What is Pulmonary Vascular Resistance (PVR)?

Pulmonary Vascular Resistance (PVR) is a critical hemodynamic measurement used to assess the resistance offered by the vasculature of the lungs. It measures the force that the right ventricle must overcome to pump blood through the pulmonary circulation. Elevated PVR is a hallmark of pulmonary hypertension and provides vital information for clinicians managing heart failure, lung disease, and congenital heart defects.

How the PVR Formula Works

To calculate PVR, clinicians use parameters obtained typically via right-heart catheterization. The basic formula is defined as the pressure gradient across the pulmonary circuit divided by the total blood flow (Cardiac Output). The specific formula is:

PVR = (mPAP - PCWP) / CO

Where:

• mPAP: Mean Pulmonary Arterial Pressure.
• PCWP: Pulmonary Capillary Wedge Pressure (an estimate of left atrial pressure).
• CO: Cardiac Output (the volume of blood pumped by the heart per minute).

Clinical Significance and Normal Ranges

PVR is usually expressed in Wood Units. To convert Wood Units to SI units (dyn·s/cm⁵), the value is multiplied by 80. A normal PVR is typically less than 2 Wood Units (or 160 dyn·s/cm⁵). Values significantly higher than this may indicate pulmonary arterial hypertension (PAH) or other forms of pulmonary vascular remodeling.

Frequently Asked Questions

Why is PCWP subtracted from mPAP?

Subtracting the PCWP (downstream pressure) from the mPAP (upstream pressure) gives the "transpulmonary gradient," which is the net pressure drop specifically across the pulmonary vascular bed.

What is the difference between PVR and SVR?

While PVR measures resistance in the lung circulation, Systemic Vascular Resistance (SVR) measures the resistance in the rest of the body's systemic circulation. SVR is normally much higher than PVR because the left ventricle must pump blood to the entire body.