Interstitial Fluid Pressure: III. Its Effect on Resistance to Tissue Fluid Mobility

TLDR

Resistance to fluid movement in interstitial spaces was measured using perforated catheters and capsules in dog subcutaneous tissue. The study proposes that water entrapment in the gelatinous matrix of the interstitial ground substance causes the observed resistance differences. Pressure‑volume curves were derived from pressure‑conductance data to relate interstitial fluid pressure to mobile fluid volume. When interstitial fluid pressure reaches or exceeds atmospheric pressure, resistance falls over 100,000‑fold and tissue space volume suddenly increases; below atmospheric pressure, mobile fluid volume approaches zero even though the measured volume remains large.

Abstract

The resistance to fluid mobility in the interstitial fluid spaces has been measured between perforated catheters inserted into the subcutaneous abdominal tissues of the dog and between perforated capsules implanted in the tissues 1 month previously. When the pressures in the catheters or perforated capsules were less than atmospheric pressure, the resistance to fluid movement was almost infinite, but when the pressures were increased almost to or above atmospheric pressure the resistance usually decreased more than 100,000-fold, indicating a suddenly increased size of the tissue spaces. The shape of the pressure-volume curve relating (a) interstitial fluid pressure to (b) volume of mobile interstitial fluid was calculated from pressure-conductance curves recorded in these experiments. On comparing this pressure-volume curve with a previously measured pressure-volume curve of the entire interstitial fluid compartment, two important points were observed: first, both curves exhibit a sudden increase in volume when the interstitial fluid pressure rises above atmospheric pressure. Second, the mobile interstitial fluid volume approaches zero when the interstitial fluid pressure falls below atmospheric pressure while the measured volume is still very great. It is postulated that this difference is caused by entrapment of large amounts of water in a relatively immobile state in the gelatinous matrix of the ground substance filling the interstitial spaces.