Functional Correlates of Central Arterial Geometric Phenotypes

Abstract

We have assessed the functional correlates of common carotid artery (CCA) arterial geometry, derived by combining a measure of vascular mass (VM) with the wall-to-lumen (W/L) ratio in both untreated hypertensive (HT) and normotensive (NT; blood pressure <140/90 mm Hg) subjects of a broad age span (30 to 79 years) of both genders. Brachial systolic, diastolic, and pulse (SBP, DBP, PP) pressures; CCA SBP and PP; CCA diameter (D); intima-media thickness (IMT); relative distensibility; circumferential wall stress (MBP×W/L); fluid shear stress (FSS); strain; augmentation index (AGIh); and aortic pulse wave velocity (PWV) were measured in 680 NT and 635 untreated HT Taiwanese men and women. Carotid geometric phenotypes (CGPs) were derived from ultrasonographic measures of VM and W/L ratio. A normal CGP (CGP1) was defined as that within the 95th NT percentile of age- and gender-specific VM and W/L means. Three “deviant” CGPs were defined as follows: CGP2 or remodeling, ie, a normal VM coupled with an increased W/L; CGP3 or hypertrophy, ie, an increase in both VM and W/L; and CGP4 or hypertrophy with dilation, ie, an increased VM with normal W/L. The prevalence of specific CGPs in the total sample was 83.4% for CGP1, 5.5% for CGP2, 2.2% for CGP3, and 8.9% for CGP4. Compared with CGP1, all deviant CGPs had increased carotid resistance, had higher CCA circumferential wall stress, and varied in blood flow velocity. Compared with CGP1, CGP2 subjects were more likely to be women (69.3% versus 45.9%), were on average 10 years older, and had similar central and brachial BP levels, PWV, and AGIh but had increased strain, higher distensibility, lower flow, and a higher FSS. CGP3 subjects did not differ in age or gender but had a higher prevalence of HT; higher circumferential stress, PWV, and distensibility; and lower flow, as well as a trend toward higher SBP, PP, and AGIh and lower FSS. CGP4 subjects did not differ in age or gender but exhibited higher AGIh and aortic PWV, lower distensibility and FSS, and unchanged strain and flow. CGP4 was the only deviant CGP in which the average brachial or central arterial pressures were significantly increased. CGP4 subjects also had the highest prevalence of HT among all the CGPs (77.8% versus 45% in CGP1). CGPs exhibit some common mechanical or functional properties but each also exhibits a unique profile. Although differing quantitatively in NT and HT and at young and older age, the characteristic functional profile of a given CGP is preserved, regardless of age or BP status. A normal CGP is characterized by a low circumferential wall stress and high FSS. Each deviant CGP is characterized by a unique combination of increased circumferential wall stress, with variable FSS, strain, distensibility, central BP, and late pressure augmentation. The interplay among these factors, particularly circumferential wall and FSS, likely determines the CGP; conversely, the resultant CGP may modulate the FSS and wall stress for a given pressure and flow.