Quantifying assumptions underlying peak oxygen consumption equations across the body mass spectrum.

The goal of this study is to quantify the assumptions associated with the Wasserman-Hansen (WH) and Fitness Registry and the Importance of Exercise: A National Database (FRIEND) predictive peak oxygen consumption (pVO2 ) equations across body mass index (BMI). Assumptions in pVO2 for both equations were first determined using a simulation and then evaluated using exercise data from the Stanford Exercise Testing registry. We calculated percent-predicted VO2 (ppVO2 ) values for both equations and compared them using the Bland-Altman method. Assumptions associated with pVO2 across BMI categories were quantified by comparing the slopes of age-adjusted VO2 ratios (pVO2 /pre-exercise VO2 ) and ppVO2 values for different BMI categories. The simulation revealed lower predicted fitness among adults with obesity using the FRIEND equation compared to the WH equations. In the clinical cohort, we evaluated 2471 patients (56.9% male, 22% with BMI >30 kg/m2 , pVO2 26.8 mlO2 /kg/min). The Bland-Altman plot revealed an average relative difference of -1.7% (95% CI: -2.1 to -1.2%) between WH and FRIEND ppVO2 values with greater differences among those with obesity. Analysis of the VO2 ratio to ppVO2 slopes across the BMI spectrum confirmed the assumption of lower fitness in those with obesity, and this trend was more pronounced using the FRIEND equation. Peak VO2 estimations between the WH and FRIEND equations differed significantly among individuals with obesity. The FRIEND equation resulted in a greater attributable reduction in pVO2 associated with obesity relative to the WH equations. The outlined relationships between BMI and predicted VO2 may better inform the clinical interpretation of ppVO2 values during cardiopulmonary exercise test evaluations.

Comparison of the FRIEND and Wasserman-Hansen Equations in Predicting Outcomes in Heart Failure.

Background Percentage of age-predicted peak oxygen uptake (VO2) achieved (ppVO2) has been widely used to stratify risk in patients with heart failure. However, there are limitations to traditional normal standards. We compared the recently derived FRIEND (Fitness Registry and the Importance of Exercise: A National Data Base) equation to the widely used Wasserman-Hansen (WH) ppVO2 equation to predict outcomes in patients with heart failure. Methods and Results A subgroup of 4055 heart failure patients from the FRIEND registry (mean age 53±15 years) was followed for a mean of 28±16 months. The FRIEND and WH equations along with measured peak VO2 expressed in mL/kg-1 per min-1 were compared for mortality and composite cardiovascular events. ppVO2 was higher for the FRIEND versus the WH equation (66±30% versus 58±25%; P<0.001). The areas under the receiver operating characteristic curves were slightly but significantly higher for the FRIEND equation for mortality (0.74 versus 0.72; P=0.03) and cardiac events (0.70 versus 0.68; P=0.008). Area under the receiver operating characteristic curve for measured peak VO2 was 0.70 (P<0.001) for mortality and 0.73 (P<0.001) for cardiovascular events. For each 1-SD higher ppVO2 for the FRIEND equation, mortality was reduced by 18% (hazard ratio, 0.82; 95% CI, 0.69-0.97; P<0.02); for each 1-SD higher ppVO2 for the WH equation, the mortality was reduced by 17% (hazard ratio, 0.83; 95% CI, 0.71-0.97; P=0.02). The corresponding reductions in risk per 1 SD for cardiovascular events for the FRIEND and WH equations were 23 and 21%, respectively (both P<0.001). Conclusions Peak VO2 expressed as percentage of an age-predicted standard strongly predicts mortality and major cardiovascular events in patients with heart failure. The FRIEND registry equation exhibited test characteristics slightly superior to the commonly used WH equation.

Prognostic comparison of the FRIEND and Wasserman/Hansen peak VO2 equations applied to a submaximal walking test in outpatients with cardiovascular disease.

AIMS: The aim of this study was to determine the ability to predict all-cause mortality using established per cent-predicted (%PRED) equations for peak oxygen consumption (VO2peak) estimated by a submaximal walk test in outpatients with cardiovascular disease. METHODS: Male patients (N = 1491) aged 62 ± 10 years at baseline underwent a moderate and perceptually regulated (11-13 on the 6-20 Borg scale) 1-km treadmill-walking test to estimate VO2peak. %PRED was derived from the Fitness Registry and the Importance of Exercise: A National Data Base (FRIEND) and the Wasserman/Hansen equations. RESULTS: There were 215 deaths during a median 9.4-year follow-up. The FRIEND prediction equation provided better prognostic information with receiver operating curve analysis showing significantly different areas under the curve (0.72 and 0.69 for the FRIEND and the Wasserman/Hansen equations respectively, p = 0.001). Overall mortality rate was higher across decreasing tertiles of %PRED using FRIEND, with 26%, 11% and 5% for the least fit, intermediate and high fit tertiles, respectively (p for trend < 0.0001). Compared with the least fit tertile, the adjusted hazard ratios for the second and third tertiles were 0.54 (95% confidence interval 0.34-0.87, p = 0.01) and 0.45 (95% confidence interval 0.25-0.81, p = 0.008), respectively. Each 1% increase in %PRED conferred a 3% improvement in survival (p = 0.0004). CONCLUSION: Low %PRED VO2peak in cardiac outpatients determined by the FRIEND equation was associated with a high mortality rate independent of traditional cardiovascular risk factors and clinical history. The FRIEND equation may provide a suitable normal standard when applied to clinically stable outpatients with cardiovascular disease.

