BACKGROUND OF THE INVENTION

This invention relates generally to fluid pressure measurement, and, more particularly, to apparatus for detecting the pressure in a fluid line. The invention has particular application in connection with systems for administering parenteral fluids to the human body.

The administration of parenteral fluids to human patients conventionally involves use of a solu- tion administration set. The set typically is a disposable plastic product, and includes a drip chamber adapted to be connected to a fluid source, a length of tubing extending from the chamber to the patient, and a valve mechanism, such as a roller clamp on the tubing.

In recent years, a variety of mechanical and electrical monitoring systems, controllers and infusion pumps have been developed to sense and regu¬ late the rate of fluid flow into the human body. Such apparatus may include an electromechanical output device for manipulating the tubing of a conventional administration set in a ppescribed manner, as by using a series of cam followers that sequentially

tubing and generate a peristaltic pumping action. For use in other apparatus, the tubing may include a syringe that is cyclically driven by the jelectro- mechanical output device through alternate fill and pump strokes, to draw and deliver precise amounts of fluid from the fluid source to the patient. Alterna¬ tively, instead of a conventional administration set, a self-contained syringe may be used in an apparatus designed for a single, controlled pump stroke, to deliver the fluid contained in the syringe to a patient.

A common feature of each of these apparatus is the capability of developing positive pressure in the tubing. Some, of the apparatus have also been capable of activating alarms when an out-of-limit condition exists, thus freeing medical personnel to some extent for other duties.

Although such apparatus have generally served their purpose, there has been a need for an effective, safe and reliable means of sensing fluid pressure in the tubing leading to the patient. Specifically, concerns have been raised about the capability of monitoring and controlling the fluid pressure developed in the tubing by such positive pressure electromecha¬ nical devices.

Hence, those concerned with the development and use of fluid administration systems, and particu¬ larly those concerned with the design of parenteral administration systems, recognize the need for improve¬ ment in devices for fluid pressure measurement. The present invention fulfills this- need.

SUMMARY OF THE INVENTION

The present invention resides in an apparatus for detecting the pressure in a fluid line and provi¬ ding an electrical signal whenever the apparatus has not been properly initialized and whenever the pressure in the fluid line exceeds a prescribed threshold. The apparatus includes a pressure diaphragm communicating with the fluid line and having a flexible membrane that is movable in accordance with the fluid pressure in the line, along with a frame having means for retaining the pressure diaphragm in a prescribed position. In accordance with the invention, the apparatus further includes follower means mounted on the frame and movable in accordance with the position of both the pressure diaphragm and its flexible membrane, along with first and second electrical contact assemblies coupled to the frame and movable with respect to each other in accordance with movement of the follower means. The two contact assemblies provide an electri- cal signal whenever the pressure diaphragm is not installed in its prescribed position and, if it is installed, whenever the pressure 'in the fluid line exceeds the prescribed threshold.

More particularly, the apparatus of the invention has particular utility in a system for administering parenteral fluids to human patients. The flexible membrane of the pressure diaphragm is gene¬ rally disc-shaped and the follower means includes a substantially planar face membrane for conforming engagement with the membrane. The pressure diaphragm further includes a flange around the periphery of the flexible membrane, and the retaining means includes an inwardly-projecting flange defining a slot -for receiv¬ ing the flange of the diaphragm and thereby removably retaining the diaphragm in its prescribed position.

In other aspects of the invention, each electrical contact assembly includes a flexible contact spring fixed at one of its ends to the frame and an electrical contact fixed to the free end of the contact '5 spring. The follower means includes an axially-movable shaft with a collar that is disposed between the two contact springs and functions like a control finger to move the two contacts together and apart from each other in a prescribed fashion. The follower means -0 ^' further includes spring biasing means for urging the shaft and the face member outwardly in the direction of the installed pressure diaphragm.

The follower means is movable between an initial position, an intermediate position, and a 5 high pressure position, in accordance with the position of the pressure diaphragm and its flexible membrane. When the diaphragm is not installed in the retaining means, the follower means is urged to the initial position, where the shaft collar engages ^' the first 0 contact spring and thereby urges the first contact away from the second contact. When the diaphragm is in-= stalled, and the fluid pressure does not exceed the prescribed threshold, the follower means is urged to the intermediate position, where the shaft collar is ^ disposed intermediate the two contact springs and the two contacts are in electrical contact with each other. When the diaphragm is installed and the fluid pressure does exceed the threshold, the follower means is urged to the high pressure position, where the shaft collar 0 engages the second contact spring and thereby urges the second contact away from the first contact.

The apparatus can further include f inger means fixed to the frame aj d engagable with the contact springs of the two contact assemblies . Specifically,

whenever the contact spring of the first assembly is engaged by the follower means, and retains the first assembly whenever the contact spring of the second assembly is engaged by the follower means.

