Systemic hypertension at 4,300 m is related to sympathoadrenal activity

Residence at high altitude has been associated with elevation in systemic arterial blood pressure, but the time course has been little studied and the mechanism is unknown. Because plasma epinephrine (E) and norepinephrine (NE) also increase at altitude, we hypothesized that heightened sympathoadrenal activity may cause increased arterial pressure. We measured ambulatory blood pressure by cuff monitor in relation to 24-h urinary excretion of E and NE at sea level and during 3 wk of residence at 4,300 m (Pikes Peak, CO) in 11 healthy men. In five subjects taking placebo, arterial pressure progressively increased at 4,300 m from 82 +/- 1 (SE) mmHg at sea level to 88 +/- 3 on day 2, 91 +/- 3 on day 8, and 97 +/- 6 on day 17. In six subjects, propranolol (240 mg/day) decreased pressure from 85 +/- 4 to 77 +/- 1 mmHg at sea level but did not prevent sustained increase in pressure at 4,300 m (84 +/- 1, 81 +/- 1, and 85 +/- 3 mmHg on days 2, 8, and 17, respectively). Compared with the placebo group, blood pressure did not increase further over the initial elevation observed on day 2 in the propranolol group. There was interindividual variability in the blood pressure responses in both groups, with some subjects demonstrating a more marked increase in blood pressure. Urinary excretion of NE increased concomitantly with pressure at altitude in both groups, with a greater rise in the placebo group.(ABSTRACT TRUNCATED AT 250 WORDS)