Description.

The invention relates to a biomedical monitoring apparatus comprising «a disposable sensor for monitoring ionic activity in biological fluids and a process for obtaining the sensor. In the biomedical field, and especially in the field of dialysis, it is essential to identify both presence and quantities of ions of chemical elements in diluted biological fluids such as blood, and in recent years much effort has been expended in the search for improvements in monitoring apparatus for the purpose. Up until now, determining ionic activity, that is, assessing the concentration of one or more ions in a fluid, is performed in a laboratory after having drawn a quantity of the fluid to be analyzed at predeterm ned time intervals, with considerable discomfort on the part of the patient. Present laboratory techniques do not provide instantaneous answers, which may be necessary in certain circumstances as well as in some

pathological states, where the doctor needs results fast in order to be able to proceed to a cure or therapy. A principal aim of the present invention is to quantify one or more ions in a biological fluid in real time as well as continuously during treatment, such as di-alysis, on an individual patient. With the invention, the doctor can follow the activity of the ion on a monitor, and can record the results so that later a comparison can be made with other results and a full pathology documented.

A further aim of the invention is to provide an apparatus which can rapidly be calibrated according to the type of ion to be assessed, the calibration being done only once and before commencing a treatment.

A still further aim of the invention is to provide a stable sensor, guaranteeing a uniform signal overall during a therapy.

These and other aims besides are all achieved by the present invention, which is characterised as in the accompanying claims. Further characteristics and advantages of the present invention w ll better emerge from the

detailed description that follows, of an embodiment of the invention, illustrated in the form of a non-limiting example in the accompanying drawings, in which: - Figure 1 shows a longitudinal section of a conduit insertable in a circulation circuit of a fluid, and bearing a se_sor for ionic activity; - figure 2 shows the conduit according to section 1-1 of figure 1 ; - figure 3 schematically shows the" totality of components which make up the apparatus. With reference to figure 3, the apparatus comprises a dedicated part, denoted by 1, which is inserted between a fluid inlet conduit 2 and a fluid outlet conduit 3 through which flows a liquid containing a determined quantity of ions, and also comprises a data processing unit k receiving electrical signals coming from the dedicated part through two electrical conductors 5.

As can be seen in figures 1 and 2, the dedicated part 1 is constituted by a section of plastic tube 6, advantageously made in stiff PVC , which is provided with two projections 7 through which a single through-hole is made. Two conical plugs

made in the same material as the plastic tube 6 are inserted in the two ends of the through-hole. Each plug is provided with a central through hole 9 in which an electrode 10 is inserted, made of a specially treated metal such as silver chloride.

On its lower surface facing the central through- hole of the plastic tube 6, the upper plug 8 bears a membrane 12 constituting a sensor. The disposable sensor 12 monitors the activity of one or more ions. The manufacturing process of the sensor 12 w ll be described hereinafter.

The projection throgh-hole 9 is closed at either end by sunk contacts 11 forced along the walls of the projections up until they contact with the electrodes 10.

In more detail, the upper metal electrode 10a is inserted between the sensor 12 and the upper contact, while the lower metal electrode 10b touches the lower contact and penetrates into the plastic tube 6 hole sufficiently deeply to contact with an inert membrane 13, such that both the membranes 12 and 13 are in contact with the liquid to be analyzed. The tube segment constituting the dedicated part 1

can be sterilized according to normal standard procedures.

In the dedicated part, following the passage of biological fluid containing unknown ions, a millivolt electrical signal is generated, the numeric value of which is correlated to the ionic activity in the fluid, which signal is then sent to the data processing unit to be collected, memorized and processed in order to be translated into a numeric value, and which is then visualized in alphanumeric and/or graphic form.

In the illustrated embodiment reference is made to two only projections 7 with two electrodes 10 and one only sensor 12, though it is evident that further couples of projections could be provided along the plastic tube 6, together with electrodes and sensors for reading various ions, without having to modify the invention significantly. The process for obtaining the sensor 12 w ll now be described. The process is based on the preparation of a solution for a certain quantity of PVC powder in a solvent suitable not only for PVC but also for an additive carrier matrix solution. When the PVC solution is ready, it is poured in an evaporation

dish and left until it has completely evaporated.

Thus a membrane or film is obtained which can be removed from the dish and packed in card in a dark room.

Various methods can be used to mount the membrane on the lower face of the plug, for example by cutting the film into discs which can then be cemented on to the plug. The membrane can also be directly formed on the plug, if so desired.

To obtain the above, a determined volume of the solution can be poured directly on to the plugs, which are specially prepared so that the solution does not drip off them during the hardening process.

The above-described process, though relatively rather long to achieve, obviates thermal stress on the membranes, which therefore last longer and are more stable.

Now a practical and non-limiting example of the process will be described, for making a film which will be sensitive to the sodium ion.

The following are poured into a hermetical 1 y- sealable glass container:

1) two illilitres of a suitable solvent for all the components which w ll make up the film, viz:

2) two hundred microlitres of matrix solution with the additive (5mg/ml);

3) close, shake, reopen;

4) two hundred microlitres of carrier matrix solution (50 mg/ml ) ; 5) add one millilitre of solvent;

6) close, shake, reopen;

7) add one hundred and sixty eight microlitres of PVC plasticizer;

8) due mil li litres of solvent; 9) close, shake, reopen;

10) sprinkle two hundred mg . of PVC powder;

11) close and shake for two minutes;

12) shake for one-minute spells every 15 minutes, up until the PVC is solubilized; 13) pour the mixture into an covered evaporation dish and leave in a quiet place;

14) wait until the film is completely formed;

15) remove the film from the dish and leave it in a dark place. If the film is to be made directly on the plug, proceed up until point 12 above and then deposit 64 microlitres of the mixture obtained directly on the centre of the lower face of the plug. Then wait until the mixture has completely evaporated.

The inert membrane 13 can be made using the same process as the membrane 12, with the only difference being that operation no. 4 above will be excluded, so that no ion carrier is introduced.