Fig. 3.
Ventilation circuit. Filtered, regulated house air flows along tubing line to lungs. Along the tubing line are a tee branch with a manually controlled bleed valve through which most airflow exits; a computer-controlled, normally open, proportional inflation valve; a tee branch with a computer-controlled, normally closed, proportional deflation valve, distal to which pressure is atmospheric PATM or negative PVAC; and a tee branch leading to a pressure transducer used for monitoring airway entrance pressure, PAW. A custom Labview program sends control signals, via a data acquisition (DAQ) device and proportional drivers, to the 2 proportional valves; receives the transduced PAW signal via the same DAQ; and records PAW.