Pulmonary vascular resistance

Pulmonary vascular resistance (PVR) is analogous to systemic vascular resistance (SVR), except that it refers back to the arteries that offer blood to the lungs. If the pressure within the pulmonary vessels is high, the suitable ventricle must work harder to maneuver blood forward through the pulmonary valve. Over time, this will likely cause the suitable ventricle to dilate and require additional volume to satisfy left ventricular preload needs (Breitenbach, 2010).

How to calculate PVR

PVR could be calculated by subtracting the left atrial pressure from the mean pulmonary artery pressure (PAP), divided by cardiac output (CO), and multiplied by 80. To obtain left atrial pressure, a pulmonary artery catheter (PAC) is required to perform a blood pressure test pulmonary artery occlusion pressure (PAOP), also referred to as pulmonary artery wedge pressure (PAWP). Normal PVR is 100 – 200 dynes/s/cm^-5.

Here is an example:
If a patient’s average PAP is 16 mmHg, his PAOP is 6 mmHg, and his cardiac output is 4.1 L/min, his PVR will likely be 195 dynes/s/cm^-5.

Factors increasing PVR

Factors that increase PVR include (Breitenbach, 2010):

• Vasoconstrictor drugs
• Hypoxia
• Acidosis
• Hypercapnia (high partial pressure of carbon dioxide in arterial blood [PaCO₂])
• Atelectasis

Factors reducing PVR

Factors that reduce PVR include (Breitenbach, 2010):

• Vasodilators
• Alkalemia
• Hypocapnia (low PaCO₂)
• Heavy exercise

The accuracy of PVR is determined by direct pressure measurements and indirect cardiac outputs from the catheter to the pulmonary artery, that are subject to error. However, PVR is helpful in diagnosing the severity of pulmonary hypertension (Fleitman, 2022). Understanding these parameters will help the bedside physician higher manage medications and hemodynamic instability.

Breitenbach, J. (2010). No more perfusion confusion. (3), 50-60. https://www.doi.org/10.1097/01.NME.0000393028.13649.14

Fleitman, J. (2022, July 6). Pulmonary artery catheterization: interpretation of hemodynamic values ​​and waveforms in adults. https://www.uptodate.com/contents/pulmonary-artery-catheterization-interpretation-of-hemodynamic-values-and-waveforms-in-adults

Gowda, C. (2008). Don’t be fooled by cardiovascular concepts. (4), 27-30. https://www.doi.org/10.1097/01.NME.0000324936.03867.c5