WO2006079862A2 - Pulse oximeter and casing for anchoring a sensor - Google Patents

Pulse oximeter and casing for anchoring a sensor Download PDF

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Publication number
WO2006079862A2
WO2006079862A2 PCT/HU2006/000010 HU2006000010W WO2006079862A2 WO 2006079862 A2 WO2006079862 A2 WO 2006079862A2 HU 2006000010 W HU2006000010 W HU 2006000010W WO 2006079862 A2 WO2006079862 A2 WO 2006079862A2
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WO
WIPO (PCT)
Prior art keywords
head
sensor
circuitry
pulse oximeter
casing
Prior art date
Application number
PCT/HU2006/000010
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French (fr)
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WO2006079862A3 (en
Inventor
Hunor SÁNTHA
Gábor HARSÁNYI
Original Assignee
Santha Hunor
Harsanyi Gabor
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Application filed by Santha Hunor, Harsanyi Gabor filed Critical Santha Hunor
Publication of WO2006079862A2 publication Critical patent/WO2006079862A2/en
Publication of WO2006079862A3 publication Critical patent/WO2006079862A3/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/683—Means for maintaining contact with the body
    • A61B5/6834—Means for maintaining contact with the body using vacuum
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0002—Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • A61B5/14552—Details of sensors specially adapted therefor

Definitions

  • the invention relates to a pulse oximeter sensor-head which is composed of electrical units, and comprises at least two light sources of different wavelengths to emit light into the part of the body under examination and a light detector to sense the light either transmitted through or reflected from the part of the body under examination.
  • the invention presented here is a measuring system comprising said sensor-head and a measuring method performed with said sensor-head.
  • the invention relates to a method and a casing for anchoring a sensor-head, particularly according to the invention.
  • the pulse oximeter sensor-head and measuring system according to the invention is particularly appropriate to the continuous monitoring of arterial oxygen levels of tissues by attaching it to the surface of the human body, or to the surface of other living organisms, and is of particular use where currently available pulse oximeter devices cannot be used.
  • Applications include but are not confined to, for example, the monitoring of tissue oxygenation of the presenting part of the fetus through the dilated cervix during parturition and delivery. It can also be used to monitor tissue oxygenation of premature neonates that are very small in size. A further example is the monitoring of tissue oxygenation of humans whilst undertaking sporting activities.
  • the metabolic state of every living substance is particularly characterized by the extent to which it is supplied with oxygen. Since the researches in medical spectroscopy of the 1940s, it is well known that the extent of oxygenation of the blood content of living tissues that receive blood circulation can be determined by photometric methods. This is cited in the work published tjy G.A. Millikan: "The oximeter, an instrument for measuring continuously the oxygen saturation of arterial blood in man” (Rev of Scientific Instrument, Vol.
  • oximetry was the pulse oximetry method which additionally utilises the principle of pletismography during the oximetry measurement.
  • the ratio of oxygenated and deoxygenated blood content of the arterial blood surplus pumped by each heartbeat into the portion of tissue falling in the optical path can be calcuated without knowing the exact optical path length by transmissive or reflective, in fact transflective, spectrometric measurements performed in the aforementioned wavelength ranges on living tissues that receive blood circulation, if the rhythmical changes of the blood content of tissue caused by the pulsation of arteries are taken into account.
  • the physiological parameter to be detected by a pulse oximeter device is called the oxygen saturation index (henceforth SpO 2 ), because only the ratio of oxygenated hemoglobin molecules (HbO 2 ) compared to the total hemoglobin content (Hb+HbO 2 ) is needed by a physician, since in ordinary situations hemoglobin can only occur in either the oxygenated or the deoxygenated state.
  • pulse oximetry Numerous patents has been filed concerning the topic of pulse oximetry during the recent decades, and several producers use the method of pulse oximetry in their products.
  • the most widespread use of pulse oximetry is the continuous attachment of a finger clip type oximeter to a patient during surgical operation or within intensive care departments in order to non-invasively monitor the metabolic state of the patient.
  • the most typical class of pulse oximeter apparatuses has a central control and data processor device connected through a multiple-core cable to a transmissive or reflective type measuring head, which has only passive role during the measurement and is directly attached on the individual under examination.
  • the raw measurement data transmitted through the cables from the measuring head are processed, evaluated and displayed by the central device.
  • the anchoring of the pulse oximeter sensor-head onto the surface of the examined part of the body is a key issue for the feasibility and accuracy of a pulse oximetry measurement.
  • some kinds of clamping tools or biocompatible adhesive is used in order to anchor the sensor-head.
  • Such a device is described for instance in the patent specification EP0481612 but other solutions are known as well when the pulse oximeter head is anchored by a suture onto the part of the body under examination e.g. in the patent specification US 5,727,547 or an external vacuum pump sucks out a part of the air from the space between the measuring head of the pulse oximeter and the part of the body to ensure an anchoring, e.g. in the patent specification US . 5,497,771.
