WO2009072024A1

WO2009072024A1 - Forehead mounted biometric sensor with motion artifact reducing system and method

Info

Publication number: WO2009072024A1
Application number: PCT/IB2008/054842
Authority: WO
Inventors: William Crone
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2007-12-05
Filing date: 2008-11-18
Publication date: 2009-06-11

Abstract

A biometric sensor includes an optical transmitter and optical receiver facing a patient's skin and an accelerometer which are attached to a headband for positioning on the patient's forehead. An optical signal is emitted from the optical transmitter onto the patient's forehead and reflected signals are received at the optical receiver. The accelerometer produces an output corresponding to motion of the patient. The output of the optical receiver is processed to extract biometric information and is filtered according to the output of the accelerometer to reduce artifacts in the optical receiver output caused by movement of the patient.

Description

FOREHEAD MOUNTED BIOMETRIC SENSOR WITH MOTION ARTIFACT REDUCING SYSTEM AND METHOD

[001] This invention generally relates to systems and methods for obtaining biometric information and, more particularly, for obtaining patient biometric information from the forehead of a patient.

[002] In an emergency situation, a patient must often be moved quickly to transport the patient to a hospital for treatment. When the emergency event is cardiac arrest, the patient may also be coupled to an automatic external defibrillator (AED) for treatment. An AED is programmed to monitor the patient's heart function and to administer a shock at appropriate times. However, such patient movement can result in inaccurate readings from sensors used to measure the patient's vital signs.

[003] In view of the foregoing it would be advantageous to provide a means for detecting and compensating for patient movement in emergency settings or in other monitoring settings where the patient may be moving or is being handled by rescue personnel.

[004] In accordance with the principles of the present invention a system is provided for monitoring patient biometric information. The system includes a headband adapted to secure to the forehead of a patient with an accelerometer attached to the headband. An optical transmitter and optical receiver are also attached to the headband. The optical transmitter is positioned to transmit optical signals into the patient's forehead and the optical receiver is positioned to receive at least a portion of the optical signals reflected from the patient's forehead. A signal processor circuit is electrically coupled to the accelerometer and the optical receiver. The signal processor circuit is operable to produce an output related to the patient biometric information and based on an output of the optical receiver and an output of the accelerometer.

[005] In another aspect of the invention, the system includes a force sensor and a visual indicator. The visual indicator is activated when the force indicated by the force sensor falls within a range of values corresponding to tension in the headband suitable for maintaining the electrodes in contact with the patient's forehead while not overly restricting blood flow. [006] In another aspect of the invention, the processed output of the optical receiver is compared to threshold data to evaluate the patient's vital signs. If the comparison indicates that the patient requires attention, then a visible or audible alert is activated either on the headband or a remote monitoring device. [007] Another aspect of the invention provides a method for monitoring a patient's biometric information. The method includes emitting an optical signal onto the patient's forehead and receiving a reflected optical signal and converting the reflected optical signal to a receiver output. Patient movement is detected by an accelerometer positioned adjacent the patient's forehead to generate an accelerometer output. The receiver output is filtered according to the accelerometer output to remove information from the receiver output caused by patient movement and the filtered receiver output is processed to extract patient biometric information. [008] In the drawings:

[009] Figure 1 is a schematic representation of a patient wearing a headband suitable for monitoring biometric data with reduced motion artifact effects in accordance with an embodiment of the present invention.

[010] Figure 2 is a top plan view of the headband of Figure 1.

[011] Figure 3 is a schematic block diagram of a system for monitoring biometric data while reducing motion artifact effects in accordance with an embodiment of the present invention. [012] Figure 4 is a flow diagram of a method for reducing motion artifact effects in biometric data in accordance with an embodiment of the present invention. [013] Figure 5 is a top plan view of an alternative embodiment of a headband for monitoring biometric data with reduced motion artifact effects in accordance with another embodiment of the present invention. [014] Figure 6 is a schematic block diagram of an alternative system for monitoring biometric data with reduced motion artifact effects in accordance with an embodiment of the present invention.

[015] Figure 7 top plan view of an alternative embodiment of a headband for monitoring biometric data with reduced motion artifact effects in accordance with another embodiment of the present invention.

[016] Figure 8 is a schematic block diagram of an alternative system for monitoring biometric data with reduced motion artifact effects in accordance with an embodiment of the present invention.

[017] Referring to Figure 1, a system 10 for measuring blood flow characteristics includes a headband 12 worn around the head of a patient 14. The headband 12 is preferably made of a biocompatible fabric such as Lycra/Nylon that is stretchable and comfortable to wear. The headband 12 may extend completely around the patient's head, be adhered to the patient's forehead by an adhesive, or partially encircle the patient's head and be maintained in place by the elasticity of the headband 12 biasing itself against the head of the patient.

