Assessment of protein permeability in normal human systemic circulation

Vascular permeability to oncotic agents is an important determinant of transvascular fluid flux (J) and systemic fluid balance. In this study, a technique was developed to measure protein reflection coefficients (omega) for albumin (Alb), immunoglobulin (Ig) G, and IgM in the intact human systemic circulation to evaluate the role of vascular protein permeability in health and disease. A mathematical model was developed to calculate omega in the forearm circulation from changes in venous hematocrit and protein concentration that occur during edema formation. Assumptions required for the model were validated in an initial set of experiments in normal subjects when edema was induced by inflating a pneumatic cuff on the upper arm. A second series of experiments assessed omega for Alb, IgG, and IgM in men (n = 7) and in women in the follicular (n = 5) and luteal (n = 4) phases of the menstrual cycle. There was an increasing trend in omega with molecular size in aggregated subjects [omega Alb = 0.81 +/- 0.12 (SE), omega IgG = 0.88 +/- 0.12, omega IgM = 0.92 +/- 0.18; P = 0.088]. These values were consistent with those obtained with in vitro preparations. omega values were lower in women in the luteal than in the follicular phase (P = 0.047). We conclude that the assumptions required for this model can be achieved in the intact forearm circulation and that there are menstrual phase-related differences in vascular protein permeability in normal women.