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Involuntary breathing movements improve cerebral oxygenation during apnea struggle phase in elite divers

We investigated whether the involuntary breathing movements (IBM) during struggle phase of apnea, together with peripheral vasoconstriction and progressive hypercapnia, have a positive effect in maintaining cerebral blood volume. The central hemodynamics, arterial oxygen saturation, brain regional oxyhemoglobin, deoxyhemoglobin and total hemoglobin changes (bO2Hb, bdHb and bTHb, respectively) and IBM were monitored during maximal dry apneas in 8 elite divers. The frequency of IBM increased and their duration decreased towards the end of the struggle phase, whereas the amplitude was unchanged. In all subjects a consistent increase in bdHb and bTHb was also found during struggle phase, whereas bO2Hb changed biphasically. Mean arterial pressure (MAP) was elevated during the struggle phase although there was no further rise in the peripheral resistance, suggesting unchanged peripheral vasoconstriction and implying the beneficial influence of the IBM on the cardiac output recovery. The IBM‐induced short lasting sudden increases in MAP were followed by similar oscillations in bO2Hb. These results suggest that an increase in the cerebral blood volume observed during the struggle phase of dry apnea is most likely caused by the IBM at the time of the hypercapnia‐induced cerebral vasodilatation and peripheral vasoconstriction.