WO2021193201A1

WO2021193201A1 - Vital sensor

Info

Publication number: WO2021193201A1
Application number: PCT/JP2021/010398
Authority: WO
Inventors: Shinya Okuno; Toshiki Aoki; Satoru Togo
Original assignee: Nihon Kohden Corporation
Priority date: 2020-03-27
Filing date: 2021-03-15
Publication date: 2021-09-30
Also published as: JP2021153951A

Abstract

A probe is adapted to be attached to a body of a subject, and configured to output a signal corresponding to a vital sign of the subject. A signal processor is configured to process the signal. A cable (4) is connecting the probe and the signal processor. The cable (4) includes a conductive wire (40), a first heat-insulating layer (41), and a second heat-insulating layer (42). The conductive wire (40) is configured to transmit the signal to the signal processor. The first heat-insulating layer (41) is covering the cable from a radially outer side of the cable (4). The second heat-insulating layer is formed between the conductive wire (40) and the first heat-insulating layer (41).

Description

VITAL SENSOR

The presently disclosed subject relates to a vital sensor adapted to be attached to a body of a subject to acquire a vital sign of the subject.

Background

Japanese Patent Publication No. 2019-122476A discloses a vital sensor adapted to be attached to a body of a subject to acquire a vital sign of the subject.

Summary

It is demanded to provide a vital sensor particularly suited for use in magnetic resonance imaging (MRI) examinations.

In order to meet the above demand, an illustrative aspect of the presently disclosed subject matter provides a vital sensor, comprising:
a probe adapted to be attached to a body of a subject, and configured to output a signal corresponding to a vital sign of the subject;
a signal processor configured to process the signal; and
a cable connecting the probe and the signal processor,
wherein the cable comprises:
a conductive wire configured to transmit the signal to the signal processor;
a first heat-insulating layer covering the cable from a radially outer side of the cable; and
a second heat-insulating layer formed between the conductive wire and the first heat-insulating layer.

Vital signs of a subject may have to be monitored during an MRI examination. However, in a case where the conductive wire is used as the cable that transmits the signal outputted from the probe, the conductive wire may generate heat due to the influence of an RF pulse induced from a coil of the MRI apparatus. Accordingly, it is necessary to take measures for preventing the heat from reaching the subject.

As an example of the countermeasure, it is conceivable to transmit the signal outputted from the probe by an optical fiber cable made of glass. However, glass optical fiber cables should be handled with care because they are relatively expensive and tend to be damaged by bending. An optical fiber cable made of a less expensive plastic has a large transmission loss of an infrared signal.

According to the cable described above, although it is used the conductive wire that is easier to suppress the component cost and has more flexibility than the optical fiber cable made of glass, the transfer of the heat generated from the conductive wire to the outside of the cable due to the influence of the RF pulse induced from the coil of the MRI apparatus is suppressed by the first heat-insulating layer and the second heat-insulating layer that cover the conductive wire from the radially outer side of the cable. Accordingly, the vital sensor that is particularly suitable for use in the MRI examination can be provided.

FIG. 1 illustrates an appearance of a vital sensor according to one embodiment. FIG. 2 illustrates an example of a probe in the vital sensor of FIG. 1. FIG. 3 illustrates another example of a probe in the vital sensor of FIG. 1. FIG. 4 illustrates a cross section of a cable in the vital sensor of FIG. 1. FIG. 5 illustrates a case where a spacer is disposed in the cable of FIG. 4. FIG. 6 illustrates an example of the shape of the spacer of FIG. 5. FIG. 7 illustrates another example of the shape of the spacer. FIG. 8 illustrates another example of the shape of the spacer. FIG. 9 illustrates another example of the shape of the spacer. FIG. 10 illustrates a case where the spacer of FIG. 9 is disposed in the cable.

Examples of embodiments will be described in detail below with reference to the accompanying drawings. In the drawings, the scale is appropriately changed in order to make each element to be described have a recognizable size.

FIG. 1 illustrates an appearance of a vital sensor 1 according to an embodiment. The vital sensor 1 includes a probe 2, a casing 3, and a cable 4.

