Reference values for peak exercise cardiac output in healthy individuals

Background Cardiac output (Q˙) is a key parameter in the assessment of cardiac function, its measurement being crucial for the diagnosis, treatment, and prognostic evaluation of all heart diseases. Until recently, Q˙ determination at peak exercise has been possible through invasive methods, so that normal values were obtained in studies based on small populations. Methods Nowadays, peak Q˙ can be measured noninvasively by means of the inert gas rebreathing (IGR) technique. The present study was undertaken to provide reference values for peak Q˙ in the normal general population and to obtain a formula able to estimate peak exercise Q˙ from measured peak oxygen uptake (V˙O2). Results We studied 500 normal subjects (age, 44.9 ± 1.5 years; range, 18-77 years; 260 men, 240 women) who underwent a maximal cardiopulmonary exercise test with peak Q˙ measurement by IGR. In the overall study sample, peak Q˙ was 13.2 ± 3.5 L/min (men, 15.3 ± 3.3 L/min; women, 11.0 ± 2.0 L/min; P < .001) and peak V˙O2 was 95% ± 18% of the maximum predicted value (men, 95% ± 19%; women, 95% ± 18%). Peak V˙O2 and peak Q˙ progressively decreased with age (R2, 0.082; P < .001; and R2, 0.144; P < .001, respectively). The V˙O2-derived formula to measure Q˙ at peak exercise was (4.4 × peak V˙O2) + 4.3 in the overall study cohort, (4.3 × peak V˙O2) + 4.5 in men, and (4.9 × peak V˙O2) + 3.6 in women. Conclusions The simultaneous measurement of Q˙ and V˙O2 at peak exercise in a large sample of healthy subjects provided an equation to predict peak Q˙ from peak V˙O2 values.