There has been an ongoing debate about why wearing compression (really, really tight) socks improves sleep apnea. The theory for why it may be effective is that there are fluid shifts within the body throughout the night, due to a laying down position. Fluid accumulates in the legs during the day, causing a very large shift away from the legs during the night. In theory, fluid shifts from the legs to around the neck, creating a situation where the airway becomes more crowded from the fluid. This crowdedness makes the airway more susceptible to collapse during the night, which causes apneas and hypopneas. By wearing compression socks during the day, fluid regulation in the legs is improved and there is less of a build-up. This lessens the amount of fluid that shifts, which may improve sleep apnea. This is a solid theory, but is it true?
In order to investigate the possible fluid-apnea connection, a research team set up a study to induce a greater amount of fluid around the neck during the night. This fluid increase was created by injecting saline (which is a harmless liquid) into the neck of non-obese men who did not suffer from sleep apnea. These men first underwent an overnight sleep study without the excess fluid, and then a second sleep study with the additional neck fluid. The amount of apneas and hypopneas throughout the night (AHI) were compared before and after fluid administration.
Results showed that in the younger group of men (those below 40), there was not an increase in AHI when the fluid was added around the neck. However, in the older men group, the AHI increased by an average of 3-fold. In addition, age was the greatest predictor of an increase in AHI, as there was a direct relationship between the increase of AHI and age of the subjects1.
Interestingly, the reason why the older man had a greater increase in AHI than the younger men is already known. In this study, it was seen that the accumulation of fluid around the necks of the older men was larger than that of older men. Because the older men had a greater accumulation of fluid, it seems that they were more likely to develop apneas and hypopneas. Additionally, because the airway is more collapsible in older adults than in younger adults, the fluid likely had a greater affect on the older, weaker airways. This study suggests that those with disorders or circumstances that cause a large leg fluid build up (like deep vein thrombosis or pregnancy), and thus a large fluid shift, may need to take steps towards minimizing fluid build up around their legs through the use of socks (if they work!) or greater elevation under their head during the night.
1. Pre-publication: Journal Sleep: “A Randomized, Double Cross-over Study to Investigate the Influence of Saline Infusion on Sleep Apnea Severity in Men Subtitle: Inducing sleep apnea by fluid overload”