Predictive Value of Spirometric PIF to Produce PIF Rate Needed for the Use of Current DPI's.

The main aim is to study correlations between Peak inspiratory flow measured during a spirometry (PIFspiro) and Peak inspiratory flow measured over a pre-set resistance (PIFresist) in COPD patients and severe asthma patients. PIFresist will be measured using 5 different resistances, representing all DPI's relevant for the treatment of obstructive lung diseases. If this shows a distinct relationship between PIFspiro and PIFresist, PIFspiro cut-off points will be sought in an attempt to predict which patients are likely to be able to produce optimal flows for DPI use. If successful, this will make the actual measurement of PIFresist redundant in clinical practice. Also the relationship between PIFresist and device internal resistance in addition to PIFspiro (which corresponds to a very low resistance) will be examined.