Use of a two-way non-rebreathing valve to simplify the measurement of twitch mouth pressure using an inspiratory pressure trigger and the establishment of an optimal trigger threshold for healthy subjects and COPD patients

•The measurement of Tw Pmo by the use of two way set-up is of clinical value for the investigation the suspected diaphragm contractility.•The controlled trigger-technique using a two-way non-rebreathing valve is superior to previous ones.•−2 cmH2O is the greatest trigger threshold for clinical applications.

ObjectiveControlled twitch mouth pressure (Tw Pmo) via the use of a two-way non-rebreathing valve is a new method to assess diaphragm contractility. The optimal trigger threshold was confirmed.DesignWe sought to determine the optimal trigger threshold for 17 healthy subjects (29 ± 4 years) and 17 COPD patients (64 ± 10 years). The Tw Pmo, twitch oesophageal pressure (Tw Pes) and twitch transdiaphragmatic pressure (Tw Pdi) in response to phrenic nerve stimulation were measured using an inspiratory pressure trigger at −1, −2, −3, −4, −5 and −6 cmH2O.ResultsThe lung volume did not change during triggering at different trigger thresholds using a two-way non-rebreathing valve. The highest correlation between Tw Pmo and Tw Pes in healthy subjects and COPD patients occurred for a −2 cmH2O trigger threshold (r = 0.939 and r = 0.869, P < 0.0001). The narrowest limits of agreement for Tw Pmo and Tw Pes both occurred at −2 cmH2O in healthy subjects, with a bias (range) of −0.4 cmH2O (−1.85 to 1.41), and in COPD patients, with a bias (range) of 0.16 cmH2O (−1.36–1.67).ConclusionsWe conclude that the measurement of Tw Pmo using a two-way non-rebreathing valve is of clinical value to investigate the suspected diaphragm contractility. The highest trigger threshold for clinical applications was −2 cmH2O.