Breathing response of the tegu lizard to 1–4% CO 2 in the mouth and nose or inspired into the lungs

Abstract

This study investigated the influence on ventilation of elevated CO 2 in the nasal and buccal cavities (NaBuCO 2) vs the effect of elevated CO 2 levels inspired into the lungs (LuCO 2). Separate gas sources were used to independent alter NaBuCo 2 and LuCo 2. As little as 1% NaBuCO 2 or LuCO 2 significantly increased the pause duration between the active expiratory-inspiratory cycles. Elevated NaBuCO 2 caused minor changes in tidal volume, mean inspiratory and expiratory flow, and inspiratory and expiratory durations with a significant reduction in total ventilation. Elevated LuCO 2 had little effect on inspiratory or expiratory durations but unlike CO 2 in the upper airways, significantly increased tidal volume and mean inspiratory and expiratory flows. This study demonstrates that the increased pause duration seen in the tegu lizard to elevated environmental CO 2 is due to a receptor response in the buccal or nasal cavities and also to elevated CO 2 concetrations inpired into the lungs. Sensitivity of the ventilatory response to CO 2 in the upper airways is well within a physiologically relevant range.