Pulmonary Vascular Resistance (PVR) Calculator
Enter the mean pulmonary arterial pressure (MPAP), pulmonary capillary wedge pressure (PCWP), and cardiac output (CO) to calculate pulmonary vascular resistance in both Wood units and dynes per second per square centimetre. Results include a severity classification based on current clinical thresholds, a worked breakdown of the calculation, and a reference table of normal and elevated PVR ranges.
Formula
Worked example
A patient with MPAP 25 mmHg, PCWP 10 mmHg, and CO 5 L/min: gradient = 25 - 10 = 15 mmHg; PVR = 15 / 5 = 3.0 Wood units = 240 dynes·sec/cm5. This is at the upper boundary of mild elevation.
What is pulmonary vascular resistance?
Pulmonary vascular resistance (PVR) is a measure of the opposition to blood flow through the pulmonary circulation. It quantifies how hard the right ventricle must work to drive blood through the lungs. PVR is derived from the transpulmonary pressure gradient divided by cardiac output, and is analogous to systemic vascular resistance (SVR) on the right side of the heart. A high PVR means the pulmonary arteries and arterioles are narrowed, stiff, or otherwise obstructed, forcing the right ventricle to generate higher pressures to maintain flow. Over time, chronically elevated PVR causes right ventricular hypertrophy, dilation, and ultimately failure. PVR is measured invasively via right heart catheterisation and is a cornerstone of pulmonary hypertension assessment, heart transplant evaluation, and haemodynamic monitoring in the intensive care unit.
How to calculate PVR: the formula explained
The formula is PVR = (MPAP - PCWP) / CO, where MPAP is the mean pulmonary arterial pressure in mmHg, PCWP is the pulmonary capillary wedge pressure (a bedside surrogate for left atrial pressure) in mmHg, and CO is cardiac output in litres per minute. The result is in Wood units (WU), also written as mmHg·min/L. To convert to the CGS unit dynes·sec/cm5, multiply by 80. For example, if MPAP is 25 mmHg, PCWP is 10 mmHg, and CO is 5 L/min, the transpulmonary gradient is 15 mmHg and PVR = 15 / 5 = 3.0 WU = 240 dynes·sec/cm5. Normal adult PVR is 1-2 Wood units or approximately 80-160 dynes·sec/cm5. Values above 2 Wood units alongside an elevated MPAP (>20 mmHg) and a normal PAWP define pre-capillary pulmonary hypertension per the 2022 ESC/ERS guidelines.
Causes of elevated and low PVR
Elevated PVR can result from pulmonary embolism, chronic hypoxia (which triggers hypoxic vasoconstriction), acidemia, hypercapnia, atelectasis, pulmonary vasculitis, idiopathic pulmonary arterial hypertension (PAH), and connective tissue diseases such as scleroderma. Chronic left heart failure can raise PCWP, which increases MPAP without necessarily raising PVR (this is called post-capillary pulmonary hypertension). A low PVR is seen with vasodilator medications (calcium channel blockers, prostacyclin analogues, PDE-5 inhibitors, endothelin receptor antagonists), alkalemia, hypocapnia, supplemental oxygen delivery, and high-output states during exercise. Distinguishing pre-capillary from post-capillary pulmonary hypertension requires knowing the PAWP: a PAWP above 15 mmHg shifts the diagnosis toward left heart disease.
PVR in transplant evaluation and vasodilator testing
A PVR above 5 Wood units that does not normalise with vasodilator challenge is broadly considered a contraindication to orthotopic heart transplantation at most centres, because the donor right ventricle, adapted to normal pulmonary pressures, cannot acutely overcome the high afterload. Vasodilator challenge testing with inhaled nitric oxide, iloprost, or intravenous adenosine is therefore performed before listing a patient for transplant. A reduction in PVR below 3-5 WU during challenge indicates reversibility and may permit listing. Patients with fixed severe PVR elevation may instead be considered for heart-lung transplantation. Indexed PVR (PVRi), calculated by multiplying PVR by body surface area, is used in paediatric and congenital heart disease evaluation to normalise for body size.
