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.