FLUID WAVES IN RENAL TUBULES.

Autoregulation of renal blood flow is ineffective when arterial pressure perturbations occur at frequencies above . 05 Hz. To determine whether wave propagation velocity to the macula densa is rate limiting, we estimated compliances of the proximal tubule and the loop of Henle, and used these values in a model of pressure and flow as functions of time and distance in the nephron. Compliances were estimated from measurements of pressures and flows in early proximal, late proximal, and early distal tubules in rats under normal and Ringer-loaded conditions. A model of steady pressure and flow in a compliant, reabsorbing tubule was fitted to these results. The transient model was a set of nonlinear hyperbolic partial differential equations with split nonlinear boundary conditions, and was solved with finite difference methods.