May 20, 2008 (Toronto, Ontario) — Patients who have had a stroke are at greater risk for an early death if they have obstructive sleep apnea (OSA) rather than central sleep apnea (CSA), according to research presented here at the American Thoracic Society 2008 International Conference.
"We were interested in seeing if obstructive sleep apnea or central apnea was related to mortality in patients who have suffered a stroke," said Karl A. Franklin, MD, PhD, an associate professor of respiratory medicine at the University of Umea in Umea, Sweden. "Previous studies had not separated out the type of sleep apnea, whether it was obstructive or central, and evaluated if there was a relationship to the risk of mortality."
By prospectively following up patients, investigators aimed to determine if sleep apnea is an independent risk factor for mortality in patients who have had a stroke. A total of 132 of 151 patients who were admitted for in-hospital stroke rehabilitation in Umea, Sweden, from April 1995 through May 1997 underwent overnight sleep apnea recordings at 23 days after the onset of stroke. Patients had a mean age of 77 years, and 78 patients were women. Patients, none of whom were lost to follow-up, were followed up for a mean of 10 years; death was the primary outcome.
Patients had other conditions apart from sleep apnea including hypertension (61%), diabetes mellitus (34%), and atrial fibrillation (34%). Computed tomography scans were performed and the Mini-Mental State Examination (MMSE) was conducted to assess the severity of the stroke.
When the obstructive apnea–hypopnea index exceeded 15, patients were considered to have OSA. When the central apnea–hypopnea index exceeded 15, patients were considered to have CSA. Patients who had both obstructive apnea–hypopnea and central apnea–hypopnea index scores less than 15 were categorized as control patients.
A total of 116 of 132 patients died in the follow-up period. After controlling for possible confounding risk factors such as age, sex, body mass index, smoking, hypertension, diabetes mellitus, atrial fibrillation, MMSE, and the Barthel activity of daily living, researchers determined the risk for mortality was greater among the 23 patients with OSA than for control patients (adjusted hazard ratio, 1.76; 95% confidence interval, 1.05 - 2.95; P = .03). They found no dissimilarity in mortality between the 28 patients with CSA and control patients (adjusted hazard ratio, 1.07; 95% confidence interval, 0.65 - 1.76; P = .053).
"The desaturation in obstructive sleep apnea is much more severe than in central sleep apnea," said Dr. Franklin, speculating the mechanism of action of OSA and its impact on survival in stroke patients. "You have profound changes in cerebral circulation in obstructive apneas that are not seen in central apneas."
Dr. Franklin said it is significant to identify patients who have had a stroke and have OSA and to offer therapies such as continuous positive airway pressure (CPAP) or ensure they sleep in the lateral rather than supine position.
Mary Morrell, PhD (physiology), head of the clinical and academic unit of sleep and breathing, Royal Brompton Hospital, National Heart and Lung Institute, Imperial College, London, United Kingdom, said there is typically increased prevalence of sleep apnea in patients after a stroke, but the research does not address if apnea triggered the stroke.
"There is a question of whether they had obstructive sleep apnea before they had the stroke and if it caused the stroke," said Dr. Morrell, noting the study limitation. "They can't answer that question. There is a suggestion from the literature that having a stroke can cause sleep apnea."
Dr. Morrell, who moderated a news conference here where the study results were presented, said the research indicates that OSA should be treated in stroke patients and CPAP should be considered as a treatment for these patients.
"The stroke patients may be elderly, and may have other problems such as confusion and inability to express themselves, and it may be traumatic trying to put a mask on their face when they are faced with other issues," Dr. Morrell said. "However, if the findings of this study are correct, it [CPAP] may be a therapy that we should be thinking about."
Dr. Morrell suggested future research would observe patients with OSA who had a stroke, randomize patients to CPAP therapy or no CPAP, and assess the differences in outcome.
"We don't know if CPAP therapy would enhance quality of life," she added.
Dr. Franklin has disclosed no relevant financial relationships. The Swedish Heart and Lung Foundation funded the study. Dr. Morrell has disclosed no relevant financial relationships.
American Thoracic Society 2008 International Conference: Abstract A292. Presented May 19, 2008.
Am J Respir Crit Care Med. 2008;177(suppl):A292.
