Arterial stiffness is the loss of flexibility in the large arteries, especially the aorta. Healthy arteries stretch and relax with each heartbeat. As people get older, this ability becomes weaker. The elastic fibers in the artery wall break down, while stiff collagen fibers increase. As a result, the arteries become less flexible. This can raise blood pressure and increase the risk of heart attack, stroke, and kidney disease. Understanding arterial stiffness is important because it is an early sign of poor cardiovascular health [1].
Types of Arteries and Their Functions
Arteries carry blood from the heart to the rest of the body. They are not all the same. Different types of arteries have different structures and functions. In general, there are three main types of arteries: large elastic arteries, muscular arteries, and arterioles. Each type has an important role in controlling blood flow and blood pressure [2]:
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Large Elastic Arteries:
Large elastic arteries are the largest arteries in the body. The aorta is the best-known example. These arteries stretch when the heart pumps blood during systole and return to their normal size during diastole. This helps keep blood flowing smoothly, even between heartbeats.
You can think of large elastic arteries as cushions. They absorb the pressure created by each heartbeat and protect smaller blood vessels from sudden changes in blood pressure. As people get older or develop certain health conditions, these arteries become stiffer. They lose their ability to stretch and cushion blood flow. This can increase systolic blood pressure, reduce blood flow to organs, and make the heart work harder. Over time, arterial stiffness increases the risk of cardiovascular disease [3].
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Muscular Arteries:
Muscular arteries are medium-sized blood vessels that take blood from elastic arteries and deliver it to specific organs and tissues. They are also called distributing arteries. Examples include the femoral and popliteal arteries in the legs. Their main role is to control where blood goes in the body.
These arteries have a thick middle layer made of smooth muscle. This muscle allows them to change their diameter by narrowing or widening. This ability to adjust is essential for maintaining proper blood circulation and overall vascular health. In this way, they control blood flow according to the body’s needs. Compared with large elastic arteries, muscular arteries have more muscle and less elastic tissue, which makes them naturally stiffer. As a result, pulse pressure (the difference between systolic and diastolic blood pressure) is usually higher in muscular arteries than in elastic arteries [4].
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Arterioles:
Arterioles are the smallest arteries in the body. They are usually less than 100 micrometres (µm) wide and have one to three layers of smooth muscle cells. These muscles allow arterioles to become narrower (vasoconstriction) or wider (vasodilation), helping regulate blood flow to different organs and tissues.
Arterioles play a key role in controlling blood pressure. When they narrow, blood pressure increases. When they widen, blood pressure decreases. They also direct more blood to areas that need extra oxygen and nutrients, such as active muscles.
Because arterioles create most of the resistance to blood flow, they are often called resistance vessels. Their smooth muscle is controlled by the nervous system, hormones, and local chemical signals. Many medicines used to treat high blood pressure work by relaxing these muscles, allowing the arterioles to widen and reducing blood pressure [5].
Aging and Arterial Stiffness: Why Arteries Become Less Flexible
Aging is one of the strongest factors linked to arterial stiffness. Over time, changes in the artery walls can affect how well blood vessels respond to each heartbeat. These changes usually happen slowly and may begin before any symptoms appear.
The increase in arterial stiffness is not only caused by age itself. Other factors, such as high blood pressure, diabetes, smoking, and lack of physical activity, can speed up this process. These conditions place extra stress on the artery walls and may lead to earlier changes in vascular health.
Although arterial stiffness increases naturally with age, lifestyle choices can influence how quickly these changes develop. Regular exercise, a balanced diet, and good control of blood pressure can help maintain healthier arteries and reduce cardiovascular risk.
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 assessment of aortic stiffness. For smaller arteries and arterioles, the Augmentation Index (AIx) is the key parameter used to evaluate arterial stiffness and function indirectly. 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.