Abstract:
The invention provides a low cost, fully integrated, disposable patch for the non-invasive, continuous monitoring of fetal electrocardiogram (ECG). The patch detects fetal ECG by filtering the dominant maternal ECG therefrom. In one embodiment, an upper electrode is used to obtain a relatively pure maternal ECG signal for its cancellation from the signal obtained from the abdominal fetal ECG. In another embodiment, multiple abdominal electrodes are used and the dominant periodic features of maternal ECG are identified and eliminated. The fetal monitor patch is thin, flexible, and incorporates a battery and an alarm within. The alarm is activated during an adverse health condition for the fetus. The fetal monitor patch is particularly designed for long-term wear applications exceeding one week and lasting up to several months. The patch is unobtrusive and thus worn continuously, even during sleep and bathing. In another embodiment, the fetal monitor patch is programmable and stored fetal ECG data can be transmitted to a remote receiver.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The invention relates to non-invasive monitoring of fetal vital signs. More particularly, the invention relates to fetal electrocardiogram (ECG) monitoring.  
         [0003]     2. Description of the Prior Art  
         [0004]     Techniques to monitor the fetal status during pregnancy have been developed and are widely used in clinical settings. These methods are necessary to detect possible abnormalities. Early detection of fetal morbidity can have a profound influence on the fetal outcome.  
         [0005]     Monitoring of fetal heart activity is particularly useful in assessing the general health of the baby, as well as the baby&#39;s vascular system in particular. Vital signs, such as fetal heart rate and beat-to-beat rate, and variability are altered by the sympathetic and parasympathetic nervous system, and thus provide an excellent indication of the well-being of the baby. For example, the absence of variability in fetal heart rate is an ominous sign requiring further investigation and possible intervention by medical personnel.  
         [0006]     The high cost and inconvenience of current instruments excludes continuous long term monitoring of high-risk pregnancies. This effectively eliminates the possibility of detecting abnormalities in normal and low risk pregnancies. Monitoring of fetal heart rate can half the incidence of neonatal seizures, which have a close correlation with long-term handicaps (Kam, 1999). In addition to the diagnosis of the general well-being of a fetus, fetal ECG monitoring is particularly useful in detecting congenital heart abnormalities which are present in approximately 0.5-0.8% of all deliveries in the normal population.  
         [0007]     There are several methods commonly used today in non-invasive fetal monitoring: 
        acoustic, ultrasonic, and electrocardiography (ECG).        
 
         [0009]     Acoustic methods involve obtaining fetal acoustics, including heart sounds. This includes using a fetoscope, a stethoscope, or phonographic instruments employing acoustic transducers. However, acoustic fetal monitors are generally difficult to administer, particularly for self-administration, require training, and generally provide limited diagnostic data.  
         [0010]     Ultrasonic methods use reflected acoustic energy in the ultrasonic range to localize and visualize various fetal structures, including heart valves. Heart rates can also be detected using ultrasonic instruments. However, ultrasonic monitoring requires training and the results lack electrophysiologic information. It also requires proper alignment, and thus can be a challenge for self-administration when considering the movement of the fetus in the uterus. Ultrasonic equipment is expensive and consumes a large amount of power, and thus is not suitable for long-term battery-operated applications. For the above reasons, ultrasound monitoring has not been widely employed in ambulatory applications, particularly at home settings.  
         [0011]     Fetal ECG monitoring provides essential diagnostic data particularly that pertaining to the heart. Invasive methods involve placing an electrode on the scalp of the fetus during delivery time. Other invasive methods involve inserting an electrode inside the uterus, i.e. U.S. Pat. No. 5,431,171 to Harrison et al, and U.S. Pat. No. 6,115,624 to Lewis et al Obviously, invasive methods are not practical for screening and ambulatory applications because they generally require the rupture of the protective amniotic sac.  
         [0012]     Body surface potential of ECG from the mother&#39;s abdomen is non-invasive but has many challenges. First, the fetal ECG signal is highly contaminated with the maternal ECG, which may be an order of magnitude stronger than the fetal ECG signals. Second, the fetal ECG signal is inherently weak, and thus easily contaminated by electromagnetic interference (EMI) from power lines and equipment, as well as electromyogram (EMG) from muscle activity.  
