Non-invasive ultrasonic cardiac output monitoring in exercise testing

Background The purpose of this study was to evaluate the relationship of breath-by-breath oxygen uptake (VO2) and CO, cardiac index (CI), stroke volume (SV) and heart rate (HR) determined by a non-invasive continuous wave (CW) Doppler-based system (USCOM) in healthy adolescent and adult athletes during exercise treadmill testing. Methods Twenty athletes were enrolled for a standardized ramp treadmill test including transthoracic echocardiography at rest, incremental breath-by-breath spiroergometry, lactate kinetics and CW Doppler. Results VO2 max was 51 ± 11 ml/min/kg in the adolescent cross country skiers (CI 8.2 ± 1.2 l/min/m2) and 50 ± 12 ml/min/kg in adult soccer referees (CI 7.1 ± 1.2 l/min/m2). CW Doppler hemodynamic variables showed significant correlation with VO2 (p < 0.01, n = 95) across the total of measures, with excellent correlation demonstrated for CO and CI (0.904 and 0.897), while HR and SV showed good to very good correlation with r values of 0.842 and 0.766, respectively. Correlation of the variables at peak exercise and 1 and 3 min after recovery, demonstrate that CO and SV show superior correlation with peak oxygen consumption (VO2 max). The regression equation for VO2 and COUSCOM was VO2 = 4.43COUSCOM–10.3. Conclusion CW Doppler measurement of cardiac output is feasible as a measure of cardiac performance during standardized treadmill testing in adolescent and adult athletes.