Autonomic Dysreflexia

Autonomic dysreflexia is a medical emergency caused by an uncontrolled autonomic response to a stimulus below the neurological level of a spinal cord injury. It occurs most often with injuries at or above T6, where descending supraspinal control can no longer adequately inhibit sympathetic activity arising from the spinal cord. A full bladder, bowel distension, skin injury or another stimulus below the lesion sends afferent signals into the cord. Sympathetic neurons in the intermediolateral cell column respond with widespread vasoconstriction below the injury, especially in the splanchnic vascular bed. Systemic vascular resistance rises abruptly, and so does blood pressure. Baroreceptors detect the pressure increase and activate vagal slowing of the heart. Parasympathetic vasodilation also produces flushing and sweating above the lesion. These compensatory responses cannot reach the vascular beds below the injury, so they do not remove the cause or reliably correct the hypertension. The heart rate may slow, remain normal or rise; heart rate is not part of the diagnostic definition. An injury below T6 lowers the probability but does not eliminate it. Episodes have been described with neurological...