Gas flow (V) through the endotracheal tube was measured with a pneumotachograph (Hans Rudolph, Kansas City, MO) and differential pressure transducer (Honeywell, Freeport, IL). Volume (V) was derived by integration of the flow signal. Airway opening pressure (Pao) was measured 1 cm from the oral end of the endotracheal tube. Inspired and expired CO* concentrations were continuously monitored between pneumotachograph and endotracheal tube with an infrared capnograph (Puritan Bennett, Los Angeles, CA). The arterial oxygen saturation (SaOJ was monitored with a fingertip pulse oximeter (Nellcor Inc, Hayward, CA). Arterial blood samples were obtained from an indwelling radial artery catheter, and gas tensions were measured with a blood gas instrument (Instrument Laboratories, Lexington, MA, IL 813). Rib cage and abdominal motion were continuously monitored with a respiratory inductive plethysmograph (Respigraph, NIMS, Miami Beach, FL) during the weaning period. All data were displayed on an eight-channel hot pen recorder (Astro-Med, West Warwick, RI).
Respiratory Systems Mechanics: To minimize extraneous influences on ventilation, patients were studied in a quiet room. Treatment with short-acting sedatives and narcotics had been withheld for 4 h prior to testing. Long-acting benzodiazepine therapy had been withheld for at least 24 hours prior to study.
The Control of Breathing during Weaning from Mechanical Ventilation (3)