FIGURE 1.

Shape of the interstitial volume–pressure relationship. Zero represents euvolemia. At low interstitial volume, compliance is low, and an increase in volume causes pressure to rise steeply (from A to B), opposing further filtration. This steep increase in pressure is produced by tensile forces applied by fibroblasts and extracellular matrix. With further interstitial fluid accumulation, typically interstitial volume 20–50% above euvolemia, interstitial compliance markedly increases as a result of structural changes, and large changes in volume result in a minimal increase in pressure (from Point B to C). Modified from references (50, 51, 55, 121).