Transcutaneous carbon dioxide measurement device

Abstract

This invention provides a transcutaneous carbon dioxide measuring device that can improve detection sensitivity by improving the device body and measuring electrodes in a device that detects carbon dioxide diffused from the skin of patients, etc., by dissolving it in an aqueous solution and measuring it as a change in hydrogen ion concentration. [Solution] The transcutaneous carbon dioxide measuring device comprises a main body case, a holding block housed in a through-opening of the main body case and immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride, a glass electrode in a first through-hole of the holding block, a reference electrode in a second through-hole, a thermistor in a third through-hole, a film portion that seals the through-opening, holds the mixed aqueous solution, and allows carbon dioxide produced from the skin to pass through to the holding block, and a cap that protects the film portion and is fitted onto the main body case.

Description

Technical Field

[0005]

[0001] The present invention relates to a transcutaneous carbon dioxide measuring device, and particularly to a device that non-invasively measures the carbon dioxide concentration and partial pressure in blood through the skin by contacting the skin surface of a subject to be measured.

Background Art

[0002] <00000When the oxygen concentration in the blood decreases due to chronic respiratory diseases such as chronic respiratory failure seen during sleep, acute aversion such as neuromuscular diseases, measures such as artificial respiration under intubation are required. In this case, PaCO2 by arterial blood gas analysis is used when applying the treatment and determining the treatment effect. However, since it is an invasive measurement, there are many problems such as causing pain to the patient and difficulty in continuous measurement. Also, even during the stable period of chronic respiratory failure, the alveolar ventilation volume decreases as the disease progresses. In particular, hypoventilation is likely to occur during nighttime sleep.

[0003] Therefore, devices for measuring the respiratory state of a patient through carbon dioxide in the blood have been proposed. For example, a device that is installed on the body surface of a patient and estimates carbon dioxide from transcutaneous gas. Carbon dioxide is known to absorb specific infrared wavelengths, and it is a device that estimates from the change in the absorption amount of infrared rays (see Patent Document 1). However, sufficient measurement accuracy cannot be obtained with the estimation based on the absorption of infrared rays, and a more accurate measuring device has been demanded.

[0004] As a method different from infrared absorption, a device has been proposed that dissolves carbon dioxide diffusing from the skin in an aqueous solution and detects it as a change in the electrical properties of the aqueous solution, mainly the hydrogen ion concentration (see Patent Document 2). According to this device, although the detection sensitivity is improved compared to the estimation based on the absorption of infrared rays, it is not necessarily sufficient.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The present invention has been made in view of the above points, and provides a transcutaneous carbon dioxide measuring device that can improve detection sensitivity by improving the device body and measuring electrodes in a device that dissolves carbon dioxide diffusing from the skin of a patient, etc. in an aqueous solution and detects it as a change in hydrogen ion concentration. [Means for solving the problem]

[0007] In other words, the transcutaneous carbon dioxide measuring device of the embodiment is characterized by comprising: a main body case; a holding block (silver billet type) housed in a through-opening of the main body case and immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride; a glass electrode with a large coefficient of linear thermal expansion that does not cause cracks, housed in a first through-hole of the holding block; a reference electrode housed in a second through-hole of the holding block; a thermistor housed in a third through-hole of the holding block; a film portion that seals the through-opening to hold the mixed aqueous solution and allows carbon dioxide generated from the skin of the person being measured to pass through to the holding block; and a cap that protects the film portion and is fitted onto the main body case.

[0008] Furthermore, in a transcutaneous carbon dioxide measuring device, the glass electrode may have a flat portion on the film side and a hemispherical portion on the opposite side of the film side, comprising a glass container portion containing a potassium chloride aqueous solution and an electrode wire member made of silver and silver chloride inserted into the glass container portion.

[0009] Furthermore, in the transdermal carbon dioxide measuring device, a zirconium oxide layer may be provided on the inner surface of the flat portion of the glass container.

[0010] Furthermore, in the transcutaneous carbon dioxide measuring device, the reference electrode may be a silver wire member, fixed in the second through-hole with conductive resin.

[0011] Furthermore, in the transdermal carbon dioxide measuring device, a nonwoven fabric may be interposed between the main body case and the film portion.

[0012] Furthermore, in the transcutaneous carbon dioxide measuring device, the outer surface of the film portion is the skin of the person being measured. It may also be provided with double-sided tape for secure adhesion.

