Gender Predicted Stroke Risk in Sleep Apnea

BY KERRI WACHTER
Elsevier Global Medical News

An obstructive apnea-hypopnea index associated with more than 15 events per hour increased the risk of ischemic stroke by 30% in men in the Sleep Heart Health Study of nearly 5,500 adults.

Risk began to increase at rates above 5 events per hour, and each unit of increase in the obstructive apnea-hypopnea index was estimated to increase the hazard ratio by 6%. The index was defined as the average number of obstructive apneas plus hypopneas per hour of sleep.

The apnea-hypopnea index was not associated with stroke risk in women after adjustment for other risk factors such as age, diabetes, hypertension, and smoking history.

Further, the researchers found that a higher sleep arousal index was associated with a reduced incidence of stroke in women, such that women who had an arousal index of greater than 12, had a 40%-60% decreased hazard ratio for ischemic stroke, compared with women with a lower arousal index.

The authors suggested several possible explanations for the gender differences, including statistical power for events in women.

The study addresses some of the shortcomings of previous studies in which the “temporal associations between stroke and OSA [obstructive sleep apnea] could not be determined,” wrote Dr. Susan Redline and her coinvestigators (Am. J. Respir. Crit. Care Med. 2010 [doi:10.1164/ rccm.200911-1746OC]).

The Sleep Heart Health Study (SHHS) is a community-based, prospective cohort study of the cardiovascular consequences of OSA. Quality data were analyzed on 5,422 men and women at least 40 years of age. At the baseline SHHS examination, participants filled out questionnaires for sleep habits, general health, and medication use. At the same time, researchers measured height, weight, and blood pressure and obtained overnight unattended polysomnography. At intervals of 3-5 years after the baseline polysomnogram, a survey regarding diagnosis of and treatment for OSA was performed. Subjects were followed for an average of 8.7 years.

Participants were followed until a first stroke occurred between the date of the polysomnogram and the final censoring date. Those who did not develop a stroke were censored at the date of death or last contact. Participants who developed strokes were censored at the time of the stroke occurrence.

The cohort consisted of 2,462 men and 2,960 women without a history of stroke, and who were untreated for OSA with pressure therapy at the baseline exam. During follow-up, a total of 193 ischemic strokes were observed (85 in men; 108 in women). The estimated incidence rates were 4.4 ischemic strokes per 1,000 person-years in men and 4.5 in women.

Incident stroke was associated with increasing age and systolic blood pressure, use of antihypertensives, and atrial fibrillation. In women, stroke was higher in blacks and lower in Native Americans, and was marginally associated with diabetes. However, stroke was not associated with body mass index, smoking status, or alcohol use in men or women.

In men, the unadjusted increased odds of incident stroke for an individual with OSA, compared with someone without OSA, was 2.26, which is approximately equivalent to the increased risk associated with a 10-year increase in age (odds ratio 2.37), noted Dr. Redline, who is the academic program director of the Center for Clinical Investigation at Case Western Reserve University, Cleveland.

A lower odds ratio for stroke was observed in women (1.65), which is roughly equivalent to the risk of stroke associated with diabetes in this cohort (1.79).

The National Heart, Lung, and Blood Institute funded the study. One author reported that he is a coinventor of the BiPAP device, manufactured by Philips Respironics Inc., and is a scientific consultant to the company. Another author reported receiving honoraria from Respironics.