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OF CARDIOVASCULAR DATA |
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OF CARDIOVASCULAR DATA |
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| |LEVEL 0| |HOMEPAGE| |
Amount of power per unit (density) of frequency (spectral) as a function of the frequency
The power spectral density, PSD, describes how the power
(or variance) of a time series is distributed with frequency. Mathematically,
it is defined as the Fourier Transform
of the autocorrelation sequence of the time series. An equivalent definition
of PSD is the squared modulus of the Fourier transform of the time series,
scaled by a proper constant term.
Being power per unit of frequency, the dimensions are those of a power
divided by Herz. For instance, typical units of PSD are mmHg2/Hz
for blood pressure signals, ms2/Hz for interval
tachograms, (beats/min)2/Hz for instantaneous
heart-rate signals.
Different algorhythms are used for the estimation of PSD. The more
popular in the field of cardiovascular signals analysis are those based
on the direct computation of the squared modulus of the Fourier transform
of the time series (often termed periodogram estimators) through FFT,
and those based on an autoregressive modeling of
the time series.
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Kay SM, Marple SL Jr. (1981) Spectrum Analysis - A
Modern Perspective. Proceeding of the IEEE, vol.69 (11), 1380-1419