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[Effects of noninvasive positive pressure ventilation on respiratory muscle fatigue in patients with acute exacerbations of chronic obstructive pulmonary disease: a randomized controlled trial].

OBJECTIVE
To study the effects of noninvasive positive pressure ventilation (NPPV) on respiratory muscle fatigue in patients with acute exacerbations of chronic obstructive pulmonary disease (COPD).


METHODS
Thirty-two COPD patients were randomly assigned to group I (conventional therapy + NPPV) and group II (conventional therapy alone). Sixteen normal volunteers served as the healthy control group (normal lung function). Scale for accessory muscle use, dyspnea score, lung function, arterial blood gases, P(0.1) and phrenic nerve conduction were measured before and after the treatment.


RESULTS
Before treatment, dyspnea and accessory muscle use were present in group I and group II. P(0.1) in the two groups was higher than that in the normal volunteers. Phrenic nerve conduction latency showed no significant difference among the three groups, but the diaphragmatic compound muscle action potential in group I and group II were lower than that in the normal volunteers (P < 0.01). On the 8th day of treatment, symptoms improved in both group I and group II. PaCO2 showed a decreased of (31.0 +/- 17.6) mm Hg in group I, the difference being significant compared to group II (P < 0.05). All the parameters of lung function improved in group I, but only forced expired volume in one second (FEV1) increased in group II. Compared with group II, the P(0.1), in group I decreased significantly [(2.8 +/- 1.0) cm H2O vs (0.3 +/- 0.5) cm H2O, P < 0.01] , and the diaphragmatic compound muscle action potential increased significantly after treatment [left: (188 +/- 62) microV vs (138 +/- 50) microV, P < 0.05; right: (200 +/- 52) microV vs (150 +/- 52) microV, P < 0.01].


CONCLUSION
Respiratory muscle fatigue was evident in patients with acute exacerbations of COPD. NPPV led to a more rapid improvement in gas exchange and respiratory muscle fatigue.