Autonomic dysreflexia occurs in individuals with spinal cord injury at or above which level?

• A. At or below T6
• B. Below T12
• C. Above T6
• D. At L1

Answer: (C)

Autonomic dysreflexia happens when descending brain control over the autonomic reflexes is lost after a spinal cord injury, so a noxious stimulus below the injury triggers an unchecked sympathetic surge. The critical level is around the upper thoracic region because the major sympathetic outflow to the splanchnic vascular bed lies roughly from T5 to T9. When the injury is at or above T6, those neurons are disconnected from the brain, so a stimulus such as a full bladder or bowel impaction causes widespread vasoconstriction below the lesion, producing a sharp rise in blood pressure. The heart may respond with parasympathetic activity via the vagus, causing bradycardia, but this cannot counteract the severe peripheral vasoconstriction. If the injury is below this level, enough supraspinal regulation remains to prevent such an unregulated reflex, making autonomic dysreflexia much less likely.