Gender affects respiration during sleep

According to anecdotal evidence, most snoring complaints come from women about men. Scientific studies support that evidence, confirming that men are at least two times more likely than women to have sleep apnea, or cessation of breathing during sleep. M. Safwan Badr, MD, wants to know why.

Dr. Badr, associate professor of internal medicine, says the higher prevalence of sleep apnea in men suggests a gender difference, but contrary to popular belief, the difference is not in the upper airway, but in the central control mechanisms of respiration.

In an upcoming issue of the Journal of Applied Physiology, Dr. Badr will publish his findings showing that females are less susceptible than men to the development of hypocapnic central apnea during non-REM sleep. This research is funded in part by the National Institutes of Health and the American Lung Association.

When Dr. Badr and his colleagues were investigating the effect of induced central apnea on upper airway patency, they noticed that it required greater reduction in carbon dioxide to cause abnormal respiration in women. After further studies, they found that the gender difference cannot be explained by differences in upper airway mechanics or baseline carbon dioxide levels, but instead, by central response systems.

“A woman’s ventilation control system is more resistant to perturbation,” said Dr. Badr. “We are trying to determine why that is true. We believe it may have something to do with hormone levels, because our preliminary data suggests that postmenopausal women behave like men in these apnea studies. Clearly, though, the central controls are at work.”

In related research, Dr. Badr and his colleague Dr. James Rowley, are among only a few researchers using tiny fiber optic scopes to study the mechanics of the upper airway during sleep. The fiber optic catheters take pictures of the airway five times per second, making it possible to detect very subtle respiratory events.

“Using this technology, we have discovered that the upper airway is stiffer during REM sleep. This is a new idea, because it was previously thought to be floppy. This is an important distinction in studying breathing perturbations and stabilization.”

Although sleep apnea may seem like nothing more than a nuisance, Dr. Badr says it is a disease that contributes to increased mortality. It is a comorbid factor in many urban populations, just like obesity, hypertension and heart disease. “It’s not simply a co-existing condition,” said Dr. Badr. “Sleep apnea actually has a role in causing other complications.”