An extravascular hydraulic system to control blood pressure by a feedback regulation of the venous return

Since increases in blood pressure may be effectively controlled by hydraulic feedback by reducing the venous return through the inferior vena cava in proportion to the blood pressure this principle was applied using a totally implantable extravascular system consisting of a periaortic blood pressure sensor and a pericaval cuff around the inferior vena cava. The two cuffs were supported externally by hard skeletons, filled with water, and connected directly to each other. The two devices were tested separately and together in 10 anaesthetised mongrel dogs with normal and high blood pressure induced by a metaraminol infusion. With the periaortic sensor an increase in blood pressure of 100 mmHg caused a mean(SD) isotonic volume displacement of 0.41(0.11) ml, and an increase in the pericaval balloon energy content of 100 ml.mmHg-1 caused a fall in blood pressure of 37.8(18.3)%. The whole system prevented an excessive rise in blood pressure when metaraminol was infused, with a feedback gain of about 2.8. It is concluded that blood pressure can be maintained at acceptable levels despite strong hypertensive stimuli, by this system, without additional treatment with drugs or an external energy source. The system is totally implantable and is applied extravascularly so that no anticoagulation is needed.