WO2010149984A1 - Appareil de surveillance de l’hydratation et méthode associée - Google Patents

Appareil de surveillance de l’hydratation et méthode associée Download PDF

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Publication number
WO2010149984A1
WO2010149984A1 PCT/GB2010/001260 GB2010001260W WO2010149984A1 WO 2010149984 A1 WO2010149984 A1 WO 2010149984A1 GB 2010001260 W GB2010001260 W GB 2010001260W WO 2010149984 A1 WO2010149984 A1 WO 2010149984A1
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WIPO (PCT)
Prior art keywords
hydration
blood
human
microwave
microwave radiation
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PCT/GB2010/001260
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English (en)
Inventor
Richard A. Dudley
Mira Naftaly
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The Secretary Of State For Business, Innovation & Skills
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Publication of WO2010149984A1 publication Critical patent/WO2010149984A1/fr

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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
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/0507—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  using microwaves or terahertz waves
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/48—Other medical applications
    • A61B5/4869—Determining body composition
    • 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
    • A61B5/6813—Specially adapted to be attached to a specific body part
    • A61B5/6814—Head
    • A61B5/6815—Ear
    • A61B5/6816—Ear lobe

Definitions

  • Monitoring hydration levels is important in many instances, in particular to seek to prevent loss of human or animal efficiency.
  • a low level of hydration in a human, for instance, can result in reduced mental faculty and reduced physical energy.
  • Impedance measurement devices exist but have the disadvantage that they measure the total water content of the body.
  • Ultrasound devices can measure blood flow of the body non-invasively and, as disclosed in US-7,291,109, can be used to monitor hydration levels in soft tissue by changes in the ultrasound velocity, but do not have the sensitivity to measure the hydration of human or animal circulating blood.
  • ultrasound is surface contact critical, requiring coupling gels for a successful measurement to be made and adding complexity and error to any measurement scenario.
  • US2008/0,234,600 discloses an ear mounted temperature sensor.
  • WO2008/0, 112,136 and US2008/0,220,512 disclose measuring body water content by detecting the absorption of electromagnetic radiation in the near-infrared region of the spectrum.
  • the near- infrared region of the spectrum is employed since it has a distinctive absorption band for water.
  • penetration of near-infrared radiation into a human or animal body part is restricted by high levels of absorption and scattering resulting in measurements being limited to near to a subjects skin surface, which can limit the accuracy of any blood hydration measurement estimation.
  • the present invention seeks to provide an improved method and apparatus for measuring hydration level of a human or animal.
  • a method of measuring the hydration of the blood of a human or animal comprising the steps of: transmitting microwave radiation into a body part; detecting the microwave radiation leaving the body part; calculating the absorption of the microwave radiation by the body part; and determining the hydration of the blood from the absorption of the microwave radiation.
  • the step of calculating the absorption of the microwave radiation by the body part comprises calculating the absorption of the microwave radiation by blood in the body part.
  • this preferred embodiment is able to reduce or eliminate errors in the calculation of the hydration level of the blood of the person or animal under observation caused by other body elements affecting the transmission of microwave radiation.
  • the hydration level of blood provides a most effective measure of hydration of the whole body.
  • water will appear in, or be lost from, blood before other parts of the body.
  • this preferred embodiment is able to monitor hydration directly rather than infer a hydration level, as well as being able to provide a very rapid detection of changes in a person's or animal's hydration level.
  • the majority of the chosen body part consists substantially of blood.
  • the preferred body part is the earlobe, which it has been found provides access to blood.
  • microwaves While it has been known that a microwave transmission function can be indicative of water content, microwaves have been avoided for the measurement of the hydration level of humans and animals given the potential risks of microwaves and the power levels expected to be necessary.
  • the inventors have found, however, that by selecting a body part which consists substantially of blood, such as extremities like the earlobe, the microwave power can be maintained at a very low and safe level, preferably less than 1 W and more preferably of the order of milliWatts. Therefore, the risk of the microwave heating the body is substantially reduced, enabling this method to be employed safely on living creatures.
