythmic events [premature ventricular contractions (PVCs), premature atrial contractions (PACs)] and peripheral oxygen saturation (SpO 2 ) were recorded during and immediately following BH. The corrected QT‐intervals (QTc) were analyzed pre‐ and post‐acute BH. A regression‐based model was used to split BH into a normoxic (NX) and a hypoxemic phase (HX). During the HX phase of BH, BHDs showed a progressive decrease in DFAα1 during BH with face immersion ( p < 0.01) and BH with whole‐body immersion ( p < 0.01) whereas NDs did not ( p > 0.05). In addition, BHDs had more arrhythmic events during the HX of BH with whole‐body immersion when compared to the corresponding NX phase (5.9 ± 6.7 vs 0.4 ± 1.3; p < 0.05; respectively). The number of PVCs was negatively correlated with SpO 2 during BH with whole‐body immersion ( r = −0.72; p < 0.05). The hypoxemic stage of voluntary BH is concomitant with significant cardiac autonomic changes toward a synergistic sympathetic and parasympathetic stimulation. Co‐activation led ultimately to increased bradycardic response and cardiac electrophysiological disturbances.