Interstitial Fluid Pressure: II. Pressure-Volume Curves of Interstitial Space

Pressure-volume curves of the interstitial fluid spaces were estimated using four different methods. Interstitial fluid pressure was measured from implanted perforated capsules while interstitial fluid volume was varied (a) by perfusing the isolated hind limb of the dog with several types of fluid and at different perfusion pressures, (b) by elevating the venous pressure so that fluid would transude into the interstitial compartment, (c) by infusing large quantities of Tyrode's solution into the whole animal, and (d) by intravenous infusion of concentrated dextran solution. In all these studies, the compliance of the interstitial fluid system was found to be very low when the interstitial fluid pressure was negative but very high when the pressure rose slightly above atmospheric pressure. A physical model of the interstitial spaces was also constructed. Pressure-volume curves recorded from this model demonstrated a pattern of compliance changes similar to that shown by the interstitial pressure-volume curves recorded from dogs. These experiments give further support to the concept that the interstitial fluid pressure is normally negative but becomes positive as edema fluid accumulates.