Oxygen uptake and cardiac output during progressive and constant load work in patients after acute myocardial infarction

PURPOSE: Simultaneously measured oxygen uptake (VO2) and Doppler echocardiography could verify if an alteration in the VO2 response to progressive and constant load work is due to reduced cardiac output. METHODS: The study group consisted of nine patients after acute myocardial infarction (MI), five age-matched healthy subjects (HE), and five young well-trained subjects (WT). Each subject performed a progressive exercise test and two bouts of constant load work at power outputs equated to 10% below (W1) and 10% above (W2) their ventilatory thresholds. VO2 and cardiac output were measured continuously and simultaneously during the tests. RESULTS: VO2 was significantly reduced for the MI group during the initial stages of the progressive exercise test (P < .02) and remained lower throughout the entire test. During the first 60 seconds of constant load work (W2), VO2 was lower for MI (P < .05). At steady state exercise during W2, cardiac output was significantly less for MI (P < .05). VO2 for the MI group was more reliant on cardiac output during lower power outputs and differences in the arterial and venous O2 content (a-VO2 difference) during greater power outputs. CONCLUSIONS: Cardiac rehabilitation programs must be aware of this delayed VO2 and cardiac output response when setting training workloads or selecting the magnitude of the workload increments during progressive exercise tests.