Individuals with moderate to severe obstructive sleep apnea may have limited oxygen capacity while participating in strenuous aerobic exercise, according to researchers at the University of California, San Diego School of Medicine.
Sleep apnea is a chronic condition in which a person’s breathing repeatedly stops and starts during sleep. These pauses can last from a few seconds to minutes, and over 30 times an hour in severe cases. The most common type is obstructive sleep apnea, which occurs when the throat muscles relax.
For people with this condition, sleep quality is poor, and they often suffer from chronic daytime sleepiness.
The research, published in the Journal of Clinical Sleep Medicine, shows that people with sleep apnea have a lower peak oxygen uptake during aerobic activity than those who do not suffer from the sleep disorder.
Although people who suffer from apnea are more likely to be obese, the researchers found that apnea patients had reduced aerobic fitness, even compared to those of similar body mass.
“Encouraging patients to exercise more is part of the story, but that is not the whole story,” said lead author Jeremy Beitler, M.D., assistant clinical professor in pulmonary and critical care medicine.
“We believe the sleep apnea itself causes structural changes in muscle that contributes to their difficulty exercising.”
Researchers conducted sleep studies on 15 men and women with moderate to severe apnea and 19 with mild or no apnea. They monitored participants in order to evaluate apnea severity and to screen for other types of sleep disorders that could sway the results.
The participants were then asked to pedal to exhaustion on a stationary bike at incrementally harder resistance levels, as if they were riding up a hill.
Using the exercise test results, and prior measurements of participants’ resting metabolic rates, the researchers figured out each person’s VO2 max, a measure of the maximum amount of oxygen a person can receive during strenuous exercise. They then compared this number to the expected VO2 max for a person of the same age, gender and body mass index.
After adjusting for baseline differences, scientists found that people with sleep apnea had an average 14 percent lower VO2 max than healthy subjects.
“This is a big discrepancy,” Beitler said.