Pulmonary Vascular Resistance — clinical hemodynamic analysis with severity classification
Pulmonary vascular resistance (PVR) is one of the most important hemodynamic parameters assessed in cardiopulmonary medicine. It quantifies the resistance that blood encounters as it flows through the pulmonary arterial circulation, from the right ventricle through the lungs and back to the left heart. Our free PVR calculator provides an instant, accurate calculation of PVR from the three core measurements obtained during right heart catheterization: mean pulmonary arterial pressure, pulmonary capillary wedge pressure, and cardiac output. Understanding PVR is essential in the diagnosis and management of pulmonary hypertension, a condition affecting millions of people worldwide and associated with significant morbidity and mortality. PVR serves as a critical tool for distinguishing between different types of pulmonary hypertension, guiding treatment decisions, selecting surgical candidates, and monitoring response to vasodilator therapy. Cardiologists, pulmonologists, cardiac surgeons, and critical care physicians rely on PVR measurements to guide some of the most consequential decisions in cardiovascular medicine. This calculator implements the standard clinical formula derived from the fluid-dynamic analog of Ohm's law: PVR equals the difference between mean pulmonary arterial pressure and pulmonary capillary wedge pressure, divided by cardiac output. This pressure gradient across the pulmonary vasculature, normalized by flow, gives clinicians a precise measure of how much resistance the right ventricle must overcome. The result is expressed in Wood units (mmHg·min/L), the traditional clinical unit named after cardiologist Paul Wood, and simultaneously in dynes·sec/cm⁵ (the SI unit), using the standard conversion factor of 80. Beyond the basic PVR calculation, our tool also computes the Pulmonary Vascular Resistance Index (PVRI), which normalizes PVR to body surface area. This indexed value is particularly important in pediatric cardiology and in the evaluation of patients with congenital heart disease, where decisions about surgical repair of septal defects depend on PVRI thresholds. A PVRI below 6 WU·m² is generally considered acceptable for surgical correction, while higher values indicate prohibitive pulmonary vascular disease unless reversibility can be demonstrated with vasodilator testing. The transpulmonary gradient (TPG), another calculated value displayed by this tool, is the simple arithmetic difference between mPAP and PCWP. This gradient is physiologically important because it reflects the pressure drop specifically across the pulmonary vasculature itself, excluding the contribution of elevated left-sided filling pressures. A TPG greater than 12 mmHg in the presence of an elevated PCWP suggests that active pulmonary vascular remodeling is occurring on top of passive congestion, a finding with important therapeutic and prognostic implications. One of the most clinically useful features of this calculator is its pre-capillary versus post-capillary pulmonary hypertension classification. When mPAP is elevated, the PCWP value determines whether the cause is intrinsic pulmonary vascular disease (pre-capillary, PCWP 15 mmHg or below) or left heart failure and volume overload (post-capillary, PCWP above 15 mmHg). This distinction directly determines which medications and interventions are appropriate. Pulmonary vasodilators like prostacyclins, endothelin antagonists, and phosphodiesterase-5 inhibitors benefit pre-capillary PH, while post-capillary PH requires treatment of the underlying left heart disease. The severity classification provided by this calculator categorizes PVR results as normal (0.6–2.0 Wood units), mildly elevated (2.1–3.0 Wood units), moderately elevated (3.1–5.0 Wood units), or severely elevated (above 5.0 Wood units). These thresholds are widely used in clinical practice and align with published guidelines for pulmonary hypertension management. A visual gauge chart makes it immediately intuitive where a patient's PVR falls within the clinical spectrum. All three inputs — mPAP, PCWP, and cardiac output — are measured during right heart catheterization using a Swan-Ganz (pulmonary artery) catheter. This is an invasive but well-established procedure performed in cardiac catheterization laboratories. The cardiac output is typically measured by thermodilution or the Fick principle. This calculator includes physiological validation, preventing calculation when PCWP exceeds mPAP (a physiologically impossible state) and providing clear error guidance. Preset clinical examples allow clinicians and students to explore representative normal, mildly elevated, moderately elevated, and severely elevated PVR scenarios for educational comparison.
Understanding Pulmonary Vascular Resistance
Pulmonary vascular resistance is a derived hemodynamic parameter that quantifies the resistance to blood flow in the pulmonary circulation. It is calculated from three invasively measured values and expressed in Wood units or dynes·sec/cm⁵.
