Determination of vascular compliance, interstitial compliance, and capillary filtration coefficient in rat isolated...

Gravimetric methods are useful for investigating mechanisms of edema formation. In isolated lungs perfused under isogravimetric conditions, important information may be gained by analyzing the weight changes induced by a sudden change in capillary pressure. In the present study, we investigated the possibility to analyze this weight change by a biexponential equation and use the coefficients obtained to derive vascular compliance (Cv), interstitial compliance (Ci) and the capillary filtration coefficient (Kf,c). Fitting the data of the weight gain to a biexponential curve explained the data significantly better than fitting it to a monoexponential curve, suggesting that two phases can be separated. The first phase is thought to represent vascular filling and was completed for 95% after 0.57 +/- 0.21 min (n = 30). In contrast, 95% completion of phase 2, which relates to interstitial filling, took 18.4 +/- 13.9 min (n = 30). The values obtained for Cv, Ci and Kf,c were 0.064 +/- 0.018 ml/cm H2O, 0.067 +/- 0.030 ml/cm H2O, and 0.588 +/- 0.206 ml/min/cm H2O/100 g lung wet weight, respectively. Treatment of the lungs with platelet activating factor caused no changes in Cv or Ci, but increased Kf,c suggesting increased endothelial permeability. We conclude that analysis of weight changes by a biexponential equation offers a quick and reliable way to analyze factors related to edema formation.