Prolonged isometric exercise. Part 1: Effect on circulation and on renal excretion of sodium and potassium in mild essential hypertension.

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Abstract
The effect of stress, in the form of prolonged isometric exercise, on the circulation and on the renal excretion of sodium and potassium was studied in 18 patients with mild essential hypertension. Thirteen men and five women, aged 20 to 50 years with basal diastolic blood pressure (BP) between 90 and 110 mm Hg were matched by age, sex, and race with 18 controls who had basal diastolic BPs less than 85 mm Hg. After the subjects rested for 90 minutes, basal measurements of pulse rate, BP, and rates of sodium and potassium excretion were made. The subjects then underwent a 1-hour period of isometric exercise involving all four limbs in rotation, followed by 5 hours of rest during which the measurements were repeated at half-hourly intervals for the first 2 hours and at hourly intervals for the last 3 hours. On another day, the subjects were again studied after 1 hour of resting instead of exercise. Responses of each subject were then expressed as ratios of changes from the basal values observed on the exercise and rest days. Changes in systolic and diastolic BP and hart rate were not significantly different in the hypertensive and control groups. In hypertensive subjects, the rate of sodium and potassium excretion was decreased after isometric exercise compared with the rest day, whereas in normal subjects this response was reversed. For the first 3 hours after exercise, the cation excretion rate of the hypertensive group was significantly less than that of the control group. These results indicate that isometric exercise in mild hypertension induces prolonged renal retention of both sodium and potassium.