According to BMI, subjects were classified into:

a.         Normal (BMI:20-25): Included 41 subjects (40.6%).

b.        Underweight (BMI <20): Included 4 subjects (3.96 %).

c.         Overweight (BMI: 25-30): Included 26 subjects (25.7%).

d.        Obese (BMI>30): Included 30 subjects (29.7%).

2.        Laboratory tests: including: CBC, Lipid profile (serum triglycerides and cholesterol levels), Kidney function tests (urea, creatinine), Liver function tests (AST, ALT, albumin, bilirubin, ALP).

3.        Measurement of Carotid Intima Media Thickness:

a.         Carotid ultrasonography was performed for all included subjects, at the Neurovascular ultrasonographic laboratory of Kasr Al-Aini Neurology Department, Cairo University Hospitals, using Phillips HDI 5000 ultrasound equipment.

b.         Subjects lie supine with the neck extended in mild lateral rotation. Examination of the extra-cranial carotid artery (ECCA) was done bilaterally in the longitudinal and transverse views. Obtained 4 images were recorded and each image of carotid IMT was recalled with magnification and measured.

c.         IMT measurement (Figure 1):  The IMT of the posterior (or far) wall of the distal CCA is measured as the distance from the leading edge of the first echogenic line (lumen-intima interface) to the leading edge of the second line (media-adventitia interface).¹¹ Two readings of IMT of the CCA proximal to the carotid bifurcation are obtained bilaterally. The CCA1 and CCA2 are points located 0 to 1 cm and 1 to 2 cm, respectively, on the CCA proximal to the carotid bifurcation. IMT is measured at these two points bilaterally.¹² CCA IMT is a double-line observed by ultrasonography in a longitudinal view. The carotid plaque is a focal structure encroaching upon the arterial lumen of at least 0.5 mm or 50% of the surrounding IMT, or an intima-media complex thickness > 1.5 mm.¹³

Figure 1. Doppler ultrasonographic image of the Lt. CCA of a female subject, measuring the IMT on the far wall, 2 cm proximal to the carotid bifurcation.

Statistical Methods

The collected data were coded and entered using the statistical package SPSS version 15. The data were summarized using descriptive statistics: mean, standard deviation, minimal and maximum values for quantitative variables and number and percentage for qualitative values. Statistical differences between groups were tested using Chi Square test for qualitative variables, one way and two way ANOVA (analysis of variance) with multiple comparison post Hoc test for quantitative normally distributed variables and Nonparametric Mann Whitney test and Kruskal Wallis test for not normally distributed quantitative variables. Pearson Correlation Coefficient was done to test for linear relations between variables. Linear and multivariate regression analyses were done to test for significant predictors for IMT. P-values less than or equal to 0.05 were considered statistically significant, P-values less than 0.01 were considered highly significant.

RESULTS

The characteristics of study population are shown in Table (1). A statistically high significant difference was observed between age groups as regards right, left and average CIMT,  (p = 0.000 for all) with increasing IMT with age. A highly significant positive correlation was detected between mean age and Right, Left, and average CIMT, (p= 0.000 for all). A statistically high significant difference was also observed between age groups as regards mean BMI, total cholesterol and triglycerides levels, (p=0.006, 0.005, 0.001 respectively).

A statistically highly significant difference was observed between female and male participants as regards mean Right, Left, and average carotid IMT, (p= 0.006, 0.004, 0.003 respectively) being significantly thinner in females. No significant difference was detected between female and male subjects as regards mean age, BMI, serum cholesterol or triglycerides. (p < 0.05) (Table 2).

A statistically significant difference was observed between subjects of different BMI as regards mean age, being significantly lower in the underweight and normal weight groups compared to overweight and obese subjects, (p=0.011). A statistically significant positive correlation was detected between age of the study subjects and BMI, (p= 0.016). Otherwise, no significant differences were detected between subjects of different BMI groups as regards mean cholesterol, triglycerides or carotid IMT (p>0.05) (Table 3). Moreover, no significant correlation was found  between BMI and serum cholesterol, triglycerides, Right, Left or average CIMT (p>0.05).

