Abstract:
A method and system for wireless ECG monitoring is provided. An electrode connector, transmitter and receiver operate with existing electrodes and ECG monitors. The electrode connector includes connectors for attaching to disposable or reusable single electrodes. The transmitter transmits the signals from the electrodes to the receiver. The receiver passes the electrode signals to the ECG monitor for processing. ECG monitors used with an electrical conductor, for example wire connections to electrodes, are connected with the receiver, avoiding the purchase of a new monitor. Any legacy ECG monitor, including different ECG monitors, connects with the receiver using the ECG monitor&#39;s lead-wires. The ECG monitor operates as if directly connected to the electrodes without the problems discussed above associated with wires running from the ECG monitor to the patient.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of and claims the benefit of the filing date pursuant to 35 U.S.C. §119(e) of Provisional Application Serial No. 60/219,082, filed Jul. 18, 2001, for a WIRELESS EKG, the disclosure of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND  
         [0002]    This invention relates to medical monitoring systems and methods. In particular, a biomedical system and method for monitoring a patient is provided.  
           [0003]    Biomedical monitoring systems include bedside, transportable, ambulatory and discrete vital sign monitors. In vital signs monitors, electrocardiograph (ECG), temperature, blood pressure or other characteristics of a patient are monitored.  
           [0004]    ECG systems are used for monitoring activity of a patient&#39;s heart. For example, three electrodes are positioned on the patient. The signal from one electrode is used as a reference signal for a difference between the signals of two other electrodes (e.g. ECG vector). By using this reference signal, and a differential amplifier configuration, common mode interference can be essentially eliminated or reduced. As another example, nine electrodes are positioned on the patient for a “12-lead” analysis of electrical activity of the heart.  
           [0005]    Wires are connected from the electrodes to an ECG monitor. The ECG monitor processes the signals and outputs ECG data, such as a plurality of traces representing activity of the heart by measuring electrical signals at different positions on the patient. However, the wires inhibit movement by and around the patient. The wires will stress the electrodes, resulting in malfunction or disconnection from the patient. A caregiver&#39;s time is then required to reconnect or replace the electrodes. Patients are often moved during a day, requiring disconnecting one ECG monitor and reconnecting another ECG monitor. Often the electrodes also need to be removed and replaced. If not replaced in exactly the same position, the patient&#39;s ECG will be different from ECG monitor to ECG monitor, creating an artifact in the ECG.  
           [0006]    Wireless ECG systems connect the electrodes to a transmitter to avoid wires from the patient to a monitor. In the example described in WO 94/01039, a microchip is positioned proximate the electrodes on the patient. The microchip analyzes the signals from the electrodes and transmits the results (see page 42). The results are received and provided to a printer or monitor (see page 26). However, a complete system including a monitor, printer or recorder operable to receive the signals as processed by the microchip on the patient is required.  
           [0007]    Holter monitors record a patient&#39;s vital signs over a time period. The patient carries the complete monitor and recorder. The information can be downloaded or otherwise obtained for subsequent analysis. However, many of these systems limit the bandwidth of signals to suppress artifacts associated with patient movement, so information can be lost. Special monitors or other devices may be required for obtaining the stored data for analysis, preventing maximum use of other equipment.  
           [0008]    Wireless ECG systems often use patches or strips for positioning electrodes. The strip is fabricated with a plurality of electrodes electrically connected to the transmitter. If one electrode fails, the entire strip is replaced.  
         BRIEF SUMMARY  
         [0009]    The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a method and system for wireless ECG monitoring.  
           [0010]    An electrode connector, transmitter and receiver operate with existing electrodes and ECG monitors. The electrode connector includes connectors for attaching to disposable or reusable single electrodes. The transmitter transmits the signals from the electrodes to the receiver. The receiver passes the electrode signals to the ECG monitor for processing. ECG monitors used with an electrical conductor, for example wire connections to electrodes, are connected with the receiver, avoiding the purchase of a new monitor. Any legacy ECG monitor, including different ECG monitors, connects with the receiver using the ECG monitor&#39;s lead-wires. The ECG monitor operates as if directly connected to the electrodes without the problems discussed above associated with wires running from the ECG monitor to the patient.  
           [0011]    In a first aspect of the invention, an electrode connector for ECG monitoring of a patient is provided. Material is operable to interconnect a plurality of electrodes. The material includes a plurality of electrode releasable connectors.  
