RESULTS: During MIV, all groups experienced a linear increase in root mean square (RMS) of diaphragm electromyogram but showed gradual decrease in transdiaphragmatic pressure (Pdi), minute ventilation (VE) and VE/RMS. After inhalation of the corresponding drugs, the parameters of placebo group had no significant change while those of both monotherapy group and combined therapy group improved significantly. In comparison with placebo group, the values of Pdi and VE in the latter two groups at the same time point increased significantly, and those of RMS and Borg score decreased significantly, thus increasing VE/RMS (all P<0.05). No significant difference in all indices was found between monotherapy group and combined therapy group (all P>0.05). The ▵Borg was significantly correlated with ▵Pdi, ▵VE, ▵RMS, and ▵VE/RMS, respectively (all P<0.05).