Correlating Heart Rate Variability with Skin Impedance Measurements

To determine the interaction between skin impedance, measured at acupuncture points, and autonomic nervous response, as expressed through heart rate variability (HRV), we propose a method for correlating frequency components of non-uniformly sampled R-R intervals and the impedance measurements. Since vagal response typically manifests itself in the high frequency (HF) range of HRV, Lomb-Welch periodograms (LWp) are used to evaluate accurately the HF band spectral components. The resampling rate of the LWp is adjusted according to the window/filter used to meet a -20 dB anti-aliasing requirement. The record length of each individual LWp is then chosen such that the frequency component resampling rate matches the impedance sampling rate. Since it is not feasible to use the phase information, the magnitudes of the frequency component samples are used in the evaluation of the cross-covariances between the HRV components and the impedance signals