Qp/Qs Ratio Calculator

Helps evaluate atrial or ventricular septal defects by revealing right to left, respectively left to right shunts.

Refer to the text below the tool for more information about the formulas used and the result interpretation.


The Qp/Qs ratio, also known as the pulmonary-systemic shunt ratio, can be determined via the left and right ventricular outflow tract diameters and left and right subvalvular velocity time integral measurements from the 2-D echo and spectral Doppler investigations.

This ratio is useful in the evaluation of patients with atrial or ventricular septal defects.


  • Qp = RVOT VTI x π x (RVOT/2)2
  • Qs = LVOT VTI x π x (LVOT/2)2
  • Qp/Qs ratio = Qp / Qs

LVOT
LVOT VTI
RVOT
RVOT VTI
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Qp/Qs Ratio Explained

The Qp/Qs ratio, also known as the pulmonary-systemic shunt ratio, can be determined via the left and right ventricular outflow tract diameters and left and right subvalvular velocity time integral measurements from the 2-D echo and spectral Doppler investigations.

This ratio is useful in the evaluation of patients with atrial or ventricular septal defects and is based on the following formulas:

  • Qp = RVOT VTI x π x (RVOT/2)2
  • Qs = LVOT VTI x π x (LVOT/2)2
  • Qp/Qs ratio = Qp / Qs

Where:

  • RVOT = Right ventricular outflow tract diameter
  • RVOT VTI = RVOT subvalvular velocity time integral
  • LVOT = Left ventricular outflow tract diameter
  • LVOT VTI = LVOT subvalvular velocity time integral

The Qp/Qs ratio is a non-invasive method for measuring systemic and pulmonary blood flow. High correlations were found between Fick- and Doppler-derived indexed measurements of systemic and pulmonary flow as well as the pulmonary to systemic flow ratio. This can be used in the initial and serial evaluation of adult and pediatric patients presenting with intracardiac shunts.

 

Pulmonary-Systemic Shunt Ratio

Normal cardiac anatomy allows the septal separation of oxygenated and deoxygenation blood with the pulmonary and systemic circulations running in parallel, feeding one another. In healthy patients, a 1 to 1 volume relationship is maintained between the two. The pulmonary blood flow (Qp) pumps to the lungs the systemic venous return. The oxygenated blood is pumped as the systemic blood flow (Qs), which is also referred to as cardiac output.

A cardiac shunt defines an abnormal connection that allows blood to flow directly from one of the two circulations to the other. In consequence, depending on its direction, a shunt can be of two types and its severity depends on the volume of shunted blood:

Cardiac shunt Qp/Qs ratio Description Effect
Right to left shunt Qp/Qs <1.0 Allows the deoxygenated, systemic venous return to bypass the lungs and return to the body. Increased strain on ventricles.
Tissue oxygen delivery is reduced.
The work capacity of the muscles is limited.
Left to right shunt Qp/Qs >1.0 Allows the oxygenated, pulmonary venous blood to return directly to the lungs rather than be pumped in the systemic circulation.
 

References

Sanders SP, Yeager S, Williams RG. Measurement of systemic and pulmonary blood flow and QP/QS ratio using Doppler and two-dimensional echocardiography. Am J Cardiol. 1983; 51(6):952-956.

Okamoto M, Miyatake K, Kinoshita N, et al. Noninvasive determination of the ratio of pulmonary to systemic blood flow with two-dimensional Doppler echocardiography: efficacy and limitation. J Cardiogr. 1984; 14(1):189-200.

Saner H, Lawrence C, Olson J. Berechnung von intrakardialen Shunts mittels Doppler-Echokardiographie [Calculation of intracardiac shunt using Doppler echocardiography]. Z Kardiol. 1987; 76(11):677-681.


Specialty: Cardiology

System: Cardiovascular

Abbreviation: Qp/Qs

Article By: Denise Nedea

Published On: July 15, 2020

Last Checked: July 15, 2020

Next Review: July 15, 2025