         [0013]      FIG. 8   a  is a waveform for a typical fetal ECG with both fetal and mother ECG features shown. The QRS complex of the fetus (QRS f ) is typically weak as compared to the dominant mother QRS (QRS m ). Other ECG features of maternal ECG can also be seen, including the T-wave (T m ). There is no place on the mother&#39;s skin whereby only the fetal ECG can be obtained. However, the ratio of fetal ECG to maternal ECG can be improved substantially when measuring ECG at the abdomen area. Regardless of the strength of fetal ECG, additional processing is necessary to extract fetal ECG and its features for the purpose of identifying cardiac parameters such as average fetal heart rate and beat-to-beat rate.  
         [0014]     Several signal processing algorithms and methods are widely used in relatively large computer-based systems for fetal ECG filtering, including the least mean square (LMS) method, Recursive Least Square (RLS), Blind Source Separation (BSS), Genetic Algorithms, and fuzzy logic. Furthermore, combinations of signal processing methods have been applied for the proper filtering and detection of fetal ECG features. However, even with advances in instrumentation and signal processing methods, current proposed systems are generally bulky and limit the monitoring to clinical setups in the presence of trained personnel. For example, see U.S. Pat. No. 5,123,420 to Paret, U.S. Pat. No. 5,372,139 to Holls et al, and U.S. Pat. No. 5,042,499 to Frank et al. These prior art instruments and methods are expensive and exclude home monitoring and are typically limited to high-risk pregnancies.  
         [0015]     U.S. Pat. No. 4,781,200 to Baker discloses a system for automatic and continuous monitoring the well-being of a fetus. Baker&#39;s device incorporates a belt garment with multiple sensors worn about the mother&#39;s abdomen. The device incorporates a control unit  40  ( FIG. 1  of Baker) attached to the belt garment. The control box incorporates a display, an alarm, and means for processing multiple physiologic parameters, and is particularly suited for indicating movements of the fetus. Although less bulky and more suited for ambulatory purposes than prior art mentioned above, Baker&#39;s invention is relatively complex, expensive, and cumbersome for expectant mothers, particularly during sleep when considering the physical profile of the control box.  
         [0016]     One object of the invention is to provide a fetal monitor device and method that is unobtrusive and that can be worn continuously and conveniently by an expectant mother at home.  
         [0017]     A further objective of the invention is to provide a low cost fetal monitor that is suitable for use by all pregnant mothers, including those with normal and low risk pregnancies.  
         [0018]     A further objective is to develop an automated fetal monitor, which eliminates supervision or intervention by medical personnel.  
         [0019]     A further objective is to provide real-time fetal heart indications, particularly an alarm during adverse conditions.  
       SUMMARY OF THE INVENTION  
       [0020]     The invention provides a low cost patch for the non-invasive monitoring of a fetus. The patch is adhered on the abdomen area of an expectant mother for continuous and automatic monitoring of fetal electrocardiogram (ECG). The fully integrated monitor patch detects the surface potentials present on the abdomen area and filters out the maternal component of ECG which contaminates fetal ECG. Filtering is accomplished by a combination of proper electrode placement and signal processing. In one embodiment, an upper electrode obtains a relatively pure maternal ECG signal that is used for the cancellation of maternal ECG component from the abdominal fetal ECG. In another embodiment, the dominant periodic features of maternal ECG are identified and eliminated from measurements obtained from multiple abdominal electrodes.  
         [0021]     The fetal monitor patch is thin, flexible, and incorporates a battery and an alarm within. The alarm is activated during an adverse health condition for the fetus. In the preferred embodiment, the fetal monitor patch is disposable, and is thus discarded upon battery depletion. Although particularly useful for monitoring high-risk pregnancies, the simplicity and low cost aspect of the invented patch allow for use by all pregnant women.  
