A pilot study in men to show the effects of postural fluid shifts on the severity of obstructive sleep apnea

Purpose Studies reveal that rostral fluid shifts due to body posture changes from standing to lying down may narrow the upper airway. However, without credible and direct experimental evidence, it remains unclear what the role of natural fluid redistribution in the neck is in affecting obstructive sleep apnea (OSA) severity. Our aim is using direct experimental evidence to determine whether or not postural fluid shifts affect OSA severity. Methods We performed overnight polysomnography on two consecutive nights for 22 men. The bed was set horizontally on the control night, while its tail part was lowered by 30° on the experimental night to reduce the amount of fluid shifted into the neck. We measured sleep and anthropometric parameters on each night. Results The mean (95% CI) apnea-hypopnea index (AHI) in the supine head and trunk position decreased from 66.6 events per hour (57.6–75.6) to 61.2 (52.0–70.4) ( t = 4.507, p