Jet flow-regulated expiratory resistance to maintain constant CPAP during the entire respiratory phase.

We have developed a new continuous positive airway pressure (CPAP) device that consists of a microcomputer, a pressure transducer, and a pair of electronic interface valves. One of these valves creates the inspiratory demand flow, and the other creates the opposing jet flow by acting as an expiratory valve to maintain a constant CPAP. By controlling the two electronic interface valves, the airway pressure can be kept constant during the entire respiratory cycle. We compared our device with CPAP systems supplied with commercially available ventilators: the Puritan-Bennett 7200a, the Bear 5, the Servo 900C, and the CV 2000. A two-chambered spring loaded model lung was used to simulate inspiration and a piston pump model lung to simulate active exhalation. We compared both the inspiratory triggering work (WWIt) and expiratory flow-resistive work (WE) of each ventilator while in CPAP mode by calculating the corresponding areas of the pressure-volume loops using electrical integration. The WWIt of our apparatus and demand-flow ventilators was much smaller than that of the CV 2000. In our device, WE was also much smaller than those of the others. These results indicate that our device can be used for CPAP without causing airway pressure fluctuation, and therefore, without imposing an extra workload on the patient.