EFFECTS OF SMOKING AND HYPERTENSION ON CAROTID ARTERY GEOMETRY AND FUNCTION: EVIDENCE OF LAPLACE'S LAW IN VIVO.

Liane Y-L¹*, Shiel L². Teede H¹,- Branley P² , Kotsopoulos D¹, MeNeil J^2, Cameron J ³ , McGrath BP ¹

Monash University Departments of Medicine¹, Epidemiology and Preventive Medicine²  and Biomedical Engineering, La Trobe University³ Melbourne, Australia.

Objective: Parameters of carotid arterial wall thickness and function are increasingly being used as surrogate makers of cardiovascular disease, but in vivo structure-function-pressure relationships have not been well defined. In this study we examined the cross-sectional relationships between arterial structure, function and blood pressure in the subjects aged 49 to 80 years to determine the impacts of smoking status and hypertension.

Design and Methods: The study involved 679 subjects, 372 smokers (190 males, 182 females) and 307 non-smokers (110 males, 197 females), aged 49-82 years. Blood samples were taken for total cholesterol. Central blood pressure was interpolated from Dinamap brachial diastolic and mean BP. A Diasonic DRF400 ultrasound machine and custom software was used to determine carotid intima-rnedia thickness (IMT), lumen diameter (D_L), and stiffness index (S1). Circumferential stress (CS) was calculated according to Laplace law. All indices of arterial geometry and function were adjusted for age and height.

Results: Hypertension (HT: treated and/or screening BP > 140/90) was present in 71 non-smokers (HT_ns) and 186 smokers (HT_S). Total cholesterol showed no significant differences in any subgroup. Age was the key determination of all parameters of arterial structure and function. Age-and height-adjusted IMT and wall:lumen ratio increased with pulse pressure (r=0.388 and r=0.294, p<0.001). Hypertension and smoking were associated with significant increases in adjusted IMT (mean+SD: NT_NS 0.66±0.13; NT_S 0.72±0.14- HT_NS  O.76±0.16; HT_S 0.80±0.17mm), D_L (NT_NS 5.51±0.79; NT_S 6.08+0.98; HT_NS 6.06+1.07; HT_S 6.59±0.96mm), and SI (NT_NS 4.4±2.0; NT_S 5.6±2.3; HT_NS 5.6±2.5 HT_S 6.0±2.7), whilst CS was increased in hypertensives but not in smokers.

Conclusions: In an older population both hypertension and smoking were associated with increased carotid wall thickness and stiffness, whereas circumferential stress was related to hypertension but not to smoking. Laplace law may be the best explanation of the sequential changes in arterial geometry and function during hypertension and aging.

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