A common symptom of concussion is the disability to maintain proper upright postural stability. Maintaining stability in the upright posture involves complex physiological regulations. Gravitational effects on the cardiovascular system in upright posture (orthostatic stress) induce decreases in blood pressure above heart level, which if not compensated for, will cause dizziness and postural instability. Arterial baroreceptors, originated from the carotid sinus, coronary arteries, and the aortic arch, are sensitive to changes in arterial blood pressure and play an important role in maintaining the blood pressure by activating the autonomic baroreflex control mechanism. Another component in cardiovascular control, particularly in the upright posture, is skeletal muscle contractions, which compress veins and pump venous blood in the lower limbs back to the heart (i.e., skeletal muscle pump). Skeletal muscle activities induced by the postural control are crucial in maintaining not only postural stability but also cardiac output and blood pressure, indicating an interrelationship between the cardiovascular and postural control systems.
Cardiovascular, and postural reflexes have been investigated as independent control mechanisms. Physiological models of postural control systems focus on biomechanical and/or sensory-motor (somatosensory, visual, and vestibular) issues while baroreflex-mediated controls on heart rate and peripheral vascular resistance are intensively studied. However, maintaining the upright posture requires not only the coordinated sensory-motor control of postural muscles but also the cardiovascular reflexes required to preserve blood pressure through the skeletal muscle pump. Recent studies have shown the link between postural sway and prevention of syncope; subjects who had poor tilt table orthostatic tolerance but never fainted during normal standing showed greater postural sway than patients who experienced frequent syncopal episodes. Other than these efforts, however, limited in depth analyses have been conducted to investigate the coupling between the cardiovascular and postural control systems.