Resting Oxygen Consumption and Heart Failure: Importance of Measurement for Determination of Cardiac Output Using the Fick Principle

BACKGROUND: Resting oxygen consumption (VO2) is often estimated and frequently used to guide therapeutic decisions in symptomatic heart failure (HF) patients. The relationship between resting VO2 and symptomatic HF and the accuracy of estimations of VO2 in this population are unknown. METHODS AND RESULTS: We performed a cross-sectional study of HF patients (n=691) and healthy controls (n=77). VO2 was measured using a metabolic cart and estimated VO2 was calculated using the Dehmer, LaFarge, and Bergstra formulas and the thermodilution method. The measured and estimated VO2 were compared, and the potential impact of estimations was determined. In the multivariable model, resting VO2 decreased with increasing NYHA class in a stepwise fashion (beta NYHA class IV vs controls=-36 ml O2/min, P\u3c0.001). Estimations of VO2 using derived equations diverged from measured values, particularly for patients with NYHA class IV limitations. The percent difference of measured VO2 versus estimated VO2 was greater than 25% in 39% (n=271), 25% (n=170), 82% (n=566), and 39% (n=271) of HF patients when using the Dehmer, LaFarge, Bergstra, and thermodilution-derived VO2 respectively. CONCLUSIONS: Resting VO2 decreases with increasing NYHA class and is lower than controls. Using estimations of VO2 to calculate CO may introduce clinically important error