         [0022]     The fetal monitor patch is particularly suited for long-term wear exceeding one week and lasting up to several months. The patch is worn continuously even during sleep and showering, and is thus made durable and waterproof, while being flexible and unobtrusive, for inconspicuous wear underneath clothing. Alternatively, the fetal monitor patch can be used for short term or spot check applications.  
         [0023]     Real-time fetal heart activity can be indicated to the mother for continuous assurance of fetal health. This is accomplished by providing an audible tone or a flashing signal in sync with fetal QRS events.  
         [0024]     In another embodiment for diagnostic applications, the fetal monitor patch is wirelessly programmable using an external programmer. The programmable patch collects fetal ECG data in memory while providing a real-time monitoring and indications for the pregnant mother. The fetal ECG data is then transmitted to a clinic via a telephone, a personal computer connected to the Internet, or by an interrogation device at the clinic. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a frontal view of a fetal monitor patch placed on the abdomen of an expectant mother, in which the patch is vertically elongated with an upper electrode for cancellation of maternal ECG component;  
         [0026]      FIG. 2  is detailed view of the vertically elongated fetal monitor patch of  FIG. 1  showing the major internal components;  
         [0027]      FIG. 3  is a cross section view of the fetal monitor patch in  FIG. 2 ;  
         [0028]      FIG. 4  is a detailed cross section view of a section of the fetal monitor patch of  FIG. 2 , showing the various layers including a metal foil layer;  
         [0029]      FIG. 5  shows a rectangular embodiment of a fetal monitor patch having three electrodes;  
         [0030]      FIG. 6  shows a 5-electrode embodiment placed on the abdomen of an expectant mother;  
         [0031]      FIG. 7  is a schematic diagram of the electronic assembly within the fetal monitor patch, showing audible and visual indicators and wireless control by an external magnet;  
         [0032]      FIG. 8   a  shows the fetal ECG contaminated by the dominant maternal ECG;  
         [0033]      FIG. 8   b  shows extract QRS complex of the fetal ECG;  
         [0034]      FIG. 9  is a block diagram of a typical signal processing algorithm and a multiplexer for electrode selection;  
         [0035]      FIG. 10  shows an embodiment of the fetal monitor patch having two maternal ECG electrodes;  
         [0036]      FIG. 11  shows an abdominal-only electrode configuration of the fetal monitor patch;  
         [0037]      FIG. 12  shows a block diagram of adaptive filtering of ECG signals from an abdominal-only fetal monitor patch;  
         [0038]      FIG. 13  shows a fetal monitor patch placed on the side of the abdomen;  
         [0039]      FIG. 14  shows a programmable fetal monitor patch having a wireless programming device with a programming coil in proximity to a wireless sensor incorporated in the patch; and  
         [0040]      FIG. 15  shows a fetal monitor patch equipped with acoustic transducers for transferring ECG data acoustically over the telephone.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     The invention, shown in various embodiments of  FIGS. 1-7 ,  10 ,  11  and  13 - 15 , is non-invasive fetal electrocardiogram (ECG) monitoring device  10  in the form of a patch placed on the abdomen area  2  of an expectant mother  1 . The patch device  10  is thin and flexible for unobtrusive continuous wear.  
         [0042]     Referring to the embodiment of  FIGS. 1-3 , the patch device  10  comprises a lower abdomen electrode  20  for obtaining fetal ECG signal, a reference electrode  21 , and a maternal electrode  22  for obtaining relatively pure maternal ECG. The device  10  comprises an electronic assembly  30  including an ECG amplifier  31 , a processor  32 , and a power source  33 . The processor  32  is typically a digital signal processor for performing numerical computation from data obtained from an analog to digital converter  36  ( FIG. 7 ).  
         [0043]     In a more detailed view of the device shown in  FIGS. 2-4 , the electronic assembly  30  is mounted on a flexible circuit substrate  40  with trace extensions  41 ,  42 ,  43  and  45  connecting the electronic assembly  30  to electrodes  20 ,  21 ,  22  and the power source  33 , respectively. Conductive adhesive films  50 ,  51  and  52  cover metal electrodes  20 ,  21  and  22 , respectively. Conductive adhesive films  50 ,  51 , and  52  contact the skin directly to conduct surface ECG potentials to the ECG amplifier  31 . A non-conductive adhesive  55  provides an overall adhesive to secure the patch device  10  to the body. The device  10  also comprises a thin substrate  26  ( FIG. 3-5 ) for providing structural support. The substrate  26  is made of soft flexible sheath material, such as polyurethane or cloth. The thickness of the patch device  10  is preferably in the range of 1.5 and 2.5 mm but no more than 3.5 mm.  
