What governs blood pressure control mechanisms at high altitude is largely unknown. Many doctors recommend patients with high blood pressure not to travel to high altitude
areas. This precaution may be unnecessary because several anecdotal evidences have shown that most people with controlled blood pressure do not face any problems when they are up in the mountains. However, there is no sufficient evidence-based study to back this up. This lack of knowledge has often created panic in both travellers and doctors.
Take the case of a 44-year-old woman who was attempting to climb Everest. At 5000m, she complained of severe cold and cough. She had no past history of hypertension or any other medical problems. During the course of the examination, the doctors took her blood pressure and found it to be inordinately high (180\115 mm of Hg). The patient was then asked to take a helicopter back to Kathmandu. The doctor warned her of the possible complications if she continued further. Reluctantly, the patient returned. Her blood pressure continued to remain very high for the next few days but came back to normal without any medication. With a few additional tests, the doctors determined there was no organ (heart, kidney, eyes, and brain) damage due to her high blood pressure. (These are the organ sites which usually get affected by long-standing blood pressure). Following this, the woman went back and successfully climbed Everest.
The above story is a common instance where doctors face dilemma regarding treatment for patients whose blood pressures shoot up at high altitudes. If a simple blood pressure study had been done in a large cohort of people travelling to high altitude, doctors could give more appropriate advice based on the study results.
This fall, the Himalaya Rescue Association (HRA) is helping to undertake a blood pressure study in the Everest region. The study will measure the change in blood pressure in a large population of trekkers as they ascend from Lukla (2800m) to Pheriche (4300m). A subset of this study population will also have ambulatory blood pressure measurements (a blood pressure cuff will be tied around their arm and a small mobile-phone like machine will take their blood pressure at intervals and keep a record). This will ensure more accurate blood pressure reading.
Part of the same study will also examine 50 hypertensive trekkers on blood pressure medicines and record how their blood pressure responds as they ascend to high altitude. The HRA study, if carried out, will be helpful for doctors advising hypertensive patients travelling to high altitude and other groups including thousands of pilgrims who travel to high altitude religious sites.
Finally, this study will also address the question of high blood pressure and predisposition to acute mountain sickness (AMS). In all likelihood, high blood pressure does not lead to AMS. But it will be useful to have scientific evidence from our own backyard answer some of these simple but vexing questions regarding blood pressure and high altitude. It is high time.
Altitude illness awareness
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