Monaghan 225 ventilator use under hyperbaric conditions.

The Monaghan 225 ventilator was tested to ambient pressures of 6 atmospheres absolute (ATA) in a hyperbaric chamber. The ventilator would function with delivered tidal volume which was independent of ambient pressure. Ventilatory rate declined in an exponential fashion. At 6 ATA, the ventilatory rate was 45 percent of the preset rate at 1 ATA. By decreasing the circuit resistance and increasing the inspiratory flow rate, the 6 ATA rate could be increased to 72 percent of the 1 ATA value. The maximum minute ventilation of the ventilator at 1 ATA was approximately 48 L/min; at 6 ATA, its maximum was 18 L/min. Synchronized intermittent mandatory ventilation, assist/control, and PEEP functions were satisfactory at 6 ATA. While using 100 percent O2 to power the ventilator at 2.82 ATA, the oxygen leakage was 57.7 L/min (converted to 1 ATA pressure, 20 degrees C), of which 33.7 L/min was successfully scavenged using simple techniques. A minor modification was made to the ventilator, allowing it to be driven by compressed air while maintaining complete flexibility in setting the FIo2. The ventilator has proven stable and reliable in clinical use at ambient pressures up to 6 ATA.