Fibre types in skeletal muscles of chronic obstructive pulmonary disease patients related to respiratory function and exercise tolerance

This study aimed to investigate the relationship between skeletal muscle, fibre type composition, functional respiratory impairment and exercise tolerance in patients with moderate to severe chronic obstructive pulmonary disease (COPD). A group of 22 COPD patients and 10 healthy control subjects were studied. In COPD patients, vital capacity (VC) and forced expiratory volume in one second (FEV1) were reduced to 79% and 51%, respectively. Diffusion indices (transfer factor of the lung for carbon monoxide (TL,CO) and carbon monoxide transfer coefficient (KCO)) were also reduced. Arterial oxygen tension (Pa,O2) was normal or slightly altered. A maximal exercise test was performed and anaerobic threshold was calculated. Muscle samples from vastus lateralis were obtained by needle biopsy. Myosin heavy chain (MHC) and light chain (MLC) isoforms were separated by gel electrophoresis and quantified by densitometry. MHC isoforms were considered as molecular markers of fibre types. The proportion of the fast MHC-2B isoform was increased in COPD patients. TL,CO, KCO, VC and FEV1 were positively correlated with slow MHC isoform content. TL,CO and KCO were also negatively correlated with the content of the fast MHC-2B isoform. No correlation was found between exercise parameters and MHC isoform composition. The co-ordinated expression between MHC and MLC isoforms was altered in COPD patients. We conclude that reduced oxygen availability, probably in combination with muscle disuse, may determine muscle alterations in chronic obstructive pulmonary disease patients. The altered correlations between myosin heavy chain and light chain isoforms suggest that co-ordinated protein expression is lost in chronic obstructive pulmonary disease muscles.