Effect of inflation on interstitial cuff and pressure in liquid-filled rabbit lung

Degassed rabbit lungs were inflated to 15 cmH2O pressure with 3% albumin solution. To study cuff growth, lungs were frozen in liquid N2 at several (20-120 min) inflation times. Cuff-to-vessel area ratio measured from frozen lung pieces increased with time reaching a maximum value (0.5-0.9) by 1 h. Time constants (to) of cuff growth were similar to those (28 min) of the interstitial pressure (Pi) response measured by micropuncture at the lung hilum. Pi response was slower with saline (to = 84 min) than with albumin. Compared to saline, positively charged protamine sulphate increased the Pi response (to = 44 min). Time constants for cuff growth and Pi response were smaller at 15 cmH2O than at 5 cmH2O inflation pressure (30 vs. 60-120 min). Electrical analog models indicated a doubling of interstitial resistance with a four-to eight-fold decrease in interstitial specific compliance at the higher inflation pressure, the latter attributed to nonlinear elastic behavior of lung parenchyma.