Definition of Hyperventilation and CO2 (Carbon Dioxide)

Hyperventilating girl How to define hyperventilation? The most common medical definition of hyperventilation is: Hyperventilation (or overbreathing) is the state of breathing that is faster and/or deeper than normal. This mechanical definition of hyperventilation is based on calculations of normal minute ventilation (that is 6 L/min at rest for a 70-kg man) and can be found in many sources (Wikipedia, National Institute of Health, WebMD, and many medical textbooks). Although this hyperventilation definition works in most situations, it is not suitable for some cases described below.

In contrast, Dr. Buteyko's definition of hyperventilation (or what he implied in relation to hyperventilation) is based on the pathological physiological effects that are caused by reduced CO2 levels in the alveoli of the lungs due to hyperventilation.

Indeed, the above medical hyperventilation definition incorrectly includes numerous positive situations, for example:
Young woman running - Breathing gets much deeper and faster during physical exercise, however, alveolar and arterial CO2 increase for nose breathing (in and out) during exercise
- Fire breath in hatha yoga is an example of very fast breathing, but due to a small tidal volume, which is close to dead volume, arterial and alveolar CO2 may get even higher during this special breathing practice
- Buteyko reduced breathing exercise (where CO2 accumulation in the alveoli can be achieved by frequent and small breathing for students with less than 20 s CP) also leads to CO2 increase
- Breathing exercises with various breathing devices (the Frolov breathing device, Samozdrav device, Cosmic Breath, Amazing DIY breathing device, etc.) can be accompanied by increased minute ventilation (depending on the amount of additional volume) and low breathing frequency, but with increased CO2 levels in the alveoli of the lungs due to CO2 getting trapped in the device
- Breathing CO2-rich air (carbogen and other mixtures) increases minute ventilation (leading to faster and deeper breathing), but alveolar and arterial CO2 concentrations usually become higher. (They could become lower, if a person is in a state of panic after starting to breathe CO2-rich air).

During all these situations, the levels of CO2 in the arterial blood and cells get higher than before these situations, while classical overbreathing (or voluntary hyperventilation with normal air) reduces cell O2 and CO2 content.

CO2 molecule model Many medical textbooks suggest to define hyperventilation basing on arterial hypocapnia. The most common example of this is: Hyperventilation is a physiological state when the partial pressure of arterial CO2 is less than 35 mm Hg. However, people with ventilation-perfusion mismatch normally have elevated minute ventilation (e.g., over 10-12 L/min at rest for bronchitis, COPD, cystic fibrosis, etc.) with obvious alveolar hypocapnia (reduced CO2 in the alveoli of the lungs), but their arterial CO2 can be very high (e.g., up to 50 mm Hg and more). Physiologically, it is obvious that these patients require more CO2 in order to restore airways and lung tissues due to CO2 bronchodilating effects (expansion of airways) and the abilities of CO2 to heal alveoli. Breathing less for all these groups of patients leads to a reduction of the abnormally high arterial CO2 and an increase in arterial O2 content due to the reduced ventilation-perfusion abnormality. This effect can be easily confirmed using finger oximeters and other types of devices that measure oxygen content of the blood.

How to define hyperventilation

Hence, the most logical and physiologically strict way to define hyperventilation is following. Hyperventilation is the physiological state of the human organism characterized by alveolar hypocapnia (CO2 deficiency in the alveoli of the lungs). This definition of hyperventilation is based on an abnormally low concentration of CO2 (carbon dioxide) in the functioning alveoli of the lungs causing reduced oxygen transport, tissue hypoxia (low O2 in cells) and other pathological effects that intensify hyperventilation.

This hyperventilation definition satisfies various practical situations with no exceptions due to its physiological (or biochemical) basis: abnormally low CO2 tension in the alveoli of the lungs. It has an important therapeutic value since it is based on known physiological and biochemical effects of carbon dioxide on airways, lung tissue, blood vessels, and other organs and tissues of the human body.

However, since alveolar CO2 is very difficult to measure, in most situations, the "mechanical" definition of hyperventilation works fine and this is the reason why many tables on this site quote minute ventilation. Indeed, when minute ventilation is above 10 L/min at rest, while metabolic rate might be only slightly above normal, it is obvious that this "mechanical" hyperventilation causes physiological hyperventilation (alveolar hypocapnia).

