WO1995000194A1

WO1995000194A1 - High-precision flow regulator for medicinal infusion lines

Info

Publication number: WO1995000194A1
Application number: PCT/EP1994/001908
Authority: WO
Inventors: Luciano Casarotto; Fiorenzo Casarotto; Giuseppe Dall'ara
Original assignee: Plasti Medical S.P.A.
Priority date: 1993-06-23
Filing date: 1994-06-13
Publication date: 1995-01-05
Also published as: IT1270781B; ITVI930108A0; ITVI930108A1

Abstract

The present invention relates to a high-precision flow regulator for medicinal infusion lines. The regulator includes a fixed body (2) with a substantially cylindrical internal cavity (5) that has an intake duct (7) and a discharge duct (8), and a moving valve part (3) which is rotatably inserted in the internal cavity of the body to selectively vary the flow-rate between the ducts (7, 8). The valve part (3) includes a closing means (15) adapted to interact with a gauded slot (13) which is formed on the side wall of the fixed body (2) at the intake duct (7), parallel to the axis of the cavity (5), for a length that is approximately equal to the internal diameter of the intake duct (7). The moving part (3) has a tubular portion (11) which has an edge (15), at one end, with a helical profile that forms the closing means. The regulator is constituted by just two parts and is therefore extremely economical as well as scarcely sensitive to variations in fluid pressure and viscosity.

Description

HIGH-PRECISION FLOW REGULATOR FOR MEDICINAL INFUSION LINES

The present invention relates to a high-precision flow regulator for devices for the intravenous infusion of biological or medicinal fluids.

Flow regulators of the above indicated type can be generally divided into two types: low-precision and high- precision.

Low-precision devices, which were the first to appear on the market, are generally based on the principle of partially closing a flexible tube that connects the reservoir of the fluid to be administered to the infusion needle inserted in the vein. The simplest of these devices are constituted by thin rectangular plates made of aluminum or other easily deformable metals which are folded a first time longitudinally along their centerline to wrap around the tube and a second time transversely in order to bend the tube, reducing its useful passage section. In these devices the flow-rate is approximately proportional to the angle at which the plate is bent, but it does not guarantee continuity and cannot be quantified at all. Due to these reasons, these devices are generally intended exclusively for emergency applications, as in home therapy or in field hospitals.

A later type of regulator, termed "roll-clamp", has a substantially rigid part which is provided with a channel that has a substantially U-shaped cross-section on the bottom of which a portion of flexible tube rests. A roller acts on the tube and can move along a guide which is inclined with respect to the bottom in order to gradually compress the tube. By rotating the roller from outside, the roller moves along the guide and compresses the outer wall of the tube more or less intensely against the inclined bottom, correspondingly reducing the fluid passage section according to the relative distance between the guide and the bottom of the part.

These devices also fail to offer sufficient assurances in terms of constant flow-rate, as required for particularly critical therapies.

High-precision regulator models differ from the previous ones in that they do not act on the wall of the tube to vary the fluid passage section but instead act on an independent and external component which is inserted along the infusion line. Electronic-type regulators have been devised, but their costs are too high and they cannot have widespread diffusion.

Research has accordingly aimed at high-precision mechanical regulators that offer the best compromise between price and quality.

These known mechanical-type regulators generally include a first fixed body having an intake connector and a discharge connector which are connected, by means of flexible tubes, respectively to a reservoir of the fluid to be administered and to the intravenous needle, and a second moving body, that can be operated manually from outside to interact with the inside walls of the fixed body to change the flow-rate of the fluid between the two connectors.

The following devices are examples of regulators of the above described type: STAT-2^^R', manufactured by Master Medical according to US patent no. 4,802,506; DIAL-O- FL0W^^R-⁾, manufactured by Abbot Ireland and disclosed in US patent no. 4,296,949; D0SI-FL0w(^R) , manufactured by Eurospital; and EXADROP'^R) , manufactured by Braun.

These known regulators have considerable advantages but also have some recurrent drawbacks.

A first drawback is the large number of relatively complex and precision-made components which must be assembled with rather time-consuming and troublesome procedures. Accordingly, the finished product has a rather high manufacturing cost and discourages once-only use.

A second drawback is the influence that the characteristics of the liquid to be regulated have on the operating conditions of the device. In these known regulator models, the moving part in fact generally has a duct that has variable cross-section and length and is meant to connect the fluid intake and discharge connectors. This duct has a minimum, capillary-like cross-section with respect to its average length and to the general dimensions of the device, producing a laminar-type flow with prevailing tangential forces between the fluid and the duct walls. It is known that in such conditions the flow-rate is governed by Poiseuille's equation:

Q = C ΔP d< μ 1 where p = pressure variation; d = duct diameter; μ = duct length; and

C = proportionality constant.

