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Pulmonary Vascular Resistance Calculator

Q: What is the difference between PVR and systemic vascular resistance?

Systemic vascular resistance (SVR) measures afterload on the left ventricle as blood circulates through the body; PVR measures afterload on the right ventricle through the lungs. The pulmonary circulation is a low-pressure, high-compliance system, so normal PVR is roughly one-fifth of normal SVR. SVR elevation reflects systemic hypertension or shock; PVR elevation suggests pulmonary hypertension, intracardiac shunting, or left heart disease transmitted backward.

Q: Why is the conversion factor 80 used in the PVR formula?

The factor 80 converts units from the practical haemodynamic parameters (mmHg and L/min) into standard dynes·sec·cm⁻⁵. Without this constant, pressure would be in mmHg and flow in mL/min, yielding Wood units directly. The 80 multiplier accounts for the differences in unit definitions and makes PVR calculation consistent with how resistance is reported in haemodynamic laboratories worldwide.

Q: Can PVR be normal if cardiac output is very low?

Mathematically, yes—a low cardiac output can yield a seemingly normal PVR despite elevated mean pulmonary artery pressure. However, this scenario often signals cardiogenic shock: the heart cannot maintain forward flow, so pressure backs up. In such cases, clinicians focus on improving cardiac output and perfusion rather than treating isolated PVR elevation. Serial measurements help distinguish progressive disease from transient haemodynamic instability.

Q: What vasodilators are used to lower PVR?

First-line agents include phosphodiesterase-5 inhibitors (sildenafil, tadalafil), soluble guanylate cyclase stimulators (riociguat), endothelin receptor antagonists (ambrisentan, bosentan), and prostacyclin analogues (epoprostenol, treprostinil). Acute vasoreactivity testing during catheterisation using inhaled nitric oxide or adenosine helps predict who will respond. Response is assessed by serial PVR measurement; PVR reduction of >20% often predicts long-term survival benefit.

Q: How does body size affect PVR measurement?

PVR is not indexed to body surface area in the same way cardiac output sometimes is. However, cardiac output itself varies with body size; a larger patient typically has a higher absolute cardiac output. Since PVR is calculated from cardiac output, it remains independent of weight or height when proper measurement technique is used. Individual variation in lung vascular architecture and exercise capacity can still influence 'normal' PVR thresholds.

Pulmonary vascular resistance (PVR) quantifies the afterload facing the right ventricle as blood flows through the pulmonary circulation. Clinicians use PVR to identify pulmonary hypertension, stratify heart failure severity, and guide vasodilator therapy. This calculator converts bedside haemodynamic measurements—mean pulmonary artery pressure, left atrial pressure, and cardiac output—into PVR in Wood units or dynes·sec·cm⁻⁵, enabling rapid assessment of whether resistance has crossed the threshold for intervention.

Last updated: May 1, 2026

Creators Adena Benn, BSc

Reviewers Łucja Zaborowska and Małgorzata Koperska

961 people find this calculator helpful

Understanding Pulmonary Vascular Resistance

Pulmonary vascular resistance reflects the ease with which blood traverses the pulmonary arteries and capillary bed en route to the lungs for oxygenation. The right ventricle must overcome this resistance to pump deoxygenated blood forward; when resistance climbs, the chamber dilates and weakens, triggering right heart failure.

PVR sits at the intersection of three haemodynamic variables: the pressure gradient across the pulmonary vascular bed (mean pulmonary artery pressure minus left atrial pressure) and the volume of blood pumped per minute (cardiac output). Normal values remain below 250 dynes·sec·cm⁻⁵ (or 3 Wood units), though modern criteria for pulmonary hypertension diagnosis require both elevated mean pressure and elevated PVR.

Unlike systemic vascular resistance, the pulmonary circulation operates as a low-pressure, high-compliance system. Small increases in PVR can signal disease: chronic hypoxia, left heart dysfunction, thromboemboli, or primary pulmonary hypertension.

PVR Calculation Formula

PVR is derived from the fundamental relationship between pressure gradient and flow. Multiply the pressure difference by a conversion factor (80) to convert from mmHg and L/min into dynes·sec·cm⁻⁵:

PVR = 80 × (MPAP − LAP) / CO

MPAP — Mean Pulmonary Arterial Pressure in mmHg (normal: 10–20 mmHg)
LAP — Left Atrial Pressure in mmHg (normal: 6–12 mmHg), estimated from pulmonary capillary wedge pressure
CO — Cardiac Output in L/min (normal: 4–8 L/min)
PVR — Pulmonary Vascular Resistance in dynes·sec·cm⁻⁵ (normal: <250)

Clinical Interpretation and PVR Ranges

A PVR below 250 dynes·sec·cm⁻⁵ (3 Wood units) is considered normal in most populations. Values persistently above this threshold, especially when paired with a mean pulmonary artery pressure exceeding 25 mmHg at rest, meet diagnostic criteria for pulmonary hypertension.

