Cerebrovascular reactivity of free divers measured with fNIRS

Abstract

Although breath-hold diving is nowadays practiced as a competitive sports dis- cipline, its underlying physiological mechanisms enabling divers to tolerate great dive depths and durations are still not fully understood. E ect of consecutive maximal dry breath-holds was compared between two groups of free divers with di erent ex- perience levels and a control group. Hemoglobin concentration (by functional near infrared spectroscopy, fNIRS), heart rate and systemic oxygen saturation (by pulse oxymetry) measurements were performed during four consecutive maximal dry breath- holds. Breath-hold durations increased with consecutive trials in all the groups while the experienced free divers outperformed both the beginner free divers and the con- trol group. Change in hemoglobin concentration from fNIRS measurements increased in parallel with increasing breath-hold durations in free divers but remained almost constant in the control group. Systemic oxygen saturation decreased with increasing breath-hold durations for all the groups with a greater decrease for experienced free divers due to longer breath-hold durations. Breath-hold indices calculated using change in hemoglobin concentration and independently using change in Systemic oxygen sat- uration normalized to hold durations showed signi cant di erences between groups (p<0.00005 for both indices). Free diver groups exhibited a higher slope of increase of the indices among consecutive breath holds compared to the control group elucidating an enhanced reactivity to hypoxia. Our results indicate that cerebrovascular reactivity to hypercapnia can be learned and trained and the level of reactivity can be reliably quanti ed by fNIRS.|Keywords: functional Near Infrared Spectroscopy, Apnea, Breath-hold, Divers.