Acoustic guide pad: a simple innovation that dramatically reduces the risk of misdiagnosis in respiratory muscle ultrasound examinations.

BACKGROUND: Respiratory muscle ultrasound is increasingly applied in clinical practice, but its heterogeneity and operator dependency limit quantitative assessments. This study first introduces the use of acoustic guide pads to improve reproducibility, and further evaluates their clinical applicability in the stratification of COPD.

METHODS: This single-center, prospective study was conducted at the respiratory medicine and ultrasound departments of a tertiary hospital over a period of 18 months, from January 2024 to July 2025. This study comprised two parts. Firstly, a prospective reproducibility study enrolled 80 subjects (46 healthy individuals and 34 patients with stable chronic obstructive pulmonary disease), who underwent repeated respiratory muscle ultrasound examinations performed by two sonographers. Parameters including respiratory muscle thickness, thickening fraction, and shear wave elasticity were measured using both direct transthoracic and acoustic-guided pad techniques. Intraclass correlation coefficients (ICC) and Bland-Altman analysis assessed reproducibility, with limits of agreement (LoA) compared using historical data. A separate prospective cross-sectional study enrolled 128 participants (50 healthy subjects, 35 patients with mild-to-moderate COPD, and 43 patients with severe COPD), utilizing acoustic-guided pads for examination. Clinical utility was assessed by analyzing intergroup differences in diaphragm and intercostal muscle parameters.

RESULTS: In the reproducibility study, the ICC values for respiratory muscle ultrasound parameters measured using acoustic guide pads were higher than those obtained with the direct measurement method, and statistically significant differences were observed for all parameters except ICMTF. Bland-Altman analysis showed narrower LoA compared with the direct method, all within clinically acceptable error margins, reducing the risk of diagnostic misclassification. In clinical applicability studies, the MDC95 (Minimal Detectable Change at the 95% confidence level) for respiratory muscle ultrasound parameters measured by the acoustic guide pad was smaller. The mean differences between COPD severity groups for most parameters exceeded the MDC95 values, indicating superior precision in assessing respiratory muscle ultrasound functional variations.

CONCLUSIONS: Acoustic guide pads improve the reproducibility of two-dimensional ultrasound and shear wave elastography in the assessment of respiratory muscles. Their simplicity and clinical convenience underscore their potential clinical utility, particularly in settings requiring standardized bedside assessment.