A statistically significant difference was found between non- smoker group and both ex-smoker and smoker groups as regards the mean Left CIMT (p= 0.018, 0.038 respectively). However no significant difference was found between the ex- and current smokers groups as regards the Lt. CIMT (p= 0.869). Also, a statistically significant difference was found between non-smoker and ex-smoker groups as regards the mean average CIMT, (p= 0.036) (Table 4). No significant correlation was detected between number of cigarettes per day and BMI, cholesterol, TG, Right, Left or average CIMT, (P>0.05).

A statistically high significant positive correlation was found between duration of smoking  and Right, Left and average CIMT, (p= 0.000 for all), however, no significant correlation was detected between smoking duration and mean BMI, cholesterol or TG levels, (P>0.05) (Table 5).

Linear regression analysis was done to find significant predictors for CIMT in both males and females. Age, BMI and smoking status were entered in the regression model, only age was found to be the significant predictor for CIMT in both males and females. The higher the age, the more the CIMT, (p= 0.000). In males smoking is also about to be a significant predictor of CIMT, (p= 0.07).

By testing age, sex and smoking as independent variables affecting carotid IMT, it was found that age, smoking and interaction of age with smoking were found to be the only independent factors (p=0.000, 0.043, 0.04 respectively).

Table 1. Characteristics of study population (n=101).

SD standard deviation

Table 2. Comparison of different variables among male and female subjects.

** Statistically highly significant at p<0.01

Table 3. Comparison of mean age, cholesterol, TG and CIMT between subject groups distributed according to BMI.

* Statistically significant at p<0.05.

Table 4. Comparison of mean age, BMI, cholesterol, TG and CIMT between subject groups distributed according to smoking data.

** Statistically highly significant at p<0.01

Table 5. Correlation of CIMT with age, BMI, smoking data, cholesterol and TG levels in the study population.

r: Pearson’s correlation

* Statistically significant at p<0.05     ** Statistically highly significant at p<0.01

DISCUSSION

An increased carotid IMT has been associated with a number of atherosclerosis risk factors and the incidence of new coronary and cerebral vascular events.^14,15

Our results showed a highly significant positive correlation between carotid IMT and age, a finding that agreed with many previous studies.^16-18 Tosetto et al.¹⁹ showed a constant increase over age, an effect present both in male and in females. Juonala et al.²⁰ also found a highly significant correlation between carotid IMT and age, however the association between age and IMT was slightly attenuated after adjustment with other risk factors and vessel diameter, but remained significant, (P<0.001). Aging is associated with geometrical modifications of both large elastic and medium sized muscular arteries, independent of blood pressure changes. Furthermore, enlargement of arterial diameter and thickening of the arterial wall have opposite effects on the functional parameters of these arteries. An alteration in elastic properties is observed for the carotid artery, but functional properties are preserved in the radial artery²¹.

Results of our study showed a statistically significant difference between female and male participants as regards mean carotid IMT, where females had a thinner carotid IMT when compared to males. This agreed with the results of Stensland-Bugge et al.²² and Takato et al.²³, Tan et al.¹⁸ investigated gender differences associated with a thinner intima-media thickness (IMT) of the common carotid artery (CCA) in more than 200 healthy volunteer women. They concluded that, traditional vascular risk factors explain only a small amount of variance in multivariate regression models supporting the hypothesis that other behavioral, sex hormone-related or genetic factors, which have not been sufficiently explored so far, may play a role in the gender differences of IMT.

The present study showed a significant positive correlation between mean age and mean BMI, mean total cholesterol, TG and carotid IMT. An increase in intensity of some atherogenic risk factors with aging might suggest that the latter represents the interval of time necessary for atherogenic noxae to act. However, even in the absence of recognized risk factors, aging induces intrinsic changes in the arterial wall, in particular progressive intimal thickening²⁴. Supporting this finding, we found that age was the only significant predictor for carotid IMT in both males and females.

