Which of the following can cause decreased pulmonary artery pressure (PAP)?

Decreased pulmonary artery pressure (PAP) can occur due to hypovolemia, which refers to a reduced volume of blood in the circulatory system. When blood volume is low, there is less blood returning to the right side of the heart, which leads to less blood being pumped into the pulmonary circulation. Consequently, this results in a lower pressure within the pulmonary artery because pressure is directly related to the volume of blood and flow within the vessels.

In contrast, hypervolemia would typically increase PAP due to the increased volume of fluid within the circulation, creating higher pressure. Increased peripheral vascular resistance can also contribute to elevated pressures in the pulmonary system, as it presents more resistance to blood flow. Lastly, mitral stenosis is associated with increased pressures in the pulmonary circulation due to backflow from the left atrium, so it does not lead to decreased PAP.

Understanding these physiological responses helps clarify why hypovolemia is linked with decreased PAP.