SEPARATE AND COMBINED EFFECTS OF TEMPERATURE AND HYPOXIA ON BREATHING PATTERN IN THE DOMESTIC-FOWL

Minute ventilation (.ovrhdot.VE), tidal volume (VT), repsiratory frequency (f) and clavicular air sac gas composition were measured in conscious domestic fowl breathing air and hypoxic gas mixtures at neutral (18 .+-. 1.degree. C) and raised (33 .+-. 1.degree. C) air temperatures. Increases in .ovrhdot.VE caused by inhalation of 10%, 8% or 6.5% O2 in N2, respectively, were independent of temperature although at each level the absolute .ovrhdot.VE was ca. 2 l .cntdot. min-1 greater in the panting birds. Changes in respiratory pattern during hypoxia were markedly dependent on temperture. At 18.degree. C almost all of the increased .ovrhdot.VE resulted from increased f. At 33.degree. C hypoxia led to a strong suppression of f and increase in VT. It is concluded that hyperthermia and hypoxia are additive and non-interactive in their effects on ventilatory drive, in agreement with previously reported effects of hypercapnia and physical exercise on breathing in panting fowl.