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 and Results
Nowadays, peak Q can be measured noninvasively by means of inert gas rebreathing technique (IGR). 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 (VO2).We studied 500 normal subjects (age 44.9±1.5 years, range 18-77, 260 males, 240 females) 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 (males: 15.3±3.3 L/min; females: 11.0±2.0 L/min, p<0.001) and peak VO2 was 95±18% of the maximum predicted value (male: 95± 19%; female: 95±18%). Peak VO2 and peak Q progressively decreased with age (R2: 0.082, p<0.001 and R2: 0.144, p< 0.001, respectively). The VO2-derived formula to measure Q at peak exercise was (4.4 x peak VO2) + 4.3 in the overall study cohort, (4.3 x peak VO2) + 4.5 in males and (4.9 x peak VO2) + 3.6 in females.
The simultaneous measurement of Q and VO2 at peak exercise in a large sample of healthy subjects provided an equation to predict peak Q from peak VO2 values.