Predominantly Structural Cardiac Differences in Untreated Normal-Weight Obstructive Sleep Apnea: A Comprehensive Echocardiographic Study

Background and Objectives: Obstructive sleep apnea (OSA) is associated with cardiac remodeling, although the frequent coexistence of obesity complicates interpretation of cardiovascular abnormalities. We investigated the distribution of structural and functional echocardiographic differences across cardiac domains in untreated normal-weight adults with OSA. Material and Methods: In this prospective, single-center, cross-sectional study, 29 untreated patients with OSA and 15 controls without OSA, all with body mass index < 25 kg/m2, underwent respiratory polygraphy and comprehensive transthoracic echocardiography. Left ventricular (LV) mass index (LVMI) was the primary outcome. Results: Most patients with OSA had mild disease (21/29, 72%). Patients with OSA had higher LVMI than controls (79.3 ± 17.1 vs. 64.5 ± 9.1 g/m2; p < 0.001), together with greater interventricular septal and posterior wall thickness and higher LV end-diastolic volume index. In contrast, no consistent between-group differences were observed across conventional indices of LV systolic and diastolic function, atrial structure, or right ventricular function. Standardized effect sizes were largest for LV structural measurements, whereas estimates across functional, atrial, and right ventricular domains were generally smaller and less precise. After adjustment for age, sex, body mass index, and arterial hypertension, the association between OSA and higher LVMI persisted in the primary model (B = 10.56 g/m2; p = 0.047; bias-corrected and accelerated (BCa) bootstrap 95% CI, 1.71–21.16), although sensitivity analysis indicated limited robustness. Conclusions: In untreated normal-weight adults with predominantly mild OSA, comprehensive echocardiographic assessment revealed findings suggestive of a predominantly structural pattern of cardiac differences, centered on the LV, without a consistent parallel signal across conventional functional, atrial, or right ventricular indices. These findings provide a multidomain characterization of cardiac involvement in OSA in the absence of excess body weight and warrant confirmation in larger longitudinal studies.