There is much evidence to suggest that arterial stiffness causes hypertension, and this is supported by many studies, whether the stiffness is a result of aging of the arteries resulting in reduced or calcified elastin in the walls, increased collagen content, atherosclerosis or whether stiffness occurs due to activation of the sympathetic nervous system, causing constriction of the smooth muscle in the artery walls. It is thought that arterial stiffness increases blood pressure, because with a decrease in compliance of the arterial walls, a pressure wave is created that moves faster than, and therefore ahead of, the main pulse wave of the blood. This pressure wave reaches the heart whilst it is still in systole, adding to the systolic pressure.
There are many environmental and social factors that, by different mechanisms, cause arterial stiffness leading to hypertension. These include obesity, which is believed to activate the sympathetic nervous system due to the excess circulating leptin and smoking which causes wall stiffening through inflammation and atherosclerosis. In addition, the consumption of large amounts of alcohol is a risk factor for the development of arterial stiffness, leading to increased blood pressure. However, the Rotterdam study gives results to suggest that the opposite is in fact true, and that hypertension results in stiffening of the arteries, due to the high pressure stimulating a number of mechanisms in the vessel walls.
Results from the Framingham study also appear to partly support this theory, as it suggests that the relationship between stiffening of arteries and hypertension is cyclical, and one can exacerbate the other. However, there are a large number of other causes of hypertension aside from arterial stiffness. A significant cause has been shown to be an imbalance in the renin-angiotensin-aldosterone system (RAAS) which can either cause an increase in activation of the sympathetic nervous system (and hence support the theory of arterial stiffness being a cause of hypertension) or can cause an increase of sodium in the blood and therefore volume of blood.
The Guyton theory of hypertension states that the only way for blood pressure to be permanently elevated is due to a dysfunction in the kidneys resulting in a shift in the pressure-natreuresis curve and therefore is not related to the stiffness of the arteries at all. The imbalance in the RAAS which leads to the curve shift, could be as a result of conditions such as Cushing’s disease or chronic kidney disease, both of which cause salt retention in the blood and therefore an increase in blood volume leading to increased blood pressure.
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