Abstract
We present a new physiological model that discriminated between changes in the systemic arterial and venous circulation. To test our model, we studied the effects of dobutamine and hypovolemia in intact pentabarbital-anesthetized piglets. Aorta pressure (Pao), central venous pressure (Pcv), mean systemic filling pressure (Pmsf) and cardiac output (CO), were measured in 10 piglets, before, during and after dobutamine infusion (6 µg kg⁻¹ min⁻¹), as well as during hypovolemia (-10 mL kg⁻¹), and after fluid resuscitation to normovolemia. Venous (Rv) and total systemic (Rsys) resistance were determined from Pao, Pcv, Pmsf and CO. The quotient of Rv/Rsys was used to determine the predominant location of vascular changes (i.e. vasoconstriction or dilatation on either venous or arterial side). Administration of dobutamine increased heart rate and CO, whereas it decreased Pmsf, Rsys, Rv and Rv/Rsys. The decrease in Rv was significantly greater than Rsys. Pao and Pcv did not change. Hypovolemia decreased CO, Pcv, Pmsf, Rv and Rv/Rsys, but kept Rsys constant and increased heart rate. Hypovolemia and dobutamine differentially alter Pmsf, Rsys, Rv and Rv/Rsys ratio. The increase in CO during dobutamine infusion was attributed to the combined increased cardiac function and decreased Rv. The decrease in CO with hypovolemia was due to a decreased Pmsf but was partly compensated for by a decrease in Rv tending to preserve venous return and thus CO.
Published Version
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