TIME-FREQUENCY SPECTRAL-ANALYSIS OF ELECTRIC-FIELD PLETHYSMOGRAPHY SIGNALS

Cardiac activity contaminates respiratory electric field plethysmograp hy (EFPG) signals, and vice versa, and is usually treated as an artefa ct. On the other hand, simultaneous information on respiration and car diac activity is often required in clinical practice. Hence, we use ti me-frequency spectral analysis (TFSA) by means of the spectrogram (SG) to investigate the instantaneous cardio-respiratory information conta ined in EFPG-signals and show that it is a practical means of extracti ng this information out of a single EFPG-signal. Comparisons with a Wi gner distribution reveal sufficient time-frequency resolution of the S G for detection of physiological events in EFPG-signals. SC-analysis i ndicates spectral peaks related to respiration and cardiac activity (d epending on the electrode configuration, up to the third and fifth har monic, respectively) and the possibility to detect respiratory sinus a rrhythmia by means of EFPG-measurements. Intermodulation products caus e overlaps of respiratory and cardiac spectra pointing out nonlinear r elationships. Additionally, SC-analysis supplies essential information for the separation of EFPG-signals into respiratory and cardiac compo nents, by means of filter techniques.