What Is the Normal Range for Pulmonary Vascular Resistance?

Healthy lungs offer very little resistance to blood flow, so a normal pulmonary vascular resistance (PVR) is a small number, usually close to 1 on a report. In healthy adults lying down it runs about 1 Wood unit, roughly 80 dynes·s/cm5, a little under 1 in young adults and slightly above 1 after 50. Current European guidelines treat anything above 2 Wood units as elevated when pulmonary hypertension is being assessed. Some reports give the same value multiplied by 80 in a different unit.1PubMed. Pulmonary Hypertension by the Method of Paul Wood What counts as normal also creeps up with age and shifts with pregnancy, exercise and altitude.

Normal PVR Values by Age

PVR describes how hard the lung blood vessels push back against the blood your right heart pumps through them. Wide, flexible vessels give low numbers, while narrowed or stiff vessels give high ones. Published normal resting values, measured lying down, look like this:

Those ranges come from people lying flat and resting. Resting PVR is higher sitting or standing than lying down.6PubMed. Pulmonary vascular resistances during exercise in normal subjects: a systematic review A number taken in a different setting is not directly comparable to the table. If your report mentions that you were sedated, on supplemental oxygen or acutely ill, ask whether those conditions could have shifted the value. A single reading is also a snapshot of one moment, and the same person tested on two days can differ a little. Doctors judge your number alongside the pressure and flow figures printed next to it.

PVR increases gradually with healthy aging.7PubMed Central. The Pulmonary Circulation and Exercise Responses in the Elderly In people free of heart disease, those 60 and older averaged about 124 dynes versus 70 dynes in younger adults.8PubMed. Influence of aging on pulmonary hemodynamics in a population free of coronary artery disease A value inside the normal spread that has risen noticeably since an earlier test is worth raising with your doctor, since the trend adds information.

Wood Units, Dynes and How PVR Is Calculated

PVR equals the mean pressure in the lung artery minus the pressure on the left side of the heart, divided by how much blood flows each minute.9MDApp. Pulmonary Vascular Resistance (PVR) Calculator The left-side pressure is usually estimated by the wedge pressure (PCWP), taken by briefly blocking a small lung artery with a balloon catheter.10PubMed Central. The Pulmonary Circulation and Exercise Responses in the Elderly If your lung artery pressure is 15, wedge pressure 8 and flow 5 liters a minute, PVR is 7 divided by 5, or 1.4 Wood units.

To find these inputs on your own report, look for mPAP, PCWP or wedge pressure, and cardiac output. Pressures are in mmHg, and cardiac output is in liters per minute. Some reports index PVR to body size, shown as units times square meters, which gives larger numbers. Ask which version your report uses before comparing.

Because flow sits in the denominator, the same pressure drop gives a lower PVR when flow is high. That is why pressure alone doesn’t tell the whole story, and why doctors look at all three inputs together. With the earlier pressure drop of 7 and flow of 7 liters a minute, PVR would be 1.0. With flow of only 3.5 liters a minute, PVR would be 2.0, so a weak pump alone can push the number up. A report with a high lung pressure but a normal PVR can therefore mean the pressure comes from high flow rather than narrowed vessels.

Wood units are the common unit for PVR, while body-wide resistance is usually given in dynes.11OpenAnesthesia. Calculation of Pulmonary and Systemic Vascular Resistance One Wood unit equals 80 dynes·s/cm5.12OpenAnesthesia. Calculation of Pulmonary and Systemic Vascular Resistance

To go from Wood units to dynes, multiply by 80, so 3 Wood units corresponds to 240 dynes. To go the other way, divide dynes by 80, so 400 dynes is 5 Wood units. Check the unit printed beside the number before judging it. A value of 240 would be very high if mistaken for Wood units, but in dynes it is only 3 Wood units.

