Resting Oxygen Consumption and Heart Failure: Importance of Measurement for Determination of Cardiac Output With the Use of 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 control subjects (n = 77). VO2 was measured with the use of a metabolic cart, and estimated VO2 was calculated with the use of the Dehmer, LaFarge, and Bergstra formulas and the thermodilution method. The measured and estimated VO2 were compared and the potential impact of estimations determined. In the multivariable model, resting VO2 decreased with increasing New York Heart Association (NYHA) functional class in a stepwise fashion (beta NYHA functional class IV vs control = -36 mL O-2/min; P < .001). Estimations of VO2 with the use of derived equations diverged from measured values, particularly for patients with NYHA functional class IV limitations. The percentage difference of measured VO2 versus estimated VO2 was >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 estimations of VO2 respectively. Conclusions: Resting VO2 decreases with increasing NYHA functional class and is lower than in control subjects. Using estimations of VO2 to calculate CO may introduce clinically important error.