Fig. 2. Sample data from two experimental runs in one volunteer ( ID number 1641 ) showing the decline in end-tidal sevoflurane and halothane concentration during 90 s of rebreathing from a 1-l bag. Symbols represent end-tidal sevoflurane ( filled symbols ) and halothane ( open symbols ) concentrations. Solid lines show monoexponential model fits (y = ae –t/τ ) for each set of data points. For ease of comparison, data are expressed relative to the first end-tidal value recorded during rebreathing.