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Thread: Explanation of Sympathetic Changes shortly and long-term after spinal cord injury

  1. #1

    Explanation of Sympathetic Changes shortly and long-term after spinal cord injury

    Somebody recently emailed me to ask the following questions:

    1. Shortly after injury, why is the skin below the injury site cool and people have slow pulses?

    2. Will autonomic dysreflexia go away?

    Spinal cord injury disconnects the lower spinal cord from the brain. Many sympathetic centers in the lower spinal cord are driven by brainstem centers. For example, temperature control (sweating and skin blood flow) is mediated from the brainstem. Spinal cord injury initially depresses sympathetic activity below the injury site. At the same time, the parasympathetic nervous system continues unabated. Parasympathic activity is mediated by the vagus nerve (the 10th cranial nerve) which bypasses the spinal cord and directly inhibits the heart and guts, as well as other organs.

    Therefore, shortly after injury, when the sympathetic centers in the lower spinal cord have reduced activity while the inhibitory influence of the parasympathetic system (vagus) continues unabated. This is manifested by a loss of sweating, reduced skin blood flow (cool skin), reduced blood pressure, slower heart rate (because sympathetic increases heart rate and parasympathetic from the vagus nerve reduces heart rate unopposed).

    As time passes after injury, sympathetic nervous system becomes hyperactive, sort of like "spasticity" of the sympathetic system. People begin to develop profuse sweating, bladder spasticity, increased skin blood flow (even though their brainstems telling them that they are feeling cold). Drugs like baclofen and ditropan may counteract some of the sympathetic hyperactivity.

    Autonomic dysreflexia (AD) occurs when some irritating sensory input (i.e. bladder infection, decubitus, back pain, gallbladder or gut pain, etc.) stimulates the sympathetic nervous system. One major manifestation of AD is increased blood pressure. It can lead to headaches and other problems. A variety of drugs (nitrates, calcium channel blockers) can reduce the blood pressure response in AD. Sweating is also common. The best approach is to identify and reduce the sensory signals that cause AD.

    Wise.

  2. #2
    Senior Member alan's Avatar
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    Damn good thing central pain doesn't cause AD, or my brain would have exploded years ago.

    Alan

    "Was it over when the Germans bombed Pearl Harbor?"

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