Ventricular function. Is the total more than the sum of the parts?

Abstract

For the life of the body is more than the sum of the properties of the cells of which it is composed. D'Arcy Wentworth Thompson (based on a statement by Goethe)l F undamental to evolution in biology has been the trend toward growing complexity, from the molecular to the cellular level, toward multicellularity, and finally the whole-organ level. At any level, biological systems are composed of interacting subsystems, which in turn are also systems, albeit on a smaller scale. Interaction between subsystems may add entirely new properties to the composite system. In the cardiovascular system, consideration of the interaction between the left ventricle and arterial load and the efficiency of this interaction is not new.2-4 In the heart, already on smaller scales, several interaction processes seem to be incorporated as we move up from a subcellular to the whole-organ level (Figure 1). From the subsequent discussion on ventricular function, it will follow that interaction processes constitute an essential and obligatory property of ventricular function, in which the mechanisms involved are still largely unknown. Therefore, one cannot easily extrapolate from mere subcellular or molecular events to whole-organ function without considering these interaction processes at increasingly larger levels.Several interaction processes have been considered at different levels. We will focus on three of these: Upgrading of system performance through interaction of subsystems, uniformity of system performance through interaction of subsystems, and modulation of system performance through cell communication.Upgrading of System Performance Through Interaction of Subsystems The most generally accepted model of cardiac contraction at the molecular level is the cyclical attachment and detachment of the globular portionThe opinions expressed in this article are not necessarily those of the editors

Effect of dysfunctional vascular endothelium on myocardial performance in isolated papillary muscles.

“…It would thus appear that, in rabbit papillary muscles, increasing the extracellular calcium concentration to at least 25 mM or increasing the myofibrillar affinity for calcium at 15 mM calcium concentration22,31,39-41 is necessary for the myocardium to reach maximal performance, with additional interventions not necessary in the cat or ferret. 9,38 Recently, Wang and Morgan5 and McClellan et a131 have demonstrated that both endocardial and vascular endothelium appear to modify the contractile characteristics of adjacent myocardium by increasing myofilament calcium responsiveness or affinity. In this study done in rabbit myocardium, the addition of phenylephrine to 15 mM extracellular calcium concentrations was necessary to completely normalize total twitch tension and time to peak total tension in papillary muscles with dysfunctional vascular endothelium.…”

Cardiac failure: quo vadis?

“…How in the heart as a dissipative structure, fluctuations, interactions, and a perfectly tuned coherence of adjacent subsystems at each smaller hierarchic scale would lead to spontaneous auto‐organization of a super‐system with emerging properties is as yet not entirely clear 15–16. At the lowest, subcellular hierarchic scale, current large‐scale quantitative analysis of gene expression, including cDNA microarrays and proteomic analysis, have already suggested the existence of numerous molecular interactions acting in functional modules.…”

“…of functional non‐uniformities in space and time. As a dissipative structure the heart thus functions as an ordered pluri‐cellular optimizing pump 15–16 ( Figure ).…”

“…In a dissipative structure, each part is expected to affect the whole through interactions and coherence with the other parts, hence the whole is more than the sum of parts 14–16. It is therefore a bit surprising that in heart failure most cardiologists continue to restrict their attention to only a few, stereotypic targets.…”

The Second Law of Thermodynamics and the Heart

“…The description of the heart as a dissipative structure was first made by Dirk Brutsaert [35,36]. Brutsaert introduced the concept that the interactions among different levels of complexity at molecular, cellular and tissue levels may induce the development of emerging new features that are not apparent when the heart is only considered as the sum of the properties of the cells of which it is composed [37].…”