Abstract 13554: Highest Exercise Circulatory Equivalents are Reproducible in Heart Failure Patients Despite Wide Differences in Ramp Rate Increments
BACKGROUND: Gas exchange measurements during exercise in chronic heart failure (CHF) provide important prognostic and diagnostic information, but are infrequently used, in part due to their complexity in acquisition, display and interpretation. The values of circulatory equivalents [the ratios of O2 uptake (VO2) and CO2 output (VCO2) to ventilation (VE)] offer advantages, especially when visualized as a moving average on a single X-Y plot. Their highest values do not require maximal exercise, are easy to obtain, and, without other data, appear to evaluate the severity of heart failure. However, their reproducibility has not been tested. We hypothesized that circulatory equivalents would be reproducible in CHF patients over a wide range of ramp rates.
METHODS and RESULTS: Eighteen men 62.8±10.7 years old (mean±SD), 173±7.5 cm tall, and 90±15.3 kg, with medically optimized NYHA Class I and II CHF due to ischemic heart disease or dilated cardiomyopathy underwent exercise testing 3 times, each test separated by 7 days. The individually selected rates of randomized ramp increases during cycle ergometry were 19±6 (fast; 346±29 s), 9±4 (medium; 585±82 s), and 5±1 (slow; 904±112 s) W/min. Gas exchange and ventilation were assessed by a 30 breath moving average at rest, l0 W baseline and incremental exercise to the limit of tolerance. There were no significant differences between ramp protocols for highest VO2/VE (32.3±3.9 mL/L; range 24.6 to 38.6), highest VCO2/VE (29.4±3.2 mL/L; range 24.7 to 34.4), or peak VO2 (14.5±2.6 mL.min-1.kg-1; range 10.6 to 19.6). Test-retest coefficients of variation were different by ANOVA (p<0.01) among the peak VO2 (6.3±3.7 %) and the highest circulatory equivalents (VO2/VE, 4.6±2.3 %; VCO2/VE, 3.1±1.9 %). For each individual the graphical patterns of response from rest through the highest VO2/VE and VCO2/VE also were similar. These highest VO2/VE and VCO2/VE values are lower than for normal men but higher than for men with severe heart failure.
CONCLUSION: Displays and values for VO2/VE and VCO2/VE are robust, useful, and more reproducible than peak VO2 in 18 CHF patients.
- © 2012 by American Heart Association, Inc.