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 (ThFRC) and total lung capacity (ThTLC), diaphragm thickening ratio (DTR), excursion (EFRC and ETLC), and dynamic indices during maximum voluntary (EVS, VVS, and ECHO-MRR). Statistical methods included spearman correlation, univariable and multivariable regression, stepwise regression, and paired comparisons. Multivariable analysis revealed that RVVS and LThTLC were associated with MIP, MEP, and HGS, right-sided parameters (RDTR, REVS, RECHO-MRR) with MIP and MEP, while RThTLC with MIP and HGS. Stepwise regression pinpointed the most predictive parameters: RVVS and LThTLC together for MIP, while RDTR alone for MEP and RThTLC 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 RThTLC, RVVS+LThTLC, and RDTR to overall, inspiratory, and expiratory strength, respectively. These findings offer a practical and objective approach for early respiratory sarcopenia screening.