Abstract
Background and Purpose— To explore relationships among gender, body size, neck size, and the diameters of the common carotid artery (CCA) and internal carotid artery (ICA).
Methods— Using multivariate regression, the best predictors of sonographic diameters of CCA and ICA were determined based on age, height, weight, body mass index, body surface area, neck circumference, neck length, and blood pressure.
Results— Measurements were obtained in 500 consecutive patients (age 52±15 years; 61% women). Mean diameters of ICA (4.66±0.78 mm) and CCA (6.10±0.80 mm) in women were significantly smaller than in men: 5.11±0.87 mm and 6.52±0.98 mm, respectively. Sex significantly influenced the diameters after controlling for body size, neck size, age, and blood pressure.
Conclusions— Carotid arteries are smaller in women even after adjusting for body and neck size, age, and blood pressure.
Women appear to be at higher risk of early complications associated with carotid endarterectomy (CEA) and lower risk of stroke for any degree of stenosis compared with men.1–4 This may negate the potential benefit of carotid intervention in women, particularly in the setting of an asymptomatic stenosis.1,4
Body size may confound the effect of gender in carotid surgery because the procedure may be more difficult in smaller patients who may have proportionally smaller arteries.1,2,5 Smaller patients also likely have shorter necks, which may limit surgical access to the arteries. This study explored relationships among sex, body size, neck size, and the diameters of carotid arteries.
Patients and Methods
Patients were eligible if they gave informed consent and underwent routine cerebral angiographic and neurosonographic examinations for the purpose of a larger trial comparing the 2 methods. The institutional review board approved the study protocol. A total of 306 women and 194 men (mean 52±15 years; range 14 to 103) were prospectively studied over 17 months. Clinical history about atherosclerotic risk factors was obtained from the patient or medical record.
Sonography of Carotid Arteries
Four experienced investigators performed carotid ultrasound examinations using a 7.5-MHz probe (Aplio 80; Toshiba Medical System). On longitudinal high-resolution harmonic gray-scale images, internal diameters were measured at the most distal plaque-free portion of the internal carotid artery (ICA) above the carotid bulb and at the common carotid artery (CCA) &15 to 20 mm below the bifurcation.6
Clinical Measurements
Height and weight were obtained from the medical record or patient interview. Body mass index (BMI) and body surface area (BSA) were calculated as: BMI=weight/height2 and BSA (m2)=0.20247× height (m)0.7256×weight (kg)0.425. Neck circumference was measured midway between the sternoclavicular notch and the jaw, whereas neck length was measured bilaterally from the sternoclavicular notch to the mastoid process and averaged between sides.
Heart rate (HR), cuff systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean blood pressure (MBP) were measured using an automated sphygmomanometer.
Statistical Analysis
Normal distribution of data were verified by the probability plot method. Measurements from both sides were compared using a paired 2-sided t test and averaged. Sex differences were analyzed with nonpaired 2-sided t test. Effects of body and neck size on diameters of ICA or CCA were determined using univariate and multivariate linear regression analysis and these variables, adjusting for blood pressure, heart rate, and age. The relationships between diameters and clinical parameters were derived by maximizing the F statistic in multivariate regression models (SYSTAT for Windows [Microsoft]; SYSTAT). This method simultaneously incorporates multiple variables, and the model with the maximum F statistic best fits the existing data. A P value <0.05 indicated statistical significance.
Results
Women had lower values of height, weight, BSA, neck circumference, and neck length as well as slightly lower mean blood pressure and diastolic blood pressure than men (Table 1). Diameters of the ICA and CCA were significantly greater in men than in women (Table 1). The right CCA (6.15±0.91) was slightly larger than the left (6.05±0.87; P<0.05) in women, but there was no side-to-side difference of the CCA in men. There were no side-to-side differences in the ICA diameter. Carotid diameters increased with male sex, height, weight, BMI, BSA, neck circumference, and blood pressure, predominantly with SBP (Table 2).
TABLE 1. Baseline Characteristics of the Studied Population
TABLE 2. Effect of Age, Sex, Height, Weight, BMI, BSA, Neck Size, Blood Pressure, and Heart Rate on Diameters of Carotid Arteries
The relationships between ICA and CCA diameters and the clinical parameters were derived as follows (both models F=13; R2=0.17; P<0.001): ICA diameter (mm)=0.449 (sex, male=1)+0.813(BSA, 0.1 m2)−0.113 (neck length, cm)+0.003(age, years)+0.007 (SBP, mm Hg)+4.36 mm and CCA diameter (mm)=0.26 (sex, male=1)+1.21(BSA, 0.1 m2)−0.05 (neck length, cm)+0.003 (age, years)+0.004 (SBP, mm Hg)+0.789 mm.
Discussion
This study demonstrates that carotid arteries are smaller in women, even after adjusting for body and neck size, age, and blood pressure. An association between sex and carotid artery diameter has been reported previously,7–12 but these studies did not investigate combined effects of these potential confounders. In contrast to previous reports,8–10,12 no significant relationships between carotid artery size and age were found, most likely because of the relatively young patient population in our study. As expected, carotid artery diameter was influenced by blood pressure.
CCA diameter was related to body height and weight independent of sex.9–12 However, blood pressure, which is usually lower in women, was not controlled for in most studies.7,8 Moreover, BMI was the body size parameter that was most often controlled for,11,12 whereas BSA, height, and neck size appeared to better predict carotid artery diameter in our patients, presumably because BMI is a marker for nutritional and conditioning status.
The relationships between neck size and carotid size have not been explored previously. Neck circumference was found to be a stronger predictor of carotid artery diameter than neck length; however, only the latter was included in our regression models because of weaker correlation with BSA.
It has been reported that body size contributes to the risk of CEA,5 suggesting that greater surgical risk may be attributable in part to smaller patient size. This study demonstrates that women have smaller carotid arteries even after adjusting for body size. This finding may further explain the gender gap in the natural history and treatment of carotid artery disease. Further analyses are needed in CEA or stenting studies to more directly address the issue of whether women have higher complication rates related to reduced arterial diameter.
Acknowledgments
This work was supported by American Heart Association established investigator award grant 044099N to J.K. We express our thanks to Dr Oleg Bronov for his help with diagnostic studies.
- Received December 13, 2005.
- Accepted December 21, 2005.
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