The ventilatory responses of the Caecilian Typhlonectes natans to hypoxia and hypercapnia

Typhlonectes natans empty their lungs in a single extended exhalation and s ubsequently fill their lungs by using a series of 10-20 inspiratory buccal oscillations. These animals always use this breathing pattern, which effect ively separates inspiratory and expiratory airflows, unlike most urodele an d anuran amphibians that may use one to many buccal oscillations for lung i nflation and typically mix expired and inspired gases. Aquatic hypoxia had no significant effect on the breathing pattern or mechanics in these animal s. Aerial hypoxia stimulated ventilatory frequency and increased the number of inspiratory oscillations but had little effect on inspiratory and expir atory tidal volume. Aquatic hypercapnia elicited a large significant increa se in air-breathing frequency and minute ventilation compared to the small stimulation of minute ventilation seen during aerial hypercapnia. Some anim als responded to aquatic hypercapnia with a series of three or four closely spaced breaths separated by long nonventilatory periods. Overall, T. natan s showed little capacity to modulate expiratory or inspiratory tidal volume s and depended heavily on changing air-breathing frequency to meet hypoxic and hypercapnic challenges. These responses are different from those of anu rans or urodeles studied to date, which modulate both the number of ventila tory oscillations in lung-inflation cycles and the degree of lung inflation when challenged with peripheral or central chemoreceptor stimulation.