Pressure-volume relationships in the interstitial spaces.

This paper will discuss the recent finding that the normal interstitial fluid pressure is negative rather than positive and will present a method for recording dynamic changes in interstitial fluid pressure. Especially important is the shape of the pressure-volume curve of the interstitial spaces. So long as the interstitial fluid pressure is negative, the interstitial fluid volume remains almost exactly constant; the amount of fluid in the interstitial spaces under these conditions is fust that amount necessary to fill all the tissue voids. However, when the pressure rises into the positive pressure range, the stability of interstitial fluid volume regulation is lost, and the person very rapidly develops edema. Thus, interstitial fluid pressure is negative under normal conditions and is positive in edema.