We investigated whether the involuntary breathing movements (IBM) during struggle phase of breath holding, 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 breath holds in 8 elite divers. The frequency of IBM increased (by approximately 100%) and their duration decreased (~30%) towards the end of the struggle phase, whereas the amplitude was unchanged (compared to the beginning of the struggle phase). In all subjects a consistent increase in bdHb and bTHb was also found during struggle phase, whereas bO₂Hb changed biphasically; it initially increased until the middle of the struggle phase, with the subsequent relative decline at the end of the breath hold. 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 (primarily by restoration of the stroke volume). 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.