Summary
Sheep were exposed to thermoneutral conditions and then to either mild heat stress (40° C dry bulb/26° C wet bulb temperature) or to severe heat stress (42/39° C). The following measurements were made: regional distribution of cardiac output, deep body and skin surface temperatures, respiratory frequency, heart rate, blood pressure, cardiac output, oxygen consumption, haemoglobin concentration, theP CO 2,P O 2, pH,S O 2 andC O 2 of arterial, mixed venous, dorsal sagittal sinus and transverse sinus blood. Body temperature and heart rate increased, and panting resulted in a marked respiratory alkalosis during severe heat stress, but otherwise, changes in gross cardiorespiratory functions were small. During both mild and severe heat stress approximately 11% of the cardiac output passed through arteriovenous anastomoses, compared with approximately 1.5% under thermoneutral conditions. Changes in blood flow to the skin, nasal mucosa and turbinates, tongue, heart, thyroids, adrenals, gut, spleen, kidneys, skeletal muscle, brain and spinal cord, illustrate a redistribution of cardiac output appropriate to combat the heat stress, but with probable influences of the respiratory alkalosis and alterations in local tissue metabolic rate.
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Hales, J.R.S. Effects of exposure to hot environments on the regional distribution of blood flow and on cardiorespiratory function in sheep. Pflugers Arch. 344, 133–148 (1973). https://doi.org/10.1007/BF00586547
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DOI: https://doi.org/10.1007/BF00586547