Journal of Applied Physiology, Vol 56, Issue 3 596-601, Copyright © 1984 by American Physiological Society
Gas trapping in excised rabbit lungs depends on volume history and method of degassing
W. Hida, W. J. Lamm and J. Hildebrandt
Trapped gas volume (Vtg) was obtained after 5 and 10 repeated
inflation-deflation cycles between transpulmonary pressure (Ptp) = 0 and 30
cmH2O in 12 experimental groups of freshly excised rabbit lungs. Gas flow
rate was 1.0 ml/s except in one group (0.4 ml/s). In lungs degassed by O2
absorption (Dabs), Vtg increased from an initial 12-15% total lung capacity
(TLC) (1st cycle) to 40% TLC (10th cycle), whereas in vacuum-degassed lungs
(Dvac) the final Vtg was almost unchanged, remaining at less than 20% TLC.
However, with the slower flow rate, Vtg in Dvac became 60% TLC. Increased
lung water was not found in Dabs and therefore could not account for the
above difference. In lungs not degassed after excision, Vtg increased
roughly in proportion to the duration of passive collapse at Ptp = 0.
However, a single brief exposure to a negative airway pressure (Pao = -10
cmH2O) resulted in a greater rate of increase of Vtg than 15-min collapse.
When any of the foregoing groups were vacuum degassed after 5 cycles, they
then resembled the Dvac group and showed almost no increase of Vtg in
successive cycles. In Dvac, negative Pao and 15-min collapse had only minor
effects on increasing Vtg. Thus, at a flow rate of 1 ml/s vacuum degassing
almost eliminated all tendencies to trap gas in rabbit lungs, but the
tendency was more than restored at slower flows. Brief airway closure by
negative tracheal pressure can markedly enhance subsequent trapping of
collapsed lungs. Differences arising from degassing methods might be due to
effects on bronchomotor tone or on the physical characteristics of airway
lining.
