WO2012106219A1 - Monitoring of uterine contraction intensity and fetal heart rate - Google Patents

Monitoring of uterine contraction intensity and fetal heart rate Download PDF

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Publication number
WO2012106219A1
WO2012106219A1 PCT/US2012/023060 US2012023060W WO2012106219A1 WO 2012106219 A1 WO2012106219 A1 WO 2012106219A1 US 2012023060 W US2012023060 W US 2012023060W WO 2012106219 A1 WO2012106219 A1 WO 2012106219A1
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Prior art keywords
eum
electrode
uterine
according
substrate
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PCT/US2012/023060
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French (fr)
Inventor
Gal Ben-David
Ilan Calderon
Maayan Lia YIZREELI
Libi Lea HAVIVI
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Obt Ltd.
Klein, David
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Priority to US201161437745P priority Critical
Priority to US61/437,745 priority
Priority to US61/440,421 priority
Priority to US201161440419P priority
Priority to US201161440422P priority
Priority to US201161440421P priority
Priority to US61/440,422 priority
Priority to US61/440,419 priority
Application filed by Obt Ltd., Klein, David filed Critical Obt Ltd.
Publication of WO2012106219A1 publication Critical patent/WO2012106219A1/en

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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/43Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4356Assessing uterine contractions
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/04Measuring bioelectric signals of the body or parts thereof
    • A61B5/0402Electrocardiography, i.e. ECG
    • A61B5/0444Foetal cardiography
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/04Measuring bioelectric signals of the body or parts thereof
    • A61B5/0488Electromyography
    • A61B5/04882Electromyography of genito-urinary organs
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/43Detecting, measuring or recording for evaluating the reproductive systems
    • A61B5/4306Detecting, measuring or recording for evaluating the reproductive systems for evaluating the female reproductive systems, e.g. gynaecological evaluations
    • A61B5/4343Pregnancy and labour monitoring, e.g. for labour onset detection
    • A61B5/4362Assessing foetal parameters
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/04Arrangements of multiple sensors of the same type
    • A61B2562/046Arrangements of multiple sensors of the same type in a matrix array
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/08Sensors provided with means for identification, e.g. barcodes or memory chips
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/683Means for maintaining contact with the body
    • A61B5/6831Straps, bands or harnesses
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/684Indicating the position of the sensor on the body

Abstract

An electrical uterine monitor (EUM) electrode (10) characterised by one or more uterine activity sensors (12) mounted on a substrate (14), and at least one fiduciary mark (18) that has repeatable positioning capability relative to an anatomic feature of a woman for repeatable positioning of the EUM electrode (10).

Description

MONITORING OF UTERINE CONTRACTION INTENSITY AND FETAL HEART

RATE

FIELD OF THE INVENTION

The present invention relates generally to monitoring (e.g., measuring, imaging and displaying) of myographic activity, such as that of the uterus as well as sensing fetal heart signal.

BACKGROUND OF THE INVENTION

A normal uterus does not contract vigorously throughout most of pregnancy and thus provides a tranquil environment for the growing fetus. At term, the myometrium (muscular tissue of the uterus) undergoes a series of changes that lead to synchronous, rhythmic uterine contractions, that is, labor. Contractions of the uterus are directly proportional to the underlying electrical activity of the muscle. The frequency, duration and magnitude of a uterine contraction are directly proportional respectively to the frequency, duration and propagation of action potentials in the myometrium and other muscle cells associated with movement of the uterus. Between bursts of action potentials, the uterus relaxes and recovers. The relaxation phase in the uterus is very important in providing a respite for both the muscle and the fetus.

Uterine contractions and fetal heart rate are common practice in evaluating well being of the fetus during pregnancy and during labor.

Two technologies are commonly used in the prior art to measure uterine contraction:

a. Tocodynamometer - This is a non-invasive method that does not directly measure contractions, but instead measures abdominal stiffness. The tocodynamometer can measure contraction time parameters (e.g., start time, peak time, end time, duration, frequency of contractions over a given period of time), but it does not measure intensity of contraction.

b. Intra Uterine Pressure Catheter (IUPC) - This is an invasive device that is inserted into the uterus after rupture of the membrane, and directly measures pressure. The device is considered to be the "gold standard", and can measure contraction time parameters as well as intensity. However, it cannot be used during pregnancy, and it may be blocked by the fetus, blood, etc.

Fetal heart rate (FHR) is usually measured by Doppler sensors. Some monitors, such as the HP Viridia Series 50 XM Fetal Monitor, monitor both contractions using either TOCO or IUPC and FHR.

