Ultrasonographic assessment of the diaphragm in systemic lupus erythematosus: cut-off values and predictive indicators of diaphragm thickness

Respiratory complications significantly result in morbidity and mortality in patients with Systemic Lupus Erythematosus (SLE). However, the impact of SLE on respiratory muscle function, particularly diaphragm thickness and strength, has been the subject of limited investigation. The study aims to investigate the key physiological and respiratory parameters affecting diaphragm thickness in SLE patients and to assess its role as a predictive indicator of respiratory dysfunction. The cross-sectional study included 29 patients with SLE and 48 healthy individuals. Diaphragm muscle thickness in both the inspiration and expiration phases was evaluated by ultrasonography. Fatigue, self-reported physical activity, pulmonary function tests, and respiratory muscle strength were assessed in the study. Diaphragm thickness during inspiration and expiration phases, along with maximal inspiratory pressure (MIP) values, fatigue, and physical activity levels, were significantly lower in SLE patients compared to healthy controls (p < 0.05). Diaphragm thickness during the inspiratory phase showed a strong association with key pulmonary function parameters, particularly the FEV₁/FVC% and FEV₁%, while during expiration, it was mainly influenced by the FEV₁/FVC% and FVC%. Maximal expiratory pressure had a greater impact on diaphragm thickness compared to MIP. In SLE patients, the optimal cut-off values for diaphragm thickness were 1.50 mm during inspiration and 1.075 mm during expiration. These findings provide valuable information on diaphragm functionality and establish a strong foundation for clinical applications, emphasizing the potential of predictive models in diagnosing and managing respiratory dysfunction.