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Pulmonary Vascular Resistance (Pvr) Calculator

Compute PVR from mPAP, PCWP, and cardiac output via right heart catheterization or echocardiography. Results in Wood units or dyn·s·cm⁻⁵.

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Inputs

Calculation Method

Output Unit

Mean Pulmonary Artery Pressure (mPAP)

Pulmonary Capillary Wedge Pressure (PCWP)

Cardiac Output (CO)

Tricuspid Regurgitant Velocity (TRV)

TVI of RVOT

Pulmonary Vascular Resistance

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Pulmonary Vascular Resistance—Wood units

The formula

How the
result is
computed.

What Is Pulmonary Vascular Resistance?

Pulmonary vascular resistance (PVR) quantifies the opposition to blood flow through the pulmonary vasculature. Clinicians use PVR to distinguish pre-capillary pulmonary hypertension — driven by intrinsic vascular disease — from post-capillary pulmonary hypertension caused by elevated left-heart filling pressures. Accurate PVR measurement guides diagnosis, treatment selection, and prognosis in pulmonary arterial hypertension (PAH), heart failure, and congenital heart disease.

Core Formula

The standard hemodynamic equation for PVR is derived from an analogy to Ohm's law applied to the pulmonary circuit:

PVR = (mPAP − PCWP) ÷ CO

Each variable carries a precise clinical definition:

mPAP (mean pulmonary artery pressure, mmHg): The time-averaged pressure measured directly in the main pulmonary artery, representing the driving pressure across the pulmonary vascular bed.
PCWP (pulmonary capillary wedge pressure, mmHg): A surrogate for left atrial pressure obtained by advancing a balloon-tipped catheter into a wedge position in a small pulmonary artery branch. It represents downstream back-pressure and is subtracted to isolate true pulmonary vascular resistance from left-heart loading effects.
CO (cardiac output, L/min): The volume of blood pumped per minute, measured by thermodilution or the Fick principle during right heart catheterization.

The result is expressed in Wood units (WU), equivalent to mmHg·min/L. To convert to the CGS unit dynes·s·cm^-5, multiply Wood units by 80. For example, a PVR of 3 WU equals 240 dyn·s·cm^-5. As highlighted by the systematic analysis published in Pulmonary Circulation (2019) on getting PVR units right, consistent unit reporting is essential for cross-study comparisons and clinical decision-making.

Normal Values and Clinical Thresholds

In healthy adults at rest, PVR typically ranges from 0.25 to 1.6 Wood units (20–130 dyn·s·cm^-5). The 2022 ESC/ERS guidelines for pulmonary hypertension define pre-capillary PH as mPAP > 20 mmHg combined with PCWP ≤ 15 mmHg and PVR ≥ 2 WU. Values exceeding 3 WU frequently serve as a threshold for intervention decisions in congenital heart disease and cardiac transplant candidacy evaluation.

Invasive Measurement: Right Heart Catheterization

Right heart catheterization (RHC) remains the gold standard for PVR determination. A Swan-Ganz catheter is advanced from a central vein through the right heart into the pulmonary artery. Direct pressure transduction yields simultaneous mPAP and PCWP readings, while CO is calculated by thermodilution or Fick method. The resulting PVR carries the highest diagnostic certainty and is mandatory for confirming PAH before initiating targeted therapies including prostacyclin analogues, endothelin receptor antagonists, and PDE-5 inhibitors.

Non-Invasive Estimation: Echocardiography

When invasive catheterization is not feasible, Doppler echocardiography provides a validated PVR estimate. Abbas et al. (2003), published in the Journal of the American College of Cardiology, demonstrated that the ratio of peak tricuspid regurgitant velocity (TRV, in m/s) to the time-velocity integral of the right ventricular outflow tract (TVI_RVOT, in cm) correlates strongly with invasively measured PVR:

PVR (WU) ≈ (TRV ÷ TVI_RVOT) × 10 + 0.16

In the original validation cohort, this formula achieved a sensitivity of 79% and specificity of 93% for detecting PVR > 2 WU, making it a clinically useful screening method. Further echocardiographic PVR estimation approaches are reviewed at the Rutgers Robert Wood Johnson Medical School echocardiography resource.

