1. University Department of Surgery, The Royal Free Hospital, Pond Street, London NW3 2QG, U.K.
2. Vascular Haemodynamic Laboratory, University Department of Surgery, Royal Free and University College Medical School, University College London and The Royal Free Hospital, London NW3 2QG, UK
3. Cardio Tech International LTD., Cambrian House, Hawrd Road, Brymbo, Wrexham, LL11 5EA, UK