Cardiovascular and blood gas changes during panting responses induced by ambient or spinal cord heating in the pigeon

We measured respiratory frequency (fR), oxygen consumption (VO2), cardiovascular responses and arterial and mixed venous PCO2, PO2, pH and CO2 in six pigeons during hyperthermia caused by ambient heating (increase in body temperature = 1 degrees C) and during heating of the spinal cord alone (increase in vertebral canal temperature = 3 degrees C). Spinal cord heating caused an increase in fR to 546 min-1 (+/- 13 min-1 SE) and increases in VO2, heart frequency (fH) and cardiac output (CO); PaCO2 and PVCO2 decreased 3.4 and 4.6 torr, respectively, while PaCO2 increased 6.8 torr. fR during ambient heating was 489 +/- 36 min-1; cardiovascular and blood gas changes were, generally, in the same direction as those during spinal cord heating but of lesser magnitude. In six other pigeons, we characterized fR, VO2, cardiovascular and blood gas changes during a 4 degrees C rise in body temperature caused by increased ambient temperature. Those data showed that with increasing hyperthermia fR increased rapidly, though not stepwise, to a maximum while VO2, fH, CO, PaO2, pHa and the arterial-venous CO2 difference all gradually increased; PaCO2 and PVCO2 gradually decreased. We conclude that, generally, whole body heating by increased ambient temperature and heating of the spinal cord alone produce the same responses and that these responses are dependent on the magnitude of the heat stimulation.