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Fig. 1 | BioMedical Engineering OnLine

Fig. 1

From: Prediction of the mechanical response of cardiac alternans by using an electromechanical model of human ventricular myocytes

Fig. 1

Schematic diagram of excitation–contraction coupling model of ventricular cell. The left diagram represents a human ventricular cell model with electrophysiological characteristics that mimic the ion exchange phenomenon through the cell membrane of myocytes. Ito is the transient outward K+ current, IpK is the plateau K+ pump current, INaK is the Na+–K+ ion exchanger current, IpCa is plateau Ca2+ pump current, and INaCa is the Na+–Ca2+ ion exchanger current. Ek, ECa, and ENa are the equilibrium potentials of K+, Ca2+, and Na+ ions, respectively. Cm is the ventricular cell membrane capacitance in the unit surface area. IK1 is the inward rectifier K1 current, IKs is the slow delayed rectifier K+ current, IK1 is the rapid delayed rectifier K+ current, ICaL is the L-type inward Ca2+ current, IbCa denotes the background Ca2+ current, IbNa is the background Na+ current, and INa is the fast inward Na+ current. Irel is the release Ca2+ current from the sarcoplasmic reticulum (SR), Ileak is the leakage Ca2+ current from the SR, and Iup is the Ca2+ uptake current in the SR. The right diagram represents the cardiac myofilament model to simulate mechanical responses of myocytes. Nxb and Pxb are non-permissive and permissive confirmations of regulatory proteins, respectively, and XBPreR and XBPostR represent the probability that the cross-bridge is in the pre/post-rotated force-generating state. gxbT is the detachment transition rate with consuming ATP, hfT and hbT are the forward and backward transition rates, fappT and gaapT are the cross-bridge attachment rate of transition and reverse rate. Knp and Kpn are transition rates for the fraction of permissive, Knp(TCaTot)7.5 is the forward rate of the non-permissive to permissive transition in the opposite direction, and Kpn(TCaTot)− 7.5 is the backward rate of the permissive to non-permissive transition. There are two types forces: active force and passive force. The active force created by contraction of the cross-bridge, and the passive force improves the complete muscle response with titin and other cytoskeletal elements. Mass prevents prompt changes in muscle-shortening velocity for quick-release protocols. Series elastic element represents effects of compliant end connections on real muscle preparations

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