If the bicuspid (mitral) valve is not fully closing, does pulmonary circulation increase, decrease, or not change?

Answer: Decrease

It will decrees because required volume of blood will not be emptied into the pulmonary circulation to reach the lung for oxygenation. Rather blood flows back into the Right atrium, (regurgitation,) through the these valves during ventricular contraction (systole) of the Right Ventricle instead to the pulmonary circulation which reduces blood flow leading to volume overload in the heart. Eventually this affects systemic circulation,