Abstract:
A wireless biopotential monitoring system composed of a wireless electrode module which can be attached to a disposable electrode strip. Such device can be conveniently affixed to a patient&#39;s skin and will transmit the physiological signals to a remote receiver where the signals can be monitored by a clinician.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. patent application Ser. No. 60/580,776 “DEVICE AND METHOD FOR TRANSMITTING PHYSIOLOGIC DATA” and 60/580,772 “WIRELESS ELECTRODE FOR BIOPOTENTIAL MEASUREMENT” both to Fadem et al. and filed on 18 Jun. 2004, the disclosure of both of which are incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to a method and apparatus for capturing biopotential voltage signals such as electroencephalograms (EEG&#39;s), electrocardiograms (ECG&#39;s) or electromyograms (EMG&#39;s). More particularly, the present invention provides a method and describes a battery powered device which uses a digital amplification circuit attached to a disposable adhesive electrode strip to capture voltage potentials from the surface of the skin and a digital wireless transceiver tightly integrated with respect to the amplification circuit to send the voltage potential signals to a remote receiver for datalogging.  
       BACKGROUND OF THE INVENTION  
       [0003]     The measurement of voltage potentials from the surface of the skin are commonly used to detect a variety of physiological conditions. Voltage potentials generated by the beating heart called ECG&#39;s are used to evaluate the performance and condition of the heart and may be indicative of many types of heart disease. EMG&#39;s are often detected from electrodes affixed to the skin near muscles to evaluate a subject&#39;s neuromuscular activity and may be used to identify muscular dystrophy, peripheral nerve damage or other diseases. EEG&#39;s are voltage potentials generated by activity within the brain. EEG&#39;s are detected by placing electrodes on the scalp and are often used to detect neurological conditions such as schizophrenia, auditory neuropathy, or the effects of anesthesia.  
         [0004]     These voltage potentials are measured by affixing a plurality of conductive electrodes, at least one of which, the reference electrode, should be placed at a site of minimal electrical activity, and measuring the voltage differential between the reference electrode and the other, signal, electrodes. The electrodes are commonly made from a conductive material such as silver/silverchloride (Ag/AgCl) or gold (Au) and are often wetted with a conduction enhancing solution such as saline or a conductive gel.  
         [0005]     The voltage differential between the reference electrode and the signal electrodes is extremely small, on the order of millivolts (10 −3  volt) or microvolts (10 −6  volt). To detect the small physiological signal in the presence of background electrical noises requires amplification and filtering. The amplification and filtering is usually accomplished via an amplifier box connected to the electrodes with long wires.  
         [0006]     For many applications of biopotential measurement, the long electrode wires present a number of problems both in terms of the utility of the system and the accuracy of the measurements.  
         [0007]     Often it is desirable to monitor EEG&#39;s, ECG&#39;s, or EMG&#39;s in a clinical environment such as an ambulance, an emergency room, an operating room, or a recovery room. These environments are often cluttered with tubes and wires from the various life support or physiological monitoring equipment attached to the patient. Reducing the number of physical connections from the equipment to the patient, thereby decreasing the tangle of tubes and wires, would permit care givers to work more efficiently around the patient.  
         [0008]     Affixing a multitude of individual electrodes to the patient&#39;s skin and attaching the other ends to an equipment box also requires a significant amount of time. Depending on the type of electrodes used, the location on the body where the electrodes are to be attached, and the type of biopotential signals to be measured, many system parameters have to be set. These parameters may include settings for gain, filter characteristics, and sampling frequency. This extended set-up time, up to thirty minutes for many EEG or ECG systems, may be significant for many patients in need of critical attention.  
         [0009]     Not only are the long attachment wires burdensome themselves, the wires also tend to limit the accuracy of the electrophysiological signals being detected. This is for a number of reasons. First, the wires act as an antenna which will pick up stray background electrical noise. This background noise could come from other powered equipment or from electrosurgical devices used to cauterize wounds. Electrical filters in the amplifier box are used to limit the degradation caused by background noise but in doing so, also mask or modify a certain amount of the signal. The second reason that long wires limit the accuracy of the detected signals is that because the signals are very small, on the order of millivolts (10 −3  volt) or microvolts (10 −6  volt), there is a certain amount of signal loss due to the impedance of the wire. Finally, as the physicians and nurses work around the patient, the wires are often disturbed. Disturbing the wires can create noise and cause signal degradation.  
