Association between ultrasound-determined characteristics of the diaphragm and respiratory function in young adults

The purpose of this investigation was to perform a comprehensive assessment to identify relationships between ultrasound-determined characteristics of the diaphragm (thickness and excursion) and measures of respiratory muscle strength, physical characteristics, and pulmonary function assessments in healthy young males and females. Twenty-four individuals volunteered (13M, 11F; 23±3yr; 172±9cm; 74±15kg). While lying supine, ultrasound (Terason 3300) images of the right hemidiaphragm were obtained to determine diaphragm thickness (B-mode, mid-axillary line) and diaphragm excursion (M-mode, between mid-clavicular and axillary lines, below right costal margin) during tidal breathing and at end-tidal inhalation and end-maximal inhalation. Pulmonary function was assessed via spirometry and respiratory muscle strength was determined via maximal inspiratory (MIP) and expiratory pressures (MEP) (Cosmed Pony FX). Diaphragm thickness assessed at end exhalation, end-tidal inhalation and end-maximal inhalation were correlated with MIP (r=0.54, 0.45, and ρ =0.47, respectively, p<0.05). Diaphragm thickness at end exhalation was also correlated with estimated muscle mass (r=0.48, p=0.02) and forced vital capacity (r=0.45, p=0.03). Diaphragm excursion was not significantly correlated with any parameter. Males had greater diaphragm thickness at end exhalation compared to females (0.150±0.033 vs. 0.123±0.028 cm, p=0.05). These findings suggest that ultrasound-determined diaphragm thickness is related to respiratory muscle strength and whole-body muscle mass in healthy young adults. Future research is needed to investigate how conditions associated with whole body muscle mass change (e.g., aging, disease, resistance exercise) may contribute to changes in diaphragm thickness and inspiratory muscle strength/function, and to what degree sex may impact these results.