A new angle-independent doppler ultrasonic device for assessment of blood flow volume in the extracranial internal carotid artery

Objective. To evaluate a new angle-independent ultrasonic device for assessment of blood flow volume in the internal carotid artery. Methods. In vitro, a pulsatile pump was set to provide an outflow of physiological fluid at 500 mL/min through an 8-mm-diameter tube. Flow volume rates were measured 10 times by 10 different operators and compared with time-collected flow volume rates. In vivo, internal and common carotid artery blood flow volumes were measured in 28 volunteers by 2 operators using a FlowGuard device (Biosonix Ltd). Internal and common carotid artery diameters and blood flow volumes were also assessed by Duplex sonography and compared with FlowGuard measurements. In 10 volunteers, internal carotid artery blood flow volume changes in response to monitored breath manipulations were recorded. Results. In vitro, intraoperator variability was 4.04% (range, 2%-5.7%). The mean error rate ± SD was 3.54% ± 0.8% (range, 2.7%-5.2%). In vivo, the mean common carotid artery blood flow volume was 456 ± 39 mL/min (range, 417-583 mL/min) with a mean diameter of 6.7 ± 0.7 mm (range, 5.8-8.7 mm). The mean internal carotid artery blood flow volume was 277 ± 25 mL/min (range, 239-338 mL/min) with a mean diameter of 5 ± 0.5 mm (range, 4.1-6.1 mm). No significant difference was found between operators. Internal carotid artery diameter and blood flow volume measured by the FlowGuard were closely correlated with the results of Duplex sonography. Repeated shifts of end-tidal CO₂ induced reproducible changes in internal carotid artery flow volume: 187.5 ± 18.1 mL/min at 26.8 ± 1.9 mm Hg and 382.1 ± 18.2 mL/min at 47 ± 2.2 mm Hg. Conclusions. The FlowGuard showed that volume flow studies in the internal carotid artery could be easily performed, with results compatible with those of previous clinical reports. Duplex comparative results and breath-induced changes in internal carotid artery flow volume justify further evaluation of the system.