Comparative physiological responses of normotensive and essentially hypertensive men to exercise in the heat

Six essentially hypertensive men (average resting arterial pressure of 150/97 mm Hg) and eight normotensive controls (average resting arterial pressure of 115/73 mm Hg) were tested during 1 h of dynamic leg exercise in a warm environment. The groups were well matched for age, {Mathematical expression} max, body surface area, weight, and body fat. Environmental conditions were 38‡ C dry-bulb, 28‡ C wet-bulb; exercise intensity was approximately 40% {Mathematical expression} max (85-90 W). There were no significant intergroup differences in core or mean skin temperatures, calculated heat exchange variables, heart, or sweat rates. Blood pressure differences between the groups were maintained (P<0.01). The hypertensive group responded with a significantly lower stroke index (P<0.01) and cardiac index (P<0.01), and a decreased slope of the rise in forearm blood flow (P<0.01) due to an higher vascular resistance (P<0.01). The combined heat load (M + R + C) presented was not sufficient to override the hypertensives' higher cutaneous vasoconstrictor tone. However, on a practical basis, the hypertensives were able to tolerate exercise in the heat as well as their normotensive counterparts.