Pulmonary Vascular Resistance
Calculate pulmonary vascular resistance (PVR) from mean pulmonary artery pressure, wedge pressure, and cardiac output. Enter values from right heart catheterization to get PVR in dyn·s/cm⁵ or Wood units.
Estimate Pulmonary Vascular Resistance
Pulmonary Vascular Resistance Formula
Where:
- \(\text{PAP}\) — mean pulmonary artery pressure (mmHg)
- \(\text{PCWP}\) — mean pulmonary capillary wedge (PAW) pressure (mmHg)
- \(\text{CO}\) — cardiac output (L/min)
- \(\text{PVR}\) — pulmonary vascular resistance (dyn·s/cm⁵)
The difference between the mean pulmonary artery pressure and the wedge pressure is the pressure drop across the pulmonary vasculature; dividing it by the cardiac output gives the resistance to flow. The factor 80 converts the result from Wood units (mmHg·min/L) into dyn·s/cm⁵.
Pulmonary Vascular Resistance – Calculation Example
Example: a patient undergoing right heart catheterization has a mean pulmonary artery pressure of 25 mmHg, a wedge pressure of 10 mmHg, and a cardiac output of 5 L/min.
\[ \text{PVR} = \frac{80 \times (25 - 10)}{5} = \frac{80 \times 15}{5} = 240 \ \text{dyn·s/cm}^5 \]
\[ 240 \div 80 = 3 \ \text{Wood units} \]
Result: PVR = 240 dyn·s/cm⁵, or 3 Wood units — a value at the upper boundary of normal, suggesting elevated pulmonary vascular resistance.
How to Use the Calculator
- Enter the Mean PA pressure (mPAP) in mmHg, measured during right heart catheterization.
- Enter the Mean PAW pressure — the pulmonary capillary wedge pressure (PCWP) — in mmHg.
- Enter the Cardiac output in L/min, obtained by thermodilution or the Fick method.
- Read the Pulmonary vascular resistance in dyn·s/cm⁵. Divide by 80 if you need the value in Wood units.
What Is Pulmonary Vascular Resistance?
Pulmonary vascular resistance (PVR) is the resistance that the pulmonary blood vessels offer to blood flow from the right ventricle to the left atrium. It is a key hemodynamic parameter in the evaluation of pulmonary hypertension and right ventricular function. Because the pulmonary circulation is a low-pressure system, even moderate increases in PVR significantly raise the afterload on the right ventricle, which over time can lead to right ventricular hypertrophy, dilation, and failure.
PVR cannot be measured directly; it is derived from measurements obtained during right heart catheterization. The driving pressure across the pulmonary vasculature is the difference between the mean pulmonary artery pressure and the pulmonary capillary wedge pressure (a surrogate for left atrial pressure). Dividing this driving pressure by the cardiac output yields the resistance, in accordance with a simplified form of Ohm's law applied to the circulation.
Results are reported either in dyn·s/cm⁵ or in Wood units (WU), where 1 WU = 80 dyn·s/cm⁵. Wood units are often preferred at the bedside because the numbers are small and intuitive. A normal PVR is below 2 WU (below 160 dyn·s/cm⁵). Values of 3 WU or more indicate elevated pulmonary vascular resistance and, in patients with elevated wedge pressure, help distinguish combined post-capillary and pre-capillary pulmonary hypertension from isolated post-capillary disease.
PVR is also used to assess operability in congenital heart disease, to monitor response to pulmonary vasodilator therapy, and to evaluate candidates for heart or lung transplantation. If you do not have a measured cardiac output, you can estimate it first with our Cardiac Output (Fick Method) calculator; the right ventricle's pumping performance can then be assessed with the Right Ventricular Stroke Work Index calculator.
Assumptions, Limitations and Practical Tips
- Invasive measurements required: mPAP, PCWP, and cardiac output all come from right heart catheterization. Non-invasive estimates of PVR are less accurate and should not replace invasive assessment when clinical decisions depend on it.