In yet another aspect of the invention, the spring biasing means of the follower means includes first and second spring means. The first spring means yieldably resists movement of the follower means from the initial position to the intermediate position, when the pressure diaphragm is installed. The second spring means engages the follower means only after it has moved to the intermediate position, and it yieldably resists further movement of the follower .means to the high pressure position, in response to movement of the flexible membrane. In he preferred embodiment, the two spring means are in the form of coaxial, coil springs disposed around the follower shaft.

Other aspects and advantages of the present invention will become apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG . 1 is a part i al perspect ive vi ew of a representative syringe infusion pump system util izing a pres sure detector embodying the principles of the present invention ;

FIG. 2 is an enlarged, fragmentary sectional view of the pressure deteςtor, taken along line 2-2 in FIG. 1 and showing a pressure diaphragm about

installed and a pair of electrical contacts in a spaced-apart condition indicating that the diaph¬ ragm is not installed;

FIG. 3 is an enlarged, fragmentary sectional view of the pair of electrical contacts shown in contact with each other, indicating that the pressure diaphragm is installed and that the fluid pressure does not exceed a prescribed level; and

FIG. 4 is an enlarged, fragmentary sectional view of the pair of electrical contacts shown in a spaced-apart condition, indicating that the pressure diaphragm is properly installed, but that the fluid pressure does exceed the prescribed threshold.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and particu¬ larly to FIGS. 1 and 2 , there is shown a pressure detector for use in a syringe infusion pump system 11 for administering parenteral fluid to a human patient. The fluid is delivered to the patient in a conventional fashion through a length of tubing 13 connected to a syringe 15. The pressure detector includes a frame 17 and a pressure diaphragm 19, which is coupled to the tubing and has a flexible membrane 21 that is movable in accordance with the fluid pressure in _. the tubing. In use, the pressure diaphragm is installed i-n a special receptacle 23 on the frame. The pressure detector provides an electrical signal whenever the pressure diaphragm is not installed in the receptacle, and, if it is installed, whenever the- pressure in the tubing is determined to exceed a prescribed threshold.

In accordance with the invention, the pressure detector further includes a follower assembly 25 mounted in the frame 17, adjacent to the pressure diaphragm receptacle 23, for linear movement in accor¬ dance with movement of the flexible membrane 21, along with first and second electrical contact assemblies 27a and 27b, respectively, for producing the aforemen¬ tioned electrical signal. Each contact assembly includes an elongated, flexible contact spring 29a or 29b and an electrical contact 31a or 31b. The two contact springs are substantially parallel to each other and mounted at fixed ends thereof to the frame 17. The two electrical contacts are mounted on the free ends of their respective contact springs, in confronting relationship. The follower assembly is engagable with the two contact springs, to move the two electrical contacts apart from each other whenever the pressure diaphragm 19 is not installed in the recep¬ tacle or, if the diaphragm is properly installed, whenever the pressure in the tubing 13 exceeds the prescribed threshold. The aforementioned electrical signal is thereby provided on a pair of electrical leads 33a and 33b coupled to the respective contacts 31a and 31b.

More particularly, the pressure diaphragm 19 includes a rigid body portion 35 having an annular flange 37 that surrounds the flexible membrane 21. The resilient membrane is substantially planar and disc¬ shaped, in its unstressed condition, as shown by the solid line 21 in FIG. 2. As the fluid pressure in the tubing 13 increases, however, the membrane bulges outwardly from the flange by a corresponding amount, as shown by the phantom line 21' in FIG. 2.

The receptacle 23 for retaining the pressure diaphragm 19 in its prescribed position on the frame 17 includes an inwardly-projecting flange 39 that defines a slot 41 for receiving the outwardly-projecting flange 37 of the diaphragm. The diaphragm is installed by manually inserting its flange into the slot, where it is held in place by the follower assembly 25, which urges it outwardly against the inwardly-facing surface of the receptacle flange.

As ^" reviously mentioned, the pressure detector frame 17 provides support for the diaphragm receptacle 23 and also houses the follower assembly 25 and the first and second electrical contact assemblies 27a and 27b. It includes an outer housing member 43, an inner housing member 45, and a spacer ring 47, secured rigidly together by any suitable means, such as screws 49. The spacer ring is interposed between the outer and inner housing members, with, the fixed end of the first contact spring 29a positioned between the outer member and the spacer ring, and the fixed end of the second contact spring 29b positioned between the inner member and the spacer, ring. The frame further includes an end cap 51 fixed to the inner housing member. All of the frame elements are prefer- ably molded from a suitable plastic material, to provide electrical insulation for the two contact springs.

