Cardiovascular responses to dry resting apnoeas in elite divers while breathing pure oxygen

Highlights • We investigated the effects of oxygen breathing on the cardiovascular responses to apnoea. • In oxygen as in air, the three phases of the cardiovascular responses to apnoea were observed. • The values of investigated variables were the same in the two conditions, but the duration of steady phase II and unsteady phase III was longer in oxygen than in air, as hypothesized. • These results support the concept that the end of phase II may correspond to the physiological breaking point of apnoea. • The lack of hypoxaemia in oxygen apnoeas suggests that, if indeed chemoreflexes determine phase III, increasing CO2 stores might play a key role in eliciting chemoreflex activation.