Ultrasonographic assessment of diaphragmatic functions in relation to obstructive sleep apnea severity

Obstructive sleep apnea (OSA) affects 9-38% of adults and is associated with intermittent hypoxia, sleep fragmentation, and increased cardiovascular risk. Although the diaphragm contributes 60-80% of ventilatory effort, diaphragmatic functional changes in OSA remain inadequately characterized. Diaphragmatic ultrasonography offers a noninvasive, bedside method for functional assessment, but evidence in OSA is limited.

To evaluate diaphragmatic function using ultrasonography in patients evaluated for suspected OSA and to determine its association with disease severity.

This prospective cross-sectional study included 62 patients evaluated for suspected OSA attending inpatient and outpatient services at a tertiary care center between January 2024 and April 2025. OSA severity was classified using polysomnography-derived Apnea-Hypopnea Index (AHI) as per American Academy of Sleep Medicine (AASM) guidelines. Blinded ultrasonographic assessment measured right and left hemidiaphragm thickness, thickening fraction, and diaphragmatic excursion. Statistical analysis included Spearman's correlation, Kruskal-Wallis test, ordinal logistic regression, and receiver operating characteristic (ROC) analysis.

The mean age was 51 years, with male predominance (72.6%). Most participants were overweight or obese. The median AHI was 25.6 events/hour, and severe OSA was present in 41.9% of participants, while mild OSA constituted 37.1%, reflecting referral-based nature of the cohort. None of the enrolled patients had AHI < 5. Left diaphragmatic excursion showed a weak positive correlation with AHI (ρ = 0.274; P = 0.031) and a multivariable-adjusted association with OSA severity (OR 1.125; 95% CI 1.026-1.249; P = 0.017). For identifying moderate-to-severe OSA, diaphragmatic ultrasonography demonstrated an AUC of 0.72 (95% CI 0.59-0.85; P = 0.002), with 66.1% accuracy, 59.0% sensitivity, and 78.3% specificity.

Diaphragmatic function assessed by ultrasonography is largely preserved in OSA, with left diaphragmatic excursion showing a multivariable-adjusted association with disease severity, these findings primarily reflect a mixed-severity population with a substantial proportion of mild OSA. Bedside diaphragmatic ultrasound may serve as an exploratory adjunct for OSA risk stratification, particularly in resource-limited settings, pending external validation.