njit-etd2003-081 - New Jersey Institute of Technology

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3.8 Power Spectral Analysis of Heart Rate Variability
Power spectral analysis of heart rate variability is a potentially powerful tool for
evaluating the activity of the autonomic nervous system noninvasively. Power spectral
analysis is a technique which transforms a signal from the time domain to the frequency
domain. The time domain signal used for computing the heart rate variability power
spectrum is known as the interbeat interval (IBI). The following is a brief description of
how to obtain the MI signal.
To begin the analysis, the ECG is converted from analog to digital form and
stored in ASCII format on the data acquisition computer running in LabVIEW. The data
is then transferred over to a signal-processing computer. Another LabVIEW program is
used to obtain the HRV power spectrum. The following is a description of the necessary
steps to obtain the power spectrum of HRV.
The first step to obtain the power spectrum of HRV is to detect every R-wave in
the ECG. Because the R-wave complex is pronounced in the ECG, the LabVIEW
detection program can easily detect these R-waves.
Before trying to detect the R-waves, the ECG signals are detrended using a
locally weighted robust regression algorithm built in LabVIEW. To help detect each R-
wave, a vertical threshold (which the R-wave must exceed) and a horizontal threshold
(to prevent detecting an R-wave for a period of time after one was detected) can be
varied. If an error occurs during the R-wave detection, the analyst can use existing
software to manually detect or undetect the incorrectly detected R-waves.