  • the disadvantage of the former solutions is the possible negative side effects of the invasive anchoring
  • the disadvantage of the latter solutions using an external vacuum pump is the inherent need for a pipeline which has the same disadvantage as an electrical cable.
  • the object of the invention is to ensure a wireless pulse oximeter sensor-head, a pulse oximeter measuring system and a measuring method which overcome the aforementioned disadvantages.
  • Futhermore the object of the invention is to ensure a method and casing for anchoring the sensor-head which overcome the aforementioned disadvantages.
  • the object is achieved according to our recognition by means of the physical separation of the parts which perform the photometric measurement processes and the digital conversion, that is A/D data conversion of measured data, from the parts which perform processing, analysis and evaluation of measured data as well as the displaying of results; and by means of the fact that we provide a wireless communication between the physically separated devices, that means either radiofrequency or optical datacommunication.
  • a pulse oximeter sensor-head which is composed of electrical units, and said sensor-head comprises at least two light sources of different wavelengths to emit light into part of the body under examination and a light detector to sense (detect) light either transmitted through or reflected from said part of the body, additionally comprises a control circuitry connected to each electrical unit or at least to the light sources and the light detector, further comprises a data collector and A/D dataconverter circuitry connected to the output of the light detector, a wireless data communication circuitry connected to the output of the data collector and A/D dataconverter circuitry, and a current source to ensure the power supply of the pulse oximeter sensor-head.
  • the current source serving for the power supply of the circuitries of the pulse oximeter sensor-head may be a battery or an accumulator, or preferably a rechargeable accumulator, but in certain cases it may be expedient to ensure the electrical power for the operation by radiation of an external electromagnetic field through inductive coupling into a coil located in the pulse oximeter sensor-head, i.e. the current source is an inductively chargeable power supply in such a case.
  • all electrical units of the pulse oximeter sensor-head or at least the control circuitry, the data collector and A/D dataconverter circuitry and the wireless data communication circuitry is realised in a single semiconductor chip by means of ASIC (Application Specific Integrated Circuit) technology.
  • ASIC Application Specific Integrated Circuit
  • the invention is a measuring system comprising a pulse oximeter sensor-head in which said pulse oximeter sensor-head comprises at least two light sources of different wavelengths to emit light into the part of the body under examination and a light detector to sense the light either transmitted through or reflected from said part of the body and in addition said pulse oximeter sensor-head comprises a control circuitry connected to each electrical unit or at least to the light sources and the light detector, further comprises a data collector and A/D dataconverter circuitry connected to the output of the light detector, a wireless data communication circuitry connected to the output of the data collector and A/D dataconverter circuitry, and a current source to ensure the power supply of the pulse oximeter sensor-head, and in addition the measuring system comprises a receiver device having wireless datacommunication connection with the pulse oximeter sensor-head located remotely from it and said receiver device comprises dataprocessor and evaluation circuitry plus, if necessary, a displaying circuitry.
  • connection between the datacommunication circuitry and the receiver device is a wireless radiofrequency connection or a wireless optical connection.
  • the measuring system has additional pulse oximeter sensor-heads, all of which are connected to the same receiver device through wireless connections.
  • a datastorage and/or measuring command sender circuitry is connected to the dataprocessor and evaluation circuitry.
  • the invention is a measuring method performed with a measuring system comprising a pulse oximeter sensor-head in which said pulse oximeter sensor-head is placed and anchored on the surface of the body, then light at least at two different wavelengths is emitted from light sources into the living tissue and the outcoming light intensities are measured by a light detector, then the measured signals are collected and converted to a digital format by a data collector and A/D dataconverter circuitry, then the signals are transmitted from the pulse oximeter sensor-head by a wireless datacommunication circuitry, and the transmitted digital raw pulse oximetry data are received, processed and evaluated by a receiver device located remotely and maintaining a wireless communication with the pulse oximeter sensor-head, and, if necessary, the results are displayed.
  • the pulse oximeter sensor-head has to be fixed to the surface of the body during the measurement.
  • the contact surface of said pulse oximeter sensor-head is anchored to the surface of the part of the body under examination by a biocompatible adhesive layer.
  • a further objective of the invention is achieved according to our recognition by means of fixing the pulse oximeter sensor-head in an airtight, bell-jar-like casing comprising an air space in which a decrease of pressure can be realised without using any external means, and the anchoring is achieved by the decrease of pressure in the space closed between the casing of the pulse oximeter sensor-head and the surface, i. e. skin of the part of the body.
  • the invention is also a method for anchoring a sensor-head, particularly but not exclusively, according to the invention so that the sensor-head is fixed mechanically in a bell-jar-like casing by means of structural element of said casing, said casing having an internal air space and a flange, is placed together with the sensor-head onto the surface of the body so that the flange together with said surface creates an airtight sealing and a decrease of pressure is generated in said air space during the process of placing the sensor-head onto the surface of the body.
