Ventilation and gas exchange before and after voluntary static surface breath-holds in clinically healthy bottlenose dolphins, Tursiops truncatus

We measured respiratory flow (V̇), breathing frequency (fR), tidal volume (VT), breath durations, and end-expired O2 content in bottlenose dolphins (Tursiops truncatus) before and after static surface breath-holds ranging from 34 to 292 s. There was considerable variation in the end-expired O2, tidal volume VT, and fR following a breath-hold. The analysis suggests that the dolphins attempt to minimize recovery following a dive by altering VT, and fR to rapidly restore the O2 stores. For the first breath following a surface breath-hold, the end-expired O2 decreased with dive duration, while VT, and fR increased. Throughout the recovery, end-expired O2 increased while the respiratory effort (VT, fR) decreased. We propose that the dolphins alter respiratory effort following a breath-hold according to the reduction in end-expired O2 levels, allowing almost complete recovery after 1.2 min.