           [0012]    In a second aspect, a method for connecting electrodes for ECG monitoring is provided. A plurality of electrodes are placed. A plurality of expandable arms, one expandable arm provided for each of the plurality of electrodes, are expanded. The plurality of expandable arms are connected to the plurality of electrodes.  
           [0013]    In a third aspect, a system for monitoring electrical signals generated by a patient is provided. A transmitter is operable to transmit electrode signals. A receiver is responsive to the transmitter to generate the electrode signals. The receiver has an output connector operable to connect with electrode wires of an ECG monitor.  
           [0014]    In a fourth aspect, a method for monitoring electrical signals generated by a patient is provided. Signals are received from electrodes. Information representing the signals received from electrodes is transmitted. The information is received. The signals received from the electrodes are reconstructed. Existing wires from an ECG monitor are connected. The reconstructed signals are received at the ECG monitor.  
           [0015]    In a fifth aspect, a wireless ECG monitoring system for reconstructing signals at a plurality of electrodes is provided. An electrode connector is operable to connect with the plurality of electrodes. A single transmitter is operable to connect with the electrode connector. The single transmitter is operable to transmit signals from the plurality of electrodes. A receiver is operable to reconstruct the signals from the plurality of electrodes.  
           [0016]    In a sixth aspect, a method for wireless ECG monitoring with reconstructed signals from a plurality of electrodes is provided. The plurality of electrodes are connected with an electrode connector. Signals from the plurality of electrodes are transmitted with a single transmitter. The signals transmitted by the transmitter are received. The signals from the plurality of electrodes are reconstructed.  
           [0017]    Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a block diagram of one embodiment of an ECG monitoring system.  
         [0019]    FIGS.  2 A-D are front views of various embodiments of electrode connectors and transmitters of the ECG monitoring system of FIG. 1.  
         [0020]    [0020]FIG. 3 is a perspective view of one embodiment of an expandable arm of the electrode connectors of FIGS.  2 A-D.  
         [0021]    [0021]FIG. 4 is a front view of one embodiment of a belt used with the electrode connector of FIG. 2D.  
         [0022]    [0022]FIG. 5 is a flow chart of one embodiment for operation of the ECG monitoring system of FIG. 1.  
         [0023]    [0023]FIG. 6 is a perspective view of another embodiment of an ECG monitoring system.  
         [0024]    [0024]FIG. 7 is a block diagram of one embodiment of a transmitter.  
         [0025]    [0025]FIG. 8 is a block diagram of one embodiment of a receiver. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    A wireless ECG system uses existing electrodes and ECG monitors. The wireless ECG system wirelessly bridges between conventional electrodes on a patient and a conventional ECG monitor. The wireless ECG system is an accessory that augments the capability of conventional, or legacy, ECG monitors or systems. The wireless ECG system functions as a wireless extension cord that physically un-tethers a patient from a conventional lead-wire cable connected to a conventional ECG monitor.  
         [0027]    The wireless ECG system includes three components: an electrode connector (e.g. sensor array), a transmitter (e.g. ECG-radio) and a receiver (e.g. base station). These components interpose between conventional electrodes worn by a patient and a conventional lead-wire cable of a conventional ECG monitor without requiring any additional changes to the conventional electrodes, the conventional lead-wire cables, or the conventional ECG monitoring systems. An electrode connector with releasable connections, such as snap terminals, and expandable arms electrically connects with existing electrodes, such as snap terminal type electrodes. A transmitter provides signals received from the electrodes to the receiver. The receiver connects to the ECG monitor via conventional lead-wires or electrode wires of the ECG monitor. Signals representing the electrode signals measured or sampled on a patient are provided to the ECG monitor. The existing ECG monitor processes the signal to output ECG data, such as ECG vector data. Consequently, physical coupling between the patient and the electrocardiograph or vital signs monitor is eliminated. This enables the patient to freely ambulate while being monitored by the ECG.  
         [0028]    [0028]FIGS. 1 and 6 show a wireless ECG monitoring system  20 . The ECG monitoring system  20  includes an electrode connector  22 , a transmitter  24 , a receiver  26  and an ECG monitor  28 . Additional or fewer components can be used, such as providing the system  20  without the ECG monitor. Alternative components can be used, such as a strip or patch with electrodes rather than an electrode connector  22  or a printer rather than an ECG monitor  28 .  
