Errors in velocity measurement by the Pitot principle in fluids with slowly propagated pressure waves.

An attempt has been made to develop a velocity probe using the Pitot principle for the measurement of fluid velocities in cerebrospinal fluid. Pressures were measured using conventional transducers and amplifiers and the pressure difference signal has the predicted relationship to the square of fluid velocity in the steady state. However, in the clinical situation where slowly propagated pressure waves accompany cerebrospinal fluid movement the pressure difference incorporates an indeterminate term unrelated to velocity, and this imposes severe limitations on the technique. Measurements and discussion are presented.