Derivation of stroke volume from the central aortic pressure tracing: Basis for a noninvasive method. Noninvasive cardiac output

In this study a method is described for deriving the stroke volume from information contained in the central aortic pressure tracing. The fundamental finding was that left ventricular energy expenditure per stroke, deduced from the tension-time relationship (systolic pressure (SP) x systolic ejection time (SET)) is proportional to the product of the mean rate of pressure generation (pulse pressure (PP)/SET) and the mean rate of volume generation (stroke volume (SV)/SET) during systolic ejection. Thus, SP x SET is proportional to [PP/SET] x [SV/SET], and SV becomes equal to k x SP x [SET]³/PP. This formulation was applied to 120 patients who had undergone diagnostic cardiac catheterization for suspected coronary artery disease and in whom the SP, PP and SET were determined from the central aortic pressure tracing. When k was adjusted for the pulse pressure, the SV derived by this formulation varied from the directly determined SV by ± 15% in 95% of instances and by > ± 15% in 5% of instances; mean variance was 7.7%. When the same methodology was applied to an additional 100 patients utilizing the iliac artery pressure tracing, comparable findings pertained, but the variable of pulse pressure augmentation diminished the degree of reliability of results. It is concluded that the formulation may provide the basis for a noninvasive method if the variable of pulse pressure augmentation in the peripheral arterial system can be controlled.