The reference method for the assessment of diaphragm function relies on the measurement of transdiaphragmatic pressure (Pdi). Local muscle stiffness measured using ultrafast shear wave elastography (SWE) provides reliable estimates of muscle force in locomotor muscles. This study aimed at investigating whether SWE could be used as a surrogate of Pdi to evaluate diaphragm function. Fifteen healthy volunteers underwent a randomized stepwise inspiratory loading protocol of 0-60% of maximal isovolumetric inspiratory pressure during closed-airways maneuvers and 0-50% during ventilation against an external inspiratory threshold load. During all tasks, Pdi was measured and SWE was used to assess shear modulus of the right hemidiaphragm (SMdi) at the zone of apposition. Pearson correlation coefficients ( r) and repeated-measures correlation coefficients ( R) were computed to determine within-individual and overall relationships between Pdi and SMdi, respectively. During closed-airways maneuvers, mean Pdi correlated to mean SMdi in all participants [ r ranged from 0.77 to 0.96, all P < 0.01; R = 0.82, 95% confidence intervals (0.76, 0.86), P < 0.01]. During ventilation against inspiratory threshold loading, Pdi swing correlated to maximal SMdi in all participants [ r ranged from 0.40 to 0.90, all P < 0.01; R = 0.70, 95% confidence intervals (0.66, 0.73), P < 0.001]. Changes in diaphragm stiffness as assessed by SWE reflect changes in transdiaphragmatic pressure. SWE provides a new opportunity for direct and noninvasive assessment of diaphragm function. NEW & NOTEWORTHY Accurate and specific estimation of diaphragm effort is critical for evaluating and monitoring diaphragm dysfunction. The measurement of transdiaphragmatic pressure requires the use of invasive gastric and esophageal probes. In the present work, we demonstrate that changes in diaphragm stiffness assessed with ultrasound shear wave elastography reflect changes in transdiaphragmatic pressure, therefore offering a new noninvasive method for gauging diaphragm effort.
Keywords: diaphragm; shear wave elastography; skeletal muscle; transdiaphragmatic pressure; ultrasound imaging.