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The follower assembly 25 includes a face member 53, a shaft 55, and spring biasing means 57, all axially aligned with each other and housed within the frame 17. The shaft is urged outwardly by the spring biasing means into engagement with the face member, which, in turn, is urged into engagement with the flexible membrane 21 of the installed pressure diaphragm 19. The shaft is slidably received in bores 59 and 61 formed in the inner housing member 45 and the end cap 51, respectively. The face member 53 is retained in its position in the frame by a flexible, annular ring 63 that is seated in annular seats 65 and 67 formed in the face member and the outer housing member 43, respectively. The annular ring also func- tions to seal the interior of the frame, to prevent contamination by dust and other foreign particles. The face member is also retained within the frame by an inwardly-projecting annular flange 69 on the outer housing member, which functions as a stop for an outwardly-projecting annular lip 71 on the face member. The face member further includes a plurality of circum- ferentially-spaced slots 73, to facilitate insertion of the face member lip 71 past the outer housing member flange 69. A shoulder 75 on the face member is engag- able with the outer housing member flange, to prevent insertion of the face member too far into the frame.

In one aspect of the invention, the follower shaft 55 includes a collar 77 that projects into the spacing between the two contact springs 29a and 29b. The collar functions as a control finger that engag ^' es the contact springs and thereby moves the two elect¬ rical contacts 31a and 31b toward .or away from each other in accordance with the position ^' of the shaft.

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In operation, when the pressure diaphragm 19 is not installed in the receptacle 23, the follower shaft 55 and face member 53 are urged outwardly by the spring biasing means 57, as depicted in FIG. 2. in this outward or initial position, the shaft collar 77 engages the first contact spring 29a, to move it and the first contact 31a away from the second contact spring 29b and the second contact 31b. This provides an open circuit condition on the two electrical leads 33a and 33b. When the pressure diaphragm is properly installed in the receptacle, and the pressure in the tubing 13 does not exceed the prescribed threshold, the follower shaft and face member are moved by the dia¬ phragm to an intermediate position, against the resis- tance of the spring biasing means. In this interme¬ diate position, the shaft collar is disposed interme¬ diate the two contact springs, to allow the two elec¬ trical contacts to contact each other, as depicted in FIG. 3. This provides a closed circuit condition on the two electrical leads.

If the pressure in the tubing 13 increases, the face member 53 and shaft 55 are urged inwardly by the diaphragm membrane 21 against the resistance of the spring biasing means 57. When the pressure exceeds the prescribed threshold, the resistance of the spring biasing means is overcome, and the face member and shaft are moved to a high pressure position. In this position, the shaft collar 77 engages the second contact spring 29b, to move it and the second contact 31b away from the first contact spring 29a and the first contact 31a. This restores the open circuit condition in the two electrical leads 33a and 33b. If the fluid pressure again drops below the prescribed threshold, the spring biasing means urges the shaft, and thus the shaft collar, outwardly, to bring the

second contact back into electrical contact with the first contact (FIG. 3).

In the preferred embodiment, the pressure detector further includes a finger 79 integral with the spacer ring 47 of the frame 17 and disposed between the two contact springs 29a and 29b. It funtions to retain the second contact spring 29b whenever the shaft collar 77 engages the first contact spring 29a (FIG. 2) , and to retain the first contact spring whenever the.collar engages the second contact spring (FIG. 4) .

The spring biasing means 57 for urging the follower assembly 25 outwardly against the flexible membrane 21 of the pressure diaphragm 19 includes first and second coil springs.81 and 83, respectively. The two springs surround a reduced-diameter portion 85 of the follower shaft 55, in a chamber 87 formed by the inner housing member 45 and the end cap 51.

The first coil spring 81 is disposed between a first annular shoulder 89 on the follower shaft 55 and the inner face of the end cap 51, inside an annular spring retaining wall 91. It provides a continuous outward force on the shaft, to urge the follower assembly to the initial position whenever the pressure diaphragm 19 is not installed. The force is small enough to be overcome readily by a manual insertion of the diaphragm into the receptacle 23.

The second coil spring 83 surrounds the first spring 81 and is disposed between a flat ring 93 that surrounds the shaft 55 at the outer end of the chamber 87, and the inner face of the end cap 51, immediately outside the spring retainiig wall 91. The follower shaft 55 includes a second annular shoulder 95 engag-

able with the flat ring, and thus the second spring, only when the shaft has been urged inwardly by. he diaphragm membrane 21 to the intermediate position (FIG. 3) . Only when the pressure in the fluid line exceeds the prescribed threshold, is there sufficient force to overcome the biasing force of the second spring, and thereby to move the follower assembly 25 to the high pressure position.

It will be appreciated from the foregoing description that the present invention provides -.an improved pressure detector for particular use- in a system for administering parenteral fluid to a human patient. The pressure detector includes a conventional pressure diaphragm having a flexible membrane that is movable in accordance with the pres¬ sure of the fluid being administered. The detector further includes a special follower assembly and an associated pair of electrical contacts, for detecting both an installation of the pressure diaphragm and the relative position of its flexible membrane and thereby providing an electrical signal whenever the diaphragm is not installed and, if it is installed, whenever the fluid pressure exceeds a prescribed threshold.

Although the invention has been described with reference to its presently preferred embodiment, it should be understood by those of ordinary skill in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the^ invention be limited, except as by the appended claims.

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