What Is Pulmonary Vascular Resistance?
Pulmonary vascular resistance (PVR) represents the total resistance that the right ventricle must overcome to pump blood through the pulmonary circulation. It is derived from Ohm's law applied to fluid dynamics: resistance equals pressure gradient divided by flow. In the pulmonary circuit, the pressure gradient is the difference between mean pulmonary arterial pressure and pulmonary capillary wedge pressure, and the flow is cardiac output. Normal PVR ranges from 0.6 to 2.0 Wood units (48 to 160 dynes·sec/cm⁵). Elevated PVR indicates increased resistance in the pulmonary arteries, which forces the right ventricle to work harder and can eventually lead to right heart failure. PVR is primarily determined by the caliber of small pulmonary arterioles, which can be altered by vascular remodeling, vasoconstriction, thrombosis, or external compression.
How Is PVR Calculated?
PVR is calculated using the formula: PVR (Wood units) = (mPAP − PCWP) / CO, where mPAP is mean pulmonary arterial pressure in mmHg, PCWP is pulmonary capillary wedge pressure in mmHg, and CO is cardiac output in L/min. To convert to dynes·sec/cm⁵, multiply by 80 (one Wood unit = 80 dyn·s/cm⁵). The Pulmonary Vascular Resistance Index (PVRI) normalizes PVR to body surface area: PVRI = PVR × BSA (WU·m²), or equivalently = (mPAP − PCWP) / CI where CI is the cardiac index (CO/BSA). The transpulmonary gradient (TPG) is simply mPAP minus PCWP and reflects the pressure drop across the pulmonary vascular bed itself. All three input values are measured invasively via right heart catheterization using a Swan-Ganz pulmonary artery catheter, considered the gold standard for hemodynamic assessment.
Why Does PVR Matter Clinically?
PVR is essential for diagnosing and classifying pulmonary hypertension, guiding treatment selection, and assessing surgical eligibility. In pulmonary arterial hypertension (PAH), elevated PVR reflects pathological remodeling of the pulmonary arteries, and the degree of elevation correlates with disease severity and prognosis. PVR guides transplant listing decisions — patients with PVRI exceeding 6 WU·m² are generally not candidates for isolated heart transplantation without prior mechanical circulatory support or combined heart-lung transplantation. For congenital heart disease patients with left-to-right shunts (ASD, VSD, PDA), PVRI determines operability: PVRI below 6 WU·m² generally favors repair, while higher values indicate Eisenmenger-risk physiology. PVR monitoring tracks response to pulmonary vasodilator therapy with prostacyclins, endothelin receptor antagonists, and PDE-5 inhibitors. Acute vasodilator testing with inhaled nitric oxide or adenosine identifies patients likely to respond to calcium channel blockers.
Pre-Capillary vs Post-Capillary Hypertension
A critically important clinical distinction is whether elevated pulmonary arterial pressure originates from intrinsic pulmonary vascular disease (pre-capillary PH) or elevated left-sided filling pressures from left heart disease (post-capillary PH). Pre-capillary PH is defined by mPAP at or above 25 mmHg with PCWP at or below 15 mmHg; the problem lies in the pulmonary arteries themselves. Post-capillary PH occurs when PCWP exceeds 15 mmHg; pulmonary arterial pressures are elevated passively due to back-pressure from a failing or stiffened left heart. Combined pre- and post-capillary PH occurs when both elevated PCWP and elevated TPG (≥12 mmHg) are present, indicating that pulmonary vascular remodeling has developed on top of chronic left heart disease. This distinction is critical because pulmonary vasodilators are beneficial and appropriate for pre-capillary PH but potentially harmful in isolated post-capillary PH from left ventricular failure.
PVR Formulas & Equations
Pulmonary Vascular Resistance (Wood Units)
PVR (WU) = (mPAP − PCWP) ÷ CO
The standard clinical formula for PVR, derived from the fluid-dynamic analog of Ohm's law. mPAP is mean pulmonary arterial pressure in mmHg, PCWP is pulmonary capillary wedge pressure in mmHg, and CO is cardiac output in L/min. Normal range is 0.6–2.0 Wood units.