  • the wall of the casing is made at least partially of a resilient material, and pressing this resilient wall during the process of placing the sensor-head onto the surface of the body a part of the air content of the air space is pressed out and the flange is pressed against the surface of the body.
  • the decrease of pressure is created by a micro-vacuum pump fixed in the casing, after the flange is pressed against the surface of the body.
  • the micro-vacuum pump is integrated with the pulse oximeter sensor-head and is fabricated by MEMS (Micro Electro-
  • the invention is a casing for anchoring a sensor-head, particularly but not exclusively, according to the invention, where said casing is bell-jar- like, comprises an internal air space, a flange which can rest against the surface of the body and creates an airtight sealing with it, and comprises a structural element for the mechanical holding of the sensor-head, and the wall of the casing is at least partially made of a resilient material.
  • the pulse oximeter sensor-head of the measuring system according to the invention can be miniaturised to a much higher extent, both in weight and volume, compared to the size of the actually known wearable devices comprising data processor and displaying systems, too, and in addition, no cables restrain the usage of the sensor-head.
  • This measuring system is particularly appropriate to the continuous monitoring of arterial oxygen levels of tissues by attaching it to the surface of the human body, or to the surface of other living organisms, and is of particular use where currently available pulse oximeter devices and their anchoring methods cannot be used.
  • the individual under examination may freely move, since there are no external cables and the size of the pulse oximeter sensor-head is small. By means of the reduced size it becomes feasible to perform pulse oximetry examinations under special circumstances, as well, for instance:
  • FIG. 1 Schematic drawing of a preferred embodiment of the pulse oximeter sensor-head and measuring system according to the invention
  • Figure 2 Cross-sectional drawing of a preferred embodiment of a casing according to the invention for anchoring of the sensor-head
  • a measuring system for reflective pulse oximetry measurement where both the light emitting surfaces 1a and 2a of the light sources 1 and 2 and the light detecting surface 3a of the light detector 3 are on the outer surface of the same side of the sensor-head 8, that is at the contact surface 8a which faces towards the surface of the body 9 when the sensor- head 8 is placed.
  • the reflective pulse oximetry measuringment is in fact a socalled transflectance pulse oximetry measurement, since the photons are transmitted into different depths of the tissue before they are reflected or absorbed by it.
  • the light sources 1 and 2 having different wavelengths and the light detector 3, as well, are driven by the control circuitry 4 of the sensor-head
  • the light sources 1 , 2 are Light Emitting Diodes (LED) which emit light at wavelengths of 660 nm and 940 nm, respectively.
  • the two LEDs are turned on alternately by the control circuitry 4 for intervals of 150-150 microseconds in such a way that between each interval an intermission of 50 microseconds is made.
  • the light detector 3 is a photodiode having a current generated by the detected photons which current is proportional to the actual light intensity arriving in the photodiode from one of the LEDs after interacting with the tissue, whilst concurrently the other LED is switched off.
  • the light absorption capability (extinction coefficient) of the transilluminated living tissue at the specific wavelength and during that specific interval can be calculated.
  • the measured values of the current of the photodiodes, as raw pulse oximetry data, are forwarded to the data collector and A/D dataconverter circuitry 5.
  • Numerous known solutions for circuitries published in the scientific literature of. electrical engineering are suitable for the data collector and A/D dataconverter circuitry
  • the digital raw pulse oximetry data are forwarded from the data collector and A/D dataconverter circuitry 5 to the wireless data communication circuitry 6.
  • the wireless data communication circuitry 6 the digital raw pulse oximetry data are transmitted at radiofrequency to the receiver device 7 by using one of the Industrial - Scientific - Medical (ISM) frequency bands.
  • ISM Industrial - Scientific - Medical
  • the wireless data communication circuitry 6 of the standard Blue Tooth Class I. is applied operating at 2,4 GHz of ISM band having a transmission range of 10 m.
  • the digital raw pulse oximetry data are processed in such a manner that functions are fitted to the measured values of the current of the photodiode and appropriate mathematical operations are performed with these functions, then the actual extinction coefficient corresponding to the wavelengths of 660 nm and 940 nm is calculated, and then the actual SpO 2 value is calculated and displayed.
  • the arrows shown in the figure represent the flow of information in the form of electrical signals.
  • the current source 10 is connected with each unit in order to ensure their power supply.
  • the current source 10 is a 3.3 V Lithium-ion accumulator and for the duration of the measurement the stabile anchoring between the sensor-head 8 and the surface of the body 9 is ensured by a biocompatible adhesive layer, not shown in the figure.
  • FIG. 2 shows the pulse oximeter sensor-head 8, having two light sources 1 , 2, a light detector 3 and further electrical units, is fixed in a casing 11.
  • the casing 11 is bell-jar-like, having an internal air space 12, and comprises a flange 14 which rests against the surface of the body 9 and creates an airtight sealing with it, further has a structural element 11b for the mechanical holding of the sensor-head 8 and a resilient wall 11a which is made of silicone rubber.
