Abstract
Assessment of compression dynamics of the marine mammal tracheobronchial tree at depth is crucial to understanding vital physiologic processes such as gas exchange during diving.1,2 Study of the unique anatomy of marine mammal airways has led to much thought regarding the possible compression of these structures under pressure.3,4 No studies to date have quantified changes in tracheobronchial volume with increasing diving pressures in cetaceans or pinnipeds. A freshly deceased harbor seal, grey seal, harp seal, harbor porpoise, and common dolphin were imaged post-mortem via CT in a radiolucent hyperbaric chamber as previously described by Moore et al. (2011).5 Volume reconstructions of the trachea and bronchi of the pinnipeds and bronchi of the cetaceans provided volume measurements of all airways for each simulated diving treatment. Significant decreases in airway volume with increasing pressure occurred in all species, with the harbor seal and common dolphin nearing complete collapse at the highest pressures. Differences between 50% and 100% lung inflation treatments in the common dolphin indicated the importance of air in maintaining patent airways, and caudal to cranial airway collapse patterns were observed. These findings indicate potential species-specific variability in tracheobronchial compliance, and that cessation of gas exchange may occur at greater depths than that predicted in models assuming rigid airways. This may increase the likelihood of decompression sickness in these animals during diving.6
Acknowledgements
We wish to thank the following for their technical advice and assistance: Nicholas Hemphill and Katie Tucker-Mohl, VMD, DAVCR, Marina Ivančić, DVM, DAVCR and Debra A. Fiorito, DVM, FAVD, DAVDC. We also recognize the help of Darlene Ketten, Julie Arruda and Scott Cramer in generating the original data, a project funded by US Office of Naval Research Award Number: N000140811220. Deceased animals were received under NOAA permit no. 932-1905-00/MA-009526 if fishery bycaught, and under a letter from the NOAA Greater Atlantic Regional Fisheries Office to M.M. if stranded.
*Presenting author
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