Prediction of oxygen consumption in cardiac rehabilitation patients performing leg ergometry

The purpose of this study was two-fold. First, to determine the validity of the ACSM leg ergometry equation in the prediction of steady-state oxygen consumption (VO₂) in a heterogeneous population of cardiac patients. Second, to determine whether a more accurate prediction equation could be developed for use in the cardiac population. Thirty-one cardiac rehabilitation patients participated in the study of which 24 were men and 7 were women. Biometric variables (mean ± sd) of the participants were as follows: age = 61.9 ± 9.5 years; height = 172.6 ± 1.6 cm; and body mass = 82.3 ± 10.6 kg. Subjects exercised on a Monarch_TM cycle ergometer at 0, 180, 360, 540 and 720 kgm$\dot{}$min-1. The length of each stage was five minutes. Heart rate, ECG, and VO₂ were continuously monitored. Blood pressure and heart rate were collected at the end of each stage. Steady state VO ₂ was calculated for each stage using the average of the last two minutes. Correlation coefficients, standard error of estimate, coefficient of determination, total error, and mean bias were used to determine the accuracy of the ACSM equation (1995). The analysis found the ACSM equation to be a valid means of estimating VO₂ in cardiac patients. Simple linear regression was used to develop a new equation. Regression analysis found workload to be a significant predictor of VO₂. The following equation is the result: VO₂ = (1.6 x kgm$\dot{}$min-1) + 444 ml$\dot{}$min-1. The r of the equation was.78 (p <.05) and the standard error of estimate was 211 ml$\dot{}$min-1. Analysis of variance was used to determine significant differences between means for actual and predicted VO₂ values for each equation. The analysis found the ACSM and new equation to significantly (p <.05) under predict VO₂ during unloaded pedaling. Furthermore, the ACSM equation was found to significantly (p <.05) under predict VO ₂ during the first loaded stage of exercise. When the accuracy of the ACSM and new equations were compared based on correlation coefficients, coefficients of determinations, SEEs, total error, and mean bias the new equation was found to have equal or better accuracy at all workloads. The final form of the new equation is: VO₂ (ml$\dot{}$min-1) = (kgm$\dot{}$min-1 x 1.6 ml$\dot{}$kgm-1) + (3.5 ml$\dot{}$kg-1$\dot{}$min-1 x body mass in kg) + 156 ml$\dot{}$min-1.