In our study, overweight and obese groups showed significantly higher carotid IMT compared to normal and underweight subjects. This finding agreed with Kotsis et al.²⁵, who found that the mean IMT was significantly higher in obese subjects compared with normal ones. Freedman et al.²⁶ in the Bogalusa Heart Study found that high IMT levels were seen only among obese adults (BMI ≥ 30 kg/m2) who used to be overweight children (BMI ≥ 95th percentile). In the present study, no significant correlation was detected between the mean BMI of the study group and mean carotid IMT. On the contrary, several studies showed significant positive correlation between BMI and measures of carotid IMT^16,27-29. This controversy may be attributed to difference in subject selection.

In this study, the mean serum triglycerides and cholesterol were not significantly higher in overweight and obese subjects compared to normal and underweight subjects. However, Ozdemir et al.³⁰ showed that blood levels of triglycerides and cholesterol were significantly higher in the overweight group than in normal weight group. A highly significant positive correlation was detected between mean plasma total triglycerides and mean carotid IMT in our study population, which agreed with the results of Fox et al.¹⁶, who showed that mean serum TG level was significantly positively correlated with IMT measures (p<0.05). Tan et al.¹⁸ also found similar results, as they showed a highly significant positive correlation between serum TG level and mean carotid IMT, (p = 0.003). Labreuche et al.³¹ performed a systematic review of literature for epidemiological studies that examined the association of TG level with carotid IMT. Eleven studies reported a significant positive correlation between CIMT and triglyceride levels. This difference in results may be due to normal serum TG and cholesterol levels in all of our subjects.

In our study, a statistically highly significant difference was found between non-smokers, ex-smokers and current smokers as regards mean carotid IMT being significantly thinner in the non-smoker group. Moreover, a statistically highly significant positive correlation was found between smoking duration and mean carotid IMT, (p=0.000). A significant positive correlation emerged in our study between duration of smoking and mean carotid IMT. The relationship between increased CIMT and smoking in the Atherosclerosis Risk in Communities (ARIC)³² study showed significant progression of atherosclerosis after 3 years of follow-up, which was related to lifetime pack-years of cigarette smoking. The authors theorized that the effects of smoking are cumulative and irreversible. Liang et al.⁹ showed that current smokers had the highest mean CCA-IMT, followed by former smokers, whereas never smokers had the lowest for both men and women, after adjustment for other cardiovascular risk factors. CCA-IMT increased significantly as the pack-years of smoking increased in men and women (p<0.05). Unlike the ARIC study and Liang et al. studies^9,32 our results showed no significant correlation between lifetime pack-years of cigarette smoking and mean carotid IMT. In the ARIC study³² studied population included 16,000 individuals, mixed races both black and white, and their ages ranging from 45–64 years, while Liang et al.⁹ studied an Asian Chinese population.

In Conclusion; In normal Egyptian subjects; age was a significant predictor for CIMT in both males and females. Smoking duration was also a significant predictor of CIMT In males. Interaction of age with smoking were found to be the significant independent factor for increased CIMT.

[Disclosure: Authors report no conflict of interest]

REFERENCES

1.      Hodis HN, Mack WJ, LaBree L, Selzer RH, Liu CR, Liu CH, et al. The role of carotid arterial intima-media thickness in predicting clinical coronary events. Ann Intern Med. 1998; 128(4): 262-9.

2.      Bots ML, Hoes AW, Koudstaal PJ, Hofman A, Grobbee DE. Common carotid intima-media thickness and risk of stroke and myocardial infarction: the Rotterdam Study. Circulation. 1997; 96(5): 1432-7.

3.      Bots ML, Hofman A, Grobbee DE. Increased common carotid intima-media thickness. Adaptive response or a reflection of atherosclerosis? Findings from the Rotterdam Study. Stroke. 1997; 28(12): 2442-7.

