In total, 8 chronic obstructive pulmonary disease (COPD) patients, 8 patients with interstitial lung disease (ILD) and 8 healthy subjects were recruited.
The patient was studied at the afternoon in a semirecumbent position. After the application of topical anaesthesia (2% xylocaine), the patient was asked to swallow two balloon-tipped catheters and the multi-pair esophageal electrode catheter through the nose into the their right position.
At the first period, the stable signals of unassisted spontaneous breathing (about 5min) were chosen to be recorded. After this period, the patient was placed on noninvasive pressure support ventilation(PSV). The inspiratory positive airway pressure (IPAP) was initially titrated by patient's tolerance . The noninvasive ventilation lasted at least 20 minutes until the breathing was stable. All the raw signals were recorded. The last 15 minutes of the stable computer-stored data were calculated and analyzed. The leaks were monitored by the display of the ventilator and the computer during the procedure. When the leak was observed, the mask was carefully adjusted to prevent. Esophageal and gastric balloon-catheters were used to detect the intra-thoracic and abdominal pressure. Airway pressure was also measured simultaneously. EMGdi was recorded from a multipair esophageal electrode .During ventilation Airflow and ventilation were measured with pneumotachograph.
Respiratory rate, tidal volume,the time difference between the initial increase and the termination of the diaphragm electromyogram(EMGdi) , time difference between maximal value of EMGdi and the end of inspiratory flow,time difference between the point of zero flow between inspiration and expiration ,and the time difference between the onset of the upward deflection in transdiagramic pressure( Pdi) and the return of Pdi were calculated during the unassisted spontaneous breathing and mechanical ventilation.