When PVR Is Considered High

The 2022 European heart and lung society guidelines define pulmonary hypertension as a mean lung artery pressure above 20 mmHg, with PVR above 2 Wood units marking the vessel-related type. Older definitions used a lung pressure of 25 and a PVR of 3 Wood units, so some doctors and older reports still use those numbers. Under the newer definition, among people with lung pressures of 21 to 24 once called normal, about half now count as having the vessel-related type.13PubMed Central. Predictors of outcomes in mild pulmonary hypertension according to 2022 ESC/ERS Guidelines: the EVIDENCE-PAH UK study

That is why a PVR between 2 and 3 can feel confusing. One source may call it normal and another mildly high, and the difference is the guideline version, not your lungs. A PVR of 2.5, for example, is normal under the old cutoff and elevated under the new one. A reasonable question for your doctor is which cutoff they use, and whether a value in the gray zone changes what they plan to do.

Wedge pressure helps sort the cause.14PubMed. Definition and classification of pulmonary hypertension A wedge pressure of 15 or lower with high PVR suggests the trouble starts in the lung arteries themselves, the group where targeted lung-vessel medicines are usually considered. A wedge pressure above 15 with a PVR of 2 or less suggests pressure is backing up from the left heart, so treatment focuses on the heart condition, such as heart failure or a valve problem. When wedge pressure is high and PVR is also above 2, both problems can be present, which often calls for specialist review.

High PVR matters because of what it does to the right ventricle. That chamber has thinner walls than the left and is built for low-pressure pumping, so it struggles when the lung vessels resist more. At first it thickens to compensate. Over time it can stretch and weaken, which lowers the amount of blood it can send to the lungs.

Shortness of breath with effort, unusual tiredness and ankle swelling are common symptoms, but they also occur in many other conditions and do not confirm high PVR. Echo measurements of the right ventricle’s size and how well it moves are often used to follow this strain between catheter tests.

Exercise, Pregnancy, Altitude and Other Normal Shifts

In healthy people 50 and under, moderate exercise lowers PVR by about 12% even as blood flow nearly doubles.15PubMed. Pulmonary vascular resistances during exercise in normal subjects: a systematic review The lung vessels widen and extra vessels open, which is how resistance can fall while more blood moves through. Between 51 and 69 there is little drop, and over 70 PVR stays about the same during moderate exercise.16PubMed. Pulmonary vascular resistances during exercise in normal subjects: a systematic review

In pregnancy, PVR falls about 13 to 16% in the second trimester and up to about 17.5% in the third.17PubMed Central. Serial Changes in Pulmonary Hemodynamics During Pregnancy: A Non-Invasive Study Using Doppler Echocardiography This lets the much larger blood volume pass through the lungs without raising pressure.18PubMed. Respiratory physiology in pregnancy After delivery the number gradually moves back toward the non-pregnant range over the following weeks.19PubMed Central. Serial Changes in Pulmonary Hemodynamics During Pregnancy: A Non-Invasive Study Using Doppler Echocardiography A pregnant woman whose PVR fails to fall, or is elevated, may be at higher risk, so a high value in pregnancy is taken seriously and not assumed to be normal.

Low oxygen narrows lung vessels. At simulated extreme altitude, PVR rose from about 1.2 to 4.3 Wood units, and that rise was not immediately reversed by breathing oxygen.20PubMed. Operation Everest II: elevated high-altitude pulmonary resistance unresponsive to oxygen The narrowing is a normal reflex that sends blood toward better-ventilated parts of the lung. At high altitude it is widespread, so lung pressure and PVR rise in nearly everyone, by different amounts. People who live at high altitude long-term may have somewhat higher baseline values, so where you live can affect how your number is read.

If you are being tested, tell your doctor if you are pregnant or recently lived at high altitude. A test done during an illness that lowers your oxygen may read higher.

How PVR Is Measured and How Reliable Estimates Are

A right heart catheterization threads a thin tube through a vein into the heart and lung artery to measure pressures and flow directly. It is the test doctors use to confirm pulmonary hypertension. It measures lung artery pressure, wedge pressure and cardiac output during the test instead of estimating them from images. Because every input to the formula is measured at once, the calculated PVR is the number that guidelines and treatment decisions rest on.

