An Electric Device for Instantaneous and Continuous Computation of Aortic Blood Velocity

An electric device is described which computes the instantaneous aortic blood velocity from the pressure difference between two points along the aorta. The pressure difference was obtained from a specially designed double lumen catheter attached to a differential pressure gage. The aortic blood velocity curves obtained from 20 dogs compare closely with most of those appearing in the literature. RECENTLY a method has been describedwhereby the instantaneous aortic blood velocity may be computed from the instan-taneous pressure difference between two points located along the axis of flow.1 The equation describing this relationship is: p = p&x — + aw at (1) where p is the instantaneous pressure difference, p is the blood density, Ax is the separation of ft 01 the pressure pickup points, — is the blood Civ acceleration, a is the coefficient of friction, and u is the blood velocity. The boundary condition for u is that it must return to and remain at zero at the end of diastole. The value of a which will satisfy this condition is the proper value. It can be demonstrated that a must lie somewhere between 0 and 2A.-C. The proper value may be obtained by a tedious graphic method. However, analog computer technics are available which permit the ad-justment of a to satisfy the boundary condition for u and which will then solve equation (1) for u continuously. An equation analogous to equation (1) is at R (2) which is the relationship between the line current, / , and the voltage drop across a parallel connection of a resistance, R, and