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By Dr. Artour Rakhimov, Buteyko breathing teacher and educator

Breathing education
Part 11. Life style factors that matter
(Why do we breathe too heavily?)
D. Does mouth breathing affect health?
When seeing people on Western city streets and in other public places, one may notice that up to 20-40% of them breathe through their mouths while walking or even while quietly standing or sitting. This phenomenon seems more common among children. What are the negative effects of mouth breathing?

Reduced oxygenation and carbon dioxide stores

Scientific literature on respiration often mentions a physiological parameter known as dead space volume. It is about 150-200 ml in an average adult: inside the throat, nose and bronchi. This space preserves additional carbon dioxide for the organism, since inhalations take CO₂ enriched air from dead space back into the lungs. When the mouth is open, the dead space volume becomes smaller due to a continuous exchange of air. That does not happen with nasal breathing. In addition, nasal breathing provides more resistance to respiratory muscles during breathing as compared to mouth breathing (the mouth-breathing route is shorter and has a larger cross sectional area). During nasal breathing we can either breathe more resulting in more mechanical work for the respiratory muscles or to breathe slightly less while generating less mechanical work. What is the practical result? Due to an in-built tendency to optimise physiological processes, the human organism is ready, as during nose-breathing, to breathe less and tolerate higher aCO₂, than to exert more demands on constantly working respiratory muscles.

In the abstract of a physiological study "An assessment of nasal functions in control of breathing" (Tanaka et al, 1988) the researchers wrote:
"Breathing pattern and steady-state CO₂ ventilatory response during mouth breathing were compared with those during nose breathing in nine healthy adults...We found the following. 1) Dead space and airway resistance were significantly greater during nose than during mouth breathing. ...These results fit our observation that end-tidal PCO₂ was significantly higher during nose than during mouth breathing. It is suggested that a loss of nasal functions, such as during nasal obstruction, may result in lowering of CO₂, fostering apneic spells during sleep."

This Japanese article, which studied a group of healthy volunteers, gives average end-tidal CO₂ 43.7 mm Hg for nasal breathing and only 40.6 mm Hg for mouth breathing. Practically, in terms of BHT that means 45 s and 37 s at sea level. Hence, mouth breathing reduces oxygenation of the whole body.

Cleaning, warming and humidification of air

Our nasal passages are created to clean, humidify and warm the incoming flow of air due to the thin layer of protective mucus. This layer of mucus can trap almost all (95-99%?) dust particles, bacteria, viruses and other airborne objects. This is what long, narrow, and intricate nasal airways are for.

When the mouth is used for inhalation, this air route is shorter, wider and almost straight. Now the same airborne objects can easily get into the alveoli and the blood, creating stress, first of all, for the immune system (detection, marking, isolation, and deactivation of intruders) and then for organs of elimination (kidneys, liver, skin, and GI patches). Some pathogens, can even multiply in the lungs causing more severe problems.
If you are an asthmatic and endurance athlete, you should train mostly, or better only using your nose, and for really important competitions mouth-breathing can be used, if you have no problems with your asthma. What is important for training is to have an aerobic training effect. That is possible while breathing through the nose, as these western results indicate.

“The major cause of exercise-induced asthma (EIA) is thought to be the drying and cooling of the airways during the 'conditioning' of the inspired air. Nasal breathing increases the respiratory system's ability to warm and humidify the inspired air compared to oral breathing and reduces the drying and cooling effects of the increased ventilation during exercise. This will reduce the severity of EIA provoked by a given intensity and duration of exercise. The purpose of the study was to determine the exercise intensity (%VO₂ max) at which healthy subjects, free from respiratory disease, could perform while breathing through the nose-only and to compare this with mouth-only and mouth plus nose breathing. Twenty subjects (11 males and 9 females) ranging from 18-55 years acted as subjects in this study. They were all non-smokers and non-asthmatic. At the time of the study, all subjects were involved in regular physical activity and were classified, by a physician, as free from nasal polyps or other nasal obstruction. The percentage decrease in maximal ventilation with nose-only breathing compared to mouth and mouth plus nose breathing was three times the percentage decrease in maximal oxygen consumption. The pattern of nose-only breathing at maximal work showed a small reduction in tidal volume and large reduction in breathing frequency. Nasal breathing resulted in a reduction in FEO₂ and an increase in FECO₂. While breathing through the nose-only, all subjects could attain a work intensity great enough to produce an aerobic training effect (based on heart rate and percentage of VO₂ max)” (abstract, Morton et al, 1995).

