Washington: In a significant find, an expedition to Mount Everest by Italian researchers has shown for the first time that blood pressure monitored over a 24-hour period rises progressively as people climb to higher altitudes.
The findings have implications not only for the people engaged in skiing and trekking at high altitudes, but also for people at lower altitudes who may be temporarily deprived of an adequate oxygen supply - a condition known as hypoxia.
"Our study provides the first systematic demonstration that exposure to progressively higher altitudes is associated with a progressive and marked increase in blood pressure," said Gianfranco Parati, a professor of cardiovascular medicine at University of Milano-Bicocca.
Hypoxia can lead to sickness at high altitudes, but is also seen at sea level in people who suffer from sleep apnea when their breathing is temporarily interrupted by a blocked airway.
For the study, 13 of the 15 authors joined an expedition of 47 volunteers to the Mount Everest south base camp (altitude 5400 metres) and Namche Bazaar (3400 metres).
During the expedition, their blood pressure was taken in the conventional way over a five-minute period in the morning.
They also wore a device that measured their blood pressure every 15-20 minutes over a 24-hour period.
They were also administered 80 mg of a blood pressure lowering drug called Telmisartan.
It was found that exposure to the very high altitude of 5400 metres was responsible for an increase of 14 mmHg in ambulatory systolic blood pressure and 10 mmHg in ambulatory diastolic blood pressure.
They also found that Telmisartan significantly reduced ambulatory blood pressure at sea level and at 3400 metres, while no effects could be seen at 5400 metres.
The study appeared in the European Heart Journal.