Impedance analysis applicable to cardiac muscle and smooth muscle bundles

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Abstract
An electrical equivalent circuit was constructed to represent a chain of five myocardial cells in a cardiac muscle bundle with various degrees of cell-to-cell coupling, and an impedance analysis was performed. The impedance across the entire network was measured at frequencies ranging from 10(1) to 10(6) Hz. The Bode plots were nearly superimposable for 1, 10, and 100 tunnels; for 10(3), 10(4), and 10(5) tunnels, the absolute zeta at 10 Hz was lower: e.g., 9.82 M omega for 1 tunnel compared to 6.64 M omega for 10(5) tunnels. The delta zeta 1/2 values were shifted to the left in the well-coupled cases: e.g., for 1 tunnel, f1/2 was 37.8 kHz, and for 10(5) tunnels, f1/2 was 1.2 kHz. For high coupling, the Bode plots contained a double component due to the end membranes. When Ro was increased by eight times, zeta increased by 7.47 fold (for 1 tunnel, 10 Hz), and by 3.72 fold (for 10(5) tunnels, 10 Hz). Raising Ro to x 12, x 100, and x 1000 produced a further and further shift to the left of the Bode plots. The total tissue resistivity (Rt) increased as a function Ro. Thus, in low coupling cases, almost all of the applied current passes through the interstitial space; e.g., at 1 tunnel (10 Hz), 1.0% of the current passes through the cell pathway (Rcell). The ratio of impedances at 10 kHz to 10 Hz (zeta 10kHz/zeta 10Hz) decreased with increasing tunnels (for Ro x 1). The ratio of resistivities at Ro x 8 to Ro x 1 (Rt'/Rt) was 7.47 for 1 tunnel. In contrast, the ratio at 10(5) tunnels was 3.73. It is concluded that it is difficult to determine the degree of cell coupling from such impedance analysis, unless the same tissue can be used for its own control, i.e., before and after a large change in cell coupling is introduced.

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