Development and Preliminary Validation of the Breath Motor Pattern Index (BMPI): An Observational Measure of Respiratory Pattern Quality in Children

Background/Objectives: Breathing is increasingly recognized as an integral component of the motor system, interacting with postural control and movement. Despite this, clinical assessment of respiratory function in children remains largely limited to physiological parameters, with relatively few tools available to evaluate breathing as an organized motor pattern. The aim of this study was to develop and preliminarily validate the Breath Motor Pattern Index (BMPI), an observational tool designed to assess the organization of respiratory motor patterns in children. Methods: A scoping review was conducted to identify key components of respiratory motor pattern organization. Based on these findings, the BMPI was developed and evaluated in a cohort of 210 children aged 0–72 months, divided into three groups: healthy controls, children with neurological conditions, and children with respiratory disorders. Inter-rater and test–retest reliability was assessed using intraclass correlation coefficients (ICC). Measurement error was quantified using the standard error of measurement (SEM) and minimal detectable change (MDC95). Construct-related validity was examined through correlations with the Gross Motor Function Measure (GMFM-88) and comparisons between clinical groups. Results: The BMPI showed high inter-rater reliability (ICC = 0.998) and test–retest reliability (ICC = 0.999), with low measurement error (SEM = 0.55; MDC95 = 1.53). A weak but statistically significant correlation with GMFM-88 was observed (rho = 0.23, p < 0.001). BMPI scores differed significantly between groups (p < 0.001), with lower values observed in the neurological group and higher values in the pulmonary group. Conclusions: The BMPI appears to be a promising observational tool with potential clinical applicability for assessing respiratory motor pattern organization in children. The findings support the conceptualization of breathing as an integrated component of the motor system while highlighting the need for further psychometric and longitudinal validation studies. Future research should further investigate the responsiveness of the BMPI as well as its potential utility in clinical decision-making and therapeutic monitoring.