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Energetics Equivalent of the Cardiac Force-Length End-Systolic Zone: Implications for Contractility and Economy of Contraction. | LitMetric

AI Article Synopsis

  • Researchers have identified a specific area on the cardiac mechanics stress-length plane called "The cardiac end-systolic zone," which encompasses all contraction profiles at the end-systole phase of the heart cycle.
  • This zone is defined by three boundaries: isometric end-systolic relation, work-loop end-systolic relation, and zero-active stress isotonic end-systolic relation, indicating the relationship between contraction mode and force-length dynamics in the heart.
  • The study also proposes a similar zone exists for cardiac metabolism, as seen through distinct heat-stress relations during different contraction modes, with findings showing that enhancing contractility increases both mechanical and energetic zones, supporting the hypothesis.

Article Abstract

We have recently demonstrated the existence of a region on the cardiac mechanics stress-length plane, which we have designated "The cardiac end-systolic zone." The zone is defined as the area on the pressure-volume (or stress-length) plane within which all stress-length contraction profiles reach their end-systolic points. It is enclosed by three boundaries: the isometric end-systolic relation, the work-loop (shortening) end-systolic relation, and the zero-active stress isotonic end-systolic relation. The existence of this zone reflects the contraction-mode dependence of the cardiac end-systolic force-length relations, and has been confirmed in a range of cardiac preparations at the whole-heart, tissue and myocyte levels. This finding has led us to speculate that a comparable zone prevails for cardiac metabolism. Specifically, we hypothesize the existence of an equivalent zone on the energetics plane (heat vs. stress), and that it can be attributed to the recently-revealed heat of shortening in cardiac muscle. To test these hypotheses, we subjected trabeculae to both isometric contractions and work-loop contractions over wide ranges of preloads and afterloads. We found that the heat-stress relations for work-loop contractions were distinct from those of isometric contractions, mirroring the contraction mode-dependence of the stress-length relation. The zone bounded by these contraction-mode dependent heat-stress relations reflects the heat of shortening. Isoproterenol-induced enhancement of contractility led to proportional increases in the zones on both the mechanics and energetics planes, thereby supporting our hypothesis.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6985585PMC
http://dx.doi.org/10.3389/fphys.2019.01633DOI Listing

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