Symptoms of autonomic nervous system dysfunction are often non-specific and therefore a high index of suspicion is warranted. Common symptoms include dizziness, feeling faint (especially on standing), headaches, and gastrointestinal symptoms. Autonomic nervous system dysfunction leading to exercise intolerance and or orthostatic intolerance can occur after a mTBI/concussion and is associated with chronic disability when prolonged.338, 339
An orthostatic challenge measuring heart rate and blood pressure changes before and after standing from recumbency are relatively easy to perform and is a good screening tool. If symptoms are provoked and there is a change in heart rate of greater than 30 beats per minute in adults (or 40 beats per minute in children) without a change in blood pressure 5 minutes after standing this could indicate postural tachycardia syndrome and warrants further investigation. A decrease in systolic blood pressure of greater than 20mmHg indicates orthostatic hypotension and also warrants further investigation. Autonomic dysfunction is also one cause of exercise intolerance. An exercise tolerance test performed by a qualified health professional can help identify whether autonomic dysfunction is possibly contributing to post-concussion symptoms.
Autonomic dysfunction in the setting of mTBI/concussion often responds to graded sub threshold exercise program. Specialist referral and further investigation (e.g. Tilt Table testing) is warranted if symptoms do not resolve.
N/A New Further relevant investigations include an orthostatic challenge using the Active Standing Test (see the Sport Concussion Office Assessment Tool (SCOAT) – orthostatic vital signs), the Buffalo treadmill and bike test.