njit-etd2003-081 - New Jersey Institute of Technology

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4.1.2.1 Autonomic Testing. HR Variability and BP Variability: These tests were
carried out for rest, deep breathing, Valsalva maneuver, isometric contraction, and
exercise. These were established noninvasive methods for the quantitative assessment of
autonomic activity based on the analysis of the variability of the cardiac R-R interval
through the assessment of parasympathetic (PNS), sympathetic (SNS), and
sympathovagal balance (S/V). Our laboratory used an established and validated routine
for the spectral decomposition of heart rate variability. Specifically, interbeat 0130
intervals were derived from the electrocardiogram (ECG) using a peak detection routine.
The sequence of the IBI was interpolated to provide a continuous data steam, and the
resulting IBI data were detrended using a robust locally weighted regression procedure.
The resulting data were split in sections, and each section is tapered using a split cosine
window. Finally, the data were transformed into frequency spectra using fast Fourier
transform algorithms and smoothed across blocks of frequencies to produce a spectrum.
The power of the heart rate variability is calculated by measuring the area under
the spectra in the established frequency bands. Power spectra within the 0.04 to 0.15 Hz
range were defined as low frequency components, whereas those at the frequency of
0.15 to 0.40 Hz were defined as the high frequency components. The ratio between low
frequency (LF) and high frequency (HF) components is considered representative of the
sympathovagal balance.