Maximal METs Calculated from Treadmill Work vs Estimated from Questionnaire
Figure 4 illustrates the relationship between exercise capacity, expressed in METs, estimated from a specific activity questionnaire, and that calculated from treadmill speed and grade at peak exercise. The correlation between the 2 was 0.69 (p<0.001), and the regression equation was Y = 0.48X + 4.6 (SEE = 1.72 METs).
The individualized approach offers several advantages for cardiopulmonary exercise testing. First, most protocols employ fixed work increments between stages. These increments are large for some patients and small for others. Relatively large increments for some patients can cause a discrepancy between oxygen uptake and treadmill work rate, which can lead to premature termination of exercise and limit the evaluation of cardiopulmonary function. Panza and coworkers, for example, recently observed that the correlation between ischemic responses on treadmill testing vs those on 48-h ambulatory monitoring was markedly improved when using a gradual protocol (<1 MET increments) compared with a protocol using large increments (Bruce protocol, 2 to 3 MET increments). Second, uneven increments in work limit the application of some gas exchange parameters, such as the V<VWR relationship and the ventilatory threshold. Third, several recent studies have suggested that a test duration of 8 to 12 min is “optimal” for assessing cardiopulmonary function.