Present state of the electrocardiographic forward problem.
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Biomedical subjects
L V Corbin
Publications and source records attributed to L V Corbin.
Zero offset in electromagnetic flowmeters.
In electromagnetic square-wave flowmeters, it should be theoretically possible to determine zero flow by turning off the magnet drive. In actuality, this is not possible. A major source of zero offset in many commercial flowmeters lies in the fact that the very large voltage transients, seen as the flowmeter drive switches polarity, are distorted by the input amplifiers. This can be corrected by improved amplifier design. A second source of zero offset when flow probes have been immersed in conducting fluids is resistive leakage between the drive voltage and the input electrodes. This can be minimized through the use of shielded coils, with shield grounded, and by the use of a magnet drive isolated from ground. If both of these sources of zero offset are corrected, offset is greatly reduced. Polarization of the flowmeter electrodes, which has previously been suggested as a cause of zero offset, was not detected.
Animals↗
The canine heart as an electrocardiographic generator. Dependence on cardiac cell orientation.
Traditionally it is assumed that during cardiac depolarization the macroscopic current generators that produce electrocardiographic voltages can be represented as a uniform double-layer source, coincident with the macroscopic boundary between resting and depolarized cardiac fibers as measured with extracellular electrodes ("uniform" hypothesis). A segment of this boundary is thus considered as a current dipole oriented perpendicular to the boundary. We present evidence that, contrary to the above, the effective dipoles largely parallel the long axes of cardiac fibers ("axial" hypothesis). Calculated potentials in volume conductors differ markedly in the two cases. The magnitudes of rapid local "intrinsic" deflections also differ markedly. In our experiments, potential fields prodlced by stimulation at several cardiac sites and measured magnitudes of intrinsic deflections during normal depolarization and that caused by stimulation support the axial hypothesis and are incompatible with the uniform hypothesis. Our results suggest that axial orientation of sources is sufficiently strong so that predictions assuming the uniform hypothesis would be seriously in error, although the axial theory alone does not exactly describe all the measured potentials. Axial orientation of current generators must be considered in quantitative prediction of electrocardiographic potentials. tfurther study of the geometry of the intracellular depolarization boundary and its relation to fiber direction and to the frequency of lateral intercellular junctions is required to describe the generators exactly.
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