Updating and validating a currently-used gas dynamics model using parameter estimates for California sea lions (Zalophus californianus)

Theoretical models are used to predict how breath-hold diving vertebrates manage O2, CO2, and N2 while underwater. One recent gas dynamics model used available lung and tracheal compliance data from various species to predict O2, CO2, and N2¬ tensions in multiple tissues of diving marine mammals.

As variation in respiratory compliance significantly affects alveolar compression and pulmonary shunt, the objective of this thesis was to evaluate changes in model output when using species-specific parameters from California sea lions (Zalophus californianus). I explored the effects of lung and dead space compliance on the uptake of N2, O2, and CO2 in various tissues during a series of hypothetical dives.

The updated parameters allowed for increased compliance of the lungs and an increased stiffness in the trachea. When comparing updated model output with a model using previous compliance values, there was a large decrease in N2 uptake but little change in O2 and CO2 levels. Therefore, previous models may overestimate N2 tensions and the risk of gas-related disease, such as decompression sickness (DCS), in marine mammals.

Using recently-collected empirical arterial and venous PO2 data, I was able to test the model output against species-specific data for the first time. This showed that lung collapse can be altered by changing physiological parameters and that model input parameters may need to vary between dives. The results of this study suggest that previous models using data that is not species-specific may inaccurately predict the risk of gas-related disease in marine mammals. Future research can use physiological parameters from other marine mammal species as they become available to best estimate the risk of DCS in those species.