- Updated on April 24, 2023
By Dr. Artour Rakhimov, Alternative Health Educator and Author
BPT (Buteyko Practitioner Training) Module
Does etCO2 correlate well with the Buteyko CP test?
It is not the first time, when someone asked me about the study by Rosalba Courtney and Marc Cohen “Investigating the Claims of Konstantin Buteyko, M.D., Ph.D.: The Relationship of Breath Holding Time to End Tidal CO2 and Other Proposed Measures of Dysfunctional Breathing” (Journal of Alternative & Complementary Medicine; March 2008, Vol. 14 Issue 2, p. 115) since this study found the opposite result: people with higher BHT (breath holding time, or the Buteyko CP test) had lower end-tidal CO2. This topic was discussed in 2008 on the BPSN forum for Buteyko practitioners (see extracts from one of my posts below).
Buteyko teachers know and are often able to evaluate the CP of their students and other people just by watching how they breathe. Those who have heavier breathing have smaller CP numbers. Therefore, let us look what was investigated in this study and how.
Origins of the BHT – CP formula
Everybody who studied Buteyko works would suggest that the linear relationship between the alveolar CO2 and CP, which was patented by Buteyko in 1986, follows from the Buteyko Table of Health Zones. Here is this Health Table.
Buteyko Table of Health Zones (average parameters at rest)
|AP, s||CP, s||MP, s|
How did Dr. Buteyko receive this Table? Mainly, by measuring data of his patients who learned his breathing technique in the 1960s. Who were these patients and what do they achieve? He worked mostly with severely sick and hospitalized patients. Typical CP numbers of such people are less than 10 seconds. These patients were taught by Dr. Buteyko and other Buteyko breathing doctors to get up to 60 s and more. Among these people, some got even higher numbers: up to 2-3 min for the CP test.
Dr. Buteyko recorded their parameters during this process of breathing retraining and then he discovered the linear links between all these parameters present in the Table. If we look at the Table then we can see that the level of alveolar carbon dioxide is then detected in accordance with the formula:
where P is the percentage of CO2 in the alveolar air; P0 is the 3.5 minimum percentage of CO2 in the alveolar air; K=0.05 is the dependency ratio between the level of CO2 and the breath-holding time, and T is the CP result. This link works between 5 and 60 s CP.
The range of alveolar CO2 values in this Table is from 3.5% up to 6.5% CO2. The absolute difference for this range is 86%.
If we look at the Courtney & Cohen study, their normal range is 36-42 mm Hg or 4.74% – 5.53%. The absolute difference for this range is less than 17%. Therefore, by CO2 values, the Courtney & Cohen study focused on less than a fifth (20%) of the Buteyko Table range. (The Table even goes to larger CP and CO2 numbers, but these numbers are not covered by the linear link.)
If we consider the CP range, the linear CO2-CP link works from 5 to 60 s CP, while the study’s subjects had between 20 and 30 s CP. The maximum CP for the Table is 12 times greater than the minimum number, while in the Courtney & Cohen study, it is only 1.5 times larger.
1. Therefore, this Courtney & Cohen study focuses only on less than a fifth (a narrow range in comparison to the CP-CO2 range in Buteyko studies) what it claims to investigate.
Is there a link between the CP and CO2 within 20-30 s CP range?
Experience with our students suggests that even within one zone of the Table (20-30 s CP), there is still a positive link between the CP and CO2. When a student with 20 s previous CP comes to the class and now has about 30 s CP, breathing of such student is different. This is exactly the range where people make a transition from chest to diaphragmatic breathing for their automatic patterns.
What is going to take place with their end-tidal CO2 during this transition? This transition makes one trick that was described on the webpage of NormalBreathing.com that is devoted to capnography.
This page has the following capnography waveforms in order to explain how and why those people who can breathe 2 times the norm (for minute ventilation) can have nearly normal (40 mm Hg) etCO2 values. You can see these graphs on the right side.
For more details, you can visit this page (capnography) and study this trick related to end-tidal CO2. This was one of the reasons why the Buteyko patent with linear CP-CO2 link and the Buteyko Table of Health Zones, both focus only on alveolar CO2. The word “end-tidal” cannot be found in any of the Buteyko patents or in his Health Table.
