COMPARISON OF RAMP TREADMILL PROTOCOLS IN CARDIAC PATIENTS WITH LIMITED FUNCTIONAL CAPACITY.

Abstract

1261 Treadmill ramp protocols are becoming increasingly popular and commercially available. The main benefits of ramp protocols are the smaller work increments, optimization of test duration, and patient preference. We employ individualized ramp protocols, where a different slope is computed for each patient based on desired speed, target test time (12min), and target MET level. In contrast, researchers from Ball State University have proposed the use of a Bruce Ramp (BR) protocol where each of the 3-minute stages of a standard Bruce protocol are broken into nine 20-second increments. The purpose of this study was to compare maximal responses and prediction of functional capacity in low fit (<6METS) cardiac patients undergoing both the BR and individualized ramp (IR) protocols. Twelve patients (mean age=63±12, mean MET= 4.6±.8) with limited functional capacity (<6METs) enrolled in the Wake Forest Cardiac Rehabilitation Program, underwent two symptom-limited maximal treadmill tests in random order on a motor driven treadmill with direct measurement of expired gases. Maximal values for oxygen consumption (VO2), heart rate (HR), test duration, speed, grade, rating of perceived exertion (RPE), respiratory exchange ratio (RER), systolic blood pressure (SBP), diastolic blood pressure (DBP) and ventilation (VE) were compared using analysis of variance. Comparisons were also made between measured and estimated MET levels using standard ACSM formulae to estimate MET levels for both treadmill protocols. There were no significant differences in peak values for VO2, HR, RPE, RER, SBP, DBP or VE. However, test duration (min) was significantly lower in the BR (BR=5.5±1.1 vs. IR=9.2±2.1) while both speed (mph) and grade (%) were significantly higher (BR= 2.5±.3 vs. IR 2.1±.2, BR 11.5±1.3 vs. IR 7.8±2.6 respectively). The table below provides a comparison of the mean (±SD) measured and estimated MET values for the two protocols as well as correlations (r), and standard error of the estimates (SEE).TableConclusion: In patients with low functional capacity the ACSM equation significantly overpredicts MET levels from the BR, but does not significantly overpredict with the IR protocol. However, the low correlation and high SEE for both protocols indicates that estimating MET levels with the ACSM equation will result in substantial variability and potential inaccuracy. Therefore, direct measurement of VO2 is recommended for accurate assessment of functional capacity in cardiac patients with low functional capacities.