Determination of delay time in individual transfer function for central aortic pressure reconstruction

In previous research, time-delay (Δt) was a more important parameter than the reflection coefficient in the individual transfer function of central aortic pressure reconstruction. The Δt can be obtained by electrocardiography (ECG) or phonocardiography (PCG). Because the pre-ejection period remains an uncertain factor, the present study used ECG and PCG to define the delay time and analyzed the accuracy of the reconstruction results. The Δt pre is the actual delay time derived from the aorta to the carotid pressure wave, Δt PCG is the time delay between the aortic valve component of the second heart sound and the dicrotic incisura of the carotid pressure wave, and Δt ECG represents the delay from the interval of the ECG R-peak to the foot of the carotid pressure wave. Compared with the measured aortic pressure, the reconstruction result obtained by Δt=Δt PCG slightly differed from the best result estimated by Δt=Δt pre. However, the differences between the result obtained by Δt=Δt ECG and the best result were significant in terms of the diastolic blood pressure, and pulse pressure, and especially in terms of the augmentation index and root-mean-square-error. Thus, the Δt should be determined by PCG for central aortic pressure reconstruction in practice.