Reassessment of chemical control of breathing in undisturbed bullfrogs, Lithobates catesbeianus, using measurements of pulmonary ventilation

• Preexisting techniques were adapted to measure pulmonary ventilation in 
 conscience bullfrogs. 

• Ventilatory responses to hypoxia and hypercarbia have distinct dynamic profiles with tidal volume and frequency differentially regulated.
• Responses to hypercarbia were small; they mainly involved increases in tidal volume (VT), but a robust post-hypercarbic hyperpnea.

Despite the importance of bullfrogs (Lithobates catesbeianus) as models in respiratory control, chemical control of breathing in conscious bullfrogs has never been assessed with methods that measure the tidal volume (VT). This has precluded the calculation of important respiratory variables like minute ventilation (V.E) and air convection requirement. To address this, we adapted airflow pneumotachography for use in bullfrogs and reassessed chemical control of breathing. We show that V.E measured with pneumotachography produces breathing pattern and metabolism values consistent with anurans. Second, we confirm that bullfrogs have small ventilatory responses to hypercarbia that include increases in tidal volume and a post-hypercarbic hyperpnea. We observed that the magnitude of the post-hypercarbic hyperpnea does not depend on ventilatory responses during hypercarbia. Finally, we showed that increases in breathing frequency and VT during hypoxia are differentially regulated with time. These findings comprise the first complete assessment of hypercarbic and hypoxic V.E responses in intact bullfrogs and emphasize the importance of measuring VT.