Cigarette Smoking And The Risk Of Stroke

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Heavy smoking (>20 cigarettes/day) increases both the incidence [37-41] and mortality from stroke [40,41], Cigarette smoking is a major modifiable risk factor for subarachnoid hemorrhage [42-48], In contrast, evidence concerning the role of tobacco in the risk of intracerebral hemorrhage is still controversial, yet it appears that heavy, but not light-to-moderate cigarette smoking, increases the risk [9,38,49,50], Smoking is dose-dependantly associated with the risk of ischemic stroke [38,46], Cessation of smoking reduces stroke risk [37,39], with major reduction within 2-5 years after cessation [37,39,46], indicating that part of the effects of smoking is reversible. The risk of stroke seems to return to the level of never-smokers in light smokers, but heavy smokers seem to retain an increased risk even though also they benefit from cessation [37], There are several mechanisms by which smoking may cause stroke. Cigarette smoking causes an immediate, yet reversible increases in blood pressure [42,51-55] and cerebral blood flow [56], In epidemiologic studies, however, it has consistently been associated with reduced blood pressure in normotensive people [18,52,5760], although blood pressure has been elevated in diabetic [61] and hypertensive smokers [62], and cerebral blood flow has been decreased in chronic smokers [40] compared with respective nonsmokers. It is not plausible that smoking decreases blood pressure, but smokers may initially have lower blood pressure than those who remain nonsmokers [63], They may also have a reduced 'white coat effect', which would lead to artificially low measurements of blood pressure in clinics [59], There is no evidence that smoking causes hypertension, but in heavy smokers the rise in blood pressure may persist during waking hours because of frequent smoking factually causing a hypertensive state [55], Even though smoking may not be causally related to hypertension, it clearly modifies the effect of hypertension on stroke [40,51] and other cardiovascular risks [64] which are much higher in hypertensive than normotensive smokers. Cigarette smoking is associated with reduced levels of serum HDL cholesterol [18,20,51,57, 58,60,65,66] and increased levels of serum triglycerides [18,57,65-67], It increases platelet activity [51,53,68,69], plasma fibrinogen levels [27,51,57], hematocrit [57,65], and blood viscosity [57], It is also associated with endothelial dysfunction [57,70,71], Cigarette smoking increases the risks of carotid stenosis [72,73] and diabetes [36], which both are risk factors for ischemic stroke.

Tobacco smoke has over 4000 compounds, the effects of which are mostly unknown [51], Many of the effects of smoking are attributed to nicotine, which increases systolic and diastolic blood pressure and heart rate in a dose-response manner [74,75], Despite these hemodynamic effects, nicotine does not appear to enhance thrombosis [75,76], and the mechanism by which smoking is related to thrombogenesis is unclear. Besides nicotine, carbonmonoxide is a potential mediator of the effects of tobacco smoke on cardiovascular diseases [51,77], It may injure the vascular endothelium [77] and thus promote atherogenesis. The causal role of smoking in the development of atherosclerosis is plausible but so far unproven.

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