  • hydration monitoring apparatus for measuring the hydration level of blood of a human or animal, comprising a probe element provided with microwave emitter element and a microwave sensor element facing the emitter element and spaced therefrom by a gap; the probe including a fixing element designed to fix the probe to a body of a human or animal part such that a selected body part fits within the gap between the emitter and sensor.
  • hydration monitoring apparatus for measuring the hydration level of blood of a human or animal, comprising a probe element provided with microwave emitter element, a microwave sensor element and a microwave reflection element, the reflection element being spaced from the emitter element and sensor element by a gap; the probe including a fixing element designed to fix the probe to a body of a human or animal part such that a selected body part fits within the gap.
  • the emitter and sensor elements are located adjacent one another and both facing the reflection element.
  • the apparatus provides, in the preferred embodiments, a probe element which can fit to a patient's ear so as to measure the water levels in blood passing through the earlobe, and an indicator unit coupled to the probe element which can indicate the hydration level of the person.
  • the indicator is usefully a unit which can be held or worn by a person and can provide a visual indication of hydration and/or an acoustic or tactile indication of hydration level, preferably including one or more warning indicators when hydration is determined to fall below, or exceed, predetermined thresholds.
  • Figure 1 is a schematic diagram of an embodiment of hydration monitoring device
  • Figure 2 is a side sectional view of a wave guide according to an embodiment of the invention
  • Figure 3 is a front sectional view of the wave guide of Figure 2;
  • Figure 4 is a side sectional view of a wave guide according to an embodiment of the invention
  • Figure 5 is a front sectional view of the wave guide of Figure 4;
  • FIG. 6 is an exploded view of a microwave emitter in accordance with an embodiment of the invention.
  • Figure 7 is a perspective view of the assembly of Figure 6 showing how the components thereof fit together;
  • Figure 8 is a perspective view of the assembly of Figures 6 and 7 in completed form;
  • Figure 9 is a schematic diagram of another embodiment of probe assembly.
  • Figure 10 is a perspective view of a preferred embodiment of probe unit of the monitor assembly, fitted to a person's ear;
  • Figures 11 and 12 are perspective views of two embodiments of monitor assembly, one using a wired connection to a control unit and the other a wireless coupling to these components;
  • Figure 25 is a schematic system diagram of the principal components forming the hydration monitoring device of the preferred embodiments.
  • Figure 14 is a graph showing the microwave absorption in liquid water;
  • Figures 15 to 26 are graphs of preliminary experiments showing the transmission loss as a function of weight of microwave radiation passing through a cellulose sponge saturated with pharmaceutical grade saline solution at frequencies of 5GHz, 6GHz, 12.4GHz, 13GHz, 14GHz, 15GHz, 16GHz, 18GHz, 20GHz, 22GHz, 24GHz and 26GHz respectively;
  • Figure 27 is a graph showing the relationship between the absorption coefficient of liquid water and the observed slope of the transmission loss for the preliminary experiments of Figures 15 to 26;
  • Figures 28 to 33 show the results for a prototype, showing transmission loss as a function of weight of a sponge saturated with controlled amounts of pharmaceutical grade saline for a microwave signal at frequencies of 13GHz, 14GHz, 15GHz, 16GHz, 17GHz and 18GHz respectively;
  • Figure 34 is a graph showing the relationship between the absorption coefficient of liquid water and the observed slope of the transmission loss for a prototype
  • Figure 35 is a graph showing transmission loss of an athlete exercising and losing weight as a result of loss of hydration.
  • the embodiment of hydration monitoring device shown comprises a microwave emitter 12 and a microwave receiver 14. Both the microwave emitter 12 and the microwave receiver 14 are provided as free space coupling elements such as a horn antenna, waveguide launch or antenna structure.
  • the microwave emitter 14 preferably comprises a microwave source 18 and a shielding element 16.
  • the microwave receiver 14 preferably comprises a shielding element 20 and a microwave detector 22.
  • the microwave emitter 12 and microwave receiver 14 can also be provided as unshielded elements, such as patch antennas.
  • the microwave emitter and receiver can also be provided as a coax cavity or a waveguide.
  • shielding elements 16, 20 which are waveguides arranged to produce a parallel waveform.
