Pulmonary Mechanoreceptors and the Modulation of Ventilatory Pattern and Variability in the Marine Toad, Bufo marinus

Abstract

Previous studies reveal that chemoreceptors and pulmonary stretch receptors (PSR) have distinct effects on respiratory patterns and mechanics in toads. Removal of pulmonary feedback by vagotomy modifies behavior of glottal and narial valves, but has no effect on respiratory patterns. Since vagotomy may have a transformational effect on ventilation, I looked at the relationships between pulmonary feedback and ventilatory mechanics, pattern, and variability by unidirectionally ventilating (UDV) toads’ lungs to set lung pressure and volume. UDV dampens oscillations in both slowly and rapidly adapting PSRs. Changes in lung pressure did not affect narial and glottal timing during inflation breaths in UDV toads. This result indicates that the coordination of narial and glottal valves do not depend directly on PSR output and that studies reporting alteration of valve timing in vagotomized toads may be looking at a transformational effect caused by denervation. Buccal pump stroke, also became significantly slower while ventilatory entropy became smaller as static lung volume was increased. I conclude that levels of PSR output are relevant to the control of buccal pumping frequency but not valve timings and that qualitative aspects of PSR activity (presence of oscillations) are important for generation of adaptive variation in the system’s output.