[0013] Furthermore, the transcutaneous carbon dioxide measuring device may also be equipped with a glass electrode, a reference electrode, and a control unit that is wired and connected to the thermistor. [Effects of the Invention]

[0014] The transcutaneous carbon dioxide measuring device of the present invention comprises a main body case, a holding block housed in a through-opening of the main body case and immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride, a glass electrode housed in a first through-hole of the holding block, a reference electrode housed in a second through-hole of the holding block, a thermistor housed in a third through-hole of the holding block, a film portion that seals the through-opening to hold the mixed aqueous solution and allows carbon dioxide generated from the skin of the person being measured to pass through to the holding block, and a cap that protects the film portion and is fitted to the main body case. As a result, the detection sensitivity of the device, which dissolves carbon dioxide diffusing from the skin of a patient or the like into an aqueous solution and detects it as a change in hydrogen ion concentration, is enhanced. [Brief explanation of the drawing]

[0015] [Figure 1] This is an overall perspective view of the transcutaneous carbon dioxide measurement device according to the embodiment. [Figure 2] This is an exploded perspective view of the transdermal carbon dioxide measurement device according to the embodiment. [Figure 3] This is an enlarged perspective view of the holding block. [Figure 4]This is a schematic cross-sectional view of a glass electrode. [Modes for carrying out the invention]

[0016] The transcutaneous carbon dioxide measurement device of this embodiment is a device that measures the partial pressure of carbon dioxide in arterial blood transcutaneously by contacting the skin of the person being measured, in a non-invasive manner. Because the transcutaneous carbon dioxide measurement device can maintain contact with the person being measured, it is possible to continuously measure the partial pressure of carbon dioxide. Therefore, it is possible to measure carbon dioxide levels throughout sleep in patients with chronic respiratory diseases. In addition, it is possible to measure the partial pressure of carbon dioxide in patients undergoing surgery under general anesthesia, newborns, etc., enabling early detection of respiratory distress and intervention for treatment and therapy.

[0017] Figure 1 is an overall perspective view showing the external appearance of the transcutaneous carbon dioxide measuring device 1 according to the embodiment. The illustrated transcutaneous carbon dioxide measuring device 1 is shown in the process of measurement, and the transcutaneous carbon dioxide measuring device 1 is in contact with the surface of the subject's skin 2. The transcutaneous carbon dioxide measuring device 1 enables non-invasive measurement without perforation of the skin or body tissue. A control unit 5 for calculating the detection results is wired to the transcutaneous carbon dioxide measuring device 1 by wiring 4. In order to improve the contact between the transcutaneous carbon dioxide measuring device 1 and the skin 2, the transcutaneous carbon dioxide measuring device 1 may be fixed to the subject's body surface by a wrapping bag.

[0018] In the transcutaneous carbon dioxide measuring device 1 shown in Figure 1, the cap 45 (see Figure 2) is removed, exposing the measuring body 16 of the main case 10. The lower end 11 of the measuring body 16 is in contact with the skin 2. As shown in Figure 2 below, the through-opening 12 (lower end 11) is sealed by the film 42. The inside of the measuring body 16 is explained in Figure 2. A case lid 14 is placed over the top of the main case 10.

[0019] The control unit 5 is provided with a display unit 6 for displaying the carbon dioxide partial pressure, the state of the device, etc., a percutaneous carbon dioxide measuring device 1, and a switch 7 for controlling the control unit 5 driven by a lithium battery (Li-Po). The control unit 5 is an arithmetic device such as a microcomputer, and includes an arithmetic element for estimating the carbon dioxide partial pressure from the changes in voltage and current obtained by detection within the main body case unit 10 of the percutaneous carbon dioxide measuring device 1, a ROM for storing necessary programs and calibration data, a PLD for storing measured values and calculated values, a RAM, etc., which are appropriately mounted. Note that the control unit 5 may be connected to a known device such as a smartphone or a tablet terminal via Bluetooth or the like so that measurement data can be displayed, or may be connected to the main body case unit 10 of the percutaneous carbon dioxide measuring device 1 by wire via the wiring 4, or wirelessly by omitting the wiring 4.

[0020] Figure 2 is an exploded perspective view showing the internal structure of the percutaneous carbon dioxide measuring device 1 disclosed in Figure 1. A cylindrical through-opening 12 (accommodation recess) is formed in the main body case unit 10, and a holding block 20 is accommodated in the through-opening 12. The lower end portion 11 of the through-opening 12 can abut against the skin 2 as disclosed in Figure 1. A wiring port 15 for drawing out the wiring 4 is formed in the main body case unit 10. A glass electrode 50, a reference electrode (not shown), and thermistors 21, 22 are inserted into the holding block 20. Terminals of the glass electrode 50, the reference electrode (not shown), and the thermistors 21, 22 are connected to the substrate portion 13 by soldering or the like, and the wiring 4 is connected to the substrate portion 13.

