Cardiac frequency and blood pressure were measured during voluntary diving in the bullfrog,
Lithobates catesbeianus, exposed to 15°C or, alternatively, 25°C. Diving caused bradycardia and reduction of blood pressure. Cardiac frequency was 27.1  2.2 for breath periods and 19.3  2.7 for diving periods at 15°C, and 47.7  4.4 and 35.3  3.6 for 25°C. Systolic blood pressure was 39,6  0,9 for breath periods and 36,2  0,4 for diving periods at 15°C, and 42,4  1,0 and 39,8  0,5 at 25°C. Diastolic blood pressure was 32,3  0,6 for breath periods and 29,5  0,5 for diving periods at 15°C, and 35,3  0,9 and 33,2  0,6 at 25°C. The animal was artificially ventilated during diving with normoxic, hypoxic (5% O2) and hypercarbic gas mixtures (6% CO2). None of these procedures produced any change of blood pressure or cardiac frequency. Cardio-vascular effects
have, however, been reported in some other studies on amphibians. As a new aspect, we applied artificial ventilation during a voluntary dive in the frog. Surfacing, elicited tachycardia and elevated blood pressure, These cardiovascular reflexes depend on a stimulus that still needs to be identified.