Aortic flow velocity indices during upright exercise: reliability and relationship to cardiac output

To determine the intra- and interobserver reproducibility of Doppler-derived ascending aortic flow velocity measurements at rest and during upright exercise of increasing intensity; and to determine the relationship between Doppler-derived measurements and cardiac output obtained by the indirect Fick carbon dioxide rebreathing method in the same conditions.

Twenty young healthy adults participated in the study; eight participated in the first part and 12 in the second.

For the intra-observer study, subjects were submitted to three workloads (50, 100 and 150 W) of 5 mins duration on two occasions, seven days apart. The intra-observer reproducibility was determined by two technicians taking the Doppler measurements within 90 s during the steady state of each workload during the first session. The relationship between cardiac output and aortic flow velocities was studied by measuring cardiac output by carbon dioxide rebreathing and flow velocities by continuous wave Doppler ultrasound simultaneously at rest as well as during the last minute of the three workloads (50, 100 and 150 W) of 5 mins duration.

The interobserver reproducibility was very good, with r values of 0.87 for peak velocity (PV) and 0.97 for peak acceleration (PA). The intra-observer reproducibility at the seventh day interval showed r values of 0.93 for PV and 0.96 for PA for one of the technicians. PV and PA of the ascending aortic flow correlated well with cardiac output (r = 0.85 and 0.82, respectively, P < 0.01). ANOVA showed that PV and PA increase proportionately with exercise intensity.

PV and PA of ascending aortic flow are reproducible and reflect changes in left ventricular function during exercise.