Effects of Raised Venous Pressure in the Circulation of the Isolated Perfused Rabbit Ear

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Abstract
Simultaneous outflow and inflow rates with a constant driving pressure but varying hydrostatic (venous outflow) pressure were measured in 37 isolated ears perfused with Ringer-Locke solution. Flow increased as the hydrostatic pressure was raised (due to passive distension of the vessels) but in six cases there was a decrease in both inflow and outflow at the highest hydrostatic pressures. As hydrostatic pressure was raised outflow fell below inflow, indicating increased capillary filtration, and this complicated the interpretation. It was concluded that in less than half the cases there may have been a ‘veno-vasomotor reflex’ to raised venous pressure. Evidence of the reflex was definite in six (15%) of the cases. The results cannot distinguish between a ‘reflex’ or a possible ‘myogenic effect,’ but do show that it can occur without central nervous connections.