Hydromechanical principle of the different actions of the intrathoracic pressure changes on the two venous return systems

AIM To investigate the mechanism of the different influences of the intrathoracic pressure change (ITPC) on the two venous return systems. METHODS Two models that simulated the anatomic arrangement of the venous return systems and chest cavity were established to investigate the hydromechanic principle of the different influences of ITPC on the venous returns. RESULTS Model tests demonstrated that the same ITPC had different actions on the simulated venous return systems. ITPC would not change the pressure in the simulated right heart but its volume while it changed the pressure in the simulated left heart without directs influencing its volume. CONCLUSION Results of the model tests lead to a proposition of a new hypothesis about the mechanism of the cardiovascular effects of respiratory cycle: the respiratory ITPC is actually applied on the left side of the interatrial and ventricular septa and tends to move them left and rightward and change the end diastolic volume of the ventricles and, thus, respiration driven hemodynamic variation occurs.