Circulatory effects of apnoea in elite breath‐hold divers

Aim: Voluntary apnoea induces several physiological adaptations, including bradycardia, arterial hypertension and redistribution of regional blood flows. Elite breath‐hold divers (BHDs) are able to maintain very long apnoea, inducing severe hypoxaemia without brain injury or black‐out. It has thus been hypothesized that they develop protection mechanisms against hypoxia, as well as a decrease in overall oxygen uptake. Methods: To test this hypothesis, the apnoea response was studied in BHDs and non‐divers (NDs) during static and dynamic apnoeas (SA, DA). Heart rate, arterial oxygen saturation (SaO₂), and popliteal artery blood flow were recorded to investigate the oxygen‐conserving effect of apnoea response, and the internal carotid artery blood flow was used to examine the mechanisms of cerebral protection. Results: The bradycardia and peripheral vasoconstriction were accentuated in BHDs compared with NDs (P < 0.01), in association with a smaller SaO₂ decrease (?2.7% vs. ?4.9% during SA, P < 0.01 and ?6% vs. ?11.3% during DA, P < 0.01). Greater increase in carotid artery blood flow was also measured during apnoea in BHDs than in controls. Conclusion: These results confirm that elite divers present a potentiation of the well‐known apnoea response in both SA and DA conditions. This response is associated with higher brain perfusion which may partly explain the high levels of world apnoea records.