Use of twitch mouth pressure to assess diaphragm strength in patients with chronic obstructive pulmonary disease.

This study was undertaken to determine whether twitch mouth pressure (TwPmo) can reliably assess diaphragm strength in patients with chronic obstructive pulmonary disease (COPD) using fully automatic trigger techniques. Fifteen patients with COPD were recruited. TwPmo, twitch oesophageal pressure (TwPes) and twitch transdiaphragmtic pressure (TwPdi) were generated by phrenic nerve stimulation and were measured using an inspiratory flow trigger (40 ml/s, Experiment 1) using an inspiratory pressure trigger (-5 cmH2O, Experiment 2) and using no trigger at functional residual capacity (Experiment 3). The correlation between TwPmo and TwPes was as follows: r=0.832; P<0.0001 (Experiment 1), r=0.900; P<0.0001 (Experiment 2); there was no significant correlation in Experiment 3. A Bland-Altman plot of the difference between TwPmo and TwPes showed the limits of agreement in Experiment (1) bias (range) 0.18 cmH2O (-2.05 to 2.41) and Experiment (2) bias (range) 0.32 cmH2O (-1.69 to 2.32). Measuring TwPmo using a fully automatic technique is a simple and convenient method for assessing diaphragm strength.