The effects of breathing retraining techniques on end-tidal CO2 measures in patients with asthma and healthy volunteers

Physiotherapists and others routinely use breathing retraining to treat patients with symptoms of dysfunctional breathing (e.g. asthma). One of the hypotheses underpinning this practice is that patients with dysfunctional breathing have lower CO2 levels and are more sensitive to CO2 than healthy controls. It is suggested that altering the breathing pattern will raise individuals' CO2 levels and that this 'densensitises' patients to CO2 and hence reduces the sensation of breathlessness. In this pilot cross-over study 6 patients with asthma and 4 healthy volunteers were taught two breathing techniques to assess the effect on end-tidal CO2 (ETCO2) levels. Baseline data consisted of demographic and anthropometric data, lung function data, Nijmegen questionnaire, HAD scale, ETCO2 and O2 saturations (SpO2). The intervention consisted of two breathing techniques ('slow breathing' and 'breath-holds') taught in random order by a senior clinical physiotherapist. Measures of ETCO2, SpO2, pulse and respiratory rate were recorded non-invasively before, during and after each intervention using a capnograph (BCI Sleep Capnocheck). Slow breathing resulted in a significant rise (mean 0.65 kPa SD 0.19) in ETCO2 levels during the intervention (t 9.797, p <.001). No significant changes in ETCO2 were detected after breath holds. This study lends support to the theory that ETCO2 can be raised by manipulating breathing pattern