Components of aircraft life support systems interact with each other and the user

Figures

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  FIGURE 1. Comparison of minimum inspiratory pressures (peak inspiratory pressure) as a function of flow to the inspiratory portion of the “trumpet curve” of MIL STD 3050. Solid line: standard. Symbols: measured values. Data are labeled with their nominal supply pressures. Points above the solid line are within the standard. Peak flows with two separate pressures plotted were generated with different tidal volume—frequency combinations set on the breathing simulator.

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  FIGURE 2. Exposure profiles for Phase 2 testing in the 6, 4, and 2 psig conditions. Each horizontal line between minutes 12 and 17 represents a separate exposure level, with a single level delivered per study session.

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  FIGURE 3. Regulator outlet pressure relative to room pressure showing flow limitation from the regulator. Data are from participant 3 with a nominal regulator inlet pressure of 10 and 2 psig. Regulator inlet pressure in reality varied from breath to breath depending on breathing characteristics. Inspiratory flow is given in negative values to correspond to negative mask pressures, but is plotted here with magnitude increasing to the right. At 2 psig supply pressure, the CRU-103 could not support flows greater than roughly 1.25 L/s, resulting in negative pressures at the regulator outlet relative to the room as the participant drew air out of the breathing hose faster than the regulator could deliver it.

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  FIGURE 4. A sample of mask and regulator output pressures relative to room pressure as a function of time for 10 s. Participant 16, with the CRU-103 supplied with 2 or 10 psig. Solid black line: mask pressure. Dashed blue line: regulator outlet pressure. Dotted black line: nominal safety pressure. Mask pressures below safety pressure represent inspiration, and those above, expiration. Note pressure spikes at the start of expiration when the regulator inlet pressure is 2 psig.

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  FIGURE 5. Mask and regulator output pressures when valves open or close. Means and SE across participants (200 s averages of breath-by-breath values) are shown. P = pressure, vI = inspiratory valve, vE = expiratory; black line: nominal safety pressure. Letters and horizontal lines above the bars indicate significant differences. The letters identify individual columns/comparisons and the horizontal lines indicate averaged values across conditions. For example, Column “a” (P vI closes at 2 psig) is significantly different from the mean of the same variable at 4 and 6 psig (indicated by the dashed line with “a,b” above it), which in turn is significantly different from Column “b” at 10 psig. Similarly, the mean of “P vI opens” across 2 and 4 psig is different from the mean across 6 and 10 psig.

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  FIGURE 6. Correlation of maximum regulator outlet pressure with peak inspiratory flow. Data are one-minute averages from individual participants. Best fit lines are shown. Conditions: 10 psig ■ and - -; 6 psig ◇ and···; 4 psig, Δ and—· –; and 2 psig ○ and –· ·–. Note that all values shown on the y-axis represent regulator overshoot; the axis starts at 4 cm H2O.

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  FIGURE 7. Minute ventilation vs. supply pressure. Each line represents a single subject.

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  FIGURE 8. Minimum mask pressures vs. supply pressure. Each line represents a single subject.

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  FIGURE 9. Estimated PaCO2 vs. supply pressure. Each line represents a single subject. The two dashed horizontal lines show the normocapnic range, 40 ± 2 mm Hg. The Jones correction (Jones et al., 1979) was applied to end-tidal measurements.