HRV ...

 

WHAT IS HRV?

Heart Rate Variability Biofeedback is being taught is a variety of formats, and definitions do vary. Some use HRV to refer just to the Min vs Max HR difference, and train to find techniques that will elicit the biggest 'difference.' This is particularly true when the detection instrument for HR is an unregulared  finger-sensor photophlysmograph. Since the market is flooded with these devices, a learge segment of the biofeedback users see HRV and Min-Max HRV. And technically they are right. It was originally a peak-to-trough difference in HR.
Others have extended HRV feedback to require a DFT spectral display. DFT band Low Frequency is seen as the band to elevate, as it is widely taught that LF elevations rflect autonomic balance. Derived signals like LF/HF ratios and the misterious VLF wave is also taught as an important target for any kind of 'HRV' biofeedback.
To add to the confusion is how to link the 'HR wave' [min-max HR] to the respiration wave, and still call it 'HRV feedback.'

In this manual, we will try to reduce confusion by using  seperate terminology for these different kind of feedback:

HRV Feedback : Refers strictly to the HR wave, the min-max HR.
RSA Feedback: Refers to the HR wave assocated with easy breathing. Traditionally respiration was not recorded, so RSA should be restriced to simple HRV [min-max HR] feedback.
Spectral HRV Feedback. Refers to any feedback training involving watching either the spectral DFT graph or the VLF, LF and/or HF bands.

CardioRespiratory Synchrony/Coherance: Refers strictly to the synchtony [timing] between HR acceleration and Inhaling. [If you like, it also refers to HR decelleation timed with the exhale as well].
Resonant Frequency Training. Refers to Paul Leher's protocol combining Breathing Pacer and Cardio-Respiratory Feedback. Spectral HRV is involved, too. Resonant Frequency Training focused on the LF elevations and min-max HR.


Finally whatever you call it, most HRV-linked feedback protocols do not emphasize watching screens, as much as they emphasize testing stratagies to alter screen displays. This is different form more liner feedback models such as EMG. This means that the field of HRV-linked feedback has a variety of non-biofeedbsack techniques used to alter these signals. We recommed you first learn these techniques from experts in the field, as these are properly not a part of a basic HRV users manual and require adatation and clinical skills from an expert.

DEFINITIONS
HRV Feedback : Refers strictly to the HR wave, the min-max HR.

Min vs Max HR

This is a display of heart rate variability averaged over 30 seconds.  The software measures the minimum and maximum heart rate values for 30 seconds [HRV_30 =], then averages the difference of these values and displays them in a line graph. HRV_30 is a good graphical display of increasing or decreasing HRV trends.
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Spectral HRV Feedback. Refers to any feedback training involving watching either the spectral DFT graph or the VLF, LF and/or HF bands.

DFT (Discrete Frequency Transform)
The DFT  display is a spectral display for HR with a horizontal scale of 0 -.4 Hz.  All the peaks at different frequencies in this display represent the power of different rhythms present in the inter-beat interval (IBI) measurement.  The calculation always includes a fixed number of beats, either 64 or 128 beats depending upon the application, recalculated as each new IBI measurement is received.  For example, in a subject with a breathing rate of 6 breaths per minute (equaling one breath per 10 seconds =  .1 cycles per second = .1 Hz) a cyclic variation of heart rate every ten seconds would occur.  This would result in a peak in the DFT display in the green area at .1 Hz on the scale.

The bands of color in the DFT display represent the frequency ranges of the Very Low Frequency (VLF), Low Frequency (LF), and High Frequency (HF) signals as follows:

VLF= 0 - .05 Hz

LF = .05 - .15 Hz

HF = .15 - .4 Hz

    * The total power of all frequencies is related to autonomic balance ( for example, people suffering from depression tend to have lower total power). 
    * VLF is thought to be influenced primarily by the Sympathetic Nervous System (SNS) with slight Parasympathetic, or Vagal, influence. The VLF value rises when people are intellectually engaged in activities such as thinking, worrying, or self-criticizing. 
    * LF seems to be related to both SNS and Vagal activity associated with barorecepter regulation. The goal of breathing training is to achieve a peak in the .08 to .12 range of the LF band, allowing for variation in the breathing rate of the individual.  This peak indicates increased Vagal tone. 
    * Respiration is a major influence over HF activity. Decreasing the breath rate causes this value to go down, while values of 10-24 breaths per minute cause the HF value to go up.

VLF,LF,HF
The values for each of these signals, which represent the summation of power in a particular band,  are displayed at the top of each DFT display  and are also used in line graph displays , bar graph displays and digital number displays.

If the Respiration signal is available, the trainer should  record changes in respiration patterns, not only chages inHRV bands.
In practice HRV Feeedback tends to focus more on the VLF band as an indicatory of rumination and/or worry.
Often used in desensitization protocols, with coaching to reframe cognitive-arousal thoughts.

SKIPPED and DOUBLE BEAT DETECTOR
Skipped beats or double beats have a major effect on HRV feedback.
J&J has added a special missed or double beat correction circuit to keep spectral HRV bands more stable. Missed or double beats are still shown in the ECG and HR signals.

TASK FORCE HRV

J&J provides 2 kinds of HRV calculations:

    * J&Js 'Feedback' HRV Calculation, based on J&Js propriatory HRV developed in 1989. This calculation is used on all J&J application screens.

    * The 'Task Force'HRV calculation, based on the International Task Force formula in 1994. Task Force signals ar found on some screens - they have the designation - 'tf.'


The J&J HRV Signals are much more responsive than the Task Force version. That means there is less delay of reinforcement, an important consideration for operant learning.

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CardioRespiratory Synchrony/Coherance: Refers strictly to the synchtony [timing] between HR acceleration and Inhaling. [If you like, it also refers to HR decelleation timed with the exhale as well].

"CRS" is probably the most useful tool for training HRV, because it gives feedback for both Respiration and HR waves. Adding the Breathing Pacer allows a quick tchnique to focus training.

NOTE: Generally HR and Resp Displays are autothresholding - they will automatically scale and center the signal if you are patient - wait about 1 minute for the signals to stabilize.

CRS/ RSA FEEDBACK IS DYNAMIC. This is a different kind of feedback than for EEG and EMG.

    * The subject is trained to make a wave, rather than achieve a static levlel of a signal.
    * HR FB is triggered when HR accelerates.
    * Resp FB is triggered when Resp. accelerates. This means FB is given during INHALE.
    * RSA FB is given ONLY when BOTH HR and Respiration accelerate together.


A more discriptive term is CardioRespiratory Synchrony.
The BREATH PACER can be used to shape RSA.
Often used as a deep relaxation exercise for home training.

Although many devices claim to detect RSA using only a HR sensor, these devices can not monitor respiration. RSA training without measuring Respiration should be explored towards the end of training; in the beginning train respiration, then train HR waves, then add the two together. Only when the subject can demonstated good HR waves, should you give HR Wave feedback without respiration. All these steps can occur in a single 20 minut session.

Movements, skipped beats and  double beats have lasting effecst on RSA feedback.
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Resonant Frequency Training. Refers to Paul Leher's protocol combining Breathing Pacer and Cardio-Respiratory Feedback. Spectral HRV is involved, too. Resonant Frequency Training focused on the LF elevations and min-max HR.
Since both ECG and Respiration are detected, the trainer can use the BREATH PACER to find the optimal breathing rate, that is, the rate of breathing that fully triggers a burst of LF activity. This rate is called 'resonant frequency.

Manuals:
For those interested in HR and HRV, here are the J&J Manuals for PhysioPilot 5
Click here to download pdf manual for HRV and Peripheral Biofeedback