The most significant pathophysiology change of COPD patients is persistent incompletely reversible airflow obstruction and increased lung volume. As a result, the work of breathing(WB) and neural respiratory drive (NRD)increased. Noninvasive positive pressure ventilation (NPPV) can reduce the load of respiratory muscles. Detection of NRD can be the index of monitoring for titration of optimal level of ventilator support in the future. As electromyography(EMG) is the most reliable measurement in evaluating NRD that can be used for human. Currently the standard method for evaluation of NRD with EMG is using esophageal multi-paired electrodes catheter(EMGdi) ,it is reliable but invasive .Surface respiratory EMG (sEMG）is a noninvasive measurement. Although it subjected to contamination and less sensitive, recently, advance in technology with multiple pair of surface electrodes is possible to sufficient signals for evaluation of NRD.So the investigator compare the NRD measured by EMGdi and sEMG,and consider that the correlation between them is well in different levels.

The most significant pathophysiology change of COPD patients is persistent incompletely reversible airflow obstruction and increased lung volume. As a result, the work of breathing (WB) and neural respiratory drive (NRD) increased. Noninvasive positive pressure ventilation (NPPV) is the first-line treatment in acute exacerbation of COPD (AECOPD). One of the mechanisms is to reduce the load of respiratory muscles. It has been reported that NRD decreased in response to increase of pressure support. Detection of NRD can be the index of monitoring for titration of optimal level of ventilator support in the future.

NRD can be measured with minute ventilation, inspiratory pressure change、mean inspiration flow and electromyography(EMG) of inspiratory muscles. However, the first three methods are subjected to the influenced of lung volume, airway resistance and compliance of respiratory system. So, electromyography is the most reliable measurement in evaluating NRD that can be used for human. Currently the standard method for evaluation of NRD with EMG is using esophageal multi-paired electrodes catheter ,since it is far away from chest wall and close to diaphragm , so the contamination from other respiratory muscles can be reduced .However, catheter placement into esophagus is necessary for this measurement, which limits its use in daily practice. Surface respiratory EMG is a noninvasive measurement. Although it subjected to contamination and less sensitive, recent advance in technology with multiple pair of surface electrodes, including surface diaphragm EMG、parasternal EMG and so on, it is possible to sufficient signals for evaluation of NRD. It has been the hot topics of research recently due to its noninvasive, easiness of use and appropriate for continuing monitor.

Purpose：

1. To explore the feasibility of surface respiratory electromyography and its correlation with esophageal EMG in conditions of different level of respiratory central drive.
2. To investigate the dynamic change esophageal EMG and surface EMG in response to increase of pressure support level during noninvasive ventilation, in order to evaluate the feasibility of using surface EMG for titration of pressure support during noninvasive ventilation.

Methodology:

1. Electromyography: Multi-paired electrodes esophageal catheter was used for detection of esophageal diaphragm electromyography (EMGdi); Surface electrodes for left and right diaphragm and parasternal muscle were used to detect surface electromyography (sEMG).
2. Monitoring of respiratory physiology parameters: Pneumotachometer and differential pressure transducer were used for measurement of respiratory flow and pressures. lung volume change was calculated with integration of flow.
3. Regulate neural respiratory drive:1.in normal volunteer,increase the inspiratory threshold load step by step(30%-80%MIP),in order to increase neural respiratory drive;2.in sever COPD patients,increase the pressure support ventilation step by step, in order to decrease neural respiratory drive.
4. Methods for adjustment of respiratory central drive: (1) The increase of respiratory central drive was induced by inspiratory threshold load step by step (30%-80%MIP) in normal volunteer. (2) The reduction of respiratory central drive was induced by stepwise increase of pressure support level with noninvasive ventilation in COPD patients.

Analysis and statistics:

1. The correlation between sEMG and EMGdi at different level of respiratory central drive was analyzed with Pearson correlation analysis. The change of Ventilation central drive coupling was calculated.
2. In COPD patients, the change of respiratory central drive in response to increase of pressure support level (IPAP increase from 8cmH2O to 20cmH2O) during NPPV was evaluated.
3. The feasibility using sEMG as guidance for adjustment of pressure support level during NPPV was analyzed.

Inclusion Criteria:

• normal cardio-pulmonary function
• without low inspiratory muscle strength
• non-smoker
• without history of the nervous system and respiratory system disease
• sever to very severe stable stage

Exclusion Criteria:

• systemic application of corticosteroids nearly 4 weeks