The volume, time, and rate of collapse of the lungs following tracheal occlusion were studied in rats breathing O2 at ambient pressures between 1,520 mm (2 atm) and 190 mm (equivalent to 33,000 ft altitude). Theoretical calculations and experimental data show that 1) the rate of lung collapse is directly related to the O2 uptake and inversely related to the barometric pressure minus the sum of alveolar CO2 and water vapor pressure, and 2) the total time required for producing complete lung collapse is proportional to the lung volume at the time of occlusion and to the barometric pressure minus the sum of alveolar CO2 and water vapor pressure and inversely proportional to the O2 uptake. In both these relationships, lung volume is expressed at BTPS, while the O2 uptake is at STPD. The collapse time, with the lungs occluded at functional residual capacity dropped from 22.6 sec at sea level to 3.5 sec at 190 mm Hg. The rate of collapse was found to remain essentially constant during any experiment, as could be predicted from the analysis of the factors involved. The time required for collapse, in any species, at any lung volume and Vo2, can be determined with a nomogram.
atelectasis; altitude; oxygen breathing; gas resorption; O2 stores
Submitted on July 7, 1964
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