Dysregulated Cardiovascular Autonomic Responses to Orthostatic Challenge in Mild Traumatic Brain Injury

Area of Science:

• Neuroscience
• Physiology
• Autonomic Nervous System Research

Background:

• Mild traumatic brain injury (mTBI) can cause persistent symptoms like dizziness and headache.
• These symptoms are often linked to autonomic nervous system dysfunction and altered cerebral blood flow post-injury.
• Arterial baroreflex function is crucial for regulating cerebral perfusion and is of interest in head trauma research.

Purpose of the Study:

• To characterize sympathetic and parasympathetic baroreflex function in individuals with recent mTBI (≤14 days post-injury).
• To assess the relationship between autonomic impairment and the severity of post-concussion symptoms.
• To investigate autonomic nervous system responses during orthostatic stress.

Main Methods:

• Seventy participants (35 mTBI, 35 controls) underwent standardized autonomic testing.
• Testing included heart rate variability during deep breathing, Valsalva maneuver, and head-up tilt (HUT) with beat-to-beat monitoring.
• Primary outcome was low-frequency (LF) power of mean blood pressure during HUT; symptom severity was measured using the Rivermead Post-Concussion Symptom Questionnaire-13.

Main Results:

• mTBI participants exhibited significantly lower heart rate and blood pressure variability compared to controls.
• Reduced LF power of mean blood pressure during HUT was observed in the mTBI group (p = 0.002).
• LF power of heart rate was also significantly lower in mTBI individuals (p = 0.011), indicating blunted sympathetic baroreflex responses.

Conclusions:

• Individuals with recent mTBI demonstrate impaired sympathetic baroreflex responses to orthostatic challenges.
• Reduced autonomic variability post-mTBI suggests physiological impairment in sympathetic activation.
• While autonomic dysfunction may contribute to some symptoms, it does not fully account for the global symptom burden after mild TBI.