Ambulatory Blood Pressure in Tourists at Low Versus High Altitude: Colorado High Altitude Monitoring Pressure Study.

IntroductionLimited evidence exists to guide travelers about blood pressure (BP) changes at high altitude (HA). Our primary objective compared 24-h ambulatory BP at low altitude (LA) vs HA in a cohort of tourists. Exploratory analyses compared results by sex and history of underlying hypertension.MethodsThis prospective observational cohort study measured ambulatory BP with Welch-Allyn ABPM 6100 monitors at LA (<1000 m) and HA (median 2751 m). Measurements included heart rate/BP every 30 min while awake and hourly overnight, BP≥180/100 mm Hg, sleep quality, and Lake Louise score (acute mountain sickness).ResultsAmong 33 participants (median age 61 y, 17 with hypertension, 12 on BP medication), 25 completed LA and HA measurements. Average 24-h mean arterial pressure (MAP) increased at HA by 6 mm Hg (95% CI, 2-10 mm Hg; P=0.04). When analyzed by the presence of preexisting hypertension, 24-h MAP was similar between LA and HA in those with underlying hypertension (mean difference, 4 mm Hg; 95% CI, -4 to 11 mm Hg; P=0.3) but rose at HA in those without (mean difference, 9 mm Hg; 95% CI, 5-14 mm Hg; P=0.001). At HA, 24-h MAP was similar in both groups (mean difference, 9 mm Hg; 95% CI, 0-19 mm Hg; P=0.05). Results did not differ by sex. Severe-range BP was common in all groups and asymptomatic.ConclusionsAmong this tourist cohort, we observed an increase in average 24-h MAP at HA. Altitude-related changes in BP varied greatly between individuals. This variation was related in part to underlying hypertension but not sex. Our data suggest that BP changes are not of clinical concern in HA travelers.