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)2Qs = LVOT VTI x π x (LVOT/2)2Qp/Qs ratio = Qp / Qs
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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)2Qs = LVOT VTI x π x (LVOT/2)2Qp/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 · 12:00 AM
Last Checked: July 15, 2020
Next Review: July 15, 2025