1 Intensive Care Unit, Geneva University Hospitals, 1205 Geneva, Switzerland.
2 Faculty of Medicine, University of Geneva, 1206 Geneva, Switzerland.
3 Geneva Hemodynamic Research Group, 1206 Geneva, Switzerland.
4 Department of Cardio-thoracic Surgery Istituto Clinico Sant'Ambrogio, Gruppo Ospedaliero San Donato, Milan, and Chair of Cardiac Surgery, University of Milan, 20149 Milan, Italy.