Dysautonomia following severe traumatic brain injury: evidence of persisting over-responsiveness to afferent stimuli

Objective: To differentiate between dysautonomic and nondysautonomic subjects with acquired brain injury by measuring sympathetic reactivity after a nociceptive clinical procedure and to determine the utility of heart rate variability as an indicator of sympathetic overresponsivity in dysautonomic subjects.Design: This case-controlled study recruited subjects with acquired brain injury (mean, 5 yrs postinjury) attending a hospital-based outpatient clinic, comprising seven dysautonomic subjects with traumatic brain injury, eight nondysautonomic traumatic brain injury subjects, and 11 nondysautonomic subjects with nontraumatic acquired brain injury. Sympathetic reactivity after nociceptive stimuli (limb assessment and botulinum toxin injection for spasticity management) was compared among groups.Results: Sympathetic overactivity in dysautonomic subjects was evident across all physiologic parameters, whereas nondysautonomic subjects demonstrated limited reactivity. Heart rate variability measures of the balance between sympathetic and parasympathetic cardiac control showed a significant elevation in response to nociceptive stimuli, a response not observed in either nondysautonomic group. This sympathetic overactivity showed a normalizing tendency with increasing time postinjury.Conclusions: This study found persistent sympathetic overactivity in response to nociceptive stimuli in dysautonomic subjects (mean, 5 yrs postinjury). This significantly extends the duration over which such sympathetic overactivity has been quantified in this group, contributing to the accumulating empirical evidence that dysautonomic paroxysms result from sympathetic overresponsiveness. Given that sympathetic overactivity has now been observed from day 7 through 5 yrs postinjury, quantitative evaluation of patients for overresponsiveness to stimuli should be added to current diagnostic procedures at all stages of recovery.