JP2008512162A - Sensor - Google Patents

Abstract

A physiological sensing device that combines a sensor (4) for measuring the partial pressure of carbon dioxide (pCO ₂ ), a body temperature sensor (5), and a heart rate and oxygen saturation sensor (54). This sensing device is used to continuously monitor a patient's life support signals.

Description

  The present invention relates to a physiological sensor.

A single sensor is particularly suitable for measuring the partial pressure of carbon dioxide (pCO ₂ ) and is described in WO 00/04386, in particular as part of a technique for monitoring ischemia.
WO00 / 04386

In addition to detecting ischemia, measuring pCO ₂ is useful for diagnosing severely life-threatening conditions that can lead to changes in blood perfusion, respiration and / or metabolism in tissues such as stroke and septic disease It turned out to be. Therefore, it would be advantageous to provide a sensing device suitable for monitoring hospitalized patients, particularly when they are outside the intensive care unit, to detect the onset of rot.

In a first aspect, the present invention provides a physiological sensing device that combines a sensor for measuring the partial pressure of carbon dioxide (pCO ₂ ), a body temperature sensor, a heart rate, and an oxygen saturation sensor.

In accordance with the present invention, a single device is provided that measures important life support signals such as pCO ₂ , body temperature, pulses and oxygenation. Indeed, the measurement and monitoring of these four parameters allows the physician to confirm the onset of a dangerous condition that requires treatment in a patient such as rot. As a result, the device according to the present invention allows a physician to conveniently and accurately monitor a patient who has started rot.

Usually, the pCO ₂ sensor is shaped to be inserted through the patient's skin. This sensor is inserted into tissue such as the patient's muscle. Thus, the sensor is sized to be inserted into tissue so that patient tissue destruction is minimized. The pCO ₂ sensor may be shaped to penetrate the patient's skin (and tissue). Thus, a normal pCO ₂ sensor or device may be provided with a sharpened, eg sharpened tip. Alternatively, the pCO ₂ sensor may be configured to be inserted into an incision in patient tissue.

In another aspect, the present invention provides a physiological sensing device comprising a pCO ₂ sensor shaped to be inserted through a patient's skin and a pointed tip that pierces the patient's skin upon insertion of the pCO ₂ sensor.

This sensor provides an insertion device for inserting a pCO ₂ sensor through the patient's skin. In one embodiment, the insertion device is a removable core which is accommodated in a sheath which is connected to the pCO ₂ sensor, when inserted once pCO ₂ sensor patients within tissue pCO ₂ sensor and engaging Push it through the patient's skin.

Alternatively, the sensor device may include a hollow needle that houses a pCO ₂ sensor that is inserted through the patient's skin. This hollow needle can be removed from the sensor device after insertion of the pCO ₂ sensor. Conveniently, the hollow needle has a curved opening. This has the advantage that an electrical connection to the pCO ₂ sensor can be made through the needle and that the electrical connection can be separated from the needle when the needle is removed from the patient. For example, the cross section of the needle can be U-shaped, V-shaped or C-shaped.

  The device is conveniently provided with a self-sealing membrane that closes the hole by the needle (or other insertion device) when the needle is removed.

In order to quickly apply the sensor device to the patient in an emergency, the sensor device and / or the insertion device is advantageously bactericidal, especially against pCO ₂ sensors, temperature sensors or pointed tips. The sensor device may be packaged so that it is bactericidal against these surfaces in contact with the patient.

The pCO ₂ sensor is connected to an electric cable that is electrically connected at the tip of the sensor and transmits a signal from the sensor. The device may include a sheath mechanically connected to the pCO ₂ sensor and surrounding and extending along at least a portion of the cable length. In one aspect, the sheath comprises a plurality of flexible portions extending substantially longitudinally and divided by a plurality of slits, and the proximal end moves toward the distal end of the sheath. This reduces the distance between the ends of the flexible portion and causes the flexible portion to protrude outward, thereby increasing the effective diameter of the sheath in the flexible portion and, as a result, the protruding flexibility. The pCO ₂ sensor can be held in the tissue by the sex part.

Thus, according to the present invention, the sensor is inserted into the patient's tissue and the cable is pulled to pull the end of the flexible portion to protrude outward. While the sensor monitors the physiology of the organ, the protruding flexible portion engages the patient's tissue and holds the pCO ₂ sensor in place. When monitoring is complete, the proximal end of the sheath is removed and the flexible portion is returned to its original position so that the sheath is flush and disengaged from the tissue. The sensor is then easily removed from the patient.

  The flexible part may be elastic, for example constituted by an elastic material. The flexible portion may be biased to the surface portion by, for example, its own elasticity or by a separate elastic component.

  In order to hold the end portion of the sheath at a position where the flexible member protrudes outward, a fixing mechanism may be provided at the proximal end portion of the sheath, for example.

  The device may further comprise a wire, such as a Kevlar wire, mechanically connected to the sheath tip. The line may extend longitudinally along a cable that assists in pulling the distal end of the sheath toward the proximal end of the sheath. Such a wire has the advantage that the electrical connection to the cable and / or sensor need not be strong enough to resist the force required to bend the flexible member.

  Although not preferred, it is also possible to enclose the cable with additional conduits in addition to the sheath. In a simple embodiment, the cable is surrounded only by the sheath.

Conveniently, the sheath forms the carbon dioxide permeable membrane of the pCO ₂ sensor. This provides a particularly simple structure. Preferred materials for the sheath in this case are PTFE, silicone rubber and polyolefin.

