1. Laboratory for Aero and Hydrodynamics, Delft University of Technology, Leeghwaterstraat 21, 2628 CA Delft, The Netherlands
2. British Heart Foundation Cardiovascular Sciences Unit, National Heart and Lung Institute, Imperial College London, London W12 0NN, UK
3. Department of Anatomy and Embryology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands