Abstract:
A method and apparatus for generating a signal representing uterine activity. The method including the acts of obtaining a uterine electromyography (EMG) signal, and processing the uterine EMG signal to produce a signal representative of uterine activity. The apparatus including a sensor for acquiring a uterine electromyography (EMG) signal, and a signal processor for generating a signal representative of uterine activity in response to the uterine EMG signal.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method and apparatus for generating a signal representing uterine activity, and particularly to a monitor for obtaining and processing a uterine electromyography signal to produce a signal representative of uterine activity. 
     Uterine activity and fetal heart rate are two primary parameters measured in fetal monitoring during birth delivery. Current practice uses two methods to measure uterine activity. The first method is internal to the patient and uses an intrauterine pressure sensor (hereinafter referred to as a “IUP” sensor). The IUP sensor is an invasive device that can only be used after rupturing membranes. The IUP sensor produces an output that is a true function of uterine pressure and monitors contraction frequency and contraction duration. The second method is external to the patient and uses a tocodynamometer (hereinafter referred to as “toco”). The toco is a non-invasive device that is placed on the maternal abdomen and is secured with an elastic belt or strap. The toco does not provide any information representative of uterine pressure, and is used to monitor contraction frequency and contraction duration. The output from the IUP sensor or the toco is processed by the fetal monitor and is printed or displayed on a uterine activity chart. An example uterine activity chart is shown in FIG. 1 where the uterine activity chart  10  displays a uterine activity waveform  15  resulting from a processed toco signal. 
     SUMMARY OF THE INVENTION 
     Uterine contractions are the result of coordinated contractions by individual myometrial cells of the uterus. At the cellular level, the contractions are triggered by an action potential. The action potential is a voltage signal that can be measured as an electromyography (hereinafter referred to as “EMG”) signal. During pregnancy, cellular electrical connectivity increases such that the action potential propagates to produce a coordinated contraction involving the entire uterus. The action potential during a uterine contraction can be measured with electrodes placed on the maternal abdomen resulting in a uterine EMG signal. The EMG signal is then processed to produce a signal that is functionally equivalent to a uterine activity signal created by a toco. The equivalent uterine activity signal provides contraction frequency and contraction duration information. In addition, the EMG signal approximates at least one component that would be acquired by an IUP sensor. 
     Accordingly, the invention provides a monitor. The monitor includes a sensor for acquiring a uterine EMG signal and a signal processor for generating a signal representative of uterine activity in response to the uterine EMG signal. The signal representative of uterine activity indicates uterine contraction frequency and contraction duration information. Additionally, the signal representative of uterine activity approximates a signal that would be acquired using either a toco or approximates at least one component of a signal that would be acquired using an IUP sensor. 
     In a first embodiment, the signal processor includes a receiver that receives the uterine EMG signal from the sensor and generates an analog signal representative of uterine activity. The signal processor further includes a microprocessor electrically connected to the receiver for receiving the analog signal representative of uterine activity and converting the analog signal representative of uterine activity into a digital signal representative of uterine activity. The signal processor also includes a memory unit electrically connected to the microprocessor for storing the digital signal representative of uterine activity. 
     In a second embodiment, the signal processor includes a microprocessor that receives the uterine EMG signal and generates a signal representative of uterine activity. The received uterine EMG signal can be a signal that is received directly from the sensor or can be a uterine EMG signal that has be processed by an amplifier and band-pass filter. The microprocessor includes software to perform digital signal processing techniques on the received uterine EMG signal. 
     The invention further provides a method of generating a signal representing uterine activity. The method includes the acts of obtaining a uterine EMG signal and processing the uterine EMG signal to produce a signal representative of uterine activity. In a first embodiment, the act of processing this uterine EMG signal includes the acts of amplifying the EMG signal, filtering the EMG signal, rectifying the EMG signal to obtain a rectified signal, applying the rectified signal to a peak detector to obtain an analog signal representative of uterine activity, sampling the analog signal representative of uterine activity to obtain data for a digital signal representative of uterine activity, and storing the data of the digital signal representative of uterine activity. In a second embodiment, the act of processing the uterine EMG signal includes the acts of sampling the uterine EMG signal to create a bipolar digital waveform, converting the bipolar digital waveform to a unipolar digital waveform, and time averaging the unipolar digital waveform to obtain the signal representative of uterine activity. 
     The invention further provides a system for generating a signal representing uterine activity. The system includes a sensor for obtaining a uterine electromyography (EMG) signal, and means for processing the uterine EMG signal to produce a signal representative of uterine activity. 
     The invention further provides a software program for operating a monitor. The monitor includes a sensor for acquiring a uterine electromyography (EMG) signal and a microprocessor for executing the software program. The software program operates the monitor by sampling the uterine EMG signal to obtain a bipolar digital waveform, and processing the sample uterine EMG signal to produce a signal representative of uterine activity. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a chart displaying a typical uterine activity waveform resulting from a toco sensor. 
     FIG. 2 is a schematic representation of a monitor embodying the invention. 
     FIG. 3 is a chart displaying a “raw” uterine EMG signal. 
     FIG. 4 is a chart displaying an equivalent uterine activity waveform. 
     FIG. 5 is a schematic representation of a monitor embodying the invention. 
    
    
     DETAILED DESCRIPTION 
     Before one embodiment of the invention is explained in full detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     Shown in FIG. 2 of the drawings is a monitor  20  embodying the invention. In general terms, the monitor  20  includes a sensor  25 , a central processing unit  35 , and output units  125 ,  130 ,  135  and/or  140 . The sensor  25  acquires a “raw” uterine electromyography (EMG) signal  27  (FIG. 3) from a patient (not shown). The sensor  25  includes one or more pairs of electrodes  30  that are placed on the patient&#39;s (i.e., the mother&#39;s) abdomen (not shown). The electrodes  30  generate action potentials that are measured differentially across the one or more pairs of electrodes  30  resulting in the raw uterine EMG signal  27 . Additional driven or passive electrodes (not shown) may be placed on the patient to establish a reference potential on the patient or to cancel out unwanted common mode signals and noise. The electrodes  30  include lead wires (not shown) that connect to an interface cable  40 . The interface cable  40  allows for transmission of the raw uterine EMG signal  27  from the electrodes  30  to the central processing unit  35 . The interface cable  40  is preferably a passive cable between the electrodes  30  and the central unit  35 . Alternatively, the cable may contain active circuitry (not shown) for amplifying and/or combining lead signals. 
     The central processing unit  35  has a housing  45 . The housing  45  includes communication ports  50 ,  55 ,  60 ,  65  and  70 . Additional communication ports can be added as needed. 
     The central unit  35  includes a signal processor  85 . or means for generating a signal representative of uterine activity in response to the uterine EMG signal. The signal processor  85  receives the raw uterine EMG signal from the sensor  25  and processes the uterine EMG signal into a signal representative of uterine activity. The signal representative of uterine activity is printed or displayed on a uterine activity chart  87  (FIG. 4) as an equivalent uterine activity waveform  90  (FIG.  4 ). The equivalent uterine activity waveform  90  is equivalent to the typical uterine activity waveform  10  (FIG.  1 ). 
     As shown in FIG. 2, the signal processor  85  includes a receiver  95  that receives the uterine EMG signal from the sensor  25  and generates an analog signal representative of uterine activity. The receiver includes an amplifier and band-pass filter  100 , a full-wave peak rectifier  105  electrically connected to the amplifier and band-pass filter  100 , and a peak detector  110  electrically connected to the full wave rectifier  105 . 
     The signal process  85  further includes a microprocessor  115  electrically connected to the receiver  85 . The microprocessor  115  receives the analog signal representative of uterine activity and converts the analog signal into a digital signal representative of uterine activity. The signal processor  85  further includes internal memory  120  electrically connected to the microprocessor  115 . If only an analog signal representative of uterine activity is desired, then the microprocessor  115  and internal memory  120  are not required. Furthermore, the signal processor  85  can further include addition circuitry (not shown) to perform additional fetal monitoring parameters (e.g., fetal heart rate). 
     As shown in FIG. 2, output units  125 ,  130 ,  135  and  140  are connected to the central unit  35  at communication ports  55 ,  60 ,  65  and  70 . The output units include a printer  125 , a video display unit  130 , a storage device  135  (e.g., magnetic disc drive, read/write CD-ROM, etc.), and a server  140  or other processing unit (e.g., a personal computer). The server  140  is connected via a distributed network  145 . Of course, other output units can be attached or the output units (e.g., the visual display unit  130 ) can be incorporated within the central unit  35 . Additionally, not all of the output units are required for operation of the monitor. 
     In operation, the electrodes  30  of the sensor  25  are connected to a patient (not shown). The electrodes  30  obtain a raw uterine EMG signal  27  (FIG. 3) that is transmitted to the signal processor  85  of the control unit  45  via interface cable  40 . Upon receiving the raw EMG signal from the sensor  25 , the signal processor  85  processes the signal to create a signal representative of uterine activity. The resulting signal representative of uterine activity can be stored in internal memory  123 , printed by the printer  125 , displayed on the visual display unit  130 , stored in storage device  135 , and/or provided by communication link  145  to another computer or server  140 . The signal representative of uterine activity is displayed or printed on a uterine activity chart  87  as an equivalent uterine activity waveform  90  as shown in FIG.  4 . The equivalent uterine activity waveform  90  is representative of a typical uterine activity waveform  15  (FIG. 1) generated by a toco or is representative of at least one component of a typical uterine activity waveform (not shown) generated by a IUP sensor. 
