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Annual changes of gas exchange characteristics (PaO2, PaCO2) shown as mean ± SEM of repeated annual measurements over the age range 5 to 18 years (halftone symbols), stratified into measurements concomitantly obtained under normal FEV1 > -2 SDS (open symbols) and abnormal, FEV1 < -2 SDS solid symbols. Measurement numbers (n) are given along the x-axis.
