Bronchoconstriction: Definition, Symptoms, Causes, Treatment

Mechanism of bronchoconstriction Bronchoconstriction (definition) is defined as the narrowing of the airways in the lungs (bronchi and bronchioles). Air flow in air passages can get restricted due to 3 factors:
- a spasmodic state of the smooth muscles in bronchi and bronchioles
- an inflammation of the airways
- excessive production of mucus due to an allergic reaction or irritation caused by mechanical friction of air (due to shear stress), overcooling or drying of airways.

Bronchoconstriction is common in people with respiratory problems, such as asthma, COPD, and cystic fibrosis. What is known about breathing parameters for people with these conditions?

Minute ventilation rates (chronic diseases)

Condition	Minute ventilation	Number of people	All references or click below for abstracts
Normal breathing	6 l/min	-	Medical textbooks
Healthy Subjects	6-7 l/min	>400	Results of 14 studies
COPD	14 (±2) l/min	12	Palange et al, 2001
COPD	12 (±2) l/min	10	Sinderby et al, 2001
COPD	14 l/min	3	Stulbarg et al, 2001
Asthma	13 (±2) l/min	16	Chalupa et al, 2004
Asthma	15 l/min	8	Johnson et al, 1995
Asthma	14 (±6) l/min	39	Bowler et al, 1998
Asthma	13 (±4) l/min	17	Kassabian et al, 1982
Asthma	12 l/min	101	McFadden & Lyons, 1968
Cystic fibrosis	15 L/min	15	Fauroux et al, 2006
Cystic fibrosis	10 L/min	11	Browning et al, 1990
Cystic fibrosis*	10 L/min	10	Ward et al, 1999
CF and diabetes*	10 L/min	7	Ward et al, 1999
Cystic fibrosis	16 L/min	7	Dodd et al, 2006
Cystic fibrosis	18 L/min	9	McKone et al, 2005
Cystic fibrosis*	13 (±2) l/min	10	Bell et al, 1996
Cystic fibrosis	11-14 l/min	6	Tepper et al, 1983

Bronchoconstriction due to hypocapnia As a result of heavy breathing, all these people suffer from alveolar hypocapnia (lack of CO2 in airways).

Cause of bronchoconstriction

It is a known physiological law that all smooth muscles are highly sensitive to CO2 levels. Thus, spasm in the smooth muscles of bronchi and bronchioles is a normal physiological reaction to alveolar hyperventilation (Badier et al, 1998; Clarke et al, 1982; Jamison et al, 1987; O'Cain et al, 1979; Sterling, 1968).

While there are many chemicals that can cause either bronchoconstriction or bronchodilation, CO2 plays the key role due to two factors: its high bronchodilatory potency and additional negative systemic effects caused by alveolar hypocapnia (lack of CO2). What are those?

Chronic hyperventilation (breathing more air than the medical norm) also leads to cell hypoxia, generation of reactive oxygen species (free radicals), and immunosuppression. (This can happen with or without ventilation-perfusion mismatch: blood CO2 levels can be below the norm or too high)

As a result, overbreathing produces additional effects that worsen conductivity of airways, such as immunosuppression, frequent respiratory infections, excessive production of sputum (mucus) and airway inflammation (see links to studies below).

Furthermore, overbreathing also leads to increased losses of water from the mucosal layers of airways and overcooling of airways due to increased heat losses. These effects also favor frequent respiratory infections.

Symptoms of bronchoconstriction

Woman coughing These effects cause further airway obstruction, difficulty breathing, wheezing, coughing, and dyspnea (shortness of breath) amplifying the effects of bronchospasm.

Causes and mechanism of bronchoconstriction

Consider medical evidence related to breathing parameters at rest in people with bronchoconstriction (see the Table above). We see that these patients breathe at rest (in stable conditions) much more air than the medical norm. Over breathing leads to low CO2 in the airways and causes other effects summarized here.

