What is the Vascular Resistance: Systemic, Pulmonary and Peripheral

Deifnition:

Vascular resistance describes the degree to which the blood vessels of the cardiovascular system – the arteries, capillaries and veins – affect the blood flow of the various organs of the body.

The main characteristics that determine the amount of resistance are the diameter, the length of the vessels and the viscosity or thickness of the blood. Of these three factors, the diameter of the vessel is the most significant.

Vasoconstriction, which is the constriction or narrowing of the diameter of the blood vessels, increases vascular resistance in the same way that the tap nozzle restricts and increases the pressure of water flowing through a tube or hose.

There are three types of vascular resistance: systemic vascular resistance, pulmonary vascular resistance and peripheral pulmonary resistance.

Systemic Vascular Resistance

It is the resistance that blood “sees” as it travels through the body’s circulatory system. It is controlled by three different factors: blood vessel length (l), blood vessel radius (r), and blood viscosity (η). The equation that relates these three factors to the resistance is known as the Poiseuilles equation:
R ≈ (η x L) / R4

The systemic vascular resistance is influenced by the length and radius of the blood vessels, as well as the viscosity of the blood. It is calculated from mean arterial pressure, central venous pressure, and cardiac output.

Systemic vascular resistance plays a vital role in maintaining blood pressure within the established ranges so that organ perfusion is maximized.

Pulmonary Vascular Resistance

It occurs when the pulmonary artery creates resistance against the blood that flows in it from the right ventricle. Resistance is, naturally, created by the disposition of the blood vessels of the lungs and is healthy at low levels.

The problem of pulmonary vascular resistance is created when there is an increase in the amount or viscosity of blood flow to the pulmonary artery and therefore an increase in resistance.

The heart, when healthy, functions as a system for pumping and filtering blood. The deoxygenated blood used enters the right atrium of the inferior and superior vena cava and flows into the right ventricle.

The right ventricle contracts and pumps blood into the pulmonary artery, which carries blood to the heart for filtration and oxygenation. This new blood flows into the left atrium and then into the left ventricle, forcing blood to flow into the aorta and the rest of the body.

There is a certain natural resistance to the blood flow created by gravity, particularly when the veins and arteries flow upward at a vertical angle. The contractions of the ventricles of the heart normally provide enough force for enough blood to flow despite the resistance.

Pulmonary vascular resistance is a particular type of resistance created by the vasculature, or the arrangement of blood vessels in the lungs. The heart faces this resistance in the pulmonary artery, where blood enters the lungs for filtration.

The most common cause of pulmonary vascular resistance are circulatory problems. Changes in blood viscosity, which may be caused by a change in the hematocrit, will affect the level of resistance in the pulmonary vessels.

Another factor that affects resistance is arterioles, which can expand and contract to a limited degree in order to increase or reduce blood flow.

When communication between the left and right sides of the heart is interrupted, usually due to circulatory problems, blood will flow to the area of ​​least resistance. This often results in an increase in blood flow to the pulmonary artery.

The increase in blood flow creates an increase in pulmonary vascular resistance. If left untreated, the increased resistance can cause permanent damage to the blood vessels of the lungs.

Pulmonary vascular resistance is quite difficult to detect, since it involves the internal functioning of the heart and lung cavities. Scientists are working on non-invasive methods to detect this disorder.

One of these methods that has been subjected to limited testing is echocardiographic evaluation. This method is effective in detecting low levels of vascular resistance, but is not as effective when dealing with higher levels.

Total Peripheral Resistance

Total peripheral resistance (RPT) is the amount of resistance to the flow of blood present in the body’s vascular system. It can be considered as the amount of work force against the heart, since it expels blood in the vascular system.

Although total peripheral resistance plays an integral role in determining blood pressure, it is a measure defined exclusively by the cardiovascular system and should not be confused with the pressure against arterial walls, which is a measure of blood pressure.

The vascular system, which is responsible for the flow of blood to and from the heart, can be divided into two components: systemic and pulmonary.

The pulmonary system carries blood to and from the lungs, where it is oxygenated, and the systemic vasculature is responsible for transporting this blood to the cells of the body through the arteries and returning blood to the heart after perfusion.

The total peripheral resistance is calculated by using a specific equation. This equation is RPT = change in the pressure / cardiac output.

Change in pressure is the difference in mean arterial pressure and venous pressure. The mean arterial pressure is equal to the diastolic blood pressure, more than a third of the difference between the systolic and diastolic pressure.