Partitioning the resistances along the vascular tree: effects of dobutamine and hypovolemia in piglets with an intact circulation.
OBJECTIVE
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.


METHODS
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).


RESULTS
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.


CONCLUSIONS
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.
Geerts
Bart F
BF
Department of Anesthesiology, Leiden University Medical Center, P-05, Albinusdreef 2, P.O. box 9600, 2300 RC, Leiden, The Netherlands. b.f.geerts@lumc.nl
Maas
Jacinta J
JJ
Aarts
Leon P
LP
Pinsky
Michael R
MR
Jansen
Jos R
JR
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002316:Cardiotonic Agents / Q000494:pharmacology; D002496:Central Venous Pressure / Q000187:drug effects; D004280:Dobutamine / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D020896:Hypovolemia / Q000503:physiopathology*; D008955:Models, Cardiovascular; D015203:Reproducibility of Results; D034421:Sus scrofa; D014655:Vascular Resistance / Q000187:drug effects* / Q000502:physiology*
D002316:Cardiotonic Agents; D004280:Dobutamine
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