The rise and fall and rise of CO2 in Hyperventilation, breathing pattern disorders and Dysfunctional breathing

The assessment of CO₂ levels in breathing pattern disorders has gone through a few cycles and has evolved significantly from its historical roots to current practices. Historically, the understanding of CO₂ role in conditions such as hyperventilation syndrome was assumed to be important in almost all cases. In the 1960s and 1970s, research highlighted the role of CO₂ in regulating breathing and its connection to symptoms like dizziness and anxiety in hyperventilation. This period saw increased awareness of hypocapnia (low CO₂  levels) resulting from rapid or deep breathing, which could lead to various physiological disturbances. However just as this popularity peaked in the 1990s a seminal paper by Hornsveld et al in 1996 which essentially found manipulation of CO₂ did not correlate to the symptoms expressed in the Nijmegen Questionnaire. Many therapists gave up on CO₂ assessment, and a recent survey from the UK found that almost no therapists were assessing CO₂  with capnography in clinical practice, leading to questions over how specific clients are being assessed and managed with hypocapnia symptoms.

Tasked with understanding and reframing what to do with this information on CO₂ many researchers chose to ignore it and carry on with the rehabilitation aspect, and the biomechanical aspects of Breathing Pattern Disorders and Dysfunctional breathing, and the term Hyperventilation fell out of fashion. However, CO₂ didn’t go away and some practitioners started to use capnography as a way to diagnose and manage these disorders.

Today, the assessment of CO₂  in breathing pattern disorders is highly sophisticated, and it appears to be involved in conditions such as long COVID, specific cases and phenotypes of BPD / DB and also in POTS.  Treatment and assessment is covered in detail in BradCliff Level 1 and Level 2, and we are always learning more about how specific CO₂ assessment and treatment can improve our patients' symptoms and quality of life!

This historical evolution underscores the critical role of CO₂  assessment in diagnosing and treating breathing pattern disorders, reflecting a journey from rudimentary observations to advanced, evidence-based practices.

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References

Hornsveld HK, Garssen B, Dop MJ, van Spiegel PI, de Haes JC. Double-blind placebo-controlled study of the hyperventilation provocation test and the validity of the hyperventilation syndrome. Lancet. 1996 Jul 20;348(9021):154-8. doi: 10.1016/s0140-6736(96)02024-7. PMID: 8684155.

Grillo L, Russell A, Shannon H, et al. Physiotherapy assessment of breathing pattern disorder: a qualitative evaluation. BMJ Open Respiratory Research 2023;10:e001395. doi: 10.1136/bmjresp-2022-001395

Stewart JM, Pianosi P, Shaban MA, Terilli C, Svistunova M, Visintainer P, Medow MS. Postural Hyperventilation as a Cause of Postural Tachycardia Syndrome: Increased Systemic Vascular Resistance and Decreased Cardiac Output When Upright in All Postural Tachycardia Syndrome Variants. J Am Heart Assoc. 2018 Jun 30;7(13):e008854. doi: 10.1161/JAHA.118.008854. PMID: 29960989; PMCID: PMC6064900.

El-Medany, A., Adams, Z.H., Blythe, H.C. et al. Carotid body dysregulation contributes to Long COVID symptoms. Commun Med 4, 20 (2024). https://doi.org/10.1038/s43856-024-00447-5