WEDNESDAY, Aug. 27, 2014 (HealthDay News) -- In a new study done from the heights of Mount Everest, Italian researchers found that your blood pressure steadily increases if you ascend to great heights.
They also found that a drug widely used to treat high blood pressure was ineffective once climbers reached above a certain altitude.
The findings, reported online Aug. 27 in the European Heart Journal, could impact not just high-altitude trekkers but those at sea level who have sleep apnea, in which a blocked airway temporarily halts their breathing, as well as others with some chronic diseases.
The researchers joined an expedition of 47 volunteers who traveled to the Mount Everest base camp, which is at an altitude of 5,400 meters, or approximately 17,700 feet. The volunteers wore blood pressure monitors that took round-the-clock readings as they climbed up to the base camp.
The participants were also randomized to receive either 80 milligrams (mg) of the blood pressure-lowering drug telmisartan (MIcardis), or a placebo. Telmisartan is angiotensin receptor blocker (ARB) because it blocks the effects of a peptide called angiotensin II, which causes blood vessels to narrow. The researchers collected blood samples as well.
They found that exposure to the very high altitude of 5,400 meters was responsible for an increase of 14 mmHg in systolic blood pressure and 10 mmHg in diastolic blood pressure, averaged over a 24-hour period of monitoring. They also found that while telmisartan significantly reduced blood pressure at sea level and at 3,400 meters (11,155 feet), no effects could be seen shortly after arriving at 5,400 meters.
"This blood pressure increase is due to several factors, the most important being the effects of oxygen deprivation in increasing activity in the body's sympathetic nervous system. This leads to the heart working harder and the peripheral blood vessels constricting," he added.
The findings may have a number of implications for those who have diseases or conditions that can result in oxygen deprivation, study leader Gianfranco Parati, director of the Cardiology Research Laboratory at the Istituto Auxologico Italiano in Milan, said in a journal news release.
They may help in "the management of patients with chronic diseases, including chronic heart failure, in which breathing is interrupted periodically, acute worsening of chronic obstructive pulmonary disease, obstructive sleep apnea and severe obesity. Together, these conditions affect more than 600 million people worldwide, making our results highly significant from a clinical perspective," he said.
"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," Parati concluded.
The U.S. National Heart, Lung, and Blood Institute explains the causes of high blood pressure.