Measuring and testing – Instrument proving or calibrating – Fluid pressure
Reexamination Certificate
2002-09-25
2003-11-04
Raevis, Robert (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Fluid pressure
Reexamination Certificate
active
06640611
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for testing sensors of the type for measuring a specific quantity. More particularly, the present invention relates to a method for testing differential pressure sensors in an apparatus for the extracorporeal treatment of blood, such as a dialysis monitor.
BACKGROUND OF THE INVENTION
In apparatus for the extracorporeal treatment of blood, there are usually arranged several identical sensors for measuring a specific quantity. This is intended to achieve improved control and monitoring, as well as increased safety. For example, a dialysis monitor comprises several sensors for measuring the pressure in fluid conduits utilized during dialysis.
On the one hand, these fluid conduits transport blood from the patient to the blood side of the dialyser and from there back to the patient and, on the other hand, they transport dialysis fluid from the dialysis fluid source to the dialysate side of the dialyser, and from there to an outlet. The blood-carrying conduits are generally exchanged after each treatment, while the conduits transporting the dialysis fluid are permanently connected to the dialysis monitor and are disinfected and rinsed after each treatment.
The monitoring of pressure during dialysis, both in the blood-carrying conduits and in the conduits carrying the dialysis fluid, is important for several reasons. One important reason is, for example, surveillance of the transmembrane pressure at the membrane present in the dialyser that separates dialysis fluid from blood, and which is semi-permeable. This transmembrane pressure is the pressure difference between the pressure on the blood side and the pressure on the dialysate side, and determines the direction and quantity of fluid transport through the membrane. If the transmembrane pressure is positive, then the fluid will be drawn out of the blood. This process is also called ultra-filtration. With a negative transmembrane pressure no excess fluid will be drawn from the patient. The removal of excess fluid is, however, one of the principal functions of dialysis, so that the importance of monitoring the pressure in the dialysis fluid conduits and blood conduits is evident from this alone.
A further important reason is monitoring of the arterial and venal pressure in the blood-carrying conduits during treatment. If, for example, the arterial pressure should be below a specific negative pressure, then the arterial needle could be blocked or lodged in the fistula wall, or the conduit could be folded over. In order to avoid damage to the fistula, the machine will automatically be stopped, and an alarm triggered. If the arterial pressure exceeds a predetermined negative pressure, then the arterial needle could have come loose and be sucking in air. In this case also an alarm will automatically be triggered, and the machine stopped.
On the other hand, if the venal pressure should fall below a predetermined value, then the blood feedback to the patient could be not sealed or interrupted. If the venal pressure exceeds a specific predetermined value, then the venal needle could be blocked, or the feedback tube bent. In this case the machine will likewise be stopped, and an alarm automatically triggered.
However, in order to reliably monitor the pressure, operation of the sensors must be trouble-free. These are thus checked prior to operation of the dialysis monitor during a check phase, in which a functional check of the entire dialysis monitor takes place.
Thus, for checking the sensors that measure the pressure in the dialysis fluid conduits (hereinafter referred to as dialysate pressure sensors), at least two of which are provided, a static pressure is generated in these conduits. For the present case, static pressure means that the dialysis fluid does not flow through the conduits, but rather sits in the conduits, and that a pressure is applied to the stationary dialysis fluid. In this way, the effects on the pressure measurement of the valves, throttles, pumps, etc. that are arranged in the tubes, are excluded. The values supplied by the individual dialysate pressure sensors are compared with one another; the individual dialysate pressure sensors must all supply the same value, as they are subjected to the same pressure.
If the individual dialysate pressure sensors supply different values, then a sensor malfunction has occurred, and the control or monitoring unit of the dialysis monitor generates a corresponding alarm.
The pressure sensors generally used in this case are so-called differential pressure sensors that utilize atmospheric pressure as a reference value. These sensors are checked by applying two different static pressures in the described manner, one generally being positive with respect to atmospheric pressure and one being negative with respect to atmospheric pressure. On the one hand, the values supplied by the sensors are compared with one another in order to determine a possible sensor malfunction. On the other hand, the values supplied by each individual sensor at the different pressures are also used to determine the constant allocated to each individual sensor. This constant is necessary for precise determination of the pressure, and can be determined only with the aid of at least two values supplied at different pressures.
The sensors that measure the pressure in the blood conduits, of which at least two are provided, (hereinafter referred to as blood pressure sensors) are usually also differential pressure sensors. In contrast to the dialysate pressure sensors that are permanently connected with the dialysis fluid conduit, the blood pressure sensors are not permanently connected to the blood conduits. As mentioned above, new blood conduits are used for each treatment, so that the blood pressure sensors must be connected to the blood conduits by the operating personnel before each treatment. During the check phase before the treatment, the blood pressure sensors are generally not connected to the blood conduits, thus no pressure or different pressures may be generated in the blood conduits and applied to the blood pressure sensors for testing same. It is, therefore, only possible to examine whether the blood pressure sensors each supply the same reference value corresponding to atmospheric pressure. However, this provides no information as to whether the blood pressure sensors will supply the same values at the same applied pressure above or below atmospheric pressure.
It is possible to test the blood pressure sensors during the check or test phase by connecting the blood pressure sensors with a separate conduit and to generate one predetermined pressure, or different predetermined pressures, in this conduit. However, this requires, on the one hand a supplementary material complexity, as the dialysis monitor must be correspondingly adapted to enable this additional test option. Furthermore, additional, specially constructed conduits are necessary, so that the material complexity and the cost as a whole increases. On the other hand, the operating complexity for the operating personnel is markedly increased as, in the test phase, the operating personnel must first attach the special test tube to the dialysis monitor and connect it to the blood pressure sensors. After completing the test, the operating personnel must then remove the special test tube before the blood conduits and the dialyser can be connected to the dialysis monitor, and the blood pressure sensors can be connected to the blood conduits.
In view of this background, it is an object of the present invention to provide a method and apparatus for testing identical sensors for measuring a specific quantity, in particular for checking differential pressure sensors with a reference side and a measurement side, with which these disadvantages can be alleviated.
In particular, testing of the blood pressure sensors of dialysis monitors without additional manipulation by the operating personnel, and without the attachment of separate tubes to the dialysis monitor that need removing
Ericson Björn
Wictor Per-Ola
Gambro AB
Lerner David Littenberg Krumholz & Mentlik LLP
Raevis Robert
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