Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2000-12-19
2003-03-11
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
Reexamination Certificate
active
06530262
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining the presence of leaks in a system with flowing fluid and an apparatus for the same.
It is known with regard to systems with flowing fluid to determine the flow rate and/or flow velocity into the system at the input and out of the system at the output in order to control the flow of the fluid through the system with these determined values.
For example, in dialysis devices, among other things, the flow velocity of the dialysis fluid is detected both before the dialyser and after the dialyser in order to control the flow of the dialysis fluid through the dialyser, and therefore the dialysis itself.
Accordingly, it is known from International Application No. WO 95/22743 to arrange a first sensing means comprising a throttle, a pump and a pressure sensor both before and after the dialyser in the dialysis fluid conduit, the pressure sensor thereby measuring the pressure between the throttle and the pump. Thus, on the one hand as a result of the relationship between pressure and flow velocity at the throttle, a constant rate of flow can be set by maintaining a constant pressure with the pump. On the other hand, the flow velocity before and after the dialyser can be calculated with the aid of the measured pressure values, and compared.
In addition, second sensing means are arranged between the pump and the dialyser for precisely measuring the flow velocity both before and after the dialyser. In this way the ultrafiltration may be exactly defined by comparing the measured values, the difference between the values thus providing the rate of ultrafiltration.
In order to permit exact and reliable control of the dialyser fluid through the dialyser, as well as precise ultrafiltration, the sensing means before and after the dialyser must be calibrated against one another.
This is usually carried out with a constant dialysis fluid rate through the dialyser apparatus with the dialyser disconnected, the sensing means thereby being calibrated against one another such that they indicate the same value. For example, the dialysis treatment, which generally lasts about four hours, is interrupted briefly every thirty minutes for such calibration.
When a leak is present, either dialysis fluid will escape or air will enter from outside. In this case the sensing means before and after the dialyser detect or measure different values, respectively, it being impossible to determine whether these different values result from leaks or from variations within the sensing means themselves.
Thus, when a leak is present, if the sensing means are calibrated against one another such that they indicate the same value, although they actually detect or measure different dialysis fluid currents, this can lead to control defects.
This is dangerous, particularly for dialysis machines where it is important that the fluid currents supplied to and discharged from the dialyser are precisely tared. As a result of deposits, specifically on the sensing means that are connected downstream of the dialyser and in contact with the contaminated fluid in the dialyser, the detection becomes more and more imprecise with increasing operational time. For example, proteins, urea, cholesterols and the like, which have been removed from the blood in the dialyser, can be deposited at that point. Consequently the sensing means are calibrated against one another in a regularly repeated taring phase, for which the first sensing means connected upstream of the dialyser deliver(s) the reference levels. The first sensing means are in contact only with fresh dialysis fluid so that deposits, for example of the above-mentioned substances, and the resulting increasing imprecision in operation, are improbable.
The above-mentioned fat and protein deposits occurring essentially at the downstream sensing means can be dissolved and flushed out with highly alkaline sodium carbonate or other suitable means so that, for cleaning purposes, sodium carbonate, for example, is advantageously passed through the dialyser apparatus at regular intervals.
However, it is also possible that, when using a dialysis fluid containing bicarbonate, as well as calcium carbonate among other components, which under certain conditions can be precipitated out of the dialysis fluid, will be deposited on both sensing means. These calcium deposits can be removed easily with an acid, such as citric acid, for example. Therefore, an acid that dissolves and flushes away these calcium deposits is likewise advantageously passed through the apparatus at regular intervals for cleaning purposes.
The precision of the dialysis process can be maintained over a long period of time by means of the calibration and the described cleaning procedure, provided that a leak does not occur. If, for example, dialysis fluid were to escape from the system as a result of a leak, the second sensing means will indicate a lower value than that indicated by the first sensing means. This value corresponds to the actual flow, however, during taring it would be presumed that deposits were present on the second sensing means and the second sensing means would be calibrated to the higher value supplied by the first sensing means.
A consequence of this is that, for example, during ultrafiltration, a lower quantity of fluid than necessary is extracted, which can lead to severe complications for the patient.
A method for determining blood leaks in a dialyser during a high flux hemodialysis treatment is known from International Application No. WO 97/11771. If the pressure on the blood side sinks during the treatment below the pressure on the dialysate side, the dialysate flow is halted and the rate of ultrafiltration is increased so that the pressure on the blood side becomes positive relative to the pressure on the dialysate side. In this way, in the event of a leak, blood arrives on the dialysate side, and upon recommencing the dialysis flow is conducted to a blood leak detector. In this manner it is possible to detect blood leaks in the membrane of the dialyser, however other leaks in the dialyser or in the conduits leading to the dialyser cannot be determined with this apparatus.
U.S. Pat. No. 5,350,357 describes an apparatus for peritoneal dialysis with a pump apparatus for pumping the dialysate, the pump apparatus comprising a diaphragm. This is operated with fluid pressure or pressurised air, as are valves for controlling the dialysate flow. In order to determine whether the pump apparatus or the valves have leaks a positive and negative air pressure is alternately applied in a test phase. If the applied pressure falls or rises during a predetermined time period above or below a predetermined value, an error indication is generated. This allows the pump apparatus, and the control valves, to be checked for leaks. However, it cannot be determined e.g. if the dialysis conduits have a leak.
It is known from European Patent No. 298,587 to arrange two flow meters both in the dialysate conduit before the dialyser and in the dialysate conduit after the dialyser. These are calibrated against one another in a calibration phase so that each pair indicates the same value. If these values should then deviate from one another during operation an alarm is generated. However, it is not ascertainable whether the deviations result from a leak, from errors in the flow meters, or from deposits on the measurement elements of the flow meters.
In view of this background an object of the present invention according to a first aspect is to provide a method and an apparatus with which leaks can be determined in a system with flowing fluid.
According to a second aspect it is another object of the present invention to provide a method and an apparatus with which it can be determined whether a leak exists or whether deposits are present on the sensing means, in order to ensure an exact calibration of the sensing means, particularly for dialysis apparatus.
SUMMARY OF THE INVENTION
In accordance with the present invention, these and other objects have now been
Gambro Lundia AB
Garber C D
Lerner David Littenberg Krumholz & Mentlik LLP
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