Skeletal muscle oxygenation and oxygen uptake kinetics following constant work rate exercise in chronic congestive heart failure.

The aim of the present study was to determine the kinetics of recovery of muscle oxygenation (MO) from comparable levels of exercise in patients with chronic congestive heart failure (CHF) and in normal subjects, and to relate MO kinetics to the level of exercise intolerance. Ten patients with stable CHF secondary to ischemic cardiomyopathy (ejection fraction 34 +/- 6%) (mean age 47 +/- 10 years) and 8 healthy matched control subjects underwent an upright incremental cycle ergometer exercise test with gas exchange analysis and a 6-minute constant work rate protocol at 60% of peak oxygen consumption (VO2). Oxygenation of the vastus lateralis muscle was continuously monitored during exercise and recovery using near infrared spectroscopy. Recovery VO2 and MO mean response times for the constant work rate exercise test were longer in patients with CHF than in control subjects (p <0.05). Both VO2 and MO mean response times were inversely related to peak VO2 (r = -0.73 and -0.52, respectively; p <0.05 for both). Thus recovery of muscle and total body oxygenation from submaximal exercise is more delayed the greater the cardiac dysfunction, as assessed by peak VO2. This suggests that regeneration of phosphocreatine and/or resaturation of venous oxyhemoglobin take place more slowly the worse the cardiac function.