Introduction: Careful assessment and monitoring of respiratory function is crucial for timely identification and prevention of respiratory complications in patients with spinal muscular atrophy (SMA). Conventional methods (spirometry, sniff nasal inspiratory pressure – SNIP test) can detect inspiratory weakness but this discovery is often late. Therefore, it seems that diaphragm ultrasound (US) for assessment of the diaphrahm thickness and its function is appropriate additional method, as it is non-invasive and easy to perform for the patient and investigator. Purpose: The purpose od this study was to establish whether diaphragm US could be clinically useful method to detect diaphragm weakness in SMA patients. We also wanted to establish possible correlations between US values and standard respiratory tests, and possible differences with US values in healthy population. Methods: The study included 22 SMA patients and 21 healthy volunteers. All subjects participated in spirometry tests and sniff nasal inspiratory pressure test (SNIP). Diaphragm US was used to assess thickness and movement of the muscle. Results: Correlation was found between some of the US and spyrometry values (VC, PEF) and SNIP in all participants. SMA patients showed higher diaphragm thickness (DEBi) and speed at snip maneuver (Hsnip) than healthy volunteers. DEBi also correlates with all parameters of spirometry and SNIP in SMA patients. SMA individuals with normal respiratory function had better outcomes in DEBi and movement of diaphragm during deep breathing (AMPgv) compared to SMA individuals with decreased respiratory function. There was also moderate to high correlation between all spirometry parameters and SNIP and Hammersmith functional motor scale expanded (p<0,05). Discussion and conclusion: US assessment of the diaphragm seems to be appropriate method for respiratory insufficiency and disfunction. Diaphragm thickness during normal and deep breathing, movement during deep breathing and the difference between movement during quiet and deep breathing (DEBi, DEBv, AMPgv, ΔAMP) proved to be the most suitable parameters fort he assessment of respiratory status. It was found that SMA patients have preserved (and stronger) diaphragmal function than healthy participants. Within SMA group, diaphragm function is better and more intact in individuals with normal respiratory function. Due to small number of participants this research seems to have potential to be continued on bigger number of healthy and SMA subjects.
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