Peak Circulatory Power during Maximal Cardiopulmonary Exercise Testing: Reference Standards from the FRIEND Registry

Purpose Normative standards for key cardiopulmonary exercise (CPX) test variables, including peak circulatory power (CircP), are needed to guide the interpretation of clinical exercise responses in individuals with and without disease. Objective This study aimed to establish age- and sex-specific reference standards for peak CircP derived from a healthy cohort from the Fitness Registry and the Importance of Exercise: A National Database (FRIEND). Methods CPX test data from apparently healthy males and females from eight FRIEND United States exercise laboratories were considered. Inclusion criteria included ages 20-79 yr and a maximal, symptom-limited exercise test performed on a treadmill or cycle ergometer. CircP was calculated as the product of peak oxygen consumption and peak systolic blood pressure. Reference values were determined on both treadmill and cycle ergometer for males and females per age decade. A stepwise linear regression to predict CircP was derived from two-thirds of the sample while the remaining one-third was used as a validation cohort. Results A total of 6736 CPX tests (47% treadmill, 53% female) were included in the analysis. Overall, CircP was higher in males, higher on tests conducted on a treadmill, and decreased with age. Sex, exercise mode, age, and body mass index were the most significant contributors to CircP (multiple R = 0.75, R-2 = 0.57, root-mean-square error = 1200 mm Hg center dot mL O-2 center dot kg(-1)center dot min(-1), P < 0.001). Using the generated prediction equation, the average percent-predicted CircP for the validation cohort was 101.3% +/- 28.1%. Conclusions These results establish reference standards for CircP, a potentially important prognostic indicator of cardiovascular health. Future research exploring the role of percentiles and percent-predicted values for CircP is necessary as they may provide additional prognostic insight.