The respiratory mechanics of the yacare caiman (Caiman yacareDaudine)

The structure and function of crocodilian lungs are unique compared to other reptiles. We examine the extent to which this, and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. Respiratory mechanics of juvenile caiman were additionally measured while floating in water and submerged at 30°, 60°, and 90° to the water's surface. The static compliance of the juvenile pulmonary system (2.89±0.22 mL cmH2O 100g−1) was greater than that of adults (1.2±0.41 ml cmH2O 100g−1), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 for lungs, versus 3.39 and 1.67 mL cmH2O 100g−1 for body wall, in juveniles and adults respectively). Whole system dynamic mechanics decreased with increasing ventilation frequency (fR), but was unaffected by changes in tidal volume (VT). The vast majority of work of breathing was required to overcome elastic forces, however work to overcome resistive forces increased proportionally with fR. Work of breathing was higher in juvenile caiman submerged in water at 90°, due to an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high fR and low VT for any given minute ventilation (V̇E) in caiman of all ages.