To view the full text, please login as a subscribed user or purchase a subscription. Click here to view the full text on ScienceDirect. FiguresFigure 1Multiple Breath Washout Trace. Flow is shown in the upper trace with the scale on the left hand y-axis. Tracer gas (in this case, 0.2% SF6) concentration is shown in the lower trace. There is a fall in peak expiratory SF6 concentration with each successive breath until it reaches 1/40th of the starting concentration when washout terminates.