  • the waveguides comprise a metallic casing 36, preferably aluminium or copper, which partially encloses an area containing an antenna 40 which emits or detects a microwave signal.
  • the casing 36 has an opening 38 on the axis along which the microwaves are intended to travel.
  • the casing 36 can be cylindrical, as shown in these Figures, with an axis corresponding to the axis along which the microwaves are intended to travel.
  • the casing may be cuboidal such that its cross-section taken through a plane perpendicular to the axis of microwave travel is square.
  • the opening 38 can be circular, but is preferably square and formed by the cubical casing 36 being provided with only five sides so that one side is open.
  • a cuboidal casing 36 enables the waveguide to be made smaller than a cylindrical casing.
  • a high dielectric constant therefore enables the size of the waveguide to be reduced in comparison to an air-filled cavity.
  • the dielectric medium 42 is PTFE with a dielectric constant of 2.5.
  • the waveguides can be manufactured as blocks of PTFE to five sides of which are attached sections of copper foil which are soldered together to provide the casing 36.
  • the blocks of PTFE can then be drilled to suit the core diameter of a coaxial cable to provide the electrical signal and the braided exterior of the cable can be soldered to the copper foil.
  • FIGS. 6 to 8 show a series of views of an early prototype of probe useful in the description of the components use din the preferred embodiments.
  • the structure of this example is similar for both the emitter 12 and the receiver 14, although the description below focuses solely upon the emitter 12 for the sake of conciseness.
  • the cover comprises a front part 50 and a rear part 52, in this example made of a plastics material, and typically shaped to be comfortable against the skin.
  • the front cover part 50 and the rear cover part 52 can be secured together to contain the waveguide.
  • the front cover part 50 comprises an opening 54 in the centre of its front face through which the microwave signal can pass.
  • An internal cover 56 is provided to sit within the opening 54 and comprises a lip 58 to abut against the inside surface of the flange of the front cover part 50, to prevent the internal cover 56 from falling out through the opening 54.
  • the internal cover 56 can be made of the same dielectric material 42 which fills the casing 36 of the waveguide, which is preferably PTFE.
  • Resilient elements such as springs 60 are provided between the rear cover part 52 and the internal cover 56 to ensure that the lip 58 is held in abutment with the flange of the front cover part 50.
  • the waveguide comprises the dielectric material 42 and casing 36 as described above. These are contained within a mid-assembly 62, which may be made of aluminium.
  • the mid-assembly 62 is provided with protrusions 64 which abut against the cover 50, 52 and serves to hold the waveguide securely in a central position within the emitter 12.
  • the mid-assembly also comprises a channel 66 for the insertion of a coaxial cable comprising the antenna 40.
  • the coaxial cable and antenna 40 are held securely in position in the channel by a clamping plate 68.
  • the coaxial cable is preferably soldered to the clamping plate 68, which in turn is soldered to the mid-assembly 62.
  • the microwave emitter 12 and microwave receiver 14 are attached to a frame or other housing (not shown) able to be secured to a human or animal such that the microwave emitter 12 and receiver 14 are placed either side of a human or animal body part.
  • the emitter and receiver are arranged in use such that a primary microwave signal 11 emitted from the microwave emitter 12 passes through the body part to receiver 14. In a preferred embodiment, this is achieved by having the microwave emitter 12 and microwave receiver 14 arranged such that they face each other but are separated by a small gap into which the human or animal body part can be placed. This arrangement is shown in Figure 1. Another embodiment is shown in schematic form in Figure 9.
  • the emitter 12 and receiver 14 are arranged on the same side of the human or animal body part 28 when they are in position.
  • On the other side of the human or animal body part 28 and across a gap 13 is a reflector plate 30.
  • the emitter 12 and the receiver 14 are configured to be at an angle with respect to each other so that a primary microwave signal 11 emitted from the microwave emitter 12 and reflected from the reflector plate 30 will reach the microwave detector 14.
  • This embodiment has the advantage that the primary microwave signal 11 passes through the human or animal body part 28 twice, in slightly different locations. It is therefore able to average out anomalies that may occur in an arrangement in which the microwave signal 11 passes only once through the human or animal body part 28.
