Predicted vs Measured Vo2 Throughout Exercise
The slope of the relationship between measured and predicted oxygen uptake (Figure 2) is an expression of the degree of change in one variable for a given change in another. The ramp test lends itself well to an evaluation of slope since the change in the variable expressed on the X axis (the work rate) is constant. Thus, the slope illustrates how well ventilatory oxygen uptake (Y axis) increased in accordance with the demands of the work (X axis) throughout the test. We have previously reported that the slope of this relationship is reduced using protocols with large increments in work (for example, slopes of roughly 0.60 were observed on the Bruce treadmill and 50 W/stage cycle ergometer vs roughly 0.80 on ramp treadmill and cycle ergometer tests) in a combined group of patients and normal subjects.
The slope of 0.78 and the correlation of 0.93 observed in the present study confirm our previous results. It is noteworthy that the standard error of the Y estimate (3.96 ml/kg/min) suggests that any given submaximal exercise level can be predicted within approximately ± 2 METs with 95% confidence. It should be noted further that the present group was free of cardiovascular disease, and since patients with disease are known to have reduced oxygen kinetics, this accounts in part for the high slope.