Blood pressure and altitude: An observational cohort study of hypertensive and nonhypertensive Himalayan trekkers in Nepal.

Objectives To determine how blood pressure (BP) changes with altitude in normotensive versus hypertensive trekkers. Secondary aims were to evaluate the prevalence of severe hypertension (BP ≥180/100 mmHg), and efficacy of different antihypertensive agents at high altitude. Methods This was an observational cohort study of resting and 24-h ambulatory BP at 2860m, 3400m and 4300m in normotensive and hypertensive trekkers at 2860m, 3400m and 4300m in Nepal. Results We enrolled 672 trekkers age 18 years and older, 60 with a prior diagnosis of hypertension. Mean systolic BP was similar across altitudes in normotensive [127 mmHg (95% confidence interval 126 to128 vs. 127 (126 to129) vs 128 (95%CI 126 to130), p=NS] and hypertensive trekkers [151 mmHg (145 to156) vs. 150 (144 to157) vs 144 (136 to152), p=NS]) as were mean diastolic pressures. However, there was large inter-individual variability. At 3400 m, the majority (60%, n=284) of normotensive subjects had a BP within 10mmHg of their BP at 2860 m while 21% (n=102) increased and 19% (n=91) decreased. The pattern was similar between 3400m and 4300m (65% (n=202) no change, 21% (n=65) increased, 15% (n=46) decreased). A greater proportion of hypertensive trekkers had a decrease in blood pressure at higher altitudes versus normotensives (36% (n=15) vs. 21% at 3400m, p=0.01 and 30% (n=7) vs.15% at 4300m, p=0.05). Severe hypertension occurred in both groups, but was asymptomatic. It occurred most frequently in trekkers on angiotensin converting enzyme inhibitors or angiotensin receptor blockers, and not at all on those taking beta-blockers or thiazides. Nocturnal BP decreased in normotensive and increased in hypertensive trekkers. Conclusions Most travelers, including those with well controlled hypertension, can be reassured that their blood pressure will remain relatively stable at high altitude. Though extremely elevated blood pressure may be observed at high altitude in normotensive and hypertensive people, it is unlikely to be symptomatic. The ideal antihypertensive regimen at high altitude remains unclear.