  • this gap 13 should preferably be no more than around 8mm across, more preferably no more than around 6 mm and most preferably no less than 3mm across. In one embodiment, the gap is 5.4mm across.
  • the gap between the components can be preset, and is preferably so, but it is not excluded that the probe could be adjustable so as to give a gap of varying size to accommodate different physiologies.
  • the probe can be fitted to any part of the human or animal body which is composed substantially of blood.
  • the body part 28 is a physiologically simple part of the body which is substantially devoid of muscle, bone or major organs.
  • the preferred body part 28 is the ear and, in the case of humans, most preferably the earlobe.
  • the body part 28 can be other extremities of the body that are devoid of muscle, bone or major organs, such as the webbing between the fingers or toes.
  • the probe can be secured to the body part by any of a variety of methods temporary adhesive, with a clip holding the emitter and receiver units or the emitter/receiver units and reflector element.
  • a clip should not impart a force which might cause causes pain or restrict blood flow to the body part being tested.
  • the probe can additionally be secured, for example in the case of a human ear, by an appropriate ear fitting one which a preferred embodiment is shown in Figure 10. Referring to Figure 10, the probe has an ergonomic shape designed to hold onto the ear 28, in such a manner that it remains securely located and yet is not uncomfortable.
  • a hook element 26 locates in to the bottom of the outer ear with the emitter 12 and receiver 14 positioned either side of the earlobe.
  • the probe housing 32 extends to below the earlobe and includes, in this example, a cable which is coupled to a control and indicator unit, described below.
  • the probe housing 32 has rounded surfaces able to conform to the lower ear shape and which do not present any sharp surfaces which might cause discomfort or injury.
  • the hook element 26, in conjunction with the positioning of the emitter 12 and receiver 14 units close to the ear lobe are sufficient to hold the probe in position even during sport, exercise or work.
  • the probe could be in the form of a sprung arm arrangement in which the emitter 12 and probe 14 are located on respective sprung arms and thus held to the earlobe by the force of the spring, in a manner akin to some pinless earrings.
  • the emitter 12 and receiver 14 units could include magnetic elements to cause these to be attracted to one another.
  • the microwave emitter 12 is configured to emit microwave radiation within a range of 0.1GHz to 110GHz, more preferably in the range of 3GHz to 110GHz, even more preferably in the range of 10GHz to 26GHz.
  • the preferred embodiments us a range of 13GHz to 18GHz or of 14GHz to 20GHz. This range, it has been found, is able to balance error (which is high at low frequency) and absorption (which is too high at high frequency).
  • the emitter 12 preferably emits the microwave signal at a power in the range from 200 ⁇ W to 1W.
  • the device 10 can be configured to alter the specific power in response to the level of signal received at the receiver 14. More preferably, the power output is in the order of milliwatts.
  • the microwave emitter 12 and the microwave receiver 14 are preferably coupled to a separate processing and control unit 24.
  • the processing and control unit 24 provides closed loop control of the microwave power, phase, frequency and modulation.
  • the processing and control unit comprises some of the functionality of a Vector or Scalar Network Analyser (VNA and SNA) to make transmission and/or reflection absorption measurements similar to S 2 i and Sn methodologies.
  • VNA and SNA Vector or Scalar Network Analyser
  • the processing and control unit preferably includes conventional electronic processing components programmed to provide calibration and normalisation of the system, and to determine the hydration of the blood of the human or animal body part 28.
  • the hydration is preferably calculated from a calibration curve of hydration against microwave loss. Such a calibration curve can be determined from a plot of microwave losses against corresponding readings from blood tests.
  • the processing and control unit 24 can be provided in different forms. In one embodiment, it is integral with the probe. In other embodiments, the unit 24 is separate from the probe. Figure 11 shows the processing unit 24 linked to the probe by a wire or cable, while Figure 12 shows the unit 24 being coupled to the probe by a wireless connection. In both embodiments there is preferably also a coupling, advantageously wireless, to a display of a wrist carried device such as a multi function watch (the latter may also provide other physiological measures such as heart rate and so on).