However, all of these three technologies do not allow women to move during clinical test. TOCO will not sense abdominal stiffness. IUPC is an invasive device, so it needs a clean environment. Doppler sensors need to be aimed at the fetal heart and lose signal when fetus or sensor moves.

It is also known that by recording uterine electrical activity, one can assess the contractility of the myometrium. US Patent 7,447,542 to Calderon et al. describes an improved system for three-dimensional monitoring (e.g., measuring, imaging and displaying) of myographic uterine activity. The system includes an electromyogram (EMG) system that senses electromyographic activity generated in a muscle, one or more position sensors, and a processor in communication with the EMG system and the position sensors. The processor processes data of the EMG system and the three- dimensional position information from the position sensors to provide an output of electromyographic activity data in the three dimensional space.

SUMMARY OF THE INVENTION

The electrical uterine monitor (EUM) technology as presented in US Patent 7,447,542 is much more robust to maternal movements compared with TOCO/IUPC/Doppler. The present invention seeks to use this EUM technology to provide a portable maternal-fetal monitoring device for home monitoring and for the hospital/clinic environment. A major advantage of the present invention is allowing the patient to move freely at home or in hospital. In hospitals, the invention may help free up expensive hospital beds (monitoring may take 30-60 minutes). Using the invention at home allows the patient to minimize unnecessary hospitalization and travel to and from the hospital.

There is thus provided in accordance with a non-limiting embodiment of the present invention an electrical uterine monitor (EUM) electrode(s) including one or more uterine activity sensors mounted on a substrate, and at least one fiduciary mark that has repeatable positioning capability relative to an anatomic feature of a woman for repeatable positioning of the EUM electrode(s). The fiduciary mark may be located on the substrate, e.g., an opening formed in the substrate corresponding to a position of a navel of the woman. The fiduciary mark may include scale markings.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:

Figs. 1 and 2 are simplified pictorial and enlarged illustrations, respectively, of an electrical uterine monitor (EUM) for monitoring myographic activity, constructed and operative in accordance with a non-limiting embodiment of the present invention;

Figs. 3A, 3B and 3C are simplified sectional illustrations of a uterine activity sensor mounted on a substrate with adhesive, in accordance with three different embodiments of the invention;

Fig. 4 is a simplified illustration of the EUM, showing the pre-defined locations of the uterine activity sensors on the substrate;

Fig. 5 is a simplified illustration of the EUM as part of a uterine monitor (home or hospital/clinic system), in accordance with a non-limiting embodiment of the present invention;

Fig. 6 is a simplified block diagram of components in a EUM unit of the uterine monitor of Fig. 5, in accordance with a non-limiting embodiment of the present invention;

Fig. 7 is a simplified flow chart of a method for measuring intensity of uterine activity, in accordance with an embodiment of the present invention.

Fig. 8 is a simplified graphical illustration of uterine activity as measured by EUM (electrical uterine monitor electrodes) compared with TOCO activity measurement, in accordance with an embodiment of the present invention;

Fig. 9 is a simplified graphical illustration of a comparison of EUM contraction length vs. IUPC contraction length, in accordance with an embodiment of the present invention;

Fig. 10 is a simplified graphical illustration of a comparison of EUM peak energy vs. IUPC peak pressure, in accordance with an embodiment of the present invention; and

Fig. 11 is a simplified schematic illustration of a non-invasive method and apparatus for measuring fetal heart rate, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to Figs. 1-4, which illustrate an electrode for electrical uterine monitor (EUM) 10 for monitoring myographic activity and fetal heart activity, such as but not limited to, uterine contractions, constructed and operative in accordance with a non-limiting embodiment of the present invention. The system may come packaged in a UV protected package.

EUM electrode 10 includes one or more uterine electrical activity sensors 12 mounted on a substrate 14, which is placed on the abdominal wall of the pregnant woman. As seen in Fig. 4, substrate 14 may be in the form of a "tree" 16, with the sensors 12 mounted on a portion of "branches" 36 that extend from a "trunk" 38.

One or more fiduciary marks 18 are provided to enable repeatable positioning of EUM electrode 10, i.e., positioning EUM electrode 10 at the same place on the abdomen at each use.

