The effects of stress and caffeine on hypertensives.

Eighteen male hypertensives on diuretic medication between the ages of 37 and 60 were studied in a double-blind, randomized, crossover design under three conditions: 200 mg of caffeine and mental arithmetic; placebo and mental arithmetic; and 200 mg of caffeine alone. Systolic and diastolic blood pressure, heart rate, and skin conductance were recorded. During rest, caffeine compared to placebo increased blood pressure by 8/6 mm Hg, but had no effect on heart rate or skin conductance. During mental arithmetic, the combined effect of mental stress and caffeine led to a further increase of 17/7 mm Hg, reaching a pressure level of 163/100 mm Hg. Heart rate and skin conductance were increased above their prior caffeine levels. There were no significant differences between the blood pressure response to mental arithmetic with caffeine and that response to mental arithmetic with a placebo, which may have been due to the fact that the hypertensives were already responding at ceiling level during the mental stressor.