Washin curves and calculations of the six indexes for one studied animal at 5 cm H
O PEEP. Graphs (a, c, e) show curves as observed from the actual lung. Graphs (b, d, f) show curves as calculated from an ideal lung (well-mixed one-compartment model) that has the same FRC, VD and tidal volume as the actual lung. Text boxes below the graphs contain the expressions to calculate these indexes. Horizontal axes display breath number (lower) and volume turnovers (upper). Vertical axes display expired end-tidal oxygen concentration (a, b), change in oxygen volume content in the lung (mL) (c, d) and mean expired oxygen concentration (e, f). Dotted horizontal lines represent the initial and final levels of expired end-tidal or mean concentrations (a, b, e, f) and of oxygen volume change in the lung (c, d). Dashed horizontal lines represent crossing reference lines. Dashed vertical lines determine the specific numbers of volume turnovers or number of breaths, used in the expressions to calculate the indexes.