     For the embodiment shown in FIG. 2, the signal processor  85  processes the raw uterine EMG signal  22  by first providing the signal to the receiver  95 . Upon receiving the raw uterine EMG signal  22 , the receiver  95  generates an analog signal representative of uterine activity. This is accomplished by first providing the acquired raw uterine EMG signal to the amplifier and band-pass filter  100  to create a processed uterine EMG signal. Amplifying and filtering the raw uterine EMG signal distinguishes the EMG signal from other biological signals and noise sources. After amplifying and filtering the raw EMG signal, the processed EMG signal is provided to the full-wave rectifier  105 . The full-wave rectifier  105  inverts the negative portion of the processed EMG signal resulting in a rectified signal. The rectified signal is then applied to the peak detector  110 . The peak detector  110  generates a peak value signal having the peak values of the rectified signal. The generated peak value signal is the analog signal representative of uterine activity. 
     The signal processor  85  shown in FIG. 2 further processes the EMG signal by creating a digital signal representative of uterine activity from the analog signal representative of uterine activity. To create the digital signal representative of uterine activity, the peak value signal is provided to the microprocessor  115 . The microprocessor  115  receives the peak value signal and samples the peak value signal. After sampling the peak value signal, the microprocessor  115  temporarily holds or stores the sampled signal in internal memory  120 . As the signal is being sampled or after the signal has finished being sampled, the microprocessor  115  scales the data for displaying, printing, storing or transmitting the sampled signal. The microprocessor  115  scales the sampled data to a scale that is comparable to a typical uterine activity chart  10 . In other words, by scaling the sampled data, the scaled data, when displayed, appears to a user to approximate a typical uterine activity waveform. After the data has been scaled, the resulting scaled data can be printed in hardcopy by the printer  135 , displayed on the visual display unit  130 , stored in the storage device  135 , or provided to the server  140  via the distributed network  145 . The resulting scaled data provides a digital signal that, when viewed by an operator (e.g., on a visual display), is substantially equivalent to the uterine activity waveform  90  as shown in FIG.  4 . 
     FIG. 5 illustrates a monitor  200 , which is an alternative embodiment of the invention. Like parts are identified using like reference numerals. As shown in FIG. 5, the signal processor  85  includes a microprocessor  122  and internal memory  123 . In this embodiment, the microprocessor  122  receives a uterine EMG signal and generates a signal representative of uterine activity. The received uterine EMG signal can be either the raw uterine EMG signal  27  from the electrodes  30  or can be a processed uterine EMG signal resulting from an amplifier and filter (not shown). Upon receiving the uterine EMG signal, the microprocessor  122  executes digital processing software that processes the received EMG signal resulting in the signal representative of uterine activity. 
     For the embodiment shown in FIG. 5, the signal processor  85  processes the raw EMG signal  27  by first providing the signal to microprocessor  122  (assuming an amplifier and filter is not present). The microprocessor  122  samples the raw EMG signal for digital signal processing and stores the sampled data in internal memory  123 . When executing the digital signal processing software, the microprocessor  122  first digitally filters the raw EMG signal  27  from other biological signals and noise sources. The filtering of the EMG signals is accomplished by spectral analysis techniques, wavelet analysis techniques, recognition of EMG wave characteristics, and/or cross signal verification techniques. 
     If the signal processor  85  shown in FIG. 5 includes an amplifier and filter (not shown), then the raw EMG signal  27  is first provided to the amplifier and filter. The amplifier and filter performs the same function as the amplifier and filter  100  of FIG. 2 resulting in a processed uterine EMG signal. The processed uterine EMG signal is then provided to the microprocessor  123  where the microprocessor  123  samples the processed signal for digital signal processing. 
     Once the raw uterine EMG signal has been amplified and filtered, the microprocessor  122  processes the signal to produce an equivalent uterine activity waveform  90 . One possible digital signal processing technique performs a bipolar to unipolar conversion (similar to rectifier  105 ) and a time averaging of the converted waveform with adjustments made to the presented uterine contraction intensity based on signal characteristics (similar to the peak detector  110 ). The microprocessor  122  then scales the data to a scale that is comparable to a typical uterine activity chart  10 . After the data has been scaled, the resulting signal can be printed in hardcopy by the printer  135 , displayed on the visual display unit  130 , stored in the storage device  135  or provided to the server  140  via the distributed network  145 . 
     The uterine activity monitor and method of operation of the uterine activity monitor should be apparent from the description and drawings herein and additional details are not provided. Many possible forms of the invention may be constructed based on the teachings set forth herein. Therefore, while the present invention has been described in reference to particular embodiments and examples, it should be understood that the invention is not confined to the particular construction and arrangement of the components illustrated and described, but embraces all forms encompassed by the following claims.