Microcirculatory response to periodic pulsations in capillary pressure

Abstract

A mathematical analysis of time-dependent convection and diffusion in the microcirculation is presented in order to ascertain the effect on capillary-tissue fluid exchange of cardiac pulsatility and the rhythmic contractions of arterioles and precapillary sphincters. Disturbances to the hydrostatic pressure and protein concentration in the capillary and in the surrounding interstitial fluid resulting from such fluctuations are determined. It is established that the small cardiac pulsations that exist at the microcirculatory level have little effect on fluid exchange, and the quantitative nature of this effect is determined. However, the contractions of arterioles and precapillary sphincters are found to substantially affect the various Starling forces, resulting in a complex pattern of filtration and reabsorption over a period of oscillation. The analysis shows that blood flow reduction achieved through rhythmic contraction of arterioles or sphincters results in less fluid reabsorption than a corresponding reduction achieved through a sustained steady contraction. Therefore, rhythmic contractility provides a mechanism for blood flow regulation that avoids excessive tissue dehydration.