Bronchoconstriction mechanism

Bronchospasm can also happen due to an allergic reaction caused by the release of histamine. This allergic reaction leads to edema and inflammation of airways, as often happens in asthma, bronchitis, emphysema, and other COPD-related conditions. However, chronic hyperventilation causes immune dysfunction, and, therefore, it also promotes the appearance of allergies.

Since cell hypoxia promotes chronic inflammation, people with these health conditions (asthma, bronchitis, and so on), as well as people with cystic fibrosis, tuberculosis, sarcoidosis, bronchiectasis, bronchiolitis, and many other lung diseases, experience chronic spasm in the smooth muscles of airways or bronchospasm, combined with other negative effects caused by hypocapnia.

Note about coughing. Coughing through the mouth multiplies all these negative effects of hyperventilation several folds. There are effective breathing techniques how to suppress coughing.

Treatment of bronchoconstriction

MDs smiling Over 170 Russian medical doctors found an effective way to deal with bronchoconstriction. This medical therapy is based on restoration of normal alveolar CO2 levels. The Buteyko method is approved by the Russian Ministry of Health and has been applied on more than 200,000 people with health problems that involve bronchoconstriction (such as asthma, bronchitis, COPD, cystic fibrosis and many others). According to these Russian doctors, patients need to slow down their heavy breathing and achieve more than 20 s for the body oxygen test to prevent symptoms of bronchospasm at rest. Nose breathing at exercise prevents exercise-induced asthma.

Breathing exercises with breathing devices (such as the Frolov breathing device, DIY breathing device, and Samozdrav) are very effective ways to increase body oxygen levels. Oxygen Remedy online breathing classes is probably the easiest way to learn and most effective therapy for bronchoconstriction. Lifestyle changes are also necessary to prevent overbreathing due to sleep (supine sleep and mouth breathing), meals (overeating), exercise, and other factors.

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
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

References

Badier M, Beaumont D, Orehek J, Attenuation of hyperventilation-induced bronchospasm by terfenadine: a new antihistamine, J Allergy Clin Immunol. 1988 Feb;81(2):437-40.

Clarke PS, Jarrett RG, Hall GJ, The protective effect of ipratropium bromide aerosol against bronchospasm induced by hyperventilation and the inhalation of allergen, methacholine and histamine, Ann Allergy. 1982 Mar;48(3):180-3.

Jamison JP, Glover PJ, Wallace WF, Comparison of the effects of inhaled ipratropium bromide and salbutamol on the bronchoconstrictor response to hypocapnic hyperventilation in normal subjects, Thorax. 1987 Oct; 42(10): 809-14.
....This suggests that bronchoconstriction in response to hypocapnic hyperventilation in normal subjects is not mediated via a cholinergic reflex.

O'Cain CF, Hensley MJ, McFadden ER Jr, Ingram RH Jr, Pattern and mechanism of airway response to hypocapnia in normal subjects, J Appl Physiol. 1979 Jul;47(1):8-12.
We examined the bronchoconstriction produced by airway hypocapnia in normal subjects... Pretreatment with a beta-sympathomimetic agent blocked the response, whereas atropine pretreatment did not, suggesting that hypocapnia affects airway smooth muscle directly, not via cholinergic efferents.

Reynolds AM, McEvoy RD, Tachykinins mediate hypocapnia-induced bronchoconstriction in guinea pigs, J Appl Physiol. 1989 Dec;67(6):2454-60.
... We conclude that, in the guinea pig lung, HIBC [hypocapnia-induced bronchoconstriction] is mediated by TKs [tachykinins] that are released after the activation of bronchial axonal reflexes.

Sterling GM, The mechanism of bronchoconstriction due to hypocapnia in man, Clinical Science 1968 Apr; 34(2): p. 277-285.

Straub NC, Section V, The Respiratory System, in Physiology, edited by. Berne RM & Levy MN, 4th edition, Mosby, St. Louis, 1998.

* Upper illustration by Victor Lunn-Rockliffe

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