Patients with spinal cord injury or disease (SCI/D) are 3 to 4 times more likely to have sleep disordered breathing (SDB) than individuals in the general population. The prevalence of SDB — both central and obstructive sleep apnea — ranges from 27% to 82% in patients with subacute and chronic SCI/D.
The Why and How of SDB in SCI
The type of spinal cord injury affects the prevalence of SDB; patients with quadriplegia are more likely to have SDB than patients with paraplegia. Likewise, patients with cervical vs thoracic SCI have a higher prevalence of SDB (93% vs 55%, respectively). Even in patients with nontraumatic SCI, such as multiple sclerosis, rheumatoid arthritis, and spinal muscular atrophy, SDB prevalence is higher than in the general population.
The sleep fragmentation and intermittent hypoxemia of SDB have shown deleterious effects on cardiovascular outcomes, especially nocturnal hypertension and increased mortality. In patients with quadriplegia, SDB is associated with neuropsychological dysfunction such as impaired information processing, immediate recall, and attention.
During sleep, the respiratory system works harder due to pharyngeal narrowing and the collapsibility of the upper airway. Adding to the difficulty of nighttime breathing are neuromuscular weakness, abnormal chest wall mechanics, reduced lung volumes, and central nervous system suppressants.
Even the Best Treatments Are Not Optimal
Continuous positive airway pressure (CPAP) therapy is considered first-line therapy in patients with SCI/D who have SDB. However, because of the inconvenience, limited upper extremity mobility, and nasal congestion, CPAP therapy is not always practical and is often discontinued.
To improve treatment in SDB, clinicians need to provide better facilities for diagnosing the type of SDB in specialized sleep centers that can accommodate patients with SCI/D, including wheelchair accessibility, lifts, and well-trained staff. Future therapies could target nerve stimulation of the laryngeal and oropharyngeal muscles in patients with obstructive SDB.
The Consequences of SDB
Schembri and colleagues sought to determine whether sleep apnea leads to neurocognitive dysfunction and daytime sleepiness in patients with acute-onset cervical SCI. In the study, 104 patients (mean age, 45.6 years; 90 men) were tested for attention, information processing, memory, executive function, learning, mood, and quality of life. Although severe sleep apnea did not affect memory, it did result in worse outcomes in attention, information processing, and immediate recall.
The researchers noted that patients who were younger and of higher intelligence prior to the injury tended not to have severe SDB. They also suggested that treating patients with SCI with CPAP therapy might counteract the deficits caused by SDB.
“We believe that sleep disordered breathing, specifically obstructive sleep apnea, is highly prevalent in tetraplegia and that physiatrists and others caring for people living with SCI need to have it on their radar,” said David J. Berlowitz, PhD, professor of physiotherapy from the University of Melbourne in Australia, in an interview with Pulmonology Advisor. “It is a real problem that matters.”
To determine whether the neurocognitive impairment and daytime sleepiness in patients with acute quadriplegia could be ameliorated with auto-titrating CPAP, Dr Berlowitz and colleagues examined the effects of the therapy in 149 patients with SCI (mean age, 46 years; 134 men). Patients’ attention and information processing were measured with the Paced Auditory Serial Addition Task (PASAT) and daytime sleepiness with the Karolinska Sleepiness Scale.
Despite treatment with CPAP a mean 2.9 hours per night, none of the patients’ neurocognitive deficits had improved according to the PASAT. Daytime sleepiness, however, did improve. The researchers noted that ameliorating sleepiness benefitted overall outcomes in patients with SCI, even with a low adherence to CPAP therapy However, CPAP adherence is difficult even in the general population and more so in patients with SCI, with success rates of 20% to 50%. Untreated SDB can negatively affect learning during the rehabilitation process in patients with SCI.
“Treating obstructive sleep apnea with cPAP in these patients is very challenging; adherence is poor,” explained Dr Berlowitz. “Despite poor adherence, sleepiness improves as much as it does in the able-bodied population.”
Assessing Respiratory Outcomes and Ventilator Weaning
In patients who have undergone traumatic cervical SCI, bedside examinations and fluoroscopy allow clinicians to check diaphragm movement and predict how patients will recover respiratory function. Kim and colleagues studied 67 patients with recent acute SCI (mean age, 56.6 years; 56 men) who had C2 to C5 neurologic injuries, as specified by the American Spinal Injury Association (ASIA) standard. Despite the high cervical SCI that Kim and colleagues observed, they found no significant association with the patients being weaned off the ventilator at hospital discharge. Diaphragm movement during deep breathing, however, was associated with eventual ventilator weaning. In previous studies, pulmonary function determined how long it would take to recover from muscle flaccidity.
“If physicians see high cord injured patients, they need a simple understanding of the neurological examination for weaning of these types of patients,” explained Yong Beom Shin, MD, PhD, professor of rehabilitation medicine at the Pusan National University School of Medicine and Biomedical Research Institute in Busan, Korea. “For example, if the elbow is not fully flexed in the supine position (C5 key muscle) or there is an impaired pinprick sensation in the acromioclavicular joint (C4 key sensory point), the possibility of respiratory failure and respiratory complication will be high. In the opposite case, ventilator weaning will be successful.”
Summary and Clinical Applicability
Sleep is not considered a restful period for the respiratory system, and that is especially true when SCI exacerbates SDB. The poor sleep quality that results from SDB contributes to adverse outcomes in patients with SCI such as cardiovascular events and rehabilitation challenges.
References
- Sankari A, Vaughan S, Bascom A, Martin JL, Badr MS. Sleep-disordered breathing and spinal cord injury: a state-of-the-art review [published October 12, 2018]. CHEST. doi:10.1016/j.chest.2018.10.002
- Schembri R, Spong J, Graco M, Berlowitz DJ; for the COSAQ study team. Neuropsychological function in patients with acute tetraplegia and sleep disordered breathing. Sleep. 2017;40(2).
- Berlowitz DJ, Schembri R, Graco M, et al; COSAQ Collaborative. Positive airway pressure for sleep-disordered breathing in acute quadriplegia: a randomised controlled trial [published online December 11, 2018]. Thorax. doi:10.1136/thoraxjnl-2018-212319
- Kim TW, Yang JH, Huh SC, et al. Motor and sensory function as a predictor of respiratory function associated with ventilator weaning after high cervical cord injury. Ann Rehabil Med. 2018;42(3):457-464.
Suzanne Bujara
