Collapsibility of the internal jugular veins in the lateral decubitus body position: A potential protective role of the cerebral venous outflow against neurodegeneration.

Recent research has revealed that patients with neurodegenerative disease sleep longer in the supine position, while healthy controls prefer sleeping in the lateral decubitus position. Thus, sleeping in the lateral position seems to be protective against neurodegeneration. It has also been suggested that a protective role of this body position could be associated with better cerebral venous drainage in this body position, which results in more active glymphatic system of the brain (the system responsible for clearance of the cerebral tissue from waste products, e.g. amyloid-β). Since no published evidence exists regarding venous outflow from the cranial cavity in the lateral decubitus position, we performed a pilot sonographic study of the internal jugular veins in 3 young healthy volunteers and 2 patients presenting with abnormal jugular valves. In all healthy volunteers both internal jugular veins were opened in the supine position and collapsed in the sitting one. In the right lateral decubitus position the right internal jugular vein was opened, while the left one was partially collapsed; and-vice versa-in the left lateral decubitus position the right internal jugular vein was partially collapsed and the left one opened. In patients with abnormal jugular valves both internal jugular veins were opened in both lateral decubitus body positions. We hypothesize that in the lateral decubitus body position, because of decreased flow resistance in the extracranial veins, cerebral venous outflow is optimal, which in turn optimizes the activity of the glymphatic system. Therefore, people intuitively prefer this body position during sleep, while other positions are associated with a higher risk of neurodegenerative disorders. Yet, it should be emphasized that our results need to be interpreted with caution, since only a few individuals have been assessed and this discovery should be confirmed in more patients and healthy controls, and by precise quantitative measurements.