Abstract Rationale Diaphragmatic Kinesiological Ultrasound (USD) has become an increasingly valuable tool for evaluating respiratory function, particularly in infants, as it is safe, non-invasive, and suitable for bedside use. Despite its growing application, most studies assessing diaphragmatic function and reliability using ultrasound have focused on adult populations, leaving a gap in pediatric research. Furthermore, ultrasound measurement interpretation may be influenced by evaluator experience and technical factors, emphasizing the importance of establishing the reliability of USD in infants. This study aimed to address this gap by determining intra- and inter-rater reliability for key diaphragmatic parameters in healthy infants and to propose a standardized assessment protocol. Methods A cross-sectional observational study was conducted involving 80 healthy infants aged 29 days to 24 months. Two trained examiners independently performed USD evaluations of the diaphragm. Variables analyzed included inspiratory (TDI) and expiratory (TDE) thickness, thickening fraction (TFD), inspiratory (EDi) and expiratory (EDe) excursion, and contraction (VCD) and relaxation (VRD) velocities. Statistical analysis included Intraclass Correlation Coefficients (ICC) to assess relative reliability, Minimal Detectable Difference (MDD) to estimate measurement error, and Bland-Altman plots for agreement analysis. Results Overall, the results demonstrated excellent (ICC 0.90) or good (ICC 0.50-0.75) relative reliability for most parameters. The smallest inter-rater variability was observed for TDI, TDE, and EDi, while greater variability was found for TFD, VCD, and VRD. Regarding absolute reliability, the narrowest limits of agreement were identified for TDE (1.41 mm) and TDI (1.54 mm), whereas the widest limits were seen for TFD (64.31%) and VCD (16.94 mm). The VRD variable exhibited an agreement range (12.95 mm) nearly identical to its MDD (12.94 mm), indicating a predictable measurement error. For all parameters, the limits of agreement exceeded the MDD, suggesting that inter-rater variability was greater than the minimal detectable error. Conclusions This study supports the use of diaphragmatic kinesiological ultrasound as a reliable and reproducible tool for assessing diaphragmatic function in healthy infants, particularly for inspiratory thickness and excursion measurements. Although some dynamic parameters demonstrated higher variability, the findings confirm USD as a promising, standardized, and clinically feasible method for pediatric respiratory evaluation and research, providing a foundation for future studies in infants with respiratory or neuromuscular disorders. This abstract is funded by: None
Figueirêdo et al. (Fri,) studied this question.