Computer determined compliance of the respiratory system (Crs) in ventilated newborn infants

We describe a simple, low cost technique for computerized measurements of compliance of the respiratory system (Crs) by airway occlusion technique in intubated newborn infants. Tidal volumes of 5, 7.5, and 10 mL/kg were injected from a calibrated syringe into the endotracheal tube via a three-way stop cock and a t-piece. Airway pressure was measured by means of a differential pressure transducer. The analog pressure signal was fed into an optically isolated signal conditioning termination panel and an analog input board which was connected to the PC bus. The signal was amplified and A/D converted by the input board and processed by the digital computer. Crs was determined as the ratio of the injected tidal volume to the difference between the endexpiratory pressure and the pressure at airway occlusion. The software is written in Turbo Pascal (Borland Int.) and includes a patient data base and facilities for system configuration, calibration of transducers, data acquisition, handling, calculation of Crs, reporting and archive storage. Data sampling frequency may be individually set at 60 to 200 Hz. Synchronous measurements in 10 newborn infants using analog pressure amplification and polygraphic recording showed that pressures were correctly determined by the computer and that amplitude and frequency response of the pressure recordings were adequate.