Reference values and determinants of diaphragmatic ultrasound parameters in an adult population

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This study aimed to establish normative reference values for diaphragmatic thickness (DT) and elasticity (E) in healthy adults and to examine the effects of sex, age, and body mass index. This observational cross-sectional study enrolled 363 healthy volunteers. Ultrasonographic measurements of DT at end-inspiration and end-expiration, thickening fraction, and E were obtained at the eighth and ninth intercostal spaces. Data were analyzed using paired t tests, t tests, analysis of variance, and Pearson’s or Spearman’s correlations, as appropriate. Normal reference ranges (5%–95% percentiles) were established. Significant univariate predictors were further assessed by multiple linear regression. Normative reference ranges for DT and E were established. Gender, age, and body mass index (≥24 kg/m 2 ) were identified as independent determinants of DT (β = −0.245, P < .001; β = 0.153, P < .001). Age-related changes followed a nonlinear pattern, with thickness peaking in middle age and declining in older adults. This study provides foundational reference values for diaphragmatic ultrasound assessment encompassing both thickness and E, introduces a dual assessment methodology (fixed-site longitudinal tracking and functional cross-group comparison), establishes demographic determinants of thickness, and applies shear wave elastography for stiffness evaluation.