Cardiac output (Symbol) 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, Symbol 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 Symbol can be measured noninvasively by means of the inert gas rebreathing (IGR) technique. The present study was undertaken to provide reference values for peak Symbol in the normal general population and to obtain a formula able to estimate peak exercise Symbol from measured peak oxygen uptake (Symbolo2).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 Symbol measurement by IGR. In the overall study sample, peak Symbol 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 Symbolo2 was 95% ± 18% of the maximum predicted value (men, 95% ± 19%; women, 95% ± 18%). Peak Symbolo2 and peak Symbol progressively decreased with age (R2, 0.082; P < .001; and R2, 0.144; P < .001, respectively). The Symbolo2-derived formula to measure Symbol at peak exercise was (4.4 × peak Symbolo2) + 4.3 in the overall study cohort, (4.3 × peak Symbolo2) + 4.5 in men, and (4.9 × peak Symbolo2) + 3.6 in women.CONCLUSIONS:
The simultaneous measurement of Symbol and Symbolo2 at peak exercise in a large sample of healthy subjects provided an equation to predict peak Symbol from peak Symbolo2 values.