AJP - Heart and Circulatory Physiology, Vol 242, Issue 4 512-H519, Copyright © 1982 by American Physiological Society
Colloid osmotic pressure changes in isolated isogravimetric cat hindlimb
P. D. Watson
The development of osmotic pressure, following the addition of bovine serum
albumin (BSA) to the perfusate, was measured in an isogravimetric cat
hindlimb fully dilated with papaverine. The changes in colloid osmotic
pressure were followed by recording the changes in venous pressure (PVI)
necessary to maintain constant weight. Capillary filtration coefficient
(CFC) and vascular compliances were calculated from weight changes
following steps in venous pressure. Venous BSA levels reached arterial
within 1 min, and PVI reached a new steady state 13.1 +/- 0.9 (SE) min (n =
9 in 6 limbs) after adding BSA. This apparent delay in the development of
the osmotic pressure agrees with earlier reports. However, when the BSA was
added under constant venous pressure conditions, the fluid reabsorption
reached its maximum rate within 1.5 min. The data suggest that the BSA is
osmotically fully effective after the capillary washin. The slowness of the
rise of PVI in the isogravimetric state is probably caused by the time
necessary to absorb sufficient fluid from the interstitium to raise the
capillary pressure to a level that balances the increased oncotic pressure.
A mathematical model supports this explanation.
