Physiology

Climbers’ ambulatory blood pressure rises at higher altitudes

Efficacy of widely used antihypertensive is preserved during acute exposure to moderate altitude but is impaired at higher altitude.

Test on ambulatory blood pressure

The volunteers’ blood pressure was continuously monitored during the study

Ambulatory blood pressure rises progressively as people reach higher altitudes, according to the results of a study that monitored a group of volunteers on a trek to the basecamp of Mount Everest.

The study, published in European Heart Journal (online, 26 August 2014)[1], also showed that the angiotensin receptor antagonist telmisartan was effective at lowering blood pressure at 3,400 metres above sea level but not at 5,400 metres.

Researchers accompanied 47 Italian people – all aged under 65, healthy and normotensive – from Milan (120 metres above sea level) to Kathmandu (1,355 metres above sea level) in Nepal, where they stayed for three days.

The group travelled on to Namche Bazaar (3,400 metres above sea level) where they stopped for three days, before climbing to the base camp of Everest at 5,400 metres, where they stayed for 12 days.

The volunteers’ blood pressure and heart rate were measured every morning over a five-minute period. Each volunteer also wore a 24-hour ambulatory blood pressure measuring device that recorded measurements every 15 minutes during the day and every 20 minutes during the night.

The volunteers were also randomised to receive either 80mg telmisartan or placebo during the expedition.

In the placebo group, exposure to altitude at 3,400 metres and 5,400 metres was associated with a progressive increase in both conventional and ambulatory diastolic and systolic blood pressure. There was a similar pattern in changes to heart rate, the researchers found.

Telmisartan did not have a significant lowering effect on conventional blood pressure measurements but it did cause a significant reduction in ambulatory blood pressure at sea level and at an altitude of 3,400 metres. The lowering effects of the drug were not evident on arrival at 5,400 metres or after the 12-day stay, the researchers found.

According to the researchers, the study provides solid evidence that “high altitude has an acute and persistent, albeit reversible, pressor effect on daily life blood pressure with a similarly acute, persistent and reversible alteration to its circadian pattern”.

It is also the first study to demonstrate that the efficacy of one of the most common treatments of hypertension is preserved during acute exposure to moderate altitude but is impaired at higher altitude, they say.

“Patients should be warned that the antihypertensive effect of an angiotensin II receptor blockade will likely be lost at very high altitudes, at which they will probably move from a controlled to an uncontrolled BP state,” the researchers say.

Citation: The Salvadore DOI: 10.1211/PJ.2014.20066281

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