Heart rate variability training with Biotrace+
Heart rate variability (HRV) refers to the natural variability of the intervals between consecutive heart beats. It is actually a very sophisticated measurement to take with high HRV being associated with overall health. In other words the healthy heart naturally speeds up and slows down even at rest.
The parasympathetic nervous system (associated with “rest and digest”) and the sympathetic nervous system (associated with the so called “fight or flight” response) are the branches of the autonomic nervous system (ANS) that control the heart and many associated neurophysiological processes. The higher the HRV exhibited by an individual the greater their ability to cope with stress. Stress, blood pressure, respiration, emotions, and thermoregulation, among others, are all stimuli that influence the heart rate through the ANS.
The HRV tends to reduce with age, and reduced HRV is also associated with chronic diseases and poor outcomes, e.g., diabetes, systematic inflammation, depression and sudden cardiac death. Therefore, it is beneficial to investigate methods of intervention to increase HRV to achieve balance in the ANS. It is also used in training protocols for elite athletes seeking higher performance. The usefulness of HRV biofeedback has been reported in many studies.
We also know that the way we breathe affects heart rate variability. When we inhale our heart accelerates and the sympathetic nervous system is stimulated. When we exhale that our heart decelerates and the parasympathetic branch of the ANS is activated. This natural flow and balance is called the Respiratory Sinus Arrhythmia or RSA.
When we are in a balanced state we can talk about the concept of coherence. When the HRV is increasing an decreasing smoothly and in sync with our breathing pattern we understand that coherence is high and we are likely to feel calm and at peace. When HRV is chaotic and not in sync with our breathing, coherence is low and stress levels are likely to be high.
To measure HRV we need to be able to capture the heart rate and this is typically done with a Blood Volume Pulse (BVP) sensor or via an ECG method. The BVP sensor is easily slipped over a finger and it is quick and easy to apply. The BVP approach is prone to movement artefacts and is not ideal in every situation. The ECG approach is more specific and best for research and other critical applications. The NeXus Biotrace+ software supports both approaches in an easy plug and play manner.
Once you have captured the HRV you will want to quantify it in some way. This can be done by so called time domain or frequency domain methods.
The time domain approach is all about the statistics of the timing of each beat whilst the frequency domain approach represents the HRV signal as individual frequency components - typically classifying the behaviour as a proportion of high, low and very low frequencies.
When we are looking to train HRV we need to measure the respiration rate as well and this is easily done with a respiration sensor. The goal of HRV training is typically to maximise HRV through what is referenced to as Resonance Frequency (RF) training. When we breathe at the so called resonant frequency, the amplitude of the heart rate variations is maximised. The exact RF differs from person to person but is typically found when breathing at a rate of between 5 and 8 breaths per minute. The BioTrace+ built-in breathing pacer can be used to set the breathing pattern for the user to follow. The Inhale time, Sustain time, Exhale time and and Pause time can all be controlled.
Respiration has a cardiac vagal efferent modulation effect on the heart rate. In HRV biofeedback, the idea is to breathe at a specific but individual-dependent respiration rate which brings about a RF. The resonant frequency is the rate of delivery of the feedback that controls blood pressure.
This feedback loop elevates or lowers the heart rate in the case of a drop or rise in blood pressure, respectively. By breathing at this rate, the feedback from respiration and blood pressure can be made coherent and, hence, more efficient. This method is called resonant frequency breathing and has the potential to enhance baroreflex gain and improve HRV.
With the NeXus Biotrace+ software there are a number of built-in screens that allow easy access to HRV measurement and training. These can be modified to suit extended applications. The standard screens are
- BVP - HRV Basic
- BVP - HRV Low Frequency
- BVP - HRV Coherence
- BVP - HRV and Oxygen
- ECG - HRV Basic
- ECG - HRV Low Frequency
- ECG - HRV Coherence
- BVP - HRV measurement
- ECG - HRV measurement
Because the NeXus biofeedback systems are multimodal HRV measurement can easily be combined with other measurements such as EDA, EMG, skin temperature, Oximetry, respiration and so on.
If long term monitoring is of interest the NeXus 10 has some nice features. The NeXus 10 allows capture of up to 10 multimodal signals at the same time. By using an SD memory card in the NeXus 10 these signals can be recorded for up to 24 hours.