High altitudes raise blood pressure, according to a study conducted on Mount Everest.

Researchers followed 47 people as they climbed Mount Everest to monitor changes in blood pressure as part of the study. Participants wore blood pressure monitors that took constant readings and agreed to give blood samples for testing. The group was split in order to randomly assign a medication meant to lower blood pressure to some and a placebo to others.

The participants and researchers then climbed to a base camp located 5,400 meters, over 17,000 feet, above sea level. As they climbed, readings from the monitors revealed that their blood pressures climbed as well. At the highest point in the climb, systolic numbers increased an average of 14 mmHg and diastolic numbers went up an average of 10 mmHg in just 24 hours time.

The blood pressure lowering drug, called telmisartan, assigned to some of the group did not appear to work to keep blood pressure levels down at high altitudes despite being effective at sea level.

Reasons behind the increase are related to the lack of oxygen available at high altitudes, researchers say. The body’s reaction to oxygen deprivation is to activate the sympathetic branch of the nervous system, causing the heart to work harder. Additionally, peripheral blood vessels react to the stress by constricting.

Findings from this study have the potential to change how many chronic illnesses resulting in oxygen deprivation are managed, according to Gianfranco Parati, who headed up the study. The treatment of medical problems such as chronic obstructive pulmonary disorder, chronic heart failure that interrupts breathing, chronic sleep apnea and severe obesity could benefit from the results of this study.

At the very least, insight gleaned from the study could serve as a much needed warning for people with these types of issues who plan to be exposed to high altitudes.