TIME-VARIANT POWER SPECTRUM ANALYSIS FOR THE DETECTION OF TRANSIENT EPISODES IN HRV SIGNAL

A time-variant algorithm of autoregressive (AR) identification is intr oduced and applied to the heart rate variability (HRV) signal. The pow er spectrum is calculated from the AR coefficients derived from each s ingle RR interval considered. Time-variant AR coefficients are determi ned through adaptive parametric identification with a forgetting facto r which obtains weighed values on a running temporal window of 50 prec eding measurements. Power spectrum density (PSD) is hence obtained at each cardiac cycle, making it possible to follow the dynamics of the s pectral parameters on a beat-by-beat basis. These parameters are mainl y the LF (low frequency) and the HF (high frequency) powers, and their ratio LF/HF. These together account for the balanced sympatho-vagal c ontrol mechanism affecting the heart rate. This method is applied to s ubjects suffering from transient ischemic attacks. The time variant sp ectral parameters suggest an early activation of LF component in the ' 'RV power spectrum. It precedes by approximately 1.5-2 min the tachyca rdia and the ST displacement, generally indicative of the onset of an ischemic episode. The results suggest an arousal of sympathetic system before the acute attack.