The sensor device may be provided with an attachment for attaching the device to the surface of the patient's skin. In one convenient embodiment, the attachment is an adhesive patch such as a plaster. In the context of the pCO ₂ sensor, this is certain to be a feature of the present invention. In another aspect of the invention, the present invention provides a pCO ₂ sensor configured to be inserted through a patient's skin, and a device for applying the device to the patient's skin to hold the inserted pCO ₂ sensor in place. A physiological sensing device comprising an adhesive patch is provided.

Providing a plaster not only keeps the sensor device in place but also has several other advantages. In particular, the part where the pCO ₂ sensor is inserted through the patient's skin is sealed by a plaster, thereby reducing the risk of infection. In this regard, disinfectants or antibiotics are placed on the side of the plaster facing the patient. In addition, the plaster is conveniently provided with wires, other sensors or wireless communication devices.

Such a device is conveniently applied to the patient and held in place while the patient is being monitored. It is desirable that the electrical and mechanical connection to the pCO ₂ sensor, such as an electrical cable or sheath, be flexible. This minimizes patient discomfort when the pCO ₂ sensor is inserted.

The pCO ₂ sensor comprises a closed chamber defined at least in part by a membrane that is permeable to carbon dioxide, and at least two electrodes in the closed chamber, the closed chamber being a liquid that contacts the electrode and the membrane. You may make it accommodate the liquid which does not contain electrolyte substantially.

Due to the substantial absence of electrolyte, the liquid has an ionic osmolarity that is not greater than the osmolarity of ions at 37 ° C. of a 5 mM aqueous sodium chloride solution, preferably 500 μM sodium chloride. It means not greater than the concentration of the solution, more specifically not greater than the concentration of the 10 ⁻⁵ to 10 ⁻⁶ M HCl solution.

The liquid in contact with the electrode is preferably water-soluble, and particularly preferably water that does not substantially contain an electrolyte as described above. For example by generating or neutralization of ions, increases the conductance, or other solvents that react with CO ₂ to reduce also it can be used as well. In practice, however, deionized water or strong acid (eg HCl) is added or not added to a concentration of 0.1 to 100 μM, preferably 0.5 to 50 μM, more specifically about 1 μM. Distilled water has been found to work particularly well. This ability to add a small amount of acid generally keeps the pH of the liquid below 6 to avoid significant contribution to conductance by hydroxide ions and to maintain the linearity of the pCO ₂ measurement. It is to be.

  This liquid contains non-ionic excipients. This can increase the osmolarity of the liquid in the chamber without affecting the electrical properties of the liquid to prevent liquid permeation through the membrane.

  The excipient should be at least at the same osmotic pressure, that is, the same osmotic pressure as the 0.9% w / v NaCl aqueous solution. Preferably, the excipient concentration is hyperosmotic, i.e. the hypertonicity of a 0.9% w / v NaCl aqueous solution. Thus, the osmolarity of the indoor excipient is greater than that of the 0.9% w / v NaCl aqueous solution, preferably greater than the 1.8% w / v NaCl aqueous solution (twice the isotonic pressure). An osmolarity greater than an aqueous solution of 4.5% w / v NaCl (5 times the isotonic pressure) or an osmolarity greater than an aqueous solution of 9% w / v NaCl (10 times the isotonic pressure) may be used. Good.

  Suitable excipients are used that are responsible for the indoor bicarbonate reaction. The excipient must also be soluble in the liquid, for example water is used. The excipient should also be pharmaceutically acceptable for intravenous use and have a low viscosity to easily fill the room. The excipient preferably has sterilization and storage stability. Desirably, the excipient inhibits microbial growth.

  The preferred excipient is polyethylene glycol (PEG) and the presently preferred excipient is propylene glycol.

The main components of the pCO ₂ sensor include an electrode chamber, a CO ₂ permeable membrane that forms at least part of the wall of the electrode chamber, a first electrode having a surface in the chamber (or providing an inner surface for the chamber) and a first electrode 2 electrodes, and liquid in the electrode chamber in contact with the membrane and the first and second electrodes (generally water substantially free of electrolyte). The sensor may include or be connected to an AC power source, a conductance (or resistance) determining device, a signal generating device (which may be part of the determining means), and optionally a signal transmitter.

The mechanism by which pCO ₂ is determined using the sensor device of the present invention is simple. In pure protic solvents such as water, the electrical resistance is high due to a lack of ionic species. By adding CO ₂ , H ⁺ ions and HCO ₃ ⁻ ions are formed (reacting with water), thus reducing the electrical resistance. Since the only factor that plays a role in reducing the resistance of the sensor is CO ₂ permeating through the membrane, it is possible to measure pCO ₂ by the change in resistance.

From the equilibrium constant from H ₂ O + CO ₂ equilibrium to H ⁺ + HCO ₃ ⁻ equilibrium, the CO ₂ concentration is equal to αpCO ₂ (α at 25 ° C. is 0.310). The conductivity of protons _is ^{G H + = 349.8Scm 2 / mol} , in the case of hydroxyl group _G OH- = 198.3Scm ² / mol, in the case of bicarbonate _G HCO3- = 44.5Scm ² / mol is there. The concentrations of H ⁺ and OH ⁻ vary in the opposite direction, and the concentrations of H ⁺ and HCO ₃ ⁻ are directly proportional to pCO ₂ . Therefore, since the contribution of OH ⁻ is minimal, the total conductance of the solution is virtually proportional to pCO ₂ . From the above, the conductivity G _solution of the _solution is given by:
^{_{G solution = θ H + [H}} +] G H + + θ OH- [OH -] G OH- + θ HCO-3 [HCO 3 -] G HCO3-
In the above equation, θ _H− , θ _OH− , and θ _HCO 3− are activity coefficients of three ionic species.

