Bronchodilator and Most Potent Natural Bronchodilators: CO2 and NO
A bronchodilator is a substance that relaxes smooth muscles or airways and causes dilation of bronchi and bronchioles. Bronchodilators reduce resistance in the respiratory tract and improve airflow to the alveoli of the lungs. Bronchodilators are divided as either endogenous or natural bronchodilators (originating naturally within the human body), or they may be medical drugs that are used for treatment of breathing problems in people with COPD, asthma, cystic fibrosis and other respiratory conditions. In order to find the best bronchodilators, consider the cause of bronchospasm in these people.
CO2: the chief natural bronchodilator
Ventilation rates (chronic diseases)
| 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|
|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|
|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|
|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|
We see that those sick people who suffer from bronchoconstriction have heavy breathing or they breathe too much air. Therefore, they have too low levels of CO2 in airways. What are the effects?
Carbon dioxide is probably the most powerful among all bronchodilators since it is the most potent relaxant of smooth muscles and vasodilator (see links to studies below). Hence, normal breathing parameters include 40 mm Hg CO2 pressure in the alveoli of the lungs to keep these air passages open wide (see on the left) due to bronchodilation, while hypocapnia (CO2 deficiency) in airways leads to bronchoconstriction or bronchospasm.
"Agents that tend to dilate airways include increased CO2 (hypoventilation or inspired CO2)..." Normal C. Straub, Sr., Professor Emeritus, University of California at San Francisco School of Medicine; Textbook on physiology: Straub NC, Section V, The Respiratory System, in Physiology, eds. RM Berne & MN Levy, 4-th edition, Mosby, St. Louis, 1998.
Carbon dioxide is listed in this medical textbook as the Number 1 bronchodilator. When the CO2 level in the lungs is low, the bronchi constrict (the right picture below: bronchoconstriction), causing wheezing, feelings of breathlessness, and difficulty breathing. These effects are particularly known to asthmatics, patients with bronchitis, emphysema, and COPD. Hence, bronchodilation is another carbon dioxide effect that is crucial for normal health.
Research devoted to natural bronchodilators
In 1968, in his research article The mechanism of bronchoconstriction due to hypocapnia in man (“hypocapnia” means abnormally low CO2 concentrations) Sterling explained that carbon dioxide deficiency leads to an excited state of the cholinergic nerve (Sterling, 1968). Since this nerve is responsible for the tone or relaxation of the smooth muscles in bronchi, its excited state prevents bronchodilation.
Dr. Herxheimer was probably the first scientist who proposed that CO2 is a natural bronchodilator, while low CO2 is the cause of bronchial asthma. His articles Hyperventilation asthma and The late bronchial reaction in induced asthma were published in 1946 and 1952 (see references below).
Soviet Doctor K Buteyko independently proposed this link in the 1950’s (his first publication was in 1964) when he discovered that CO2 is among potent natural bronchodilators and overbreathing in the development and degree of COPD and asthma (Buteyko, 1964).
He and his colleagues also found that asthma patients got immediate relief from their asthma attack symptoms, if they practiced reduced breathing exercise which is the main exercise of the Buteyko breathing therapy. Indeed, as soon as a person with bronchoconstriction starts to breathe less, their carbon dioxide level in the alveoli rises, and this leads to bronchodilation.
Correction of causes of hyperventilation is also necessary in order to permanently normalize one's breathing and alveolar carbon dioxide levels to ensure effects of this natural bronchodilator. This is the most logical and natural treatment and relief from asthma.
Hence, hypocapnic bronchoconstriction or bronchospasm is the law of physiology, while CO2 is a most powerful natural bronchodilator.
Nasal nitric oxide is a natural bronchodilator if you are a nose breather
Nitric oxide is also a bronchodilator (see the study done in the Harvard Medical School Bronchodilator Action of Inhaled Nitric Oxide in Guinea Pigs). NO (nitric oxide) is another substance that is produced in different parts of the human body including sinus passages. Mouth breathing prevents absorption of nasal nitric oxide and causes additional problems due to spread of pathogens since nitric oxide has powerful antiviral and anti-bacterial properties. Therefore, CO2 and NO are most effective natural bronchodilators.
Buteyko KP, An Instruction for VBN Therapy for Bronchial Asthma, Angina Pectoris, High Blood Pressure and Obliterating Endarteritis: Preprint. - Novosibirsk, 1964.
Herxheimer H, Hyperventilation asthma, Lancet 1946, 6385: p.
Herxheimer H, The late bronchial reaction in induced asthma, Int Arch Allergy Appl Immunol 1952; 3: p. 323-328.
Sterling GM, The mechanism of bronchoconstriction due to hypocapnia in man, Clin Sci 1968 Apr; 34(2): 277-285.
Straub NC, Section V, The Respiratory System, in Physiology, eds. RM Berne & MN Levy, 4-th edition, Mosby, St. Louis, 1998.
Reference pages: Breathing norms and the DIY body oxygen test:
- Breathing norms: Parameters, graph, and description of the normal breathing pattern
- Body-oxygen test (CP test) : How to measure your own breathing and body oxygenation (two in one) using a simple DIY test
References: pages about CO2 effect:
- 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 body tissues
- Nerve stabilization: Carbon dioxide has powerful calmative and sedative effects on brain neurons and nerve cells
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* Illustrations by Victor Lunn-Rockliffe
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