The nature of the ventilatory period in crocodilian respiration

Abstract

This paper examines the ventilatory phase of respiratory cycles of caimans and alligators to see if the terms diphasic and triphasic as defined by Boelaert are appropriate. Impedance pneumograms and mechanical recordings show triphasic ventilatory cycles for single breaths and for the last breath in a series, but other breaths in a series are diphasic. Experiments using EMG, an intrapulmonary pressure gauge, and a whole body plethysmograph show that (1) with respect to muscular activity, ventilation is diphasic; (2) with regard to intrapulmonary-endotracheal pressures, ventilation is triphasic; (3) with regard to total body volume, ventilation in quiet animals is diphasic, but triphasic during excitement. It is concluded that all breaths are normally diphasic and changes in intrapulmonary-endotracheal pressure, external dimensions, and impedance, simulating an E 2 phase, are brought about by passive recoil of viscera. It is suggested that the term “shift” rather than the “E 2 expiration” of Boelaert or the “compression” of McCutcheon is appropriate to the change seen after the last inspiration of a series or after an isolated inspiration.