         [0044]     The patch assembly  10  may comprise as few as two electrodes or as many as five or more electrodes, depending on the desired fetal ECG results. Two or three electrodes are sufficient for basic monitoring applications, whereby only the basic features (also known as singular points) of fetal ECG are required, such as for the identification of R-wave. In these embodiments, feature extraction of maternal and fetal ECG based on singular value decomposition is applicable. Feature extraction of fetal R-wave is particularly useful due to its intensity relative to other fetal ECG waveform features.  
         [0045]      FIG. 1-3  show an elongated patch arranged in a vertical electrode configuration. One advantage of this configuration is that it places at least one electrode near or at the chest area  3  for obtaining a relatively pure maternal ECG signal.  FIG. 5  shows an alternate  3  electrode configuration whereby the patch is rectangular in shape, having a single upper electrode (E M ), and two electrodes, E R, , E L  for placement on the right and left sides of the lower abdomen.  
         [0046]     Recent research indicates that a more detailed feature extraction of fetal ECG signals can be valuable in detecting vascular abnormalities of the fetus. This type of diagnostic analysis would require additional details of fetal ECG not easily attained with two or three electrodes.  
         [0047]      FIG. 6  shows a 5-electrode embodiment, having an upper electrode E M  for maternal ECG monitoring and four abdominal electrodes E 1 , E 2 , E 3  and E 4 , for fetal ECG monitoring.  
         [0048]     The multi-abdominal electrode configuration is also useful in applications to minimize the effects of fetal position movement in the uterus, thereby ensuring the strongest fetal ECG signal possible regardless of fetus position. This is partially accomplished by the application of a multiplexer (MUX,  35 ;  FIG. 7 ), whereby any two electrode leads can be paired as a differential input to the ECG amplifiers  31 A,  31 B,  31 C. Because the multiplexer  35  is under the control of the processor  32 , network selection of electrodes can be dynamically performed in real-time for obtaining the desired fetal ECG signal.  
         [0049]     Optimal fetal ECG signal is also partially accomplished by the application of adaptive signal processing algorithms. In its simplest form shown in  FIG. 9 , filtered fetal ECG is obtained by optimizing a filter function H(z)  70  by an adaptive filtering algorithm  71 , leading to optimal cancellation of the maternal ECG component from the fetal ECG.  
         [0050]     Because fetal ECG is typically an order of magnitude smaller than maternal ECG (see  FIG. 8   a ), the optimal algorithm is obtained when filtered fetal ECG magnitude is minimized at the output of the summer  72 . The optimization process is made periodically to select optimal abdominal electrode selection dynamically ( FIG. 9 ), or pairing ( FIG. 7 ) of electrodes E 1  through E n .  FIG. 8   b  shows filtered fetal ECG with maternal ECG components removed and fetal QRS (QRS f ) identified.  
         [0051]     Various filtering methods are known in the field of signal processing and particularly pertaining to ECG signals. Filtering is not only necessary for removing the maternal component of ECG but also for filtering out various noise forms, such as electromagnetic interference (EMI) and muscle activity (EMG). For example, notch filters are effective in removing 60 Hz noise present in the environment. To minimize interference further, a metal foil  38  ( FIG. 4 ) is preferably provided over the substrate  26 , either over the entire device patch, or selectively over certain electronic traces and components sensitive to interference.  
         [0052]     The power source  33  in the preferred embodiments is a primary battery with long shelf life. However, a rechargeable power source, such as rechargeable battery or charge capacitor, can be employed in conjunction with an external charging device (not shown). Wireless recharging methods are well known in the field of biomedical implants including inductive coupling whereby a coil within the device (not shown) is used to receive a charging energy from an external coil introduced in proximity.  
