A servomechanical system to control high blood pressure using sodium nitroprusside.
A servomechanical device was used to control the intravenous administration of a sodium nitroprusside solution, without using electrical energy or a pump, the aim being the fast and smooth reduction of high arterial pressure (BP). The device senses BP via an intra-arterial catheter which leads to two containers, to one through a narrow tube (slow system) and to the other through a wide tube (fast system). The two systems integrate the BP with time constants that are the product of the tube resistance to flow and the compliance of the containers. The two systems lead to small bellows that interfere with the legs of a clamp regulating an intravenous nitroprusside drip. The distension of the bellows releases the clamp in proportion to the pressure in the slow system and to the difference in pressure between the fast and the slow systems. A screw-spring could determine the desired slow system pressure below which the flow of the nitroprusside solution was stopped. The whole device was applied 11 times in five anaesthetized dogs under a continuous intravenous metaraminol infusion. The BP was always reduced smoothly within 2 to 24 min to a value near that predetermined by the screw-spring. It is concluded that a purely mechanical system involving integral, proportional and derivative components may achieve fast and smooth reduction of elevated BP to a predetermined level, when using fast-acting hypotensive agents.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003201:Computers; D004285:Dogs; D005292:Ferricyanides / Q000627:therapeutic use*; D006973:Hypertension / Q000188:drug therapy*; D007263:Infusions, Parenteral / Q000295:instrumentation*; D009599:Nitroprusside / Q000008:administration & dosage / Q000627:therapeutic use*
D005292:Ferricyanides; D009599:Nitroprusside