PHYSIOLOGICAL BASIS OF HRV

The physiological basis of HRV is the fluctuations of the activity in brain cardiovascular vasoconstrictor and vasodilatatory centers. Normally, these fluctuations are a result of:

* Blood pressure oscillation – baro-reflex modulated;

* Respiration (para-sympathically mediated via thoracic stretch receptors;

* Thermoregulation (sympathetically mediated via thermoregulatory peripheral blood flow adjustments) and

* Circadian biorhythm.

All these factors can influence the length of beat-to-beat intervals, named cardio intervals or R-R intervals. Their values are an object of mathematical estimation yielding the amount of HRV.

The increase or decrease of HRV is reflected by the difference of cardio intervals length (expressed with a time-based measurements as ms), and by the difference of the spectral power (expressed with a frequency-based measurement as Hz). Thus, there are two types of HRV measurements – time-domain measures and frequency-domain measures, explained in detail in the Stress test – Summary section.