Placing the electrode using fiduciary marks may reduce the need for using a position sensor, as one is only needed once. Fiduciary mark 18 may include, without limitation, a mark on substrate 14 with repeatable positioning capability relative to an anatomic feature of the woman. For example, as shown in Fig. 4, mark 18 may be an opening positioned at the navel of the woman. Another option is using corners tips to realign the electrode with a mark made by a care taker using a permanent marker. Accordingly, the fiduciary marks 18 may be at the corners of branches 36 or along the branches or any other suitable place. The woman simply places substrate 14 on her abdomen so that mark 18 is aligned over her navel and trunk 38 is aligned with her sternum. The combination of mark 18 and trunk 38 (or any other portion or point on substrate 14) defines the correct orientation of EUM electrode 10 on the abdomen with excellent repeatable accuracy. The opening may include scale markings 20, which enable definite documentation of the exact placing of the sensors 12.

The sensors 12 are thus placed on substrate 14 at pre-defined locations which are known with respect to a reference (mark 18). The location of the sensors 12 when initially placed on the woman's abdomen may be sensed by a position sensing system 50 (an example of which is described below). Since EUM electrodes 10 can be placed over and over again on the woman's abdomen with accurate repeatability due to the fiduciary marks 18, the spatial position (three-dimensional position and orientation) of the sensors 12 is known each time from the initial position sensing and there is no need to use the position sensing system 50 each time EUM electrode 10 is placed on the abdomen. The same argument allows other electrodes, made in similar size and shape to be placed in the same location. Electrodes may be manufactured in several sizes (small, medium, large, etc.) to allow use with low BMI preterm to high BMI term patients. In accordance with a non-limiting embodiment of the present invention, uterine electrical activity sensors 12 include electromyogram (EMG) electrodes, such as but not limited to, nine EMG surface recording Ag/AgCl electrodes and an optional reference electrode. It is noted that the invention may optionally also include TOCO sensors (toco transducers or tocodynamometers), for example, but in one embodiment of the invention the uterine activity is satisfactorily sensed and monitored without TOCO sensors.

Position sensing system 50 may be as described in US Patent 7447542, the disclosure of which is incorporated herein by reference. Position sensing system 50 may be, without limitation, the "PCI BIRD" or "MINIBIRD" position sensing system, commercially available from Ascension Technology Corporation, PO Box 527, Burlington, Vermont 05402, USA. These systems measure the position of one or more receiving antenna sensors with respect to a transmitting antenna fixed in space. The transmitting antenna may be driven by a pulsed DC signal, for example. The position sensing system 50 has a processor that controls and coordinates operation of the receiving antenna and the transmitting antenna, and processes the signals into position outputs.

Figs. 1 and 2 illustrate EUM electrode 10 with the side that attaches to the woman on the top. The uterine activity sensor 12 is located on a bottom surface of substrate 14. The area near, at or around each uterine activity sensor 12 is at least partially covered with an adhesive 22, such as but not limited to, a solid hydrogel adhesive. This adhesive 22 is covered by an adhesive patch 24. The adhesive patch 24 should be strong enough to stick to the abdomen during movement (rotating in bed, walking) yet permit removing EUM electrode 10 with as little pain as possible. Patch 24 can be made of a hypoallergenic material which prevents moisture accumulation. Possible materials include MED 5764A, 3M 9907, or similar materials. Patch 24 may be disposable, and may have cut outs in a way that skin covered by the patch is minimal, so that a Doppler transducer could be placed on the patient's abdomen, for example.

In Fig. 3A, uterine electrical activity sensor 12 is placed against substrate 14 and the adhesive 22 overlays sensor 12. In Fig. 3B, uterine activity sensor 12 is placed in a cutout 26 (groove, notch, crevice and the like) formed in substrate 14, with adhesive 22 overlaying the top and sides of sensor 12. In Fig. 3C, uterine activity sensor 12 is placed in another cutout 28 formed in substrate 14, with adhesive 22 overlaying the top of sensor 12. In accordance with another embodiment of the invention, instead of adhesive 22, sensor 12 may be held in place by a press fit or with mechanical fasteners. As seen in Fig. 2, EUM electrode 10 may be provided with a sensor upper cover 30, which is removed before placing on the abdomen.

Substrate 14 may be formed with non-symmetrical identification elements 40, such as cutouts or other markings (e.g., particular geometric shapes, such as triangles or hexagons, placed at pre-determined positions), in order to prevent incorrect mounting of the device on the abdomen.

