Signal analysis of rhythmical discharge in cardiac preganglionic fibers and of heart rate variability

A signal processing technique is proposed for the extraction of short-term variability rhythms from the discharge of cardiac sympathetic fibers. In decerebrated and artificially ventilated cats the impulse activity of cardiac preganglionic fibers was recorded in a closed chest preparation together with ECG, arterial pressure, and respiration. The neural signal was fed into an analog spike counter, obtaining a stepwise count signal. Beat-by-beat variability series were extracted; the spike-count signal is sampled once per cardiac cycle convolving with a FIR low-pass filter. The presence of low-frequency and high-frequency rhythms was demonstrated by parametric spectral and cross-spectral analyses