Which formula defines Pulmonary Vascular Resistance (PVR)?

Which formula defines Pulmonary Vascular Resistance (PVR)?

• A. ((Mean PAP - PCWP) / CO) × 80
• B. ((MAP - CVP) / CO) × 80
• C. (MAP / CO) × 60
• D. ((PCWP - mean PAP) / CO) × 80

Answer: (A)

Pulmonary vascular resistance is the pressure the right side of the heart must overcome to push blood through the lungs, expressed as a pressure drop across the pulmonary circuit divided by flow, with units in dynes·s·cm⁻⁵. The pressure drop is the difference between mean pulmonary artery pressure and the left atrial pressure (approximated by PCWP), and the flow is cardiac output. To get the standard unit, multiply by 80. So the correct expression is (mean PAP − PCWP) / CO × 80. This uses the actual pressure gradient across the pulmonary vasculature and the forward flow, converted to the conventional units. The other formulas aren’t PVR: one uses systemic pressures (MAP and CVP), which defines systemic vascular resistance, not pulmonary. The remaining option either reverses the gradient (PCWP − mean PAP) or omits the gradient and uses an incorrect factor, which doesn’t reflect the pulmonary circuit’s resistance.

Pulmonary vascular resistance is the pressure the right side of the heart must overcome to push blood through the lungs, expressed as a pressure drop across the pulmonary circuit divided by flow, with units in dynes·s·cm⁻⁵. The pressure drop is the difference between mean pulmonary artery pressure and the left atrial pressure (approximated by PCWP), and the flow is cardiac output. To get the standard unit, multiply by 80.

So the correct expression is (mean PAP − PCWP) / CO × 80. This uses the actual pressure gradient across the pulmonary vasculature and the forward flow, converted to the conventional units.

The other formulas aren’t PVR: one uses systemic pressures (MAP and CVP), which defines systemic vascular resistance, not pulmonary. The remaining option either reverses the gradient (PCWP − mean PAP) or omits the gradient and uses an incorrect factor, which doesn’t reflect the pulmonary circuit’s resistance.