         [0010]     Aspect Medical markets the BIS system, described in U.S. Pat. No. 6,298,255, for measuring EEG&#39;s to evaluate sedation levels during surgery. While the BIS system includes electrode contacts, like those described in U.S. Pat. No. 5,305,746, and an identifier memory chip affixed to an adhesive strip, this strip must be plugged into an interface box which is in turn plugged into a monitor. While this system and the device described in U.S. Pat. No. 6,654,626 do shorten setup time, these systems still require a cable between the electrode strip and the monitor. This wire can get in the way of the care givers and, if disturbed, could cause the electrode strip to become detached. The long electrode wire can also cause signal noise and degradation.  
         [0011]     Physiometrix likewise markets the PSA 4000 system. This system also includes an adhesive electrode strip connected by a long wire to an interface box then into a monitor. This system suffers from many of the same shortcomings previously mentioned.  
         [0012]     BioSemi markets a preamplified electrode for biopotential measurements. With this system, BioSemi has developed an electrode contact with integrated amplifiers. This system has the advantage of amplifying the signal close to the contact point. The signals are then sent along a wire to a junction box where the signal is amplified again and then converted to a digital signal. While this system amplifies a cleaner signal, the long wires between the electrode and the junction box are still problematic. This system also requires an additional amplification step before the signal is digitized so that any noise picked up from the long wire will be included in the digitized signal. The BioSemi system requires an additional wire attached to a separate reference electrode.  
         [0013]     Thought Technology LTD markets a variety of biopotential electrodes:  
         [0014]     MyoScan-Pro, MyoScan, and EEG-Z. These are preamplified electrodes which can be attached to an integrated electrode strip. This system, like the BioSemi system, amplifies the signal close to the electrode contact but uses long electrode wires to send the signal to an interface box for analog to digital conversion.  
         [0015]     Cleveland Medical Devices markets the Crystal Monitor and the BioRadio Jr. The Crystal Monitor is a wireless interface/junction box which accepts standard, non-amplified, wired electrodes. This system, described in U.S. Pat. No. 5,755,230 eliminates the need for the wires between the junction box and the monitor but still uses discrete wired electrodes affixed to the skin. This system does not amplify the signal close to the skin contact point. Instead, standard wired electrodes are affixed to the skin and are attached by long electrode wires to the wireless junction box. This does not eliminate the problems associated with the clutter of wires and signal degradation can occur because of the long electrode wires.  
         [0016]     The BioRadio Jr. does include a signal amplifier, an analog to digital converter, and a radio transmitter, and is battery powered, but this system does not utilize a preformed, adhesive electrode strip. The device, as described in their marketing literature, does not include a practical packaging arrangement. There is also no discussion of a method to automatically identify the specific biopotential measurement taken and therefore there is no method to preset the signal gain, filtering, or data capture or transmit rate.  
         [0017]     U.S. Pat. No. 6,577,893 describes a wireless sensor device which can include sensors for biopotential measurement. This device is deficient for biopotential measurements for several reasons. First, the sensors are packaged close together and do not provide enough separation between the signal and reference electrodes to get an accurate measurement of voltage potential. Next, the device does not include a disposable contact to ensure sterility. The device also does not include an identification chip to facilitate automatic system configuration.  
         [0018]     U.S. Pat. No. 6,611,705 describes a system and method to measure the biopotential signals related to an electrocardiograph (ECG). This system is primarily a replacement for the wires between the electrode junction box and the monitor commonly used in existing ECG systems. While this system does eliminate this wired connection, other issues of usability are not addressed.  
         [0019]     Consequently, a significant need exists for an improved device for obtaining and wirelessly transmitting biopotential data received from a patient.  
       BRIEF SUMMARY OF THE INVENTION  
       [0020]     The invention overcomes the above-noted and other deficiencies of the prior art by providing a wireless biopotential measuring device with improved signal detection that is simple to set up and use in a clinical environment.  
         [0021]     A device is described which includes a means to automatically configure biopotential measurement parameters, a means to detect biopotential signals from the surface of skin, a means to amplify the biopotential signals, and a means to wirelessly transmit the signals to a remote monitor.  
