Effects of Viscosity Reduction by Means of Defibrination (Arvin) and Moderate Hemodilution (0.9% NaCl) in a Shock Model with Intact Animals
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A reduction in viscosity was induced by means of defibrination (Arvin) and moderate hemodilution (0.9% NaCl) in intact dogs. A shock-protocol was followed by stepwise withdrawal of blood (5 ml/kg body weight/5 minutes). After a period of one hour at an aortic pressure of 35 mmHg, the original volume of blood was reinfused.
The differences between the Arvin group (A) and the controls (C) in the intact series were significant in phase 7 (after reinfusion) with regard to: the amount of blood withdrawn AW (A < C), the pressure in the aorta PAo (A < C), the cardiac output CO (A < C), the peripheral resistance TSR (A < C), the pulmonary artery pressure PAP (A < C), the pulmonary capillary wedge pressure PCWP (A < C), the pulmonary vascular resistance PVR (A > C), the transcutaneous PO2 (A < C), the O2 -consumption VO2 (A < C), the O2-availability O2AV (A < C) and the O2-extraction O2EX (A > C), as well as the viscosity at lower shear rates ηLS (A < C). The hemodilution group (B, hemodiluted with 0.9% NaCl) showed significant differences when compared to the control group C only with regard to the following parameters: the amount of blood withdrawn AW (B > C) and the viscosity at lower shear rates ηLS (B<C).
In the case of Arvin, the significant differences which were observed between the defibrinated group and the controls were all in favor of the latter. This is in sharp contrast to the results of defibrination with Arvin in a model of an “isolated peripheral circulation” carried out with the aid of total heart-lung bypass (see Paper I).
As far as Arvin is concerned, the conclusion seems obvious that the problems do not arise at the level of the systemic microcirculation but at the level of the heart-lung system.
The differences in the Arvin group usually only became significant after shock provocation, accompanied by signs of relative hypovolemia. These signs were absent in the hemodilution series, even though the decrease in viscosity produced by Arvin and hemodilution were comparable. It seems likely that a reduction in viscosity with Arvin should be combined with expansion of the blood volume to assure normovolemia. There is an obvious parallel between this and peripheral vasodilatation, which is also of little use without compensation for the relative hypovolemia.
KeywordsShear Rate Pulmonary Artery Pressure Pulmonary Vascular Resistance Pulmonary Capillary Wedge Pressure Blood Viscosity
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