Why is sleep disordered breathing common after SCI?

Author: Sharon Jang | Reviewer: Viet Vu | Published: 10 March 2020 | Updated: ~

A few hypotheses have been made by scientists as to why sleep apnea is prevalent in SCI. In general, sleep apnea is attributed to a complex interaction of a variety of factors:

Sleep disordered breathing is more prevalent in individuals with tetraplegia compared to those with paraplegia. Having a higher

level of injury

is usually associated with decreased muscle functioning and neural control over your organs. These impairments can create troubles with breathing, specifically with inhaling, exhaling, and the amount of air your lung can hold.

Refer to our article on Respiratory Changes After SCI for more information.

After an SCI, your body becomes more sensitive to the amount of carbon dioxide circulating throughout your body. So, when there is a slight increase in carbon dioxide in the body, the brain senses it as a large change, which cues the body to

hyperventilat

e

, or rapidly breathe. However, since the change in carbon dioxide was small to start with, hyperventilation results in excess removal of carbon dioxide, resulting in very low carbon dioxide levels. During sleep, breathing is dependent on the amount of carbon dioxide circulating in the body. If this level drops below the level required for breathing, then central sleep apnea occurs. While some researchers believe this may be a cause of central sleep apnea, others note that there is currently only weak evidence to support this hypothesis.

Measures of body composition, including body mass index (BMI), neck circumference, and waist circumference, may be linked to the prevalence of sleep disordered breathing. Weak research evidence has suggested that a greater neck circumference or BMI can increase the odds of having sleep disordered breath. This is concerning for individuals with SCI, as 44-66% of this population are overweight or obese. However, other studies have found no relationship between BMI or neck circumference and sleep disordered breathing in SCI.

One weak evidence study has suggested that there is more than a 50% increase in apneic events that occur when you sleep on your stomach or on your back, rather than on your side. More specifically, tetraplegics who sleep on their backs experienced more apneas and hypopneas per hour compared to those who slept in other positions. Despite this evidence, other researchers found that sleeping on your back enhances overall breathing functions after SCI. More research is required to determine the optimal sleeping position for health benefits, keeping in mind that bed mobility and turns overnight also help to maintain skin health.

Common medications used by individuals with SCI can also impact breathing during sleep. These include: narcotics, baclofen, benzodiazepines (lorazepam, diazepam, clonazepam), testosterone, and heart medications to treat high blood pressure or arrhythmias. Although medications can cause sleep disordered breathing, they are not likely to be the main contributor to the issue.

Individuals with tetraplegia may find it harder to breathe in with their nose (i.e.,

nasal resistance

) because swelling of the blood vessels and a thickening of the mucus in the nose is a common effect of cervical spinal cord injury. One

moderate evidence

study found that individuals with tetraplegia experienced greater nasal resistance in comparison with able-bodied individuals. Since increases in breathing resistance can cause the airways to collapse, some researchers believe that this may contribute to the higher prevalence of obstructive sleep apnea in individuals with tetraplegia.