In accordance with a non-limiting embodiment, substrate 14 is a flexible printed circuit board (PCB) and the sensors 12 are embedded on the PCB as shown in Figs. 3A- 3C. Each uterine electrical activity sensor 12 is connected to a connector 32 which is connected on the PCB (e.g., at the edge of the PCB as shown in Fig. 4). Resistors or other circuitry may also be embedded in patch 24 in order to enable the system to recognize the mating of the connector and to identify the size of the patch. Connector 32 connects the uterine activity sensors 12 and patches 24 to a processor (controller) 34 (shown in Fig. 4; connector 32 may be any distance from processor 34). Processor 34 may include a memory, in which pertinent data may be stored, such as but not limited to, the name of the woman, date, time of contractions and other data.

The three-dimensional position and orientation of each uterine activity sensor 12 is known as described above. Processor 34 processes electrical signals of the uterine activity sensors 12 and the three-dimensional position and orientation to provide an output that comprises electromyographic activity data as a mathematical function of the three-dimensional position and orientation of the uterine activity sensor 12.

Connector 32 may have, for example, without limitation, channels (connections) for the EMG electrodes, and status connections that may be used to indicate different parameters or system status. For example, the status connections may be shorted in different manners uniquely corresponding to different electrode (sensor) sizes in order to enable automatic detection of the electrode size. For example, status connections may be encoded to indicate the following different statuses:

No shorts - patch is not inserted to EUM connector

Pin 1 shorted to pin 2 - Small patch

2-3 - Medium patch

1-3 - Large patch

1-2-3 (all three spare pins are shorted) - Extra large patch. Non-limiting examples of nominal sizes for the disposable sensor patch are the following (in cm): small size 20 x 20; medium 27 x 27; large 32 x 32; extra large 36 x 36.

Without limitation, skin to electrode impedance is about 5 Kohm and the conductor impedance is less than 100 ohm. All materials of EUM electrode 10 that contact the patient skin may be biocompatible.

EUM electrode 10 is generally intended for single use only, staying functional for at least 18 hours (relatively long labor time), for example. However, the invention is not limited to such a device and the invention can be used for multiple uses as well.

EUM electrode 10 is able to identify individual sensors 12 and their positions. For example, the sensors 12 may be marked in numbers left to right, top to bottom, and/or may be color-coded and/or may be each uniquely shaped, for easy visual identification. Additionally or alternatively, each sensor 12 may be assigned a unique position code that processor 34 identifies, so that the position of each sensor 12 is known.

Reference is now made to Fig. 5. The invention may be provided as part of a uterine monitor (home or hospital/clinic) system. EUM electrode 10 is attached to the woman in the confines of her home. EUM electrode 10 senses and monitors data for contractions, heartbeat, fetal position, and communicates the data to a remote site (e.g., a website) via processor 34, also referred to as EUM unit 34 (which may be worn around the neck or mounted on another part of the body).

Reference is now made to Fig. 6, which illustrates a block diagram of components in EUM unit 34. The components include, without limitation, an EMG amplifier 36 for amplifying/band limiting the signals received from EUM electrode 10, an A/D (analog-to- digital) unit 38, which samples the data, a DSP (digital signal processing) module 40, which extracts fetal heart and uterine activity, a transmitter 42, such as a USB cable, a local transmitter for the hospital environment or cellular communication for home monitoring, and a memory 44 for storing data until transmitted. The EUM unit 34 can communicate with a clinical hub receiver unit 46, which may communicate with a computer 48 used to collect data, perform analysis and/or present results/data to medical staff. In order to minimize patient and fetus exposure to radiation and improve signal quality, the communication may be turned off during monitoring and turned on for communication periods. In a non-limiting example for carrying out the invention, implementation of EMG amplifier(s) 36 may be done, for example, using operational amplifiers or may be based on Teledyne A0401 modules (Teledyne Inc., CA).

Each EMG channel may have a fixed gain of 5000, 100 dB common mode rejection, a first-order high-pass filter with a cutoff frequency 0.5 Hz and a sixth-order anti-aliasing low-pass filter with a cutoff frequency of 500 Hz. The nine channels may be sampled at IK samples per second using Analog Devices Inc. (Norwood, MA) AD7490 16 channels, 12 bit A/D. USB communication may be used for communicating the signals, wherein the A/D signals may be converted to USB using, for example, a Cypress Inc. (San Jose, CA) High Speed USB peripheral CY7C68013A-100AXC controller. Again, these are non-limiting examples for carrying out the invention.

