Differential flow-meter for measuring the weight loss in haemodialysis treatments

Abstract

A differential flow-meter for measuring the weight loss in dialysis treatments. The differential flow-meter is of the thermal anemometer type.

Claims

1. A differential flow-meter comprising a first separate channel and a second separate channel in which two fluids flow, said fluids being same or different; said first channel comprising the following devices: a first thermal device that functions as a first heater means of the fluid flowing in the first channel, the amount of heat supplied by said first heater means being controlled by a differential measuring device, the first thermal device also functioning as a first temperature detector means, the temperature of said first temperature detector means being also detected by means of the differential measuring device; and said second channel comprising the following devices: a second thermal device that functions as a second heater means of the fluid flowing in the second channel, the amount of heat supplied by said second heater means being controlled by said differential measuring device, the second thermal device also functioning as a second temperature detector means, the temperature of said second temperature detector means being also detected by means of the differential measuring device; wherein said differential measuring device can transform the instantaneous temperatures detected by the temperature detector means into differential flow rate or speed measurements of the two fluids passing in the two channels, wherein said first and said second thermal devices are integrated in a micro-machined chip.

2. The differential flow-meter according to claim 1, wherein each channel comprises cylindrical end portions (PC) connected to a central prismatic portion (PP).

3. A Haemodialysis machine comprising: at least a differential flow-meter, the differential flow meter comprising: a first separate channel and a second separate channel in which two fluids flow, said fluids being same or different; said first channel comprising the following devices: a first thermal device that functions as a first heater means of the fluid flowing in the first channel, the amount of heat supplied by said first heater means being controlled by a differential measuring device, the first thermal device also functioning as a first temperature detector means, the temperature of said first temperature detector means being also detected by means of the differential measuring device; and said second channel comprising the following devices: a second thermal device that functions as a second heater means of the fluid flowing in the second channel, the amount of heat supplied by said second heater means being controlled by said differential measuring device, the second thermal device also functioning as a second temperature detector means, the temperature of said second temperature detector means being also detected by means of the differential measuring device; wherein said differential measuring device can transform the instantaneous temperatures detected by the temperature detector means into differential flow rate or speed measurements of the two fluids passing in the two channels.

4. The Haemodialysis machine according to claim 3, wherein the two channels of said differential flow-meter are hydraulically connected to two ducts in which dialysate flows in order to calculate weight loss.

5. The Haemodialysis machine according to claim 3, wherein the two channels of said differential flow-meter are hydraulically connected to two ducts in which blood flows in order to calculate weight loss.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention it will be now described a preferred embodiment, purely for non limitative purposes and with a reference to the attached drawings, in which:

(2) FIG. 1 shows a schematic view of a differential flow-meter using the calorimetric principle;

(3) FIG. 2 shows a schematic view of a differential flow-meter made according to the present invention using the principle of the thermal anemometer;

(4) FIG. 3 shows a blood circuit of a haemodialysis machine to which it is applied a differential flow-meter according to the present invention;

(5) FIG. 4 shows a 3D view of the differential flow-meter whose components have been assembled; and

(6) FIG. 5 shows an exploded view of the differential flow-meter of FIG. 4.

DETAILED DESCRIPTION

(7) In FIG. 2 1000 indicates, as a whole, a differential flow-meter using the principle of the thermal anemometer flow-meter, which is one of the objects of the present invention.

(8) The differential flow-meter 1000 comprises a first separate channel 20 and a second separate channel 30 in which two fluids flow, said fluids being same or different.

(9) A thermal device 200 is attached on the inner wall of channel 20. In said device 200, the temperature sensor 22 seen in FIG. 1 corresponds in principle to the heating plate 21. In particular, it is a resistor overheated thanks to the Joule effect, namely by imposing a suitably high current, with the resulting resistance increase, said resistor being cooled by the moving fluid, with the resulting temperature decrease. Therefore this resistance variation is inversely proportional to the fluid flow rate.

(10) Analogously, a thermal device 300 is attached on the inner wall of channel 30. In said device 300, the temperature sensor 32 seen in FIG. 1 corresponds in principle to the heating plate 31.

(11) In this way the variation of heat flow from the plate to the fluid can be measured by means of the differential measuring device 40.

(12) In FIG. 3, 100 indicates, as a whole, a blood circuit of a haemodialysis machine (not shown in its entirety).

(13) The blood circuit 100 comprises a dialyzer 50 fed, on the one side, by the dialysate through a duct 51 and, on the other side, by the arterial blood flowing through a duct 52 thanks to a peristaltic pump 53. The exchange of impurities between the blood and the dialysate takes place according to the previously described system.

(14) The dirty dialysate exits the dialyzer 50 flowing in a duct 54, whereas the treated blood is re-introduced in the human body (BD) through a channel 55 connected to a patient's vein.

(15) In a known way, in the duct 52 a certain amount of heparin is pumped into the arterial blood by means of a pumping device 56 in order to avoid blood coagulation.

(16) The duct 52 is provided with a device 57 for measuring the arterial pressure. Analogously, the duct 55 is associated to a device 58 for measuring the venous pressure and for detecting the presence of unwanted air.

(17) FIGS. 4,5 show a further embodiment of a differential flow-meter 10* object of the present invention.

(18) The differential flow-meter 10*, 1000 can be connected to the ducts 51, 54 of the blood circuit 100 (FIG. 3) to calculate the so-called weight loss, namely the liquid mass subtracted to the patient.

