1. Department of Occupational and Social Medicine, University Hospital of Tuebingen, Tüebingen, Germany
2. Maquet Cardiopulmonary AG, Hirrlingen, Germany
3. Department of Thoracic, Cardiac and Vascular Surgery, University Hospital Tuebingen, Tuebingen, Germany
4. Department of Thoracic, Cardiac and Vascular Surgery, University Hospital Tuebingen, Tuebingen, Germany,