The probe 2 is configured to output a signal corresponding to carbon dioxide concentration of a subject. Specifically, the probe 2 includes a light emitting element and a light detecting element. The probe 2 may be attached to an adaptor 5 as illustrated in FIG. 2. The adaptor 5 is attached to a face of a subject 6. The adaptor 5 includes a passage 51 through which expired air of the subject 6 passes. The probe 2 is disposed such that the light emitting element and the light detecting element face each other with the passage 51 therebetween. The light emitted from the light emitting element is absorbed by the carbon dioxide contained in the expired air of the subject 6 when the light passes through the passage 51. Accordingly, the intensity of the light detected by the light detecting element changes in accordance with the carbon dioxide concentration. The carbon dioxide concentration is an example of the vital sign. The face is an example of the body of the subject.

In place of the probe 2 illustrated in FIG. 1, a probe 2 illustrated in FIG. 3 may be used. The probe 2 is configured to output a signal corresponding to transcutaneous arterial oxygen saturation (SpO2) of the subject 6. The probe 2 includes a light emitting element and a light detecting element. The probe 2 is attached to a fingertip of the subject 6. The light emitted from the light emitting element passes through a tissue of the fingertip, and is incident on the light detecting element. The incident intensity in the light detecting element is changed in accordance with oxyhemoglobin concentration contained in the arterial blood of the subject 6. The SpO2 corresponds to the oxyhemoglobin concentration. The SpO2 is an example of the vital sign. The fingertip is an example of the body of the subject.

As used herein with reference to the probe 2, the expression "adapted to be attached to a body of a subject" is meant to include a case where the probe is attached to the body of the subject indirectly via an adaptor as illustrated in FIG. 2, as well as a case where the probe is attached to the body of the subject directly as illustrated in FIG. 3.

As illustrated in FIG. 1, the casing 3 accommodates a signal processor 31. The signal processor 31 includes a signal conversion circuit and a microcontroller that process the signal outputted from the probe 2. The processed signal is transmitted to an external device such as a vital monitor device, and is subjected to display processing or analysis processing. The signal transmission to the external device may be performed through wired communication or wireless communication.

The cable 4 connects the probe 2 and the casing 3. Specifically, the cable 4 electrically connects the probe 2 and the signal processor 31.

FIG. 4 illustrates a section of the cable 4 as seen in the direction of the arrow along the line IV-IV in FIG. 1. The cable 4 includes a conductive wire 40, a first heat-insulating layer 41, and a second heat-insulating layer 42.

The conductive wire 40 is a wire-shaped member formed of a conductive material. The conductive wire 40 is configured to transmit the signal outputted from the probe 2 to the signal processor 31. The conductive wire 40 may also be configured to supply power from the signal processor 31 to the probe 2.

The first heat-insulating layer 41 covers the conductive wire 40 from a radially outer side of the cable 4. An outer peripheral face of the first heat-insulating layer 41 forms an outer peripheral face of the cable 4.

The second heat-insulating layer 42 is formed between the conductive wire 40 and the first heat-insulating layer 41 in the radial direction of the cable 4. In this example, the second heat-insulating layer 42 is formed as an aerial layer.

According to the cable 4 of the present embodiment, although it is used the conductive wire 40 that is easier to suppress the component cost and has more flexibility than the optical fiber cable made of glass, the transfer of the heat generated from the conductive wire 40 to the outside of the cable 4 due to the influence of the RF pulse induced from the coil of the MRI apparatus is suppressed by the first heat-insulating layer 41 and the second heat-insulating layer 42 that cover the conductive wire 40 from the radially outer side of the cable 4. Accordingly, the vital sensor 1 that is particularly suitable for use in the MRI examination can be provided.

In particular, in this example, since the second heat-insulating layer 42 is formed as a hollow aerial layer, not only the suppression of the material cost for lowering the thermal conductivity but also the enhancement of the flexibility of the cable 4 can be further facilitated.

The second heat-insulating layer 42 may be formed of cellulose fiber or the like as long as desired flexibility of the cable 4 can be ensured. The second heat-insulating layer 42 may be formed of glass wool or the like as long as bending of the cable 4 is not expected.

The first heat-insulating layer 41 may be formed of a foamed material such as silicone sponge. In this case, since the first heat-insulating layer 41 has a porous structure, the heat-insulating property and the flexibility of the cable 4 can be further enhanced.

