Method and apparatus for regulating the fluid flow rate to and

Abstract

The invention relates to an apparatus and method for limiting the pressure of inflation fluid injected into a drug delivery catheter balloon, while permitting continuous and uninterrupted flow of such fluid to the balloon. The apparatus includes an elongated hollow housing having a fluid entrance, a fluid exit and a bore extending therebetween which forms an interconnecting chamber and passageway. A piston and piston shaft assembly is disposed inside the housing and is longitudinally movable within the chamber. The piston and piston shaft assembly is biased against the fluid pressure of the fluid entering the housing by a spring. The piston shaft has a distal end which extends toward the passageway inlet. As the incoming fluid pressure increases and approaches the predetermined maximum pressure level of the apparatus, the piston shaft distal end moves within the chamber against the biasing force of the spring toward a position adjacent the passageway inlet. When the incoming fluid pressure reaches and exceeds the predetermined maximum pressure level, the piston shaft distal end enters and extends into the passageway, thereby forming an annulus within the passageway. The annulus functions to restrict the flow rate and limit the pressure of the fluid exiting the housing and entering the catheter balloon.