Reduced tolerance of simulated altitude (4200 m) in young men with borderline hypertension.

BACKGROUND: Primary hypertensives who are acutely exposed to hypoxic hypoxia show an enhanced reactivity of arterial chemoreceptors as well as an exaggerated response of the sympathetic nervous system. Since these phenomena could influence their ability to tolerate sustained hypoxic hypoxia, this study was performed to determine whether persons predisposed to hypertension have a normal tolerance of simulated high altitude.
METHODS: Subjects were 18 young men with a family history of hypertension (sons of hypertensives, SOHT) whose BP values were in the upper normal or borderline hypertensive range. Controls were 15 young men without parental hypertension (sons of normotensives, SONT) who had normal BP values. Each subject underwent both a control and an altitude experiment. The latter consisted of an 8-h exposure to hypobaric hypoxia (equivalent to 4200 m) while resting supine in an altitude chamber. Fluids were administered by mouth and by intravenous line to produce sustained diuresis. Variables measured included heart rate, BP, respiratory rate, O2 saturation, urine flow rate, and sodium excretion.
RESULTS: All subjects tolerated the control experiment and all SONT also completed altitude exposure. However, 8 of 18 SOHT developed antidiuresis and had to leave the chamber early due to symptoms of mild acute mountain sickness. Compared with SONT, SOHT exhibited more stable cardiorespiratory parameters at altitude.
CONCLUSIONS: The data support the hypothesis that borderline hypertensives have stronger cardiorespiratory responses to altitude than controls, a response that is compatible with higher excitability of their arterial chemoreceptors. However, their altitude tolerance is reduced even at rest, probably because of the renal effects of an exaggerated response in the sympathetic nervous system.