  • the structural element 11 b and the resilient wall 11 a of the casing 11 are fixed to each other in an airtight manner by glue.
  • the air space 12 communicates with the surface of the body 9 through the opening 13.
  • the sensor-head 8 is embedded in a one step process when said sensor-head 8 is embedded as a whole piece. There is also a possibility to embed the units of the sensor-head 8 separately into the structural element 11 b.
  • the air content is partially expelled from the air space 12 by means of pressing the resilient wall 11a, then the 14 flange is pressed against the surface of the body 9 and the resilient wall 11a is released and starts to spring back to its original position, whereby a decrease of pressure is generated in the air space 12 which anchors the sensor-head 8 to the surface of the body 9 for the duration of the measurement.

Abstract

The invention is a pulse oximeter sensor-head (8) which is composed of electrical units and comprises at least two light sources (1, 2) of different wavelengths to emit light into the part of the body (9) under examination and a light detector (3) to sense the light eigther transmitted through or reflected from the part of the body (9) under examination, further comprises a control circuitry (4) connected to each electrical unit or at least to the light sources (1, 2) and the light detector (3), a data collector and A/D dataconverter circuitry (5) connected to the output of the light detector (3), a wireless data communication circuitry (6) connected to the output of the data collector and A/D dataconverter circuitry (5), and a current source (10) to ensure the power supply of the pulse oximeter sensor-head (8). The invention is also a measuring system comprising said sensor-head (8) and a measuring method with said sensor-head (8). The invention relates also to a method and a casing (11) for anchoring a sensor-head (8) where the sensor- head (8) is fixed mechanically in a bell-jar-like casing (11) by means of structural element (11b) of said casing (11), said casing (11), having an internal air space (12) and a flange (14), is placed together with the sensor- head onto the surface of the body (9) so that the flange (14) together with the surface forms an airtight sealing, and a decrease of pressure is generated in said air space (12) during the process of placing the sensor-head (8) onto the surface of the body (9).

Description

4
PULSE OXIMETER SENSOR-HEAD, MEASURING SYSTEM AND
MEASURING METHOD WITH SAID SENSOR-HEAD, METHOD AND
CASING FOR ANCHORING A SENSOR-HEAD
The invention relates to a pulse oximeter sensor-head which is composed of electrical units, and comprises at least two light sources of different wavelengths to emit light into the part of the body under examination and a light detector to sense the light either transmitted through or reflected from the part of the body under examination. In addition, the invention presented here is a measuring system comprising said sensor-head and a measuring method performed with said sensor-head. In addition, the invention relates to a method and a casing for anchoring a sensor-head, particularly according to the invention. The pulse oximeter sensor-head and measuring system according to the invention is particularly appropriate to the continuous monitoring of arterial oxygen levels of tissues by attaching it to the surface of the human body, or to the surface of other living organisms, and is of particular use where currently available pulse oximeter devices cannot be used. Applications include but are not confined to, for example, the monitoring of tissue oxygenation of the presenting part of the fetus through the dilated cervix during parturition and delivery. It can also be used to monitor tissue oxygenation of premature neonates that are very small in size. A further example is the monitoring of tissue oxygenation of humans whilst undertaking sporting activities.
The metabolic state of every living substance is particularly characterized by the extent to which it is supplied with oxygen. Since the researches in medical spectroscopy of the 1940s, it is well known that the extent of oxygenation of the blood content of living tissues that receive blood circulation can be determined by photometric methods. This is cited in the work published tjy G.A. Millikan: "The oximeter, an instrument for measuring continuously the oxygen saturation of arterial blood in man" (Rev of Scientific Instrument, Vol.
13, pp. 434-444, 1942), namely, blood freshly saturated with oxygen and transported in the arteries has higher extinction coefficient values in the infrared wavelength range, whereas blood indigent in oxygen and transported in the veins has higher extinction coefficient values in the red wavelength range. This phenomenon is caused by the significant difference between the red infra-red light absorption spectrum of oxyhemoglobin (henceforth HbO2) which carries 4 oxygen molecules (henceforth O2) and deoxyhemoglobin (henceforth Hb) which has already released the O2 molecules.
A further development of oximetry was the pulse oximetry method which additionally utilises the principle of pletismography during the oximetry measurement. In this method the ratio of oxygenated and deoxygenated blood content of the arterial blood surplus pumped by each heartbeat into the portion of tissue falling in the optical path can be calcuated without knowing the exact optical path length by transmissive or reflective, in fact transflective, spectrometric measurements performed in the aforementioned wavelength ranges on living tissues that receive blood circulation, if the rhythmical changes of the blood content of tissue caused by the pulsation of arteries are taken into account. The physiological parameter to be detected by a pulse oximeter device is called the oxygen saturation index (henceforth SpO2), because only the ratio of oxygenated hemoglobin molecules (HbO2) compared to the total hemoglobin content (Hb+HbO2) is needed by a physician, since in ordinary situations hemoglobin can only occur in either the oxygenated or the deoxygenated state. In accordance with the description given above the mathematical definition of SpO2 is: SpO2 = HbO2/ (Hb + HbO2).
