Interpreting peritoneal membrane osmotic reflection coefficients using a distributed model of peritoneal transport.

The relationship between the osmotic reflection coefficient for the peritoneal membrane and that for peritoneal capillaries was derived theoretically using a distributed model of peritoneal transport. The distributed model predicted that the osmotic reflection coefficient for the peritoneal membrane was equal to that for peritoneal capillaries only when the capillary wall was the dominant diffusive solute transport resistance. Under these conditions, moreover, all peritoneal capillaries equally contributed to transperitoneal ultrafiltration. If, on the other hand, interstitial tissue was the dominant diffusive solute transport resistance, then the osmotic reflection coefficient for the peritoneal membrane was lower than that for peritoneal capillaries and only superficial capillaries participated in transperitoneal ultrafiltration. Previous experiments have demonstrated that the capillary wall is not the dominant diffusive solute transport resistance for small osmotic solutes across the peritoneal membrane; thus osmotic reflection coefficients for the peritoneal membrane are likely several times less than those for peritoneal capillaries.