Weight loss, not CPAP, best improves cardiac risk factors in sleep apnea
By Gene Emery
NEW YORK (Reuters Health) - Losing weight does far more to reduce cardiovascular risk factors in people with obstructive sleep apnea than therapy with continuous positive airway pressure (CPAP) alone, according to a study in the June 12 New England Journal of Medicine.
"Whether or not you get CPAP, the weight loss is the essential component for reducing cardiovascular risk," Dr. Julio Chirinos of the Philadelphia Veterans Affairs Medical Center, chief author of the report, told Reuters Health by phone. "It's obesity that needs to be targeted."
The finding, originally released March 10 at the 62nd Annual Scientific Session of the American College of Cardiology in San Francisco, comes in the wake of observational studies suggesting the CPAP might reduce the risk of cardiovascular problems.
The proposed link is complicated by the fact that sleep apnea is strongly linked to obesity - a 10% drop in body weight can lower the apnea-hypopnea index by 26% to 32% - and weight loss itself can reduce those cardiovascular risk factors.
"This study was designed to separate the effects of obesity versus sleep apnea. We did it by treating obesity, or treating sleep apnea, or both," said Chirinos.
He and his colleagues found that 24 weeks of weight-loss intervention, whether or not it was combined with CPAP treatment, reduced levels of C-reactive protein (p=0.01 in the per-protocol analysis), insulin resistance (p=0.04) and serum triglycerides (p<0.001).
"They improved whether you had CPAP or not," Chirinos said.
None of the three treatments produced significant changes in LDL (p=0.07 for CPAP vs. weight loss plus CPAP), nor did they generate significant improvements in HDL levels.
All three groups had reductions in blood pressure. But weight loss combined with CPAP produced the largest declines in systolic and mean arterial blood pressures, according to an exploratory analysis.
So weight loss will reduce blood pressure, but "a physician can expect an incremental benefit in blood pressure if you add CPAP, as long as the patient complies," said Chirinos.
The volunteers in the study had a BMI of 30 or higher, at least 15 apnea or hypopnea events per hour, and CRP levels higher than 1.0 mg/L.
Only 136 of the 181 original volunteers completed the study. Only 90 of the 136 completed their treatments -- 39 used CPAP for an average of at least four hours per night, 27 in the weight loss group managed to lose at least 5% of their body weight and 24 in the combination group managed to lose weight and use CPAP successfully.
"As reported in previous studies, weight loss significantly reduced CRP levels, insulin resistance, dyslipidemia, and blood pressure. In contrast, CPAP therapy did not have a significant effect on CRP level, insulin sensitivity, or dyslipidemia, even among participants who adhered to the therapy," the researchers concluded. "Our findings suggest that both obstructive sleep apnea and obesity have an independent causal relation to hypertension."
The Journal also published the results of a study known as HeartBEAT, which found that CPAP therapy reduced blood pressure, even in patients whose blood pressure was well controlled.
The average 24-hour mean arterial pressure after 12 weeks of therapy dropped by 2.4 mm Hg among the 90 CPAP recipients compared to the 97-member control group (p=0.04). Average adherence for CPAP was 3.5 hours per night.
"Even though this study didn't look at long-term outcomes like heart attack and stroke, a decline of this magnitude has been shown to produce about a 20% reduction in stroke mortality and about a 15% reduction in total cardiovascular mortality," the chief author, Dr. Daniel Gottlieb of the Veterans Affairs Boston Healthcare System told Reuters Health by phone.
The study also found that giving supplemental oxygen at night, a fallback treatment for apnea patients when they can't use a CPAP machine, produced no decline in blood pressure in 94 volunteers.
Oxygen therapy "does prevent the fall in blood oxygen levels that you seen in sleep apnea," Gottlieb said. "But in this study we didn't find any benefit in terms of blood pressure or other cardiovascular risk markers. So we have little evidence to suggest that it's effective in sleep apnea," at least for the typical patient.
About 4% of adult women and 9% of adult men have moderate to severe sleep apnea, and most of that is undiagnosed, Gottlieb said.
The HeartBEAT findings were originally presented in June 2013 at the SLEEP 2013 meeting in Baltimore, Maryland.
SOURCES: http://bit.ly/1mBZ4Kp and http://bit.ly/1pZPWWd
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