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.
Wagner
P D
PD
Department of Medicine, University of California, San Diego, La Jolla 92093.
Sutton
J R
JR
Reeves
J T
JT
Cymerman
A
A
Groves
B M
BM
Malconian
M K
MK
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