Spatial energy balance within a structural model of the left ventricle

From Organ to Molecules: Steps and Consequences

The classic cardiac research programs revolved around measurable properties such as pressures, work done, vascular blood flow, electrical propagation, and other such parameters that defined the global heart functions in health and decease. Consistently, the first Henry Goldberg Workshop, held in Haifa in 1984, focused on the interactions between cardiac mechanics, electrical activation, perfusion, and metabolism of the whole heart. Questions focused on the macroscale cardiac function and performance. These studies involved engineering science, simulation, and modeling tools that were essential for the understanding of the complex interactions within the cardiac system. Three-dimensional imaging, ventricular structure, fiber mechanics, circulation and cardiovascular flow, electrical propagation, and blood pumping were all major foci of research at that time. However, it was soon obvious that in order to understand organ level characteristics, one must explore the complex cellular and intracellular control mechanisms; these became the foci of our subsequent workshops. Better understanding of organ level performance required integrated studies of organ and tissue structure and function with genetic, molecular, and cellular characteristics, including cellular communication and ionic and molecular signaling. Analysis of the cardiac system thus depends on continuous probing of the heart system with modern measurement techniques and on integrating data and acquired knowledge with analytical models, constantly evolving to match reality.

Effects of partial left ventriculectomy on left ventricular pump function studied by theoretical analyses

Although partial left ventriculectomy (PLV) was devised to reduce myocardial wall stress in patients with severe heart failure, whether the operation acutely improves cardiac pump function has not been determined either clinically or experimentally. Because precise control of preload, afterload, and heart rate is virtually impossible in animal experiments as well as clinically before and after surgery, we took advantage of the theoretical analysis to study quantitatively the changes in pump function by PLV. We reconstructed the endsystolic and end-diastolic pressure-volume relationships based on two different geometric conditions (i.e., before and after volume reduction) but from the same myocardial stress-strain relationship. The effect of volume reduction surgery on left ventricular pump function depended on preoperative conditions. We found that the improvement in pump function was achieved only if elastance (Ees) was low and if the end-systolic strain-axis scaling parameter (k) value was low. The presence of hypertrophy amplified the improved function, but again with low Ees and low end-systolic k. We conclude that the favorable hemodynamics are expected only in limited cases during the acute phase. Candidates for favorable preoperative factors include low end-systolic Ees, an end-systolic pressure-volume relationship being less convexed toward the volume axis (low k), and large left ventricular mass.

Mechanical pathophysiology of some heart diseases: a theoretical model study

Sarcomere dynamics are related to the global left ventricular (LV) function in some representative pathological states, by using a theoretical model which combines sarcomere function, LV fibrous structure and geometry with the haemodynamic loading conditions. The analysis shows that pressure (concentric) hypertrophy due to hypertension or aortic stenosis is associated with an increase of the normal endocardial-to-epicardial gradient(s) of oxygen demand, which may be one of the causes for the development of endocardial fibrosis. The analysis also indicates that sarcomere shortening is relatively normal in compensated volume (eccentric) hypertrophy. Mitral stenosis demonstrates a case of decreased LV function, secondary to a chronic decrease in LV end diastolic volume, with sarcomeres that operate at their lowest length range. Conversely, the sarcomere function is depressed in cardiomyopathy; the heart's pumping function is maintained by appropriate adjustment mechanisms. However, the sarcomeres show minimal shortening and function at their highest length range with low (or zero) functional reserve. The study thus provides a quantitative tool that relates global LV function to local sarcomere dynamics in various pathological states.