Applying current normative data to prognosis in heart failure: The Fitness Registry and the Importance of Exercise National Database (FRIEND).

INTRODUCTION: Percent of predicted peak VO2 (ppVO2) is considered a standard measure for establishing disease severity, however, there are known limitations to traditional normative values. This study sought to compare ppVO2 from the newly derived "Fitness Registry and the Importance of Exercise: a National Database" (FRIEND) registry equation to conventional prediction equations in a clinical cohort of patients undergoing cardiopulmonary exercise testing (CPX). METHODS AND RESULTS: We selected 1094 patients referred for evaluation of heart failure (HF) symptoms who underwent CPX. ppVO2 was calculated using the FRIEND, Wasserman/Hansen and Jones equations. Participants were followed for a median of 4.5 years [Interquartile range 3.5-6.0] for the composite endpoint of death, advanced HF therapy, or acute decompensated HF requiring hospital admission. Mean age was 48 ±â€¯15 years and 62% were female. The FRIEND registry equation predicted the lowest ppVO2 (measured/predicted; 71 ±â€¯31%), compared to the Wasserman/Hansen (74 ±â€¯29%) and Jones equations (83 ±â€¯33%) (p < 0.001). All expressions of peak VO2 were significant as univariate predictors of outcome with no significant differences between equations on pairwise analysis of receiver operating characteristic curves. When compared at a similar threshold of ppVO2 the event rate was significantly lower in the FRIEND registry equation versus the currently used Wasserman and Jones equations. CONCLUSION: The use of the newly derived FRIEND registry equation predicts HF outcomes; however, it appears to predict a higher predicted VO2; the clinical implication being a lower threshold of percent predicted peak VO2 should be considered when risk stratifying patients with HF.

Determining the best percent-predicted equation for estimated VO2 peak by a 1-km moderate perceptually-regulated treadmill walk to predict mortality in outpatients with cardiovascular disease.

OBJECTIVES: To determine the prognostic ability of established percent-predicted equations of peak oxygen consumption (%PRED) estimated by a moderate submaximal walking test in a large cohort of outpatients with cardiovascular disease (CVD). DESIGN: Population-based prospective study. METHODS: A total of 1442 male patients aged 25-85 years at baseline, underwent a moderate perceptually-regulated (11-13 on the 6-20 Borg scale) treadmill walk (1k-TWT) for peak oxygen consumption estimation (VO2 peak). %PRED was derived from ACSM, Ades et al, Morris et al, and the Wasserman/Hansen equations, and their prognostic performance was assessed. Overall mortality was the end point. Participants were divided into quartiles of %PRED, and mortality risk was estimated using a Cox regression model. RESULTS: During a median 8.2year follow-up, 167 all-cause deaths occurred. The Wasserman/Hansen equation provided the highest prognostic value. Mortality rate was lower across increasing quartiles of %PRED. Compared to the first quartile, after adjustment for confounders, the mortality risk decreased for the second, third, and fourth quartiles, with HRs of 0.75 (95% CI 0.44-1.29, p=0.29), 0.67 (95% CI 0.38-1.18, p=0.17), and 0.37 (95% CI 0.10-0.78, p=0.009), respectively (p for trend <0.0001). Each 1% increase in %PRED conferred a 4% improvement in survival. CONCLUSIONS: The percent-predicted VO2 peak determined by Wasserman/Hansen equations applied to the 1k-TWT is inversely and significantly related to survival in cardiac outpatients. The 1k-TWT is a simple and useful tool for stratifying mortality risk in patients participating in secondary prevention programs.

Determining the preferred percent-predicted equation for peak oxygen consumption in patients with heart failure.

BACKGROUND: Peak oxygen consumption (Vo(2)) is routinely assessed in patients with heart failure undergoing cardiopulmonary exercise testing. The purpose of the present investigation was to determine the prognostic ability of several established peak Vo(2) prediction equations in a large heart failure cohort. METHODS AND RESULTS: One thousand one hundred sixty-five subjects (70% males; age, 57.0+/-13.8 years; ischemic etiology, 43%) diagnosed with heart failure underwent cardiopulmonary exercise testing. Percent-predicted peak Vo(2) was calculated according to normative values proposed by Wasserman and Hansen (equation), Jones et al (equation), the Cooper Clinic (below low fitness threshold), a Veteran's Administration male referral data set (4 equations), and the St James Take Heart Project for women (equation). The prognostic significance of percent-predicted Vo(2) values derived from the 2 latter, sex-specific equations were assessed collectively. There were 179 major cardiac events (117 deaths, 44 heart transplantations, and 18 left ventricular assist device implantations) during the 2-year tracking period (annual event rate, 10%). Measured peak Vo(2) and all percent-predicted peak Vo(2) calculations were significant univariate predictors of adverse events (chi(2)> or =31.9, P<0.001) and added prognostic value to ventilatory efficiency (VE/Vco(2) slope), the strongest cardiopulmonary exercise testing predictor of adverse events (chi(2)=150.7, P<0.001), in a multivariate regression. The Wasserman/Hansen prediction equation provided optimal prognostic information. CONCLUSIONS: Actual peak Vo(2) and the percent-predicted models included in this analysis all were significant predictors of adverse events. It seems that the percent-predicted peak Vo(2) value derived from the Wasserman/Hansen equations may outperform other expressions of this cardiopulmonary exercise testing variable.