Ventilatory response of the diamondback water snake,Natrix rhombifera to hypoxia, hypercapnia and increased oxygen demand

Summary

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.