- Accuracy of inputs matters: a wedge pressure that overestimates left atrial pressure (for example, in severe mitral stenosis or with an overwedged catheter) will underestimate PVR. Cardiac output errors also propagate directly into the result.
- High output states: in conditions such as severe anemia, sepsis, or large left-to-right shunts, elevated flow can lower calculated PVR even when the pulmonary vasculature is remodeled. Interpret the value together with pressures and the clinical picture.
- Single-point measurement: PVR varies with volume status, exercise, oxygenation, and vasoactive drugs. Measurements during supine rest may miss exercise-induced pulmonary hypertension.
- Interpret in context: an elevated PVR should always be read alongside mPAP, wedge pressure, and cardiac index, following current pulmonary hypertension guidelines, rather than in isolation.
For a broader hemodynamic picture, you may also find the Mean Arterial Pressure calculator and the Ejection Fraction calculator useful, and the Framingham Heart Disease Risk calculator can help frame overall cardiovascular risk.
Frequently Asked Questions
How do I convert PVR between Wood units and dyn·s/cm⁵?
Multiply Wood units by 80 to get dyn·s/cm⁵, and divide dyn·s/cm⁵ by 80 to get Wood units. For example, 3 WU equals 240 dyn·s/cm⁵. Wood units (mmHg·min/L) are preferred in clinical settings because the numbers are small and easy to compare with guideline thresholds, while dyn·s/cm⁵ appears in older literature and some research papers.
What is the difference between PVR and systemic vascular resistance (SVR)?
PVR describes resistance in the pulmonary circulation (right ventricle to left atrium), while SVR describes resistance in the systemic circulation (left ventricle to right atrium). SVR is calculated as \(80 \times (\text{MAP} - \text{RAP}) / \text{CO}\) using mean arterial pressure and right atrial pressure. Normal SVR is around 900–1400 dyn·s/cm⁵, roughly ten times higher than normal PVR, reflecting the high-pressure systemic versus low-pressure pulmonary circuit.
Can I use LVEDP instead of the wedge pressure?
Yes. Left ventricular end-diastolic pressure (LVEDP) is an alternative surrogate for left atrial pressure and can replace PCWP in the formula when wedge measurement is unreliable or unavailable, for example in mitral stenosis or after mitral valve replacement. The two values are normally close, but they can diverge in left heart disease, so note which measurement you used when reporting PVR.
Can I use cardiac index instead of cardiac output?
No, not directly — the formula requires cardiac output in L/min. If you only have the cardiac index (L/min/m²), first multiply it by the patient's body surface area to recover the cardiac output. Using cardiac index without this correction will systematically distort PVR, overestimating it in larger patients and underestimating it in smaller ones.
How is PVR different from the transpulmonary gradient (TPG)?
The transpulmonary gradient is simply the pressure difference \(\text{mPAP} - \text{PCWP}\) in mmHg, without dividing by cardiac output. PVR adds the flow dimension, so it accounts for how much blood is being pumped. This matters because a high TPG with very high cardiac output may still yield a normal PVR, and vice versa — PVR is generally the more flow-sensitive indicator of vascular remodeling.
What are common mistakes when calculating PVR?
Frequent errors include using systolic or diastolic pulmonary artery pressure instead of the mean PAP, entering pulmonary artery diastolic pressure as the wedge pressure, using cardiac index without converting to cardiac output, and mixing up the direction of the unit conversion (divide by 80 to get Wood units, not multiply). Also ensure all pressures are in mmHg and cardiac output in L/min before applying the formula.
What does a PVR between 2 and 3 Wood units mean?
Values of 2–3 WU fall in a borderline grey zone — above the normal limit of 2 WU but below the threshold of 3 WU that typically defines elevated PVR in pulmonary hypertension guidelines. Such values warrant careful interpretation alongside mPAP, wedge pressure, and cardiac index, and sometimes repeat measurement, since borderline results can shift with volume status, oxygenation, or measurement error. Clinical decisions should be made with a specialist.