Alignment of successive cardiac signals for analyzing changes in performance

A technique is described for aligning two recordings of a cardiovascular signal obtained at different times. Alignment allows comparison in analyzing changes in hemodynamic state. The technique is intended for use in patients during and immediately after cardiac surgery. A left-ventricular diameter signal is recorded in dogs. A fast Fourier transform is obtained using a window which results in accuracy of magnitude calculation within 0.1%. The fundamental frequency is also calculated. Using the magnitudes, the fundamental frequency, and the original digitized waveform, the phase angles are calculated using the periodogram method. This results in phase accuracy to within 0.35 degrees . The phase of the first frequency component is set to 0, and the phase of each successive harmonic is adjusted accordingly.<>