PVR in Dynes·sec/cm⁵
PVR (dyn·s/cm⁵) = PVR (WU) × 80
Converts PVR from Wood units (the traditional clinical unit) to the CGS unit of dynes·sec/cm⁵. The conversion factor of 80 accounts for the unit transformation from mmHg·min/L. Normal range is 48–160 dyn·s/cm⁵.
Transpulmonary Gradient (TPG)
TPG (mmHg) = mPAP − PCWP
The pressure drop across the pulmonary vasculature, excluding left-sided filling pressure contributions. A normal TPG is below 12 mmHg. Elevated TPG with elevated PCWP indicates combined pre- and post-capillary pulmonary hypertension with active vascular remodeling.
Total Pulmonary Resistance (TPR)
TPR (WU) = mPAP ÷ CO
Total pulmonary resistance includes the contribution of left atrial pressure (approximated by PCWP), unlike PVR which subtracts it. TPR is sometimes used in pediatric cardiology and when PCWP measurement is unreliable. It overestimates true pulmonary arteriolar resistance when left-sided pressures are elevated.
PVR Reference Tables
PVR Normal Ranges and Severity Classification
Clinical classification of pulmonary vascular resistance by severity, with corresponding ranges in both Wood units and dynes·sec/cm⁵, and associated clinical significance for treatment and prognosis decisions.
| Severity | PVR (Wood Units) | PVR (dyn·s/cm⁵) | Clinical Significance |
|---|---|---|---|
| Normal | 0.6–2.0 | 48–160 | Healthy pulmonary circulation; right ventricle functions normally |
| Mildly Elevated | 2.1–3.0 | 168–240 | Early pulmonary vascular disease; warrants investigation and monitoring |
| Moderately Elevated | 3.1–5.0 | 248–400 | Significant PH; pulmonary vasodilator therapy typically indicated |
| Severely Elevated | >5.0 | >400 | Severe PH; right heart failure risk; transplant evaluation may be needed |
WHO Pulmonary Hypertension Classification
World Health Organization classification of pulmonary hypertension into five clinical groups based on etiology, hemodynamic profile, and treatment approach. PVR and the pre/post-capillary distinction guide group assignment.
| WHO Group | Name | PCWP | PVR | Key Examples |
|---|---|---|---|---|
| Group I | Pulmonary Arterial Hypertension (PAH) | ≤15 mmHg | Elevated | Idiopathic PAH, heritable PAH, drug-induced, connective tissue disease |
| Group II | PH due to Left Heart Disease | >15 mmHg | Variable | HFrEF, HFpEF, valvular heart disease, congenital cardiomyopathy |
| Group III | PH due to Lung Disease/Hypoxia | ≤15 mmHg | Mildly elevated | COPD, interstitial lung disease, sleep-disordered breathing, high altitude |
| Group IV | Chronic Thromboembolic PH (CTEPH) | ≤15 mmHg | Elevated | Chronic PE, pulmonary artery obstruction; may be surgically treatable |
| Group V | PH with Unclear/Multifactorial Mechanisms | Variable | Variable | Sarcoidosis, hematologic disorders, metabolic disorders, systemic diseases |
PVR Worked Examples
Standard PVR Calculation with PH Assessment
A 55-year-old patient undergoes right heart catheterization showing mPAP 35 mmHg, PCWP 12 mmHg, and cardiac output 5.0 L/min. BSA is 1.8 m².
Calculate PVR in Wood units: PVR = (mPAP − PCWP) / CO = (35 − 12) / 5.0 = 23 / 5.0 = 4.6 WU.
Convert to dyn·s/cm⁵: PVR = 4.6 × 80 = 368 dyn·s/cm⁵.
Calculate TPG: TPG = 35 − 12 = 23 mmHg (elevated, >12).
Calculate PVRI: PVRI = PVR × BSA = 4.6 × 1.8 = 8.3 WU·m².
Calculate CI: CI = CO / BSA = 5.0 / 1.8 = 2.78 L/min/m².
Classify severity: PVR of 4.6 WU = Moderately Elevated (3.1–5.0 range).
Classify PH type: mPAP ≥25 with PCWP ≤15 = Pre-capillary pulmonary hypertension.
PVR = 4.6 WU (368 dyn·s/cm⁵), PVRI = 8.3 WU·m², TPG = 23 mmHg. Classification: Moderately elevated pre-capillary pulmonary hypertension (WHO Group I, III, or IV). Pulmonary vasodilator therapy is indicated. Further workup including CTEPH screening, connective tissue disease panel, and vasodilator testing is recommended.
