Function and bulk of respiratory and limb muscles after lung transplantation for cystic fibrosis

Abstract

We recently reported that, for a given lean body mass, the bulk of the diaphragm and abdominal muscles is greater in patients with cystic fibrosis (CF) than in normal controls, whereas the bulk of the quadriceps is similar, which is consistent with a specific training of the respiratory muscles (Pinet et al, AJRCCM 2003, June 26). Lung transplantation produces dramatic changes in the clinical status of patients with CF, but whether or not respiratory and limb muscles recover a normal function and bulk after surgery is unknown. We therefore assessed diaphragm mass, abdominal muscle thickness, diaphragm and abdominal muscle strength, quadriceps cross-section and isokinetic strength, and lean body mass in 12 stable CF patients who had undergone lung transplantation 48 months earlier; 12 normal subjects matched for sex, age, and height were studied for comparison. Patients had normal pulmonary function. Five patients were taken ciclosporine and 7 patients were taken tacrolimus; the average daily dose of prednisolone since transplantation was11.8 ± 6.3 mg. Diaphragm strength and mass and abdominal muscle strength were similar in the two groups, but quadriceps strength and cross-section were decreased by ≈30% in the patients. Patients had greater diaphragm mass, similar abdominal muscle thickness, and smaller quadriceps cross-section than controls when compared at a given lean body mass. In a multivariate analysis, the cumulative dose of prednisolone received between surgery and study was a significant predictor of quadriceps weakness and wasting. Quadriceps strength and cross-section in the patients showed tight positive correlations with maximal oxygen uptake, which averaged 59 ± 13 % of predicted. We conclude that in patients transplanted for CF, diaphragm and abdominal muscle function and bulk are preserved, but quadriceps strength and cross-section are markedly reduced. This impairment closely correlates with the reduction in exercise capacity.