How is PVR (Pulmonary Vascular Resistance) calculated?

Pulmonary Vascular Resistance (PVR) is a measure of the resistance that must be overcome for blood to flow through the pulmonary circulation. It is calculated using the difference between the mean pulmonary arterial pressure (MPAP) and the pulmonary capillary wedge pressure (PCWP), divided by the cardiac output.

This formula works by first determining the pressure gradient across the pulmonary vessels, which is the difference between the MPAP (the pressure in the pulmonary arteries) and the PCWP (which reflects the left atrial pressure and is used as an estimate of the pressure in the pulmonary circulation). By taking this pressure difference and dividing it by cardiac output, which indicates the volume of blood flowing through the circulation, you can derive the resistance encountered by the blood as it travels through the pulmonary vasculature.

This calculation is vital in assessing conditions that affect pulmonary circulation, such as pulmonary hypertension, as it helps to evaluate the workload on the heart and the health of the pulmonary vessels. The other options do not correctly apply the formula and would result in incorrect assessments of pulmonary vascular resistance.