Echocardiography Techniques II Exam 2 Practice

Qp:Qs is the ratio of pulmonary blood flow to systemic blood flow, used to gauge how large a shunt is. It reflects how much blood is circulating through the lungs compared with the body, which tells you the magnitude of a left-to-right shunt. When the ratio is about 1, there’s no significant shunt; as it rises above 1, more blood goes through the pulmonary circulation than the systemic circulation, indicating a larger shunt. In practice, this ratio is often estimated from Doppler measurements of stroke volumes across the pulmonary and aortic valves: Qp equals the pulmonary valve cross-sectional area times its velocity-time integral, and Qs equals the aortic valve cross-sectional area times its velocity-time integral; the ratio of these two gives Qp:Qs. Accurate measurement is essential because errors in valve size or VTI can skew the ratio.