How can the jet of tricuspid regurgitation be used to estimate the pulmonary systolic pressure?

During systole, the pulmonary valve is open. In the absence of pulmonary stenosis, the right ventricular systolic pressure (RVP) is a good representative of the pulmonary systolic pressure. The tricuspid regurgitation jet reflects the pressure gradient (_rP) between the right ventricle and the right atrium during systole (that is,_rP = RVP - RAP, where RAP is right atrial systolic pressure). If _rP is known, it is possible to solve for RVP (RVP = RAP+ _rP).