Orthostatic responses in Caucasians and Bantu

Nine Caucasian and 13 Bantu young men, all untrained and unacclimated to heat, were tilted head-up for 20 min before and after 4 h of exercise performed at a load of 35 W at room temperature of 23 degrees C and in heat (33.9 degrees C DB, 32.2 degrees C WB). In heat, all Bantu but only four Caucasians completed the 4 h of exposure. The change in systolic blood pressure from recumbency to orthostasis was negligible in the Bantu and adverse in the Caucasians, during pre-exercise tilting at 23 degrees C. Similar differences were found during tilting after exercise at 23 degrees C. Post-exercise orthostatic heart rate did not differ between the two groups despite higher exercise heart rats of the Bantu. Seven subjects in each group fainted during heart-orthostatism, and the difference in systolic blood pressure between recumbency and orthostasis in heat was substantially more adverse in the Caucasians. High relationships were found between exercise heart rate, orthostatic heart rate, and fainting episodes. The results suggested that Bantu make better orthostatic adjestments than Caucasians.