Table 1 below shows, by way of example, the measured pCO ₂ and pH values and the corresponding calculated values for the concentrations of H ⁺ , OH ⁻ , HCO ₃ ⁻ . H ⁺ and HCO ₃ ⁻ are shown to increase with increasing pCO ₂ .

The conductivity is measured in the solvent film of the pCO ₂ sensor of the present invention. This can be done by applying a constant voltage (or current) to the electrode and measuring the change in current (or voltage) corresponding to the change in conductivity as CO ₂ enters the solvent through the membrane. However, it is preferred that an alternating sine wave function voltage having a constant peak value is applied and the voltage drop across the electrode is measured. Thus, the conductivity of the solution is equal to the current flowing through the electrode divided by the voltage drop across the electrode.

A pCO ₂ sensor can function by applying an alternating potential to the electrodes, thereby creating an alternating current in the liquid. The liquid should react with carbon dioxide and change the conductance of carbon dioxide. The potential can have a frequency of 20 to 10,000 Hz, preferably 100 to 4,000 Hz.

The pCO ₂ sensor of the present invention comprises or can be connected to a power source configured to apply an alternating potential across the electrodes at a frequency of 100 to 10,000 Hz. The frequency is preferably higher than 1 kHz and lower than 5 kHz, and more preferably lower than 2 kHz. At frequencies below 100 Hz, the sensitivity of pCO ₂ determination is low due to electrical polarization, and the instrument response time is too slow, while at frequencies above 10 kHz, the sensitivity is low impedance of the sensor capacitance. To fall again.

  The power source can be an AC power source or alternatively a DC source associated with an oscillator, ie an AC power source comprised of a combination of both.

The power source has a maximum current density through the liquid at the electrode not exceeding 50 A / m ² , preferably not exceeding 30 A / m ² , more preferably not exceeding 20 A / m ² , in particular not exceeding 10 A / m ² , Most preferably, it is about 1 A / m ² or less. Larger current density values of 20 A / m ² or higher should only be used at higher frequencies, such as 1-10 kHz. The smallest maximum current density is determined by the detection limit, but values up to 10 ⁻⁸ A / m ² can be used. The smallest maximum current density is generally at least 0.1 μA / m ² .

By operating at such a current density and voltage frequency and having a suitable structure, the sensor is a liquid in which CO ₂ migrates into without having any significant loss of accuracy as a result of the electrical polarization of the electrodes. Conductance / resistance can be determined.

  For particularly high accuracy, the potential or current across the electrodes (and thus the resistance or conductance of the liquid between the electrodes) is determined using a lock-in amplifier set at the same frequency as the voltage generator or power source. .

  Furthermore, it is preferable to incorporate a high-pass filter in the detector in order to shield currents having a frequency below 100 Hz, preferably below 150 Hz. The filter is preferably a passive filter, such as a capacitor and a resistor.

  A power source and detector circuit can be included in the sensor of the present invention if desired. In this case, if it is desirable for the sensor to be wireless, it is also preferable to provide means enabling the signal to be detected remotely, for example a transmitter which is an RF transmitter.

  It is also possible to provide further electrodes that are electrically connected to the patient, such as through the patient's skin. The signal from this further electrode may be processed with the signal from the sensor to compensate for electromagnetic noise from the patient.

  The effect of electrical polarization is in contact with the liquid, such as by placing the electrode in a recess provided away from the surface of the membrane, or by using a non-smooth electrode surface such as a rough or woven surface This is significantly reduced by increasing the surface area of the electrode. Thus, in general, it is desirable to have the greatest possible ratio of electrode surface area to liquid contact and the shallowest possible liquid depth over the largest possible contact area with the membrane. In this way, response time is shortened, electrical polarization is reduced, lower frequencies can be used, and the effects of stray capacitance are significantly reduced.

  Increasing the electrical resistance relative to the resistance at the electrodes reduces the liquid depth for a part of the path between the electrodes, or ensures a relatively large contact area between each electrode and the liquid, etc. This can be achieved by limiting the cross-sectional area of the electrical path through the liquid between the electrodes in the contacting zone.

  The resistance of the liquid in the membrane and between the electrodes can be increased by using structural elements that define a liquid channel through the membrane between the electrodes. For example, it can be increased by placing the membrane so that such a channel traverses or is adjacent to the insulating chamber wall portion formed by etching or the like. Similarly, a porous spacer can be placed between the membrane and the chamber wall to define the depth of the liquid.

  In fact, such spacers are used when the membrane is sufficiently flexible and the liquid depth below the membrane is sufficiently small so that the measured conductance changes with pressure under the pressure conditions experienced in use. It is important to use.

In a preferred configuration, the sensor is
A sensor body having a vertical axis;
At least two electrodes spaced apart in a direction transverse to the longitudinal axis of the sensor body;
A plurality of support members extending outwardly from the axis of the sensor body and defining at least one liquid channel between adjacent support members to provide a fluid path between the electrodes;
A gas permeable membrane supported by a support member and providing an outer wall of the liquid channel.

