Dear Ali,

Great question! And I guess the controversial shouldn't be there!

In my opinion and experience, paced and not paced should be performed for a deep analysis of the ANS.

Using a paced (and symmetrical ) breathing, chronic imbalances of ANS can be assessed with an excellent repeatability of the results. Because ANS is a complex regulatory loop and the respiration being a major regulation factor (acting like a "negative feedback" for ANS stability), controlling this "input" of the loop provides fast and valuable information on the ANS. Of course, this is valid with proper mathematical processing of the HRV (delivering new markers), different from the known LF-HF method. In the other hand, spontaneous breathing ANS assessment provides natural regulation capability of the ANS and in general, research protocols are longer.     

I also believe that most of controversial you are referring to, comes from the traditional LF-HF spectral analysis method. When using controlled breathing, the spectral analysis of HRV reveal a peak at the corresponding respiratory pace and therefore the LF-HF analysis becomes just meaningless. Because of the RSA mechanism (with paced breathing), all the power of RR signal is concentrated on the frequency related to respiration (e.g. 0.1Hz for 6 cycles/min, 0.15Hz for 9 cycles/min...). Therefore almost all the power falls in LF band so reporting LF-HF results in a study becomes irrelevant. That's why some researchers prefer natural breathing, as spectral power is distributed over LF-HF bands and those markers become again "usable".                   

 In my view (and not only), the actual LF-HF method is a limitation not only on the ANS understanding but also on the various possible research protocols, like paced breathing.

This is the reason why, during several years we developed a new mathematical ANS method that provides dynamically and simultaneously, the Sympathetic and Parasympathetic ANS activities without any limitation related to a given research protocol or breathing conditions, or duration.       

An example of the power and the pertinence of our method and tool is illustrated on the attached document where you can see the ANS dynamic assessment and also the frequency peak I was talking before.    

For any scientist interested on trying and assessing this method with their own RR files, the tool can downloaded from:  http://www.codesna.com/en/products/codesna_hrv/

To answer your second question, for the paced breathing, the frequency should be in a range of 6-8 cycles/min. We have conducted a study with more than 100 subjects from 11 to 87 years (2 minutes paced breathing) and:  ~80% are able to breathe at 6 cycles/min, ~15% prefer 8 cycles/sec and less than 5% are not able to  follow this pace. In general, people which are able to follow the protocol do not feel this type of respiration like a constraint, at least during 2minutes.          

Hope this helps!

Research Case study on HRV – Real time monitoring of meditation shows...

Dear Vasile,

thanks for the detailed response.

Regarding the second question, lets assume that we are going to evaluate effects of slow breathing (0.1 Hz) on baroreflex function. We need a control condition to control for the effects of attention and paced breathing at the normal breathing frequency is one good option. However, as normal breathing rate varies a bit, the question is whether the paced breathing for the control condition must be at a fixed rate based on assumed avarage breathing rate of the population under study or it should be at the normal breathing rate of each individual?

Yes, correct, you need a control condition on breathing like a visual stimulus in order to make sure the subject inhalation and exhalation are controlled. Such stimulus are available on the web (e.g. 5sec inhalation and 5 sec exhalation) and the subject can follow this visually.

I don't know how to define the "normal" breathing rate for an individual since there will be variations over time based on he's emotional feeling and physiological state of the moment. For baroreflex (and for fast ANS assessment in general), having the same stimulus for everyone at a fixed rate of ~6 cycles/min (so 10 second inhalation + exhalation) will be ok assuming it is comfortable enough lasting 2 min. The important thing here is to have a "symmetrical" breathing and a fixed pace in a range of 6-8 cycles/min for every suject.

In our study, slow breathing itself is the main intervention. We need a control condition to control for any possible factor other than breathing frequency, such as paying attention to breathing, pacing, etc... that can affects BRS and autonomic activity.

Because natural breathing frequency is variable in different situations it may not be a good estimate to consider the mean breathing frequency at rest in the laboratory condition as the normal breathing frequency and then perform the paced breathing at that frequency. In my opinion, it is better for the control condition to fix the breathing frequency at 0.20 to 0.25 Hz.

Using a breathing protocol  the autonomic nervous system’s equilibrium level is measured through several physiological markers, allowing to prevent the risk of depression, “burn-out” or exhaustion. Please do you have any reference to find an evidence based for HRV breathing and  prevention of the the risk for depression, “burn-out” or exhaustion. If you prefere : [email protected]

In my opinion for an adequate assessment of HRV measurements should be carried out in the normal state and at controlled breathing.

Chapter The Complex Approach to a Multipurpose Estimation of a Sport...

Dear Alexander! In normal state anybody does not controls his or her breathing.

I believe that the finding of HRV during free breathing is the best method. After all, we wish to know the status of the ANS in real life, is not it?

Dear Nicholas, on the one hand you are right. However, if we talk about the tone and reactivity ANS, which is an important position in the diagnosis of the condition of the organism, in this case the tests with controlled breathing considerably supplement the data obtained during spontaneous breathing.

I agree with Alexander: both (spontaneous and controlled breathing) are complementary to provide valuable ANS information, they shouldn't be opposed, in my view. Spontaneous breathing is modulated by the instantaneous emotional state, therefore isolating pure physiological information might be challenging sometimes.

With controlled breathing, long term ANS imbalances can be assessed since ANS regulation loop is going into a known "steady state" compared to instantaneous breathing.

Dear Giorgio,

Having physiological markers showing ANS imbalances as a consequence of chronic stress allows the physiological objectification of long term (negative) emotions. This is part of the prevention in the sense of quantifying physiological effect of emotions and it provide awareness. Then having physiological history of physiological improvements related to an adequate treatment or just life habits. We clearly observed that people have an increased and sustainable motivation for changing things in their life when having regular measured numbers than just having their perception. So this contributes to the overall prevention of more severe disorders. At some extend, a similar case to a weighing machine for someone who needs to lose weight.

Deae Giorgio,

There is not yet strong evidence that HRV biofeedback or paced or slow breathing can prevent depression or help in the treatment of depression. All available evidence are preliminary, if any!