njit-etd2003-081 - New Jersey Institute of Technology

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Figure 3.10 Example of power spectral density of HRV. Blue: power of spectrum of
RR interval in VLF range, red: power in LF range and yellow: power in HF range.
(From www.skyaid.org/S kyaid%20 Org/Medical/HRV_Courses htm, 12/2001.)
To date, the best-known and best-defined peak in power spectral analysis of
heart rate variability is the high frequency peak. The high frequency peak reflects
changes in the interbeat interval that cycles up and down at the same frequency as
respiration. This influence of respiration on heart rate has been known for more than
one century and is called respiratory sinus arrhythmia (RSA). Properly defined, RSA is
a rhythmical fluctuation in heart periods at the respiratory frequency that is characterized
by a shortening and lengthening of heart periods in a phase relationship with inspiration
and expiration, respectively [15]. RSA is being used increasingly as a measure of vagal
control of the heart. As a result, the high frequency peak, which often occurs at the
same frequency as the respiration peak, corresponds approximately to the RSA and it is
purely parasympathetic in origin [17]. From experience, one might contest that the
frequency of respiration is not limited to within the narrow band of 0.15 Hz to 0.4 Hz.