Lack of Association Between Carotid Artery Volume Blood Flow and Cardiac Output

Objective: The correlation of cardiac output and cerebral perfusion is unclear. We tested this potential association by correlating cardiac output data obtained by echocardiography and cerebral blood flow data as determined by color M-mode measurements of carotid artery blood flow.

Methods: We studied 43 patients with a broad spectrum of cardiac performance by means of transthoracic echocardiography. In these patients, different cardiac indices such as stroke volume, ejection fraction, and heart minute volume were determined. The data were correlated with volumetric flow measurements (color M-mode duplex system) of the common carotid arteries bilaterally.

Results: Heart minute volume ranged from 1.632 to 9.836 mL/min (mean +/- SD, 4.652 +/- 1.621 mL/min); ejection fraction ranged from 18% to 76% (mean, 48% +/- 16%). The relative fraction of carotid volume flow compared with heart minute volume was 15% +/- 6%. There was no correlation between ejection fraction, stroke volume, or heart minute volume and absolute volume flow in the carotid arteries when being adjusted for age. There was a highly significant inverse correlation (r = -0.8; P < .0001) of the relative fraction of the carotid volume flow (carotid volume flow/heart minute volume [percent]) and the heart minute volume.

Conclusion: Our data support the concept that cerebral blood flow is independent of cardiac output.