Reproducibility of individual response to exposure to high altitude.

1269 Reproducibility of individual response to exposure to high altitude The response of people who live at sea level to the low oxygen concentrations at high altitude varies widely. Some people are relatively unaffected while others suffer severe acute mountain sickness.' Anecdotal reports and experiments in decompression chambers have indicated that responses to high altitude are reproducible,2 but this has been difficult to substantiate under controlled field conditions. A two year study of the staff manning an astronomical observatory 4200 m above sea level permitted an examination of individual performance during repeated ascents.3 Methods and results The 3-8 m United Kingdom infrared telescope is sited at the summit of Mauna Kea (4200 m) in Hawaii. Staff alternately work on the mountain for five days and rest at sea level for five days. During work shifts they sleep at 3000 m and work for 10 hours at the summit. The daily ascent from 3000 m to 4200 m takes 30 minutes by vehicle. Self assessment questionnaires listing the symptoms of acute mountain sickness and scoring their severity on a scale of 0 to 10 were completed by 18 men (aged 17-45) during two separate five day shifts at the telescope. Arterial capillary blood was drawn from the ear lobes of 12 men on days 1 and 5 of each shift. Oxygen and carbon dioxide tensions were measured with an Instrumentation laboratory IL213 analyser. Comparison of scores for symptoms of altitude sickness recorded by 18 men on day 1 of two five day work shifts at 4200 m. Five men were asymptomatic at the summit. The remaining 13 experienced characteristic symptoms of acute mountain sickness (headache, lethargy, insomnia, and anorexia). The figure shows that the order of the 18 men ranked according to severity of altitude sickness on the first day of the two shifts correlated significantly (r= 0-63, p < 0-001, Kendall's rank test). After five days on the mountain most workers were free of symptoms. Arterial oxygen tension on day 1 of the two shifts ranged from 4-4 kPa (33 mm Hg) and 5-1 kPa (38 mm Hg) in one man to 7-0 kPa (53 mm Hg) and 7-6 kPa (57 mm Hg) in another; the mean for the group was 5-5 kPa (41 mm Hg). The two values for each man correlated well (r= 0-74, p < 0-01). The order of men ranked according to arterial oxygen tension on …