On the other hand, ventilation-perfusion abnormalities are confined to only a small portion of people with emphysema, severe asthma, severe bronchitis, COPD, cystic fibrosis, and some others. Hence, arterial hypocapnia, as a definition and criterion of hyperventilation, is also a sensible idea since, for most people in most situations, arterial hypocapnia means deep and/or fast breathing with low CO2 levels in the alveoli.

References

Dr Konstantin Buteyko Dr. Buteyko about physical exercise and its relation to CO2 changes and physiology:
"Next is about physical activity, labor, and sports. Here again the fact that in our press and everywhere else, there are people who are illiterate in physiology. They have imposed upon us a thought, and again contrary to the truth, that physical activity, sport and labor deepen our breathing. This is quite the opposite! It is wrong to consider any function bureaucratically, as a fact detached from life. After all, breathing is done to ensure metabolism. Therefore, breathing must be considered in parallel with metabolism. It turns out that physical labor, sports, and workouts increase metabolism, i.e., they increase production of carbon dioxide and carbon dioxide increases, during exercise, in the blood, while oxygen is reduced. This is what physical exercise does." Dr. Buteyko's Lecture at the Moscow State University

Reference Web Pages: Breathing norms, Medical Graphs and Tables about Breathing Rates (Minute Ventilation) and Body Oxygen in Healthy, Normal and Sick People
Breathing norms Parameters, graph, and description of the normal breathing pattern
6 breathing myths 6 myths about breathing and body oxygenation (prevalence: over 90%)
Hyperventilation Definitions of hyperventilation: their advantages and weak points
Hyperventilation Syndrome in the Sick. Table 1. Western scientific evidence about prevalence of CHV (chronic hyperventilation) in patients with various chronic conditions (34 medical studies)
Normal Minute Ventilation in Healthy Subjects: Easy and Light Breathing (14 Studies)
Hyperventilation Prevalence Present in Over 90% of Normal People (24 medical publications)
HV and hypoxia How and why deep breathing reduces oxygenation of cells and tissues of all vital organs
Body oxygen test How to measure your own breathing and body oxygenation (a simple DIY test)
Body oxygen in healthy Table 4. CP (body oxygen level) in healthy people (27 medical studies)
Body oxygen in sick Table 5. CP (body oxygen level) in sick people (14 medical studies)
Buteyko Table of Health Zones with clinical description of most common zones
Morning HV Morning hyperventilation effect or how and why critically ill people are most likely to die during early morning hours

References: CO2 Effects Web Pages
Vasodilation: CO2 expands arteries and arterioles facilitating perfusion (or blood supply) to all vital organs
The Bohr effect How and why oxygen is released by red blood cells in tissues
Cell Oxygen Levels and oxygen transport are controlled by alveolar CO2 and breathing
Oxygen Transport depends on breathing and these two effects (Vasoconstriction-Vasodilation and the Bohr effect) are parts of two diagrams that summarize influences of hypocapnia (low CO2 content in the blood and cells) on circulation and O2 delivery
Free Radical Generation takes place due to anaerobic cell respiration caused by cell hypoxia. Hence, antioxidant defenses of the human body are also regulated by CO2 and breathing
Inflammatory Response is controlled by breathing since hypoxia leads to or intensifies chronic inflammation through over-expression of the hypoxia-inducible factor 1, while normal breathing reduces these processes
Nerve stabilization takes place due to calmative or sedative effects of carbon dioxide in neurons or nerve cells
Muscle relaxation or relaxation of muscle cells is normal at high CO2, while hypocapnia causes muscular tension, poor posture and, sometimes, aggression and violence
Brochodilation - dilation of airways (bronchi and bronchioles) by carbon dioxide, and their constriction due to hypocapnia
CO2: Best Natural Cough Suppressant and "home remedy" since it calms urge-to-cough nerve receptors located in the tracheobronchial tree and larynx
Blood pH regulation and regulation of other bodily fluids
CO2: Lung Damage Healer: Elevated carbon dioxide prevents injury and promotes healing of lung tissues
CO2: Skin and Tissue Healer
Synthesis of Glutamine in the Brain, CO2 fixation, and other chemical reactions
CO2 myth "CO2 is a toxic waste gas" myth
Breathing control How is our breathing regulated? Why hypocapnia makes breathing uneven and erratic?

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