When the basic formula derived flow (1,34) and (1,35), in order to simplify, will assume that the rate of catheter-wide cross-section of the same.

In fact, catheter-section on the distribution rate is changing. This is due to fluid on the wall, and friction at different speeds the flow of fluid between the particles caused by friction.

Assume that the container in the viscous fluid (10) is static and mobile in which a flat (-wall). When the flat-panel mobile, fluid particles also brought its Reply, and the flat side of the plate to the fluid-speed mobile. The farther from the plate, while the lead of the fluid of the speed of the smaller. In fact reduce the speed of the line.

Figure 10 viscosity of the diagram