         [0022]     A method of transmitting biopotential signals from a patient, comprising the steps: sampling voltage differentials between a reference electrode and a signal electrode; amplifying the voltage differentials; converting the voltage differentials to a digital format; storing a plurality of digital samples in a memory device; and transmitting the stored samples via a wireless transmitter while continuing to sample.  
         [0023]     A biopotential measurement device affixable to skin of a patient, comprising: an adhesive substrate; a disposable electrode strip disposed on the adhesive substrate to position a pair of electrode contacts; voltage potential detection circuitry responsive to a biopotential signal across the pair of electrode contacts; processing circuitry operatively configured to signal amplify and digital convert the sensed biopotential signal; and wireless data transmission circuitry operatively configured to transmit the amplified, digitized biopotential signal.  
         [0024]     These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0025]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.  
         [0026]      FIG. 1  is a perspective view of a wireless biopotential measurement device.  
         [0027]      FIG. 2  is an exploded view of the device in  FIG. 1 .  
         [0028]      FIG. 3  is a close-up view of an unfolded flex circuit which is used in the device in  FIG. 1 .  
         [0029]      FIG. 4  is a perspective view of an alternative embodiment of the electrode strip used in the device in  FIG. 1 .  
         [0030]      FIG. 5  is a perspective view of a battery charging and wireless receiver.  
         [0031]      FIG. 6  is a cross-section view from  FIG. 1  of an electrode pad used in the device in  FIG. 1 .  
         [0032]      FIG. 7  is a cross-section view from  FIG. 1  of an alternative embodiment of an electrode pad used in the device in  FIG. 1 .  
         [0033]      FIG. 8  is a functional block diagram of the circuit used in the device in  FIG. 1 .  
         [0034]      FIG. 9  is a functional block diagram showing the signal communication path.  
         [0035]      FIG. 10  is a functional block diagram of an alternative signal communication path. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]     A sealed electronics module is described which encloses a flexible printed circuit with various integrated circuit devices attached. These integrated circuits include amplifiers, analog to digital converters, a microcontroller, random access memory, and a digital radio. Also included in the module are a battery and an antenna integrated onto the flexible circuit.  
         [0037]     The invention also includes a flexible electrode strip with at least one electrode contact affixed to each end. A memory chip containing a digital identifier is affixed to the electrode strip. Contact plugs are affixed to the electrode strip and are electrically connected to electrode pads and to the identifier memory chip.  
         [0038]     The electrode strip has an adhesive backing so that it can be adhesively affixed to a location on a subject&#39;s skin, such as the forehead. The electrode contacts may be impregnated with an electrolytic substance to enhance the skin conductance. Once the electronics module is attached to the electrode strip by inserting the electrode strip plugs into the mating sockets on the electronics module, the device becomes electrically energized. The electronics module reads the identification data from the contact strip and configures itself for the appropriate gain, data capture rate, and wireless transmission rate.  
         [0039]     Turning to the Drawings, in  FIG. 1 , the wireless electrode module  20  is a sealed package which can be attached to an electrode strip  21 .  
         [0040]     In  FIG. 2 , electrode module cover  22  has been separated from electrode module base  25  to reveal the flexible circuit assembly  23 . The flexible circuit assembly  23  has electrical contacts  36  which are electrically connected to the integrated circuit components  37 . An antenna  34  and a battery  24  are also electrically connected to the integrated circuit components  37 . The flexible circuit assembly  23  is assembled to the electrode module base  25  with the use of solder or conductive glue between electrical contacts  36  and electrode receptacles  38  which are permanently affixed to electrode module base  25 . The wireless electrode module  20  is connected to the electrode strip  35  by inserting contact conductor plugs  26 - 28  into electrode receptacles  38  which are electrically connected to reference contact  32 , signal contact  34 , and the identification memory chip  29 . The identification memory chip  29  stores the parameters for the specific desired biopotential measurement. These parameters may include: signal gain, filter settings, sampling rate, and transmission rate. The signal conductive adhesive pad  30  is affixed to the skin of a test subject in close proximity to the location desired for the biopotential measurement. The reference conductive adhesive pad  33  is affixed to the skin at a location of minimal electrophysiological activity such as the forehead.  
