GB2028976A - Device for stopping a liquid flow in the presence of gas bubbles - Google Patents

Abstract

The device, particular for extracorporeal blood circulation, as in hemodialysis, comprises a chamber 11 kept in an upright position, with an inlet 12 at the top, an outlet 14 at the bottom and a float 16 therein. When the liquid level is under a certain height, the float engages with the tapered inner wall 15 of the chamber outlet duct and preventing air bubbles from passing on downstream of the device. In a preferred embodiment the float member is housed within a filter 18 mounted within the chamber and has a tapered shape with a ballast to better engage with the bottom of the chamber and to give rise to an air- tight seal. <IMAGE>

Description

SPECIFICATION Device for stopping a liquid flow in the presence of gas bubbles in hydraulic circuits of clinical systems, in particular for extracorporeal circulation The present invention relates to a device for stopping a liquid flow in the presence of gas bubbles in hydraulic circuits of clinical systems, in particular for extracorporeal circulation.

It is known that the problem of stopping liquid flows in the presence of gas bubbles is frequent in hydraulic circuits, mainly when there is used a pump capable of giving rise to vacuum conditions in some parts of the circuit, thus allowing air to be intaken and drawn through the liquid flow in the form of bubbles. Such a problem is particularly important for those apparatuses of clinical use, which are directly inserted in the circulatory system of a patient, such as perfusion devices, artificial kidneys, extracorporeal circulation pumps, etc., since a possible air inlet in veins or arteries causes aeroembolism, with a serious danger to the patient's life.

The most frequent solution that has been adopted for this problem is the use of a sensor device, such as of the ultrasonic or of the capacitive type, capable of detecting the presence of gas bubbles in the conduits of a hydraulic circuit and, if this is the case, causing the pump to stop.

Such a solution affords undoubted advantages whenever small quantities of gas have to be detected in a liquid medium, but only provided that a high quality sensor device is available.

However its use shows so many drawbacks to be not advisable in a number of circumstances. In particular, the reliability of the stop device is a consequence of the features of the sensor which is a sophisticated device and therefore is often delicate and easily subject to failures. Furthermorn the efficiency status of the sensing device is difficult to be recognized by a non-qualified operator.

Finally, the manufacture of such a system based on a sensor device is highly expensive, both for making the sensor and for connecting the same to the pump.

It is clear from the foregoing that in the technique there is a strong demand for the availability of devices for stopping in the presence of gas bubbles a liquid flow in a hydraulic circuit without the need of using such a sophisticated and costly apparatus as a sensor device of the above-mentioned type.

According to the present invention there is provided a device for stopping a liquid flow in hydraulic circuits, in the presence of gas bubbles, which while not being based on the use of a sensing device or similar sophisticated electronic apparatus for its operation, affords performances at least as reliable as with such expensive prior art devices, being also extremely responsive and precise in detecting the presence of gas bubbles and timely causing the pump operation to stop as the volume of air (or other gas) included in the liquid flowing in a hydraulic circuit exceeds a predetermined value limit.

The device according to the invention comprises a vertically extending chamber provided at its top with a duct for feeding a liquid to the chamber and at its bottom with an outlet duct for the liquid from the chamber, having a floating member housed therein of such a shape to mate with the chamber bottom or the opening of said outlet conduit from the chamber, thereby providing, at the lowered position of the floating member in the chamber, for an absolute air-tight seal to stop the liquid flow between the floating member and the chamber wall or the opening of the outlet duct for the liquid from the chamber.

According to a preferred embodiment of the present invention said chamber comprises an upper portion of cylindrical shape and a lower portion of frusto-conical shape tapering from the bottom of said cylindrical portion to the opening of said liquid outlet duct.

According to a particular embodiment of the present invention the floating member is housed for a free vertical movement in a tubular filter mounted in the chamber.

