Preliminary investigations into the effects of breathing retraining techniques on end-tidal carbon dioxide measures in patients with asthma and healthy volunteers during a single treatment session

Objectives: Preliminary investigations into the physiological effects of breathing retraining techniques in order to establish the feasibility of the proposed methodology, produce data for power calculations and determine the potential for future research in this area.Design: Two preliminary, exploratory studies with an experimental design.Setting: Research laboratories.Participants: Study 1: 15 patients with mild to moderate asthma and nine healthy volunteers. Study 2: 15 healthy volunteers.Interventions: Physiological data from asthma patients and healthy volunteers were recorded before, during and after a single session of slow breathing and breath holds. A separate group of healthy participants carried out the slow breathing technique with and without visual biofeedback.Outcome measures: The primary outcome was end-tidal carbon dioxide (ETCO2), and the secondary outcomes were respiratory rate, pulse rate, oxygen saturation and lung function.Results: All groups showed an increase in ETCO2 from baseline during slow breathing. Study 1 found a mean rise in ETCO2 of 0.48 kPa [95% confidence interval (CI) 0.28–0.68] for healthy participants and 0.46 kPa (95% CI 0.29–0.63) for asthma patients. In healthy volunteers, ETCO2 stayed above baseline for 5 minutes after the intervention. ETCO2 rose minimally (mean 0.06 kPa) in both groups after breath holds. Study 2 found a mean rise in ETCO2 of 0.35 kPa (95% CI 0.09–0.60) during slow breathing with visual feedback, and 0.36 kPa (95% CI 0.13–0.60) during slow breathing without visual feedback.Conclusions: The results of these preliminary studies provide data to power larger studies. They suggest that ETCO2 rises during slow breathing in both asthma patients and healthy volunteers, and that this effect may persist beyond the intervention itself in healthy volunteers. The use of visual biofeedback had no effect on ETCO2 in healthy volunteers