Accordingly, the flow-rate is regulated through the variation in the length of the duct as well as through the variation in cross-section. However, the flow-rate is considerably affected by a change in the viscosity of the liquid, which is matched by a considerable change in the hydraulic resistance applied to the fluid. Incidentally, it is noted that the viscosity also varies according to the temperature, which is therefore yet another parameter to be monitored during regulation. This causes the manufacturers of these devices to advise against their use for blood and its derivatives, and in any case for highly viscous liquids, such as for example lipid or glucose solutions above 10%.

Furthermore, in these known regulators the flow-rate varies in proportion to the pressure differential inside the circuit, which varies as a function of the difference in level between the container of the parenteral liquid and the needle inserted in the vein and, last but not least, due to the blood pressure of the patient. Accordingly, the use of these known devices is not recommended in the presence of "pressure" infusion devices, i.e. devices equipped with pumps.

It is evident that these flow-rate variations force medical staff to consider empirically the scales placed on the devices, making infusion control unreliable.

The aim of the present invention is to eliminate the above described drawbacks by providing a flow regulator which is highly precise and reliable as well as extremely simple and extremely economical.

Within the scope of this general aim, a particular object is to provide a regulator which is composed of a minimal number of parts which have a relatively simple structure, such as to allow their easy assembly with manual or automatic operations in a very short time.

Another particular object is to provide a high-precision regulator that is scarcely sensitive both to the viscosity of the infusion liquid and to the pressure inside the circuit.

This aim and these objects are achieved with a high- precision flow regulator for medicinal infusion lines, comprising:

— a fixed body with a substantially cylindrical internal cavity which is provided with an intake duct and with a discharge duct, said ducts being connectable, by means of external tubes, respectively to a reservoir of parenteral liquid and to an intravenous infusion needle; and — a moving valve part which is rotatably inserted in the internal cavity of said body to selectively vary the flow- rate in said ducts; characterized in that said moving valve part comprises a closing means adapted to interact selectively with a gauged slot formed on the side wall of said fixed body at said intake duct to vary the useful passage section of said intake duct.

Preferably, the fixed body has a substantially cylindrical side wall in which the slot is arranged parallel to the axis of the body and is approximately as long as the internal diameter of the intake duct.

The slot is formed by the intersection of the substantially cylindrical side wall of the fixed body with a tapered portion of the intake duct that has a preset minimum length and is suitable to produce a turbulent-flow condition downstream so as to make its flow-rate substantially independent of the viscosity of the fluid.

Furthermore, the flow-rate of the fluid is proportional to the square root of the pressure and therefore it is less sensitive to changes in the level of the liquid reservoir with respect to the intravenous needle and to the blood pressure of the patient.

Conveniently, the moving part has a tubular portion whose outer diameter is slightly smaller than the diameter of the internal cavity of the fixed body, where the closing means is constituted by an edge with a helical profile which is formed at a free end of the cylindrical longitudinal portion.

The internal cavity of the body furthermore has a circumferential seat which is meant to retain an annular collar formed on the cylindrical portion of the part.

By virtue of this simple coupling it is possible to ensure the tightness and arrangement of the two components, avoiding the use of expensive gaskets to be interposed during assembly.

This structure also enormously simplifies the assembly operations, which can be performed in a fully automatic manner, further reducing manufacturing costs.

For a better understanding of the invention, a preferred but not exclusive embodiment of a flow regulator according to the invention is described hereinafter and illustrated by way of non-limitative example with the aid of the accompanying drawings, wherein:

Figure 1 is an enlarged-scale exploded perspective view of the flow regulator according to the invention;

Figure 2 is a partially sectional side view of the device of Figure 1; Figure 3 is a front view of the device of Figure 2;

Figure 4 is a sectional view of a detail of Figure 2, taken along the plane IV-IV;

Figures 5a to 5c are views of three steps of the operation of the regulator according to the invention;

Figure 6 is a diagram of a test section to compare the regulator according to the invention with another commercially available one;

Figures 7 and 8 are charts related to two tests conducted with the test section shown in Figure 6.

With reference to the above figures, a flow regulator according to the invention, generally designated by the reference numeral 1, is constituted by just two parts, specifically a fixed body 2 and a moving valve part or shutter 3.

The fixed body 2 is generally constituted by a side wall 4 that internally forms a substantially cylindrical cavity 5 which is closed downward by a transverse and substantially flat bottom 6.

An intake duct 7 and a discharge duct 8 extend respectively from the side wall 4 proximate to the bottom 6; both are connected to the internal cavity 5 and have Luer-Lok connectors. Respective flexible tubes 9 and 10 can be mounted on the connectors and are connected respectively to an infusion reservoir and to a needle inserted in the vein of a patient, not shown in the drawings.

