Growth rate of perivascular cuffs in liquid-inflated dog lung lobes

In the early stages of pulmonary edema, excess liquid leaving the pulmonary exchange vessels accumulates in the peribronchovascular interstitium where it forms large peribronchovascular cuffs. The peribronchovascular interstitium therefore acts as a reservoir to protect the air spaces from alveolar flooding. The rate of liquid accumulation and the liquid storage capacity of the cuffs determine how quickly alveolar flooding is likely to follow once edema formation has begun. To measure the rate and capacity of interstitial filling we inflated 11 isolated degassed dog lung lobes with liquid to an inflation pressure of 14 cmH2O (total lung capacity) for 1-300 min, then froze the lobes in liquid N2. We made photographs of 20 randomly selected 12 X 8-mm cross sections from each lobe and measured cuff volume from the photographs by point-counting. We found that cuff volume increased from 2.2% of air-space volume after 1 min of inflation to 9.3% after 300 min. To measure the driving pressure responsible for cuff formation we used micropipettes to measure subpleural interstitial liquid pressure at the hilum of three additional lobes. With liquid inflation pressure set to 14 cmH2O interstitial pressure rose exponentially to 11.5 cmH2O. Interstitial compliance calculated from our volume and pressure measurements equaled 0.09 ml X cmH2O-1 X g wet wt-1, a value similar to that measured in air-inflated lungs. Goldberg [Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H189-H198, 1980] has likened interstitial filling to the charging of a capacitor, a process that follows a monoexponential time course.(ABSTRACT TRUNCATED AT 250 WORDS)