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, \(\dot V_{{\text{O}}_{\text{2}} }\) max, body surface area, weight, and body fat. Environmental conditions were 38‡ C dry-bulb, 28‡ C wet-bulb; exercise intensity was approximately 40% \(\dot V_{{\text{O}}_{\text{2}} }\) 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.