Blood Flow in the Internal Jugular Veins in the Lateral Decubitus Body Position in the Healthy People

Background: Some studies have suggested that the lateral decubitus position during sleep may protect the brain from neurodegenerative processes. Although the mechanisms of such possible protection are not known, an optimal venous outflow may be responsible. Venous outflow from the cranial cavity is dependent on the body's position. However, to date, flow in the internal jugular veins (IJVs) in the lateral position has not been studied quantitatively. Methods: Using ultrasonography, we measured the cross-sectional areas and flow volumes in the IJVs in a group of 25 healthy individuals aged 20-52 ± 12.1 years. These measurements were performed in the supine, upright, and lateral decubitus positions. Results: In the lateral decubitus position, we revealed a collapse of the IJV located higher, dilatation of the opposite vein, and a shift in flow from one vein to the opposite. In the right lateral position, the mean cross-sectional area and flow in the right IJV were 88.6 ± 71.1 mm² and 74.3 ± 97.5 mL/min, in the left IJV: 37.2 ± 33.4 mm² and 48.8 ± 82.8 mL/min. In the left lateral position, the right IJV was 38.4 ± 30.7 mm² and 56.7 ± 56.1 mL/min, and the left IJV was 75.9 ± 51.9 mm² and 99.7 ± 123.9 mL/min. However, there was also a high heterogeneity of the cross-sectional area changes, and in many participants, this pattern was not observed. Regarding flow volumes in the lateral body positions, in comparison with the supine position, the total outflow through both internal jugular veins was not significantly different. Conclusions: In terms of venous outflow, the lateral decubitus position did not differ significantly from the supine position. The working hypothesis of a potentially protective effect of this body position during sleep against neurodegeneration through improved venous outflow has not been proven, at least in healthy individuals.