Standardised Ultrasound Assessment of Tongue Characteristics in Adolescents With Obesity and Obstructive Sleep Disordered Breathing: a Research Protocol

Scientific Background and Rationale Amongst obstructive sleep disorders, Obstructive sleep apnea (OSA) is characterized by repetitive complete (apnea) or partial (hypopnea) collapse of the upper airway during sleep. Upper airway collapsibility in OSA results from the interaction of multiple contributing mechanisms, including craniofacial morphology (retrognathia, maxillary constriction, reduced posterior airway space), adenotonsillar hypertrophy - a predominant anatomical risk factor in the pediatric population -, obesity-related peripharyngeal fat deposition, neuromuscular control deficits of upper airway dilator muscles, and environmental exposures such as prenatal or passive tobacco smoke exposure, associated with increased upper airway inflammation and altered respiratory control.

Among the anatomical structures implicated in upper airway collapsibility, the tongue plays a central role as the largest muscular structure of the oropharynx. Morphological and biomechanical alterations (incl. increased volume, fat infiltration at the base, posterior positioning, and modified tissue stiffness) have been identified as relevant contributors to airway obstruction and are increasingly investigated as potential screening markers.

In the pediatric population, OSA remains substantially underdiagnosed. Access to polysomnography is limited, parents seldom spontaneously report nocturnal symptoms, and prevalence estimates vary widely in the literature (1.2% to over 60% in children with obesity), partly due to heterogeneous diagnostic criteria. This epidemiological uncertainty underscores the need for accessible, non-invasive tools capable of characterizing tongue biomechanical properties in younger populations - a gap that the present study directly addresses.

Ultrasound is non-invasive, non-ionizing, widely accessible, and well tolerated, including in adolescents. Existing studies applying these modalities to the tongue in OSA have been conducted exclusively in adult populations and report heterogeneous, sometimes contradictory findings. Methodological variability in acquisition parameters, probe positioning, and region-of-interest definition substantially limits reproducibility and inter-study comparability. No study to date has applied this multimodal quantitative ultrasound approach to adolescents with obesity and obstructive sleep-disordered breathing, nor examined the longitudinal trajectory of these parameters in response to a structured weight-loss intervention. The present study is therefore the first to address this population and this clinical question.

Tongue morphology and tongue fat in patients suffering from OSA have been assessed several times with ultrasound, a non-invasive, widely accessible imaging modality that provides real-time visualization of tissues and is generally well tolerated, with minimal to no associated discomfort. Ultrasound echo intensity has been validated with MRI to estimate tongue fat percentage. Advanced ultrasound modalities, such as shear wave elastography (SWE) and attenuation imaging (AI), provide quantitative measures of tissue stiffness and its attenuation properties, respectively Existing studies on tongue SWE and echo intensity (EI) have been conducted exclusively in adults and report heterogeneous, and sometimes contradictory, findings in patients suffering from OSA. Raw data in EI values would increase in the case of high lipidic impregnation or fibrous accumulation and decrease when the amount of muscle is higher, but the results are still variable depending on the location. Methodological variability in acquisition parameters, probe positioning, region-of-interest definition, and data analysis substantially limit reproducibility and comparability. Arbitrary region-of-interest sizing that does not account for individual tongue morphology may further introduce systematic bias.