ELECTRICAL IMPEDANCE OF PULSATILE BLOOD FLOW IN RIGID TUBES AND IN ISOLATED ORGANS

The present concept underlying electrical impedance rheography holds that the wave of conductive blood perfusing the resistive tissue cells causes an increase of conductivity or a decrease in electrical impedance.’ Until now it has not been possible to convert this seemingly simple bioelectrical event into a reliable clinical method because it still lacks the main prerequisite of a scientific method; i.e., it cannot be quantitated reproducibly in absolute physical units. Despite the plethora of mathematical theorems on the one hand, and of diligent clinical empiricism on the other, there is a scarcity of animal experimentation to prove or to disprove the present concept. One century after the publication of Claude Bernard’s Introduction to the Study of Experimental Medicine, there is certainly nothing unusual in taking an indirect and variable method, like clinical impedance rheography, out of its impenetrable clinical complexity and subjecting it to controlled experimentation. This is the only way open to us to distinguish between coincidence and cause, between statistical and biological significance, or between the propter hoc and the ergo hoc. It is unusual, however, that miles of paper have rolled off from a variety of instruments in Europe and on this continent for the last three decades without experimental evidence of the hemodynamic cause of the measured phenomenon. The first part of the present studies was devised in an effort to define the factors influencing impedance pulses in rigid tubes by changing the blood perfusate. The second part of the studies deals with the hemodynamic factors producing the tissue electrical impedance waves in mechanically perfused isolated organs. Such a system permits the control of total inflow, stroke volume, pulse pressure, pulse rate, and composition of the perfusate.