Oscillometric ındices in obstructive sleep apnoea are more closely related to obesity than to disease severity.

Impulse oscillometry (IOS) abnormalities have been described in obstructive sleep apnoea syndrome (OSAS), but it remains unclear whether they reflect OSAS itself or the accompanying obesity. Using a body mass index (BMI)-comparable design, we examined the relative associations of obesity and OSAS severity with peripheral oscillometric indices. In this cross-sectional study, 124 adults (86 with OSAS and 38 BMI-comparable non-OSAS participants) underwent overnight polysomnography and daytime IOS. The full panel of oscillometric parameters was examined in relation to BMI and to OSAS diagnosis and severity, using Spearman' correlation and multivariable regression adjusted for age, sex, BMI and smoking status. Analyses were also stratified by obesity status and repeated using the oxygen desaturation index (ODI). No oscillometric parameter differed between the OSAS and BMI-comparable non-OSAS groups. BMI was strongly associated with the resistive and impedance indices (R5, R5-R20, R20 and Z5; Spearman ρ 0.35-0.62, all p < 0.001), and multivariable models explained approximately one quarter of their variance, whereas OSAS diagnosis and AHI-defined severity were not consistently associated after adjustment for BMI. Although AX, X5 and Z5 showed univariate trends with severity, none remained significant after adjustment, and none discriminated severe OSAS individually or in combination (AUC range, 0.60-0.66; DeLong p ≥ 0.31). Findings were unchanged in both obesity strata and with ODI. Peripheral oscillometric indices in OSAS appear to be more closely related to obesity than to OSAS severity. These findings do not support the use of IOS as a standalone tool for screening or grading OSAS and suggest that IOS is better interpreted as an obesity-related rather than an OSAS-specific signal.