[018] The headband 12 includes at least one optical transmitter 16, such as a light- emitting diode (LED), and at least one optical receiver 18 facing the skin of the patient's forehead. The optical transmitter 16 is disposed on the headband such that it transmits light through the skin of the patient's forehead. An optical receiver 18 such as an optical photodiode receives light reflected or scattered from the tissue and bone of the patient 14 back through the skin. One effective configuration for the transmitter and receiver is to surround a grouping of several transmitters on all sides with receivers. If the headband moves or lifts partially away from the forehead, a receiver on one side of the transmitter may become ineffective. However a receiver on the other side may still be in sufficient contact with the skin to receive adequate reflected or scatter light for an accurate measurement.

[019] In one embodiment, the optical transmitter 16 transmits light having a wavelength distribution about equal to the isosbestic wavelength of oxy- and deoxyhemoglobin in order to measure blood perfusion in a manner that is substantially unaffected by blood oxygenation. For example, the optical transmitter 16 may transmit light having wavelengths between 805 and 810 nanometers. Other isobestic points may also or alternatively be used, such as 569 nanometers.

[020] An accelerometer 20 is mounted to the headband 12. In a preferred embodiment, the accelerometer 20 is a three-axis accelerometer. One and two axis accelerometers may also be used. The accelerometer 20 may measure one or both of translational and rotational movement. For example, the accelerometer 20 may measure acceleration for up to three translational axes and up to three rotational axes.

[021] The outputs of the optical receiver 18 and accelerometer 20, or data derived therefrom is transmitted to a monitoring device 22. The monitoring device 22 may process, display, and/or record the outputs or data. In some embodiments, the monitoring device 22 is controlled based on the outputs or data. For example, the monitoring device 22 may be an automatic external defibrillator (AED) which is programmed to deliver defibrillating shocks according to a heart rate measured using the optical receiver 18.

[022] In other embodiments, the monitoring device 22 is a cardiopulmonary resuscitation (CPR) device that provides instructions regarding the administration of CPR, provides feedback, and/or records CPR performance. The outputs of the optical receiver 18 and accelerometer 20 may be used to measure blood profusion in order to assess the effectiveness of CPR. Use of a headband to provide blood profusion information is particularly useful in the context of CPR. Patient movement due to chest compressions is not as evident at the patient's forehead as it is at the thorax. Furthermore, use of an accelerometer can provide a measurement of patient motion that facilitates removal of artifacts caused by patient motion during CPR.

[023] Referring to Figure 2, the optical transmitter 16 and receiver 18 may mount to the headband 12 such that they are positioned between the headband 12 and the patient's forehead. In some embodiments, an indicator 24, such as an LED, indicates the location of the optical transmitter 16 and receiver 18 in order to aid an operator in placing the headband 12 on the patient 14. In other embodiments, the indicator 24 is a visible marker printed or otherwise secured to the headband 12. The headband may also include a piezoelectric loudspeaker which provides audio feedback to a rescuer.

[024] Referring to Figure 2, in a preferred embodiment, the headband 12 encircles the patient's head, as shown, and includes a fastener 26 for securing ends 28a, 28b of the headband 12 to one another. In some embodiments, the fastener 26 is a hook and loop fastening system such as VELCRO^®. Other fastening systems such as buckles, snaps, a knot, or the like may be used to secure the ends 28a, 28b to one another. In other embodiments, the headband 12 is a continuous loop with elastic portions to enable the headband 12 to bias itself against the patient's head. In other embodiments, the headband 12 includes both elastic portions and a fastener 26.

[025] A controller 30 is secured to the headband 12 and includes circuits for driving the optical transmitter 16 and detecting the output of the optical receiver 18. The controller 30 may be coupled to other devices, such as the monitoring device 22 by means of wires or wirelessly to transmit measurements and and/or to receive control signals. A power source 32, such as a battery, is also secured to the headband 12. In one embodiment the controller and the battery are connected to or mounted on wiring such as flex circuitry located inside the headband which will bend as the headband conforms to the shape of the patient's head. In an alternative embodiment, the power source 32 and/or the controller 30 are separate from the headband 12 and are electrically coupled to the headband 12 by means of wires.

[026] Referring to Figure 3, an exemplary controller 30 includes a driving module 34.

The driving module 34 provides signals to activate the optical transmitter 16. In a preferred embodiment, the driving module 34 periodically activates the optical transmitter 16 with intervals between activations. The power source 32 provides an energizing potential to accelerometers 20.

[027] The illustrated controller 30 further includes a sensing module 36 for receiving outputs from the optical receiver 18 and the accelerometer 20. The sensing module 36 amplifies and conditions the outputs. For example, the sensing module 36 may process the output of the optical receiver 18 to produce the appropriate signals in order to identify portions of the output corresponding to activation of the optical transmitter 16 and portions corresponding to ambient light. In a constructed embodiment an automatic gain control circuit (AGC) amplifies the sensed signals as a function of the force signal discussed below to maintain the signals within a desired range of signal levels.

