Autonomic dysreflexia (AD) is a condition in which your involuntary nervous system overreacts to external or bodily stimuli. It’s also known as autonomic hyperreflexia. This reaction causes:

  • a dangerous spike in blood pressure
  • slow heartbeat
  • constriction of your peripheral blood vessels
  • other changes in your body’s autonomic functions

The condition is most commonly seen in people with spinal cord injuries above the sixth thoracic vertebra, or T6.

It may also affect people who have multiple sclerosis, Guillain-Barre syndrome, and some head or brain injuries. AD can also be a side effect of medication or drug use.

AD is a serious condition that’s considered a medical emergency. It can be life-threatening and result in:

To understand AD, it’s helpful to understand the autonomic nervous system (ANS). The ANS is the part of the nervous system responsible for maintaining involuntary bodily functions, such as:

  • blood pressure
  • heart and breathing rates
  • body temperature
  • digestion
  • metabolism
  • balance of water and electrolytes
  • production of body fluids
  • urination
  • defecation
  • sexual response

There are two branches of ANS:

  • sympathetic autonomic nervous system (SANS)
  • parasympathetic autonomic nervous system (PANS)

How they typically work

The SANS and PANS operate in opposite ways. This maintains the balance of the involuntary functions in your body. In other words, if the SANS overreacts, the PANS can compensate for it.

Here’s an example. If you see a bear, your sympathetic nervous system might initiate a fight-or-flight reaction. This would cause your heart to beat faster, your blood pressure to rise, and your blood vessels to get ready to pump more blood.

But what if you realize you were mistaken and it wasn’t a bear? You wouldn’t need the stimulation of your SANS, so your parasympathetic nervous system would jump into action. Your PANS would bring your heartbeat and blood pressure back to normal.

What happens with AD

AD interrupts both the sympathetic and the parasympathetic nervous systems. This means that the body’s SANS overreacts to stimuli, such as a full bladder. What’s more, the PANS can’t effectively stop that reaction. It may actually make it worse.

Your lower body still generates a lot of nerve signals after a spinal cord injury. These signals communicate your bodily functions, such as the status of your bladder, bowels, and digestion. The signals can’t get past the spinal injury to your brain.

However, the messages still go to the parts of the sympathetic and parasympathetic autonomic nervous systems that operate below the spinal cord injury.

Signals can trigger the SANS and PANS, but the brain can’t appropriately respond to them so they no longer work effectively as a team. The result is that the SANS and PANS can get out of control.

Your heart rate may slow down radically because pressure sensors located in the carotid arteries or aorta (called baroreceptors) respond to the abnormally high blood pressure and send a signal to the brain that the blood pressure is too high.

The symptoms of AD may include:

  • anxiety and apprehension
  • irregular or slow heartbeat
  • nasal congestion
  • high blood pressure with systolic readings often over 200 mm Hg
  • a pounding headache
  • flushing of the skin
  • profuse sweating, particularly on the forehead
  • lightheadedness
  • dizziness
  • confusion
  • dilated pupils

Triggers of AD in people with spinal cord injuries can be anything that generates nerve signals to the SANS and PANS, including:

  • a distended bladder
  • a blocked catheter
  • urinary retention
  • a urinary tract infection
  • bladder stones
  • constipation
  • a bowel impaction
  • hemorrhoids
  • skin irritations
  • pressure sores
  • tight clothing

AD requires an immediate medical response, so your doctor will usually treat the condition on the spot. Treatment is based on the apparent symptoms, as well as pulse and blood pressure readings.

Once the immediate emergency passes, your doctor will probably want to do a thorough examination and run diagnostic tests. These tests can help your doctor determine the exact cause and rule out other possible causes.

The goal of emergency treatment is to lower your blood pressure and eliminate the stimuli triggering the reaction. Emergency measures may include:

  • moving you into sitting position to cause the blood to flow to your feet
  • removing tight clothes and socks
  • checking for a blocked catheter
  • draining a distended bladder with a catheter
  • removing any other potential triggers, such as drafts of air blowing on you or objects touching your skin
  • treating you for fecal impaction
  • administering vasodilators or other drugs to bring your blood pressure under control

Long-term treatment and prevention should identify and address the underlying issues that trigger AD. A long-term treatment plan might include:

  • changes in medication or diet to improve elimination
  • improved management of urinary catheters
  • medications for high blood pressure
  • medications or a pacemaker to stabilize your heartbeat
  • self-management to avoid triggers

The outlook is more uncertain if your condition is due to situations that are hard to control or unknown causes. Repeated episodes of uncontrolled spikes or drops in blood pressure can result in strokes or cardiac arrest.

Work with your doctor to identify your triggers and take precautionary steps.

If you can manage the triggers for AD, the outlook is good.