STRUCTURE OF SKELETAL-MUSCLE IN HEART-TRANSPLANT RECIPIENTS

Objectives. This study sought to define the ultrastructural characteri stics of skeletal muscle in heart transplant recipients (HTRs) in rela tion to exercise capacity compared with that in age-matched control su bjects. Background. Muscle structural features seem to play an importa nt role in the limitation of exercise capacity of HTRs long after tran splantation. Methods. The structure of the vastus lateralis muscle was analyzed by ultrastructural morphometry in 16 HTRs and 20 healthy con trol subjects. Maximal oxygen consumption (peak VO2) was determined by an incremental exercise test. Results. Peak VO2 was significantly low er (by 35%) in HTRs. Fiber size, volume density of mitochondria and in tramyocellular lipid deposits were not significantly different between HTRs and control subjects. In contrast, the capillary density and the capillary/fiber ratio were both significantly reduced in HTRs (by 24% and 27%, respectively). Conclusions. A normal volume density of mitoc hondria and a reduced capillary network are the main characteristics o f muscle ultrastructure in HTRs by 10 months after transplantation. Th e muscle structural abnormalities and reduced exercise capacity might be related to immunosuppressive therapy with cyclosporine and corticos teroids as well as deconditioning.