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

Abstract

We measured respiratory frequency (f R), oxygen consumption (V̇ O 2 ), cardiovascular responses and arterial and mixed venous P CO 2 , P O 2 , pH and C O 2 in six pigeons during hyperthemia caused by ambient heating (increased in body temperature = 1 °C) and during heating of the spinal cord alone (heating in vertebral canal temperature = 3 °C). Spinal cord heating caused an increased in f R to 546 min −1 (±13 min −1 SE) and increases in V̇ O 2 , heart frequency (f R) and cardiac output (CO); Pa CO 2 and P V CO 2 decreased 3.4 and 4.6 torr, respectively, while Pa O 2 increased 6.8 torr. f R 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 f R, V̇ O 2 , cardiovascular and blood gas changes during a 4 °C rise in body temperature caused by increased ambient temperature. Those data showed that with increasing hyperthemia f R increased rapidly, though not stepwise, to a maximum while V̇ O 2 , f H, CO, PA O 2 , P V O 2 , pHa and the arterial-venous CO 2 difference all gradually increased; Pa CO 2 and P V CO 2 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.