         [0053]     Other configurations of the invented patch include multiple maternal electrodes, as shown in  FIG. 10 . In this configuration, two maternal electrodes E m1  and E m2  are used for receiving relatively pure maternal ECG and two abdominal electrode E f1  and E f2  for receiving fetal ECG contaminated with maternal ECG component. A reference electrode E R  is used as a reference node for both maternal and abdominal measurements.  
         [0054]     In yet another embodiment, abdominal-only electrodes are provided as shown in  FIG. 11 . This configuration works on the principle of equal-potential contours  62 , which are orthogonal to the maternal ECG vector  61  emanating from the maternal heart  60 , whereby the ECG waveform is substantially similar along a particular equal-potential contour. In contrast, the fetal ECG vector  66 , emanating from the fetal heart  65 , results in substantially varied waveform at points along a maternal equal-potential contour. By extracting the highly similar maternal ECG component from multiple abdominal electrodes along a maternal equal-potential contour, a filtered fetal ECG is obtained. In this particular embodiment, abdominal electrodes E f1 , E f2  and E R  are substantially aligned horizontally as shown in  FIG. 11 . To enhance the cancellation of a maternal ECG, a filtering function H(z)  70  ( FIG. 9 ) is applied with an adaptive signal processing algorithm  71  to produce optimal cancellation signal at input of the summer  72  and resulting in a filtered fetal ECG (FFECG) at the output.  
         [0055]      FIG. 13  shows another embodiment placing the fetal monitor patch device  10  on the side of the abdomen. Other embodiments envisioned (not shown) include providing an abdominal patch extending to the back of an expectant mother.  
         [0056]     A major feature of the abdominal patch of the invention is the incorporation of an indicator transducer  34  for indicating the status of the fetus to the mother. For example an alarm transducer is activated during a hazard event detected by the monitor device  10 . The indicator transducer  34  may be in the form of an audible transducer ( 44 ,  FIG. 7 ), such as a buzzer or a speaker; or it may be in the form of visual display  46 , such as a light emitting diode (LED) or a liquid crystal display (LCD). Another example of an indicator transducer is a vibrating element for imparting tactile sensations for the mother. The indicator may also be used to indicate other cardiac activity, such as fetal heartbeat events. For example, beeping sounds or LED flashes synchronized with fetal heartbeats detected by the patch device system.  
         [0057]     The use of Blind Source Separation (BSS) or any other suitable algorithm may also be used to detect further and separate the ECG of twins. Multiple gestation cases (mostly twins) occur in about 1% of all pregnancies. The indication for twin ECG must be distinguished appropriately from single fetal ECG. For example, by presenting double beeps, double flashes, or alternatively presenting a different pitch or tone for each fetal ECG.  
         [0058]     The heart activity indication through indicator transducer  34  is preferably under the remote control of the mother for activation and deactivation. For example, the mother may choose to turn off sounds representing QRS, to create a quiet mode of operation. For reassurance, these sounds can be reactivated by the mother periodically. Similarly, visual indications can also be activated and deactivated by the mother.  
         [0059]      FIG. 7  is a schematic diagram that shows major components of an embodiment comprising a remote control device  76  in the form of magnet  78  having a magnetic field  77 . A reed-switch  39  (wireless sensor) incorporated in the patch device  10  responds to the magnetic field  77  of the magnet when introduced in proximity thereto. The triggering of the reed-switch by the magnetic field (closure of the reeds) causes the sound mechanism  44  and/or visual display  46  display to toggle between activation and deactivation. However, it must be understood that heartbeat indication is separate and distinct from alarm indication, and thus both must be present in clearly differentiated forms.  
         [0060]     In another embodiment of the invented fetal monitor shown in  FIG. 14 , the device is programmable to configure the operational parameters of each patch individually according to the needs and condition of the expectant mother. Operational parameters include sampling rate, filtering algorithm, electrode position and selection, alarm indication method, i.e. alarm tone selection, and alarm indication criteria, Programming is preferably by wireless means incorporating a wireless receiver  39  to receive coded wireless commands  81  from a transmitter  82  of an external programming unit  80 . In  FIG. 14 , the wireless receiver  39  is a miniature reed-switch for receiving magnetic pulses from an electromagnet coil  83  incorporated in the transmitter  82 . The transmitter is preferably in the form of hand-held wand.  
