Determinants of isogravimetric capillary pressure in the isolated dog hindlimb

The hindlimb of the dog was rapidly isolated and carefully perfused in an attempt to prevent transcapillary fluid shifts into the interstitium which may occur during normal surgical isolation and perfusion. In the control preparation before weight was allowed to increase, isogravimetric capillary pressure (Pci) averaged 8 mmHg lower than colloid osmotic pressure of the plasma (IIp). As the weight of the leg was increased, Pci increased and IIp - Pci decreased. When weight was increased by 5.8%, IIp - Pci averaged 3 mmHg; with a 9.8% increase in weight, IIp - Pci averaged 1.3 mmHg. The calculated value of compliance of the interstitial space averaged 0.50 ml/mmHg per 100 g of tissue and increased approximately 10-fold as the weight of the leg was increased. Since IIp - Pci has always been reported to be approximately 2 mmHg when the hindleg was isolated with standard surgical techniques, these data suggest that the procedures normally used to isolate and perfuse the hindlimb caused the weight of the limb to increase by 6% or more before Pci was determined. Furthermore, it appears that most of the variation in the reported value of Pci is due to variation in the value of IIp since IIp - Pci has always been reported to be very close to 2 mmHg in the isolated hindlimb.