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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.