The study of the biomechanical aspects of the act of breathing in patients with myasthenia gravis and motor neuron disease using the ultrasound

Background. As motor neuron disease (MND) and myasthenia gravis (MG) progress, the respiratory muscles are involved in the pathological process with the development of respiratory failure, which is one of the main causes of death. Respiratory disorders due to weakness and pathological muscle fatigue are often diagnosed with a delay, which is associated with the moderation of changes in the early stages of the disease. The ultrasound examination is one of the additional methods for diagnosing dysfunction of the respiratory muscles, however, the lack of methodological recommendations leads to the heterogeneity of diagnostic data.Aim. To identify subclinical signs of impaired function of the respiratory muscles in the early stages of the development of MND and MG using ultrasound.Results. Ultrasonography was performed in 19 (44 %) patients with MND and 24 (56 %) with MG; the comparison group consisted of 35 healthy volunteers. Diagnostics was carried out with application of an Philips HD11 XE device (Philips, USA), using a linear transducer with a frequency of 5–12 MHz and a convex transducer of 2–5 MHz. Compared with the control, patients with MND showed a statistically significant decrease in the following parameters: diaphragm thickness, diaphragm movement amplitude, intercostal spaces, kidney right and left respiratory mobility during calm and deep breathing, and the diaphragm thickening coefficient on the left (U, р <0.05). Patients with MG showed a statistically significant decrease in the amplitude of diaphragm movement during deep breathing on the right, the size of the intercostal spaces during deep breathing on the left, and the coefficient of diaphragm thickening on the left (U, p <0.05).Conclusions. The obtained data reflect the presence of functional and structural changes in the respiratory muscles, caused by their weakness. Ultrasound signs of dysfunction of the respiratory muscles were established, indicating the presence of pathological fatigue and/or weakness of the respiratory muscles, which may indicate either developing or developed respiratory failure. Ultrasound is a non‑invasive, inexpensive and safe diagnostic method and can be a good and convenient way to detect dysfunction of the respiratory muscles, and in some cases can be an additional diagnostic method (for example, when correct spirometry is difficult to perform due to the presence of bulbar disorders in MND and MG).