<qa>  What is the new functional imaging method?Computational Fluid Dynamics CFD is a new functional imaging method. Since CFD is very sensitive to detect small changes, it might be worthwhile to study the acute effect of formoterol and budesonide combination therapy Symbicort forte Turbohaler on the upper airway dimensions in severe COPD patients GOLD III. The increased sensitivity of this technique makes it possible to detect changes in airway caliber in early stages. The regional distribution of resistance and the change in this parameter will provide more insight into the mode of action of the product. 