Today, calculators make many things easier. No more hours of torture to check that the calculation is correct. Nowadays, we enter everything we need for the count into the calculator, getting the correct answer. If you want to calculate the Qp / Qs ratio very quickly, our calculator will help you with that. Learn about heart shunts, what they are, the causes and consequences, and how to calculate the Qp / Qs ratio.

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The circulatory system

The circulatory system consists of a series of organs that orchestrate the passage of blood through all tissues, allowing the transport of various materials such as nutrients, oxygen, carbon dioxide, and hormones. It consists of the heart, veins, arteries and capillaries.

Its primary function lies in the transport of materials. However, it also participates in creating a stable environment for vital functions.

To clarify, the circulatory systems can be open – in most invertebrates – they consist of one or more hearts, a space called a hemocele and a network of blood vessels or closed — in some invertebrates and in all vertebrates — where blood is confined to the blood vessels and the heart.

In the animal kingdom, the circulatory systems are very diverse. Depending on the animal group, the relative importance of the organs that make it up changes.

For example, the heart is decisive in the circulation process in vertebrates. While in arthropods and other invertebrates, limb movements are necessary.

The circulatory system is primarily responsible for transporting oxygen and carbon dioxide between the lungs and body tissues.
Also, the circulatory system is responsible for distributing all the nutrients processed by the digestive system to all body tissues. It serves as a transport pathway for hormones secreted by the glands and distributes them to the organs they must act. On the other hand, it participates in: thermoregulation of organisms, proper blood flow adjustment, body pH regulation, and maintenance of appropriate hydro-electrolyte balance to carry out the necessary chemical processes.

What is a shunt in the heart?

A shunt is a transfusion of blood from one circulation to another.

Namely, blood, like any other fluid, goes from the higher pressure system to the lower pressure system.

The blood passes from the pulmonary circulation to the systemic (right-left shunt). In the case of a right-left shunt, venous blood goes to the arterial system, reducing the saturation of arterial blood with oxygen, which is manifested by the appearance of cyanosis. Cyanosis is bluish skin and visible mucous membranes. Depending on the size of the shunt and the systemic volume of blood, cyanosis can be of varying degrees:

  • from barely noticeable, mild,
  • to extremely severe, in which the arterial blood oxygen saturation can be as high as 50%.

If the blood passes from the systemic circulation to the lungs (left-right shunt), there is recirculation of blood through the lungs. There is no cyanosis. The arterial blood goes to the venous system, but the right ventricle loading with additional blood volume.

Humans Heart
Humans Heart

Causes of cardic shunts

Most importantly, there are two types of heart shunt: congenital heart shunt and acquired heart shunt.

Congenital heart defects (CHD) – The most common CHDs caused by a heart shunt are atrial septal defects (ASD), open foramen ovale (PFO), ventricular septal defects (VSD), and open ductus arteriosus (PDA).

The acquired shunt also has its division:

  • Biological: Some acquired shunts are modifications of congenital ones. A balloon septostomy can enlarge a foramen ovale (if performed on a newborn), PFO or ASD; or prostaglandin can be administered to a newborn to prevent the ductus arteriosus from closing.
  • Mechanical shunts such as the Blalock-Taussig shunt are used in some CHD cases to control blood flow or blood pressure.

What is Qp/Qs? The Qp/Qs formula

Q = Blood Flow
P = Pulmonary
S = Systemic
Qp = Pulmonary flow
Qs = Systemic flow

The ratio of total pulmonary blood flow to total systemic blood flow, the Qp/Qs ratio, helps quantify the net shunt.

A Qp/Qs ratio of 1:1 is normal and usually indicates that there is no shunting.
Qp: Qs describes the magnitude of a cardiovascular shunt

Normally = 1:1
Left to right shunts >1.0
Right to left shunts <1.0

RVOT – Right ventricular output diameter;
RVOT VTI – RVOT subvalvular velocity time integral;
LVOT – Left ventricular output diameter;
LVOT VTI – LVOT subvalvular velocity time integral; and
π – Pi, a constant that is approximately equal to 3.14
Qp = RVOT VTI * π * (RVOT / 2) ^{2}
Qs = LVOT VTI * π * (LVOT / 2) ^{2}

How to use the Qp/Qs calculator?

Using our calculator is easy.

First, enter the RVOT, RVOT VTI, LVOT, and LVOT VTI values in the input section.

(For meanings of these values see previous paragraph.)

How to calculate Qp/Qs?

Have you heard of a method of echocardiography, such as Doppler echocardiography?
An echocardiogram uses high-frequency sound waves to create an image of the heart.
Doppler ultrasound is a non-invasive test that can be used to assess blood flow through your blood vessels by repelling high-frequency sound waves (ultrasound) from circulating red blood cells. Regular ultrasound uses sound waves to produce images but cannot show blood flow.

Qp/Qs values

The value of a shunt (Qp/Qs) is the ratio of the pulmonary blood flow to the systemic blood flow.

Qp = HR x SVp; Qs = HR x SVs

In conclusion, we can calculate it using echocardiography or catheterisation based on the flow or stroke volume ratio through the pulmonary artery and the aorta.

Pulmonary – Systemic Shunt Ratio

It is crucial to know that the volume ratio in healthy patients is maintained 1 to 1.

This is because pulmonary blood flow (Qp) pumps systemic venous return to the lungs. In addition, oxygen-enriched blood is pumped as systemic blood flow (Qs), called the cardiac output.
The shunt can be of two types, and its weight depends on the blood volume of the shunt:

Cardiac shuntQp/Qs ratioDescriptionEffect
Right to left shuntQp/Qs <1.0Allows the deoxygenated, systemic venous return to bypass the lungs and return to the body. Increased strain on ventricles.
Reduced Oxygen Delivery to Tissue
The work capacity of the muscles is limited.
Left to right shuntQp/Qs >1.0Allows the oxygenated, pulmonary venous blood to return directly to the lungs instead of being pumped in the systemic circulation.Increased strain on ventricles.
Reduced Oxygen Delivery to Tissue
The work capacity of the muscles is limited.