Distinguishing Post-Capillary from Combined PH
A heart failure patient has mPAP 40 mmHg, PCWP 22 mmHg, and CO 4.0 L/min.
Calculate PVR: PVR = (40 − 22) / 4.0 = 18 / 4.0 = 4.5 WU.
Calculate TPG: TPG = 40 − 22 = 18 mmHg (elevated, >12).
Assess PH type: mPAP ≥25 with PCWP >15 = Post-capillary PH.
Check for combined component: TPG of 18 mmHg exceeds 12 mmHg threshold, and PVR of 4.5 WU exceeds 3.0 WU — this indicates combined pre- and post-capillary PH.
Interpret: The elevated PCWP confirms left heart disease as the primary driver, but the elevated PVR and TPG indicate secondary pulmonary vascular remodeling on top of the passive congestion.
PVR = 4.5 WU (360 dyn·s/cm⁵), TPG = 18 mmHg. Classification: Combined pre- and post-capillary pulmonary hypertension (WHO Group II with reactive component). Treatment should focus on the underlying left heart disease, with cautious consideration of pulmonary vasodilators only under specialist guidance.
Normal Hemodynamics Confirmation
A preoperative patient has mPAP 14 mmHg, PCWP 8 mmHg, and CO 5.5 L/min.
Calculate PVR: PVR = (14 − 8) / 5.5 = 6 / 5.5 = 1.09 WU.
Convert: PVR = 1.09 × 80 = 87.3 dyn·s/cm⁵.
Calculate TPG: TPG = 14 − 8 = 6 mmHg (normal, <12).
Classify: PVR of 1.09 WU is within the normal range (0.6–2.0). mPAP of 14 is below the 25 mmHg PH threshold.
PVR = 1.09 WU (87 dyn·s/cm⁵), TPG = 6 mmHg. All hemodynamic parameters are within normal limits. No pulmonary hypertension. Patient's pulmonary circulation is functioning normally and should tolerate surgical procedures without elevated right heart afterload concerns.
How to Use This Calculator
Enter Measured Hemodynamic Values
Input the three values obtained from right heart catheterization: mean pulmonary arterial pressure (mPAP in mmHg), pulmonary capillary wedge pressure (PCWP in mmHg), and cardiac output (CO in L/min). These values are measured using a Swan-Ganz pulmonary artery catheter. Use the clinical preset examples to explore representative scenarios if you are studying hemodynamics.
Enter Body Surface Area for PVRI
Optionally enter the patient's body surface area (BSA in m²) to calculate the Pulmonary Vascular Resistance Index (PVRI) and Cardiac Index (CI). PVRI is the BSA-normalized form of PVR and is particularly important for pediatric patients and for transplant candidacy assessment. BSA can be calculated from height and weight using the Dubois or Mosteller formula.
Review PVR Results and Severity Classification
The calculator instantly displays PVR in both Wood units and dyn·s/cm⁵, along with the transpulmonary gradient (TPG) and clinical severity category (Normal, Mildly Elevated, Moderately Elevated, or Severely Elevated). The severity gauge chart shows where PVR falls on the clinical spectrum. The pre-capillary vs post-capillary classification helps identify the likely mechanism of pulmonary hypertension.
Export or Print for Clinical Documentation
Use the Print Results button to generate a print-friendly summary of all hemodynamic values for inclusion in clinical notes or patient records. The Export CSV button downloads all calculated values in a spreadsheet-compatible format suitable for research or audit documentation. All calculations are performed locally in your browser; no data is transmitted or stored.
Frequently Asked Questions
What is a normal PVR value?
Normal pulmonary vascular resistance ranges from 0.6 to 2.0 Wood units (48 to 160 dynes·sec/cm⁵) in adults at rest. Values in this range indicate a healthy pulmonary circulation where the right ventricle can pump blood through the lungs with minimal effort. Clinically, a PVR below 3 Wood units is generally considered the threshold below which most patients tolerate surgical procedures and transplantation well. A PVR of 2.1 to 3.0 WU is considered mildly elevated and may warrant further investigation or monitoring. Values above 5 Wood units (400 dyn·s/cm⁵) indicate severely elevated PVR with significant implications for right ventricular function, exercise capacity, and long-term prognosis. PVR can vary slightly with body position, lung volume, and cardiac output state.