         [0041]      FIG. 3  shows flexible circuit assembly  23  in its unfolded configuration. Battery  24  is shown before being attached to flexible circuit assembly  23 .  
         [0042]      FIG. 4  shows an alternative configuration of electrode strip  35  where the reference conductive adhesive pad  33  has been replaced with a reference conductive clip  50  attached to a tab  51  on electrode strip  35 . In this configuration, the signal conductive adhesive pad  30  is affixed to the skin of a test subject in close proximity to the location desired for the biopotential measurement. The reference conductor clip  50  is clipped to the skin at a location of minimal electrophysiological activity such as the ear lobe.  
         [0043]      FIG. 5  shows the charging stand and wireless receiver  52 . The electrode module  23  is placed in the charging sockets  53  when needing to be recharged. The charge state of the electrode module  23  is shown on charge display  55 . When the electrode module  23  is in use, the biopotential signals transmitted from the electrode module  23  are received through the receiving antenna  54  and converted and sent to a patient monitor  71  through the signal output ports  56 .  
         [0044]      FIG. 6  shows a section through the electrode pad  32  from  FIG. 2 . The contact pad  33  may be impregnated with a conduction enhancing substance such as saline. Adhesive flanges  41  surrounding the contact pad  33  on the electrode strip  35  may be coated with an adhesive  40  to facilitate the contact pad  33  maintaining constant pressure on the skin.  
         [0045]      FIG. 7  shows a section through the electrode pad  32  from  FIG. 2  in an alternative configuration. In this configuration, the electrode pad  33 ′ is coated with an adhesive which also enhances the skin conduction.  
         [0046]      FIG. 8  shows a functional block diagram of electrode module  23  and electrode strip  35 . Upon mating the electrode module  23  with the electrode strip  24 , the microcontroller unit detects the electrical connection with identification memory chip  29  and energizes the combined system. Reference contact  32  and signal contact  27  become electrically connected to amplifier/filter module  61  which is connected to A/D converter  64 , flash memory  65 , microcontroller unit  66 , and radio transceiver module  63 . Identification memory chip  29  affixed to electrode strip  35  is electrically connected to microcontroller unit  66 . Rechargeable battery  24  is connected to power management unit  62 , amplifier/filter module  61 , A/D converter  64 , flash memory  65 , microcontroller unit  66 , and radio transceiver module  63 . Additional information stored on identification memory chip  29  is read by microcontroller unit  66  which sets parameters for signal gain, filter settings, sampling rate, and transmission rate thus completing system initialization. Microcontroller unit  29  then activates the electrode by sending a Chip Select command and then clocks the data out. The amplified voltage potentials are then either transmitted wirelessly via radio transceiver module  63  or are temporarily stored in flash memory  65  and then transmitted in short bursts to increase battery life.  
         [0047]      FIG. 10  shows a functional block diagram of the communication path of the detected biopotential signals using the described device. Electrode module  23  is electrically connected to electrode strip  35  which is placed on the skin. The voltage differentials are detected, amplified, and digitized in electrode module  23 . The digital signal is then transmitted wirelessly  72  to wireless receiver  52 . The signal is then converted to a signal which can be read by existing systems and sent via wire to an existing patient monitor  71 .  
         [0048]      FIG. 11  shows a functional block diagram of an alternative configuration for the communication path. Electrode module  23  is electrically connected to electrode strip  35  which is placed on the skin. The voltage differentials are detected, amplified, and digitized in electrode module  23 . The digital signal is then transmitted wirelessly  72  to the combination wireless receiver and patient monitor  70 .  
         [0049]     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art.  
         [0050]     For example, U.S. Patent No. entitled “ACTIVE, MULTIPLEXED DIGITAL NEURO ELECTRODES FOR EEG, ECG, EMG APPLICATIONS”, Ser. No. 60/557,230, filed on 29 Mar. 2004, subsequently filed as U.S. patent application Ser. No. 11/092,395 and WO 05/010515 both on 29 Mar. 2005, the disclosures of which are hereby incorporated by reference in their entirety, all describe a novel amplified digital electrode for biopotential measurements. The disclosed electrode detects, amplifies, and digitizes the voltage potential at the point of skin contact, thereby minimizing signal noise and degradation.