Feasibility of neck electrical impedance tomography to monitor upper airway dynamics during sleep

There is a lack of non-invasive methods for monitoring the upper airway patency during sleep. Electrical impedance tomography (EIT) is a non-invasive, radiation-free tool that has been validated to monitor lung ventilation. We hypothesized that electrical impedance tomography (EIT) can be used for monitoring upper airway patency during sleep.

Sleep was induced in 21 subjects (14 males, age 43 ± 13 years, body mass index 32.0 ± 5.3 kg/m²) with suspected obstructive sleep apnea (apnea-hypopnea index: 44 ± 37 events/h, range: 1-122 events/h) using low doses of midazolam. Patients wore a nasal mask attached to a modified CPAP device, allowing variable and controlled degrees of upper airway obstruction. Confirmation of upper airway patency was obtained with direct visualization of the upper airway using nasofibroscopy (n = 6). The changes in total neck impedance and in impedance in four cranio-caudal regions of interest (ROIs) were analyzed.

Total neck impedance varied in concert with breathing cycles and peaked during expiration in all patients. Group data showed a high cross-correlation between flow and impedance curves (r = -0.817, p < 0.001). Inspiratory peak flow correlated with simultaneous neck impedance (r = 0.866, p < 0.001). There was a high correlation between total neck impedance and velopharynx area (r = 0.884, p < 0.001), and total neck impedance and oropharynx area (r = 0.891, p < 0.001).

Neck EIT is sensitive and captures pharyngeal obstruction under various conditions. Neck EIT is a promising method for real-time monitoring of the pharynx during sleep.