Ultrasound of the heart can estimate PVR, and one method typically lands within about 0.7 Wood units of the catheter value.21Journal of Cardiac Failure. What Is the Normal Range for Pulmonary Vascular Resistance? Certain echo ratios can help flag PVR above 6 Wood units.22PubMed. Noninvasive assessment of pulmonary vascular resistance by Doppler echocardiography In people with chronic heart failure, echo flow patterns can track PVR over time.23PubMed. Accurate noninvasive estimation of pulmonary vascular resistance by Doppler echocardiography in patients with chronic failure heart failure

Heart MRI can estimate pressure, wedge pressure and flow and calculate PVR without a catheter.24PubMed. Noninvasive estimation of PA pressure, flow, and resistance with CMR imaging: derivation and prospective validation study from the ASPIRE registry Still, estimates can be off by about 20%, up to about 1.5 Wood units.25PubMed Central. 4D Magnetic Resonance Flow Imaging for Estimating Pulmonary Vascular Resistance in Pulmonary Hypertension An MRI or echo number near 2 therefore doesn’t settle whether you’re above the cutoff.

Echo is often used first and for follow-up. An estimate that is clearly normal or very high may be reliable enough to guide the next steps, while one near the cutoff leaves real uncertainty. A borderline or surprising estimate usually leads to a catheter test, and so can symptoms that don’t match the estimate. Compare echo and MRI values with earlier ones from the same type of test, because different methods have different built-in errors.

Why PVR Rises and How It Can Be Lowered

Sustained high PVR comes from lung arteries tightening and their walls thickening over time.26PubMed. Cellular and molecular mechanisms of pulmonary vascular remodeling: role in the development of pulmonary hypertension Muscle and lining cells in the vessel wall overgrow and can close off small arteries.27PubMed. Cellular and molecular mechanisms of pulmonary vascular remodeling: role in the development of pulmonary hypertension Long-term low oxygen especially thickens the muscle layer.28PubMed Central. Pulmonary Vascular Remodeling in Pulmonary Hypertension Early on, the narrowing may be partly from tightening muscle, which can sometimes relax with medicine, while later thickening and scarring are harder to reverse. That is part of why early diagnosis matters, since treatment tends to work better before the walls have changed much.

Not every high PVR comes from vessel disease. Left heart failure or valve disease backs pressure into the lungs. Lung diseases like COPD and sleep apnea lower oxygen and raise PVR. Old blood clots in the lungs can block vessels, and because these may be treatable with surgery or other procedures, doctors look for them. Treating the underlying cause is often the main way PVR comes down.

To see whether the vessels can relax, doctors may give inhaled nitric oxide during the catheter test.29PubMed Central. Sildenafil versus nitric oxide for acute vasodilator testing in pulmonary arterial hypertension Only about 8 to 12% of people with pulmonary arterial hypertension respond strongly.30PubMed Central. Sildenafil versus nitric oxide for acute vasodilator testing in pulmonary arterial hypertension It matters because it can show that a person may do well on an older class of medicines called calcium channel blockers. Most people do not respond strongly, and a weak response does not mean treatment will fail, since the other drug groups work by different routes. Oxygen alone can also lower PVR, and nitric oxide plus oxygen lowers it further in some children.31PubMed. Combined effects of nitric oxide and oxygen during acute pulmonary vasodilator testing

People with this disease have too little of natural vessel-relaxing substances like prostacyclin and nitric oxide.32Nature Reviews Cardiology. Treatment of pulmonary arterial hypertension with targeted therapies Three drug groups replace or boost them: prostacyclin-type drugs, endothelin blockers and PDE5 inhibitors such as sildenafil.33PubMed. Targeted therapies in pulmonary arterial hypertension These can improve symptoms, exercise ability and the measured numbers.34PubMed. Targeted therapies in pulmonary arterial hypertension

Doctors often judge treatment by symptoms, walking ability and repeat testing of PVR, not by PVR alone. Medicines from different groups are often combined, and the plan is adjusted if the numbers or symptoms don’t improve.

After a high reading, useful questions include:

  • Which type of pulmonary hypertension does the wedge pressure suggest?
  • Was a vasodilator test done, and what was the result?
  • Which treatments fit that type?
  • How often will PVR be rechecked, and by which test?