         [0029]    FIGS.  2 A-D show electrode connectors  22  of various embodiments used with an array of electrodes  30 . The electrodes  30  comprise conductive material. For example, a foam disk with a conductive fabric or a fabric with a conductive metal layer is used. The electrodes  30  include a snap terminal (male, female or both) or tab for connection to a wire. Other connectors may be provided on the electrodes  30 . The electrodes  30  are positioned for ECG monitoring, such as positioned for hexaxial-lead monitoring as illustrated in FIGS.  2 A-C. For hexaxial-lead monitoring, the electrodes  30  are positioned in left and right arm positions and right and/or left leg positions. With these electrode positions, up to seven leads can be monitored (e.g. Lead I, II, III, aVL, aVR, aVF and chest positions). Other positions of electrodes can be used, such as associated with precordial (e.g. V1-V6) or combinations of hexaxial and precordial (e.g. “12-lead” monitoring). The electrodes  30  are attached to the patient with conductive hydrogel or other adhesives. The electrodes  30  and/or the electrode connector  22  are disposable or reusable.  
         [0030]    The electrode connector  22  includes a plurality of expandable arms  32  and a transmitter  24 . The expandable arms  32  comprise polypropylene or polyethylene fabric with an electrically conductive element such as a wire  36  and an electrode joiner  38  as shown in FIG. 3. In one embodiment, the expandable arm  32  is formed from Kapton or Mylar, manufactured by DuPont, a cloth, a fabric or another flexible material. Multiple layers of dielectric, and or electrically or magnetically conductive material can be used to shield the wire  36 . Alternatively, no shielding is provided. Fabric or other material can be attached to one or both sides of the expandable arm  32 , such as to provide comfort for a patient.  
         [0031]    The expandable arm  32  of one embodiment comprises memoryless material, such as the materials discussed above. The expandable arm  32  is die cut in a serpentine pattern as shown in FIG. 3. The expandable arm  32  expands by releasing or breaking connections between portions of the serpentine pattern. When expanded, a portion or all of the expandable arm  32  is extended. Where only a portion of the expandable arm  32  is extended, another portion remains folded or unbroken. Pressure on the electrode  30  from elastic or stretchable material is avoided, providing for more stable connection of the electrode  30  to the patient. The expandable arm  32  also allows for extension as needed without extra extension and resulting loose material to be tangled or provide discomfort. In alternative embodiments, a stretchable or elastic expandable arm  32  is used. In yet other alternative embodiments, a non-expandable arm is used.  
         [0032]    The electrical conductor or wire  36  in the expandable arm  32  preferably comprises a conductor printed on the Mlyar, Kapton or other flexible dielectric material. The printed conductor is flexible, providing electrical connection between the electrode  30  and the transmitter  24  whether expanded or unexpanded. In alternative embodiments, the wire  36  comprises a thread of copper or another conductive material. In yet other embodiments, the wire comprises a coaxial cable. One or more wires  36  are provided for each electrode  30 . For some expandable arms  32 , one wire  36  electrically connects from one electrode  30  to the transmitter  24  or another expandable arm  32 . For other expandable arms  32 , a plurality of wires  36  connect from a respective plurality of electrodes  30  on the same and/or another expandable arm  32 .  
         [0033]    The electrode joiner  38  comprises a clip (e.g. alligator clip), snap terminal, or connector (male, female or both), adhesive tab or other device for electrically and physically joining the electrode  30  to the expandable arm  32 . As shown in FIG. 2D, a plurality of electrode joiners  38  can be used on one expandable arm  32 . In other embodiments, one electrode joiner  38  is provided at an end or other portion of the expandable arm  32 . If one electrode  30  malfunctions, only the electrode  30  is removed and replaced. The electrode connector  22  is kept.  
         [0034]    The other end of the expandable arm  32  connects with other expandable arms  32  or the transmitter  24 . The plurality of expandable arms  32  are connected in any of various configurations, such as a spiral configuration shown in FIGS. 2A and 2B. The expandable arms  32  releasably or fixedly connect from a hub  40 . In the embodiment of FIG. 2A, one expandable arm  32  includes wires for all or a sub-set of the electrodes  30  to electrically communicate with the transmitter  24 . The transmitter  24  is spaced away from the hub  40 , such as being positioned on an arm band (shown), or on another location on the patient. For example, FIG. 6 shows the transmitter  24  held to the patient with an arm band  74  comprising neoprene or other fabric. In the embodiment of FIG. 2B, the transmitter  24  is positioned on the hub  40 .  
