Fluid Displacement From Legs To Neck Can Lead To Obstructive Sleep Apnea:
When a person lies down, a small amount of fluid displaced from the legs to the base of the neck can narrow soft tissue around the throat and increase airflow resistance in the pharynx by more than 100 percent, predisposing the person to obstructive sleep apnea.
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In obstructive sleep apnea, a blockage in the throat or upper airway causes victims to repeatedly stop breathing long enough to decrease the amount of oxygen in the blood and increase the carbon dioxide.
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"Our data show that 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," continued Dr. Bradley
These were healthy, non-obese people without sleep apnea. Presumably, even more fluid would be shifted in obese people, and the effect would be an even greater restriction of the airways in people already predisposed to sleep apnea (snorers, for instance).
So, should you sleep with your head raised and your feet lowered? Do astronauts in zero-gravity suffer from sleep apnea?