Figure 17-7 Passive changes in pulmonary vascular resistance (PVR) as a function of pulmonary artery pressure (Ppa) and pulmonary blood flow (T) (PVR = Ppa/QT). As T increases, Ppa also increases, but to a lesser extent, and PVR decreases. As QT decreases, Ppa also decreases, but to a lesser extent, and PVR increases. (Redrawn with modification from Fishman AP: Dynamics of the pulmonary circulation. In Hamilton WF [ed]: Handbook of Physiology, section 2. Circulation, vol 2. Baltimore, Williams & Wilkins, 1963, p 1667.)