  • the control unit 24 is coupled to a remote processing unit.
  • the remote processing unit can be, for example, a mobile telephone, a Personal Digital Assistant (PDA), a watch, a computer, or other means employing electronic processing.
  • the means of coupling the control unit to the remote processing unit can be any conventional means of communication such as a wired connection such as USB, Ethernet, or a wireless connection such as Wi-Fi or Bluetooth.
  • the remote processing unit receives data from the control unit and on the basis of the data, it performs calibration and normalisation calculations, and transmits instructions to the control unit. In response to the received instructions, the control unit adjusts if necessary the microwave power, phase, frequency and modulation.
  • the minimal components typically comprise a power source such as a battery; circuitry to control the operation of the microwave emitter 12 and microwave receiver 14; and preferably a wireless communication device for receiving instructions from and transmitting data to a remote processing unit such as those described above.
  • data storage is provided on the probe such that a substantial amount of data can be accumulated before it is transferred to a remote processing unit. This can conserve power which might otherwise be used in constant use of the communication means.
  • the processing unit can offer a variety of functions such as those shown in Figure 13.
  • the processing unit comprises a simple set of warning sounds and/or lights which are activated to warn the user in response to the processing unit determining a low level of hydration.
  • Other embodiments include a liquid crystal display for providing the user with a percentage hydration, and data storage to keep a record of hydration levels over time.
  • the processing and control unit 24 can thereby provide power to the heart rate monitor, and the heart rate monitor can provide a signal indicative of the heart rate to the processing and control unit 24.
  • the microwave emitter 12 is preferably configured to provide a microwave reference signal 34 to the microwave receiver 14 in addition to the primary signal 11. This can be achieved by direct coupling between the microwave emitter 12 and the microwave receiver 14. However, preferably, this is achieved by arranging the microwave emitter 12 such that it can emit a second microwave signal to the microwave receiver 14 which does not pass through the body part 28. This is implemented in the embodiment depicted in Figure 10, 11 and 12 by providing either an emitter 12 and a receiver 14 which extend below the lobe of the ear 28 or by providing a reference emitter and a reference receiver located below the end of the earlobe.
  • the emitter 12 is arranged to emit two microwave signals, the primary signal 11 through the lobe of the ear 28 and the reference signal 34 across the empty gap 13.
  • the primary 11 and reference 34 signals are emitted simultaneously so that their comparison allows all effects other than absorption in the body part 28 to be removed from the hydration calculations.
  • the microwave signal may be modulated or pulsed. Modulation of the microwave emitter 12 by amplitude, phase, frequency or other common modulation scheme may be used to enable the microwave receiver 14 and the processing and control until 24 to improve the dynamic range of detection and thus sensitivity of the device 10. Modulation is commonly used for the purpose of enhancing the dynamic range and sensitivity of many industrial instruments, an example is the lock-in amplifier.
  • the microwave signal may be pulsed to reduced the average power emitted by the device 10 and reduce exposure of the body part 28 and in addition increase the battery life of the device 10.
  • the time between readings is more than 30 seconds; preferably a set of readings is not taken more frequently than every minute. When readings are not being taken, the device can advantageously be switched off to conserve power.
  • the device is preferably waterproof.
  • the device 10 works in the following way in the preferred embodiment. For the purposes of the following description, it is assumed that the user is a sports person using the device 10 to monitor their hydration during exercise. However, methods analogous to that described below can be employed for other uses for the monitoring of the level of hydration of a human or an animal.
  • the user attaches the device 10 to his ear and secures it in place such that the lobe of his ear 28 is correctly aligned in the gap 13 between the microwave emitter 12 and the microwave receiver 14 (or between the microwave emitter 12 and the reflector plate 30 for embodiments such as that depicted in Figure 9).
  • the user then switches the device 10 on by operation of the control unit.
  • the control unit causes the microwave emitter 12 to emit a primary microwave signal 11 through the earlobe 28 within the preferred power and frequency ranges described above.
  • the microwave emitter 12 emits a signal at a single frequency, whereas in other embodiments the microwave emitter 12 emits a signal at multiple frequencies or sweeps the frequency between two limits.
