Key result
Simulated respiratory intrathoracic pressure changes generated a pressure gradient across the interventricular septum, driving septal swinging that was markedly amplified under conditions simulating cardiac tamponade.
Mechanical models suggest pulsus paradoxus is caused by a pressure gradient across the interventricular septum resulting from differential effects of respiratory intrathoracic pressure changes on systemic and pulmonary venous return.
May aid pulsus paradoxus interpretation; hypothesis-generating and leaves open clinical translation pending validation.
Pulsus paradoxus is an exaggeration of the normal inspiratory decrease in systolic blood pressure. Despite a century of attempts to explain this sign consensus is still lacking. To solve the controversy and reveal the exact mechanism, we reexamined the characteristic anatomic arrangement of the circulation system in the chest and designed these mechanical models based on related hydromechanic principles. Model 1 was designed to observe the primary influence of respiratory intrathoracic pressure change (RIPC) on systemic and pulmonary venous return systems (SVR and PVR) respectively. Model 2, as an equivalent mechanical model of septal swing, was to study the secondary influence of RIPC on the motion of the interventriclar septum (IVS), which might be the direct cause for pulsus paradoxus. Model 1 demonstrated that the simulated RIPC had different influence on the simulated SVR and PVR. It increased the volume of the simulated right ventricle (SRV) when the internal pressure was kept constant (8.16 cmH2O), while it had the opposite effect on PVR. Model 2 revealed the three major factors determining the respiratory displacement of IVS in normal and different pathophysiological conditions: the magnitude of RIPC, the pressure difference between the two ventricles and the intrapericardial pressure. Our models demonstrate that the different anatomical arrangement of the two venous return systems leads to a different effect of RIPC on right and left ventricles, and thus a pressure gradient across IVS that tends to shift IVS left- and rightwards. When the leftward displacement of IVS reaches a considerable amplitude in some pathologic condition such as cardiac tamponade, the pulsus paradoxus occurs.
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Xing et al. (2013) studied Pulsus paradoxus. Simulated respiratory intrathoracic pressure change (RIPC) vs. Baseline pressure was evaluated on Displacement of the simulated interventricular septum (IVS). Simulated respiratory intrathoracic pressure changes generated a pressure gradient across the interventricular septum, driving septal swinging that was markedly amplified under conditions simulating cardiac tamponade.
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