  This configuration provides a compact configuration of the sensor having a longitudinal geometry that is suitable for insertion into a patient's tissue. In addition, the support member can provide physical support to the membrane, as well as define a small cross-sectional liquid channel that allows accurate measurements.

  In order to reduce the influence of the electric polarization described above, the electrodes can be arranged in a recess in the sensor body having a larger cross-sectional area than the liquid channel. In this way, the current density around the electrode is reduced by the larger volume for the liquid.

The electrode of the pCO ₂ sensor may extend in the longitudinal direction, for example, may be parallel to the longitudinal axis of the sensor body.

Similarly, the liquid channel can be transverse, such as perpendicular to the longitudinal axis of the sensor body. In a preferred configuration, the pCO ₂ sensor comprises a plurality of liquid channels. For example, the sensor can comprise at least three liquid channels.

  The support member can traverse the longitudinal axis of the sensor body. For example, the support member can be perpendicular to the longitudinal axis of the sensor body in the circumferential direction. In a preferred configuration, the support member is in the form of a ring formed around the longitudinal axis of the sensor body. The cross section of the support member can be any suitable shape. In particular, it has been found that support members having a substantially triangular shape, in particular a sawtooth cross-section, are particularly easily formed by injection molding. Alternatively, a substantially rectangular cross section can be used. The support member can be formed integrally with the sensor body, for example, by injection molding. The sensor preferably comprises at least four support members.

  The sensor body and / or sensor can be generally cylindrical. The membrane can be configured to surround the sensor body.

The described geometry can be applied to any suitable sensor. In a preferred configuration, the sensor is a pCO ₂ sensor.

If the pCO ₂ sensor is constructed with a liquid film in place, the electrodes are preferably made of an inert material or plated with an inert material so that the resistance of the liquid does not change significantly with storage. Suitable materials include platinum (especially black platinum), gold, silver, aluminum, and carbon. Gold is particularly preferred. In general, an inert electrode that does not generate solvated ions is preferred.

Membrane is permeable to CO _2, and liquid, any electrolyte, and may be any material that is essentially impermeable to water solvents. Polytetrafluoroethylene such as Teflon®, silicone rubber, polysiloxane, polyolefin, or other insulating polymer film can be used, for example, in a thickness of 0.5 to 250 μm. As the film becomes thicker, the response time of the pCO ₂ sensor generally becomes slower. However, as the membrane becomes thinner, there is a greater risk of non-uniformity or perforation or other damage. However, the thickness of the membrane is conveniently from 1 to 100 μm, preferably from 50 to 100 μm.

The chamber wall of the pCO ₂ sensor of the present invention can be any suitable material, such as plastic. The material can withstand conditions normally used in sterilization, such as radiation sterilization (eg, using gamma radiation), or heat sterilization (eg, using a temperature of about 121 ° C. used in high pressure steam sterilization). Preferably it should be possible. In the case of heat sterilization, the liquid is sterile and fills the sensor after sterilization. The chamber wall and membrane can be the same material, such as Teflon, machined to have a self-supporting wall and a thinner gas permeable membrane.

The pCO ₂ sensor of the present invention is generally relatively inexpensive and can thus be a single-use device, unlike prior art sensors. In addition, the electrode chamber can be made extremely small without difficulty (unlike prior art glass electrodes including sensors that present impedance problems that are difficult to overcome with miniaturization).

The above arrangement provides a pCO ₂ sensor that can be easily inserted into the tissues of animals including humans, can be held in the tissues during monitoring, and can be easily removed at the end of monitoring.

The pCO ₂ sensor is small enough so as not to cause undue interference to the monitored tissue. As a result, the device can have a maximum diameter of 2 mm, preferably 1 mm.

In using the sensor device, a temperature sensor may be applied to the patient's skin. However, in one embodiment of the present invention, the temperature sensor is configured to be inserted through the patient's skin. In particular, the temperature sensor and the pCO ₂ sensor are integrated into a single sensor unit. In other words, the pCO ₂ sensor may include a temperature sensor.

  Blood oxygen saturation is measured by pulse oximetry. Thus, the device includes a pulse oximetry sensor. In pulse oximetry, the saturation of oxyhemoglobin in the patient's blood is determined by measuring the light absorption of hemoglobin. Absorbance varies depending on whether the hemoglobin is saturated or unsaturated with oxygen. The blood oxygenation sensor according to the present invention is in particular a reflectance pulse oximetry sensor. In other words, the sensor is configured to irradiate the patient with specific wavelengths of light and measure the reflectance of these wavelengths in order to determine oxygen saturation in the patient's blood. Thus, the oxygenation sensor is conveniently shaped to be held on the patient's skin by an adhesive patch.

  The sensor device includes a sensor dedicated to heart rate. However, the oxygen saturation sensor and the heart rate sensor are conveniently provided by a pulse oximetry sensor.

The sensor device can comprise a plurality of sensors for each physiological parameter. For example, the device can arrange a plurality of sensors. Such a sensor may measure one or more of carbon dioxide partial pressure, oxygen partial pressure, temperature, pH, or glucose concentration. In a preferred embodiment of the invention, the device comprises a temperature sensor, a pCO ₂ sensor, a heart rate sensor and a blood oxygenation sensor.

The pCO ₂ , oxygenation and temperature determined by the sensor device may be measured values, or simply indicate that they are greater or lesser than one or more thresholds indicating septic disease. The numerical value may be changed according to the position of the measurement site.

