Modeling sleep apnea severity using bioimpedance measurements.

Obstructive sleep apnea (OSA) is a common disorder in adults characterized by repetitive collapse of the pharynx. OSA prevalence increases in fluid retaining patients such as those with heart or renal failure, and worsens with overnight fluid accumulation in the neck. The objective of this study was to develop a new method of measuring changes in intracellular water (ICW) in the neck, and investigate metrics that represent total neck impedance and their relationship to sleep apnea severity. In 18 non-obese men, neck fluid volume (NFV) was measured before and after sleep using bioelectrical impedance at 50 kHz. For each participant, resistance and reactance was extracted from the impedance measurements. A model was developed to estimate the cell membrane capacitance which could represent changes in intracellular fluid in the neck. OSA severity was assessed using polysomnography to estimate the apnea-hypopnea index (AHI) as well as the obstructive AHI (OAHI). Our results showed a strong correlation between the changes in NFV from before to after sleep with the changes in cell membrane capacitance from before to after sleep, indicating an increase in ICW in the neck during sleep. Using linear stepwise regression we were also able to develop models to accurately predict AHI and OAHI using baseline anthropometric and bioimpedance measurements. These promising results demonstrate that non-invasive measurements of bioimpedance can be used to develop a novel biomarker to model sleep apnea severity, and assess patients at high risk of OSA.