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Fluid Displacement From Leg to Neck Can Cause Apnea

Narrowing of throat's soft tissue boosts risk of sleep obstruction, study says

TUESDAY, Dec. 19, 2006 (HealthDay News) -- Fluid displacement from the legs to the neck that occurs when a person lies down can narrow soft tissue around the throat, increasing airflow resistance by more than 100 percent and boosting the risk of obstructive sleep apnea, a new study says.

Obstructive sleep apnea, which affects about 18 million Americans, occurs when a blockage in the throat or upper airway causes a sleeping person to repeatedly stop breathing long enough to decrease the amount of oxygen in the blood and increase the amount of carbon dioxide.

"Our data show that the displacement of a small amount of fluid such as 340 ml, about 12 ounces, from the legs is sufficient to cause a 102 percent increase in airflow resistance of the pharynx in healthy, non-obese subjects," study author Dr. T. Douglas Bradley, of Toronto General Hospital in Canada, said in a prepared statement.

The researchers studied leg fluid volume, neck circumference and airflow resistance in the throats of seven men and four women, average age 36, while they lay on their backs.

A lower body positive pressure device (anti-shock suit) was then used for five minutes on each participant to displace fluid from their legs to their necks.

"Obesity and neck circumference are important risk factors in obstructive sleep apnea, but together only account for approximately one-third of the variability in the apnea-hyponea index," Bradley said.

"A factor not ordinarily considered is fluid accumulation at the nape of the neck and around pharyngeal soft tissue. Obstructive sleep apnea is very common in fluid-retaining states such as heart failure, renal failure and peripheral edema of unknown cause," he noted.

The study was published in the December issue of the American Journal of Respirator and Critical Care Medicine.

More information

The U.S. National Heart, Lung, and Blood Institute has more about sleep apnea.

SOURCE: American Thoracic Society, news release, Dec. 15, 2006
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