Treadmill-based submaximal VO2 estimation in patients with coronary artery disease: can a model derived from healthy individuals be valid?

Abstract

Background/aim: Existing treadmill-based VO₂ prediction models may not accurately estimate submaximal VO₂ in patients with coronary artery disease (CAD), as they are often derived from healthy populations. This study aimed to develop and validate a submaximal VO₂ prediction model derived from healthy individuals and tested for generalizability in CAD patients by incorporating clinically relevant parameters.

Materials and methods: A retrospective analysis was conducted with 101 participants (54 healthy, 47 CAD patients) undergoing cardiopulmonary exercise testing using the modified Bruce protocol. To better represent the submaximal VO₂ reached during exercise, the average VO₂ in the last minute of each stage was used. The model was developed using data from healthy individuals and subsequently validated in the CAD cohort. A linear mixed-effects model was employed to predict VO₂ based on speed, grade, and other confounders, including peak VO₂, body weight, and body mass index (BMI). The model's performance was evaluated and compared with previously published equations using Bland-Altman plots, mean absolute error (MAE), root mean square error (RMSE), and Lin's concordance correlation coefficient (CCC).

Results: The final model, including speed, grade, and peak VO₂, achieved an R² of 0.83 (95% CI: 0.79, 0.86; f² = 4.88). For CAD patients, the predicted-actual VO₂ difference was -0.05 ± 1.8 mL/kg/min, with MAE and RMSE values of 1.4 and 1.8 mL/kg/min, respectively. The model outperformed reference equations, achieving the highest accuracy (CCC = 0.923) and minimal bias. Incorporating peak VO₂ effectively accounted for exercise response differences between healthy individuals and CAD patients.

Conclusion: A submaximal VO₂ estimation model derived from healthy individuals and validated in CAD patients demonstrated high accuracy. Incorporating peak VO₂ effectively bridged physiological differences, supporting individualized exercise prescriptions in cardiac rehabilitation. However, larger prospective cohorts are warranted to confirm external validity.

Keywords: Cardiac rehabilitation; coronary artery disease; exercise; oxygen uptake; treadmill.