1. Department of Physiology, Free University of Brussels, B1070 Brussels, Belgium;
2. Faculty of Health Sciences, University of Copenhagen, DK-2000 Copenhagen N, Denmark;
3. Department of Intensive Care Medicine, Erasme Hôspital, B1070 Brussels, Belgium;
4. National Center for Cardiology and Internal Medicine, Bishkek, Kyrgyzstan;
5. Department of Medical Physics, Royal Hallamshire Hospital, Sheffield S10 2JF, United Kingdom