Intra- and inter-tester reliability of diaphragm thickness and excursion measurements of healthy women using rehabilitative ultrasound imaging across novice examiners

Beyond respiration, the diaphragm contributes to trunk stability and posture. Rehabilitative Ultrasound Imaging (RUSI) assesses Diaphragm Thickness (DT) and Excursion (DE), but evidence on reliability across novice examiners is limited. This study investigated intra- and inter-tester reliability of diaphragmatic RUSI across novice examiners in healthy women and compared DT and DE between parous and nulliparous participants. Healthy parous and nulliparous women participated. Exclusion criteria included pregnancy, chronic conditions, and BMI > 30 kg/m2. Two physiotherapists, novices in RUSI, measured DT during full inspiration and expiration and DE during quiet breathing. An independent examiner calculated the Thickening Fraction (TF). Three within-session measurements were taken for intra-tester reliability, whereas, for inter-tester reliability, agreement between mean measurements was analyzed via Intraclass Correlation Coefficients (ICC) and 95% Confidence Intervals (CIs). Independent samples t-tests assessed DT and DE differences between groups. Twenty women (33±14.3 years, BMI: 23.4±3.3) participated. Intra-tester reliability was moderate to good for DT (ICC:0.511-0.691) and very good for DE (ICC:0.700-0.756). Inter-tester reliability was very good for DE (ICC=0.748), and moderate for DT (ICC: 0.573-0.706). TF reliability was poor. Only one tester found higher inspiratory DT in parous women (p<0.01). Novice examiners can reliably measure DT and DE using RUSI, supporting its use in rehabilitation. Further standardization is required to enhance RUSI practices and additional research to clarify parity-related diaphragm changes.