Paired-pulse stimulation of an electric-hydraulic pump used to replace the mammalian heart

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PAIRED electric stimuli (the first stimulus initiating, the second stimulus augmenting, systole) in experiments by Katz,1 were observed to have several specific effects on the activity of the mammalian heart. There is an optimal time interval between the two stimuli, for which a maximal potentiation of the ventricular activity is observed. This positive inotropic effect is easily reproducible in the laboratory. In addition, paired or coupled stimulation has been used not only to enhance myocardial activity, but also to reduce undesirably high heart rates.2

There is general agreement that in a normal human heart, paired stimulation increases the peak systolic pressure in the ventricle, the time of ascent of this pressure's wave and the myocardial oxygen consumption, while it does not affect the cardiac output. In a failing heart, according to recent studies,2–4 the effect is different: the stroke volume is increased, but the oxygen consumption also is increased. Generally, Fisher and associates5 found paired stimulation capable of inducing maximal or nearly maximal contractility of the ventricular muscle at any specific ventricular volume, and of causing a 64 percent increase of pressure-time index (dP/dt) above maximal control values. The mechanism of these effects is not known.

An analogous observation was made while experimentally driving a compressed-air pump designed to maintain the circulation. Paired stimulation of this device increased considerably the stroke volume. This observation is reported here since it offers an example of potentiation through coupled stimulation in an exclusively electric-hydraulic system, uncomplicated by factors other than purely mechanical . . .



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