The influence of the post-hepatic septum and abdominal volume on breathing mechanics in the lizard Salvator merianae (Squamata: Teiidae).

Teiid lizards possess an incomplete post-hepatic septum (PHS) separating the lungs and liver from the remaining viscera, and within this group, Salvator merianae has the most complete PHS. In this study, we explored the combined effects of the presence of the PHS and alterations in abdominal volume on the mechanics of the respiratory system. The PHS is believed to act as a mechanical barrier, mitigating the impact of the viscera on the lungs. Using established protocols, we determined static (Cstat) and dynamic (Cdyn) compliance, lung volume and work of breathing for the respiratory system in tegu lizards with intact (PHS+) or removed (PHS-) PHS, combined with (balloon+) or without (balloon-) increased abdominal volume. The removal of the PHS significantly reduced resting lung volume and Cdyn, as well as significantly increasing the work of breathing. An increase in abdominal volume significantly reduced Cstat, Cdyn, and resting and maximum lung volume. However, the work of breathing increased less in the PHS+/balloon+ treatment than in the PHS- treatments. These results highlight the barrier function of the PHS within the tegu lizard's body cavity. The septum effectively reduces the impact of the viscera on the respiratory system, enabling the lungs to be ventilated at a low work level, even when abdominal volume is increased. The presence of the PHS in teiid lizards underscores how extrapulmonary structures, such as septal divisions of the body cavity, can profoundly affect pulmonary breathing mechanics.

Modeling of the respiratory system of the long-necked Triassic reptile Tanystropheus (Archosauromorpha).

All known species of the Triassic archosauromorph genus Tanystropheus are known to have had the longest neck in proportion to their torso. This feature is related to a series of ventilatory challenges since an increase in neck length also increases airway length and, therefore, the volume of stagnant air that does not reach the lungs, the dead space volume. Based on this challenge, the objective of the present study was to model the type of respiratory system of Tanystropheus able to meet its metabolic demands during the early Triassic period. The modeling was based on allometric relations for morphological and physiological ventilatory and metabolic variables, and to do so, the mean body mass of Tanystropheus was estimated based on three different methods. In addition, the tracheal airflow was also estimated based on the proportions of Tanystropheus elongated neck, the results of allometric modeling, and fundamental equations of fluid mechanics. The estimation of the body mass indicated that an animal of 3.6 m would possess a body mass of 50.6 ± 21.6 kg. Allometric modeling suggested that the respiratory system best suited to Tanystropheus' oxygen demands, especially during activity, would be a generic reptilian-like respiratory system composed of multicameral lungs. The best respiratory pattern to maintain adequate tracheal flow rates and effective pulmonary ventilation would be one ventilating the relatively narrower trachea at lower frequencies to deal with tracheal dead space volume.

The influence of the post-pulmonary septum and submersion on the pulmonary mechanics of Trachemys scripta (Cryptodira: Emydidae).

The respiratory system of chelonians needs to function within a mostly solid carapace, with ventilation depending on movements of the flanks. When submerged, inspiration has to work against hydrostatic pressure. We examined breathing mechanics in Trachemys scripta while underwater. Additionally, as the respiratory system of T. scripta possesses a well-developed post-pulmonary septum (PPS), we investigated its role by analyzing the breathing mechanics of lungs with and without their PPS attached. Static compliance was significantly increased in submerged animals and in animals with and without their PPS, while removal of the PPS did not result in a significantly different static compliance. Dynamic compliance was significantly affected by changes in volume and frequency in every treatment, with submergence significantly decreasing dynamic compliance. The presence of the PPS significantly increased dynamic compliance. Submersion did not significantly alter work per ventilation, but caused minute work of breathing to be much greater at any frequency and ventilation level analyzed. Lungs with or without their PPS did not show significantly different work per ventilation when compared with the intact animal. Our results demonstrate that submersion results in significantly altered breathing mechanics, increasing minute work of breathing greatly. The PPS was shown to maintain a constant volume within the animal's body cavity, wherein the lungs can be ventilated more easily, highlighting the importance of this coelomic subdivision in the chelonian body cavity.