Clinical Applications

Pulmonary arterial hypertension: Baseline and serial PVR measurement tracks disease severity and response to targeted vasodilator therapy.
Heart failure and transplant candidacy: PVR distinguishes reversible from fixed pulmonary hypertension. Most transplant programs require PVR < 3–5 WU after vasodilator challenge before listing.
Congenital heart disease: PVR before and after oxygen or inhaled nitric oxide determines operability in patients with left-to-right shunts and potential Eisenmenger physiology.
Perioperative risk stratification: Elevated PVR predicts right ventricular failure after cardiac surgery, lung transplantation, and mechanical circulatory support implantation.

Interpretation and Serial Monitoring

Serial PVR measurements provide crucial information about disease progression and treatment response. Patients with idiopathic PAH undergoing targeted therapy should demonstrate either stable or declining PVR values, with a reduction of ≥20% from baseline often indicating clinical improvement and favorable prognosis. Conversely, rising PVR despite maximal medical therapy signals disease progression and may prompt escalation to combination therapy or consideration of advanced interventions such as balloon pulmonary angioplasty in chronic thromboembolic disease.

Reference

Frequently asked questions

What is a normal pulmonary vascular resistance value?

Normal PVR in healthy adults at rest ranges from 0.25 to 1.6 Wood units (20 to 130 dyn·s·cm⁻⁵). Values above 2 Wood units raise suspicion for pulmonary vascular disease. The 2022 ESC/ERS guidelines classify PVR at or above 2 WU, combined with mPAP exceeding 20 mmHg and PCWP at or below 15 mmHg, as meeting the hemodynamic definition of pre-capillary pulmonary hypertension.

What is the difference between Wood units and dynes·s·cm⁻⁵?

Wood units (mmHg·min/L) and dynes·s·cm⁻⁵ express the same resistance quantity in different unit systems. Multiply Wood units by 80 to convert: a PVR of 3 WU equals 240 dyn·s·cm⁻⁵, and 6 WU equals 480 dyn·s·cm⁻⁵. Wood units dominate clinical cardiology practice for their intuitive scale, while dyn·s·cm⁻⁵ remains common in research publications and pediatric cardiology literature.

How is PVR estimated non-invasively using echocardiography?

The Abbas et al. (2003) formula estimates PVR from two Doppler-derived values: PVR ≈ (TRV / TVI_RVOT) × 10 + 0.16, where TRV is peak tricuspid regurgitant jet velocity in m/s and TVI_RVOT is the right ventricular outflow tract time-velocity integral in cm. The original study reported 79% sensitivity and 93% specificity for detecting PVR above 2 Wood units, providing a validated non-invasive screening alternative when right heart catheterization is contraindicated or unavailable.

What causes elevated pulmonary vascular resistance?

Elevated PVR results from pulmonary vasoconstriction, vascular remodeling, or mechanical obstruction of the pulmonary vascular bed. Common causes include idiopathic pulmonary arterial hypertension, chronic thromboembolic pulmonary hypertension, connective tissue diseases such as scleroderma, hypoxic lung diseases including COPD, congenital heart defects with left-to-right shunting, and drug or toxin exposure. Left heart failure can secondarily elevate PVR through chronic pulmonary venous congestion and reactive vasoconstriction.

Why is PVR critical for heart transplant candidacy evaluation?

A donor heart conditioned to normal pulmonary pressures faces acute right ventricular failure if implanted into a recipient with severely elevated PVR. Most transplant programs require PVR below 3 to 5 Wood units, or a transpulmonary gradient below 15 mmHg, before listing. A reversibility challenge using intravenous nitroprusside, milrinone, or inhaled nitric oxide determines whether elevated PVR is fixed or pharmacologically reversible, directly influencing transplant eligibility decisions.

How does pulmonary vascular resistance differ from systemic vascular resistance?

PVR measures resistance across the low-pressure pulmonary circuit, with a normal range of 0.25 to 1.6 Wood units (20 to 130 dyn·s·cm⁻⁵). Systemic vascular resistance (SVR) measures resistance across the high-pressure systemic circuit, with a normal range of 800 to 1200 dyn·s·cm⁻⁵ (10 to 15 WU). Normal SVR is approximately 10 times higher than normal PVR, reflecting the pulmonary circulation's design as a high-flow, low-resistance, low-pressure system optimized for gas exchange.