4.      Chambless LE, Folsom AR, Davis V, Sharrett R, Heiss G, Sorlie P, et al. Risk factors for progression of common carotid atherosclerosis: the Atherosclerosis Risk in Communities Study, 1987-1998. Am J Epidemiol. 2002; 155(1): 38-47.

5.      Salonen JT, Salonen R. Ultrasound B-mode imaging in observational studies of atherosclerotic progression. Circulation. 1993; 87(3 Suppl): II56-65.

6.      Karason K, Wikstrand J, Sjöström L, Wendelhag I. Weight loss and progression of early atherosclerosis in the carotid artery: a four-year controlled study of obese subjects. Int J Obes Relat Metab Disord. 1999; 23(9): 948-56.

7.      Howard G, Wagenknecht LE, Burke GL, Diez-Roux A, Evans GW, McGovern P, et al. Cigarette smoking and progression of atherosclerosis: The Atherosclerosis Risk in Communities (ARIC) Study. JAMA. 1998; 279(2): 119-24.

8.      Salonen R, Salonen JT. Progression of carotid atherosclerosis and its determinants: a population-based ultrasonography study. Atherosclerosis. 1990; 81(1): 33-40.

9.      Liang LR, Wong ND, Shi P, Zhao LC, Wu LX, Xie GQ, et al. Cross-sectional and longitudinal association of cigarette smoking with carotid atherosclerosis in Chinese adults. Prev Med. 2009; 49(1): 62-7.

10.    Romero-Corral A, Somers VK, Sierra-Johnson J, Thomas RJ, Collazo-Clavell ML, Korinek J, et al. Accuracy of body mass index in diagnosing obesity in the adult general population. Int J Obes (Lond). 2008; 32(6): 959-66.

11.    Pignoli P, Tremoli E, Poli A, Oreste P, Paoletti R. Intimal plus medial thickness of the arterial wall: a direct measurement with ultrasound imaging. Circulation. 1986; 74(6): 1399-406.

12.    Su T-C, Jeng J-S, Hwang B-S, Liau C-S. Application of Intima-media Thickness and Early Atherosclerosis at Carotid Arteries as a Window for Cardiovascular Diseases in Preventive Cardiology. Journal of Medical Ultrasound. 2007; 15(2): 112-25.

13.    Touboul PJ, Hennerici MG, Meairs S, Adams H, Amarenco P, Bornstein N, et al. Mannheim carotid intima-media thickness consensus (2004-2006). An update on behalf of the Advisory Board of the 3rd and 4th Watching the Risk Symposium, 13th and 15th European Stroke Conferences, Mannheim, Germany, 2004, and Brussels, Belgium, 2006. Cerebrovasc Dis. 2007; 23(1): 75-80.

14.    Stein JH, Korcarz CE, Hurst RT, Lonn E, Kendall CB, Mohler ER, et al. Use of carotid ultrasound to identify subclinical vascular disease and evaluate cardiovascular disease risk: a consensus statement from the American Society of Echocardiography Carotid Intima-Media Thickness Task Force. Endorsed by the Society for Vascular Medicine. J Am Soc Echocardiogr. 2008; 21(2): 93-111; quiz 89-90.

15.    Sharma K, Blaha MJ, Blumenthal RS, Musunuru K. Clinical and research applications of carotid intima-media thickness. Am J Cardiol. 2009; 103(9): 1316-20.

16.    Fox CS, Polak JF, Chazaro I, Cupples A, Wolf PA, D'Agostino RA, et al. Genetic and environmental contributions to atherosclerosis phenotypes in men and women: heritability of carotid intima-media thickness in the Framingham Heart Study. Stroke. 2003; 34(2): 397-401.

17.    Bauer M, Möhlenkamp S, Lehmann N, Schmermund A, Roggenbuck U, Moebus S, et al. The effect of age and risk factors on coronary and carotid artery atherosclerotic burden in males-Results of the Heinz Nixdorf Recall Study. Atherosclerosis. 2009;205(2):595-602.

