π« Pulmonary Vascular Resistance
PVR from cath numbers, in Wood units and dynes.
For informational purposes only, not medical advice. Consult a healthcare professional.
Pulmonary vascular resistance measures how hard the right heart must push to drive blood through the lungs. It is the transpulmonary pressure gradient, mean PA pressure minus wedge pressure, divided by cardiac output. Normal PVR sits under 3 Wood units (240 dynes); pulmonary arterial hypertension is defined in part by PVR above 3 Wood units with a normal wedge. This calculator converts cath numbers into both unit systems for teaching and cath-lab reference.
How to Use This Calculator
Enter the three right-heart catheterization values: mean pulmonary artery pressure, pulmonary artery wedge pressure, and cardiac output.
Take mPAP, PAWP, and cardiac output from the same catheterization, ideally simultaneous measurements.
Enter all three. The wedge pressure subtracts out the left-heart contribution, isolating the pulmonary vessels.
Read PVR in Wood units and dynes with the interpretation. Above 3 Wood units marks pulmonary vascular disease.
How the Math Works
Subtract PA wedge pressure from mean PA pressure to get the transpulmonary gradient, then divide by cardiac output in L/min for Wood units. With mPAP 35, wedge 12, and output 4.5, the gradient is 23 and PVR is 5.1 Wood units. Multiply Wood units by 80 for dynesΒ·sΒ·cm-5: 5.1 times 80 is 409. The wedge subtraction is the conceptual key: it removes left-heart filling pressure, so the remainder reflects the pulmonary arterioles themselves. A high gradient with high wedge is post-capillary disease; with normal wedge, pre-capillary.
Worked Example
With mean PA pressure 35, wedge 12, and cardiac output 4.5 L/min, the transpulmonary gradient is 23 mmHg and PVR is 5.11 Wood units, or 409 dynes/s/cm5. The calculator flags this as Moderately elevated: the wedge is normal, so the elevation sits in the pulmonary arterioles, the pre-capillary pattern of pulmonary arterial hypertension. The same pressures with a wedge of 25 would tell a left-heart story instead.
Reading Your Result
Under 3 Wood units is normal. The 3 to 5 band is mildly elevated and, with a normal wedge, meets the hemodynamic definition range for pulmonary hypertension. Above 5 is substantially elevated, and above 8 to 10 marks severe disease where transplant evaluation discussions begin in appropriate candidates. Always read PVR with the wedge: high PVR plus high wedge points at the left heart, while high PVR with normal wedge points at the pulmonary vessels, and the treatments differ completely.
| PVR | Band | Reading |
|---|---|---|
| Under 3 WU | Normal | Healthy pulmonary circuit |
| 3-5 WU | Mildly elevated | PH range if wedge normal |
| 5-8 WU | Moderately elevated | Significant vascular disease |
| Above 8 WU | Severely elevated | Advanced disease |
Limitations
PVR is derived from single-point measurements that fluctuate with volume status, sedation, and oxygen; trends across caths beat single values. The wedge must be a true wedge: damped or partial tracings corrupt the gradient. Indexed PVR divides by body surface area for size comparison. This is a cath-lab teaching tool, not a diagnostic instrument.
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For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is pulmonary vascular resistance?
The resistance of the pulmonary circulation: the pressure drop across the lungs divided by the blood flow through them. It tells how diseased the pulmonary arterioles are, independent of how much blood the heart is pumping. High PVR means the right heart works against stiff, narrowed vessels.
What are Wood units?
mmHg per L/min: the pressure gradient divided by cardiac output. Named for the physiologist who popularized the formulation. Multiply by 80 to get dynesΒ·sΒ·cm-5, the older unit still quoted in many reports. Both describe the same physiology.
What is a normal PVR?
Under 3 Wood units (240 dynes). The pulmonary circuit is normally a low-resistance system, about a tenth of systemic resistance. Values above 3 with a normal wedge pressure define the hemodynamic component of pulmonary arterial hypertension.
Why subtract the wedge pressure?
Because the wedge estimates left atrial pressure, and the gradient driving flow through the lungs is the difference between PA pressure and left atrial pressure. Without the subtraction, left-heart disease would masquerade as pulmonary vascular disease. The subtraction isolates the vessels.
What is the difference between pre- and post-capillary PH?
Pre-capillary: high PVR with normal wedge, disease in the pulmonary arterioles themselves. Post-capillary: high wedge driving the pressures, the problem is left-heart filling. Combined: both. The distinction decides treatment, since PAH drugs do little for post-capillary disease.
How is cardiac output measured in the cath lab?
Usually by thermodilution: cold saline injected into the right atrium, temperature change measured downstream. The Fick method using oxygen consumption is the gold standard but more involved. Both have error bars that propagate into PVR.
Can PVR be estimated without a catheter?
Echo estimates pulmonary pressures from the tricuspid jet, but true PVR needs invasive flow and wedge data. Echo-derived PVR formulas exist as research tools with real error. Diagnosis and treatment decisions in PH rest on right heart catheterization.
Does PVR change with exercise?
Normally it falls as vessels recruit and distend. In pulmonary vascular disease it stays fixed or rises, which is why exercise hemodynamics unmask early disease. Exercise cath is a specialized test for borderline or unexplained cases.
What lowers PVR?
Treating the cause: PAH-targeted vasodilators for pre-capillary disease, optimizing left-heart filling for post-capillary, oxygen for hypoxic vasoconstriction, and transplant evaluation for end-stage disease. PVR is the number these therapies aim to move.
Why multiply by 80 for dynes?
Unit conversion: 1 Wood unit equals 80 dynesΒ·sΒ·cm-5. The dynes unit comes from the older absolute resistance formulation. Most modern guidelines and trials quote Wood units; many cath reports still show both.