Abstract
Elevation of legs increases stroke volume (SV) as the blood moves into the intrathoracic compartment. However, the degree of effects caused by the increase in blood remains controversial as it only has temporary effect. As for hemodynamically unstable patients, special positioning and hemodynamic monitoring are essential. We investigated the effective posture to increase SV and the relationships between the hemodynamic parameters and the changes in the SV by adjusting the upper and the lower body angles. This repeated-measures cross-sectional study included 42 normal subjects to study the relationship between SV and hemodynamic variables. Hemodynamic parameters, such as SV, end-tidal carbon dioxide (ETCO2), and anterior-posterior diameter of the inferior vena cava (IVC) and internal jugular vein (IJV) were repeatedly measured with position changes. The changes in the variables were measured in the upper body elevations of 60◦ and 30◦, the supine position, and the lower body elevations of 30◦ and 60◦. The mean SV at the 30◦ lower body elevation showed the highest value among the SV values which was measured in two minutes after each position change. The SV and the SV value change showed the strongest positive correlation with the IJV’s anterior-posterior diameter and the IJV value change (odds ratio = 5.617 and 15.277; p = 0.004 and <0.001, respectively) while the ETCO2 and the IVC diameter showed no relation to the SV. The SV showed the highest value at the lower body elevation of 30◦. The scale of IJV diameter and the change were predictable factors of the SV and its changes. These findings might have clinical implications in the positioning and the hemodynamic monitoring of SV.