Reproducibility of Inert Gas Rebreathing Method to Estimate Cardiac Output at Rest and During Cardiopulmonary Exercise Stress Testing

The present study evaluated reproducibility of the inert gas rebreathing method to estimate cardiac output at rest and during cardiopulmonary exercise testing. Thirteen healthy subjects (10 males, 3 females, ages 23-32 years) performed maximal graded cardiopulmonary exercise stress test using a cycle ergometer on 2 occasions (Test 1 and Test 2). Participants cycled at 30-watts/3-min increments until peak exercise. Hemodynamic variables were assessed at rest and during different exercise intensities (i. e., 60, 120, 150, 180 watts) using an inert gas rebreathing technique. Cardiac output and stroke volume were not significantly different between the 2 tests at rest 7.4 (1.6) vs. 7.1 (1.2) liters min-1, p=0.54; 114 (28) vs. 108 (15) ml beat-1, p=0.63) and all stages of exercise. There was a significant positive relationship between Test 1 and Test 2 cardiac outputs when data obtained at rest and during exercise were combined (r=0.95, p<0.01 with coefficient of variation of 6.0%), at rest (r=0.90, p<0.01 with coefficient of variation of 5.1%), and during exercise (r=0.89, p<0.01 with coefficient of variation 3.3%). The mean difference and upper and lower limits of agreement between repeated measures of cardiac output at rest and peak exercise were 0.4 (-1.1 to 1.8) liter min-1 and 0.5 (-2.3 to 3.3) liter min-1, respectively. The inert gas rebreathing method demonstrates an acceptable level of test-retest reproducibility for estimating cardiac output at rest and during cardiopulmonary exercise testing at higher metabolic demands.