The valve part 3 is constituted by a tubular portion 11 which has a slightly smaller diameter than the internal cavity 5 of the body 2; a transverse portion 12 is connected to the portion 11 and forms an actuation part.

According to the invention, on the side wall 4 of the body 2 there is a gauged slot 13 that connects the intake duct 7 to the internal cavity 5. In particular, the slot is centered on the intake duct 7 and is formed by the intersection between a tapered portion 14 of the duct, which is approximately wedge-shaped, and the internal surface of the cavity 5. The length of the slot 13 is equal to the internal diameter of the duct 7, whereas its minimum width is gauged between 0.2 and 0.8 mm and is in any case such as to produce turbulent flow in the cavity 5 downstream of the slot.

In these conditions, the flow-rate is expressed by Bernoulli's equation:

where p = pressure variation and g = density of the fluid.

Accordingly, the flow-rate, in the various regulation conditions, is directly proportional to the square root of the pressure differential and is practically independent of the viscosity of the fluid.

Conveniently, the moving part has a closing means which is adapted to interact with the slot when the moving part 3 rotates. The closing means is constituted by the edge 15 of the free end of the tubular portion 11, which is substantially helical so as to gradually and selectively close the slot 13 during the rotation of the part 3.

Preferably, the pitch of the helical profile 15 is approximately equal to the length of the slot, so as to be able to pass from a fully open position to a fully closed one.

Conveniently, the helical profile 15 has a longitudinal recess 16, towards its end portion. The recess 16 can be aligned with the slot to expose it completely and allow free flow of the fluid.

In a similar manner, adjacent to the longitudinal recess 16 there is a protrusion or wing 17 whose sides are substantially parallel to the generatrices of the tubular portion 11 and whose outer diameter is slightly smaller than that of the tubular portion due to reasons explained hereafter.

Conveniently, on the inner wall of the cavity 5, proximate to the bottom 6, there is a tooth 18 which forms a stroke limiting abutment for the sides of the wing 17. Preferably, the ducts 7 and 8 are longitudinally staggered by a distance H that is approximately equal to the pitch of the helical profile, so that the entering fluid can collect in the cavity 5 before leaving the duct 8. Furthermore, by virtue of the smaller outer diameter of the wing 17 the fluid can in any case flow out through the duct.

Proximate to the region that connects the tubular portion 11 to the transverse portion 12 of the part 3 there is an annular ridge, or collar, 19 arranged in a corresponding circumferential seat 20 which is formed on the inner side wall of the cavity 5. The elastic coupling between the ridge 19 and the recess 20 has the purpose of firmly retaining the moving part in the seat of the body and of creating a hydraulic seal without requiring gaskets.

Advantageously, in order to monitor the operation of the device, a graduated scale 21 is superimposed on a flange 22 which is formed at the upper end of the body 2. The flange 22 can be integrated in the side wall 4 of the body 3, to which it can be connected by means of diametrical stiffening tabs 23. One of the radial ends 24 of the transverse portion 12 can be tapered to form a pointer for the graduated scale 21.

In order to assemble the device it is sufficient to insert the tubular portion 11 of the part 3 in the cavity or seat 5 of the body 2 and then apply, between the two components, a certain pressure that is sufficient to elastically insert the annular ridge 19 in the seat 20. Accordingly, no complicated assembly operations or ultrasonic welding operations or the like are required. Furthermore, it is evident that the assembly operation can be performed manually or automatically with simple robots at extremely low costs.

The two components can be manufactured by injection-molding medicinal-grade thermoplastic materials. For example, the body 2 can be made of polycarbonate or of other biocompatible plastics, preferably transparent ones, and the moving part or shutter 3 can be made of an acetalic resin or of other preferably opaque resins.

In use, the valve part 3 can be rotated, gripping the transverse portion 12 in order to move the helical profile 15 so that it covers the slot 13 to a greater or smaller extent. In Figure 5a, the slot 13 is fully closed and the wing 17 abuts against the radial protrusion 18. In Figure 5b the slot 13 is partially open, whereas in Figure 5c the slot 13 is aligned with the recess 16 and the fluid can therefore flow freely within the cavity 5.

Figure 6 schematically illustrates a test line for producing the charts of Figures 7 and 8. The line generally includes a container 100 with a physiological solution of distilled water and a container 101 with a highly viscous solution that contains 33% glucose by volume. Both containers are connected to a central duct 103 by means of a switching valve 102. At the end of the duct 103 there is a three-way connector 104 from which two tubes 105 and 106 extend. Two drip-feed chambers 107 and 108 are arranged along the tubes 105 and 106, and so are respectively the device 1 and a known device 109 of the laminar-flow type, both of which discharge into a collection container 110.

Sensors 111 and 112 of the optical type or the like are connected to the two drip-feed chambers 107 and 108 and send signals to a recorder 113 to plot the charts shown in Figures 7 and 8.

