Abstract:
A simple and inexpensive method and apparatus are provided for increasing the pressure at which fluid may be delivered by a lavage/irrigation system.

Description:
FIELD OF THE INVENTION 
     The present invention provides a method and apparatus by which a relatively low pressure medical lavage/irrigation system can be converted to perform procedures, such as hydrodissection or other medical procedures, which typically require relatively high pressures. 
     BACKGROUND OF THE INVENTION 
     The term &#34;lavage&#34; has been used in the literature in a somewhat ambiguous manner. Sometimes, the term is used to refer to the washing of tissue using a pulsating stream of fluid. The term also is used to describe aspiration of tissue. As used herein, the term &#34;lavage&#34; is used in its broadest sense, and is intended to refer to any one of, or combinations of, irrigation, pulsatile lavage, and aspiration of tissue. As used herein, lavage can be accomplished with a stream of fluid at a relatively low pressure. 
     A number of systems for performing lavage are available, most of which are mechanized. Some of the available systems theoretically may be used to perform medical procedures which require a fluid stream delivered at higher pressures; however, the pressure setting mechanism of most of the available lavage systems cannot be set beyond approximately 0-150 mm Hg. Much higher pressures, e.g., 0-1500 mm Hg, are required to perform high pressure procedures such as hydrodissection. 
     Of course, one could design a lavage system in which the pump could be set to deliver fluid at higher pressures; however, many already have purchased lavage systems which cannot be set at such high pressures. Therefore, an inexpensive but effective means for adapting relatively low pressure lavage systems so that they can produce high pressure fluid streams for medical procedures would be desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a simple, inexpensive means for converting existing, relatively low pressure lavage systems into systems capable of producing high pressure fluid streams which may be used, e.g., for hydrodissection. According to the present invention, the pumping system of a typical lavage system is provided with an additional line (a &#34;pressure decrease line&#34;) which connects the fluid supply line and the pressure sensing line. The pressure decrease line drains fluid from the pressure sensing line so that the pressure sensed in the pressure sensing line is less than the actual pressure in the demand line. The larger the diameter of the pressure decrease line, the lower the sensed pressure. The resulting measured decrease in the sensed pressure makes the existing control system push the pump to provide greater output pressure. The fluid stream delivered by such a system may be enhanced, e.g., to 25 or more times than the set pressure in the controller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation of a typical lavage system which cannot be used according to the present invention. 
     FIG. 2 is a diagrammatic representation of the lavage system of FIG. 1 after being adapted for use according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a typical lavage system includes a pump 10, a supply line 12, a demand line 14, and a pressure sensing line 16. The pressure that is generated by pump 10 is set using known means. Information about the pressure in the demand line 14 is monitored and fed back to the pump 10 by a pressure sensor or pressure transducer 18, which typically is located at the pump end 20 of pressure sensing line 16. The information from the pressure sensor 18 typically is used to control the output of the pump 10 so that the desired output pressure corresponds to the set pressure. 
     In most applications, the sensed pressure and the desired output pressure will be the same. However, some applications may require an output pressure that is higher than the highest pressure at which the lavage system can be set. In these high pressure applications, it may be necessary for the output pressure to exceed the sensed pressure. 
     FIG. 2 is a diagrammatic representation of a lavage system according to the present invention in which the output pressure can exceed the sensed pressure. The system diagrammed in FIG. 2 essentially is the same as the system diagrammed in FIG. 1 except for the addition of a pressure decrease line 22. The pressure decrease line 22 extends between the supply line 12 and the pressure sensing line 16. 
     The pressure decrease line 22 may be added to substantially any lavage system; however, the preferred embodiment disclosed herein includes a linear motor. The amount of pressure generated by a linear motor varies with the stroke length and/or speed of the motor; therefore, a linear motor can generate higher pressures by increasing the pump stroke length and/or speed without any substantial change to the motor. A preferred lavage system for use in the present invention is the system described in U.S. Pat. No. 4,561,431, incorporated herein by reference. The lavage system may be modified to include the pressure decrease line 22 of the present invention using any suitable means, e.g., &#34;T&#34;-adapters. The desired increase in the pressure of the fluid delivered can be achieved by using a pressure decrease line 22 having a particular diameter. The greater the diameter of the pressure decrease line 22, the greater the decrease in sensed pressure and the greater the increase in pump output to try to reach the set point of the controller. 
     The present invention now will be described in operation. In the following description, ΔP 1  is the pressure drop across the pressure sensing line 16 and ΔP2 is the pressure drop across the pressure decrease line 22. Fluid enters the pump 10 at a first pressure (P s  =supply side line pressure) and exits the pump at a second pressure (P d  =desired output pressure ). The pressure sensor 18 attempts to measure P d  ; however, the pressure decrease line 22 drains fluid from the pressure sensing line 16 causing a drop in the sensed pressure, P sensed . The following mathematically describes the resulting sensed pressure: ##EQU1## The pump continues to increase its output pressure in order to cause P sensed  to approach the set pressure. As a result, the desired output pressure P d  will be substantially higher than the set pressure: ##EQU2## 
     The invention is useful in lavage systems that may be already in possession by a user. The user may desire an economical way to convert an existing system to deliver more flow and/or pressure. If the controller has a low preset range, the invention allows use of the same controller but at a different range. Thus higher pressure applications are possible without significant modifications to the controller. Full use of the available pump output becomes an economic reality without expensive component replacement. 
     One of skill in the art will appreciate that many modifications may be made to the embodiment described herein and explained in the accompanying figures without departing from the spirit of the invention. Accordingly, the embodiment described herein is illustrative only and is not intended to limit the scope of the present invention.