  The sensor device may be used for a single measurement, and more preferably, for example, to first detect and quickly change a life support signal, for example in an emergency room, an intensive care room, or a ward, or an elderly person It may be used for continuous or repeated monitoring for dangerous patients at home.

Although the sensor has been described in the context of detecting rot, the sensor may be used to detect conditions that cause either hypocapnia or hypercapnia in the tissue, i.e., such The condition is one that changes the patient's breathing pattern, or one that increases the product or reduces the CO ₂ exposure. Conditions in which hypocapnia is likely to be detected include rot, fever primarily due to non-septic, mild heart failure, pulmonary edema, acute dyspnea syndrome (ARDS) and hyperalgesia based on any cause. Conditions under which hypercapnia is likely to be detected include ischemia where the sensor is located, circulatory stroke due to bleeding, respiratory failure due to heart or rot, acute or chronic obstruction such as ARDS or chronic Infectious pulmonary sac disease (COLD).

  Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

According to the present invention, the pCO ₂ sensing system comprises a sensor device 50, a surface circuit unit 2 and a monitor unit 3, as shown in FIG. The sensor device 50 includes a sensor unit 1 that combines a pCO ₂ sensor and a temperature sensor, and two pulse oximetry sensors 54.

  7-10 show a sensor device 50 according to one embodiment of the present invention. Apparatus 50 includes a self-adhesive strip 52 to which two reflectance pulse oximetry sensors 54 are attached, as will be described in detail below. The pulse oximetry sensor may be of a type commercially available from Nellcor of Pleasanton, California as a MAX FAST adhesion front sensor. The self-adhesive piece 52 is provided with a release piece 56 that is peeled away from the adhesive piece 52 to expose the adhesive surface of the adhesive piece 52 for application to the patient's skin. In order to prevent damage, contamination or evaporation, the sensor unit 50 is packaged with a sensor unit 1 in a tube (not shown) filled with a sterilized isotonic propylene glycol aqueous solution.

  The sensor device 50 includes a main shaft 58 with a finger grip 60. The main shaft 58 is housed in a flexible sheath (or catheter) 62 that includes the cable connection 6 from the sensor unit 1. As shown in FIG. 10, the main shaft 58 engages with the sensor unit 1 at the tip thereof, and by applying pressure to the finger grip 60 of the main shaft 58 by hand, the pointed sensor unit 1 passes through the patient's skin. Can be pushed In this way, the sensor unit 1 is placed under the patient's muscle, for example, the armpit of the patient.

When the pCO ₂ sensor unit 1 is correctly placed on the patient's muscle, the main shaft 58 is withdrawn from the flexible sheath 62 while leaving the sensor device 50 as shown in FIG. The sheath 62 and the cable 6 connected to the sensor unit 1 are sufficiently flexible so that even if there is a discomfort for the sensor unit 1 in a predetermined position, the patient hardly feels it.

  The sensor unit 1 is held at a predetermined position of the muscle by an adhesive piece 52 attached to the patient's skin. At the same time, the adhesion of the adhesive strip 52 to the skin leads the pulse oximetry sensor 54 to a predetermined position for use with respect to the patient's skin. In order to determine the oxygen saturation level in the patient's blood, the pulse oximetry sensor 54 measures the reflectance at a particular wavelength of light from the patient's skin.

  As shown most clearly in FIG. 7, the electrical connection 64 from the pulse oximetry sensor 54 and the sensor unit 1 extends along the length of the adhesive strip 52 for connection to the surface circuit unit 2. Extend. Instead, as shown in FIG. 9, a wireless device 70 may be provided in the sensor device 50 for communication with the surface unit circuit unit 2 or the monitor unit 3.

  The sensor device 50 is packaged for delivery and sterilized. This comprises a conductivity measuring sensor having a diameter of less than 1 millimeter and protected by a membrane, and a temperature probe 5 integral with the sensor unit 1. The wire 6 electrically connects the sensor 4 and the probe 5 with a connector to the surface circuit unit 2.

  The surface circuit unit 2 transmits a signal to the sensor device 50 and receives a signal from the sensor device 50. The surface circuit unit 2 is disposed on the patient's skin, performs signal processing from the sensor unit 1, and transmits an adjustment signal to the monitor unit 5.

  The monitor unit 3 is based on a portable personal computer 7 having a PCMCIA input / output card 8 and lab view software (available from National Instruments Corporation, Austin, Texas).

The pCO ₂ sensor 4 is used to measure the fluid CO ₂ level (partial pressure) (pCO ₂ ) according to the measurement principle shown in FIG. The measuring chamber consists of two small cavities 9, one electrode 10 being arranged on each. The two cavities 9 are connected by one or more passages 11 enclosed by a non-permeable membrane 12, ie a membrane that only allows CO ₂ to be transported into and out of the volume of the sensor 4. The entire volume is filled with deionized water and 5% propylene glycol. The conductivity of water depends on pCO _2, and information about pCO ₂ can be retrieved by measuring the conductivity between the volume electrodes 10.

  As shown in FIGS. 3 to 5, the sensor unit 1 comprises an injection molded plastic support 23, which is substantially cylindrical and surrounded by a non-permeable membrane 12. The support 23 has a conical tip 24 at the distal end and a body portion 25 extending proximally from the tip 24. On the body portion 25, two gold electrodes 10 are attached by gluing. Electrode 10 extends longitudinally along both sides of body portion 25 and is received by a respective recess in body portion 25.

