bstructive sleep apnea is a sleep disorder in which breathing repeatedly stops and starts during sleep. Certain symptoms of this condition may help predict heart disease.
A recent study found that factors associated with obstructive sleep apnea (OSA) such as oxygen level, sleep time, number of awakenings, leg movements, heart rate and daytime sleepiness were significantly and independently associated with an increased risk of cardiac events.
The researchers discovered that the apnea—hypopnea index (AHI) — the most common measurement of OSA that counts the number of times a patient’s breathing pauses or slows downs — was not significantly associated with risk of cardiac events after adjusting for potential outside factors.
The lead author of this study was Tetyana Kendzerska, MD, from the Institute of Health Policy of Management and Evaluation, in the Faculty of Medicine at the University of Toronto in Toronto, Ontario, Canada.
The study included 10,149 adults who were referred for obstructive sleep apnea, and underwent a sleep test at St. Michael's Hospital in Toronto between September 1, 1994 and December 31, 2010.
Sixty-two percent of the participants were male and the average age of the participants was 50 years old.
Participants were followed from their first sleep study to the end of March 2011, or the incidence of a heart disease event or death by any cause.
The researchers conducted follow-up after an average of 68 months.
A total of 1,172 (or 12 percent) participants died or experienced a heart disease event such as a heart attack, stroke, congestive heart failure or heart surgery.
The incidence rate for these outcomes was 2 cases per 100 person-years (number of participants multiplied by number of years in care).
The participants who spent nine minutes with oxygen saturation below 90 percent had a 50 percent increased risk of a heart disease event or death compared to the participants who spent zero minutes with oxygen saturation below 90 percent.
The researchers determined that the participants who had an average sleep time of 4.9 hours versus 6.4 hours were 20 percent more likely to experience a heart disease event or death.
Compared to the participants who woke up an average of 18 times per night, the participants who woke up an average of 35 times per night had a 6 percent increased risk of experiencing a heart disease event or death.
The participants who reported daytime sleepiness were 13 percent more likely to experience a heart disease event or death compared to the participants who did not report any daytime sleepiness.
The findings showed that many OSA-related variables were significant and independent predictors of a heart disease event after adjusting for known heart disease risk factors such as age, sex, body mass index (height to weight ratio), smoking status and history of heart disease or diabetes.
The authors wrote, "We believe a revision of the operative definition of OSA may be necessary, to reflect not simply the frequency of apneas and hypopneas, but the actual physiologic consequences that result – the severity of oxygen desaturation, sleep fragmentation, sleep deprivation and sympathetic activation. It is these 'downstream' phenomena that we have found to be more predictive of CV risk. The OSA-related predictors identified in our study could be collected using more limited recordings than PSG [polysomnography], potentially in the home setting."
AHI was not found to be significantly associated with heart disease after adjustment for risk factors.
The authors mentioned a couple limitations.
First, not all information about potential heart disease factors was available. Second, the data is based on findings from a single care center so the results may not be applicable to the general population.
This study was published on February 4 in the PLoS Medicine.
The Canadian Institutes of Health Research provided funding.