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

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

“…Previous studies have indicated that the inspiratory pressure trigger (−5 cmH 2 O) was more reliable than the inspiratory flow and expiratory triggers (Kabitz et al, 2007a,b;Topeli et al, 1999;Windisch et al, 2005). However, our previous study shows that the failure to reach the trigger threshold (−5 cmH 2 O) could be high (approximately 24%) in chronic obstructive pulmonary disease (COPD) patients (Hua et al, 2013). Furthermore, lowering the trigger threshold is not possible because of the constant time of magnetic valve occlusion (160 ms) (Hua et al, 2013).…”

“…To determine the optimal position, 60% of maximal stimulations were released between C5 and C7 until the largest stimulus intensity was observed and the TwPmo values no longer increased (Delpech et al, 2003;Similowski et al, 1989). Additional details associated with phrenic nerve stimulation have been published in our previous study (Hua et al, 2013).…”

“…The inspiratory trigger pressure was set at a level of -1, -2, -3, -4, -5, or -6 cmH 2 O. To ensure the controlled inspiratory manoeuvre did not cause different values of Pes and Pdi, the magnetic stimulations that were performed when the subjects were instructed to relax and not trigger at FRC were recorded according to previous settings (Hua et al, 2013;Kabitz et al, 2007a,b). The values of the twitch pressures were recorded until five acceptable mouth pressures reached the predefined criteria.…”

“…An inspiratory or expiratory effort is required to avoid the different degrees of glottic closure that prevent pressure changes from the thoracic cavity to the mouth Kabitz et al, 2007a,b; 1997; Mador et al, 1994;Windisch et al, 2005). Therefore, Tw Pmo, as an excellent surrogate of Tw Pes, is valuable for assessing inspiratory muscle strength when an automated and controlled trigger-technique is used (Hua et al, 2013;Kabitz et al, 2007a,b;Windisch et al, 2005). Both inspiratory and expiratory trigger efforts have been studied to investigate their influence on Tw Pmo (de Bruin et al, 1998;Hamnegaard et al, 1995;Kabitz et al, 2007a,b;Maillard et al, 1998).…”

“…However, our previous study shows that the failure to reach the trigger threshold (−5 cmH 2 O) could be high (approximately 24%) in chronic obstructive pulmonary disease (COPD) patients (Hua et al, 2013). Furthermore, lowering the trigger threshold is not possible because of the constant time of magnetic valve occlusion (160 ms) (Hua et al, 2013). Therefore, the control of the trigger technique to measure Tw Pmo could be improved.…”