Evaluation of the Accuracy of a Mechanical Insufflation-Exsufflation Device's Cough Peak Flow Measurement

Background: Mechanical insufflation-exsufflation (MI-E) is used to augment secretion clearance in neuromuscular patients with weakened cough strength. Cough peak flow (CPF) is a measure of cough function that is used to assess a patient's ability to clear secretions, with thresholds set that categorize cough as effective, ineffective or severely ineffective. MI-E is prescribed according to these thresholds, and CPF is used to assess titration of MI-E settings. The Clearway2 (Breas Medical, Stratford-upon-Avon, United Kingdom) displays a real-time CPF, measured by an internal pneumotachograph. This study sought to assess the agreement and repeatability of this displayed CPF, against the reference CPF measurement by a calibrated pneumotachograph. Methods: This study consisted of two phases (1) lung model (Group A) and (2) acutely unwell individuals with neuromuscular conditions (Group B) and clinically stable individuals with neuromuscular conditions (Group C). Simultaneous CPF measurements were recorded from the MI-E device (CPF_MI-E) and a calibrated pneumotachograph (CPF), which was inserted into the MI-E circuit. Bland-Altman analysis was used to assess agreement between methods of measurement, and repeatability was assessed using a repeated measures analysis of variance. Results: During phase 1, 805 simulated coughs were evaluated with the Clearway2. The mean bias toward CPF_MI-E was 33 L/min (95% limits of agreement 6-60 L/min). During phase 2, the mean bias increased to 66 L/min (95% limits of agreement 13-119 L/min). CPF_MI-E and CPF both had good repeatability in all groups. Conclusions: The Clearway2 MI-E device provided a real-time CPF measurement that was repeatable and systematically higher than CPF. It may therefore be a useful tool to measure change longitudinally, or in response to changes in MI-E settings, in an individual patient. Caution is advised if using the CPF_MI-E to assess cough efficacy against clinical thresholds.