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

Abstract

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 degrees 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<0.001), and the oxygen desaturation index from 69.5 events per hour (56.4-82.6) to 61.6 (50.5-72.6) (t= 3.293,p= 0.004), from the control to the experimental night with a decrease in the change of leg fluid volume from 17.7% (15.7-19.8) to 4.7% (1.9-7.5) (t= 11.659,p< 0.001). Conclusions Our findings provide direct experimental evidence to show that natural fluid shift caused by the day-to-night posture change does contribute to OSA pathogenesis and severity. It is likely that the neck fluid increase from an actual day-to-night position change, with 90 degrees change in posture, would produce a much larger AHI increase than the 11.2% found in this study, which contains only a 30 degrees change in posture. These findings suggest that reducing the amount of fluid in the neck region may relieve airway obstructions for patients with moderate and severe OSA.