Using electrical impedance tomography to estimate tidal volume in bottlenose dolphins and cape fur seals in seawater and on land.

Marine mammals possess specialized respiratory adaptations that enable efficient gas exchange and resilience to extreme pressures during diving, yet direct observation of lung mechanics under pressure has been logistically challenging. Electrical impedance tomography (EIT) measures real-time changes in thoracic impedance, and provides continuous, regional maps of pulmonary air distribution. We validated EIT for estimating tidal volume (VT) in bottlenose dolphins (Tursiops spp.) and Cape fur seals (Arctocephalus pusillus) both on land and in water. EIT reliably tracked VT in both taxa, showing strong within-trial consistency, with between-trial variability attributable to belt placement, body position and electrode contact. EIT also generated dynamic functional images of regional ventilation, revealing spatial and temporal patterns of lung filling and emptying. These results demonstrate that EIT is the first non-invasive imaging method validated for marine mammals in seawater, representing a critical step toward visualizing lung function during diving.