Inflation and deflation pressure-volume loops in anesthetized pinnipeds confirms compliant chest and lungs

Abstract

We examined structural properties of the marine mammal respiratory system, and tested Scholander's hypothesis that the chest is highly compliant by measuring the mechanical properties of the respiratory system in five species of pinniped under anesthesia (Pacific harbor seal, Phoca vitulina; northern elephant seal, Mirounga angustirostris; northern fur seal Callorhinus ursinus; California sea lion, Zalophus californianus; and Steller sea lion, Eumetopias jubatus). We found that the chest wall compliance (CCW) of all five species was greater than lung compliance (airways and alveoli, CL) as predicted by Scholander, which suggests that the chest provides little protection against alveolar collapse or lung squeeze. We also found that specific respiratory compliance was significantly greater in wild animals than in animals raised in an aquatic facility. While differences in ages between the two groups may affect this incidental finding, it is also possible that lung conditioning in free-living animals may increase pulmonary compliance and reduce the risk of lung squeeze during diving. Overall, our data indicate that compliance of excised pinniped lungs provide a good estimate of total respiratory compliance.

Respiratory function and mechanics in pinnipeds and cetaceans

“…There is evidence that muscle myoglobin concentration changes as juveniles increase their diving capacity throughout ontogeny (Noren and Williams, 2000;Noren et al, 2001), and that diving capacity alters hematology (Duffield et al, 1983;Ridgway and Harrison, 1986). In addition, studies have indicated that lung conditioning, through repeated chest compressions, alters the mechanical properties of the lung (Johansson and Schagatay, 2012;Fahlman et al, 2014). Consequently, there may be considerable physiological plasticity to alter the O 2 stores so that animals may vary muscle myoglobin concentration, pulmonary size and mechanical properties of the lungs, depending on their life history.…”

“…it has very high compliance ( Fig. 2) (Leith, 1976;Fahlman et al, 2014). In these species, relaxed FRC is close to or equal to RV.…”

“…In addition to anatomical descriptions of the thorax of some marine mammal species (Piscitelli et al, 2010), limited work has investigated the functional and mechanical properties of the respiratory system in live animals (Scholander, 1940;Olsen et al, 1969;Kooyman et al, 1971Kooyman et al, , 1973Kooyman et al, , 1975Kerem et al, 1975;Leith, 1976;Kooyman and Cornell, 1981;Kooyman and Sinnett, 1982;Kasting et al, 1989;Leith, 1989;Reed et al, 1994Reed et al, , 2000Fahlman et al, 2014Fahlman et al, , 2015bFahlman and Madigan, 2016). For example, it has been suggested that the diaphragm and intercostal muscles are important to generate high respiratory flow and rapid f R (Ridgway, 1972;Dearolf, 2003;Cotten et al, 2008).…”

“…The relationship between estimated total lung capacity (TLC est ; broken line, Kooyman, 1973) and M b for marine mammals reveals that the volume of most breaths of marine mammals is not close to the vital capacity of the animal. References: bottlenose dolphin (Fahlman et al, 2015b), gray seal (Reed et al, 1994), Weddell seal (Kooyman et al, 1971), harbor porpoise (Reed et al, 2000), California sea lion (Kerem et al, 1975;Matthews, 1977), pilot whale (Olsen et al, 1969), killer whale (Spencer et al, 1967;Kasting et al, 1989), beluga whale (Kasting et al, 1989;Epple et al, 2015), walrus (Fahlman et al, 2015a), Patagonia sea lion (Fahlman and Madigan, 2016) Denison and Kooyman, 1973;Kooyman, 1973;Tarasoff and Kooyman, 1973;Leith, 1976;Kooyman and Sinnett, 1979;Kooyman and Cornell, 1981;Fahlman et al, 2011Fahlman et al, , 2014Fahlman et al, , 2015bMoore et al, 2011Moore et al, , 2014. Studies using trained marine mammals that voluntarily participate have been used to define flowvolume characteristics (Olsen et al, 1969;Kooyman and Cornell, 1981;Fahlman et al, 2015b;Fahlman and Madigan, 2016).…”

“…Piscitelli et al, 2013), but these reviews focus on the structural properties of excised tissues, which may not always reflect the functional properties of live animals (Kooyman, 1973;Ponganis, 2015). For example, compliance estimates of excised tissues do not account for the influence of surrounding structures that encase the respiratory system (Cozzi et al, 2005;Fahlman et al, 2011Fahlman et al, , 2014Moore et al, 2014). Likewise, pulmonary volume changes during compression of entire dead specimens cannot account for the potential effects of blood engorgement of the tracheal mucosa in cetaceans (Leith, 1976;Cozzi et al, 2005;Davenport et al, 2013).…”