These features, objects and advantages of the invention will be apparent from the following description with reference to the annexed drawings, given by way of example only, in which: FIGURE 1 is an extremely diagrammatic crosssection view of a first embodiment of the device according to the invention; and FIGURE 2 is a diagrammatic cross-section view of a second embodiment of the device according to the invention, this embodiment being particularly suitable for insertion in the connecting circuit between a dialysis apparatus and a fistula needle in the circulatory system of a patient.

With particular reference to Fig. 1 , the flow stop device of the invention, generally designated D, comprises a tubular chamber 1 which in use is kept substantially upright, having its upper portion 1 a of a substantially cylindrical shape, continuously joined with a lower portion 1 b of a frusto-conical shape. The chamber 1 is axially open at its opposite ends, being provided with an inlet duct 2 for feeding a liquid to the chamber and with an outlet duct 3 for discharging the liquid from the chamber. During the operation the chamber is at least partially filled with a liquid L.

hollow floating member 4 (which in the embodiment illustrated in Fig. 1 has a substantially spheric shape) is housed in the chamber 1 and floats on the liquid L contained in the chamber 1. Some clearance exists between the inner wall of the portion 1 a and the outer wall of the float 4, whereby this latter can freely move downwards or upwards in the chamber without significant friction between the float and the inner wall of portion 1 a.

In case that liquid L fed into the chamber 1 through the duct 2 draws air bubbles therewith, these will collect at the top 1 c of chamber 1 , thus lowering the free surface of liquid L within the chamber and consequently also the float 4.

Therefore it should be appreciated that the chamber 1 first of all serves as a "trap" for the gas bubbles carried by the liquid fed to the chamber and flowing out therefrom through the duct 3. The liquid in this duct 3 is free from bubbles, which therefore cannot pass on to the circuit section which is downstream of the chamber 1.

This situation maintains as such, since liquid can continue to enter through the inlet duct 2 and to flow out through the outlet duct 3 until the gas quantity stored in the upper zone 1 c of the chamber 1 forces the float 4 to go down as it follows the lowering of the free surface of the liquid L in the chamber 1, so as to reach the position represented by a phantom line in Fig. 1, that is until engaging by its outer wall the inner wall of the frusto-conical portion 1 b of the chamber 1.The complete air-tight seal caused by the peripheral contact between the float and the inner wall of the frusto-conical portion 1 b of the chamber 1 obviously stops the liquid flow through the chamber also preventing air from passing to the circuit section which is downstream of the chamber.The interruption of the liquid flow in the chamber 1 causes a pump (not shown) actuating the circuit to stop immediately.

Instead of the substantially spheric shape represented in Fig. 1 , the float 4 may have a different configuration, such as a conical shape, complementary to the inner wall of the portion i b of the chamber 1. In this case the floating member 4 may also be provided with a ballast in order to facilitate its keeping the upright position within chamber 1 and also to have a better seal engagement with the inner wall of the frustoconical portion 1 b of the chamber 1.

With reference to Fig. 2 a preferred embodiment of the device according to the invention is represented, being housed in a drip chamber inserted in a connection circuit between a dialysis apparatus (not shown) and a fistula needle (also not shown) in the circulatory system of a patient, which re-introduces therein the blood depurated by the dialyzer unit.

A drip chamber, generally designated D', comprises a chamber 1 1 wherein a tubular filter 1 8 is housed, being closed at the top by a cap 18' and fixed at the bottom, along all its periphery, to the inner wall of the tapering portion of the drip chamber. As it is known the filter serves to prevent the patient from receiving possible small particles or blood clots which may be formed in the dialyzer unit.

According to the present invention a torpedo nose-shaped or substantially ogival hollow float 1 6 is housed in the tubular filter 18 and is provided in its lower part with a ballast 17 having the purpose of keeping it in an upright position.

The drip chamber 1 1 is closed at the upper end by a a cover 13, which is centrally provided with a through duct 12 for feeding the depurated blood from the dialyzer unit (not shown) to the drip chamber. Further two lateral ducts 12', 12" are provided through the cover 13, the function of which will be better explained in the following.