[0021] The holding block 20 is accommodated in the through-opening 12 of the main body case unit 10. The inside of the through-opening 12 is immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride, and a mixed aqueous solution always exists around the holding block 20, and the glass electrode 50, the reference electrode (not shown), and the thermistors 21, 22 are immersed in the mixed aqueous solution. A case lid 14 is placed on the upper part of the main body case unit 10. The case lid 14 protects the substrate portion 13 and the holding block 20 and seals the mixed aqueous solution in the through-opening 12. The holding block 20 is adopted as a silver billet method.

[0022] In the main body case 10, the outside of the through-opening 12 becomes the measuring body 16. The cap 45 is fitted to the outside of the measuring body 16. A packing 44 is attached to the measuring body 16 to ensure watertightness with the cap 45. A nonwoven fabric 41, a film portion 42, and double-sided tape 43 are attached in order to the lower end 11 of the through-opening 12. The nonwoven fabric 41 and the film portion 42 are fitted into the through-opening 12 to prevent them from easily falling off. The inner surface 46 of the cap 45 is fitted to the measuring body 16 of the main body case 10, so that the film portion 42 is protected by the cap 45 when the transdermal carbon dioxide measuring device 1 is not in use. In this embodiment, the cap 45 is disposable (for single use only).

[0023] The nonwoven fabric 41 is interposed between the through-opening 12 of the main body case 10 and the film 42. The nonwoven fabric 41 is installed to evenly spread the mixed aqueous solution in the through-opening 12 towards the film 42 by capillary action. The material of the nonwoven fabric 41 may be either chemical fibers or natural fibers such as cellulose.

[0024] The film portion 42 is a semipermeable membrane that seals the through-opening 12 to hold the mixed aqueous solution and allows carbon dioxide generated from the skin of the person being measured to pass through to the inside of the through-opening 12, i.e., to the holding block 20 side. In this embodiment, a fluorine film is used for the film portion 42 in order to achieve both impermeability to water (mixed aqueous solution) and permeability to carbon dioxide.

[0025] The double-sided tape 43 is provided to ensure stable adhesion between the film portion 42 and the skin 2 (see Figure 1). The adhesion of the double-sided tape 43 seals the gap between the film portion 42 and the skin 2. As a result, leakage of carbon dioxide generated from the skin 2 (body tissue) is reduced, and the error in carbon dioxide detection is reduced.

[0026] Figure 3 is an enlarged perspective view of the retaining block 20 housed inside the through-opening 12 of the transcutaneous carbon dioxide measuring device 1 according to the embodiment. The retaining block 20 is a cylindrical member with a diameter of 20 to 40 mm and is made of a metal such as aluminum, or ceramics, etc.

[0027] A first through-hole 35 is formed in the center of the holding block 20, and a glass electrode 50 is inserted into the first through-hole 35. Second through-holes 31 and 32 are formed around the first through-hole 35, and a reference electrode (not shown) is inserted into each of the second through-holes 31 and 32. In addition, third through-holes 36 and 37 are formed in the holding block 20, and thermistors 21 and 22 are inserted into each of the third through-holes 36 and 37. Furthermore, a fourth through-hole 33 is formed in the holding block 20, and a heater wire (not shown) is inserted into the fourth through-hole 33.

[0028] Figure 4 is a schematic cross-sectional view of the glass electrode 50 used in the transcutaneous carbon dioxide measuring device 1 of the embodiment. In the transcutaneous carbon dioxide measuring device 1 of the embodiment, carbon dioxide diffusing from the skin 2 (body tissue such as arteries) dissolves in the mixed aqueous solution of sodium bicarbonate and sodium chloride filled in the through-opening 12 around the holding block 20, causing a change in the hydrogen ion concentration (pH) of the mixed aqueous solution. In other words, the mixed aqueous solution becomes acidic due to carbonate ions caused by carbon dioxide that has permeated through the film portion 42. Here, the amount of dissolved carbon dioxide is calculated from the potential difference generated between the glass electrode 50 and the reference electrode, and finally the partial pressure of carbon dioxide in the subject's arterial blood can be estimated.

