Sleep apnea syndrome is a disorder characterized by frequent, brief pauses in breathing during sleep, resulting in reduced oxygen flow to the brain. The disorder occurs in 4% of the general population, most commonly in middle-aged men, and is a common cause of daytime sleepiness and cognitive dysfunction in the areas of attention, concentration, complex problem solving, and short-term recall. Sleep apnea is a serious medical problem because it is associated with increased rates of motor vehicle accidents, hypertension, depression, and mortality.
Sleep apnea is significantly more common in persons with Spinal Cord Injury (SCI), especially those with tetraplegia (paralysis of both arms and both legs), among whom an estimated 25% to 40% have the disorder. A number of factors may contribute to this high prevalence. Obesity is relatively common in this population, and individuals with SCI are predominantly males. Both of these are known risk factors for sleep apnea in the general population.
Weakness of respiratory muscles may contribute to the problem, especially in persons with tetraplegia, because the muscles cannot easily interrupt episodes of apnea. The use of sedating antispasticity medications such as baclofen is also considered a potential risk factor because these drugs are known to slow down the breathing apparatus.
Several additional factors may predispose the SCI population to sleep apnea. The supine (lying on one's back) sleeping position is known to markedly increase the rate of obstructive breathing episodes in the non-SCI population. Many individuals with SCI are unable to change position while in bed, which may result in increased time spent in the supine position.
Persons with tetraplegia often rely on neck and upper chest muscles to help with breathing because the diaphragm muscle may not have normal strength. These muscles become inactive during the rapid eye movement stage of sleep, further compromising the individual's ability to breathe. Nasal congestion is also common in SCI due to disruption of the autonomic (automatic) nervous system, and this further obstructs the airway.
Sleep apnea is often successfully treated in the general population through weight loss, avoidance of the supine sleeping position, and use of continuous positive airway pressure (CPAP) therapy, which uses a mask that fits over the nose and is attached to an air pumping device.
Unfortunately, treatment in the SCI population is more difficult. So far, CPAP has not been accepted well by many persons with SCI, possibly because limited upper limb function makes repositioning or adjusting the mask difficult. In previous studies, persons with SCI who were able to tolerate the CPAP showed decreased frequency of apnea episodes and reported increased daytime alertness.
Researchers at the University of Washington (UW) are completing a study of patients with SCI who also have sleep apnea. This study is measuring sleepiness and other symptoms of sleep apnea, and evaluating the types of treatment currently being used by patients. This is expected to lead to another study investigating a new treatment and comparing it to conventional treatment.
Sleep apnea may be even more common in the newly injured SCI population, since respiratory muscle weakness is more severe in the first several weeks following injury. A study is currently underway at the UW to investigate the prevalence of sleep apnea in newly injured patients (within three to five weeks after injury) and the extent to which the resulting cognitive dysfunction interferes with rehabilitation.
It is possible that adjusting to the CPAP early on in the rehabilitation process may improve tolerance of the device over the long run and help people avoid sleep apnea and its associated problems in the future. It also may help patients to participate fully in therapies and learn the information and skills needed to take care of themselves after leaving the hospital.
TalkAboutSleep: Dr. Burns, some of our readers may not be familiar with Spinal Cord Injury. Could you briefly explain what is Spinal Cord Injury?
Dr. Stephen Burns: Spinal Cord Injury (SCI) is damage to the main pathway of nerves running inside the spine. This disrupts the signals going from the brain to the legs, the arms, and sometimes the breathing muscles. The most common traumatic cause of SCI is motor vehicle collisions. Falls are another common cause. Many older patients develop SCI from gradual narrowing of the spinal canal from arthritis.
TalkAboutSleep: In the article above, the term "tetraplegia" is used several times. What is tetraplegia? We usually hear terms like paraplegic and quadriplegic used when describing victims of spinal cord injury.
Dr. Stephen Burns: Paraplegia means paralysis of both legs. Quadriplegia means paralysis of both arms and both legs. The derivation of these words from Greek and Latin roots was not acceptable to some linguists with too much time on their hands, and so the word "tetraplegia" was invented to replace "quadriplegia." They mean exactly the same thing.
TalkAboutSleep: You have found sleep apnea to be more common in your SCI patients than in the normal population. Do you believe that these patients develop sleep apnea AFTER the injury and caused by the injury? Or do they have apnea beforehand and their injury simply makes the apnea worse?
Dr. Stephen Burns: I think that some of these patients had sleep apnea before injury. People with untreated sleep apnea probably are more likely to have spinal cord injuries, since they are more likely to be involved in motor vehicle collisions.
I think that most SCI patients with sleep apnea developed it because of their injury. My guess is that many of them snored before injury, but their snoring was not severe and didn't affect sleep quality too much. Now that they have paralysis, involving some breathing muscles, they can't breathe in with enough strength to move air past a little airway narrowing.
There are probably other factors involved, like medicines that cause sedation, or needing to sleep on their backs, but I think weak breathing muscles must be a main factor.
TalkAboutSleep: How did you come to focus on the combination of sleep apnea and SCI? Was there a particular patient's case that piqued your interest?
Dr. Stephen Burns: During my residency training, I got really anxious when I saw one of my patients with a new SCI had obvious obstructive apnea as soon as he fell asleep. I was shocked that his nurse, who was quite experienced with SCI, didn't seem alarmed at all. I later decided that this breathing pattern is so common in patients with SCI that it is almost ignored by nurses who work at night.
TalkAboutSleep: Do you have any new or ongoing research into sleep apnea in SCI patients? What are you trying to find out?
Dr. Stephen Burns: My research team is involved in a couple of studies currently. We want to find out how soon after SCI sleep apnea begins. If it begins early, which we suspect it does, then it could be interfering with everything the patients learn during rehabilitation. The other questions that still need to be answered are: what are the exact reasons that apnea occurs so commonly in these patients; what is the most effective way to treat apnea in someone with SCI; how beneficial is the treatment in these patients?
TalkAboutSleep: If any of our readers suspect undiagnosed sleep apnea in someone with SCI, what should they do?
Dr. Stephen Burns: They should ask for a referral to a specialist in sleep medicine. People with SCI can have similar symptoms from other conditions, or from medication side effects, so sleep apnea should be confirmed with a sleep study (polysomnography).
TalkAboutSleep: Thanks, Dr. Burns, for your help in understanding the issues surrounding SCI and sleep apnea.
The following facts are summarized from a more extensive article on the University of Alabama at Birmingham's Spinal Cord Injury Information Network pages: