Effect of lung volume history on rate of edema formation in isolated canine lobe.

The effect of lung volume history and prior accumulation of interstitial fluid on rate of edema formation in isolated canine lobes was investigated. Mean pulmonary artery pressure and mean pulmonary venous pressure were kept constant at 40 and 30 cmH2O, respectively. Transpulmonary pressure (Ptp) was varied among 5, 15, and 25 cmH2O by progressive stepwise inflation and deflation. Rate of fluid accumulation was estimated by changes in slow weight gain after a change in Ptp. Although there is continuous interstitial fluid accumulation over the course of the experiment the results indicate that interstitial hydrostatic pressure around leaky vessels at Ptp of 15 cmH2O is reduced by prior lung inflation to Ptp of 25 cmH2O and increased by prior deflation to Ptp of 5 cmH2O. These results suggest that the distribution of interstitial fluid may vary as a function of lung volume history.