Indirect estimate of perimicrovascular pressure rise in edema in isolated zone 1 lung

To determine how liquid accumulation affects extra-alveolar perimicrovascular interstitial pressure, we measured filtration rate under zone 1 conditions (25 cmH2O alveolar pressure, 20 or 10 cmH2O vascular pressure) in isolated dog lung lobes in which all vessels were filled with autologous plasma. In the base-line condition, starting with normal extra-alveolar water content, filtration rate decreased by about one-half over 1 h as edema liquid slowly accumulated. We repeated each experiment after inducing edema (up to 100% lung weight gain). The absolute values and time course of filtration in the edema condition did not differ from base-line, i.e., the edema did not affect the time course of filtration. To compute the maximal initial and maximal change in extra-alveolar perimicrovascular pressure that occurred over each 1-h filtration study, we first assumed that the reflection coefficient is 0 in the Starling equation, then calculated perimicrovascular pressure and filtration coefficient from two equati...