As described above, since the outer peripheral face of the first heat-insulating layer 41 forms the outer peripheral face of the cable 4, there is a possibility that the first heat-insulating layer 41 comes into contact with the patient. Therefore, the first heat-insulating layer 41 is preferably formed of a material having biocompatibility. The silicone sponge also satisfies this condition.

In light of ensuring both the heat-insulating property and the flexibility of the cable 4, the outer diameter d of the cable 4 is preferably 15 mm or less, and the thickness t of the first heat-insulating layer 41 in the radial direction of the cable 4 is preferably 2 mm or more.

In this example, the conductive wire 40 is covered by an insulative covering 43. In this case, the transfer of the heat generated from the conductive wire 40 to the outside of the cable 4 can be further suppressed. However, the insulative covering 43 may be omitted.

As illustrated in FIG. 5, the cable 4 may include a spacer 44. FIG. 6 illustrates an appearance of the spacer 44 as viewed from the direction of the arrow VI in FIG. 5. The spacer 44 may be formed of a resin, a porous material having a relatively high hardness, a cellulose fiber, or the like.

The spacer 44 is disposed in an inner side of the first heat insulating layer 41 in the radial direction of the cable 4 so as to regulate the position of the conductive wire 40 in the second heat insulating layer 42. In this example, the spacer 44 has an annular shape. An outer peripheral face 44a of the spacer 44 is in contact with an inner peripheral face 41a of the first heat-insulating layer 41. An inner peripheral face 44b of the spacer 44 is in contact with an outer peripheral face 43a of the insulative covering 43.

In a case where the second heat-insulating layer 42 is formed as the aerial layer so that the cable 4 has a hollow structure, the conductive wire 40 may be displaced inside the first heat-insulating layer 41. However, by providing the spacer 44 that regulates the position of the conductive wire 40 in the second heat-insulating layer 42, it is possible to prevent the conductive wire 40 from approaching the first heat-insulating layer 41 as illustrated by the dashed chain lines in FIG. 5. As a result, it is possible to more reliably suppress the heat generated from the conductive wire 40 from transferring to the outside of the cable 4. In light of preventing the deflection of the conductive wire 40, the spacer 44 is preferably disposed at least in an axially central portion of the cable 4.

FIG. 7 illustrates another example of the shape of the spacer 44. In this example, a plurality of convex portions 44c are formed on the outer peripheral face 44a of the spacer 44. When the convex portions 44c are brought into contact with the inner peripheral face 41a of the first heat-insulating layer 41, a gap is formed between the outer peripheral face 44a of the spacer 44 and the inner peripheral face 41a of the first heat-insulating layer 41.

According to the above configuration, the contact area between the spacer 44 and the first heat-insulating layer 41 can be reduced while ensuring the function for regulating the position of the conductive wire 40 with the spacer 44. Accordingly, not only the transfer of the heat generated from the conductive wire 40 to the outside of the cable 4 can be further suppressed, but also the workability for attaching the spacer 44 to the inner side of the first heat-insulating layer 41 can be enhanced because the frictional resistance therebetween can be reduced.

In addition to or in place of the convex portions 44c formed on the outer peripheral face of the spacer 44, convex portions configured to be brought into contact with the outer peripheral face 44a of the spacer 44 may be formed on the inner peripheral face 41a of the first heat-insulating layer 41. Similar convex portions may be formed on at least one of the inner peripheral face 44b of the spacer 44 and the outer peripheral face 43a of the insulative covering 43.

FIG. 8 illustrates another example of the shape of the spacer 44. In this example, an opening 44d is formed so as to communicate the outer peripheral face 44a and the inner peripheral face 44b of the spacer 44 with each other. In a case where the spacer 44 has elasticity, the opening 44d can be widened.

According to such a configuration, since the attachment of the spacer 44 is completed by inserting the conductive wire 40 from the opening 44d, the attachment workability can be enhanced as compared with the case where the conductive wire 40 is inserted through the annular spacer 44.

The convex portions 44c described with reference to FIG. 7 may be formed on at least one of the outer peripheral face 44a and the inner peripheral face 44b of the spacer 44 illustrated in FIG. 8.

FIG. 9 illustrates another example of the shape of the spacer 44. In this example, the spacer 44 is formed such that a plurality of hollowed tubular members are aligned along the radial direction of each tubular member. In this case, as illustrated in FIG. 10, the spacer 44 may be disposed between the conductive wire 40 and the first heat-insulating layer 41. Namely, the conductive wire 40 is surrounded from the radially outer side of the cable 4 by the hollowed tubular members forming the spacer 44.

