Sleep apnea: what causes it? ­ Weak diaphragm muscles may be factor

Sleep apnea occurs most often among people aged 30 to 40 who are overweight. It can cause excessive sleepiness during the day, which can disrupt work and social life.

Using rats as an animal model, Gaspar Farkas, UB associate professor of physical therapy and exercise science, and colleagues showed that weakened diaphragm muscles, the muscles most responsible for breathing, may be one of the factors contributing to the condition.

The researchers measured diaphragm function in lean and obese rats over a normal 18-month lifetime, testing them when they were young (6-8 weeks), mature (10-12 months) and old (17-18 months). They found that diaphragm muscles in the obese animals lost their ability to respond forcefully as the animals aged. Diaphragm response in the obese young animals was not compromised.

"The diaphragm is the only respiratory muscle that is active during REM sleep, and in obese people it is already overloaded," Farkas said. "We have shown that these muscles become weakened with age, at a time when load and stress on these muscles are already great, so it's a double deficit.

"This finding helps to explain why an obese person may not have problems with sleep apnea at 20, but may have problems at 50," he added.

Researchers from the University of Florida at Gainesville and the University of South Dakota also participated in the study.