"People who can't tolerate CPAP can get supplemental oxygen as a 'salvage' therapy," Gottlieb said. "That's easier to manage, because it's just a nasal cannula [flexible tube under the nose], and the air isn't pressurized."
But it's less effective for lowering blood pressure, Gottlieb's team found. Over 12 weeks, CPAP patients' blood pressure dipped by an average of 2 to 3 points compared with the other two groups.
That might not sound like a big difference. "But with high blood pressure, we say that every [point] matters," said Dr. Sripal Bangalore, a cardiologist at NYU Langone Medical Center in New York City.
"You can imagine that in patients with uncontrolled [high blood pressure], there'd be a more significant effect of CPAP," he said.
Bangalore agreed that CPAP devices can be tough to use. But he suggested that before giving up, people talk with their doctor about ways to make the therapy easier -- by switching the type of mask, for instance, or adjusting the pressure on the device.
In the second study, researchers focused on 181 obese adults with sleep apnea, randomly assigning them to six months of CPAP, weight-loss counseling or both.
In the end, all three groups saw their blood pressure decline, and the combination of weight loss and CPAP worked best.
But it was patients' weight loss -- which averaged about 15 pounds -- that made a difference in other ways. Patients in both weight-loss groups showed a decline in "bad" LDL cholesterol, triglycerides (another blood fat) and C-reactive protein -- a marker of inflammation in the blood vessels.
The results suggest that while CPAP can help cut blood pressure, it's not effective for those other heart risk factors, said lead researcher Dr. Julio Chirinos, of the University of Pennsylvania in Philadelphia.
So for obese patients with sleep apnea, weight loss should be a "central component" of therapy, Chirinos said in a university news release.
That advice would apply to a lot of people. It's estimated that half of Americans with sleep apnea are overweight or obese, according to the National Institutes of Health.