Operation Everest II: pulmonary gas exchange during a simulated ascent of Mt. Everest.
Eight normal subjects were decompressed to barometric pressure (PB) = 240 Torr over 40 days. The ventilation-perfusion (VA/Q) distribution was estimated at rest and during exercise [up to 80-90% maximal O2 uptake (VO2 max)] by the multiple inert gas elimination technique at sea level and PB = 428, 347, 282, and 240 Torr. The dispersion of the blood flow distribution increased by 64% from rest to 281 W, at both sea level and at PB = 428 Torr (heaviest exercise 215 W). At PB = 347 Torr, the increase was 79% (rest to 159 W); at PB = 282 Torr, the increase was 112% (108 W); and at PB = 240 Torr, the increase was 9% (60 W). There was no significant correlation between the dispersion and cardiac output, ventilation, or pulmonary arterial wedge pressure, but there was a correlation between the dispersion and mean pulmonary arterial pressure (r = 0.49, P = 0.02). When abnormal, the VA/Q pattern generally had perfusion in lung units of zero or near zero VA/Q combined with units of normal VA/Q. Alveolar-end-capillary diffusion limitation of O2 uptake (VO2) was observed at VO2 greater than 3 l/min at sea level, greater than 1-2 l/min VO2 at PB = 428 and 347 Torr, and at higher altitudes, at VO2 less than or equal to 1 l/min. These results show variable but increasing VA/Q mismatch with long-term exposure to both altitude and exercise. The VA/Q pattern and relationship to pulmonary arterial pressure are both compatible with alveolar interstitial edema as the primary cause of inequality.
Department of Medicine, University of California, San Diego, La Jolla 92093.
P D
PD
Wagner
J R
JR
Sutton
J T
JT
Reeves
A
A
Cymerman
B M
BM
Groves
M K
MK
Malconian
D000064:Acclimatization; D000328:Adult; D000531:Altitude; D006801:Humans; D009051:Mountaineering; D005082:Physical Exertion; D011659:Pulmonary Gas Exchange; D011669:Pulmonary Wedge Pressure; D013997:Time Factors; D014109:Total Lung Capacity; D014692:Ventilation-Perfusion Ratio