Figure 4.

Pressure recordings of proximal airway pressure (Pprox; left panels) and modified Campbell diagrams (right panels) during simulated spontaneous breathing. Upper panels show recordings with continuous fresh gas flow; bottom panels show recordings with the demand-flow system. The left panels depict Pprox variation during two subsequent breaths. Thin lines represent unfiltered pressure signals and thick lines represent filtered Pprox. Note the reduced changes in both unfiltered and filtered signal with the demand-flow system (imposed pressure time product 17 cmH₂O s versus 6.8 cmH₂O s). Lines in the right panels represent mean lung pressure. Note the reduced surface area in the lower right panel. Imposed work of breathing is 1.2 J l^-1 without the demand-flow system versus 0.5 J l^-1 in the lower right panel with the demand-flow system. Pett, pressure at end of the tracheal tube.