Dysautonomia, POTs, Orthostatic Intolerance & Syncope
Dysautonomia is defined as a disruption in the Autonomic Nervous System (ANS). The ANS controls homeostasis, vascular supply, cardiac, respiratory, and vital functions. Movement and postural changes are followed by a series of physiological changes in the human body. The maintenance of stable blood pressure during a position change is crucial to keep sufficient blood flow to the brain at all times. The inability to do so is called Orthostatic Intolerance which causes a drop in blood pressure when moving from sitting to standing. POTs, Syncope, and orthostatic Intolerance are all symptoms of Dysautonomia.
Orthostatic hypotension, POTS, and syncope are conditions that fall under the category of dysautonomia. The main cause of orthostatic hypotension is an excessive decrease in cardiac output or a failure to signal vasoconstriction is blood vessels. Orthostatic intolerance can lead to dizziness and syncope (fainting).
Low blood pressure drop upon standing is typically linked to the pooling of blood pooling in the lower limbs, as well as a failure to activate vasoconstriction and shunt blood upward. The physiological changes accompanying OI can be described as a temporal mismatch between cardiac output and vascular resistance.
When humans change positions from sitting to standing, it is the job of the vestibular system to detect changes in gravity and signal to the sympathetic system to successfully constriction blood vessel, redistributing blood to the brain and increasing blood pressure.
Dysautonomia and orthostatic intolerance development when the autonomic nervous system is damaged. Proper detection of our bodies moving in gravity is vital for every activity we do as human beings. When the autonomic nervous system receives inaccurate signals from the vestibular system it becomes difficult to carry out normal tasks such as standing upright without getting lightheaded or dizzy and even more difficult to think clearly or control emotions as usual.
The vestibular system controls how blood is distributed in the body and contributes to blood pressure changes necessary during movement. The autonomic nervous system includes two very important brainstem structures. These nuclei are called the Nucleus Tractus Solitarius and the rostral ventrolateral medulla (RVLM). They have several connections to the autonomic nervous system and are involved in regulating the cardiovascular system. Both brainstem areas receive direct input from the vestibular nuclei.
The sympathetic nervous system (SNS), controls cardiac output and regulates blood pressure. In dysautonomia the sympathetic nervous system becomes imbalanced. During postural changes, a range of sensory feedback mechanisms serves to increase activation of sympathetic nerves, which, among other effects, also increased blood pressure and heart rate. A very important reflex that contributes to these mechanisms originates from the vestibular system
The vestibular system plays an important role in the activation of the SNS. The vestibulosympathetic reflex (VSR) is the connection between signals from the vestibular system activating the sympathetic nerves which regulate the cardiovascular system. The VSR is essential for preventing a drop in blood pressure and symptoms of dysautonomia. The VSR is sensitive to changes in gravity and gets activated at the onset of sensing motion. The otoliths detect motion of the head and body with respect to changes in gravity within milliseconds. The otoliths are a portion of the vestibular apparatus and play a key role in the activation of the VSR.
A decreased ability to maintain blood pressure upon standing is correlated with a decreased otolith (vestibular) response suggests that orthostatic intolerance can be treated by specifically activating the vestibular system. Vestibular stimulation or recalibration can, in turn, remap proper brain integrity and resolve symptoms of POTS and Dysautonomia