Effect of Systemic Inflammation on Inspiratory and Limb Muscle Strength and Bulk in Cystic Fibrosis

Rationale Diaphragm thickness is increased in cystic fibrosis (CF), but it shows a marked variability between patients. The variable response of the diaphragm to loading may reflect the combined and opposite effects of training by the respiratory disease and systemic inflammation. Objectives: To assess the impact of systemic inflammation on diaphragm and limb muscle strength and bulk in adult patients with CF. Methods: In 38 stable patients with CF and 20 matched control subjects, we measured fat-free mass (FFM), inspiratory muscle strength, diaphragm thickness, quadriceps and biceps strength and cross-sectional area, and circulating levels of leukocytes, C-reactive protein, IL-6, IL-8, IL-17, tumor necrosis factor-alpha, tumor necrosis factor-alpha soluble receptors, and immunoglobulin G. Measurements and Main Results: Patients had increases in several inflammatory markers that correlated with the severity of lung disease and nutritional depletion. Compared with control subjects, patients with CF had increased diaphragm thickness and inspiratory muscle strength and showed a trend toward a reduction in limb muscle strength and bulk. Multiple regression analyses identified FFM and airway resistance as independent predictors of diaphragm thickness, but systemic inflammation had no (or only a minor) predictive effect on FFM, inspiratory muscle strength, diaphragm thickness, and limb muscle strength and bulk. Conclusions: In patients with CF, the intensity of systemic inflammation does not account significantly for the variance of FFM and diaphragm or limb muscle strength and bulk. Training of the diaphragm in CF occurs despite the presence of systemic inflammation.