Abstract
Introduction/aims: Respiratory muscle dysfunction is prevalent in congenital myopathies and often leads to respiratory failure. Ultrasound shear wave elastography (SWE) measures tissue elasticity and has been proposed as an alternative to invasive measures of respiratory muscle contractility. This study aims to evaluate SWE to assess respiratory muscle function in healthy individuals and congenital myopathy patients, while also determining SWE reliability.

Methods: Shear wave velocity in the diaphragm, parasternal intercostal, sternocleidomastoid, external oblique, internal oblique, and transverse abdominal muscles was acquired in healthy participants and congenital myopathy patients during different maneuvers. Mouth pressure (Pmo) was acquired simultaneously with SWE acquisition. Furthermore, transdiaphragmatic pressure (Pdi) was acquired in healthy participants. All measurements were repeated by two observers to assess reliability.

Results: Twenty-one congenital myopathy patients and 20 healthy participants were included. Shear wave velocity did not differ between healthy participants and patients during any maneuver in any muscle, and Pmo and Pdi were not correlated with shear wave velocity. Intraobserver intraclass correlation coefficients (ICC) varied between 0.28-0.95 for healthy participants and 0.62-0.95 for patients. Interobserver ICC varied between 0.00 and 0.87 for healthy participants and 0.00-0.79 for patients. Test-retest ICC varied between 0.00-0.66 for healthy participants and 0.00-0.72 for patients.

Discussion: The absence of differences in shear wave velocity between healthy participants and patients, and the low reliability estimates, indicate that SWE of the respiratory muscles is not suitable in routine clinical care or research. The complex mechanical properties of the respiratory muscles introduce challenges that may require alternative SWE techniques.
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