  Between the tip 24 and the body portion 25, a frustoconical protrusion 26 is provided for securing the membrane 12 by a friction fit. A corresponding protrusion 26 is provided at the proximal end of the body portion 25. The membrane 12 can be bonded to the support 23, but the adhesive used to secure the membrane 12 and the electrode 10 is formed between the body portion 25 of the support 23 and the membrane 12. It is important to choose not to release ions into the water filling chamber. Furthermore, the sealing surface of the support 23 can be selectively hydrophobic in order to avoid the formation of a water film in which ions can be released.

  The membrane 12 can also be secured to the support 23 by a crimp connection and a flexible gasket, if desired. Specifically, when the film 12 is formed of silicone rubber, the film 12 can act as a gasket. As in FIG. 6, a heat shrink sleeve can be used to form the crimp connection. Alternatively, a metal crimp ring can be used at a position corresponding to the position of the sealing protrusion 26.

  The body portion 25 of the support 23 comprises a plurality of ribs 27, which are formed with a sawtooth profile so as to be easily molded. The ribs 28 provide mechanical support to the membrane 12 and define the fluid passages 11 necessary for the sensor 4 to function effectively. Between each electrode 10 and the fluid passage formed between the ribs 27, the reservoir 9 is formed by a recess in which the electrode 10 is disposed. The reservoir 9 provides a region of relatively low current density around the electrode 10 to reduce the effects of electrical polarization.

During manufacture, the membrane 12 is fixed on a support 23 while being immersed in deionized water and a propylene glycol solution so that the chamber bounded by the membrane 12, the electrode 10, and the ribs 27 is Fully filled with liquid. In this way, this chamber forms a pCO ₂ sensor, as schematically shown in FIG.

  The sensor 1 can include two or more sensing chambers. For example, two parallel electrodes 10 separated by a wall can be provided on both sides of the support 23. Thereby, the sensing chamber is connected to one electrode 10 on one side of the support 23 and one of the electrodes 10 on the other side of the support 23 via the fluid passage 11 between the ribs 27 on the support 23. Formed between. A corresponding sensing chamber is provided between the remaining electrode 10 and the fluid passage 11 on the bottom surface of the support 11. The electrodes 10 from each of these chambers can be electrically connected to corresponding electrodes from the other chambers so that the electrical signal from the sensor reflects the conductivity of both chambers. .

A temperature sensor 5 in the form of a thermocouple is embedded at the proximal end of the support 23. The temperature sensor 5 is used to correct the pCO ₂ and display on the monitor 3 the measured tissue temperature that conveys information for medical diagnosis. The temperature sensor 5 has a minimum measurement range of 33-42 ° C. and a minimum accuracy of +/− 0.2 ° C.

  A ribbon cable 6 is electrically and mechanically connected to the electrode 10 and the temperature sensor 5. The electrode 10 is formed as an extension of the conductor of the ribbon cable 6. Alternatively, the electrodes can be formed by plating on the support 23. If the cable 6 and the connection to the support 23 are strong enough, the cable 6 can be used to pull the sensor unit 1 from its use position. Alternatively, Kevlar wire can be provided, such as integrated with the ribbon cable 6 to provide a strong external mechanical connection.

  The membrane 12 can extend proximally from the support 23 with the cable 6 to form a catheter around the cable 6. Alternatively, another catheter 28 can be provided. In this case, the catheter 28 is coupled to the support 23 proximal to the electrode 10 and the membrane 12.

  As shown in FIG. 6, the catheter 28 can include a plurality of slits 29 to secure the sensor unit 1 in place in the tissue. The slit 29 forces the portion 30 of the catheter 28 between the slits 29 outward when the catheter 28 is pushed distally (in the direction of arrow B in FIG. 6) with respect to the cable 6 (or Kevlar line). The configuration shown in the perspective view in FIG. 6 is assumed. The radially protruding portion 30 of the catheter 28 holds the sensor unit 1 in the tissue in which it is implanted. The relative position of the catheter 28 and the cable 6 can be maintained with a locking mechanism (not shown) until the time when the sensor unit 1 is removed from the tissue. At this time, the locking mechanism can be released and the portion 30 of the catheter 28 returns to the relaxed position so that the sensor unit 1 can be removed from the tissue.

In order to measure the pCO ₂ that detects and monitors the effects of the above mentioned disease treatments and conditions for a period of up to 4 weeks, the tip of the catheter with integral sensor 4 is placed 0.5-4 cm in the tissue. The

The sensor unit 1 has a maximum diameter of 1 mm, and the maximum distance from the catheter tip to the sensor element is 2 mm. The sensor 4 has a minimum pCO ₂ measurement range of _{2 to} 25 kPa, and the minimum detectable pCO ₂ difference is 0.2 kPa. The maximum response of the sensor 4 is 20 seconds. The maximum possible measured current in any region of the fluid chamber is such that j <1 mA / cm ² while the measured input voltage does not exceed 50 mV RMS.

Electrode 10 is gold plated and has a total area of about 0.3 mm ² . The measurement frequency f _meas should be higher than 100 Hz. At lower frequencies, the measurement chamber polarization influences the measurement. At frequencies above 10 kHz, low impedance capacitance becomes important. Measuring resistor _{R_ its measure} is the 500kOhm the range of 7MOhm.