Numerous patents has been filed concerning the topic of pulse oximetry during the recent decades, and several producers use the method of pulse oximetry in their products. The most widespread use of pulse oximetry is the continuous attachment of a finger clip type oximeter to a patient during surgical operation or within intensive care departments in order to non-invasively monitor the metabolic state of the patient.
Knowing the SpO2 value of a patient is absolutely necessary for the physician in certain decision situations. Since the SpO2 value can be measured in a noninvasive way, the application of pulse oximetry has no inherent risks. The most typical class of pulse oximeter apparatuses has a central control and data processor device connected through a multiple-core cable to a transmissive or reflective type measuring head, which has only passive role during the measurement and is directly attached on the individual under examination. The raw measurement data transmitted through the cables from the measuring head are processed, evaluated and displayed by the central device. An apparatus of this type is described in the patent specification US
5,687,719.
There are other known wireless pulse oximeter devices, which include the measurement and the processing and evaluation of measured data plus the displaying of results integrated in one body-attachable device. Such a solution is detailed for instance in the patent specification WO0022980 which describes a relatively small size, finger clip type wireless pulse oximeter. Devices of this type pose the problem that despite the reduced size they are still relatively large, which makes their utilisation impossible in special applications, e.g. monitoring of childbirth. Furthermore, there are other known pulse oximeter systems similar to the aforementioned ones, where results (SpO2 etc.) acquired after processing the raw measurement data are transmitted through wireless radiofrequency method also to a remote location for telemonitoring purposes. Such a solution is described for instance in the patent specification CA2504252.
The disadvantage of any known solution is that either they comprise cables or their size is relatively large, thus, their utilisation in special application areas is uncomfortable or impossible. If such solutions are utilised the individual under examination is restrained in his motion and his movements falsify the results of the measurements quite often because a sufficiently stable and durable contact between the pulse oximeter device and the living tissue under examination can not be ensured.
The anchoring of the pulse oximeter sensor-head onto the surface of the examined part of the body is a key issue for the feasibility and accuracy of a pulse oximetry measurement. Generally, some kinds of clamping tools or biocompatible adhesive is used in order to anchor the sensor-head. Such a device is described for instance in the patent specification EP0481612 but other solutions are known as well when the pulse oximeter head is anchored by a suture onto the part of the body under examination e.g. in the patent specification US 5,727,547 or an external vacuum pump sucks out a part of the air from the space between the measuring head of the pulse oximeter and the part of the body to ensure an anchoring, e.g. in the patent specification US . 5,497,771. The disadvantage of the former solutions is the possible negative side effects of the invasive anchoring, the disadvantage of the latter solutions using an external vacuum pump is the inherent need for a pipeline which has the same disadvantage as an electrical cable.
The object of the invention is to ensure a wireless pulse oximeter sensor-head, a pulse oximeter measuring system and a measuring method which overcome the aforementioned disadvantages. Futhermore, the object of the invention is to ensure a method and casing for anchoring the sensor-head which overcome the aforementioned disadvantages.
The object is achieved according to our recognition by means of the physical separation of the parts which perform the photometric measurement processes and the digital conversion, that is A/D data conversion of measured data, from the parts which perform processing, analysis and evaluation of measured data as well as the displaying of results; and by means of the fact that we provide a wireless communication between the physically separated devices, that means either radiofrequency or optical datacommunication.
In accordance with the above the invention is a pulse oximeter sensor-head which is composed of electrical units, and said sensor-head comprises at least two light sources of different wavelengths to emit light into part of the body under examination and a light detector to sense (detect) light either transmitted through or reflected from said part of the body, additionally comprises a control circuitry connected to each electrical unit or at least to the light sources and the light detector, further comprises a data collector and A/D dataconverter circuitry connected to the output of the light detector, a wireless data communication circuitry connected to the output of the data collector and A/D dataconverter circuitry, and a current source to ensure the power supply of the pulse oximeter sensor-head.
The current source serving for the power supply of the circuitries of the pulse oximeter sensor-head may be a battery or an accumulator, or preferably a rechargeable accumulator, but in certain cases it may be expedient to ensure the electrical power for the operation by radiation of an external electromagnetic field through inductive coupling into a coil located in the pulse oximeter sensor-head, i.e. the current source is an inductively chargeable power supply in such a case.
For a better exploitation of the possibility for miniaturisation arising from the construction according to the invention all electrical units of the pulse oximeter sensor-head or at least the control circuitry, the data collector and A/D dataconverter circuitry and the wireless data communication circuitry is realised in a single semiconductor chip by means of ASIC (Application Specific Integrated Circuit) technology.