  • the microwave emitter 12 does not sweep frequencies but uses at most 5 distinct frequencies, most preferably 2 or 3 distinct frequencies. Recording absorption through the body part at multiple frequencies allows comparison with the expected water absorption with frequency data, for example as shown in Figure 14, for calibration and improved resolution calculation.
  • the availability of redundancy in frequency selection may be needed if a subject's body part 28 has higher than expected levels of absorption at one frequency which has operational benefits.
  • the use of multiple or swept frequencies within a final device increases both the components complexity and cost of manufacture, which may be prohibitive for some applications but not others.
  • the microwave emitter 12 simultaneously emits a reference signal 34 corresponding in power, phase, frequency, and modulation to the primary microwave signal 11 across the gap 13 but not through the earlobe 28, as described above.
  • the microwave signals 11, 34 are detected by the microwave receiver 14 and the magnitude and phase change of the signals are calculated.
  • An advantage of the embodiments in which a reference signal 34 is provided separately to the primary signal 11 is that the reference signal 34 provides a useful calibration signal.
  • a comparison of the received reference signal and the received primary signal can show how much of the signal that has passed through the body part 28 has been absorbed by the water in the body part 28, and how much is a result of, for example, attenuation, scattering or interference from the device 10 electronics and coupling to the body part.
  • a comparison of the primary 11 and reference 34 signals can effectively remove effects other than those caused by the absorption in the body part 28.
  • control unit acquires only raw and unprocessed data, and transmits them via one of the media described above to the remote processing unit for analysis.
  • the remote processing unit is in the form of a watch, and provides a percentage hydration.
  • the processing unit comprises data storage
  • the absolute hydration levels over time can be recorded and the processing unit can perform statistical analysis on them to determine a maximum, minimum and optimal hydration level for that particular user. This can be converted into a percentage score, and can be supplemented with a light unit, a sound unit, and/or a vibratory unit to warn the user when his hydration level is falling significantly below the optimum or other threshold level.
  • an early warning signal of a non-optimal hydration level such as this can help an athlete maintain peak performance.
  • it can enable an athlete to become aware of how his body responds to exercise and the intake of fluids such that he can become used to the quantity and frequency with which he needs to drink in order to maintain peak performance. This can be particularly beneficial in training for competitive situations in which the device would not be worn during the competition itself.
  • the data from the data storage of the processing unit can be downloaded onto a computer via a conventional communication link for more in depth analysis by appropriate software.
  • the hydration monitor is supplemented by a heart rate monitor.
  • the heart rate monitor provides data which can be transmitted and/or stored together with the hydration data in the manner described above. Heart rate can be indicative of physical exertion.
  • the heart rate data can be downloaded for example to a computer together with the hydration data.
  • the computer can determine a correlation to show how the hydration level of a user responds to physical exertion of different intensities and/or can present the data in a graphical format for the user to study to develop a personal plan for the optimum intake of fluids.
  • the data storage can also be used to assist in calibration. For example, since hydration levels do not change suddenly, the processing unit can determine based on the data stored in the data storage if there has been a sudden change in detected absorption. It can then attribute this to a movement of the device 10 such that the microwave signal now passes through a slightly different part of the body. This can be due to, for example, the device having fallen off and then been put back in a slightly different position. Having determined this, the processing unit can recalibrate the processing of the data by deeming the new measured absorption to correspond to the same level of hydration as for the previous data reading.
  • the device can predict when a user's hydration is likely to drop and communicate this to the user by one of the means described above. Such prediction enables a user to take on more fluid in sufficient time to prevent the drop occurring. Such a prediction can also be made by calculating the rate of change of the hydration level and thereby calculating the expected time until the hydration level falls below a preferred range.
  • An advantage of the embodiments taught herein is that they can provide a real time, non-invasive hydration monitor providing a measurement comparable to a blood test.
  • a body part which is thin By selecting a body part which is thin, hydration can be detected by the absorption of microwaves in transmission without requiring the microwave signal to be of sufficient power to carry any health risks for the subject.
  • absorption of the microwaves by that body part will be substantially as a result of absorption by the water in the blood.
