Blood pressure increases steadily as humans reach high altitudes, according to the latest findings of medical research on Mount Everest.
Italian researchers found that the drug telmisartan can counteract the rise in blood pressure up to a height of 3,400 metres but not beyond.
Kathmandu in Nepal is 1,355 metres above sea level while Denver in the USA is 1,560 metres above sea level.
The researchers camped at an Everest base camp some 5,400 metres above sea level. The mountain peak is 8,800 metres high.
They say theirs is the first study of its kind because they used ambulatory blood pressure monitoring to track changes to blood pressure throughout periods of 24 hours.
The researchers say their findings have implications not just for high altitudes but for others who may suffer from oxygen deprivation.
They found that at the level of the base camp, volunteers had experienced an increase in systolic blood pressure of 14 points and in diastolic blood pressure of ten points.
The findings have been published in the European Heart Journal.
Researcher Professor Gianfranco Parati, of the Istituto Auxologico Italiano, Milan, Italy, said: “Our study provides the first systematic demonstration that exposure to progressively higher altitudes is associated with a progressive and marked increase in ambulatory blood pressure.
"The increase occurred immediately after the high altitude was reached, persisted during prolonged altitude exposure, was seen throughout the 24-hour period but was particularly pronounced at night when there was a reduction in the night-time ‘dip’, and disappeared after return to sea level.
"After reaching Everest base camp, the effect of high altitude was greater on systolic blood pressure in people aged 50 and over compared with younger people."
He added: "Our findings will also enable us to take appropriate action to warn cardiovascular patients of the need for caution whenever they are going to be exposed to high altitudes for leisure or work."
Gianfranco Parati et al. 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. European Heart Journal 27 August 2014; doi:10.1093/eurheartj/ehu275
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