In addition, the invention is a measuring system comprising a pulse oximeter sensor-head in which said pulse oximeter sensor-head comprises at least two light sources of different wavelengths to emit light into the part of the body under examination and a light detector to sense the light either transmitted through or reflected from said part of the body and in addition said pulse oximeter sensor-head comprises a control circuitry connected to each electrical unit or at least to the light sources and the light detector, further comprises a data collector and A/D dataconverter circuitry connected to the output of the light detector, a wireless data communication circuitry connected to the output of the data collector and A/D dataconverter circuitry, and a current source to ensure the power supply of the pulse oximeter sensor-head, and in addition the measuring system comprises a receiver device having wireless datacommunication connection with the pulse oximeter sensor-head located remotely from it and said receiver device comprises dataprocessor and evaluation circuitry plus, if necessary, a displaying circuitry.
In a preferred embodiment the connection between the datacommunication circuitry and the receiver device is a wireless radiofrequency connection or a wireless optical connection.
In a preferred embodiment the measuring system has additional pulse oximeter sensor-heads, all of which are connected to the same receiver device through wireless connections.
In another preferred embodiment a datastorage and/or measuring command sender circuitry is connected to the dataprocessor and evaluation circuitry.
In addition the invention is a measuring method performed with a measuring system comprising a pulse oximeter sensor-head in which said pulse oximeter sensor-head is placed and anchored on the surface of the body, then light at least at two different wavelengths is emitted from light sources into the living tissue and the outcoming light intensities are measured by a light detector, then the measured signals are collected and converted to a digital format by a data collector and A/D dataconverter circuitry, then the signals are transmitted from the pulse oximeter sensor-head by a wireless datacommunication circuitry, and the transmitted digital raw pulse oximetry data are received, processed and evaluated by a receiver device located remotely and maintaining a wireless communication with the pulse oximeter sensor-head, and, if necessary, the results are displayed.
The pulse oximeter sensor-head has to be fixed to the surface of the body during the measurement. In a preferred embodiment the contact surface of said pulse oximeter sensor-head is anchored to the surface of the part of the body under examination by a biocompatible adhesive layer. A further objective of the invention is achieved according to our recognition by means of fixing the pulse oximeter sensor-head in an airtight, bell-jar-like casing comprising an air space in which a decrease of pressure can be realised without using any external means, and the anchoring is achieved by the decrease of pressure in the space closed between the casing of the pulse oximeter sensor-head and the surface, i. e. skin of the part of the body.
In accordance with the above, the invention is also a method for anchoring a sensor-head, particularly but not exclusively, according to the invention so that the sensor-head is fixed mechanically in a bell-jar-like casing by means of structural element of said casing, said casing having an internal air space and a flange, is placed together with the sensor-head onto the surface of the body so that the flange together with said surface creates an airtight sealing and a decrease of pressure is generated in said air space during the process of placing the sensor-head onto the surface of the body.
In a preferred embodiment the wall of the casing is made at least partially of a resilient material, and pressing this resilient wall during the process of placing the sensor-head onto the surface of the body a part of the air content of the air space is pressed out and the flange is pressed against the surface of the body.
In another preferred embodiment the decrease of pressure is created by a micro-vacuum pump fixed in the casing, after the flange is pressed against the surface of the body. Expediently, the micro-vacuum pump is integrated with the pulse oximeter sensor-head and is fabricated by MEMS (Micro Electro-
Mechanical System) technology, and in addition a channel and trench system connected to the vacuum pump is realised in the casing which connects said micro-vacuum pump with the contact surface of the sensor-head.
In addition, the invention is a casing for anchoring a sensor-head, particularly but not exclusively, according to the invention, where said casing is bell-jar- like, comprises an internal air space, a flange which can rest against the surface of the body and creates an airtight sealing with it, and comprises a structural element for the mechanical holding of the sensor-head, and the wall of the casing is at least partially made of a resilient material.
The pulse oximeter sensor-head of the measuring system according to the invention can be miniaturised to a much higher extent, both in weight and volume, compared to the size of the actually known wearable devices comprising data processor and displaying systems, too, and in addition, no cables restrain the usage of the sensor-head. This measuring system is particularly appropriate to the continuous monitoring of arterial oxygen levels of tissues by attaching it to the surface of the human body, or to the surface of other living organisms, and is of particular use where currently available pulse oximeter devices and their anchoring methods cannot be used. The individual under examination may freely move, since there are no external cables and the size of the pulse oximeter sensor-head is small. By means of the reduced size it becomes feasible to perform pulse oximetry examinations under special circumstances, as well, for instance:
- monitoring of tissue oxygenation of the presenting part of the fetus through the dilated cervix during parturition and delivery,
- monitoring of tissue oxygenation of premature neonates that are very small in size,
- monitoring of tissue oxygenation of humans whilst undertaking sporting activities,
- monitoring of tissue oxygenation of small-size animals during animal tests which require unrestrained motion of the animals etc.
