... For passive alveolar collapse, the structural properties of the respiratory system, and the diving lung volume will affect the alveolar collapse depth (Kooyman and Sinnett, 1982;Bostrom et al., 2008;Fahlman et al., 2009;Fitz-Clarke, 2009a;McDonald and Ponganis, 2012). A number of studies have defined the structural properties from excised tissues, anesthetized and awake animals (Denison and Kooyman, 1973;Tarasoff and Kooyman, 1973;Leith, 1976;Kooyman and Sinnett, 1979;Cozzi et al., 2005;Piscitelli et al., 2010;Bagnoli et al., 2011;Davenport et al., 2013Davenport et al., , 2014Fahlman et al., 2014aFahlman et al., , 2015Fahlman et al., , 2017bFahlman et al., , 2018cMoore C. et al., 2014;Fahlman and Madigan, 2016). In general, both lung and chest compliance, measures of structural compressibility, are greater in marine as compared with terrestrial mammals (Olsen et al., 1969;Denison et al., 1971;Denison and Kooyman, 1973;Tarasoff and Kooyman, 1973;Leith, 1976Leith, , 1989Kooyman and Sinnett, 1979;Cozzi et al., 2005;Piscitelli et al., 2010;Bagnoli et al., 2011;Fahlman et al., 2011Fahlman et al., , 2014aFahlman et al., , 2017bFahlman et al., , 2018bDavenport et al., 2013;Moore C. et al., 2014;Denk et al., 2020). ...