Pulpal hemodynamics and interstitial fluid pressure: balance of transmicrovascular fluid transport.

The net rate of fluid movement across the microvascular endothelium is governed by hydrostatic and protein osmotic pressures operating on each side of the vessel wall. These basic forces regulating the pulpal transmicrovascular fluid exchange are the same as in other tissues. However, the pulp is special in regard to its enclosement between rigid dentin walls, implying low interstitial compliance. In addition, the pulp has a relatively low perfusion pressure. In the low compliant pulpal interstitium, even a modest rise in net filtration will favor a relatively large increase in interstitial fluid pressure (IFP) which opposes further filtration. This will result in a minimal increase in interstitial fluid volume and, theoretically, any dilution of interstitial protein concentration is not possible. Thus, an increase in vessels' permeability to protein in this low compliant system must be balanced by a further rise in IFP, unless a washout of proteins takes place by raised lymph flow. However, a significant increase in IFP may seriously impede pulpal blood flow both by raising venous vascular resistance and secondarily by reducing pulpal perfusion pressure. The most important edema-preventing mechanisms in tissues with low compliance, as the dental pulp, seems to be a rise in IFP which initiates increased lymph flow and washout of proteins.