VENTILATORY RESPONSE OF THE DIAMONDBACK WATER SNAKE, NATRIX-RHOMBIFERA TO HYPOXIA, HYPERCAPNIA AND INCREASED OXYGEN-DEMAND

Simultaneous measurements of ventilatory frequency, tidal volume, O2 uptake, CO2 output and cardiac frequency were made in the diamondback water snake, Natrix rhombifera while breathing hypoxic (15% to 5% O2 in N2) or hypercarbic (2% to 10% CO2 and 21% O2 in N2) gases. The snakes responded to hypoxia by increasing tidal volume and decreasing ventilatory frequency resulting in little change in ventilation (50% increase at 5% inspired O2), or O2 uptake and only a light increase in CO2 output. Hypercarbia to 4.2% inspired CO2 resulted in a slight hyperventilation but ventilation was depressed at 6.3% inspired CO2 and became erratic at higher concentrations. The resting rate of O2 uptake was maintained throughout hypercapnia. Heart rate increased during hypoxia and decreased during hypercapnia. Cutaneous O2 uptake increased during extreme hypoxia (5% inspired O2) and cutaneous CO2 output increased during hypercapnia, probably due to changes in the body-to-ambient gas gradients (Crawford and Schultetus, 1970). Both pulmonary oxygen uptake and ventilation were dramatically increased immediately following 10–15 min experimental dives. The increased ventilation was achieved primarily through an increased tidal volume. © 1979, Springer-Verlag. All rights reserved.