(19) In an alternative embodiment, the person skilled in the art also finds obvious to connect the differential flow-meter 10*, 1000 to the two blood ducts 52, 55 (FIG. 3).

(20) As shown in FIGS. 4, 5 the differential flow-meter 10* comprises two channels 20*, 30*.

(21) In the embodiment shown in FIGS. 4, 5, channels 20*, 30* are identical, but they could also have different shapes.

(22) Each channel 20*, 30* is aligned along a respective longitudinal symmetry axis (Y1), (Y2), which, in use, are parallel to each other.

(23) In particular, channel 20* (but this obviously applies also for channel 30*) comprises two cylindrical end portions (PC) connected to a central prismatic portion (PP).

(24) The two cylindrical end portions (PC) are used for the insertion of the remaining portions of the duct in which they are inserted (pair of ducts 51, 54; or, alternatively, pair of ducts 52, 55).

(25) The central prismatic portion (PP), in turn, is provided with a flat back face (FP), on which a back groove (SC) is made, and a flat front face (FA) with an inspection window (WN), covered in use by a transparent panel (PN) (FIG. 5) to allow the visual inspection of the fluid flowing in said central prismatic portion (PP).

(26) The back groove (SC) supports in use (FIG. 4) a micro-machined chip 90, advantageously made of silicon, integrating the thermal devices 200, 300 and the differential measuring device 40 seen in relation to the embodiment shown in FIG. 2.

(27) More precisely, the chip 90 is glued and connected (for instance by means of the wire-bonding technique) to a substrate 91 (for instance a PCB, which stands for Printed Circuit Board) containing all the electrical connections for data control and acquisition; the two channels on the substrate 91 bearing the two flows must have a suitable opening for housing the chip 90.

(28) Once assembled, the differential flow-meter 10*, 1000 is as shown in FIG. 4.

(29) In short, according to the preferred embodiment shown in FIGS. 4, 5, the present invention refers to a differential flow-meter 10*, 1000 for measuring the difference of flow rate, or speed, between two fluids.

(30) The differential flow-meter 10* is identical to the differential flow-meter 100 shown in FIG. 2 and is characterized in that it comprises: a) a first separate channel 20* and a second separate channel 30* in which two fluids flow, said fluids being same or different; and b) a chip 90 located on either side of the two channels 20*, 30* so that a first portion 90A of the chip 90 is touched only by a first fluid flowing in the first channel 20*, and so that a second portion 90B of the chip 90 is touched only by a second fluid flowing in the second channel 30*.

(31) Moreover, the chip 90 can measure and compare, by means of the method seen with regard to FIG. 2, any possible electrical resistance change in the first portion 90A and in the second portion 90B in order to calculate any possible change of flow rate or speed occurring in the fluids flowing in the two channels 20*, 30*.

(32) The silicon micro-machining technology can be used to manufacture the sensitive portion of the differential flow-meter 10. This technology, starting from the silicon planar processing techniques, allows to create miniaturized planar and 3D structures, such as resistors resting on elastic membranes.

(33) The silicon micro-machining techniques allow the manufacture of very small objects at low costs. Small size, combined with reduced costs and accuracy, allow the creation of dialysis machines which are cheaper, smaller, lighter and with lower operating costs. In particular, the operating costs are drastically reduced and, with no active element in motion, breakage and maintenance are rare and cheaper.

(34) The objective of the device object of the present invention is the direct measurement of the difference of (mass or volume) flow rate, or speed, between two separate channels bearing the two flows.

(35) The fluids forming the two flows can have same or different chemical composition, and can have same or different physical conditions (for instance density, temperature, speed, pressure).

(36) The sensitive elements are connected and controlled in such a way to be directly affected by the difference of the two flows in question. A Wheatstone bridge connection can be used to this purpose, so that the measurement of the unbalance of the Wheatstone bridge is proportional to the flow difference in the two channels.

(37) It should be noted that the measurement in question cannot ignore the fluid temperature, which must therefore be known (measured by the sensor) and suitably balanced.

(38) The sensor manufacture comprises two steps: 1. micro-machining of silicon chips, containing all necessary sensitive elements and heaters; and 2. assembling of the aforesaid chip with other functional parts (substantially PCBs and fluidic channels), in order to obtain a flow sensor which can be used under desired thermal, fluidic and electrical conditions.

(39) In short, the micro-machining consists in the creation of a suitable network of resistors, electrically insulated with regard to the fluid and thermally insulated with regard to the substrate. Indicatively, the manufactured resistors have a micrometer-sized section and a millimeter-sized length.

(40) The sensor assembly can be carried out as follows. The chip bearing the sensitive elements configured in a differential manner is glued and connected (for instance by means of wire-bonding) to a substrate (for instance PCB) having all electrical connections for data control and acquisition; the two channels bearing the two flows must have a suitable opening for housing the chip.

(41) In a second alternative embodiment (not shown), the two channels of the differential flow-meter are formed in at least one block, one face of which is closed by a layer of suitable material (e.g. silicon) on which the elements 200, 300 and the differential measuring device 40 are formed.

(42) In a third embodiment, the sensitive elements (thermoresistances) are made by means of thermopiles or thermistors.

(43) The main advantages of the differential flow-meter of the present invention are as follows: high sensitivity and resolution; reduced size; low production costs; and better reliability over time.