Use of ultrasonography in the evaluation of patients with sleep apnea: a systematic review

•Ultrasonography may be a promising new method of assessing obstructive sleep apnea.•Lateral pharyngeal wall is a thicker structure in apneic patients.•Elastography allows measuring the tissue stiffness of the airways in apneics.•Ultrasonography demonstrated measures associated with the severity of sleep apnea. This study aims to review the current role of various ultrasonographic methods in the evaluation of the upper airway in patients with obstructive sleep apnea. A literature review was performed on the medical databases: Pubmed, Web of Science, Scopus and Embase. After analyzing the available studies, six of them were selected for data extraction. All selected studies demonstrated that it is possible to use ultrasonography as a method of evaluating the upper airway. Studies with gray-scale ultrasound concluded that the lateral pharyngeal wall and tongue are thicker in patients with obstructive sleep apnea compared to non-apneic patients. Moreover, studies with tissue characterization ultrasound, nowadays called quantitative ultrasound, have identified unique features in obstructive sleep apnea patients: standardized backscatter ultrasonography demonstrated that this particular sound wave analysis is associated with the severity of obstructive sleep apnea. Ultrasonography with elastography shows that the electrical stimulus generated in the hypoglossal nerve results in greater stiffness on the side of the tongue that is stimulated; whereas studies show conflicting results regarding the evaluation of baseline tongue stiffness in obstructive sleep apnea patients compared to non-apneic subjects. There is feasibility of different methods of ultrasonographic evaluation of the upper airway, with emphasis on ultrasonographic methods of tissue characterization, such as elastography, which proved to be a promising method of evaluating the mechanical properties of the muscles involved in the pathogenesis of obstructive sleep apnea and which require further studies for a better elucidation of its applicability.