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Velocity patterns in and distensibility of the carotid artery bulb were studied in younger (20 to 30 years; n -1 1) and older (50 to 60 years; n 9) volunteers without detectable lesions of the cervical carotid arteries by means of a high-resolution, multigate, pulsed Doppler system coupled to a B mode imager. In the bulb the axial velocities were highest on the side of the flow divider, while regions of flow separation and recirculation were observed on the side opposite to this divider. Flow separation and recirculation were less pronounced and less common in the older subjects. Flow separation was not continuously present throughout the cardiac cycle. The distensibility of the carotid arteries was significantly diminished in older subjects, especially in the bulb. The velocity patterns in the carotid artery bulb of younger subjects corroborate the patterns observed in models. The diminished flow separation and recirculation in the older subjects might result from alterations in distensibility at the transition from common to internal carotid artery with increasing age. Circulation 71, No. 3, 500-509, 1985. IN A RECENT STUDY relating data derived from autopsy specimens to flow patterns and shear stresses as assessed in model bifurcation, . ' 2Zarins et al.3 showed that in the carotid artery bulb, maximal intimal thickening and atherosclerotic plaque formation occurred in regions of flow separation and reduced shear stress. These regions were located on the side opposite to the flow divider. Regions with predominantly axial and unidirectional flow velocities and high shear stresses, located on the side of the flow divider, were relatively devoid of these wall changes. A zone of recirculation in the carotid artery bulb opposite to the flow divider was also observed in studies performed on excised human carotid artery bifurcations.4 In these investigations flow patterns were studied under conditions of steady flow, while undistensible materials and Newtonian fluids were used, conditions quite different from the situation in vivo. Although preliminary studies in models indicate that the flow patterns in the carotid artery bulb are similar under steady and pulsaFrom the

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One hundred neurologically asymptomatic male subjects (aged 50-69 years), randomly selected through population registers, were screened for atherosclerotic lesions of the cervical carotid arteries, using a high resolution multi-gate pulsed Doppler system. In 93 subjects serum was assayed for total and HDL cholesterol. Besides, cuff arterial blood pressure measurements were made. Twenty-three of these subjects (Group III) were classified as abnormal according to the Doppler investigation (degree of narrowing less than 50% in 78% of the cases). Seven of these 23 subjects also had a history of ischemic heart disease or intermittent claudication. Of the 70 subjects with a normal Doppler examination 16 had a history of ischemic heart disease and/or intermittent claudication (Group II). The remaining 54 subjects served as controls (Group I). The frequency of asymptomatic atherosclerotic lesions of the cervical carotid arteries in the population under investigation was 23%. The HDL/total cholesterol ratio was lower and the frequency of high blood pressure higher in the Groups II and III than in Group I. The findings in this study support the idea that a low serum HDL/total cholesterol ratio and high blood pressure have a high degree of association with atherosclerotic lesions of the cervical carotid arteries. This association is already apparent at an early stage of the disease, i.e. in asymptomatic subjects with a slight to moderate degree of carotid artery narrowing.