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 (VO(2)) 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: VO(2) max was 51+/-11 ml/min/kg in the adolescent cross country skiers (CI 8.2+/-1.2 l/min/m(2)) and 50+/-12 ml/min/kg in adult soccer referees (CI 7.1+/-1.2 l/min/m(2)). CW Doppler hemodynamic variables showed significant correlation with VO(2) (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 (VO(2) max). The regression equation for VO(2) and CO(USCOM) was VO(2)=4.43CO(USCOM)-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.