Modelling the heart with the atrioventricular plane as a piston unit

Abstract

Medical imaging and clinical studies have proven that the heart pumps by means of minor outer volume changes and back-and-forth longitudinal movements in the atrioventricular (AV) region. The magnitude of AV-plane displacement has also shown to be a reliable index for diagnosis of heart failure. Despite this, AV-plane displacement is usually omitted from cardiovascular modelling. We present a lumped-parameter cardiac model in which the heart is described as a displacement pump with the AV plane functioning as a piston unit (AV piston). This unit is constructed of different upper and lower areas analogous with the difference in the atrial and ventricular cross-sections. The model output reproduces normal physiology, with a left ventricular pressure in the range of 8-130 mmHg, an atrial pressure of approximatly 9 mmHg, and an arterial pressure change between 75 mmHg and 130 mmHg. In addition, the model reproduces the direction of the main systolic and diastolic movements of the AV piston with realistic velocity magnitude (∼10 cm/s). Moreover, changes in the simulated systolic ventricular-contraction force influence diastolic filling, emphasizing the coupling between cardiac systolic and diastolic functions. The agreement between the simulation and normal physiology highlights the importance of myocardial longitudinal movements and of atrioventricular interactions in cardiac pumping.

Hydraulic forces contribute to left ventricular diastolic filling

“…Experiments with this mechanical pump showed fluid dynamics similar to the human heart22, supporting the concept of hydraulic forces contributing to diastolic filling. Similarly, simulation results have shown physiological pressures and flow in the LV and aorta, respectively, when considering hydraulic forces as the sole contribution to diastolic filling25.…”

“…This complex semi-rigid AV plane easily slides along the pericardium in the longitudinal (apex-base) direction, since the pericardium is lubricated by the pericardial fluid, which allows for near frictionless contact and motion between the two structures. This back-and-forth motion of the AV plane in the apex-base direction is similar to that of a piston that displaces blood during its motion2245, as clearly visible in CMR cine images44. The piston-like movements of the AV plane allow for reciprocal volume changes between the atria and the ventricles while keeping an approximately constant total heart volume4046.…”

“…Hydraulic forces are based on Pascal’s principle, and have previously been hypothesized to contribute to diastolic filling222324. The hypothesis has been tested using a mathematical model, where the AV plane was treated as a piston unit with two different areas25. In that model, the hydraulic force was assumed to be the only contribution to diastolic filling.…”

Relations Between Aortic Stiffness and Left Ventricular Mechanical Function in the Community

“…The relation between aortic stiffness and diastolic function is often attributed to hemodynamic effects, while the relation between GLS and diastolic function has been attributed to recoil of contracted LV muscle fibers 49, 50. Recent studies have suggested that diastolic recoil of the aorta and left atrium, which are stretched during systole, facilitates LV filling and ejection 12, 51, 52, 53, 54, 55. The association between increased aortic stiffness and worse GLS observed in our study may relate to both the systolic and diastolic components of direct mechanical ventricular–vascular coupling and requires further study 48…”

Atrioventricular plane displacement is the sole mechanism of atrial and ventricular refill

“…Commonly acknowledged factors, such as skeletal and smooth muscle contractions, thoracic suction, one-way valves in the limb veins, gravity, diastolic suction (6,7,11), cannot be considered as universal mechanisms for the blood return to the heart chambers, since none of them are a valid physiological mechanism for the beat to beat, ventricular and atrial refill in normal conditions. Only the pressure gradient on the venous side and AVPD (1), which recently was considered as a piston-like mechanism having input in cardiac systolic and diastolic functions (9), comprises physiologically relevant inputs in ventricular refill.…”