Work of the heart under the effect of induced arterial pressure oscillations studied in intact anesthetized dogs.

• In several investigations in the past, Wetterer and Pieper connected a sinusoidal piston pump to the arterial system of intact anesthetized dogs in order to produce slow oscillations of the mean arterial pressure upon which the arterial pressure pulsation was superimposed. Simultaneous measurements of various parameters permitted the calculation of the elasticity coefficient of the arterial reservoir, the calculation of the total peripheral runoff: as a function of the arterial pressure,and the determination of the relationship of pressure to flow in various parts of the arterial system. In similar studies over the last two years, we have noted that at a given diastolic aortic pressure the systolic pressure rise A P was of equal magnitude, irrespective of whether the sinusoidal pump was simultaneously injecting or withdrawing. The implications of this observation can best be explained in comparison with the behavior of a physical model. The physical model consists of a pump which, as a "heart," injects rhythmically a given stroke volume into an elastic balloon which represents the arterial reservoir. Outflow from this balloon is provided by a "peripheral resistance." When, at a certain mean pressure, P,,,, outflow equals inflow, a steady state situation is established. A piston pump with a sinusoidal piston movement may be connected to the balloon and when in operation causes slow oscillations of the mean pressure, P,,,, by alternatingly Avithdrawing and rpinjecting a certain volume. Figure 1 shows