Final answer:
Pulmonary vascular resistance (PVR) reflects the afterload of the right ventricle, and is affected by conditions that alter the resistance in the pulmonary circulation. Residual volume (RV) refers to air remaining in the lungs and is not a direct measure of afterload, but can have an indirect effect on it.
Step-by-step explanation:
Pulmonary vascular resistance (PVR) is an indicator of the resistance that the right ventricle must overcome to pump blood through the lungs, and is thus a measure of right ventricular afterload. Afterload is the force required by the ventricles to eject blood into the arterial system. Conditions that increase vascular resistance, such as pulmonary hypertension, increase afterload, demanding more effort from the heart to circulate blood.
However, conditions affecting the lungs can indirectly influence the workload of the heart by affecting the vascular resistance the right ventricle faces during pulmonary circulation.
Any condition that increases resistance requires a greater afterload to force open the semilunar valves and pump the blood. Damage to the valves, such as stenosis, which makes them harder to open will also increase afterload. Any decrease in resistance decreases the afterload.