Effects of carbon dioxide on human health
Bronchodilation (dilation of airways: bronchi and bronchioles)
CO2 is a natural dilator of bronchi and smaller air passages in the lungs.
Normal CO2 concentrations keep these air passages open wide (see on the left).
"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 In the textbook on physiology: Straub NC, Section V, The Respiratory System, in Physiology, eds. RM Berne & MN Levy, 4-th edition, Mosby, St. Louis, 1998.
When the CO2 level in the lungs is low, the bronchi constrict (the right picture), causing chest tightness, feelings of breathlessness, suffocation and wheezing. These effects are particularly known to asthmatics, patients with bronchitis, and COPD.
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. Since this nerve is
responsible for the tone or relaxation of the smooth muscles in bronchi, its
excited state leads to the constriction of airways or bronchoconstriction.
Dr. Herxheimer was probably the first scientist who proposed that low CO2 is the cause of bronchial asthma. His articles Hyperventilation asthma and The late bronchial reaction in induced asthma were published 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 the central role of overbreathing in the development and degree of 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. Correction of lifestyle risk factors is also necessary in order to permanently normalize one's breathing and alveolar carbon dioxide levels. This is the most logical and natural treatment and relief for asthma.
Hence, hypocapnic bronchoconstriction is the law of physiology, while CO2 is a powerful bronchodilator.
More information about asthma, its symptoms, mechanism, and treatment options
References
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. 83-87.
Herxheimer H, The late bronchial reaction in induced asthma, Int Arch Allergy
Appl Immunol 1952; 3: p. 323-328.
Straub NC, Section V, The Respiratory System, in Physiology, eds. RM Berne & MN Levy, 4-th edition, Mosby, St. Louis, 1998.