The invention will be described hereafter in details by means of preferred embodiments with reference to drawings.
Figure 1 : Schematic drawing of a preferred embodiment of the pulse oximeter sensor-head and measuring system according to the invention
Figure 2: Cross-sectional drawing of a preferred embodiment of a casing according to the invention for anchoring of the sensor-head In Figure 1 is shown a measuring system for reflective pulse oximetry measurement, where both the light emitting surfaces 1a and 2a of the light sources 1 and 2 and the light detecting surface 3a of the light detector 3 are on the outer surface of the same side of the sensor-head 8, that is at the contact surface 8a which faces towards the surface of the body 9 when the sensor- head 8 is placed. However, the reflective pulse oximetry mesurement is in fact a socalled transflectance pulse oximetry measurement, since the photons are transmitted into different depths of the tissue before they are reflected or absorbed by it. The light sources 1 and 2 having different wavelengths and the light detector 3, as well, are driven by the control circuitry 4 of the sensor-head
8 attached to the surface of the body 9. The light sources 1 , 2 are Light Emitting Diodes (LED) which emit light at wavelengths of 660 nm and 940 nm, respectively. The two LEDs are turned on alternately by the control circuitry 4 for intervals of 150-150 microseconds in such a way that between each interval an intermission of 50 microseconds is made. The light detector 3 is a photodiode having a current generated by the detected photons which current is proportional to the actual light intensity arriving in the photodiode from one of the LEDs after interacting with the tissue, whilst concurrently the other LED is switched off. Through measuring this current the light absorption capability (extinction coefficient) of the transilluminated living tissue at the specific wavelength and during that specific interval can be calculated. The measured values of the current of the photodiodes, as raw pulse oximetry data, are forwarded to the data collector and A/D dataconverter circuitry 5. Numerous known solutions for circuitries published in the scientific literature of. electrical engineering are suitable for the data collector and A/D dataconverter circuitry
5. In the preferred embodiment presented here it incorporates a preamplifier, sample and hold circuitries, low and high pass filters, amplifier and a 16 bit A/D converter. The digital raw pulse oximetry data are forwarded from the data collector and A/D dataconverter circuitry 5 to the wireless data communication circuitry 6. By means of the wireless data communication circuitry 6 the digital raw pulse oximetry data are transmitted at radiofrequency to the receiver device 7 by using one of the Industrial - Scientific - Medical (ISM) frequency bands. In this preferred embodiment the wireless data communication circuitry 6 of the standard Blue Tooth Class I. is applied operating at 2,4 GHz of ISM band having a transmission range of 10 m. By means of the data processor and evaluation circuitry and display circuitry of the receiver device 7 the digital raw pulse oximetry data are processed in such a manner that functions are fitted to the measured values of the current of the photodiode and appropriate mathematical operations are performed with these functions, then the actual extinction coefficient corresponding to the wavelengths of 660 nm and 940 nm is calculated, and then the actual SpO2 value is calculated and displayed. The arrows shown in the figure represent the flow of information in the form of electrical signals. The current source 10 is connected with each unit in order to ensure their power supply. In this embodiment the current source 10 is a 3.3 V Lithium-ion accumulator and for the duration of the measurement the stabile anchoring between the sensor-head 8 and the surface of the body 9 is ensured by a biocompatible adhesive layer, not shown in the figure.
Figure 2 shows the pulse oximeter sensor-head 8, having two light sources 1 , 2, a light detector 3 and further electrical units, is fixed in a casing 11. By means of the casing 11 the sensor-head 8 with its contact surface 8a can be anchored to the surface of the body 9 during the measurement. The casing 11 is bell-jar-like, having an internal air space 12, and comprises a flange 14 which rests against the surface of the body 9 and creates an airtight sealing with it, further has a structural element 11b for the mechanical holding of the sensor-head 8 and a resilient wall 11a which is made of silicone rubber. The structural element 11 b and the resilient wall 11 a of the casing 11 are fixed to each other in an airtight manner by glue. The air space 12 communicates with the surface of the body 9 through the opening 13. In the structural element 11b the sensor-head 8 is embedded in a one step process when said sensor-head 8 is embedded as a whole piece. There is also a possibility to embed the units of the sensor-head 8 separately into the structural element 11 b.
During the process of placing the sensor-head 8 onto the surface of the body 9 the air content is partially expelled from the air space 12 by means of pressing the resilient wall 11a, then the 14 flange is pressed against the surface of the body 9 and the resilient wall 11a is released and starts to spring back to its original position, whereby a decrease of pressure is generated in the air space 12 which anchors the sensor-head 8 to the surface of the body 9 for the duration of the measurement.
The invention presented here may be realised in many embodiments different from those described in the examples above but still remaining within the scope and spirit of the present invention, thus, our invention cannot be considered to be restricted to the examples.

