Maximal exercise capacity and peripheral skeletal muscle function following lung transplantation

Background: There have been many suggestions that diminished exercise capac ity in patients that have undergone lung transplantation is due, in part, t o peripheral muscle dysfunction, brought on by either detraining or immunos uppressive therapy. There is limited data quantifying skeletal muscle funct ion in this population, especially in those more than 18 months post-proced ure. The present study sought to quantitate skeletal muscle function and ca rdiopulmonary responses to graded exercise in 19 lung transplant recipients , 15 of which were mostly more than 18 months post-procedure. Methods: Ten single- (SLT) and 9 double-lung transplantation (DLT) underwen t anthropometric measures and performed expiratory spirometry, whole body p lethysmography to assess lung volumes, static maximal mouth pressures to as sess respiratory muscle strength, progressive exercise testing on a cycle e rgometer (with cardiac output measurements being performed every second wor kload) and isokinetic cycling to assess peripheral muscle power and work ca pacity. Results: The DLT group was younger than the SLT group (23.0 [21.0-32.0] vs 47.5 [43.0-55.0] median [interquartile range], p <.05) with no differences in height, weight, or BMT. Despite the DLT group having significantly bette r spirometric values (FEV1: 86% vs 56.5% median) and less airtrapping (RV/T LC: 30% vs 53.5%), both groups were equally limited in exercise capacity (W -max) (38.0 percent predicted [30.0-65.0] vs 37.5 percent predicted [30.0-4 4.0], SLT vs DLT), leg power (76.1 percent predicted [53.8-81.4] vs 69.0 pe rcent predicted [58.3-76.0]) and leg work capacity (63.3 percent predicted [34.7-66.8] vs 38.4 percent predicted [27.5-57.3]). This lack of difference in performance persisted when the analysis was limited to those more than 18 months post-procedure. Respiratory muscle strength was also not differen t for the two groups, and was within normal limits. W-max was best correlat ed with leg work capacity (r =.84), but also with leg power, RV/TLC, FEV1 ( r =.49, -.52,.58). When normalized for age, height, and sex, percent predic ted W-max only correlated with percent predicted leg work capacity (r =.58) . Cardiac output was appropriate for the work performed. Conclusions: We conclude that peripheral skeletal muscle work capacity is r educed following lung transplantation and mostly responsible for the limita tion of exercise performance. While the causes of muscular dysfunction have yet to be clarified, the preservation of respiratory muscle strength with the concomitant reduction in leg power and work capacity suggests that most of the muscular dysfunction post-transplantation is attributable to detrai ning.