Objective.—Dizziness is a symptom of acute mountain sickness (AMS). This study tested whether immediate fall in systolic blood pressure (BP) on standing was more severe at altitude and whether this was associated with symptoms of dizziness.

Methods.—Eighty-five lowlanders flew into La Paz, Bolivia (3650 m), and after 4 to 5 days of acclimatization ascended in 90 minutes to the Chacaltaya Laboratory (5200 m) by road. Blood pressure was measured on 5 occasions, 3 times at 5200 m and twice at sea level, before and after the expedition using a mercury sphygmomanometer. Both a supine and an erect (within 15 seconds of standing) BP measurement were recorded. Participants recorded whether they felt dizzy on standing. A mixed-effect model was used to test for a difference in the change in BP for time and altitude.

Results.—The immediate fall in systolic BP observed on standing was significantly greater (P < .001) on all 3 altitude study days (18.2, 23.4, and 20.7 mm Hg) than at sea level (12.2 and 12.4 mm Hg). There was no significant difference in the change in diastolic BP or change in mean arterial BP between sea level and altitude.

Conclusions.—The immediate drop in systolic BP observed on standing was greater at altitude. However, mean arterial pressure was maintained, and we found no association between the degree of immediate fall in BP and dizziness or AMS.