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

We measured respiratory flow ( V ), breathing frequency ( f R ), tidal volume ( V T ), breath duration and end-expired O 2 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 O 2 , V T and f R following a breath-hold. The analysis suggests that the dolphins attempt to minimize recovery following a dive by altering V T and f R to rapidly replenish the O 2 stores. For the first breath following a surface breath-hold, the end-expired O 2 decreased with dive duration, while V T and f R increased. Throughout the recovery period, end-expired O 2 increased while the respiratory effort ( V T , f R ) decreased. We propose that the dolphins alter respiratory effort following a breath-hold according to the reduction in end-expired O 2 levels, allowing almost complete recovery after 1.2 min.