ANAHEIM, CALIF—Almost three quarters of patients who have suffered an ischemic stroke may have obstructive sleep apnea, a new study indicates. Its results also suggest that patients with sleep apnea have significantly worse functional outcomes after stroke than do patients without apnea.

If continuing investigations demonstrate that this association holds true when larger numbers of patients are included, the researchers hope to begin an interventional study to establish whether treating obstructive sleep apnea could improve outcomes for stroke patients.

The data were presented at the 2001 Scientific Sessions of the American Heart Association.[1]

APNEA, HYPERTENSION, AND STROKE

Epidemiologic studies of more than 6,000 patients have shown an “unequivocal” relationship between obstructive sleep apnea and the development of hypertension, probably through chronic activation of the sympathetic nervous system caused by sleep apnea, said senior study author T. Douglas Bradley, MD, Director of the Sleep Research Laboratory, Toronto Rehabilitation Institute, and the Centre for Sleep and Chronobiology, University of Toronto.

“Since hypertension is the number one risk factor for strokes, one would expect an excess number of patients with strokes who have sleep apnea,” Dr. Bradley explained in an interview. Indeed, other epidemiologic evidence has found that sleep apnea has a significant relationship with stroke, although the relationship does not appear to be as strong as that with hypertension, he commented.

However, the additional oxygen deprivation caused by sleep apnea could aggravate the hypoxic insult of the stroke, resulting in a worse functional outcome in stroke patients with sleep apnea.

Obstructive sleep apnea is associated with lower cardiac output and reduced cerebral blood flow, Dr. Bradley added; both contribute “further noxious stimuli” to a brain already damaged by stroke. In this setting, the stroke could potentially be extended, the brain might become susceptible to further strokes, or the lack of oxygen might cause the generation of neural inhibitory peptides, which can impair brain function, he said.

In addition, normal sleep is associated with decreased levels of platelet activation. However, it has been shown that patients with obstructive sleep apnea do not have this normal reduction in platelet activity because of frequent waking, and this may further raise their risk of ischemic events.

EXPECTED AND UNEXPECTED RESULTS

Dr. Bradley and colleagues hypothesized that among their stroke population, obstructive sleep apnea would be highly prevalent and that functional outcomes would be worse in the patients with sleep apnea than in those without this condition. To examine these questions, the researchers carried out sleep studies in 40 patients admitted to their stroke rehabilitation unit. For the purposes of their study, obstructive sleep apnea was defined as an apnea-hypopnea index of greater than 10 events per hour. Patients also underwent functional and cognitive assessments, including the Functional Independence Measure and the Mini-Mental Status Examination.

“We found that 72% of patients had sleep apnea, which is more than 10 times higher than in the otherwise healthy population,” Dr. Bradley noted. The researchers also discovered that the severity of obstructive sleep apnea had a direct relationship with functional impairment, and this relationship persisted even after the analysis was controlled for age, weight, and type and location of stroke. Nevertheless, the researchers did not detect a relationship between obstructive sleep apnea and cognitive impairment.

Perhaps the most startling finding was that obstructive sleep apnea was also associated with much longer hospitalization. The mean hospital stay for those with an apnea-hypopnea index below 10 was 49 days, compared with 67 days for those with an apnea-hypopnea index above 10, despite the fact that the two groups of patients were of roughly the same age and had the same types of stroke. At a cost of about $500 (Canadian) per hospital day, the increase in length of stay amounted to a difference of approximately $9,000 per patient in hospital costs, Dr. Bradley noted.

“The sleep apneics were spending 18 days more in hospital, and when they left the hospital they were still more impaired than the other group,” explained Dr. Bradley. Furthermore, “the functional impairment was relatively refractory to therapy,” he said.

Currently, assessment and treatment of sleep apnea are not part of standard therapy for stroke patients, he noted; when he and his coauthors presented their data to colleagues on the stroke unit at their own hospital, most of the colleagues acknowledged that snoring and daytime fatigue were common among their patients but that a diagnosis of sleep apnea had not been considered. “Despite recognition of these problems, until now awareness of sleep apnea as a factor that might contribute to functional disability in patients with strokes was very low among personnel working in our stroke unit,” he said.

TOWARD UNOBSTRUCTED OUTCOMES

Dr. Bradley’s findings have several implications. For example, if the high prevalence of apnea and its impact on functional outcome can be confirmed in larger numbers of stroke patients, then it is possible that treating sleep apnea may have an important influence in improving these outcomes and shortening hospital stays.

Already, Dr. Bradley and his coauthors have been able to almost double the number of patients they have assessed, and the trends they saw in the first 40 patients appear still to be present as their numbers grow. If the trends continue, they hope to begin an interventional study perhaps next year, treating stroke patients with obstructive sleep apnea using continuous positive airway pressure, Dr. Bradley said.

—Susan Jeffrey

Reference
1. Kaneko Y, Zivanovic V, Hajek V, Bradley TD. Sleep apnea in stroke patients predicts worse functional status and longer hospitalization. Paper presented at: Annual Meeting of the American Heart Association; November 11, 2001; Anaheim, Calif.

Return to table of contents