Physiological responses during a maximal dry static breath-hold in a world champion freediver

Few studies have described physiological and cardiac rhythm responses to maximal voluntary breath-holding in elite freedivers. This case study presents minute ventilation, PETO₂, PETCO₂, involuntary breathing movements (IBMs; surface electromyography), SpO₂, muscle and cerebral oxygenation (near-infrared spectroscopy), and cardiac rhythm changes (electrocardiogram) before, during, and after a maximal dry static voluntary breath-hold in a world champion freediver. Glossopharyngeal insufflation prior to the breath-hold increased forced vital capacity from 6.92 L (138% predicted) to 9.04 L (180% predicted). Compared to resting end-tidal gas pressures, the breathe-up in preparation of the breath-hold increased PETO₂ (108 mmHg to 135 mmHg) and decreased PETCO₂ (36 mmHg to 21 mmHg). The breath-hold was 06'07" in duration, of which 02'20" was spent in the easy-going phase and 03'47" in the struggle phase - the latter encompassing a total of 48 IBMs. Throughout the breath-hold, PETO₂ decreased to 38 mmHg and PETCO₂ increased to 65 mmHg. SpO₂ decreased from 97% to 73%. Muscle oxygenation decreased from 50% to 22%, whereas cerebral oxygenation remained relatively stable until the final ∼20 s of the breath-hold (∼68% to ∼62%). Heart rate variability-based markers of autonomic cardiac activity decreased during the easy-going phase, increased during the struggle phase, and normalized after. Asymptomatic bradycardia with competition between sinus bradycardia and junctional rhythm and (supra)ventricular extrasystoles manifested throughout the struggle phase and resolved after breath-hold cessation. This report of a world champion freediver shows that a long voluntary breath-hold induced transient asymptomatic cardiac arrhythmias, likely linked to the physiological stress of extreme voluntary breath-holding.