         [0035]    The hub  40  comprises the same material as the expandable arms  40 , such as from using a continuous sheet to form the hub  40  and expandable arms  32 . In other embodiments, the hub  40  comprises the same or different material with releasable connectors for electrically and physically connecting with the expandable arms  32 . For example, the hub  40  comprises plastic or other material with plurality of conductive snap terminals for connecting with the expandable arms.  
         [0036]    Another configuration is a “7” or “L” configuration, such as the embodiment shown in FIG. 2C. One of the electrode positions generally corresponds to the hub  40 , and expandable arms  32  expand from the hub  40 . Other alternative configuration embodiments include “C” or “U” shapes with multiple hubs.  
         [0037]    Yet another configuration is shown in FIG. 2D. A belt  42  connects with a plurality of expandable arms  32 . The belt  42  comprises neoprene, non-woven polypropylene or polyethylene fabric or other materials. One or more pockets or connectors for the transmitter  24 , other electrical components, batteries, displays, or other devices are provided on the belt  42 . In one embodiment shown in FIG. 4, the belt  42  is formed to fasten or stretch around a waist of the patient, but arm, neck, chest or leg belts can be used. One or more of the expandable arms  32  releasably connects with the belt  40 . In one embodiment, the belt  40  includes separate connectors  44  for each electrode position. In other embodiments, one or more of the connectors  44  on the belt  40  include separate electrical contacts for electrically connecting with multiple wires  36  and associated electrodes  30  on one expandable arm  32 . The connectors  44  are provided on the outer surface of the belt  42 , but can be provided in pockets. The transmitter  24  is positioned on the belt  42  or elsewhere on the patient.  
         [0038]    As shown in FIG. 2D, one or more of the expandable arms  32  may include one or more connectors  44  for connecting with other expandable arms  32 , forming a hub  40 . For example, an electrically conductive snap terminal or terminals connect the expandable arms. Other connectors, such as male and female housings with clips and wires associated with connecting multiple separate wires between the expandable arms, can be used.  
         [0039]    The configuration is associated with the desired ECG monitoring. FIGS.  2 A-C illustrate hexaxial positions for the electrodes  30 , such as associated with continuous monitoring. Electrodes  30  are positioned at hexaxial positions associated with left arm, right arm, left leg and/or right leg. Many ECG systems use three electrode positions, but some use four or more. FIGS. 2A and 2C show three electrode positions. FIG. 2B shows four electrode positions. More or fewer electrode positions, such as three to five positions, may be provided with additional electrode joiners  38  and/or expandable arms  32 .  
         [0040]    [0040]FIG. 2D shows both hexaxial and precordial positions for the electrodes  30 , such as associated with “12 lead” ECG monitoring. Two or more expandable arms  32  connect with electrodes  30  in hexaxial positions. One or more expandable arms  32 , such as expandable arm  46 , connect with electrodes  30  in precordial positions. In this embodiment, the precordial expandable arm  46  connects with another of the expandable arms  32  used for hexaxial positions. The resulting hub  40  is associated with one of the precordial electrode positions. In alternative embodiments, the hub  40  is spaced away from any electrode  30 . In yet other alternative embodiments, the precordial expandable arm or arms  46  separately connect with the belt  42 . For example, separate hexaxial and precordial electrode connectors  76  and  78  are provided as illustrated in FIG. 6. The precordial electrode connector  78  connects with the hexaxial electrode connector  76  or the transmitter  24 .  
         [0041]    The hubs  40  and expandable arms  32  may include connectors  44  for adding additional expandable arms  32  or electrodes  30 . For example, two or more expandable arms  32  are positioned for hexaxial-lead monitoring as shown in FIG. 2D without the precordial expandable arm  46 . When precordial-lead monitoring is desired, electrodes  30  are positioned along six precordial positions, and the expandable arm  46  is expanded and connected with the precordial electrodes  30 . The expandable arm  46  is also connected to the belt  42  or other expandable arm  32 . Alternatively, different electrode connectors  22  are used for different ECG systems or numbers of electrodes. Since the expandable arms  32  are flexible and expandable, the same electrode connector  22  is used for various electrode positions as represented by the bold arrows in FIGS.  2 A-D.  
