the answer to this question isn't a simple yes or no. With a disease like ours the PEF can be absolutely normal and our FEV1 absolutley miserable. For example, my last PEF was 100% of predicted and my FEV1 was only 57% of predicted. In asthma it is a bit different, the FEV1 and and PEF is a bit closer correlated because they do not have the medium and small airway damage that we have. So a quick answer, in CF a decrease in PEF will most likley show a decrease in your FEV1 but an increase in PEF might not mean a thing with regards to you FEV1. Actually a high PEF in CF may be a misleading number to your overall lung health.
hope that helps answer your question
luke
