Induced changes in the small vessel volume as determined by rheological relationships

¹ Department of Physiology, University of Louisville School of Medicine, Louisville, Kentucky

The cell and plasma volumes were determined simultaneously in dogs by means of P³²-tagged erythrocytes and albumin-I¹³¹. With these measurements the excess plasma changes, after the administration of splenic blood or plasma and other small vessel active agents, were ascertained. In splenectomized dogs small vessel dilators such as splenic blood or plasma, potassium, and serotonin increased the excess plasma, while small vessel constrictors such as vasopressin and calcium reduced it. Mathematical analysis utilizing empirically vindicated rheological equations led to the derivation of equations that allowed, in splenectomized dogs, the calculation of the mean composite radius of all small vessels with a radius <0.150 mm, the composite small vessel hematocrit of the blood in these vessels, and the small vessel volume. The fractional distribution of cell and plasma volumes among the small and large vessel compartments could also be calculated. Calculations based on these equations demonstrated, among other results, that small vessel constrictors decreased the mean composite radius of small vessels and the small vessel volume, while small vessel dilators increased the values of these parameters.