         [0042]    The transmitter  24  receives the signals from the electrodes  30 . The transmitter  24  comprises a wireless transmitter or transceiver, such as a radio, ultrasound, infrared or other transmitter. For example, a transceiver operable according to Bluetooth specifications (i.e. a Bluetooth transceiver) is used. In one embodiment, the transmitter  24  comprises an application specific integrated circuit, a processor or other circuit.  
         [0043]    [0043]FIG. 7 shows one embodiment of the transmitter  24 . The transmitter  24  includes a plurality of electrode signal channels  80 , a multiplexer  82 , an analog-to-digital converter (ADC)  84 , a controller  86 , a radio  88  and a battery  90 . Additional, fewer or different components can be used. The battery  90  comprises a replaceable or rechargeable lithium battery connected to provide power to the various components of the transmitter  24 .  
         [0044]    In one embodiment, nine electrode signal channels  80  corresponding to the typical nine electrodes used for hexaxial-lead and precordial-lead monitoring are provided. Fewer or additional electrode signal channels  80  can be provided. The electrode signal channels  80  each comprise a connector  92 , a filter  94 , an amplifier  96 , a Nyquist filter  98  and a track and hold circuit  100 . The connector  92  comprises snaps, plugs or other electrical connectors for connecting with the wires  36 . The filter  94  comprises a low pass filter, such as for removing electromagnetic interference signals. The amplifier  96  amplifies the signals from the electrodes  30 . The Nyquist filter  98  comprises a low pass filter for removing high frequency content of the amplified signals to avoid sampling error. The track and hold circuit  100  enables the system to sample all  9  channels of signals at a same or relative times so that there is no differential error created when these signals are combined later in a legacy ECG monitor.  
         [0045]    The multiplexer  82  sequentially selects signals from the electrode signal channels  80  using time division multiplexing, but other combination functions can be used. The ADC  84  converts the combined analog signals to digital signals for transmission. The controller  86  controls operation of the various components and may further process the digital signals, such as diagnosing operation, controlling any user interface (e.g. input and/or output devices), and detecting connection to electrodes. Preferably the controller comprises a digital signal processor (DSP) that decimates the digitized signals so as to lessen the bandwith required to transmit the signals. The radio  88  modulates the digital signals with a carrier signal for transmission. In one embodiment, the radio  88  includes a demodulator for receiving information. The controller  86  processes the received information.  
         [0046]    In one embodiment, the transmitter  24  is operable to minimize introducing undesired noise or signals. For example, components are matched such that later application to a differential amplifier in a legacy ECG monitor for determining a heart vector is accurate. In one embodiment, the ECG vectors are not formed by the ECG system  20 , but rather by the legacy ECG monitor. Because the ECG system  20  is essentially “in-series” with the legacy ECG monitor, any error may produce undesirable results. One potential source of error is differential error. This differential error can be observed on the legacy ECG monitor when the ECG monitor forms the ECG lead signals by combining the individual electrode signals in the ECG monitor input stage. This input stage comprises a difference, or differential, amplifier to eliminate common mode interference from the signals produced at the electrodes  30 . If there is any difference in how each of the electrode signals are processed, when the legacy ECG&#39;s differential amplifier forms the ECG lead signals or ECG vectors an artifact will be present. For example, in the transmitter  24  if there is a difference in the gain of the amplifiers, a difference in the phase shift associated with the anti-aliasing (Nyquist) filters, a difference in how the respective track and hold circuits treat the electrode signals, this differential error creates an artifact on the legacy ECG monitor. One important technique to minimize this potential source of differential error, is to choose a Nyquist filter  98  cutoff frequency that is very high. This is because each individual filter will have differing group delay performance, and to mitigate that difference the frequency that this group delay will affect is much higher than the frequency of the ECG signals, which are about 0.05 Hz to 150 Hz. By choosing a high cutoff frequency for the Nyquist filters  98 , any mismatch in the Nyquist filter  98  components will not affect accuracy of the individual electrode ECG signals. For example picking a filter cutoff frequency of 1,200 Hz mitigates this source of error. With this approach, the individual electrode ECG signals are oversampled at about 3,000 Hz in order to not introduce aliasing. Of course higher filter cutoff frequencies and correspondingly higher sampling rates may further reduce error. Lower cutoff frequencies and/or sampling rate may be used.  
