Kinetics of pulmonary gas exchange during and while recovering from exercise in patients after anterior myocardial infarction

Abstract

The effect of exercise intensity on gas exchange kinetics was investigated during exercise and recovery, as well as the relationship between the kinetics during exercise and recovery. Twenty-three patients with a history of anterior myocardial infarction performed low-intensity (38.7±8.3 W) and high-intensity (68.8±15.0 W) exercise for 6 min. The time constants of oxygen uptake (V̇O2), carbon dioxide output (V̇CO2) and minute ventilation (V̇E) were significantly prolonged during high intensity exercise compared with low-intensity exercise (61.2±8.6 vs 52.3±10.3 s, p<0.005 for the time constant of V̇O2). The time constant of V̇O2 was similar during exercise and during recovery from exercise of high (61.2±8.6 vs 66.2±12.2 s) as well as low intensity (52.3±10.3 vs 55.0±10.1 s). However, the time constants of V̇CO2 and heart rate were significantly shorter during recovery than during exercise. The time constants of V̇CO2 and V̇E were significantly longer than that of V̇O2 during both exercise and recovery. In the present study, it was found that (1) the gas exchange kinetics were influenced by the intensity, of exercise; (2) the kinetics during recovery did not necessarily reflect the kinetics during exercise except for V̇O2; and (3) the kinetics of V̇CO2 and V̇E were delayed as compared with the V̇O2 kinetics. These characteristics should be taken into account when using gas exchange kinetics to estimate cardiopulmonary responses to exercise in patients with left ventricular dysfunction.