  • a human ear lobe since it is near to the head, it has a very active flow of blood and most other surrounding tissue is fat which has a constant very low moisture content which can be accounted for in the calibration settings. Accordingly, the error level owing to absorption by nearby elements is minimised and the hydration calculation is accurate and reliable.
  • a portable, cheap, robust, easily used hydration monitor has wide applications in professional and amateur sports, in healthcare, in care for the elderly and disabled, and in veterinary care.
  • Such a device can provide significant advantages for the situations highlighted above in which the hydration level of a person or animal can change rapidly, such as in the performance of rigorous exercise, for example for an athlete or a racehorse, or in extreme conditions, such as for military service personnel.
  • the device is beneficial for people or animals, for example patients in hospitals or animals in veterinary procedures, who are either unable to communicate their dehydration or who are simply unaware of it.
  • the preliminary experiments of the project were devoted to measurements of transmission loss in a phantom with the aim of determining the optimum operating frequency of the proposed device.
  • the chosen phantom was a cellulose sponge saturated with pharmaceutical-grade saline solution so as to simulate the fluid content of living tissues (comprising blood and intercellular serum).
  • Measurements were carried out by varying the saline content in the sponge while recording the transmission loss as a function of the sponge weight.
  • the loss of a dry sponge was ⁇ 0.2 dB at all frequencies.
  • Patch antennas were used for experiments at 5 and 6 GHz; while at high frequencies horn antennas were employed.
  • the transmission loss through the phantom was measured by a VNA.
  • Microwave absorption in water increases steeply with frequency and is directly related to the number of water molecules, making it possible to obtain the water content by measuring the transmission loss.
  • Low absorption coefficients and thus loss, at frequencies below 3 GHz make the measurement of water content in a body part 28 with a thickness less than 8 mm more challenging than at frequencies above 3 GHz, it is therefore preferential to operate the device 10 above 3 GHz.
  • operation below 3 GHz is possible and may be utilised.
  • T Transmission through an absorbing material is described by the Beer-Lambert law: Wherein IT and I 0 are respectively the transmitted and incident intensity, u is the absorption coefficient, C is the concentration of the absorbing species, and t is the sample thickness.
  • IT and I 0 are respectively the transmitted and incident intensity, u is the absorption coefficient, C is the concentration of the absorbing species, and t is the sample thickness.
  • the coefficient T represents the transmission efficiency (or the loss factor) between the emitter and the receiver.
  • the measured loss in the absorbing material is expected to be linear with water concentration, and therefore with the weight of the material. The slope will be proportional to the absorption coefficient.
  • a large absorption coefficient will result in a greater differentiation, and may therefore give a better resolution in the measurement of water concentration.
  • the transmission loss is very high, the system will require high sensitivity and a low noise floor in order to provide an accurate measurement.
  • Figures 15 to 26 plot the transmission loss results as a function of weight at different frequencies for the preliminary experimental set-up described.
  • the scatter in the data is due largely to the difficulty of ensuring a uniform distribution of water across the area of the sponge.
  • Different symbols represent separate experimental runs. Solid lines are linear fits to the data.
  • Equation 2 implies that a linear relationship is expected between the slopes of the linear fits in Figures 15 to 26 and the absorption coefficient shown in Figure 14. This is indeed demonstrated by the data in Figure 27, showing the relationship between the absorption coefficient of liquid water and the observed slope of the transmission loss, and confirms the reliability of microwave hydration method measurements.
  • the slope of the linear relationship in Figure 27 depends on the sample parameters such as thickness and area.
  • a prototype devices for measuring microwave transmissions through a human earlobe was designed and tested. The device was symmetrical with respect to transmitter/receiver and used purpose-built microwave launch cavities. The device was tested using a VNA and was operated at 13-18 GHz, which has been identified as a preferred frequency range for microwave hydration measurements.
  • the prototype produced a stable, highly reproducible near-flat reference signal across its bandwidth (the reference signal was recorded in the absence of any absorber in the air gap between the transmitter and the receiver).