In the present embodiment, the length of the cable 4 is determined so as to be shorter than a half wavelength of the RF pulse induced in the MRI apparatus that is supposed to be used.

The half wavelength (λ/2)[m] of the RF pulse in air is found by the following equation.

λ/2 = (c/f)/2

Here, c represents a light speed (3×10⁸[m/sec]). f represents the frequency [Hz(1/sec)] of the RF pulse. On the other hand, the frequency of the RF pulse is proportional to the static magnetic field intensity of the MRI apparatus, and is obtained by the following equation.

f = γ・B

Here, γ represents the gyromagnetic ratio of hydrogen atoms (42.57 [MHz/T]). B represents the magnetic flux density [T] of the static magnetic field. Therefore, the relationship between the half wavelength of the RF pulse and the static magnetic field flux density of the MRI apparatus is expressed by following equation.

f = [c/(γ・B)]/2 ≒ 3.52/B [m]

In a case where use in an MRI apparatus with the static magnetic field intensity of 3 [T] is assumed, for example, since the half wavelength is 1.17 [m], the length of the cable 4 is set so as to be shorter than 1.17 [m].

Since the conductive wire 40 generates heat due to the antenna effect, heat is most easily generated when the conductive wire 40 has a length corresponding to the half wavelength of the RF pulse. According to the configuration described above, heat generation due to the antenna effect of the conductive wire 40 can be suppressed. Accordingly, it is possible to more reliably suppress the heat generated from the conductive wire 40 from transferring to the outside of the cable 4.

As illustrated in FIG. 1, at least one of the probe 2 and the signal processor 31 may include a temperature sensor 7. The temperature sensor 7 is configured and disposed so as to be able to detect the temperature of the cable 4. According to the above configuration, it is possible to perform processing such as appropriately notifying when the temperature of the cable 4 is increased by the heat generation of the conductive wire 40.

The above embodiment is merely exemplary to facilitate understanding of the presently disclosed subject matter. The configuration according to each of the above embodiments can be appropriately modified without departing from the gist of the presently disclosed subject matter.

The vital sign of the subject 6 that is acquired by the probe 2 is not limited to the carbon dioxide concentration in the respiratory air or the SpO2. According to the specification of the probe 2, pulse rate, blood pressure, oxygen concentration in respiratory air, light absorber concentration in arterial blood, and the like may be acquired.

The present application is based on Japanese Patent Application No. 2020-058254 filed on March 27, 2020, the entire contents of which are hereby incorporated by reference.

Claims

A vital sensor, comprising:
a probe adapted to be attached to a body of a subject, and configured to output a signal corresponding to a vital sign of the subject;
a signal processor configured to process the signal; and
a cable connecting the probe and the signal processor,
wherein the cable comprises:
a conductive wire configured to transmit the signal to the signal processor;
a first heat-insulating layer covering the cable from a radially outer side of the cable; and
a second heat-insulating layer formed between the conductive wire and the first heat-insulating layer.
The vital sensor according to claim 1,
wherein the second heat-insulating layer is formed by an aerial layer.
The vital sensor according to claim 2, further comprising:
a spacer configured to regulate a position of the conductive wire in the aerial layer.
The vital sensor according to any one of claims 1 to 3,
wherein the first heat-insulating layer is formed of a foamed material.
The vital sensor according to any one of claims 1 to 4,
wherein an outer diameter of the cable is no greater than 15 mm; and
wherein a thickness of the first heat-insulating layer in a radial direction of the cable is no less than 2 mm.
The vital sensor according to any one of claims 1 to 5, further comprising:
an insulative covering that covers the conductive wire.
The vital sensor according to any one of claims 1 to 6,
wherein a length of the cable is shorter than a half wavelength of an RF pulse induced in an MRI apparatus assumed to be used.
The vital sensor according to any one of claims 1 to 7,
wherein at least one of the probe and the signal processor includes a temperature sensor configured to detect temperature of the cable.
The vital sensor according to any one of claims 1 to 8,
wherein the first heat-insulating layer forms an outer peripheral face of the cable and is formed of a material having biocompatibility.