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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
Study Questions:
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?
Methods:
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.
Results:
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.
Conclusions:
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.
Perspective:
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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