Twitch mouth pressure and disease severity in subjects with COPD

Abstract

INTRODUCTION: Patients with COPD have impaired respiratory muscle strength. Twitch mouth pressure (P tw,m) in response to magnetic stimulation of the cervical nerve has been suggested to clinically reflect inspiratory muscle strength. However, studies on P tw,m values and their relationship with disease severity are limited. Thus, we tested the P tw,m values of subjects with COPD and investigated the relationship of these values with disease severity. METHODS: We recruited 75 COPD patients and 63 age-matched controls. All participants were tested for P tw,m, sniff nasal pressure (SNIP), and maximum static inspiratory mouth pressure (PImax); the BODE (body mass index, air flow obstruction, dyspnea, exercise capacity) index was evaluated for overall severity assessment and the 6-min walk distance (6MWD) was used to determine the exercise capacity of subjects with COPD. RESULTS: Subjects with COPD had markedly lower P tw,m values compared with the controls (10.00 ± 2.17 vs 13.66 ± 2.20 cm H 2 O for males, 8.83 ± 0.89 vs 11.81 ± 1.98 cm H 2 O for female; each with P < .001). The tw,m values decreased with increasing COPD severity, and similar trends were observed in the SNIP and PImax values. Regression correlation analysis showed that P tw,m values were significantly correlated inversely with the BODE index (R = 0.65, P < .001) but positively correlated with 6MWD (R = 0.59, P < .001) in the COPD group; the SNIP values of subjects with COPD were also correlated inversely with their BODE index (R = 0.49, P < .001) but positively correlated with their 6MWD (R = 0.33, P < .005). CONCLUSIONS: tw,m values are 26.8% lower in male subjects with COPD and 25.3% lower in female subjects with COPD compared with the controls. The P tw,m values of subjects with COPD decrease with increasing disease severity. P tw,m was better correlated with the BODE index and exercise capacity than SNIP and P I max, which suggests that P tw,m more accurately reflects the overall severity and burden of COPD.