Indirect estimation of filtration variables in rat lungs calculated by protein concentration or osmotic pressure method.

We reported a new way for estimating filtration variables: K(filtration coefficient), Ppmv (perimicrovascular pressure) and sigma (protein reflection coefficient), from 3 different measurements of weight gain at two protein concentrations of perfusate (Cmv) and at two vascular pressures (Pvasc). We used the Starling equation for calculating those variables using two different formulas which expressed that all protein moves by convection. In this report, we compared those two formulas: 1) 1--sigma = pi pmv/pi mv, which is already reported (Tanita et al. 1990), and 2) 1--sigma = Cpmv/Cmv. We measured filtration rate (Q) by a gravimetric method in isolated rat lung lobes in zone 1 conditions (alveolar pressure = 20 cmH2O) at two vascular pressures, Pvasc = 15 or 8 cmH2O and perfused the lobes with plasma containing a low or a high concentration of protein. By extrapolating the log of the rate of weight gain to t = 0, we obtain the initial filtration rate. Cmv was measured and pi mv was estimated by Yamada's equation (Yamada et al. 1985). The reflection coefficient calculated in 1--sigma = pi pmv/pi mv method is computed 10% higher than that in 1--sigma = Cpmv/Cmv method. However, the filtration coefficient or the perimicrovascular pressure calculated in either method was identical. We conclude that filtration variables can be estimated easily by pi method and those variables are comparable to those estimated by C method which are theoretically more acculate but more complicated in calculation.