2. The Courtney & Cohen study did not study alveolar CO2. They used a substitute: end-tidal CO2.
How was Dr. Buteyko getting alveolar Co2 numbers? He measured arterial O2 and CO2 values. Arterial O2 is going to tell us about a possible ventilation-perfusion mismatch, while arterial CO2 (in case of no mismatch) provides the same number as the alveolar CO2.
Therefore, when people have chest breathing, they get abnormally high etCO2 numbers. We can see this fact even in the Courtney & Cohen study. Here are extracts from this study:
|Normal spirometry (n=54)||Abnormal spirometry (n=29)|
|Av ETCO2 (mmHg)||37(+- 4)||39(+- 4)|
|Av BHT-DD (s)||28(+-12 )||20(+-8 )|
We see that people with “normal” spirometry (this sounds very scientific, but probably means diaphragmatic breathing) have higher CPs and lower etCO2 than people with “abnormal” spirometry (which probably relates to chest breathing).
3. The Courtney & Cohen study got abnormal results only because of the trick that relates to end-tidal CO2 (not alveolar CO2) in the narrow zone of the transition from chest to diaphragmatic breathing.
It seems that this study substituted parameters (to study a different parameter: end-tidal CO2, not alveolar CO2), then selected a narrow range (20-30 s CP), which is less than 1/5 of the formula range and which is knowingly erroneous (unrepresentative) in relation to alveolar CO2 (the parameter studied by Dr. Buteyko).
This is how the study described their finding, “The statical significance of the negative correlation between BHT and ETCO2 which is opposite to the positive correlation claimed by Buteyko, was dependant on two extreme cases who had both previously undertaken breathing training, one using yoga and the other using the BBT [Buteyko breathing technique].”
These 2 people likely had diaphragmatic breathing (that gives lower etCO2), and this explains how the study got the negative link.
Why bother with CP 20-30 people?
Many people learn the Buteyko method from Western Buteyko teachers by increasing their CPs from about 15 to about 25 s. This is a good achievement. It often allows to dramatically reduce or even to eliminate many types of medication. But this is not the whole Buteyko method. It is about 1/4 of the method in relation to the Buteyko norm (CP 60), and much less than that in the physiological and spiritual sense.
In order to see that some people do teach the real Buteyko method, we can look at the CO2 range in the cancer study conducted by Dr. Sergey Paschenko (Dr. Buteyko’s pupil) in 2001. Dr. Paschenko reduced mortality for metastatic cancer by nearly 6 times. This study measured CO2 in the exhaled air. In my view, it was not end-tidal CO2. The average initial CO2 values were about 2.4-2.5% (in both groups). In 3 years, after breathing retraining, the controlled group of about 60 people had about 5.5% CO2 (more than double for CO2). This CO2 increase is larger than to increase the CP from about 5 to 60 seconds. This seems like the real Buteyko method.
In this video below, I explain which CO2 parameters are useful in evaluating breathing retraining and which are not. In particular, I mentioned that “etCO2 has never been a part of the original Buteyko method”:
Experience of our breathing students with CP, CO2, and Buteyko claims
Each of our students with morning CP 60+ had and has 4-5 hours of natural sleep (without any sleep restrictions), a craving/joy of physical exercise, an ability to exercise at maximum intensity with nose breathing only (mouth breathing during exercise does not provide any benefits or advantages at this health state), natural desire to eat raw food, natural aversion to coffee, chocolate, and many other effects.
When our new students start their course, I can see their heavy breathing, and, in most cases, it is possible to predict their breath holding times or CPs (e.g., 10, 15, or 20 s) using visual observations. Soviet Buteyko doctors also described this effects saying that it was a contest suggested to them by Dr. Buteyko: define the CP of your next patient visually. After these visual observations and carrying out the CP test, the typical lifestyle parameters of these heavy breathers are consistent: poor physical fitness, long sleep (usually about 7-9 hours), addictions, etc.
Real reasons behind such claims
Why is there this persistent trend, for some Buteyko teachers, for many years to invent various justifications related to attempts