         [0047]    Because the electrode signals are now sampled at such a high rate, these signals may be decimated to minimize the required transmission bandwidth. For example the digital samples are decimated by a factor of 8 in the controller  86 . Greater or lesser rates of decimation can be used, such as decimation as a function of the bandwidth available for transmission, the number of electrode signals to be represented, and the Nyquist sampling rate. In alternative embodiments, the digital data is compressed, the electrode signals are not oversampled, or no decimation is provided.  
         [0048]    The selected signals are transmitted as radio or other signals modulated with a carrier signal. Various formats for transmission can be used, such as Bluetooth, TCP/IP, or other formats. The controller  86  controls the acquisition and transmission of the electrode signals. The transmitted signals comprise data representing the signals received from the electrodes  30 . In alternative embodiments, the controller  86  may also processes the signals prior to transmission, so the transmitted signals comprise ECG vector data. In one embodiment, the transmitter  24  also receives control information from the receiver  26 , such as instructions to resend signals.  
         [0049]    The transmitter  24  is positioned near the patient. In the embodiment shown in FIGS. 2A and 2C, the transmitter  24  is positioned on the hub  40  or an expandable arm  32 . In the embodiment shown in FIG. 2B, the transmitter  24  is positioned on an arm band, but leg, chest or other bands can be used. In the embodiment of FIG. 2D, the transmitter  24  is positioned on the belt. Either a pocket or a surface mount is provided for the transmitter  24 . In alternative embodiments, the transmitter  24  is positioned in a pocket of clothing or elsewhere on the patient.  
         [0050]    In one embodiment, the transmitter  24  is removable. For example, clips, screws, bolts, latches or other devices releasably hold the transmitter  24  in contact with the electrode connector  22 . Electrical contact is provided by connectors operable to withstand electrical energy produced by a defibrillator. These connectors may also provide the physical connection. The transmitter  24  is removed for recharging the battery or a plug is provided on the electrode connector  22  or the transmitter  24  for recharging the battery without removal. The battery or the transmitter  24 , like the electrode connector  22 , can be used for multiple days or multiple times and is separately disposable to avoid costly replacement of the entire system  20 .  
         [0051]    Referring to FIGS. 1 and 6, the receiver  26  receives the transmitted signals. The receiver  26  comprises a radio, infrared, ultrasound or other receiver. An application specific integrated circuit, digital signal processor or other circuit for receiving signals from the transmitter  24 , decoding the received signals, and generating representative electrode signals is used. In one embodiment, the receiver comprises a transceiver for two-way communication with the transmitter  24 . For example, a transceiver operable pursuant to the Bluetooth specification is provided.  
         [0052]    [0052]FIG. 8 shows one embodiment of the receiver  26 . The receiver  26  includes a radio  110 , a controller  112 , a digital-to-analog converter (DAC)  114 , a demultiplexer  116 , a plurality of electrode signal channels  118  and a battery or power supply  120 . Additional, fewer or different components can be used. Preferably, the power supply  120  comprises a replaceable or rechargeable battery or other power source connected to provide power to the various components of the receiver  26 .  
         [0053]    The radio  110  demodulates the received signals for identifying digital data representing the combined electrode signals. In one embodiment, the radio  10  also includes a modulator for transmitting control information. The controller  112  controls operation of the various components and may further process the signals from the radio  110 , such as interpolating data, converting the signals to digital information, generating control signals for the transmitter  24 , operating any user interface, operating any user output or input devices, and diagnosing operation of the system  20 . Preferably, the controller  112  in the receiver  26  interpolates the electrode signals to return the effective sample rate to about 3 kHz or another frequency. This enables the reconstruction filters to have a cutoff frequency many times the bandwidth of the electrode signals, thus minimizing any differences in group delay at the frequencies of interest, i.e. less than 150 Hz. The DAC  114  converts the digital signals to analog signals. The demultiplexer  116  separates the individual regenerated electrode signals onto the separate electrode signal channels  118 .  
