This study sought to define the relation between muscle function and bulk in chronic
heart failure (HF) and to explore the association between muscle function and bulk
and exercise capacity.
Skeletal muscle abnormalities have been postulated as determinants of exercise capacity
in chronic HF. Previously, muscle function in chronic HF has been evaluated in relatively
small numbers of patients and with variable results, with little account being taken
of the effects of muscle wasting.
One hundred male patients with chronic HF and 31 healthy male control subjects were
studied. They were matched for age (59.0 +/- 1.0 vs. 58.7 +/- 1.7 years [mean +/-
SEM]) and body mass index (26.6 +/- 0.4 vs. 26.3 +/- 0.7 kg/m2). We assessed maximal
treadmill oxygen consumption (VO2), quadriceps maximal isometric strength, fatigue
(20-min protocol, expressed in baseline maximal strength) and computed tomographic
cross-sectional area (CSA) at midthigh.
Peak VO2 was lower in patients (18.0 +/- 0.6 vs. 33.3 +/- 1.4 ml/min per kg, p < 0.0001),
although both groups achieved a similar respiratory exchange ratio at peak exercise
(1.15 +/- 0.01 vs. 1.19 +/- 0.03, p = 0.13). Quadriceps (582 vs. 652 cm2, p < 0.05)
and total leg muscle CSA (1,153 vs. 1,304 cm2, p < 0.005) were lower in patients with
chronic HF. Patients were weaker than control subjects (357 +/- 12 vs. 434 +/- 18
N, p < 0.005) and also exhibited greater fatigue at 20 min (79.1% vs. 92.1% of baseline
value, p < 0.0001). After correcting strength for quadriceps CSA, significant differences
persisted (5.9 +/- 0.2 vs. 7.0 +/- 0.3 N/cm2, p < 0.005), indicating reduced strength
per unit muscle. In patients, but not control subjects, muscle CSA significantly correlated
with peak absolute VO2 (R = 0.66, p < 0.0001) and is an independent predictor of peak
absolute VO2.
Patients with chronic HF have reduced quadriceps maximal isometric strength. This
weakness occurs as a result of both quantitative and qualitative abnormalities of
the muscle. With increasing exercise limitation there is increasing muscle weakness.
This progressive weakness occurs predominantly as a result of loss of quadriceps bulk.
In patients, this muscular atrophy becomes a major determinant of exercise capacity.