18.    Tan TY, Lu CH, Lin TK, Liou CW, Chuang YC, Schminke U. Factors associated with gender difference in the intima-media thickness of the common carotid artery. Clin Radiol. 2009; 64(11): 1097-103.

19.    Tosetto A, Prati P, Baracchini C, Manara R, Rodeghiero F. Age-adjusted reference limits for carotid intima-media thickness as better indicator of vascular risk: population-based estimates from the VITA project. J Thromb Haemost. 2005; 3(6): 1224-30.

20.    Juonala M, Kähönen M, Laitinen T, Hutri-Kähönen N, Jokinen E, Taittonen L, et al. Effect of age and sex on carotid intima-media thickness, elasticity and brachial endothelial function in healthy adults: the cardiovascular risk in Young Finns Study. Eur Heart J. 2008; 29(9): 1198-206.

21.    Bortolotto LA, Hanon O, Franconi G, Boutouyrie P, Legrain S, Girerd X. The aging process modifies the distensibility of elastic but not muscular arteries. Hypertension. 1999; 34(4 Pt 2): 889-92.

22.    Stensland-Bugge E, Bønaa KH, Joakimsen O. Age and sex differences in the relationship between inherited and lifestyle risk factors and subclinical carotid atherosclerosis: the Tromsø study. Atherosclerosis. 2001; 154(2): 437-48.

23.    Takato T, Yamada N, Ashida T. Effects of aging and sex on progression of carotid intima-media thickness: a retrospective 6-year follow-up study. Geriatr Gerontol Int. 2008; 8(3): 172-9.

24.    Spagnoli LG, Mauriello A, Orlandi A, Sangiorgi G, Bonanno E. Age-related changes affecting atherosclerotic risk. Potential for pharmacological intervention. Drugs Aging. 1996; 8(4): 275-98.

25.    Kotsis VT, Stabouli SV, Papamichael CM, Zakopoulos NA. Impact of obesity in intima media thickness of carotid arteries. Obesity (Silver Spring). 2006; 14(10): 1708-15.

26.    Freedman DS, Dietz WH, Tang R, Mensah GA, Bond MG, Urbina EM, et al. The relation of obesity throughout life to carotid intima-media thickness in adulthood: the Bogalusa Heart Study. Int J Obes Relat Metab Disord. 2004; 28(1): 159-66.

27.    Ciccone M, Vettor R, Pannacciulli N, Minenna A, Bellacicco M, Rizzon P, et al. Plasma leptin is independently associated with the intima-media thickness of the common carotid artery. Int J Obes Relat Metab Disord. 2001; 25(6): 805-10.

28.    Lo J, Dolan SE, Kanter JR, Hemphill LC, Connelly JM, Lees RS, et al. Effects of obesity, body composition, and adiponectin on carotid intima-media thickness in healthy women. J Clin Endocrinol Metab. 2006; 91(5): 1677-82.

29.    Ozguven I, Ersoy B, Ozguven A, Ozkol M, Onur E. Factors affecting carotid intima media thickness predicts early atherosclerosis in overweight and obese adolescents. Obesity Research & Clinical Practice. 2010; 4(1): e41-e8.

30.    Ozdemir H, Artaş H, Serhatlioğlu S, Oğur E. Effects of overweight on luminal diameter, flow velocity and intima-media thickness of carotid arteries. Diagn Interv Radiol. 2006; 12(3): 142-6.

31.    Labreuche J, Touboul PJ, Amarenco P. Plasma triglyceride levels and risk of stroke and carotid atherosclerosis: a systematic review of the epidemiological studies. Atherosclerosis. 2009; 203(2): 331-45.

32.    Howard G, Burke GL, Szklo M, Tell GS, Eckfeldt J, Evans G, et al. Active and passive smoking are associated with increased carotid wall thickness. The Atherosclerosis Risk in Communities Study. Arch Intern Med. 1994; 154(11): 1277-82.