Prediction of oxygen consumption during exercise testing in apparently healthy subjects and coronary artery disease patients

Abstract

The American College of Sports Medicine has published formulae that are widely used to predict functional aerobic capacity for any treadmill speed and grade combination. However, it has been demonstrated that these formulae overpredict oxygen consumption (V̇O₂) for patients with coronary artery disease as well as for apparently healthy individuals. To study this, we measured V̇O₂, ventilation (V̇_E), and respiratory exchange ratio (R) responses in 21 apparently healthy subjects (AH) and 16 coronary artery diseased subjects (CAD) during a modified Balke protocol. Modification of the protocol consisted of extending the stage time from two minutes to three minutes at the higher intensities to allow a greater time for a physiological steady-state to occur. The attainment of a steady-state may lead to the reduction of or the elimination of prediction errors. No differences were observed between two and three minute VO₂ responses at maximal and submaximal exercise for either group. At peak exercise, the AH group was significantly (P≤.05) different from the CAD group when compared for heart rate (164±2.6 vs 140±4.8 bts•min⁻¹ ), V̇O₂ (33.3±1.1 vs 26.7±2.3 ml•kg⁻¹•min⁻¹), and total treadmill time (9.9±.33 vs 8.1±.54 min). At submaximal exercise, V̇O₂ responses were also significantly (p≤.05) greater for the AH group when compared to the CAD group (26.6±.95 vs 21.9±1.8 ml•kg⁻¹•min⁻¹). No significant differences were observed for RPE and blood lactate at peak exercise and V̇_E and R responses at submaximal or peak exercise between the two groups. Predicted values for peak V̇O₂ were significantly (p≤.05) higher than measured values (33.3±1.1 vs 38.8±1.1 ml•kg⁻¹•min⁻¹) and (26.7±2.3 vs 34.1±1.7 ml•kg⁻¹•min⁻¹) for the AH and CAD groups, respectively. However, no significant differences were noted between predicted and measured V̇O₂ responses at submaximal exercise for either group. Individuals classified as Type A were not significantly different from classified Type B individuals when compared for the cardio-respiratory variables measured. These data demonstrate that the ACSM prediction formulae significantly overpredict V̇O₂ for both AH and CAD subjects at maximal treadmill intensities. However, at submaximal intensities, these prediction formulae are acceptable for both groups of subjects. Furthermore, these data suggest that two minutes per stage allows sufficient time for physiological steady-state to occur at clearly submaximal intensities. Although at the higher intensities, extending the stage time beyond two minutes may be indicated.