Arterial stiffness refers to the decreased flexibility of the walls of large arteries, such as the aorta. Normally, these arteries can stretch and relax easily, but due to various factors, such as aging, they lose this ability. This occurs because the special fibers that help the arteries stay stretchy (called elastin) break down, and tougher fibers (called collagen) build up instead. When arteries become stiffer, it can lead to higher blood pressure and increase the risk of other health problems, such as kidney disease and strokes. Therefore, understanding arterial stiffness is important because it is linked to various cardiovascular diseases [1].
Understanding the Arterial System: Structure and Function
The arteries in the body can be divided into three main types based on their structure and function [2]:
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Large Elastic Arteries:
The first type includes large elastic arteries, such as the aorta. These arteries play a vital role in storing blood that is pumped from the heart during its contraction phase (systole) and releasing it steadily during the resting phase (diastole). This function ensures that blood flows smoothly to different parts of the body, even when the pressure changes during the heart’s pumping cycles.
In simple terms, large elastic arteries act like cushions, absorbing pressure changes and reducing the strength of blood flow. This helps protect smaller blood vessels from harmful changes in pressure. However, as people get older or due to certain health issues, these large arteries can become stiff. When this happens, they can’t cushion the blood flow as effectively, leading to problems like high systolic blood pressure and damage to organs. Stiff large arteries also affect how the heart works with the blood vessels, which can cause heart problems [3].
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Muscular Arteries:
The second type consists of muscular arteries, especially those found in the legs, like the femoral and popliteal arteries. These arteries have the ability to change their size, which helps control the speed of blood flow. This ability to adjust is essential for maintaining proper blood circulation and overall vascular health.
Muscular arteries have relatively stiff walls compared to elastic arteries. As a result, the pulse pressure, which is the difference between the systolic and diastolic blood pressure, tends to be wider in muscular arteries than in elastic arteries [4].
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Arterioles:
The third type is arterioles, which are the smallest types of arteries in the body. They are usually less than 100 micrometers wide (which is very small). Arterioles have one to three layers of smooth muscle cells around them. hey can change their diameter, which allows them to control how much blood reaches different tissues and organs. By narrowing, arterioles increase blood pressure, while widening decreases it. They also direct blood to areas that need more oxygen and nutrients, such as active muscles, and play a key role in preparing blood for capillaries, where the exchange of nutrients and waste occurs.
The muscle fibers in arterioles are usually a little tight. This tightness helps blood flow smoothly. It also makes the inside space (called the lumen) of the arterioles smaller, about 30 micrometers wide. This smaller size creates most of the resistance to blood flow in the body, so we often call arterioles “resistance vessels” because they help control blood pressure. The size of the lumen can change; it can get smaller (called vasoconstriction) or larger (called vasodilation). These changes are controlled by signals from the nervous system, hormones, and local chemicals, which help manage how blood flows in the body [5].
In other words, blood flow resistance is mainly controlled by the tightness of smooth muscles in the arterioles. These muscles are the target of many medications that help lower high blood pressure.
How to measure Arterial stiffness
In fact, it’s not practical to measure arterial stiffness directly. Instead, doctors have developed indirect methods to assess the stiffness of the aorta and other arteries.
To measure the stiffness of the aorta, physicians typically use a non-invasive method called pulse wave velocity (PWV), which provides an indirect assessment of aortic stiffness. For smaller arteries and arterioles, the Augmentation Index (AIx) is the key parameter used to evaluate arterial stiffness and function. Both measures help assess vascular health and cardiovascular risk.
The Arteriograph, a novel and gold-standard device, is capable of measuring both pulse wave velocity (PWV) and the Augmentation Index (AIx). In addition to these, it can measure 12 different parameters, providing a comprehensive overview of the cardiovascular system. This allows for a detailed assessment of arterial stiffness across various categories and levels, making it a valuable tool for evaluating vascular health.