  The sensor 4 is electrically connected to the electronic surface unit 2 placed on the patient's skin by a ribbon cable 6 having a length between 5 cm and 1 meter. The maximum cable / catheter diameter is 1 mm. The cable / catheter is soft and flexible so as not to overly disturb nearby tissues and organs. The cable / catheter and its connections are also robust enough to withstand the strong pulling forces that can result from both normal and “abnormal” use.

  During sterilization, storage, and transport, the sensor unit 1 is deionized and covered with sterile, endotoxin-free water to ensure that there is virtually no net loss of water from the sensor reservoir.

  11 to 15 show a sensor device 50 according to another embodiment of the present invention. Except as otherwise indicated, the form of this embodiment is the same as in the sensor apparatus described with respect to FIGS. As in the previous embodiment, the device 50 comprises a self-adhesive strip 52 as described above, to which two reflectance pulse oximetry sensors 54 and a sensor unit 1 are attached. The self-adhesive piece 52 is provided with a release piece 56 that is peeled away from the adhesive piece 52 to expose the adhesive surface of the adhesive piece 52 for application to the patient's skin. In order to prevent damage, contamination, or evaporation, the sensor of the sensor device 50 is packaged with a sterilized water filling tube 72 (not shown) filled with a sterilized isotonic propylene glycol aqueous solution.

  The sensor device 50 includes an insertion needle 74 having a U-shaped cross section provided with a finger grip 60. In the packaged sensor device 50, the sensor unit 1 and the cable connection connected thereto are accommodated in the U-shaped groove of the insertion needle 74. When the protective tube 72 is removed, the insertion needle 74 is pushed through the patient's skin by manually applying pressure to the finger grip 60. The insertion needle 74 is then removed from the sensor device 50 in the general form shown in FIG. 14, leaving the sensor unit 11 located in the patient's muscle. With the U-shape of the insertion needle 74, the needle is disengaged by withdrawing the needle from the cable connection to the sensor unit 1.

  FIG. 13 shows the details of the connection between the insertion needle 74 and the sensor device 50. As shown in FIG. 13, the insertion needle 74 having a U-shaped cross section is molded in the finger grip 60. The sensor device 50 includes a plastic housing 76 which is on the self-adhesive piece 52 and engages a hole provided therein. The plastic housing 76 is bonded to the self-adhesive piece 52. A through hole through which the insertion needle 74 is passed is provided in the center of the plastic housing 76. A disk-shaped metal guide 78 overlying the plastic housing 76 and having a central hole through which the insertion needle 74 passes is coupled to the plastic housing 76. The central hole of the metal guide 78 has a U shape corresponding to the cross section of the insertion needle 74, and the insertion needle 74 is held at a predetermined position by the central hole, so that the insertion needle 74 does not rotate and No damage to the cable connection 6 to the sensor unit 1 occurs. The cable connection 6 from the sensor unit 1 passes from the insertion needle 74 between the metal guide 78 and the plastic housing 76 and is surrounded by a protective sheath 62 bonded to the metal guide 78. The through holes of the metal guide 78 and the plastic housing 76 are provided on the metal guide 78 and are closed by a silicone film 80 through which the insertion needle 74 passes. When the insertion needle 74 is removed, the silicone film 80 is elastically deformed to seal the through hole.

  As shown in FIG. 13, the bead rim 82 of the cover tube 72 snap fits into the recess of the plastic housing 76 to seal the tube 72 against the sensor device 50. When the sensor unit 1 is inserted into the patient's muscle, the tube 72 is removed from the sensor device 50 to expose the insertion needle 74.

As shown in FIGS. 1 and 2, the electronic surface unit 2 comprises a sine wave generator 13, which provides a voltage of at least 5 volts and a current supply of 50 mV and is powered by a battery 14. A filter 15 is provided to filter or average the input of the lock-in amplifier 16. Passive filters that reduce current consumption can be used. A preamplifier 17 is combined with the servo mechanism to remove DC current from the signal in order to reduce the effects of electrolyte. According to the servo configuration, the output of the preamplifier is supplied again to the input via a low-pass filter. Thus, only the output DC component is supplied again, erasing any DC current drawn by the pCO ₂ sensor. In this way, it is ensured that no DC current that degrades the electrodes flows through the pCO ₂ sensor. The operational amplifier used in this stage consumes a minimum current and has a large CMMR value. At the same time, the deflection current is minimal. A lock-in amplifier 16 amplifies the AC signal from the sensor 4. This can be constructed with an operational amplifier with an accuracy of at least 1%, or using an IC package, for signal detection at frequencies below 1 kHz. A DC electrical split 19 such as an optical coupler or coil coupler is provided to prevent noise transmission from the monitor unit 3 and associated cable 18. An optical coupler is usually used for the noise signal ratio. A temperature signal amplification and adjustment unit 20 is provided for amplifying the signal from the temperature sensor 5. The electronic unit 2 is powered by a rechargeable and replaceable standard type battery 14. The battery capacity is sufficient for 14 days of continuous monitoring. The surface unit 2 also includes an on / off indicator LED 21 and a battery status indicator (not shown). Communication between the surface unit 2 and the monitor 3 is analog via a shielded cable 18. However, the surface unit 2 may include an analog-to-digital converter so that the communication between the surface unit 2 and the monitor 3 can be digital, such as by digital wire transmission or digital wireless transmission. Is possible. The cable 18 is at least 4 m long and is lightweight and flexible.