         [0054]    In one embodiment, nine electrode signal channels  118  corresponding to the typical nine electrodes used for hexaxial-lead and precordial-lead monitoring. Fewer or additional electrode signal channels  118  can be provided. The electrode signal channels  118  each comprise a sample and hold circuit  120 , a filter  122 , an attenuator  124  and a connector  126 . The sample and hold circuit  120  is controlled by the controller  112  so that the converted electrode signals appear simultaneously on each electrode signal channel  188 . Differential error may be mitigated. Other embodiments may include individual DAC&#39;s that provide the signals substantially simultaneously. The filter  122  comprises a low pass reconstruction filter for removing high frequency signals associated with the DAC conversion process. The attenuator  124  comprises an amplifier for decreasing the amplitude to a level associated with signals at the electrodes  30 , that were earlier amplified in the amplifiers  96  of the transmitter  24 . This results in a unity system gain so as not to introduce error between the electrodes and the legacy ECG monitor. Other gains may be used. The connector  126  comprises posts, snaps, plugs, tabs or other electrical connectors for connecting with the lead wire set  70 .  
         [0055]    The controller  112  sets the demodulation frequency in response to input from the user input device or memory, or the demodulation frequency is fixed. In one embodiment, the user input comprises buttons associated with manual frequency control, with preprogrammed channels, with numbers or characters, with possible transmitters  24  or other input devices for selecting a demodulation frequency. The receiver  26  electrically connects to the ECG monitor  28 .  
         [0056]    [0056]FIG. 6 shows one embodiment of the wireless ECG system  20  where the wires  70  from a standard ECG monitor  28  attach to the electrically conductive posts  72  or other connectors on the receiver  26 . The wires  70  comprise a lead-wire set, cable or electrode connectors from or for the ECG monitor  28 . The posts  72  are labeled as electrodes  30 , and the wires  70  are connected with corresponding outputs on the receiver  26 . The receiver  26  outputs signals as if from the corresponding electrodes  30  for processing by the ECG monitor  28 . In alternative embodiments, the receiver  26  includes wires for connecting with the ECG monitor  28 .  
         [0057]    In one embodiment, the receiver  26  physically connects to the ECG monitor  28 . For example, latches, clips or straps on the receiver  26  connect the receiver  26  to the ECG monitor  28 . In alternative embodiments, the receiver  26  connects to an equipment pole or wall or is free standing. The receiver  26  may be releasably attached. When a patient is moved, the receiver  26  may be detached and moved adjacent a different ECG monitor. Alternatively, different receivers  26  operate with the same transmitter  24 , so another receiver  26  is programmed to receive signals from the transmitter  24  on the patient.  
         [0058]    The ECG monitor  28  comprises one or more of a bedside monitor, a transport monitor or a discrete (i.e. diagnostic) monitor. Bedside and transport monitors are used for continuous monitoring, such as associated with hexaxial-lead monitoring. A discrete monitor typically is used periodically for analysis, such as associated with “12-lead” monitoring or obtaining multiple vectors associated with precordial and/or hexaxial leads. The ECG monitor  28  processes the electrode signals as if the signals where received directly from the electrodes  30 . Neither of the transmitter  24  or receiver  26  includes differential amplifiers for determining a heart vector associated with two electrodes.  
         [0059]    Some ECG monitors  28  test for failure or malfunction of electrodes  30 . For example, a signal is output on the lead wire to the electrode  30  or a direct current level associated with the signal from the electrode  30  is monitored. To continue to provide this functionality, the wireless ECG system  20  tests for electrode failure or malfunction and indicates the results to the ECG monitor  28 . For example, the transmitter  24  performs the same or similar tests as the ECG monitor  28 . In other embodiments, the transmitter  24  or receiver  26  determines whether the ECG signal is within an expected range. For example, the controller  112  (FIG. 8) compares the digital electrode signals, such as after interpolation, to maximum and minimum thresholds. If either threshold is exceed by a particular number of samples or for a particular time, a lead-off or faulty electrode  30  is indicated. When one or more samples are subsequently within hysteresis limits of the thresholds, then an error is no longer indicated. When a lead-off condition is indicated, the receiver  26  opens an analog switch or, alternatively does not generate a signal for the output corresponding to the malfunctioning or failed electrode  30 . As a result, the ECG monitor  28  indicates a failure of the electrode  30 . If the transmitter  24  and receiver  26  are out of radio communication range, a lead-off condition is presented to the ECG monitor  28 .  