The chamber 1 1 is open at the lower end, being connected to an outlet duct 14 for the depurated blood from the chamber and the reintroduction thereof in the patient's circulatory system through a a fistula-needle (not shown).

Operation of the device according to the embodiment of Fig. 2 is obviously the same as described for the diagrammatic representation of Fig. 1. As the storing up of air in the upper portion of the chamber 11 causes the blood level in the chamber itself to lower, also the float 16 will follow the blood level until possibly obstructing the opening 1 5 of the outlet duct 14, thus preventing air from reaching the patient and causing the temporary stop of the whole circuit.This occurs because one of the two side through ducts, e.g. 12' is connected with a pressure gauge (not shown) and which continuously detects the pressure of air above the blood level.As soon as the float 16 stops the outlet flow, this value of pressure immediately increases due to the continued operation of the pump and the gauge sends a control signal which causes the pump of the dialysis apparatus to stop and a possible alarm to be signalled.

To resume operation, that is feeding depurated blood to the patient, it is necessary to reset the device at the initial conditions. This is carried out in a known manner by means of the other through duct, e.g. 12", which is usually closed and now will be opened by an operator to re-establish the atmospheric pressure in the chamber. Thereafter the pump of the dialyzer unit is actuated until the desired blood level in the chamber is restored, then the remaining air bubbles are removed from the filter by adequate handling of the chamber, which is made of flexible material, and finally the floating stop member will be disengaged through a similar handling of the outlet duct 14, thus being brought again afloat. In this manner the circuit is reset and the dialysis apparatus may operate for a considerable time until the air bubbles collected in the drip chamber will cause another intervention of the stop device.

It is obvious that the construction details and the embodiments of the present invention could be broadly varied with respect to those described and illustrated by way of example only, without therefor exceeding the scope of the invention. In fact it is clear that, irrespective of the shape of the chamber and of the floating member, whichever embodiment comprising a chamber with a liquid passing downwards and therethrough in use and which encloses a float so shaped as to obstruct the chamber outlet falls within the protective scope of the present invention.

Claims (5)

1. A device for stopping a liquid flow in the presence of gas bubbles within a hydraulic circuit, comprising a vertically extending chamber provided at its top with a duct for feeding the liquid to the chamber and at its bottom an outlet duct for the liquid from the chamber, characterized by the fact of having a floating member housed therein of such a shape to mate with the chamber bottom or the opening of said outlet duct from the chamber, thereby providing, at the lowered position of the floating member in the chamber, for an absolute air-tight seal to stop the liquid flow between the floating member and the chamber wall or the opening of the outlet duct for the liquid from the chamber.

2. A device according to claim 1 for hydraulic circuits of an extracorporeal circulation system in which said chamber axially open is kept in use at a substantially upright position, and comprises a substantially cylindrical upper portion and a substantially frusto-conical lower portion tapering from the bottom of said cylindrical portion to the opening of said cylindrical portion to the opening of said outlet duct of the liquid from the chamber, said floating member having a transverse crosssection size which is smaller than the inner diameter of the substantially cylindrical portion of the chamber, to freely follow the variations of height of the liquid surface in said substantially cylindrical portion, and is greater than the diameter of the outlet duct opening for the engagement of the outer wall of the floating member with the inner wall of the frusto-conical portion of the chamber, in the engagement position the peripheral configuration of the floating member complementarily mating with the wall of the frusto-conical portion for a complete air-tight seal to stop the liquid flow between floating member and wall.

3. A device according to claim 2, wherein the floating member is torpedo nose-shaped with the ogival tapered portion at the lower end and is provided with a ballast to ensure the upright position of the floating member in the chamber.

4. A device according to claim 3, wherein said floating member is freely housed within a tubular filter which is a guide for the vertical movement thereof and is fixed at the lower end to the bottom of said chamber co-axially with the opening of said outlet duct.

5. A device for stopping a liquid flow in the presence of gas bubbles, substantially as above described and illustrated in the annexed drawing.