TRAISTER, E.A.*; MCLELLAN, W.A.; PABST, D.A.; DEAROLF, J.L.; Hendrix College, Conway, AR; University of North Carolina at Wilmington; University of North Carolina at Wilmington; Hendrix College, Conway, AR: Morphological analyses of cetacean diaphragms: correlations with ventilatory functions

The diaphragm is the main muscle of inspiration in terrestrial mammals. However the role of this muscle in the ventilatory performance of cetaceans (whales, dolphins, and porpoises) is unclear. To better elucidate the role of the diaphragm in cetaceans, we designed a study to determine if correlations exist between a number of ventilatory parameters (breathing frequency, inspiratory time, and maximum breath-hold dive time) taken from the literature and selected morphological characteristics of cetacean diaphragms. These characteristics included: fiber-type profile, myoglobin concentration, and succinic dehydrogenase (SDH), nicatinamide adenine dinucleotide tetrazoleum reducatase (NADH-TR), and alpha-glycerophosphate dehydrogenase (GPD) concentrations. Interestingly, the only morphological characteristics that varied between species were fiber-type profile (range: 33 to 66% slow-twitch fibers) and myoglobin concentration (range: 0.99 to 3.94 g/100 g muscle). Neither characteristic correlated with breath-hold dive time, but preliminary analyses demonstrate that they are related to ventilatory frequency (breaths per minute) and inspiratory time. These results suggest that the diaphragm is not involved in breath-hold, but this muscle may play a role in driving inspiration. However, unlike terrestrial mammals, the concentration of oxidative enzymes (SDH and NADH-TR) in the diaphragm did not correlate with ventilatory frequency. Thus, further studies will be needed to finally identify the role of the diaphragm in cetacean ventilation.