AIRWAY REOPENING PRESSURE IN ISOLATED RAT LUNGS

In a previous modeling study, we predicted that the yield pressure for airway reopening (Pyield) should depend on airway fluid surface tensi on (gamma) and airway radius (R), according to the relationship Pyield = 8.3 gamma/R. To test this prediction, we studied tantalum bronchogr ams of isolated perfused rat lungs from three rats by using microfocal X-ray imaging. Thirty-two airways with diameters ranging from 300 to 2,400 mu m were recorded as the airways were collapsed and reinflated. Airway pressure was reduced transiently to -40 cmH(2)O to produce air way closure. Airway pressure was then slowly increased from 0 to 25 cm H(2)O. In each airway, the observed diameter remained constant until a Pyield was reached; at this pressure, airways were seen to ''pop'' op en, allowing clear identification of airway reopening pressure. When P yield was plotted against diameter at maximum inflation, the experimen tal data were in approximate agreement with predictions of Pyield made assuming a gamma of 35 dyn/cm. The close correspondence of the measur ed values with these predictions suggests that surfactant is present i n these airways and facilitates airway reopening.