Delayed kinetics of oxygen uptake during recovery after exercise in cardiac patients

PURPOSE: Little is known about cardiovascular responses during recovery from exercise in patients with cardiovascular disease. The aim of this study was to determine the time constants of the kinetics of oxygen uptake and heart rate during recovery from exercise and to evaluate the influence of resting cardiac function on these kinetics in patients with left ventricular dysfunction. METHODS: A moderate exercise test was performed by 40 patients (57+/-10 yr old) with prior myocardial infarction at a constant work rate (40+/-8 W) for 6 min on a cycle ergometer. The time constants of oxygen uptake and heart rate during 6 min of recovery were compared in patients whose left ventricular ejection fractions were > or =35% (group 1, N = 20) and those with ejection fractions <35% (group 2, N = 20). RESULTS: The time constant of the decrease in oxygen uptake during exercise recovery was significantly prolonged (oxygen requirement was increased) in group 2 compared with group 1. Heart rate during recovery was consistently higher, and its time constant was prolonged in group 2 compared with group 1. The time constant of oxygen uptake was positively correlated with the time constant of heart rate. CONCLUSION: The recovery of oxygen uptake after exercise was significantly delayed, associated with delayed recovery of heart rate, in patients with severely impaired left ventricular function.