Figure 1: The mechanism of pulmonary valve diastolic opening (revised from ref. 20).
From: A Simple Method for Noninvasive Quantification of Pressure Gradient Across the Pulmonary Valve
Hydromechanically, the circulatory system may be considered as two enclosed fluid systems: fully-intrathoracic and partially-intrathoracic (the dark and the white portions, respectively). They are characteristically arranged in a closed chamber - the chest cavity - with negative pressure. With a gradual Muller maneuver or inspiration (see the bottom panel of Fig. 3A), the pressure in the fully-intrathoracic portion decreases equally with the decrease in intrathoracic pressure (ITP) (top panel), while the pressure decrease in the right ventricle (RV) will be mostly compensated for by the systemic venous return (SVR). With the progression of the maneuver, the pressure decrease in the pulmonary artery (PA) may drop below the pressure in the RV, and the pulmonary valve may open in diastole with a small diastolic forward flow (the bottom panel). This flow may be detected by a sensitive technique such as Doppler echocardiography. PVR, pulmonary venous return; LV, left ventricle; LA and RA, left and right atria; AO, aorta.