[028] The outputs detected by the sensing module 36 are provided to a filtering module 38. The filtering module 38 adaptively filters the output of the optical receiver to remove artifacts caused by patient movement. The filtering module 38 may therefore calculate adaptive filter coefficients based on the output of the accelerometer 20 and use the coefficients to filter the output of the optical receiver 18 and produce an output having reduced noise due to patient movement.

[029] The output of the filtering module 38 is provided to a processing module 40.

The processing module 40 processes the output to extract biometric data such as the volume of blood profusion, the patient's heart rate, or the like. A transmitting module 42 transmits the biometric data wirelessly (e.g., Bluetooth), or over wires, to the monitoring device 22.

[030] Referring to Figure 4, a method 44 for monitoring heart activity using the system 10 of Figures 2 and 3 includes transmitting an optical signal at step 46 and receiving an accelerometer output at step 48. At step 50, the transmitted signal is received after at least a portion thereof is reflected back from the vascular structure of the patient's forehead. At step 52 the output of the accelerometer is processed to calculate adaptive filter coefficients effective to reduce errors caused by the patient movement that induced the accelerometer output. At step 54, the signal received at step 50 is filtered using the coefficients calculated at step 52. At step 56, the patient's biometric data is determined from the filtered signal. Step 56 may include measuring one or more of blood perfusion, blood oxygenation, carbon dioxide, carbon monoxide, pH, and nitric oxide.

[031] Referring to Figure 5, in this embodiment the system 10 further includes a force sensor 58, such as a piezo-resistive device or the like, secured to the headband 12. In a preferred embodiment, the force sensor is embodied as a piezoelectric film positioned on the headband 12 between the headband 12 and the patient's skin. The force sensor 58 may detect one or both of tension in the headband 12 and force of the headband 12 against the head of the patient 14. Monitoring of one or both of tension and force helps the operator to secure the headband 12 to the head of the patient 14 without constricting blood flow through vascular structures beneath the headband 12 and while still maintaining a good optical coupling between the patient's forehead and the optical transmitter 16 and optical receiver 18. Referring to Figures 5 and 6, the force sensor 58 is coupled to the controller 30, which is further coupled to one or more indicators 60, which may be embodied as an audible alarm or LED. The controller 30 includes a tensioning module 62 which activates one of the one or more indicators 60 when an output from the force sensor 58 indicates that the tension in the headband 12 lies within a range of values having a likelihood of maintaining optical transmitter 16 and optical transmitter 18 optically coupled with the patient's forehead without excessive constriction of blood flow. The controller 30 deactivates the activated indicator 60 when the tension exceeds or falls below the acceptable range of values, and the force signal is used by the ACG circuit previously discussed to maintain the level of the sensed optical signals when the tension is within the acceptable range. Alternatively, the controller 30 may activate a different indicator if the tension exceeds or falls below the acceptable range of values. In yet another alternative, the controller 30 activates the same indicator when tension exceeds the acceptable range but in a different manner. For example, the 30 may cause an indicator 60 embodied as an LED to remain off where tension is below an acceptable range, to emit steadily if the tension lies within the acceptable range, and to emit intermittently if tension exceeds the acceptable range. The output of the force sensor 58 may be utilized by the controller on the headband or transmitted and utilized by another device such that the tension in the headband 12 may be used in addition to the AGC function to interpret data transmitted from the headband 12. [033] Referring to Figure 7, in this embodiment the headband 12 includes a plurality of optical transmitters 16a- 16c and optical receivers 18a- 18c each adapted to measure a different biometric characteristic such as blood perfusion, blood oxygenation, carbon monoxide, or nitric oxide. Carbon dioxide level and pH may be sensed with a biochemical sensor such as an optode. Accordingly, the optical transmitters may emit light having a wavelength suitable for measuring biometric characteristics and the corresponding optical receivers may be sensitive to the same wavelength. The headband 12 in this embodiment incorporates other sensors such as a thermometer 64 in order measure the patient's temperature, and may include sensors of other bodily functions such as respiration. Permittivity may be measured at microwave frequencies to assess glucose levels. In other embodiments, the headband 12 includes a forehead mounted impedance plethysmography system and method such as is disclosed in concurrently filed Application Serial No __/ , filed 2007, entitled

"FOREHEAD MOUNTED IMPEDANCE PLETHYSMOGRAPHY SYSTEM AND METHOD" which is incorporated herein by reference.

