Ventilatory control of arterial P_{O 2} in the turtleChrysemys picta bellii: Effects of temperature and hypoxia

Summary

Ventilation, pulmonary O₂ uptake, arterial blood gases and pH were measured in fresh water turtles,Chrysemys picta bellii, during voluntary diving and surfacing at temperatures of 10, 20 or 30°C. At each temperature, the animals were also exposed to declining levels of inspired O₂ concentration with blood samples taken at various stages of breath holding and during episodes of breathing.

The breathing pattern ofChrysemys consists of a series of breaths followed by a breath hold period which usually coincides with a period of submergence. The ventilatory response to hypoxia at all temperatures involved a decrease in the diving time as well as an increase in the tidal volume. The breathing frequency during ventilatory periods decreased slightly during severe hypoxia. The increase of ventilation in response to hypoxia was most pronounced at 30°C; ventilation approximately doubled as arterialP _{O 2} decreased from 60 to 30 Torr and increased more than tenfold as arterialP _{O 2} approached 10 Torr. In comparison, the ventilatory response of animals at lower temperatures occurred at much lower levels of arterialP _{O 2}; at 10°C ventilation did not increase relative to normoxic control values until arterialP _{O 2} fell to about 5 Torr.

The observed reduction in the ventilatory response to environmental hypoxia at lower temperatures can probably be attributed to the sevenfold reduced pulmonary O₂ uptake at 10°C as compared to 30°C in combination with the shift inP ₅₀ of the blood oxygen dissociation curves from 29 (30°C) to 5 Torr (10°C). The present data suggest that desaturation of the blood during hypoxia is a leading factor for the increase in ventilation as an attempt to maintain normal O₂ uptake.