Quantifying Improvement in V˙o 2peak and Exercise Thresholds in Cardiovascular Disease Using Reliable Change Indices

Abstract

Purpose: Improving aerobic fitness through exercise training is recommended for the treatment of cardiovascular disease (CVD). However, strong justifications for the criteria of assessing improvement in key parameters of aerobic function including estimated lactate threshold (θLT), respiratory compensation point (RCP), and peak oxygen uptake (V˙o 2peak) at the individual level are not established. We applied reliable change index (RCI) statistics to determine minimal meaningful change (MMCRCI) cutoffs of θLT, RCP, and V˙o 2peak for individual patients with CVD. Methods: Sixty-six stable patients post-cardiac event performed three exhaustive treadmill-based incremental exercise tests (modified Bruce) ∼1 wk apart (T1-T3). Breath-by-breath gas exchange and ventilatory variables were measured by metabolic cart and used to identify θLT, RCP, and V˙o 2peak. Using test-retest reliability and mean difference scores to estimate error and test practice/exposure, respectively, MMCRCI values were calculated for V˙o 2 (mL·min−1.kg−1) at θLT, RCP, and V˙o 2peak. Results: There were no significant between-trial differences in V˙o 2 at θLT (P = .78), RCP (P = .08), or V˙o 2peak (P = .74) and each variable exhibited excellent test-retest variability (intraclass correlation: 0.97, 0.98, and 0.99; coefficient of variation: 6.5, 5.4, and 4.9% for θLT, RCP, and V˙o 2peak, respectively). Derived from comparing T1-T2, T1-T3, and T2-T3, the MMCRCI for θLT were 3.91, 3.56, and 2.64 mL·min−1.kg−1; 4.01, 2.80, and 2.79 mL·min−1.kg−1 for RCP; and 3.61, 3.83, and 2.81 mL·min−1.kg−1 for V˙o 2peak. For each variable, MMCRCI scores were lowest for T2-T3 comparisons. Conclusion: These MMCRCI scores may be used to establish cutoff criteria for determining meaningful changes for interventions designed to improve aerobic function in individuals with CVD.