Changes in 24 H Ambulatory Blood Pressure and Effects of Angiotensin II Receptor Blockade During Acute and Prolonged High-Altitude Exposure: A Randomized Clinical Trial
Does acute or prolonged exposure to increased altitude have an effect on ambulatory blood pressure and/or the blood pressure-lowering efficacy of an angiotensin-receptor blocker?
A cohort of 47 healthy, normotensive low-landers in the HIGHCARE-HIMALAYA study was randomized to telmisartan 80 mg or placebo in a double-blind, parallel-group trial. Conventional and ambulatory blood pressures were measured at baseline and on treatment (after 8 weeks at sea level and under acute exposure to 3400 and 5400 m altitude, the latter upon arrival and again after 12 days [Mt. Everest base camp]). Blood samples were collected for plasma catecholamines, renin, angiotensin, and aldosterone.
In both groups, exposure to increasing altitude was associated with significant progressive increases in conventional and 24-hour blood pressure, persisting throughout the exposure to 5400 m; and increased plasma noradrenaline and suppression of the renin–angiotensin–aldosterone system. Telmisartan lowered 24-hour ambulatory blood pressure at sea level and at 3400 m (between-group difference, 4.0 mm Hg; 95% confidence interval, 2.2-9.5 mm Hg), but not at 5400 m.
The authors concluded that ambulatory blood pressure increases progressively with increasing altitude, remaining elevated after 3 weeks. Therapy with an angiotensin-receptor blocker maintains blood pressure-lowering efficacy at 3400 m, but not at 5400 m.
Patients with hypertension might travel to high altitudes, with associated exposure to hypobaric hypoxia. This study suggests that blood pressure increases at elevated altitude, and that angiotensin-receptor blockers mitigate the increase in blood pressure at some, but not at more extreme elevation.
Keywords: Benzimidazoles, Catecholamines, Renin-Angiotensin System, Norepinephrine, Blood Pressure, Confidence Intervals, Hypertension, Benzoates
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