Chest
Opinions/HypothesesHypocapnia and Asthma: A Mechanism for Breathing Retraining?
Section snippets
Search Strategy
Multiple strategies were incorporated to maximize identification of suitable studies. We searched MEDLINE, EMBASE, Cochrane library, CINAHL, and reference lists of original and review articles. Authors of relevant abstracts were contacted to seek additional information.
Hypocapnia
The Paco2 reflects the balance between the production and elimination of carbon dioxide. Under normal conditions, the Paco2 is maintained at approximately 39 to 41 mm Hg by alveolar ventilation under the control of respiratory centers in the pons and medulla.5 Changes in the production of carbon dioxide are usually accompanied by corresponding alterations in alveolar ventilation with little or no change in Paco2. The main physiologic causes for hypocapnia are related to hyperventilation. Mild
Hypocapnia and Bronchoconstriction
Although hypocapnia is a consistent finding in acute asthma, it is not certain whether it has any clinically relevant pathogenic role. Proponents of the Buteyko breathing technique7 would suggest that this is the case. Also, in 1968 it was hypothesized in the New England Journal of Medicine8 that hypocapnia during an asthma attack could perpetuate bronchospasm and lead to a cycle of progressive hypocapnia and increasing bronchospasm. There is a body of experimental evidence that supports this
Hypocapnia and Asthma
In 1952, Buteyko theorized that “hidden” hyperventilation is the basic cause of asthma,7 linked to the inflammatory and structural changes characteristic of the disease. During acute episodes of asthma, hyperventilation leading to hypocapnia is well documented,62425 but very few studies192627 have suggested that patients with asthma are hypocapnic when their asthma is stable. In 1988, Hormbrey et al27 compared carbon dioxide response and breathing pattern in patients with asthma, patients with
Future Research
Although breathing control and breathing training are common interventions for respiratory conditions, there is a paucity of randomized clinical trials examining their effectiveness or the mechanism for any effect. A recent Cochrane review stated that “no reliable conclusions can currently be drawn concerning the use of breathing exercises for asthma in clinical practice.”35 However, trends for improvement are encouraging; further large-scale trials, including full descriptions of treatment
Conclusion
There is now some evidence that asthmatic individuals have lower levels of carbon dioxide than the healthy population, even when they are stable and asymptomatic. There is also some indirect evidence that a significant proportion of the stable asthmatic population have symptoms of hyperventilation. Physiotherapists and others regularly use breathing retraining techniques to alleviate these symptoms, with some reported benefits. While these may be related to raising an individual's carbon
References (35)
Acid-base
Lancet
(1998)- et al.
The structure of symptom report in asthma: a reevaluation
J Psychosom Res
(2001) - et al.
The use of complementary therapies in inner-city asthmatic children
J Asthma
(2003) - et al.
Breathing retraining for dysfunctional breathing in asthma: a randomized controlled trial
Thorax
(2003) - et al.
Sahaja yoga in the management of moderate to severe asthma: a randomized controlled trial
Thorax
(2002) - et al.
Effect of two breathing exercises (Buteyko and pranayama) in asthma: a randomized controlled trial
Thorax
(2003) - et al.
Hypocapnia
N Engl J Med
(2002) Freedom from asthma: Buteyko's revolutionary treatment
(1997)Hypoxemia and hypocapnia in asthma [abstract]
N Engl J Med
(1968)- et al.
Tachykinins mediate hypocapnia-induced bronchoconstriction in guinea pigs
J Appl Physiol
(1989)
The effects of CO2on respiratory mechanics in anesthetized paralyzed humans
Anesthesiology
Effects of airway versus arterial CO2changes on lung mechanics in dogs
J Appl Physiol
Hypocapnia-induced constriction of the canine peripheral airways exhibits tachyphylaxis
J Appl Physiol
Hypocapnia-induced contraction of porcine airway smooth muscle
Eur Respir J
The mechanism of bronchoconstriction due to hypocapnia in man
Clin Sci
Effect of alterations in end-tidal CO2tension on flow resistance
J Appl Physiol
The effect of CO2on peripheral airways
Acta Physiol Scand
Cited by (37)
Hypocapnia correction as a working mechanism for breathing retraining in asthma – Authors' reply
2018, The Lancet Respiratory MedicineControlling Asthma by Training of Capnometry-Assisted Hypoventilation (CATCH) vs slow breathing: A randomized controlled trial
2014, ChestCitation Excerpt :The reported effects are clinically important and show promise in addressing an unmet need in a population where overall level of control remains unsatisfactory. Hypoventilation training for asthma has been advocated for some time,2,12,32but despite the centrality of elevating Pco2in its therapeutic rationale, no prior study has targeted Pco2levels directly, except for our pilot study.17 In the present study, we instituted the most rigorous test possible for Pco2as the active ingredient in that the comparison group followed the same prescriptions of slow breathing and feedback of RR as CART but was not provided with shallow breathing instructions or feedback of Pco2.
Buteyko breathing method
2013, Recognizing and Treating Breathing Disorders: A Multidisciplinary ApproachHyperventilation in panic disorder and asthma: Empirical evidence and clinical strategies
2010, International Journal of PsychophysiologyAcute effects of inspiratory pressure threshold loading upon airway resistance in people with asthma
2009, Respiratory Physiology and Neurobiology
Dr. Bruton is funded by a Postdoctoral Research Fellowship from the UK Department of Health.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestjournal.org/misc/reprints.shtml).