         [0061]     Furthermore, possible features include the ability to transmit ECG data stored in memory  37  to a remote receiver (not shown) for display and clinical analysis by a medical staff. For example,  FIG. 15  shows acoustic trans-telephonic transmission of data from an audio transducer  44  incorporated within the patch device  10  to the mouthpiece of the telephone handset  85 . In this embodiment, acoustic interrogation commands from the remote unit via the earpiece of the handset can also be downloaded into the patch device  10  via the receiver audio transducer  47 . It should be obvious that both fetal and maternal ECG can be stored and transmitted to a remote receiver.  
         [0062]     The wireless reception of commands and transmission of data may be accomplished in numerous ways and methods known in the field of remote control and wireless transmission of data. This includes optical, radio frequency (RF), magnetic, ultrasonic, and acoustic transmission. Furthermore, the indicator transducer  34  mentioned above can be used for the dual function of heart activity indication and data transmission. For example, a buzzer can be used to sound an alarm, as well as to send ECG data acoustically to remote location or a receiver unit in a clinical setup. Similarly, an LED indicator can be used to indicate heart activity to the mother, as well as to send ECG data to a receiver unit equipped with an optical detector. The programming unit  80  ( FIG. 14 ) can also serve as a receiver unit. The combined programming/receiver unit can be a desktop, a portable, or a handheld instrument.  
         [0063]     The invented fetal monitor patch is particularly designed for long-term wear by the expectant mother. For this reason, many design details are incorporated for the device to function properly and reliably for extended periods of time exceeding one week and lasting to several months. The adhesion to the abdomen skin may be designed for single-use or multiple applications. In single-use applications, the patch device is applied once for continuous wear until removed for its disposal several weeks later. In this case, the patch is worn even during sleep and bathing. In multiple applications design, the adhesive allows for multiple removal and reapplication to the skin. In either design, the adhesive  55  incorporated in the device  10  must provide continuous reliable adhesion to prevent inadvertent peeling of the device from the abdomen skin. A biocompatible skin adhesive, such as hydrogel and like materials, has been shown to be effective in human skin applications. The ideal properties of the skin adhesive include being waterproof and air-permeable. Waterproof properties aid in the protection of the electrode area underneath the patch from water-born contaminants. Air permeability properties allow for the healthy aeration of the tissue underneath patch device.  
         [0064]     To achieve longevity of operation for the patch device, various means for power conservation must be considered. This includes power management (PM) circuitry ( 24   FIG. 7 ) to shut off certain electronic components selectively when not in use. The patch device  10  also incorporates stretchable areas  25  to allow for abdomen expansion expected during the gestation period. The construction of the device must be durable and protective of the components within. Metal foil  38  covering the internal components and substrate  26 , not only provides EMI protection, but also water proofing and overall protection.  
         [0065]     Proper patch adhesion to the skin is not only important for waterproofing purposes, but also to maintain proper electrode-skin contact throughout device wear and operation. This is important for obtaining adequate ECG signal-to-noise-ratio. Electrode-skin contact can be indicated indirectly by measuring the impedance between adjacent electrodes. Normal electrode-electrode impedance is generally in the range of 1 to 15 k-ohms depending on the condition of the skin and the distance between the electrodes. Measurement and detection of electrode-electrode impedance can also be used to activate the patch device  10  automatically upon its placement on the abdomen skin. Automatic activation can also be accomplished during the removal of the patch device from its package, i.e. a pouch. For example, by incorporating open-circuit and/or short-circuit conditions between the electrodes within the package. These circuit conditions are altered during the removal of the patch device  10  from the package triggering the activation of the device. These and other automatic activation means and methods will be readily recognized by those skilled in the art of electronics and medical device packaging.  
         [0066]     Although the invention is described herein with reference to the preferred embodiment, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the claims included below.