Patent Publication Number: US-2007112309-A1

Title: Withdrawal syringe

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to syringes and more particularly to a device for withdrawal of liquids from the body.  
      Under conventional practices, blood or other body liquids are withdrawn by connecting a needle to a pre-evacuated container or by a manually operated syringe. Presently available systems are not easily operated with precision with one hand. The withdrawal procedure with evacuated systems may cause collapse of the vein, especially in older people. In many mechanical systems, the forces which are exerted on the piston create reaction forces tending to make the withdrawal procedure awkward.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention, a withdrawal syringe comprises a needle or cannula connected to one end of a receiving cylinder having a filter element at the other end. A cup-shaped piston is provided around the cylinder and is movable in telescoping relation with the cylinder. A ring seal is provided between the two parts. Finger flanges extend from the piston, and a thumb rest is provided beyond the finger flanges and is connected by legs back to the cylinder. Friction or gear engagement may be provided between the legs and the outer surfaces of the piston.  
      The device is operated by pulling on the piston with the first two fingers with the thumb on the thumb rest. This allows for a very precise insertion of the needle and precise, controlled withdrawal of liquid with the force of the thumb opposing the force of the fingers. 
    
    
     THE DRAWINGS  
       FIG. 1  is a perspective assembly view of the syringe of the present invention.  
       FIG. 2  is a partial longitudinal sectional view of the assembled syringe of  FIG. 1 .  
       FIG. 3  is an enlarged view of the indicated portion of  FIG. 2 .  
       FIG. 4  is a modification of the features shown in  FIG. 3 .  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIGS. 1 and 2  show an elongated syringe  10  having a hollow needle or cannula  12  extending from one end, with the needle being protected by a removable sheath  14 . The needle is connected to one end  16  of a hollow receiving cylinder  18 . The other end  20  of cylinder  18  is provided with a microporous filter  22  retained in a cap  24  covering the cylinder end  20 . The filter  22  allows for transmission of gas or air into and out of the cylinder  18  without contamination of the cylinder interior. A flexible O-ring seal  26  is provided in a circular groove  27  formed in the outer wall of cylinder  18  near the filter end  20  thereof.  
      A cup-shaped piston  28  having a cylindrical inner surface  30  and an open and closed end is provided in telescoping coaxial relation with the cylinder  18  and in sliding sealing engagement with the seal  26 . It may be seen that when the piston  28  is moved in a direction away from the needle  12  as shown by the arrow in  FIG. 2 , pressure is reduced in the cylinder.  
      A pair of forwardly curved flanges or legs  32  and  34  extend in opposite directions from the closed end of the piston  28 , in directions generally perpendicular to the longitudinal axis of the syringe. A thumb rest  36  is provided at or beyond the outer extent of travel of the piston  28 . The thumb rest  36  extends generally perpendicular to the flanges  32 - 34  and is secured by means of pins or the like to one end of a pair of spaced parallel legs  38  and  40 . The other end of the legs are bent inwardly at  42  and are secured to the outer wall of the cylinder  18  near the forward end  16  thereof.  
      It may be seen that the distance between the facing surfaces of the legs  38  and  40  is somewhat greater than the outer diameter of the piston  28  to allow movement of the piston in an axial direction relative to the cylinder  18  and thumb rest. The device is operated by grasping the flanges  32 - 34  with the first two fingers with the thumb of the same hand resting on the thumb rest  36 . A balanced squeezing action is used to withdraw liquids through the cannula  12 .  
      To provide a more precise feel and control some degree of interaction may be provided between an outer surface of the piston  28  and the inner surface of the legs  38  and  40 . For example, as shown in  FIGS. 1, 2  and  3 , the outer surface of the piston  28  may be provided with an axially extending track having a plurality of spaced teeth  44 , with an inwardly facing cog  46  on the legs in locking engagement with successive teeth as the piston is withdrawn. If desired, the teeth may be shaped to provide a ratchet as shown, allowing only outward movement of the piston. Also, the piston may be later rotated to bring the teeth out of engagement with the cog, allowing ejection of the liquid.  
      As shown in  FIG. 4 , the surfaces between a leg  38  and the cylinder  28  may be simply roughened as shown at  48  to provide some degree of resistance to motion and improved control.