Volume loading of the heart by "leg up" position and head down tilting (-6 degrees) (HDT)

Head down tilting is widely used to increase preload and to induce intrathoracic blood pooling similar to microgravity. During daily routine, this venous pooling is performed by raising the legs up. In this study, both these approaches have been compared by invasive measurement using a right heart catheter. In patients with moderate coronary artery disease, diagnostic right heart catheterization was performed by the Swan-Genz-techniques. All measurements were performed with head down tilting (-6 degrees) and with "leg up" position. Patients then received Nitroglycerin to countermeasure the preload changes. Pressures in the pulmonary artery as well as in the wedge position increased significantly during leg up and HDT. However, changes were significantly more pronounced in the "leg up" position than during HDT. No changes were observed for arterial blood pressure, cardiac output, stroke volume and resistances. Nitroglycerin during HDT lowered blood pressure and pressures in the pulmonary artery and in PCW-position and reduced cardiac output significantly. Both approaches of volume loading of the heart induced significant changes and increases of preload. However, changes were more pronounced during the "leg up" position than during HDT. It is questioned whether HDT with -6 degrees is appropriate to truly reflect hemodynamic alterations during simulated weightlessness.