What do arteries do?
The arteries are blood vessels that deliver oxygen and vital nutrients to all the vital organs and peripheries in the body. The heart pumps blood through these vessels and with each pulse blood flows to distal circulation.
With the conversion of each pulse into adequate circulation, a system is developed. At each systole (beat of the heart), the heart squeezes to pump out blood. At each diastole (the time between two beats) the heart gets time to fill up with blood.
Pulse pressure and arterial stiffness
The pressure exerted on the walls of the blood vessels or arteries during the systole is lowest if the blood vessels are of high compliance or low stiffness. Thus people who have elastic and highly compliant arterial walls have a narrow pulse pressure.
Pulse pressure is the systolic pressure minus the diastolic pressure. This reflects low aortic wall tension. Low wall tension also means that the workload of the heart is low.
The stiffer and harder the blood vessel walls, the wider the pulse pressure and more the heart has to work to pump blood into the arteries. In persons with stiffer arterial walls only a small fraction of each cardiac stroke volume can be utilized for blood circulation without increasing the blood pressure.
Thus to compensate for the lack of blood in the peripheries the blood pressure rises. These persons thus have relatively high systolic and pulse pressures and a low diastolic pressure.
What determines wall stiffness?
The arterial wall stiffness depends on the structural elements within the arterial wall for example muscle, elastin and collagen. These bear the pressure on the wall when the wall is distended.
Impedance to flow is the relationship between varying pressure and the flow it generates. It includes:-
- resistance to flow
- energy stored during elastic distention
- energy used to accelerate the blood column
In the circulatory system there are several sites where there is obstruction resistance or impedance. This includes arterial branch points, places where there is stagnation of flow, and areas where the lumen diameter moves from large to small or vice versa.
Every pulse generates a compression wave that comes from the contraction of the heart. These compression waves of pressure and associated velocity are detected by Doppler analysis. These waves travel faster than the velocity of the column of blood. When it encounters an impedance the pressure wave rebounds back to some extent.
Diagnosis and implications of arterial stiffness
Doppler analysis can determine the rate and amount of blood flow. Arterial stiffness indicates two major terms - arteriosclerosis and atheromatosis. These are often combined to atherosclerosis.
Arteriosclerosis is a generalized thickening and stiffening of the arterial wall and is related to high blood pressure or hypertension.
Atheromatosis is an inflammatory arterial change that leads to dysfunction of the endothelial walls and excessive deposition of lipids or fats in the walls.
The two processes often coexist leading to arterial fibrosis or atherosclerosis.