Determination Of The (V)Over Dote/(V)Over Dotco(2) Slope From A Constant Work-Rate Exercise Test In Cardiac Patients

Incremental exercise testing to a symptom-limited maximum has been used to measure the ratio of the increase in ventilation ((V)over dotE) to the increase in CO2 Output (VCO2) during exercise ((V)over dotE/(V)over dotCO(2) slope), a valuable index reflecting the severity of the ventilation-perfusion mismatch in heart failure. Here we studied whether this same value for the slope of (V)over dotE/(V)over dotCO(2) could be determined from a short constant work-rate exercise test of moderate intensity. Twenty-three patients with a previous myocardial infarction underwent moderate-intensity (69 15 W) constant work-rate exercise for 6 min and an incremental work-rate exercise test to the max. The (V)over dotE/(V)over dotCO(2) slope was calculated from the incremental exercise test from the start of increasing the work-rate to the ventilatory compensation point. The (V)over dotE/(V)over dotCO(2) slope was similarly calculated from the start of constant work-rate exercise until the 4th minute, when (V)over dot and (V)over dotO(2) changed minimally. The (V)over dotE/(V)over dotCO(2) slope determined from incremental exercise was 33.8 +/- 5.9, ranging from 20.9 to 42.8. The slope obtained from constant work-rate exercise was 32.9 +/- 5.7. The (V)over dotE/(V)over dotCO(2) slopes obtained from the two exercise tests did not differ significantly. The slope obtained from constant work-rate exercise was significantly positively correlated with the slope obtained from the incremental exercise (r = 0.84, p < 0.0001). The (V)over dotE/(V)over dotCO(2) slope can be determined from constant work-rate exercise at a moderate intensity. This indicates that the relationship between ventilation and CO2 Output is consistent and independent of the mode of exercise testing.