Basics of heart rate variability biofeedback

In recent years there has been substantial support for heart rate variability (HRV) biofeedback with a variety of applications. This brief article takes a look at HRV biofeedback - what it is and how it is measured. It is true to say that practitioners have practical experience that shows HRV biofeedback can have positive effects even if we have an imperfect idea of the all the underlying psychophysiological mechanisms.  HRV is sometimes seen as an indicator of physical and emotional resilience.

There are two typical ways of gathering the raw data - either via an EXG sensor or a BVP (Blood Volume Pulse sensor).

The easiest is the BVP approach but this can be more prone to movement artifact. If using the BVP we can easily (using the Biotrace+ software with a NeXus system) identify the heart rate via the Interbeat interval (see below). The software can carry out the frequency domain operations to examine the energy characteristic of this behaviour.

In the 1990's researchers worked with a form of cardiorespiratory intervention that has become known as respiratory sinus arrhythmia (RSA) biofeedback or sometimes resonant frequency biofeedback (RFB). 

In this approach, the subject is fedback information about the beat to beat heart rate changes whilst the subject's breathing pattern is matched to a pacing device (usually on the feedback screen).  In health the beat to beat intervals of the heart can vary significantly and depend on the emotional state of the individual.  The RSA is a heart rate pattern that occurs when the breath is matched (correlated) to this changing pattern of heart rhythm. The heart rate then increases during inhalation and decreases during exhalation.  If we look at the frequency spectrum of the heart rate we might then see a "spike" at around 0.1 Hz (around 6 breaths per minute). This is a state in which the breath and heart rate are strongly correlated.  The often chaotic pattern of heart rate behaviour is being replaced by a pattern of change in which the heart speeds up and slows down in sync with the breath. As it does so, the amplitude of change in heart rate also becomes greater.

Theere is a second source of heart rate variability - blood pressure through the Baroreflex system. Cardiopulmonary and baroreceptors detect respiratory changes in cardiac filling and arterial pressure.  A rise in blood pressure stimulates the baroreceptors to signal to the SA node via the parasympathetic nervous system to slow down the heart.  A drop in blood pressure stimulates the baroreceptors to increase heart rate through the sympathetic nervous system.  The ability of blood pressure changes to regulate the heart rate is called the Baroreceptor Sensitivity.

For a nice article to explore the subject more deeply check out this article.

Lehrer, Paul M; Gevirtz, Richard (2014)
"Heart rate variability biofeedback: how and why does it work?
Foundations in Psychology, Vol. 5, Article 756, July 2014
Doi10.3389/fpsyg.2014.00756