As shown in FIGS. 1 and 2, AC current is generated by a sine wave generator 13 and supplied to one of the pCO ₂ sensor electrodes 10 and the lock-in amplifier 16. The high-pass signal from the other pCO ₂ electrode 10 passes through the filter 15 to the low noise amplifier 17 and from the low noise amplifier 17 to the lock-in amplifier 16, where the reference signal generated by the sine wave generator 13. Compared with The out-of-phase component of the signal, ie the unwanted component, is rejected and the rest of the signal is amplified. The amplified signal is proportional to pCO ₂ (or conductance) and passed to the monitor 3 for recording or further manipulation.

  The surface unit 2 is also electrically connected to a reference electrode (not shown) that is electrically connected to the patient's skin. The signal from the reference electrode can be used to compensate the signal from the sensor unit 1 for the effects of electromagnetic noise generated by the patient.

  A single surface unit 2 can receive signals from several sensor units 1 and provide a multiplexed output to the monitor unit 3.

  The monitor unit 3 comprises a portable PC 7 including CD RW and IR ports, and a PCMCIA I / O card 8 that can collect signals from at least four different surface units 2 simultaneously. The PCMCIA card 8 can have an integrated non-DC electrical coupling. The power supply 22 of the monitor unit 3 is a medical approved type that operates at both 110V and 230V.

  The software function of the monitor unit 3 can be implemented in a lab view, which is available from National Instruments [Austin, Texas] and can handle up to four different surface units simultaneously. The software provides a sensor calibration mechanism with three calibration points and a secondary calibration function. The software can be modified to support any other number of calibration points and types of calibration functions. The software also has a mechanism to smooth the signal from the sensor 4 over a defined time interval. It is possible to have at least two warning levels for the measured values and two warning levels for the slope. The slope of the measured value is calculated for each defined time interval. The warning is both visible and audible. It is possible to stop one warning display while activating other warnings. The monitor 3 can log all measurements, parameter settings, and alerts across sessions. With a 30 second log interval, there should be at least 10 two week session storage on the hard disk. The session log can be saved on a writable CD in a format readable by Microsoft Excel.

The sensor device 50 according to this embodiment of the present invention is a single device that can provide measurements of pCO ₂ , temperature and blood oxygen in a patient's muscle. Based on this information, doctors can quickly and accurately identify the patient's signs of corruption in a number of conditions.

Although the sensor device has been described herein with particular reference to pCO ₂ measurement, the general form of this sensor device is for other physiological sensors such as body temperature, oxygen partial pressure, pH or glucose concentration. You may use for a sensor.

1 is a schematic diagram of a fully sensing system incorporating a sensor of the present invention. It is the schematic which shows the measurement principle about the sensor of the system of FIG. _{2 is} a partial cutaway view of a pCO ₂ sensor according to the present invention. FIG. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3. FIG. 5 is an enlarged view of the details indicated by the circle in FIG. 4. FIG. 4 is a diagram of the sensor of FIG. 3 with the film removed. Attachment mechanism is visible, showing the deformation of the pCO ₂ sensor of FIG. It is a top view of the sensor apparatus concerning one embodiment of the present invention. It is a side part fragmentary sectional view of the sensor apparatus of FIG. It is a side view in the use position of the sensor apparatus of FIG.7 and FIG.8. FIG. 9 is an enlarged view of the pCO ₂ and the temperature sensor of the sensor device of FIGS. 7 and 8. 3 shows a sensor device according to another embodiment of the present invention. It is a fragmentary sectional perspective view of the sensor apparatus of FIG. FIG. 13 is a detailed cross-sectional view of the sensor device of FIGS. 11 and 12. It is a top view of the sensor apparatus of FIGS. 11-13 which is not provided with the insertion needle. It is a perspective view of the sensor apparatus in the position of FIG.

Claims (12)

A physiological sensing device that combines a sensor for measuring the partial pressure of carbon dioxide (pCO ₂ ), a body temperature sensor, a heart rate sensor, and an oxygen saturation sensor. The sensing device of claim 1, wherein the pCO ₂ sensor is configured to be inserted through a patient's skin.   Sensing device according to claim 1 or 2, wherein the temperature sensor is shaped to be inserted through the skin of a patient. It said temperature sensor and pCO ₂ sensor is provided by the sensor unit to be inserted through the skin of the patient, the sensing device according to any one of claims 1 to 3. The sensing device according to any one of claims 2 to 4, comprising a pointed tip that pierces the patient's skin upon insertion of the pCO ₂ sensor. A physiological sensing device comprising a pCO ₂ sensor shaped to be inserted through a patient's skin and a pointed tip that pierces the patient's skin upon insertion of the pCO ₂ sensor. When in the position where the pCO ₂ sensor is inserted through the skin of the patient, the sharp tip is provided by a removable hollow needle, sensing apparatus according to claim 5 or 6.   The sensing device according to claim 1, wherein the oxygen saturation sensor is shaped to be affixed to a surface of a patient's skin.   9. The sensing device of claim 8, wherein the heart rate sensor and oxygen saturation sensor are provided by a pulse oximetry sensor.   10. A sensing device according to any one of the preceding claims, comprising an adhesive patch for application to the patient's skin. A physiological sensing device comprising a pCO ₂ sensor configured to be inserted through a patient's skin and an adhesive patch for affixing the device to the patient's skin to hold the pCO ₂ sensor in place Physiological sensing device. The pCO ₂ sensor comprises a chamber that is at least partially defined by a membrane that is permeable to carbon dioxide and that contains a liquid substantially free of electrolyte and at least two electrodes. The sensing device according to any one of 1 to 11.

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