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Abstract:
The purpose of this work was to evaluate ultrasound modality as a non-invasive tool for determination of impact of the degree of the atherosclerotic plaque located in human internal carotid arteries on the values of the parameters of the pulse wave. Specifically, the applicability of the method to such arteries as brachial, common, and internal carotid was examined. The method developed is based on analysis of two characteristic parameters: the value of the mean reflection coefficient modulus |Γ|a of the blood pressure wave and time delay Δt between the forward (travelling) and backward (reflected) blood pressure waves. The blood pressure wave was determined from ultrasound measurements of the artery’s inner (internal) diameter, using the custom made wall tracking system (WTS) operating at 6.75 MHz. Clinical data were obtained from the carotid arteries measurements of 70 human subjects. These included the control group of 30 healthy individuals along with the patients diagnosed with the stenosis of the internal carotid artery (ICA) ranging from 20% to 99% or with the ICA occlusion. The results indicate that with increasing level of stenosis of the ICA the value of the mean reflection coefficient measured in the common carotid artery, significantly increases from |Γ|a = 0.45 for healthy individuals to |Γ|a = 0.61 for patients with stenosis level of 90–99%, or ICA occlusion. Similarly, the time delay Δt decreases from 52 ms to 25 ms for the respective groups. The method described holds promise that it might be clinically useful as a non-invasive tool for localization of distal severe artery narrowing, which can assist in identifying early stages of atherosclerosis especially in regions, which are inaccessible for the ultrasound probe (e.g. carotid sinus or middle cerebral artery).

Keywords:
Pulse wave, Ultrasound, Vascular impedance, Stenosis

Abstract:
The input vascular impedance was determined using ultrasound continuous wave Doppler flow meter and a system for tracking arterial wall movements. The study was conducted in a control group (30 volunteers) and in four groups (10 patients in each group). Patients were grouped according to the criteria ofatherosclerotic stage, which was the degree of arterial stenosis: 20–49%, 50–69%, 70–89%, and 90–99% and occlusion, based on ultrasound or duplex tests. The results of Student's t-test showed the statistically significance of the sparation of longitudinal resistance Ro results from the control group and sequentially four groups with a defined degree of atherosclerotic carotid artery at a 95% confidence level with significance level from p < 5.2E−3 for 20–49% - for the receiver operating curve (ROC), the area under curve (AUC) = 0.76; p < 8.6E−9 for the stenosis 50-69% - for the ROC curve AUC = 0.913, p < 6.3E−9 for the stenosis 70–89% for ROC curve AUC = 0.94, to p < 8.1E−10 for stenosis above 90% and occlusion, for ROC curve AUC = 0.97. After combining data for patients with internal carotid artery stenosis from 50–89% the results of Student's t-test showed the statistical significance of the separation of the longitudinal resistance results Ro derived from the control group and the combined group with a confidence level of 95% at significance level p < 2.8E−10, for ROC curve AUC = 0.942.

Keywords:
Vascular input impedance, common carotid artery, ultrasound.