Ventilation and Gas Exchange during Shallow Hypothermia in Pigeons

Ventilatory control of the composition of the gases in the air sacs was studied during entry into fasting-induced, shallow, nocturnal hypothermia in the domestic pigeon (Columba livia). Respiratory frequency (/), tidal volume (Vi) and oxygen uptake (VcO were recorded simultaneously in six pigeons; partial pressures of CO2 and O2 in the abdominal and interclavicular air sacs were measured in seven pigeons. Ambient temperature was 25°C (thermoneutral) and the body temperature (Tb) was recorded in all experiments. A reduction in Tb from 40.5 to 37.5°C paralleled decreases in / and VT from 13.3 min" and 15.2 ml BTPSkg" to 10.7 min" and 12.4ml BTPskg", respectively. There was a minor, but non-significant, simultaneous decrease in the ventilatory requirement (total ventilation/O2 uptake) from 0.38 to O.SSmlBTPsmmoP. However, in both air sacs the partial pressure of CO2 increased when Tb decreased, indicating an effective parabronchial hypoventilation. The results support the idea of a gradually developing respiratory acidosis during hypothermia.