  • Tests on human volunteers revealed that transmission loss measured by the prototype was affected by device positioning on the ear. The conclusions from the test on human volunteers were twofold:
  • microwave absorption loss in the human ear is in the range of values which can be measured sufficiently accurately with easily available instrumentation.
  • Figure 34 plots the relationship between the absorption coefficient of water and the slopes at different frequencies as obtained in Figures 28-33. Deviations from linearity in Figure 24 of the data at 15 and 16 GHz indicate effects of transmitter-receiver coupling at these frequencies, which relate to the properties of the microwave cavity launcher.
  • the weight of the athlete was monitored at intervals during the exercise. Concurrently, the loss readings given by the device were recorded throughout the exercise period.
  • the noise in the data is caused primarily by the poor fit of the prototype on the ear. As the athlete moved, the position of the device on the earlobe shifted frequently and randomly, resulting in different areas of the earlobe being measured. Moreover, the angle between the earlobe and the device contacts also varied uncontrollably.
  • a design of probe as that shown in Figures 10 to 12 is expected to overcome such difficulties, by in effect clipping the probe to the ear and holding the earlobe within the two sides of the device which hold the emitter and receiver or emitter/receiver and reflector. If necessary, the two sides of the device could be slightly sprung to hold these against the opposing sides of a user's earlobe, even as the user moves on exercising, for instance.
  • probe housing Although the preferred form of probe housing is shown in Figures 10 to 12, other embodiments are envisaged, as disclosed above. It may also be preferable in some instances to have a probe housing with a hook which hooks over and behind the outer ear. The ultimate choice of probe design may be dependent upon application and user preference.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Surgery (AREA)
  • Biophysics (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Veterinary Medicine (AREA)
  • Medical Informatics (AREA)
  • Molecular Biology (AREA)
  • Physics & Mathematics (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Otolaryngology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)

Abstract

Cette invention concerne une méthode de mesure de l’hydratation du sang chez l’homme ou l’animal,qui consiste à émettre un rayonnement hyperfréquence dans une partie corporelle (28), par exemple le lobe de l’oreille chez l’homme, à détecter le rayonnement hyperfréquence quittant cette partie corporelle (28), à calculer l’absorption du rayonnement hyperfréquence par cette partie corporelle (28) et à déterminer l’hydratation du sang d’après l’absorption du rayonnement hyperfréquence.
PCT/GB2010/001260 2009-06-26 2010-06-25 Appareil de surveillance de l’hydratation et méthode associée WO2010149984A1 (fr)

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GB0911143A GB0911143D0 (en) 2009-06-26 2009-06-26 Hyrdation monitoring device and method
GB0911143.6 2009-06-26

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WO2016118892A3 (fr) * 2015-01-22 2016-09-15 Boston Scientific Scimed, Inc. Dispositif de contrôle d'équilibre non invasif des liquides et des électrolytes
DE102015119180A1 (de) * 2015-11-06 2017-05-11 Infineon Technologies Ag Elektromagnetischer Wellensensor, um einen Hydrationsstatus eines Körpergewebes in vivo zu bestimmen

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US20080234600A1 (en) 2004-03-04 2008-09-25 Leon Thomas Lee Marsh Hydration Monitor
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Cited By (5)

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Publication number Priority date Publication date Assignee Title
WO2016118892A3 (fr) * 2015-01-22 2016-09-15 Boston Scientific Scimed, Inc. Dispositif de contrôle d'équilibre non invasif des liquides et des électrolytes
EP3636160A1 (fr) * 2015-01-22 2020-04-15 Boston Scientific Scimed Inc. Dispositif de contrôle d'équilibre non invasif des liquides et des électrolytes
US11045164B2 (en) 2015-01-22 2021-06-29 Boston Scientific Scimed, Inc. Noninvasive fluid and electrolyte balance monitor
DE102015119180A1 (de) * 2015-11-06 2017-05-11 Infineon Technologies Ag Elektromagnetischer Wellensensor, um einen Hydrationsstatus eines Körpergewebes in vivo zu bestimmen
US11039769B2 (en) 2015-11-06 2021-06-22 Infineon Technologies Ag Electromagnetic wave sensor for determining a hydration status of a body tissue in vivo

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