In particular, the chart shown in Figure 7, which plots the number of drops per minute on the ordinates and the time in minutes on the abscissas, was plotted by feeding the physiological solution into the two lines 105, 106 and then into the two devices 1 and 109. At a certain instant T- the switching valve 102 is operated to send the 33% glucose solution into the lines 105 and 106. Line A relates to the device according to the invention, whereas line B relates to the reference device 109. Both regulators are initially set to the same initial flow-rate value. The difference in the behavior of the two devices is evident. The initial flow-rate with the physiological solution is in fact practically identical for the two regulators and has for example an average value of approximately 33 drops/minute. At the instant T-^, after a variable transitional condition, the flow in the device 1 stabilizes at T₂ after approximately 10 minutes at an average value of approximately 29 drops/minute, with a 15% flow-rate reduction. In the line provided with the laminar device 109 the flow-rate stabilizes at T₃, after approximately 18 minutes, at an average value of approximately 17 drops/minute, with a reduction of approximately 50% with respect to the initial flow-rate.

The test indicates that the device according to the invention is substantially independent of the viscosity of the fluid.

A second test can be conducted by varying the pressure in the supply line, for example by reducing the difference in level between the supply containers and the collection container 111. The chart of Figure 8 relates to a level difference change of approximately 34 cm with respect to an initial level difference of approximately 75 cm, performing the test with a solution containing 20% glucose by volume. Line C relates to the flow-rate measured along the line 105 with the regulator 1 according to the invention, which at the instant T₄ varies its flow-rate from an initial value of approximately 16.6 drops/minute to an average value of approximately 8.6 drops/minute, with a variation of approximately 50%. Line D charts the flow-rate variation in the line with the reference device 109, which at the instant T₄ reduces its flow-rate to an average value of approximately 7 drops/minute, with a reduction of approximately 60%. This proves that the device according to the invention is less dependent on pressure variations caused for example by level difference changes that may occur when the patient moves.

Claims

1. High-precision flow regulator for medicinal infusion lines, comprising:

— a fixed body (2) with a substantially cylindrical internal cavity (5) which is provided with an intake duct (7) and with a discharge duct (8), said ducts being connectable, by means of external tubes, respectively to a reservoir of parenteral liquid and to an intravenous infusion needle; and

— a moving valve part (3) which is rotatably inserted in the internal cavity (5) of said body to selectively vary the flow-rate in said ducts;

characterized in that said moving valve part (3) comprises a closing means (15) adapted to interact selectively with a gauged slot (13) formed on the side wall (4) of said fixed body (2) at said intake duct (7) to vary the useful passage section of said intake duct.

2. Regulator according to claim 1, characterized in that said slot (13) runs parallel to the axis of said cavity (5) over a length that is approximately equal to the internal diameter of the intake duct (7).

3. Regulator according to claim 2, characterized in that said gauged slot (13) is formed by the intersection between the side wall (4) of the fixed body and a tapered portion (14) of said intake duct (7) which has a preset width that creates a turbulent-flow condition downstream.

4. Regulator according to claim 2, characterized in that said moving part (3) has a tubular portion (11) which has a slightly smaller outer diameter than said internal cavity (5) of the fixed body (2).

5. Regulator according to claim 4, characterized in that said closing means is constituted by an edge (15) that has a helical profile and is formed at a free end of said tubular portion (11) so as to gradually close said slot (15) in response to a rotation of said moving part (3) about its own axis.

6. Regulator according to claim 5, characterized in that said edge (15) with a helical profile has a longitudinal recess (16) that can be aligned with said slot (13) to allow free passage through said slot.

7. Regulator according to claim 6, characterized in that said edge (15) with a helical profile has, in a position that is angularly adjacent to said recess (16), a longitudinal protrusion (17) which is meant to abut against a radial stroke limiting protrusion (18) formed on the internal surface of the cavity (5).

8. Regulator according to claim 4, characterized in that said fixed body (2) is closed in a downward region by a transverse bottom (6) proximate to which said intake duct (7) and said discharge duct (8) are formed in positions which are diametrically opposite and longitudinally staggered by at least the pitch H of said helical profile.

9. Regulator according to claim 2, characterized in that the internal cavity (5) of said body has an annular seat

(20) which is meant to retain a circumferential protrusion (19) formed on the tubular portion (11) of said part.

10. Regulator according to claim 4, characterized in that said moving part (3) has a transverse end portion (12) that is substantially perpendicular to said tubular portion (11) and protrudes from said body (2) to form an external actuation part.

11. Regulator according to claim 10, characterized in that said transverse portion (12) has a tapered end that forms a pointer for a graduated scale (21) that is rigidly coupled to said body.

12. Regulator according to claim 11, characterized in that said graduated scale (21) is located on a flange (22) which is formed at the end of said body that is opposite to said transverse bottom (6) .