Carotid artery stenosis is one of the leading cause, responsible for almost one third of all ischaemic strokes, mainly in thrombo-embolic mechanism. It is also known that impairments in cerebral blood flow and cerebrovascular reserve are associated with increased risk of ischemic events and may stratify risk of occurrence of ischaemic events in patients with hemodynamically significant internal carotid stenosis or occlusion. The aim of this study was the estimation of cerebral blood flow (CBF) and characterisation of flow pathways in Doppler ultrasonography in asymptomatic patients over 65 years old with 70-99% internal carotid artery stenosis with the aim of implementation of blood flow volume measurements in clinical assessment of such patients.

53 asymptomatic patients (36 males, 17 females) aged 65-89 years old (mean age 73,4 years old) were included in the study. In all patients an extensive Doppler ultrasound examination with the measurement of the blood flow volumes in common carotid arteries (CCAs), internal carotid arteries (ICAs), external carotid arteries (ECAs) and vertebral arteries (VAs) was performed. Flow volume in the study group was compared with the previously published flow volume values established for different age groups in the group of 123 healthy volunteers ≥65 years old.

Among the study group the three subgroups with CBF differences were identified: patients with significant volumetric flow compensation - 26/53, 49% (CBF values exceeding the proposed reference values: average + standard deviation), patients with mild compensation - 17/53, 32% (in the presence of major reduction of flow in one of carotid arteries, the increase in the other vessels allows to maintain the CBF within proposed standards) and patients with no compensation 10/53, 19% - with blood flow volume lower than proposed reference value: average - standard deviation. 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 (see Figure 1). The character of the volumetric flow compensation is multivessel. The level of compensation depends on the number of the arteries, in which the compensatory increased flow volume is present. In patients with significant volumetric flow compensation, the compensatory increased flow is observed in 2-5 arteries, on average, in 3,31 artery. In mild compensation group - in 2-4 arteries, on average, in 2,18 artery, and in no compensation group only, on average, in 1 artery (see Figure 2). 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 to 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 the 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). Figure 1. Changes in the percentage of patients with different compensatory status in the study group. Figure 2. Number of the arteries with compensatory increased flow volume. Compensatory increased flow was observed, on average, in 3,31 arteries in significant compensation group (green box), in 2,18 arteries in mild compensation group (yellow box), and in one artery in no compensation group (red box).

Three subgroups with CBF differences were identified among asymptomatic patients with 70-99% ICA stenosis. Among the asymptomatic patients with significant ICA stenosis there is a subgroup without compensatory elevation of blood flow volume. The absence of "no compensation" patients in the oldest age group may indicate the protective effect of volumetric flow compensation. The volumetric flow compensation has multivessel character and is achieved by the flow volume increase in one or more extracranial arteries.

1. Kaszczewski, P.; Elwertowski, M.; Leszczynski, J.; Ostrowski, T.; Galazka, Z. Volumetric Carotid Flow Characteristics in Doppler Ultrasonography in Healthy Population Over 65 Years Old. J. Clin. Med. 2020, 9, 1375. https://doi.org/10.3390/jcm9051375 2. Kaszczewski, P.; Elwertowski, M.; Leszczyński, J.; Ostrowski, T.; Gałązka, Z. Volumetric Flow Assessment in Doppler Ultrasonography in Risk Stratification of Patients with Internal Carotid Stenosis and Occlusion. J. Clin. Med. 2022, 11, 531. https://doi.org/10.3390/jcm11030531 3. Kaszczewski, P.; Elwertowski, M.; Leszczyński, J.; Ostrowski, T.; Kaszczewska, J.; Gałązka, Z. Intracranial Flow Volume Estimation in Patients with Internal Carotid Artery Occlusion. Diagnostics 2022, 12, 766. https://doi.org/10.3390/diagnostics12030766