Autoimmunization effect

The layer of mucus moves as a carpet from sinuses, bronchi and other surfaces towards the stomach. Hence, these trapped by the mucus objects are drained (or swallowed) into the stomach where digestive enzymes and HCl (low pH) make bacteria and viruses either dead or weak. Further along the digestive conveyor, some of these substances can penetrate into the blood due to intestinal permeability effect. But now these pathogens are either dead or weakened and would not do much harm while providing a good lesson for the immune system. This is exactly how immunization, done by medical personnel, often works with success: medical doctors inject a vaccine with either dead or weakened bacteria or virus to teach and strengthen the immune response to these pathogens. Hence, nasal breathing is a natural mechanism of autoimmunization.
Practically, when some household members are sick with for example, flue or cold, the still healthy people can breathe either through the nose teaching the own immune system how to defeat the pathogenic bacteria or virus, or through the mouth allowing the same pathogens to access, settle and multiply in various parts of the human body causing the infection.

Nitric oxide

There are numerous studies published over the past 80 years regarding the negative effects of hypocapnia (low level of CO2). Hence, CO2 is the most known and investigated factor that relates to over-breathing. Which other parameters of the body become abnormal during and because of hyperventilation?

Normal nasal breathing helps the body to use its own nitric oxide. This substance is produced, among other places, in nasal passages. During normal breathing, we have quiet prolonged exhalations (that do not prevent accumulation of nitric oxide in some areas of nasal passages) and relatively quick inhalations (that allow inhalation of the accumulated nitric oxide). During hyperventilation exhalations are forceful and quick (as one can observe in many sick people) and inhalations are slow. This reversal of the main stages of breathing decreases the utilization of nitric oxide.

The roles and some important effects of this hormone on the body have been discovered very recently and there are still many questions in relation to this substance. Nitric oxide is found and synthesized in endothelial cells that line the lumen of blood vessels, neurons, and macrophages. As a gas, it is routinely found in nasal passages and measured in exhaled air. The known functions of the NO include:

1. Vasodilation of arteries and arterioles (and hence regulation of blood flow to tissues). In this respect, NO is similar to CO2 acting on the smooth muscles of blood vessels.
2. Regulation of binding and release of O2 to haemoglobin. This NO function is again similar to the CO2 function known as the Bohr effect.
3. Destruction of parasitic organisms, viruses, and malignant cells by inactivating their respiratory chain enzymes in mitochondria.
4. Inhibition of inflammation in blood vessels.
5. Neurotransmission. Learning, memory, sleeping, feeling pain, and some other processes require NO for transmission of neuronal signals. On the other hand, brain cells can probably be killed during a stroke due to excessive production of nitric oxide.
6. Hormonal effects. NO influences secretion from several endocrine glands. It stimulates the release of adrenaline from the adrenal medulla, pancreatic enzymes from the exocrine portion of pancreas, and Gonadotropin-releasing hormone from the hypothalamus.

Abnormal NO production and its availability are now associated with hypertension, heart failure, stroke, obesity, diabetes (both type I and II), atherosclerosis, rheumatism, aging, and dyslipidemias (particularly hypercholesterolemia and hypertriglyceridemia). Currently there are numerous studies world-wide related to the role of NO in human health and diseased states. It is beyond the scope of this book to provide these studies.

Practice shows that possibly for some people some health improvements can be achieved mainly through the correction of one’s breathing pattern, which can normalize production and utilization of nitric oxide, while CO2 changes could be small. Hence, in these people nitric oxide can play, during some stages of breathing normalization, the leading role in health restoration.

Compare old and modern group photos. They also provide a part of the answer regarding causes of poor health in contemporary society.

The mouth, according to Doctor Buteyko, is designed by Nature for drinking, eating and speaking. At all other times it should be shut. (Teeth flossing and brushing can be other sensible exceptions.)

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