Which of the following decreases pulmonary vascular resistance (PVR)?

Decreasing pulmonary vascular resistance (PVR) is significant for improving pulmonary circulation and ensuring adequate blood flow to the lungs for gas exchange. Hypovolemia, which refers to a decreased volume of blood in the body, can lead to a reduction in PVR through various physiological mechanisms. In a state of hypovolemia, the blood vessels dilate to accommodate the lower volume, and this vasodilation contributes to a reduction in resistance within the pulmonary vascular system.

In situations where there is decreased blood volume, the body tries to optimize blood flow to vital organs, including the lungs, thus resulting in a decrease in pulmonary vascular resistance. An increase in cardiac output during hypovolemia can further result in the recruitment of additional pulmonary capillaries, promoting better blood flow and enhancing gas exchange efficiency.

The other options relate to conditions or factors that typically lead to an increase in PVR rather than a decrease. Excessive fluid retention can lead to increased pulmonary vascular resistance due to volume overload and congestion. Increased heart rate can cause increased PVR by raising the pressure within the pulmonary circulation, and chronic lung diseases often involve pathological changes in the lung vasculature that elevate resistance.