The measurement of glomerular filtration pressure from sieving data for macromolecules.

It is possible to derive the GFP from sieving data by two means and with the following qualifications: 1. Assuming the membrane isoporous, it is possible to calculate GFP by applying Poiseuille's law. The analysis of the sieving curve should then be limited to molecules with a radius between 21 and 41 A. 2. Assuming a log-normal distribution of pore radii, it is possible to obtain a value for GFP by computation. In this case the values for phi higher than 0.7 will not be considered in the calculation of sigmaE used to determine the most satisfactory adjustment of the calculated sieving curve to the experimental data. Although the second method allows a perfect adjustment of the curves, it gives more scattered results than the first for the calculation of GFP. However, a close correlation exists between both sets of results.