Quote:

Sleep apnea results from fluid displacement problem

Reported by Susan Aldridge, PhD, medical journalist

Fluid displacement from legs to neck contributes to sleep apnea, according to new experiments.
In obstructive sleep apnea, an obstruction in the upper airway causes temporary cessation of breathing during sleep. This lowers the levels of oxygen in the blood, which may have a long-term impact upon health. Researchers at Toronto General Hospital now report upon a mechanism that can cause this obstruction.

They measured leg fluid volume, neck circumference and airflow resistance in the throats of 11 healthy and non-obese subjects lying on their backs. Then they applied a lower body positive pressure device for five minutes to displace fluid from the legs to the neck.

The findings showed that displacement of around 12 ounces of fluid from the legs to the neck is enough to cause around 100 per cent increase in airflow resistance in the throat of a healthy person. This might be why sleep apnea is common among those with fluid-retaining states like heart failure and renal failure. This study sheds new light on sleep apnea. Till now, it had not been understood what factors, other than obesity, contributed to the condition.

Source
American Journal of Respiratory and Critical Care Medicine December 2006