Short Term Physiological Effects of Nasal High Oxygen Flow vs Low Oxygen Flow and Noninvasive Ventilation (NIV) on Respiratory Mechanics

Subjects. 10 in-patients with stable COPD and chronic hypercapnic respiratory failure with no history of neurological or chronic cardiac disease will be recruited. They need to be in a phase of clinical stability and were for a short period of rehabilitation. Patients with X-ray evidence of pulmonary edema or congestion and pulmonary infiltrate will be excluded from the study. Written consent will be obtained from all subjects, and the protocol will be approved by the Ethics Committee.

Measurements. Static and dynamic lung volumes assessed by body plethysmography (MasterLab-Jaeger, Hochberg, Germany).

Flow measured with a pneumotachograph (Screenmate Box 0586, Jaeger GmbH, Hochberg, Germany), connected to a rigid mouthpiece.

Airway pressure measured through tubing inserted in the mouthpiece and connected to a differential pressure transducer (Honeywell 300 cm H2O, Freeport, IL, USA). VT obtained by integration of the flow signal. The inspiratory (TI), expiratory (TE) and total breathing cycle (TTOT) duration, respiratory frequency (RR), and duty cycle (TI/TTOT) calculated as average values of 10 consecutive breaths, after 5 minutes of breathing.

Baseline from peak changes in esophageal (Pes), gastric (Pga), and transdiaphragmatic (Pdi) pressures measured using the balloon-catheter technique. Pressure at the airway opening (Paw) measured via a side port.