[0029] The glass electrode 50 consists of a glass container portion 55 having a flat portion 51 on the film portion 42 side and a hemispherical portion 52 on the opposite side of the film portion 42, with the flat portion 51 and the hemispherical portion 52 connected by a body portion 53. The glass container portion 55 has a so-called bell shape. A potassium chloride aqueous solution is contained inside the glass container portion 55. It is desirable that the glass electrode 50 be made of glass material with a large coefficient of linear thermal expansion that does not crack.

[0030] An electrode wire member 54 made of silver (Ag) and silver chloride (AgCl) is inserted inside the glass container portion 55 and is in contact with the surrounding potassium chloride aqueous solution. At the connection point between the electrode wire member 54 and the hemispherical portion 52 of the glass container portion 55, the electrode wire member 54 is protected by a tubular protective member 56 made of platinum (Pt), and the potassium chloride aqueous solution inside the glass container portion 55 is sealed. The electrode wire member 54 is connected to a platinum (Pt) wire 57, and the wire 57 is connected to the substrate portion 13 (see Figure 2).

[0031] In the glass container portion 55, the diameter of the flat portion 51 is approximately 3.5 mm, and the total length of the glass container portion 55 is approximately 7 mm. In the glass container portion 55 of the glass electrode 50, one end portion is formed as a flat portion 51, which increases the area of ​​the glass electrode 50 that directly faces the film portion 42, thereby improving the sensitivity to detect electrical changes.

[0032] Furthermore, a zirconium oxide (ZrO2) layer is provided on the inner surface of the flat portion 51 of the glass container portion 55. The zirconium oxide layer on the inner surface of the flat portion 51 increases the strength of the flat portion 51 and improves its resistance to stress applied to the glass container portion 55. In addition, the zirconium oxide layer has excellent temperature characteristics for the glass electrode 50 (glass container portion 55) and possesses good properties as a pH-responsive film. As a result, it becomes sensitive to electrical changes, and the detection sensitivity of the electrode wire member 54 that comes into contact with the potassium chloride aqueous solution is improved. The performance of the glass electrode 50 is an impedance of 1000~1500MΩ (25℃) as a film resistance, a pH-mV output of 56mV / pH, and a pH7 offset of ±30mV.

[0033] The glass electrode 50 is inserted into the first through-hole 35 of the retaining block 20, and the retaining block 20 is immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride. The electrical change caused by the absorption of carbon dioxide into the mixed aqueous solution is detected through the glass electrode 50. However, the amount of change is calculated from the difference with a reference electrode inserted into the second through-holes 31 and 32. The reference electrode is a silver wire (Ag metal wire) and is fixed in the second through-holes 31 and 32 with conductive resin. This makes it easy to miniaturize the reference electrode and fix it to the retaining block 20. The conductive resin is a viscoelastic resin such as epoxy resin or urethane resin into which silver powder and copper powder are kneaded, giving it conductivity derived from the metal.

[0034] Since temperature conditions affect the solubility of carbon dioxide, the relationship between the amount of carbon dioxide and the hydrogen ion concentration is corrected as needed based on the temperature at the time of measurement. Therefore, thermistors 21 and 22 are used to measure the temperature at the time of measurement. The specifications and standards of thermistors 21 and 22 are as appropriate and are not limited as long as they are large enough to be inserted into the third through-holes 36 and 37 of the holding block 20. In addition, a fourth through-hole 33 is formed in the holding block 20, and a heater wire (not shown) is inserted into the fourth through-hole 33. The heater wire moderately heats the holding block 20. The purpose of the heater wire is, for example, to reduce the difference between the temperature of the skin 2 of the person being measured and the temperature of the holding block 20 (the temperature of the surrounding mixed aqueous solution), thereby reducing the impact on the accuracy of carbon dioxide measurement.

[0035] The glass electrode 50, reference electrode (not shown), thermistors 21 and 22, and heater wire terminals, which are inserted into the holding block 20, are connected to the substrate 13 by soldering or the like, and wiring 4 is connected to the substrate 13. The wiring 4 is then connected to the control unit 5 (see Figure 1). In the control unit 5, based on the temperature measurements by thermistors 21 and 22, the amount of carbon dioxide is measured from the glass electrode 50 and the reference electrode (not shown) as a change in hydrogen ion concentration, and the control unit 5 finally calculates the partial pressure of carbon dioxide in the artery. In addition, the start (heating) and stop of the heater wire are controlled based on the temperature measurements by thermistors 21 and 22.

