Detection of dicrotic notch in arterial pressure signals.

A novel algorithm to detect the di- crotic notch in arterial pressure signals is proposed. Its per- formance is evaluated using both aortic and radial artery pressure signals, and its robustness to variations in design parameters is investigated. Methods. Most previously pub- lished dicrotic notch detection algorithms scan the arterial pressure waveform for the characteristic pressure change that is associated with the dicrotic notch. Aortic valves, however, are closed by the backwards motion of aortic blood volume. We developed an algorithm that uses arterial £ow to detect the dicrotic notch in arterial pressure waveforms. Arterial £ow is calculated from arterial pressure using simulation results with a three-element windkessel model. Aortic valve closure is detected after the systolic upstroke and at the minimum of the ¢rst negative dip in the calculated £ow signal. Results. In 7 dogs ejection times were derived from a calculated aortic £ow signal and from simultaneously meas- ured aortic £ow probe data. A total of 86 beats was analyzed; the di¡erence in ejection times was ÿ0.6 ?? 5.4 ms (mean ?? SD). The algorithm was further evaluated using 6 second epochs of radial artery pressure data measured in 50 patients. Model simulations were carried out using both a linear wind- kessel model and a pressure and age dependent nonlinear windkessel model.Visual inspection by an experienced clini- cian con¢rmed that the algorithm correctly identi¢ed the dicrotic notch in 98% (49 of 50) of the patients using the linear model, and 96% (48 of 50) of the patients using the nonlinear model. The position of the dicrotic notch appeared to be less sensitive to variations in algorithm's design parame- ters when a nonlinear windkessel model was used. Conclu- sions. The detection of the dicrotic notch in arterial pressure signals is facilitated by ¢rst calculating the arterial £ow wave- form from arterial pressure and a model of arterial afterload. The method is robust and reduces the problem of detecting a dubious point in a decreasing pressure signal to the detection of a well-de¢ned minimum in a derived signal