The arterial distensibility is one of the physical properties of the arteries and expresses its ability to expand and contract to volume changes presented by variations in blood pressure.
All blood vessels, veins and arteries are compliant, however, this characteristic is not the same in all vessels, since it is affected according to the volume handled by each one. Thus, the values of this parameter are different in glasses of small caliber or other larger ones.
Cardiovascular problems affect the compliance of the blood vessels, making them more rigid at times, therefore it is considered a risk marker in patients with this type of disease.
The measurement of arterial compliance is a widely used method to determine the degree of cardiovascular disease and the response to treatment. Additionally, it can aid in the early diagnosis of conditions such as high blood pressure.
One of the most used ways to measure arterial compliance is through the calculation of the speed of the transit wave , which determines the time it takes for the pulse wave to travel from one artery to another.
Its value lies in the fact that it is a non-invasive method and has great predictive value for cardiovascular disease.
Compliance and blood pressure
Compliance is a property of blood vessels that allows them to expand according to the amount of blood that passes through them. This process is mediated by blood pressure.
In arteries, compliance is less than in veins, since the elasticity of the veins is 8 times greater, so they can increase in diameter to a greater degree.
The mathematical formula to calculate arterial compliance expresses the fraction of blood volume for each millimeter of mercury (mmHg) of blood pressure, as follows:
DA = volume / BP mmHg
Clarify that in the equation DA = arterial compliance and BP = blood pressure.
Compliance will be altered by varying any of the parameters used for its measurement. The higher the blood pressure, for example, the lower the compliance.
Measurement of arterial compliance
An advantage of measuring this value over other methods is that it can be done in a non-invasive way. It can be done directly, through ultrasound, or indirectly with nuclear magnetic resonance or by measuring the speed of the transit wave.
Ultrasound evaluation can be used to assess arterial compliance. Measurement in large arteries such as the abdominal or femoral aorta is preferred.
To perform the measurement, the doctor must look for the image where the arterial wall is best observed and start recording for a few minutes.
The video is analyzed to find the moment of greatest and least expansion of the studied vessel and with these values the compliance is calculated from a mathematical formula that includes the blood pressure value.
Despite the fact that ultrasound has the advantage of being a non-invasive method, the result depends on the doctor who is conducting the study. In other words, the reliability of the final value is conditioned on the experience of the doctor who performed it.
Nuclear Magnetic Resonance (NMR)
MRI calculates the degree of arterial stiffness quite accurately by measuring the vascular diameter. The most commonly studied artery is the abdominal aorta.
Its main disadvantage is that it is a costly study that requires qualified personnel to handle the equipment and interpret the results.
Traffic wave speed
The easiest and most widely used way to measure arterial compliance is done by calculating a parameter called the speed of the traffic wave . This is about uA wave of vibration originated by the contraction of the heart or systole, when pumping the blood.
The time it takes for this wave to travel through the arterial system is known as the speed of the transit wave. What is done is to measure the transit time of the pulse between two points of the arterial vascular tree. This time is inversely proportional to the compliance of the artery, that is, the calculation is done indirectly.
The speed of the transit wave is directly related to arterial stiffness, which is the absence of changes in expansion of an artery in relation to blood flow due to multiple reasons, including atherosclerosis and arterial hypertension.
The most widely used method is tonometry, which is performed with a device called a tonometer . The arteries to study are chosen, the ones most frequently used are the carotid and femoral, with the patient lying on his back. Two tonometers are positioned, one in each artery and these automatically record the speed of passage and express it in milliseconds.
Factors that alter arterial compliance
The expansion of the arteries before the blood volume is a phenomenon that occurs due to the elastin content in the structure of its wall.
When elastin decreases and the amount of collagen in the vascular wall increases, compliance is decreased.
Compliance is one of the first parameters to be altered in patients with high blood pressure and other diseases with cardiovascular repercussions, such as diabetes.
Physiologically, age is one of the main causes of elastin loss and decreased distension capacity.
Conversely, aerobic exercise improves elasticity and, as a consequence, the compliance of blood vessels.
In hypertensive patients, the compliance of the arteries is increased. This is due to increased arterial stiffness and arteriosclerotic changes that promote loss of elasticity of the blood vessel.
Arterial compliance is a parameter that can help diagnose hypertension in its early stages.
In addition, it is a predictive factor of cardiovascular disease since its decrease is associated with other diseases, such as obesity and hypertriglyceridemia, which alter the normal functioning of the circulatory system.
Proper treatment of high blood pressure and other cardiovascular diseases improves arterial compliance. Therefore, knowing this value, the patient’s response to the treatment administered can be evidenced.
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