Low PVR: Suggests effective pulmonary vasodilation, often seen in athletes, young patients, or those responding well to vasodilator therapy (nitrates, phosphodiesterase-5 inhibitors, endothelin antagonists).
Elevated PVR: Indicates vasoconstriction or structural disease. Causes include chronic obstructive pulmonary disease, interstitial lung disease, left heart failure (postcapillary), chronic thromboemboli, and idiopathic pulmonary arterial hypertension.
Severely elevated PVR: Above 400 dynes·sec·cm⁻⁵ often reflects advanced disease and carries a worse prognosis; right heart transplantation may be considered.

Serial PVR measurement helps track response to targeted therapy and guides treatment intensification or escalation.

Key Considerations When Using This Calculator

Accurate PVR calculation requires precise haemodynamic measurement and understanding of common pitfalls.

LAP estimation requires catheterisation — Left atrial pressure is not routinely measured non-invasively; it is estimated from pulmonary capillary wedge pressure obtained via right heart catheterisation with a swan-ganz catheter. Ensure the catheter tip lies in zone 3 (below left atrial level) to avoid erroneous readings.
Timing and respiratory phase matter — MPAP and cardiac output fluctuate with the respiratory cycle. Measure both at end-expiration to minimise artefact. In mechanically ventilated patients, readings taken at similar ventilator settings allow valid serial comparisons.
PVR alone does not confirm pulmonary hypertension diagnosis — Elevated PVR must be accompanied by mean pulmonary artery pressure ≥25 mmHg to meet current diagnostic criteria. A low cardiac output can artificially inflate PVR; clinical context and reproducibility are essential.
Distinguish precapillary from postcapillary elevation — If LAP is also elevated (e.g., from mitral stenosis or left heart failure), the pressure gradient may remain modest despite high mean pulmonary artery pressure, yielding normal or mildly elevated PVR—despite clinically evident pulmonary congestion.

Worked Example: Suspected Right Heart Failure

A 58-year-old man with unexplained dyspnoea undergoes right heart catheterisation. Results are:

Mean Pulmonary Arterial Pressure: 32 mmHg
Left Atrial Pressure (wedge): 8 mmHg
Cardiac Output: 4.2 L/min

Applying the formula:

PVR = 80 × (32 − 8) / 4.2 = 80 × 24 / 4.2 = 457 dynes·sec·cm⁻⁵

A PVR of 457 dynes·sec·cm⁻⁵ (5.7 Wood units) exceeds normal limits and confirms precapillary pulmonary hypertension. The clinician now pursues aetiology—vasoreactivity testing, ventilation-perfusion scan for thrombi, high-resolution CT for interstitial disease—and considers initiation of targeted pulmonary vasodilator therapy.

Frequently Asked Questions

What is the difference between PVR and systemic vascular resistance?

Systemic vascular resistance (SVR) measures afterload on the left ventricle as blood circulates through the body; PVR measures afterload on the right ventricle through the lungs. The pulmonary circulation is a low-pressure, high-compliance system, so normal PVR is roughly one-fifth of normal SVR. SVR elevation reflects systemic hypertension or shock; PVR elevation suggests pulmonary hypertension, intracardiac shunting, or left heart disease transmitted backward.

Why is the conversion factor 80 used in the PVR formula?

The factor 80 converts units from the practical haemodynamic parameters (mmHg and L/min) into standard dynes·sec·cm⁻⁵. Without this constant, pressure would be in mmHg and flow in mL/min, yielding Wood units directly. The 80 multiplier accounts for the differences in unit definitions and makes PVR calculation consistent with how resistance is reported in haemodynamic laboratories worldwide.

Can PVR be normal if cardiac output is very low?

Mathematically, yes—a low cardiac output can yield a seemingly normal PVR despite elevated mean pulmonary artery pressure. However, this scenario often signals cardiogenic shock: the heart cannot maintain forward flow, so pressure backs up. In such cases, clinicians focus on improving cardiac output and perfusion rather than treating isolated PVR elevation. Serial measurements help distinguish progressive disease from transient haemodynamic instability.

What vasodilators are used to lower PVR?

First-line agents include phosphodiesterase-5 inhibitors (sildenafil, tadalafil), soluble guanylate cyclase stimulators (riociguat), endothelin receptor antagonists (ambrisentan, bosentan), and prostacyclin analogues (epoprostenol, treprostinil). Acute vasoreactivity testing during catheterisation using inhaled nitric oxide or adenosine helps predict who will respond. Response is assessed by serial PVR measurement; PVR reduction of >20% often predicts long-term survival benefit.

Is Wood units or dynes·sec·cm⁻⁵ more commonly reported?

Both units describe the same quantity. Wood units (named after Paul Wood) equal approximately dynes·sec·cm⁻⁵ divided by 80. Modern haemodynamic laboratories typically report PVR in dynes·sec·cm⁻⁵ (normal <250), but older literature and some institutions use Wood units (normal <3). Understanding both allows you to interpret publications and lab reports without confusion.

How does body size affect PVR measurement?