Relationships between diaphragm ultrasound, spirometry, and respiratory mouth pressures in children

Diaphragm ultrasound (DUS) is a noninvasive method of evaluating the diaphragm's structure and function. This study explored the relationships between DUS, spirometry, and respiratory mouth pressures in 10 healthy children (median age: 11 [range: 7-14 years]; 5 females, 5 males). Thickening fraction correlated with maximal inspiratory pressure (MIP) (Spearman's rho [r_s] = 0.64, p = 0.05). During quiet breaths, excursion time correlated with MIP (r_s = 0.78, p = 0.01) while velocity correlated with maximal expiratory pressure (r_s = -0.82, p = 0.01). During deep breaths, MIP correlated with excursion (r_s = 0.64, p = 0.05) and time (r_s = 0.87, p = 0.01). Excursion time during deep breaths also correlated with forced vital capacity (r_s = 0.65, p = 0.04). Our findings suggest that DUS parameters are closely related to spirometry and respiratory mouth pressures in healthy children and further support the use of DUS as a noninvasive method of respiratory assessment.