Pressure transmission in pulmonary arteries related to frequency and geometry.

• The difficulties in analyzing pulsatile pressure and flow in the circulatory system can hardly be overestimated. Although the socalled Navier-Stokes equation expresses the general relation between pressure gradient and the resulting motion of a viscous Newtonian liquid, its exact solution depends upon the choice of boundary conditions. In pulsatile flow fluid motion A'aries from point to point and from moment to moment and must therefore be described by a time-dependent three-dimensional vector field. The present state of knowledge in the physical as well as biological sciences is inadequate for an exact solution since we are dealing with a non-Newtonion fluid, in a viseo-elastic system of branched, tapered tubes with multiple changes in geometry.