[034] Referring to Figure 8, a headband such as is illustrated in the foregoing figures is used in an emergency setting or in a hospital emergency room to facilitate triage and patient monitoring. A patient fitted with the headband of Figure 7, for example, will have a number of biometric characteristics measured. In some embodiments, the headband 12 provides audible or visible alerts, such as by means of the indicator 24, if the parameter measured by one of the optical receivers 18a- 18c or the temperature sensor 64 falls outside of an acceptable range. Alerts may also be sent wirelessly to a monitoring station such as a nurse's station or wireless device carried by a nurse or physician. In other embodiments, the headband 12 transmits an alert to the external monitoring device 22, which then produces an audible or visible alert to an attending physician, nurse, or paramedic. The controller 30 may therefore include a comparison module 66 storing a plurality of thresholds 68. The comparison module 66 compares the output of the optical receivers and/or optodes 18a- 18c, either before or after processing by the filtering module 38 and processing module 40, to the thresholds 68 to determine whether the patient's vital statistics lie within normal ranges or are likely to require attention. If the comparison module 66 determines that the patient requires attention, the comparison module 66 may cause the alerting module 70 to produce an audible or visible alert, either on the headband 12 itself or by wired or wirelessly communicating the alert to the monitoring device 22. From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Reference to modules constituting embodiments of the invention indicate structures and steps for performing the functions attributed to a module, however the structures for performing the functions attributed to a module may be operate at different times or include multiple distinct structures that may or may not be collocated. Accordingly, the invention is not limited except as by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A system for monitoring patient biometric information, comprising: a headband adapted to secure to the forehead of a patient; an accelerometer attached to the headband; an optical transmitter attached to the headband and positioned to transmit optical signals into the patient's forehead; an optical receiver attached to the headband and positioned to receive at least a portion of the optical signals received from the patient's forehead; and a signal processor circuit electrically coupled to the accelerometer and optical receiver, the signal processor circuit operable to produce an output related to the patient biometric information based on an output of the optical receiver and an output of the accelerometer.

2 The system of claim 1 , wherein the signal processor circuit is operable to produce the output related to the patient biometric information based on the results of filtering the output of the optical receiver according to the output of the accelerometer.

3. The system of claim 1, wherein the signal processor circuit is operable to filter the output of the optical receiver according to the output of the accelerometer to substantially compensate for variation in the optical signal received from the patient's forehead caused by patient motion.

4. The system of claim 1, wherein the accelerometer is a three-axis accelerometer.

5. The system of claim 1, wherein the signal processor circuit comprises an adaptive filter.

6. The system of claim 1, further comprising a defibrillator coupled to the accelerometer, the defibrillator programmed to deliver a shock to the patient only when the accelerometer output indicates that the patient is not moving.

7. The system of claim 1, further comprising a force sensor attached to the headband and positioned to detect tension in the headband, and wherein the signal processor circuit is electrically coupled to the force sensor and further operable to compare an output from the force sensor to at least one threshold value and produce an output corresponding to the comparison.

8. The system of claim 1, wherein the signal processor circuit is further operable to compare the output of the optical receiver to a threshold and to output an alert according to the comparison.

9. The system of claim 1, wherein the optical transmitter emits light having a wavelength suitable for measuring at least one of blood perfusion, blood oxygenation, pH, nitric oxide, carbon monoxide, and carbon dioxide.

10. The system of claim 1, wherein the optical transmitter and optical receiver are a first optical transmitter-receiver pair, the system further comprising a plurality of optical transmitter-receiver pairs one or more of which may comprise an optode including the first optical transmitter-receiver pair, the plurality of optical transmitter-receiver pairs and/or optode each operable to emit and receive light having a wavelength suitable for measuring a different one of blood perfusion, blood oxygenation, nitric oxide, and carbon monoxide, and optionally carbon dioxide and pH sensed biochemically, and wherein the signal processor circuit is operable to receive an input from each of the plurality of optical transmitter-receiver pairs and optode when present.

11. The system of claim 10, wherein the signal processor circuit is further operable to compare each of the outputs of the plurality optical transmitter-receiver pairs to one of a plurality of thresholds and to produce an alert according to the comparisons.

12. The system of claim 10, wherein the headband further comprises an alert indicator and the signal processor circuit is operable to activate the alert indicator to produce an alert according to the comparisons.

13. A method for monitoring a patient's biometric information, comprising: emitting an optical signal onto the patient's forehead; receiving a reflected optical signal and converting the reflected optical signal to a receiver output; detecting patient movement from an accelerometer positioned adjacent the patient's forehead to generate an accelerometer output; filtering the receiver output according to the accelerometer output to remove information from the receiver output caused by patient movement; and processing the filtered receiver output to extract patient biometric information.

14. The method of claim 13, further comprising positioning a headband on the patient's forehead, the headband including an optical transmitter and an optical receiver facing the patient's skin and an accelerometer.

15. The method of claim 14, further comprising: receiving a force sensor output corresponding to tension in the headband; comparing the force sensor output to a threshold range; and producing an alert according to the comparing step.