How does a spinal cord injury affect your body? Part 3 of 4.
Third of a series. Read part one (mobility, spasms, skin) and part two (bowel, bladder, sex).
There are some things in the human body that you don’t think about until there’s something wrong… then you notice. A spinal cord injury can do that and be the “something wrong” that messes things up. This blog post addresses the vascular system (heart, blood vessels) and breathing.
The Nervous System on Auto-Pilot
When we think about the body’s nervous system, we usually encounter the brain, spinal cord and nerves as agents for controlling movements (making your leg move in order to help you walk, for example – a motor function) or transmitting and interpreting how we experience the world (seeing a sunrise, feeling your pet’s fur, hearing music – all sensory functions). But the nervous system also has another set of tasks to help keep you alive: it keeps your heart beating, intestines digesting, and all the other “automatic” stuff you don’t think about. This part of the nervous system is called the autonomic nervous system; autonomic = can function by itself. “Autonomic nervous system” sounds much more dynamic and clinically important than its old name, “vegetative nervous system”.
The autonomic nervous system has two sub-systems that balance each other out. The sympathetic nervous system handles the “fight or flight” response: when you body is under stress and is getting you ready to defend yourself from something threatening you, or run away from the threat, the sympathetic nervous system kicks in. Your pupils dilate to let more light into your eye so you can see better, your heart rate and blood pressure increase in order to get more blood into your muscles as you try to run away and move faster. The parasympathetic nervous system is the “rest and relax” part in charge of getting more nutrition (eating, digesting food, pooping) and is more active when there is no imminent danger.
The balance between the sympathetic and parasympathetic systems becomes out of whack in a person with spinal cord injury. How this shows up in your body depends on the level of injury. Often people will have low blood pressure, or hypotension, and for some this new low blood pressure reading becomes the “new normal” as the body adjusts to it. The heart rate may also slow down, and the increase in heart rate and blood pressure you usually see with exercise may not happen.
Autonomic Dysreflexia
However the biggest, single emergency in the spinal cord injury world (and also in the Rehabilitation Medicine world) is autonomic dysreflexia, commonly known as AD. This happens in people with injuries at T6 (6th thoracic level) and above, although there have been reports of rare occurrences in people with lower thoracic levels. AD symptoms show up when a “noxious stimuli” happens below the level of injury. Noxious stimulus is anything bad: most often a urinary issue like urine unable to leave the body (an obstructed urinary catheter, for example), constipation or excessive pressure or pain in one part. Less common causes would be ingrown toenails or labor in pregnancy. A noxious stimuli will start the “fight” response. The body below the level of the injury can’t react properly, so the “normal” body above the injury does all the reacting: sweating, goosebumps, dilated pupils, feeling of anxiety and impending doom. The most dangerous bit here is uncontrolled high blood pressure, which can damage the kidneys, cause a stroke or blindness in the worst cases. I know this is a lot of information to digest and some people might be visual learners, so here’s the Christopher Reeve Foundation, Craig Hospital, and MossRehab (that’s where I did my residency). This one is a video series for people who like the information chopped up into even smaller bites.
Other Vascular Issues
Aside from AD, an SCI can give a person a low baseline heart rate and a low baseline blood pressure. These patients “live” at a lower baseline set of vital signs and the absolute numbers that look out of whack may be concerning to anyone taking vital signs. However the body of the person with SCI has learned to “live” at this lower level. At this point we can say the body has compensated for its losses. As long has the person does not have any symptoms of low blood pressure (such as lightheadedness, dizziness, fainting), clinicians can just continue to watch and monitor.
The symptoms that accompany low blood pressure may be temporary, especially in the first few months after injury. However if they persist, using an abdominal binder (like a really wide garterized belt) or compressive garments may help increase the blood pressure. Compression stockings for the legs can also help. If physical measures like the binder and stockings do not help enough and the person is still symptomatic, there are a few drugs that can be added to the medication regimen. The Shirley Ryan Abilitylab (formerly Rehabilitation Institute of Chicago) has a good education page about this.
People with SCI are also in a hypercoagulable state, meaning they are at greater risk for developing clots (hyper = above; coagulable = pertaining to clots). In particular, they are at risk for developing clots in the lungs (pulmonary embolism, or PE) and in the legs (called deep vein thrombosis, or DVT). The Christopher Reeve Foundation, University of Washington and Shepherd Center in Atlanta all have good information.
Breathing (Respiratory System)
When you think of breathing, the lungs are often the first organs that come to mind. Which is well and good, but other organs are also involved – the nose, trachea (windpipe), the diaphragm and the other muscles in the body used in breathing (the accessory muscles – individual muscles that have other primary functions, but can be called upon to help the diaphragm). A spinal cord injury at the cervical (neck) and thoracic (chest and abdomen) levels can paralyze the diaphragm and the accessory muscles. Without the movements of these muscles, the lungs do not expand and contract as well as they should. This can lead to pneumonia (lung infection) and atelectasis (poor expansion). The paralysis of these muscles also mean that people with spinal cord injury also have an impaired cough, putting them at further risk of pneumonia and prolonged recovery after such an infection. Increased secretions (phlegm, saliva) also occurs in SCI, so the inability to produce an effective cough gives these patients a double whammy: more stuff to cough up, but can’t cough very well. It can get into a vicious cycle. For all these reasons (plus a weakened immune system), people with spinal cord injury have to be very careful because they are at high risk for serious respiratory illness. The Shepherd Center in Atlanta has an excellent page about this for more information, as does the American Model Systems Knowledge Translation Center.