[0036] As described in the series of explanations, by using the transcutaneous carbon dioxide measuring device 1 of the embodiment, the detection sensitivity of the device is increased because it comprises a main body case 10, a holding block 20 housed in a through-opening 12 of the main body case 10 and immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride, a glass electrode 50 housed in a first through-hole 35 of the holding block 20, a reference electrode housed in second through-holes 31 and 32 of the holding block 20, thermistors 21 and 22 housed in third through-holes 36 and 37 of the holding block 20, a film 42 that seals the through-opening 12 to hold the mixed aqueous solution and allows carbon dioxide generated from the skin 2 of the person being measured to pass through to the holding block 20, and a cap 45 that protects the film 42 and is fitted to the main body case 10.

[0037] The glass electrode 50 has a flat portion 51 on the film portion 42 side and a hemispherical portion 52 on the opposite side of the film portion 42, and comprises a glass container portion 55 containing a potassium chloride aqueous solution and an electrode wire member 54 made of silver and silver chloride inserted into the glass container portion 55, thereby enabling miniaturization of the glass electrode 50 and improvement of measurement sensitivity.

[0038] The zirconium oxide layer provided on the inner surface of the flat portion 51 of the glass container portion 55 increases the strength of the flat portion 51 and enhances the resistance of the glass container portion 55 to stress applied to it.

[0039] The reference electrode is a silver wire component and is fixed in the second through-holes 36 and 37 with conductive resin, which allows for miniaturization of the reference electrode and simple and easy fixation to the retaining block 20.

[0040] Because the nonwoven fabric 41 is interposed between the main body case 10 and the film 42, the mixed aqueous solution in the through-opening 12 is evenly spread towards the film 42 by capillary action.

[0041] The outer surface of the film portion 42 is equipped with double-sided tape 43 for adhering to the skin 2 of the person being measured. This seals the gap between the film portion 42 and the skin 2, reducing the leakage of carbon dioxide generated from the skin 2 and thus reducing the error in carbon dioxide detection.

[0042] The device is equipped with a glass electrode 50, a reference electrode, and a control unit 5 which is wired and connected to thermistors 21 and 22. As a transcutaneous carbon dioxide measuring device 1, the amount of carbon dioxide and partial pressure are calculated from the measured values. [Explanation of Symbols]

[0043] 1. Transcutaneous carbon dioxide measurement device 2 skin 4 Wiring 5. Control Unit 6 Display section 7 Switches 10 Main case section 11 Lower end 12 Through-opening 13. Circuit board section 14 Case lid 16 Measuring section 20 Holding Blocks 21,22 Thermistor 31, 32 Second through hole 33 Fourth through hole 35 First through hole 36,37 Third through hole 41 Nonwoven fabric 42 Film section 43 Double-sided tape 44 Packing 45 caps 46 Inner surface 50 Glass electrodes 51 Flat area 52 Hemisphere 53 Torso 54 Electrode wire member 55 Glass container section 56 Protective member 57 wires

Claims

1. The main case and, A retaining block housed in a through-opening of the main body case and immersed in a mixed aqueous solution of sodium bicarbonate and sodium chloride, A glass electrode housed in the first through-hole of the retaining block, A reference electrode housed in the second through-hole of the retaining block, A thermistor housed in the third through-hole of the retaining block, A film portion that seals the through-opening to hold the mixed aqueous solution and allows carbon dioxide generated from the skin of the person being measured to pass through to the holding block side, The system includes a cap that protects the film portion and is fitted onto the main body case portion. A transcutaneous carbon dioxide measuring device characterized by the following features.

2. The glass electrode is A glass container portion having a flat portion on the film portion side and a hemispherical portion on the opposite side of the film portion, containing a potassium chloride aqueous solution, The transcutaneous carbon dioxide measuring device according to claim 1, further comprising an electrode wire member made of silver and silver chloride inserted within the glass container portion.

3. The transdermal carbon dioxide measuring device according to claim 2, wherein a zirconium oxide layer is provided on the inner surface of the flat portion of the glass container.

4. The transcutaneous carbon dioxide measuring device according to claim 1, wherein the reference electrode is a silver wire member and is fixed in the second through hole with a conductive resin.

5. The transdermal carbon dioxide measuring device according to claim 1, wherein a nonwoven fabric is interposed between the main body case and the film portion.

6. The transcutaneous carbon dioxide measuring device according to claim 1, wherein the outer surface of the film portion is provided with double-sided tape for adhering to the skin of the person being measured.

7. The transcutaneous carbon dioxide measuring device according to claim 1, further comprising the glass electrode, the reference electrode, and a control unit wired to the thermistor.

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