Monaghan 225 Ventilator Use Under Hyperbaric Conditions R.E. Moon, M.D., F.C.C.P., L.V. Bergquist, A.A.S., B. Conklin, A.AS., R.R.T, J.N. Miller, M.D.  CHEST  Volume 89, Issue 6, Pages 846-851 (June 1986) DOI: 10.1378/chest.89.6.846 Copyright © 1986 The American College of Chest Physicians Terms and Conditions

Figure 1 Gas for the patient circuit is a blend of the 100 percent oxygen used to power the ventilator and ambient air drawn through the filter on the front panel. The relative proportions can be adjusted by changing the “percent O2” knob. Inspiratory flow rate is adjusted with the knob in the middle of the bottom panel. The set screw on this knob has been loosened, allowing the inspiratory flow rate to be set maximally. Because of the greater pressure drop along the inspired circuit, a “proximal pressure” gauge has been mounted on the ventilator and connected to a point near the patient's endotracheal tube. CHEST 1986 89, 846-851DOI: (10.1378/chest.89.6.846) Copyright © 1986 The American College of Chest Physicians Terms and Conditions

Figure 2 The inspired gas mixer valve has been removed. All gas for the patient's circuit is provided by the external gas mixer now connected to the intake filter port. High pressure oxygen and air are blended and then fed into a 5 L reservoir bag. Over-filling of this bag will result in escape of excess gas through the flow meter to the oxygen scavenging system. If the gas flow from the blender is insufficient, allowing the reservoir bag to become empty, then additional gas may be provided from the ambient chamber atmosphere through the subambient pressure release valve shown. CHEST 1986 89, 846-851DOI: (10.1378/chest.89.6.846) Copyright © 1986 The American College of Chest Physicians Terms and Conditions

Figure 3 Observations are plotted on a log-log scale. The ratio of cycling rate at pressure:cycling rate at 1 ATA is plotted versus ambient pressure. Increase in the inspiratory flow rate resulted in improved performance at pressure. Test lung impedance: Resistance (R) 5.2 cm H2O/(L/S) (Measured at 1 L/s at 1 ATA) Compliance (C) 30 ml/cm H2O. CHEST 1986 89, 846-851DOI: (10.1378/chest.89.6.846) Copyright © 1986 The American College of Chest Physicians Terms and Conditions

Figure 4 Maximum gas delivery at 1 ATA could be obtained with a tidal volume from about 500 ml to 2.1 L. The maximum output decreased to about 18 L/min at 6 ATA, virtually independent of tidal volume. CHEST 1986 89, 846-851DOI: (10.1378/chest.89.6.846) Copyright © 1986 The American College of Chest Physicians Terms and Conditions

Figure 5 Maximum tidal volume is a function of ventilator rate. At any given ambient pressure, it is independent of loading conditions. The same data are used here as in Figure 4. Curves drawn by eye. Test lung impedances: Low − R = 5.2  cm H 2 O/ ( L/s ) C = 20  ml/cm H 2 O High − R = 17.7  cm H 2 O/ ( L/s ) C = 15  ml/cm H 2 O (Both resistances measured at 1 L/s at 1 ATA). CHEST 1986 89, 846-851DOI: (10.1378/chest.89.6.846) Copyright © 1986 The American College of Chest Physicians Terms and Conditions