Claims

CLAIMS:
1. Pulse oximeter sensor-head which is composed of electrical units and comprises at least two light sources of different wavelengths to emit light into a part of the body under examination and a light detector to sense the light either transmitted through or reflected from said part of the body characterised in that additionally comprises a control circuitry (4) connected to each electrical unit or at least to the light sources (1 ,2) and the light detector (3), a data collector and A/D dataconverter circuitry (5) connected to the output of the light detector (3), a wireless data communication circuitry (6) connected to the output of the data collector and A/D dataconverter circuitry (5), and a current source (10) to ensure the power supply of the pulse oximeter sensor- head (8).
2. Pulse oximeter sensor-head according to claim 1 characterised i n that the current source (10) is a battery or an accumulator, more expediently a rechargeable accumulator, or a power supply which is inductively chargeable from outside.
3. Pulse oximeter sensor-head according to claim 1 or2 characterised in that all units of the sensor-head (8) or at least its control circuitry (4), data collector and A/D dataconverter circuitry (5) and wireless data communication circuitry (6) is realised in a single semiconductor chip by means of ASIC technology.
4. Measuring system comprising a pulse oximeter sensor-head in which said pulse oximeter sensor-head comprises at least two light sources of different wavelengths to emit light into the part of the body under examination and a light detector to sense the light either transmitted through or reflected from the part of the body under examination characterised in that additionally said pulse oximeter sensor-head (8) comprises a control circuitry (4) connected to each electrical unit or at least to the light sources (1 ,2) and the light detector (3), a data collector and A/D dataconverter circuitry (5) connected to the output of the light detector (3), a wireless data communication circuitry (6) connected to the output of the data collector and A/D dataconverter circuitry (5), and a current source (10) to ensure the power supply of the pulse oximeter sensor-head (8) and, in addition the measuring system comprises a receiver device (7) having wireless datacommunication connection with the pulse oximeter sensor-head (8) located remotely from it and said receiver device (7) comprises dataprocessor and evaluation circuitry plus, if necessary, a displaying circuitry.
5. Measuring system according to claim 4 characterised in that the connection between the datacommunication circuitry (6) and the receiver device (7) is a wireless radiofrequency connection or a wireless optical connection.
6. Measuring system according to claim 4 characterised in that comprises more pulse oximeter sensor-heads (8), all of them are connected to the same receiver device (7) through wireless connections.
7. Measuring system according to claim 4 characterised in that a datastorage and/or measuring command sender circuitry is connected to the dataprocessor and evaluation circuitry.
8. Measuring method performed with a measuring system comprising a pulse oximeter sensor-head in which the pulse oximeter sensor-head is placed and anchored on the surface of the body, then light at least at two different wavelengths is emitted from light sources into the living tissue and the outcoming light intensities are measured by a light detector characterised in that the measured signals are collected and converted in a digital format by a data collector and A/D dataconverter circuitry (5), then the signals are transmitted from the pulse oximeter sensor-head (8) by a wireless datacommunication circuitry (6), and the transmitted digital raw pulse oximetry data are received, processed and evaluated by a remotely located receiver device (7) maintaining a wireless communication with the pulse oximeter sensor-head (8), and, if necessary, the results are displayed.
9. Measuring method according to claim 8 characterised in that the contact surface (8a) of the sensor-head (8) is anchored to the surface of the body (9) under examination by a biocompatible adhesive layer.
10. Method for anchoring a sensor-head particularly according to claim 1, characterised in that the sensor-head (8) is fixed mechanically in a bell-jar-like casing (11 ) by means of structural element (11 b) of said casing
(11), said casing (11), having an internal airspace (12) and a flange (14), is placed together with the sensor-head onto the surface of the body (9) so that the flange (14) together with said surface forms an airtight sealing, and a decrease of pressure is generated in said air space (12) during the process of placing the sensor-head (8) onto the surface of the body (9).
11. Method according to claim 10 characterised in that the wall of the casing (11) is made at least partially of a resilient material, and pressing this resilient wall (11a) during the process of placing the sensor-head (8) onto the surface of the body (9) a part of the air content of the air space (12) is pressed out, and the flange (14) is pressed against the surface of the body (9).
12. Method according to claim 10 characterised in in that the decrease of pressure is created by a micro-vacuum pump fixed in the casing (11), after the flange (14) is pressed against the surface of the body (9).
13. Casing for anchoring a sensor-head, particularly according to claim 1, characterised in that said casing (11 ) is bell-jar-like, and comprises an internal air space (12), a flange (14) which rests against the surface of the body (9) and creates an airtight sealing with it, further comprises a structural element (11b) for mechanical holding of the sensor-head (8), and the wall of the casing (11) is at least partially made of a resilient material.
PCT/HU2006/000010 2005-01-31 2006-01-30 Pulse oximeter and casing for anchoring a sensor WO2006079862A2 (en)

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HU0500148A HUP0500148A2 (en) 2005-01-31 2005-01-31 Wireless data communication pulse oximetry sensor and pulse oximetry system using the sensor

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