         [0060]    The ECG monitoring system  20  is used for continuous hexaxial-lead or occasional precordial-lead or both hexaxial-lead and precordial-lead monitoring. FIG. 5 shows the acts representing use of the system  20   
         [0061]    In act  50 , the electrodes  30  are positioned on the patient. For example, electrodes  30  are positioned in hexaxial positions, precordial positions or combinations thereof.  
         [0062]    In act  52 , the electrode connector  22  and transmitter are positioned. The expandable arms  32  are expanded, such as expanding a portion or all of the expandable arms  32 . Another portion of the expandable arms  32  may remain folded or unexpanded. The expandable arms  32  are expanded to reach one or more electrodes.  
         [0063]    In act  54 , the electrode connector  22  is connected with the electrodes  30 . For example, the expandable arms  32  are releasably connected with one or more electrodes  30 , such as snapping or clipping to the electrodes  30 . Expandable arms  32  may also be connected with other expandable arms  32 , hubs  40 , the transmitter  24 , and/or the belt  42 . In an alternative embodiment, the electrodes  30  are connected with the electrode connector  22  prior to positioning the electrodes  30  and expanding the expandable arms  32 .  
         [0064]    In act  56 , the transmitter  24  is operated or turned-on. In one embodiment, a switch on the transmitter  24  activates the transmitter. In alternative embodiments, connection to one or more of the wires  36 , expandable arms  32 , electrode connecter  22  and/or electrodes  30  activates the transmitter  24 . In response, the transmitter  24  radiates a signal representing the electrode signals.  
         [0065]    In act  58 , the receiver  26  is programmed. A code corresponding to the transmitter  24  is entered, or a channel (i.e. frequency) is selected. In an alternative embodiment, the receiver  26  searches a plurality of frequencies for an appropriate signal, such as a signal in an expected format or with a particular code. If more than one signal is identified, an output may be provided for user selection of the appropriate signal. A visual or audible output indicating reception of a signal may be provided.  
         [0066]    In act  60 , wires or electrode connectors from the ECG monitor  28  are connected to the receiver  26 . In alternative embodiments, act  60  occurs before any of acts  50 ,  52 ,  54 ,  56  or  58 .  
         [0067]    In act  62 , the ECG device, such as a monitor, printer or memory, is activated. Analog or digital signals corresponding to signals at the electrodes  30  are received by the ECG device from the receiver  26 . The ECG device processes the signals to generate ECG data, such as one or more heart vectors.  
         [0068]    In one embodiment, a light emitting diode, a light pipe or multiple light emitting diodes, or other output device is provided on the transmitter  24  and/or one or more of the expandable arms  32 . The output device indicates electrical operation of the transmitter or conductance of signals by the wire  36 . Different output devices may represent improper operation. In one embodiment, extending the expandable arm  32  activates operation of the output device or devices.  
         [0069]    The wireless ECG system  20  provides for fewer artifacts due to wire movement, allows the patient to wear clothing without interfering with wires, and provides less psychological intimidation of the patient due to wire connections to a machine. The electrodes  30  are less likely to disconnect because of lower mass or force due to wires connected to the ECG monitor  28 . The wireless ECG system  20  is usable with many different ECG monitors  28  and electrodes  30 . Faster setup when a patient is transferred and connected to a different ECG monitor  28  is provided since the same electrodes  30  already positioned on the patient can be used. Since the electrodes  30  are not repositioned due to a transfer, the ECG monitor output is more comparable to the output of previous ECG monitors. If an electrode  30  fails because of patient movement or perspiration, the electrode can be replaced without replacing the electrode connector  22  or other electrodes  30 .  
         [0070]    While the invention has been described above by reference to various embodiments, it will be understood that many changes and modifications can be made without departing from the scope of the invention. For example, the transmitter and receiver may each comprise transceivers for two-way communication and control. Various aspects can be used with or without other aspects, such as using the electrode connector  22  with a transmitter that processes the electrode signals into ECG vector data rather than transmitted signals representing the electrode signals. Another example is transmitting the electrode signals but using a different electrode connector, strip, patch or mere wires. Other biomedical systems, such as temperature or blood pressure, can be additionally or alternatively monitored using the systems and methods discussed above.  
         [0071]    It is therefore intended that the foregoing detailed description be understood as an illustration of the presently preferred embodiments of the invention, and not as a definition of the invention. It is only the following claims, including all equivalents that are intended to define the scope of this invention.