Volumetric Flow Assessment in Extracranial Arteries in Patients with 70-99% Internal Carotid Artery Stenosis

Background: Cerebral blood flow (CBF) can be related to the risk of occurrence of neurological symptoms. Well-developed collateral circulation is a good prognostic factor in patients with cerebrovascular disease. Understanding the mechanisms of collateral circulation may be important in the diagnosis, treatment, and monitoring in this group of patients. The aim of this study covered the assessment of CBF in patients with 70-99% Internal carotid artery (ICA) stenosis, focusing on the circulation pathways and flow volume in extracranial arteries. Materials and methods: 53 patients with 70-99% ICA stenosis (mean age 73.4 +/- 7 years old; 17 female, mean age 73.9 +/- 7.5 years old; 36 male, mean age 73.2 +/- 6.8 years old) were included in the study. In all patients a Doppler ultrasound (DUS) examination, measuring blood flow volume in the internal carotid artery (ICA), external carotid artery (ECA), and vertebral artery (VA), was performed. The cerebral blood flow (CBF) was compared to the previously reported CBF values in the healthy population > 65 years old. Results: Among the study groups three subgroups with flow differences were identified: patients with elevated CBF (significant volumetric flow compensation-26/53, 49%), patients with CBF similar to (mild compensation-17/53, 32%), and patients with CBF lower than (no compensation-10/53, 19%) the healthy, equally aged population. The percentage of patients with significant volumetric flow compensation was the highest in age groups 65-69 years old (62.5%) and >80 years old (60%). In the oldest age group (>80 years old) no patients without flow compensation (0%) were observed. The level of compensation depends on the number of the arteries with compensatory increased flow. In patients with significant volumetric flow compensation, the compensatory increased flow was observed, on average, in 3.31 arteries, in the mild compensation group-in 2.18 arteries, and in the no compensation group only in 1 artery. ICA plays the most important role in the volumetric flow compensation-the increase in the flow volume, in comparison to the reference values, was between 116.7 mL/min and 251.9 mL/min (in the ECA 57.6 mL/min-110.4 mL/min; in the VA 73.9 mL/min-104.9 mL/min). The relative flow increase was highest in the VA: 215-246%, then in the ECA: 163-206%, and finally in the ICA: 148.6-192%. The increased flow was most commonly observed in the VA-57 arteries, in second place in the ECA-42 arteries, and ICA-31 arteries. In patients with unilateral ICA stenosis, the volumetric flow increase was stated more frequently in the ipsilateral ECAs then in the contralateral ones (23 vs. 14). In the VA the opposite tendency was observed (29 contralateral vs. 23 ipsilateral). The ability of volumetric flow compensation decreased significantly with increasing age. Conclusions: Understanding the mechanisms of collateral circulation and their assessment in Doppler ultrasonography may provide a novel and easily accessible tool of identifying and monitoring patients with cerebrovascular disease.