Abstract
Pulmonary N2 washouts by either He-O2 or SF6-O2 were observed in 6 healthy laboratory workers and on 10 mongrel dogs. N2 washout by SF6-O2 was consistently faster, especially at the beginning of washout, than that by He-O2. In a model experiment where N2 was washed out from 4 anesthesia bags arranged in parallel in a lucite box, N2 washout by He was a bit faster than that by SF6.
Washout of He in the bags by air is significantly faster than SF6 washout by air. All these comparisons were made among the results obtained under approximately identical ventilatory conditions.
The third experiment was conducted to observe any difference in gas penetrations through a bronchial hollow cast of a dog into well-stirred gas phase. SF6 dispersion into the stirred gas phase was significantly greater than that of He. As duration of inspiration increased, the amount of dispersed gas and the difference between He and SF6 increased. N2 dispersion through the hollow cast into well-stirred He was consistently larger than that into SF6, which was in line with faster He washout by air from the bags.
Thus, the faster N2 washout by SF6-O2 than by He-O2 in vivo, which might be the reverse to expectation based on molecular diffusion alone, could be attributed mainly to the greater axial penetration of SF6 and to better convective mixing of SF6 in the airways during inspiration. A role of molecular diffusion between inspirate and stale gas seems to become more important when alveolar N2 concentration becomes low during washout and when SF6 or He in the lungs is washed out by air. Phenomena during expiration require further investigation.
