PVR Calculator (Pulmonary Vascular Resistance)

PVR is a hemodynamic measure of the resistance to blood flow through the pulmonary vasculature. It reflects the pressure drop across the pulmonary system — from the pulmonary artery through the capillary bed to the pulmonary veins — independent of left atrial pressure, making it more precise than Total Pulmonary Resistance for assessing pulmonary vascular disease.

PVR (dynes·sec/cm⁵) = 80 × (MPAP − PCWP) / Cardiac Output. The factor 80 converts from Wood Units (mmHg·min/L) to the CGS unit dynes·sec/cm⁵. To get PVR in Wood Units, simply divide (MPAP − PCWP) by Cardiac Output without multiplying by 80.

Normal PVR is approximately 20–130 dynes·sec/cm⁵ (or 0.25–1.6 Wood Units) at rest. Values consistently above 240 dynes·sec/cm⁵ (3 Wood Units) are generally considered elevated and may indicate pulmonary hypertension or pulmonary vascular disease.

TPR (also called pulmonary vascular resistance total) is calculated as MPAP / Cardiac Output and reflects resistance across the entire pulmonary circulation including the left atrium. PVR subtracts PCWP (wedge pressure) from MPAP first, isolating the pre-capillary pulmonary vascular resistance. PVR is considered more accurate for assessing intrinsic pulmonary vascular disease.

PCWP (also called pulmonary artery occlusion pressure) approximates left atrial pressure and left ventricular end-diastolic pressure. It is measured by occluding a pulmonary artery branch with a Swan-Ganz catheter balloon. Subtracting PCWP from MPAP isolates the transpulmonary pressure gradient, which is essential for accurately calculating PVR independent of left heart conditions.

Elevated PVR is seen in pulmonary arterial hypertension (PAH), chronic thromboembolic pulmonary hypertension (CTEPH), hypoxia, hypercapnia, increased sympathetic tone, pulmonary fibrosis, and certain congenital heart diseases. It is an important parameter in evaluating candidates for heart transplantation and guiding management of pulmonary hypertension.

Blood flows from higher to lower pressure, so the mean pulmonary arterial pressure must always exceed the downstream pulmonary capillary wedge pressure for forward flow to occur. If PCWP equals or exceeds MPAP, the calculation produces a zero or negative pressure gradient, which is physiologically impossible under normal circumstances and suggests a data entry error.

Wood Units (WU) are a simpler expression of pulmonary resistance: WU = PVR (dynes·sec/cm⁵) / 80. Equivalently, 1 Wood Unit = 80 dynes·sec/cm⁵. Wood Units are commonly used in clinical practice (especially in pediatric cardiology and transplant evaluation), while dynes·sec/cm⁵ is the standard CGS unit used in research and adult hemodynamic reports.