RELATION OF SYSTEMIC AND LOCAL MUSCLE EXERCISE CAPACITY TO SKELETAL-MUSCLE CHARACTERISTICS IN MEN WITH CONGESTIVE-HEART-FAILURE

Objectives. The present study was undertaken to further characterize c hanges in skeletal muscle morphology and histochemistry in congestive heart failure and to determine the relation of these changes to abnorm alities of systemic and local muscle exercise capacity. Background. Ab normalities of skeletal muscle appear to play a role in the limitation of exercise capacity in congestive heart failure, but information on the changes in muscle morphology and biochemistry and their relation t o alterations in muscle function is limited. Methods. Eighteen men wit h predominantly mild to moderate congestive heart failure (mean +/- SE M New Yolk Heart Association functional class 2.6 +/- 0.2, ejection fr action 24 +/- 2%) and eight age- and gender matched sedentary control subjects underwent measurements of peak systemic oxygen consumption (V o(2)) during cycle ergometrg, resistance to fatigue of the quadriceps femoris muscle group and biopsy of the vastus lateralis muscle. Result s. Peak Vo(2) and resistance to fatigue were lower in the patients wit h heart failure than in control subjects (15.7 +/- 1.2 vs. 25.1 +/- 1. 5 ml/min-kg and 63 +/- 2% vs. 85 +/- 3%, respectively, both p < 0.001) . Patients had a lower proportion of slow twitch, type I fibers than d id control subjects (36 +/- 3% vs. 46 +/- 5%, p = 0.048) and a higher proportion of fast twitch, type IIab fibers (18 +/- 3% vs. 7 +/- 2%, p = 0.001). Fiber cross-sectional area was smaller, and single-fiber su ccinate dehydrogenase activity, a mitochondrial oxidative marker, was lower in patients (both p less than or equal to 0.034). Likewise, the ratio of average fast twitch to slow twitch fiber cross-sectional area was lower in patients (0.780 +/- 0.06 vs, 1.05 +/- 0.08, p = 0.019). Peak Vo(2) was strongly related to integrated succinate dehydrogenase activity in patients (r = 0.896, p = 0.001). Peak Vo(2), resistance to fatigue and strength also correlated significantly with several measu res of fiber size, especially of fast twitch fibers, in patients. None of the skeletal muscle characteristics examined correlated with exerc ise capacity in control subjects, Conclusions. These results indicate that congestive heart failure is associated with changes in the charac teristics of skeletal muscle and local as well as systemic exercise pe rformance. There are fewer slow twitch fibers, smaller fast twitch fib ers and lower succinate dehydrogenase activity. The latter finding sug gests that mitochondrial content of muscle is reduced in heart failure and that impaired aerobic-oxidative capacity may play a role in the l imitation of systemic exercise capacity.