Identifying key diaphragm ultrasound predictors for early screening of respiratory sarcopenia

Early screening for respiratory sarcopenia lacks sensitive tools. We evaluated whether diaphragm ultrasound parameters can independently predict respiratory and overall muscle strength in healthy adults. In this cross-sectional study, 149 healthy adults underwent handgrip strength (HGS), maximal inspiratory/expiratory pressures (MIP/MEP), and right ("R-") and left ("L-") diaphragm ultrasound. Diaphragm ultrasound included thickness at functional residual capacity (Th_FRC) and total lung capacity (Th_TLC), diaphragm thickening ratio (DTR), excursion (E_FRC and E_TLC), and dynamic indices during maximum voluntary (E_VS, V_VS, and ECHO-MRR). Statistical methods included spearman correlation, univariable and multivariable regression, stepwise regression, and paired comparisons. Multivariable analysis revealed that RV_VS and LTh_TLC were associated with MIP, MEP, and HGS, right-sided parameters (RDTR, RE_VS, RECHO-MRR) with MIP and MEP, while RTh_TLC with MIP and HGS. Stepwise regression pinpointed the most predictive parameters: RV_VS and LTh_TLC together for MIP, while RDTR alone for MEP and RTh_TLC alone for HGS. Bivaria regression and paired comparisons confirmed significant bilateral heterogeneity in both diaphragm parameters and their associations with muscle strength (all p < 0.05). This study establishes a precise predictive model in which RTh_TLC, RV_VS+LTh_TLC, and RDTR to overall, inspiratory, and expiratory strength, respectively. These findings offer a practical and objective approach for early respiratory sarcopenia screening.