The relationship between elevated interstitial fluid pressure and blood flow in tumors: A bioengineering analysis

Purpose: To examine the hypothesis that elevated interstitial fluid pressur e (IPP) is a cause of reduced blood flow in tumors. Materials and Methods: A physiologic model of tumor blood how was developed based on a semipermeable, compliant capillary in the center of a spherical tumor, The model incorporates the interaction between the tumor vasculatur e and the interstitium, as mediated by IFP, It also incorporates the dynami c behavior of the capillary wall in response to changes in transmural press ure, and the effect of viscosity on blood Bow. Results: The model predicted elevated tumor IFP in the range of 0 to 56 mmH g, The capillary diameter in the setting of elevated IFP was greatest at th e arterial end, and constricted to between 3.2 and 4.4 mu m at the venous e nd. This corresponded to a 2.4- to 3.5-fold reduction in diameter along the length of the capillary, The IFP exceeded the intravascular pressure dista lly in the capillary, but vascular collapse did not occur. Capillary diamet er constriction resulted in a 2.3- to 9.1-fold steady-state reduction in tu mor blood Bow relative to a state of near-zero IFP, Conclusion: The results suggest that steady-state vascular constriction occ urs in the setting of elevated IFP, and leads to reduced tumor blood flow. This may in turn contribute to the development of hypoxia, which is an impo rtant cause of radiation treatment failure in many tumors. (C) 1999 Elsevie r Science Inc.