By Dr. Artour Rakhimov, Alternative Health Educator and Author
This is another essential topic for Buteyko practitioner training.
Let us look at the influence of O2 content on respiration when CO2 concentrations in the inspired air are negligible. Healthy people usually notice increased ventilation only when O2 content is below 10%. Smaller changes (e.g., when breathing 15-19% O2) are probably also sensed by the breathing center, but increased ventilation would also result in reduced aCO2 values. The breathing center mainly controls aCO2. As a result, these two drives cancel each other out for O2 concentrations between 15 and 19%.
What happens during heavy work? When the intensity of exercise gets higher, the amount of oxygen in tissues and in arterial blood becomes lower. As a result, increasing energy is generated without direct O2 participation (anaerobic metabolism). Such metabolism causes the appearance of lactic acid in the blood. A small amount of lactic acid is present in the blood at rest and its level gets larger, but still remains constant, for exercise with moderate intensities. At higher intensities, the lactic acid level is constantly increasing causing blood acidosis, which is sensed by the breathing center.
Fatigue and pain are the normal sensations experienced during and after strenuous physical efforts. According to a textbook on medical physiology, “Fatigue is a poorly understood phenomenon that is a normal consequence of intense exercise or mental effort. In addition, it is a symptom of many different diseases. During exercise, acidosis and other factors contribute to its production” (p. 627, Ganong, 1995).
Using these conclusions, it is possible to suggest that the breathing center can play an important or, probably, central role in the perception of sensations of fatigue and pain due to physical and mental exercise. Possibly, because it is a part of the nervous system and is sensing blood acidosis caused by increasing blood lactate, the breathing center sends intensive signals perceived as fatigue or pain. That makes heavy work, at some moment in time, physiologically impossible (blood acidosis to pH=7.0 can be fatal for humans).
In order to keep pH closer to the normal 7.4, the organism starts to remove carbonic acid as compensation for increasing lactic acid. Carbonates are the major CO2 forms in the blood and their level can be kept low due to the removal of bicarbonates by kidneys and additional ventilation.
In practical terms, only at sub-maximum intensities (80-90% of the maximum possible oxygen consumption), does aCO2 start to decline from the initial resting level (40 mm Hg) down to about 30 mm Hg for maximum possible intensities. This conclusion can be found in textbooks on exercise physiology (e.g., p.201, Brooks et al, 1996).
Brooks GA, Fahey TH, White TP, Exercise physiology: human bioenergetics and its applications, 2-nd ed., 1996,
Mountain View, California, Mayfield
Ganong WF, Review of medical physiology, 15-th ed., 1995, Prentice Hall Int., London.