Source: {"pile_set_name": "USPTO Backgrounds"}

Syringes are known in the medical art for dispensing measured volumes of fluids, i.e., liquids or gases, to a given site. The typical syringe comprises a piston or plunger enveloped in a chamber, usually a cylindrical chamber, where it forms a fluid-tight seal with the wall of the chamber so that slidable movement of the plunger forwardly empties the chamber and backwardly refills the chamber.
Since the forward movement of the plunger exerts pressure on the fluid in the chamber, the fluid is delivered from the syringe under pressure and thus a syringe is a suitable instrument for inflating various inflatable devices such as balloon catheters. Balloon catheters have been used in various medical applications, for example, angioplasty and dilation of body lumens such as the prostatic urethra. For such applications an appreciable pressure is required to fully inflate the balloon.
While a standard, single plunger syringe is normally adequate to fill the balloon, it has been found that the maximum intended pressure for optimum working of the balloon cannot be achieved by a simple one-handed operation of the syringe. Various proposals have been made in the prior art to overcome this problem. For example, it has been proposed to enhance the pressure of the liquid delivered by the syringe by using a screw thread associated with the plunger mechanism. A disadvantage of this approach is that it requires two hands to operate.
Surprisingly, it has now been found that the desired maximum pressure can be achieved with a syringe that can be operated with one hand and is relatively inexpensive to manufacture by providing a dual action or dual pressure syringe which comprises a rear chamber and a front chamber of different cross-section area and a plunger mechanism comprising a primary plunger enveloping a telescopically slidable secondary plunger. The plunger mechanism co-operates with the chambers such that the rear chamber provides high volume and low pressure and the front chamber provides low volume and high pressure. The high pressure produced by the front chamber provides the necessary boost to achieve the intended pressure in the catheter balloon.