Evidence for Abnormalities Unrelated to Blood Flow

Previous studies with 31P nuclear magnetic resonance have demonstrated that patients with chronic congestive heart failure often exhibit increased glycolytic metabolism and impaired oxidative phosphorylation in exercising skeletal muscle, but the mechanism for these changes remains unresolved. This study was conducted to determine whether these abnormalities result from impaired blood flow or oxygen delivery. Nine patients with mild-to-moderate congestive heart failure and nine ageand size-matched, healthy control volunteers were studied during repetitive submaximal finger flexion exercise under aerobic and ischemic conditions. Skeletal muscle metabolism was assessed by 31P nuclear magnetic resonance of the flexor digitorum superficialis muscle. During steady-state aerobic exercise at 33% of each subject's predetermined maximum workload, the patients with congestive heart failure exhibited significantly lower pH values (6.65 0.22 vs. 6.97+± 0.09, p<0.002) and phosphocreatine concentrations, expressed as [phosphocreatinel/([phosphocreatine]+ [inorganic phosphate]) (0.59 0.14 vs. 0.79 + 0.08, p<0.002). Similar differences were also present throughout ischemic exercise at the same workload. Based upon these measurements, calculated lactate production and adenosine 5'-triphosphate consumption rates were significantly higher in the patients with congestive heart failure. These results indicate that in many patients with congestive heart failure exercising muscle exhibits increased glycolytic metabolism and appears to be metabolically less efficient in relation to external work performed. These changes cannot be explained by impaired blood flow