In one of our studies on the effect of various breathing exercises on Vagal activity and Baroreflex Sensitivity, subjects performed uncontrolled breathing, paced breathing at 0.23 Hz, and paced breathing at 0.1 Hz.
In spectral analysis of both HR and BP based on FFT (attached picture), in addition to the peaks in the spectrum around the breathing frequency there are also other peaks (2nd harmonics) in both blood pressure and heart rate variability spectrum. What is the origin of these harmonics? are they because of the FFT method and has no physiological origins?
Dear Ali!
Some Answers there within this publication
Chapter The Complex Approach to a Multipurpose Estimation of a Sport...
Dear Ali!
I think the origin of these harmonics is not clear yet. Unfortunately, almost no one studies the physiological mechanisms of heart rate variability. Most of the studies are of a correlation nature and study the relationship between the standard parameters of heart rate variability with one or another thing. This question is of my scientific interest. I found that heart rate modulations with the period of 3 oscillations per cardiointerval is associated with the level of frontal cortex activation and mental work capacity. Probably, the source of these modulations is the highest center of regulation of the cardiovascular system located in the frontal cortex!
If your signal is not a perfect sinusoid it will have harmonics. Simple like that. Study Fourier analysis.