The primary aim of this study is to evaluate the predictive value of the inspiratory regional diaphragmatic synchrony index (RDSI-insp) during PSV-SBT for first-attempt weaning failure. Secondary objectives include: (1) assessing the correlation between RDSI-insp and conventional respiratory mechanics and diaphragmatic ultrasound parameters such as RSBI, MIP/NIF, VC, CPF, P0.1, DE, and DTF; (2) comparing differences in RDSI and DPSI between successful and failed weaning groups during inspiration, end-inspiration, and expiration; (3) exploring the association of anterior diaphragmatic dyssynchrony index, posterior/crural dyssynchrony index, and regional time-to-peak dispersion with weaning outcomes; and (4) evaluating the feasibility, analyzable image rate, and repeatability of diaphragmatic speckle-tracking and RDSI calculation in patients undergoing PSV-SBT.