PVR severity classification
| PVR (Wood units) | PVR (dynes·sec/cm⁵) | Classification | Clinical significance |
|---|---|---|---|
| < 1 | < 80 | Low | Vasodilated state or high-output; evaluate cause |
| 1-2 | 80-160 | Normal | Normal pulmonary vascular resistance in adults |
| 2-3 | 160-240 | Mildly elevated | Pre-capillary PH threshold; monitoring advised |
| 3-5 | 240-400 | Moderately elevated | Established pulmonary vascular disease |
| 5-8 | 400-640 | Significantly elevated | High right ventricular afterload; transplant risk |
| > 8 | > 640 | Severely elevated | Possible fixed vascular changes; critical risk |
Classification based on 2022 ESC/ERS pulmonary hypertension guidelines and published hemodynamic references. Values above 2 WU with MPAP > 20 mmHg and normal PAWP indicate pre-capillary pulmonary hypertension.
Frequently asked questions
What is a normal PVR value?
Normal pulmonary vascular resistance in adults is approximately 1-2 Wood units, equivalent to 80-160 dynes·sec/cm5. Per the 2022 ESC/ERS pulmonary hypertension guidelines, a PVR above 2 Wood units (>160 dynes·sec/cm5) alongside an elevated mean pulmonary arterial pressure (>20 mmHg) and a normal pulmonary artery wedge pressure defines pre-capillary pulmonary hypertension.
What is the difference between Wood units and dynes·sec/cm5?
Wood units (WU) and dynes·sec/cm5 are two different units for the same measurement. Wood units are more commonly used in clinical practice because the numbers are small and easy to work with (normal PVR is about 1-2 WU). Dynes·sec/cm5 is the CGS unit used in research and older literature; 1 Wood unit equals exactly 80 dynes·sec/cm5. To convert, multiply Wood units by 80, or divide dynes·sec/cm5 by 80.
What does a PVR above 5 Wood units mean for a transplant candidate?
A PVR above 5 Wood units that remains elevated during vasodilator challenge testing is generally considered a contraindication to heart transplantation at most centres. The normal donor right ventricle cannot suddenly pump against the high afterload created by severely elevated PVR and may fail acutely. Vasodilator testing helps determine reversibility: if PVR drops below the threshold during challenge, the patient may still be listed. Those with fixed, irreversible PVR elevation above 5 WU may instead be considered for heart-lung transplantation.
What is the transpulmonary gradient and why does it matter?
The transpulmonary gradient (TPG) is MPAP minus left atrial pressure (or PAWP). It represents the driving pressure from the pulmonary artery to the left atrium. A normal TPG is about 5-12 mmHg. An elevated TPG alongside a high PAWP distinguishes pre-capillary from post-capillary pulmonary hypertension: if PAWP is high but TPG is normal, the elevated MPAP is explained by the raised left atrial back-pressure (post-capillary), not by primary pulmonary vascular disease.
How is PVR measured clinically?
PVR is measured invasively using right heart catheterisation. A balloon-tipped catheter (Swan-Ganz catheter) is floated from a central vein through the right heart into the pulmonary artery. It records mean pulmonary arterial pressure (MPAP) and, when the balloon is inflated and the catheter wedged, the pulmonary artery wedge pressure (PAWP), which approximates left atrial pressure. Cardiac output is measured by thermodilution or the Fick method. These three values are combined in the PVR formula.
What causes PVR to be low?
PVR is reduced by vasodilator medications (calcium channel blockers, prostacyclin analogues, PDE-5 inhibitors, endothelin receptor antagonists), alkalemia (elevated blood pH), hypocapnia (low carbon dioxide), supplemental oxygen in hypoxic patients, and during aerobic exercise in healthy individuals. In clinical settings a very low PVR is sometimes seen after administration of intravenous vasodilators during haemodynamic testing.
Sources
- Humbert M, et al. 2022 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension. European Heart Journal. 2022;43(38):3618-3731.
- Naeije R, Vachiery JL, Yerly P, Vanderpool R. The transpulmonary pressure gradient for the diagnosis of pulmonary vascular disease. European Respiratory Journal. 2013;41(1):217-223.