What is the difference between PVR and PVRI?
PVR (Pulmonary Vascular Resistance) is the absolute resistance in the pulmonary circulation, calculated as (mPAP − PCWP) / CO, and expressed in Wood units or dyn·s/cm⁵. PVRI (Pulmonary Vascular Resistance Index) normalizes PVR to body surface area by multiplying PVR by BSA (or dividing the pressure gradient by Cardiac Index instead of Cardiac Output). This indexing accounts for differences in body size, making PVRI more comparable across patients of different sizes — particularly children versus adults. Normal PVRI is 3.2 to 3.6 WU·m² (255–285 dyn·s/cm⁵·m²). PVRI is the preferred metric in pediatric cardiology, in congenital heart disease surgery planning, and for transplant candidacy assessment, where PVRI thresholds (e.g., 6 WU·m²) are used in decision-making algorithms.
What does the transpulmonary gradient (TPG) mean?
The transpulmonary gradient (TPG) is the difference between mean pulmonary arterial pressure and pulmonary capillary wedge pressure: TPG = mPAP − PCWP. It represents the pressure drop specifically across the pulmonary vascular bed, excluding the contribution of elevated left-sided filling pressures. A normal TPG is below 12 mmHg. An elevated TPG (≥ 12 mmHg) combined with an elevated PCWP (> 15 mmHg) suggests that pulmonary vascular remodeling is occurring in addition to passive congestion from left heart disease — this is called combined pre- and post-capillary pulmonary hypertension. The TPG helps identify patients with long-standing left heart failure who have developed secondary reactive pulmonary vascular disease, which may affect transplant candidacy and prognosis differently from pure left heart failure.
What is the difference between pre-capillary and post-capillary pulmonary hypertension?
Pre-capillary pulmonary hypertension occurs when mPAP is elevated (≥ 25 mmHg) but PCWP is normal or low (≤ 15 mmHg), meaning the problem lies within the pulmonary arteries themselves — from vascular remodeling, vasoconstriction, thrombosis, or other intrinsic pulmonary vascular disease. This category includes pulmonary arterial hypertension, PH due to lung disease, chronic thromboembolic PH, and others. Post-capillary PH occurs when elevated pulmonary artery pressures are driven by elevated left-sided filling pressures (PCWP > 15 mmHg) from left ventricular failure, valvular heart disease, or diastolic dysfunction. The distinction is crucial because pulmonary vasodilators (prostacyclins, endothelin antagonists, PDE5 inhibitors) are appropriate for pre-capillary PH but are not recommended as primary treatment for isolated post-capillary PH.
How are mPAP, PCWP, and cardiac output measured?
All three values are obtained during right heart catheterization using a Swan-Ganz (pulmonary artery) catheter inserted through a central vein (typically internal jugular or femoral vein) and floated through the right atrium, right ventricle, and into the pulmonary artery. Mean pulmonary arterial pressure (mPAP) is measured directly from the catheter tip position in the pulmonary artery. Pulmonary capillary wedge pressure (PCWP) is obtained by inflating a small balloon at the catheter tip, which wedges the catheter in a small pulmonary artery branch and reflects left atrial pressure through the downstream pulmonary capillaries. Cardiac output is typically measured by thermodilution (injecting cold saline and measuring temperature change) or by the Fick principle (using oxygen consumption and arteriovenous oxygen difference). This procedure is performed in a cardiac catheterization laboratory under fluoroscopic guidance.
What PVR levels affect transplant candidacy or surgical decisions?
Pulmonary vascular resistance thresholds play a critical role in transplant candidacy assessment. For heart transplantation, a PVRI greater than 6 WU·m² (or PVR > 5 WU with a TPG > 16 mmHg or pulmonary artery systolic pressure > 60 mmHg) is generally considered a relative contraindication to isolated orthotopic heart transplantation because the donor right ventricle may not tolerate the elevated afterload. Some programs accept candidates up to PVRI of 8 WU·m² if vasodilator testing shows reversibility. For congenital heart disease surgery (closure of ASD, VSD, PDA), a PVRI below 6 WU·m² in children is generally considered acceptable for repair. Values of 7–8 WU·m² may still allow repair in simple shunts if vasodilator testing demonstrates adequate hemodynamic response. These thresholds should always be interpreted in the context of the full clinical picture and institutional protocols.
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