Relationship of Fluid Accumulation in the Neck to Sleep Structure in Men during Daytime Sleep

Induction of fluid overload during sleep in older men causes fluid accumulation in the neck, worsens obstructive sleep apnea (OSA), and reduces sleep efficiency and slow wave sleep. However, it is not clear whether disrupted sleep structure was related to age, fluid accumulation, or to OSA severity as assessed by the apnea-hypopnea index (AHI). We hypothesize that fluid accumulation in the neck is a significant contributor to the sleep structure.

Twenty non-obese men, 46 ± 11 years, underwent a daytime sleep study following a night of sleep deprivation. Before and after sleep, neck circumference (NC), upper airway cross-sectional area, and neck fluid volume (NFV) were assessed. Stepwise regression analyses were used to determine factors that contributed to sleep structure, AHI, and arousal frequency. Independent factors were age, NC, ΔNC, ΔNFV, and AHI (excluded for AHI and arousal).

Subjects slept for 145 ± 44 minutes with a mean AHI of 26 ± 25. After sleep, NC and NFV increased and the upper airway narrowed (all: p < 0.001). ΔNC and ΔNFV correlated directly with %N2 and inversely with %N3 sleep. Regression analyses revealed that only ΔNC correlated directly with %N2 sleep (r² = 0.44, p = 0.001). ΔNC, ΔNFV, and pre-sleep NC correlated inversely with %N3 sleep (r² = 0.76, p < 0.001). Pre-sleep NC and ΔNC correlated directly with AHI and arousal frequency.

Fluid accumulation in the neck and larger neck circumference are related to impaired sleep structure with reduced %N3 sleep. Fluid accumulation in the neck had stronger contribution to sleep structure than AHI or age.