Reference is now made to Fig. 7. Without limitation, in one example, the digital signals are filtered to 1-300 Hz using an equi-ripple FIR (finite impulse response) filter. Signals outside the pass band are attenuated to -60 dB. Two second order IIR (infinite impulse response) notch filters reject 50 Hz and 60 Hz.

The algorithm is based on the following model. It is assumed that there are S sources of EMG signals located at (xs , ys , zs ) s = \,.., S . Each source emits the source signal xs (n) , wherein n is the discrete time variable. Selection of S depends on computational limitations. Actual experiments were done with S near 20.

The locations of an E number (e.g., 9) of EUM electrodes are in Cartesian coordinates {xe , ye, ze) e = 1, .. , E . The electrode signal measured by each EUM electrode is ye(n) . The relation between the EMG source signal and the EUM electrode signal is

S K

assumed to be an FIR filter - ye{n) = '' he s(k) - xs(n - k) , wherein he s axe filter s=l k=0

coefficients.

The separation of the source signals xs (n) from the measured electrode signals ye(n) may be done, for example, by the well-known technique of Blind Source

Separation. A suitable algorithm for use is that of Chan et. al., Multi-Channel Multi-Tap Signal Separation by Output De-correlation. CUED/F. INFENG/TR.250, Department of Engineering, Cambridge University. ISSN 0951-9211. 1996.

Knowledge of the location of the electrodes and the filter coefficients he s(n - k) enables locating the source coordinates (xs , ys , zs ) s = l,.., S , using the assumption that recei ed signal energy is inversely proportional

Figure imgf000011_0001

Knowledge of the distances from all electrodes enables locating the sources using simple triangulation.

The contraction energy is calculated by summing the energy of the signals over a

S Νϊ

defined time period (e.g. , order of few seconds) c(m) = ^ ^ [¾ (^)]2 · The variable n s=l n=N1

represents time in samples scale, e.g. 1 KHz. The variable m represents a decimated time display scale, e.g., once a second.

The contraction energy over time may be plotted in a graph over time to represent the contraction, similar to commonly used TOCO and IUPC.

Results of measuring the contractions are shown in Figs. 8-10. Fig. 8 is a graph of uterine activity as measured by EUM (top) compared with TOCO activity measurement (bottom).

Fig. 9 is a comparison of EUM contraction length vs. IUPC contraction length. Fig. 10 is a comparison of EUM peak energy vs. IUPC peak pressure.

It is seen in Figs. 8-10 that the methods of the invention closely correlate with the data from IUPC.

Reference is now made to Fig. 1 1 , which illustrates a non-invasive method and apparatus for measuring fetal heart rate, in accordance with an embodiment of the present invention.

Preprocessing with LP and HP filters

The preprocessing stage is done to improve the adaptive filter performance by removing known sources of noise. A LP filter is used to remove the 50 or 60 Hz AC electrical noise (and its harmonics). The LP filter removes part of the ECG signal information, which in one example, is up to about 100 Hz (this non-limiting value being taken from references M. A. Hasan, M. B. I. Reaz, M. I. Ibrahimy, M. S. Hussain, and J. Uddin, Detection and Processing Techniques of FECG Signal for Fetal Monitoring, Biological Procedures Online, Volume 11 , Number 1 , 2009; and Reza Sameni and Gari D. Clifford, A Review of Fetal ECG Signal Processing; Issues and Promising Directions, The Open Pacing, Electrophysiology & Therapy Journal (TOPETJ), 3:4-20, November 2010). However, the main features of the ECG that are needed for FHR detection, such as the QRS wave, are preserved (this being in accordance with Bert-Uwe Kohler, Carsten Hennig, Reinhold Orglmeister, The Principles of Software QRS detection, IEEE ENGINEERING IN MEDICINE AND BIOLOGY, Jan/Feb 2002).

A HP filter is used to attenuate the baseline drift noise that is typically present in ECG signals. This noise originates from sources, such as respiration, movement, and electrode contact. It is characterized by a shift in the baseline amplitude of the signal, and is typically in the low frequency range up to about 5 Hz (according to Hasan et al. and Sameni et al., above). There is some overlap between the FECG signal frequency range and the frequency range of the baseline drift noise (according to Hasan et al. and Sameni et al., above). In an embodiment of the present invention, a 3 Hz HP filter has been used to effectively reduce most of the baseline drift noise, but without harming the FECG desired signal in that frequency range too much.

For better preservation of the ECG features (but less noise reduction) a different preprocessing may be done with a 100 Hz LP filter, a 0.1 Hz HP filter, and a notch filter at 50 or 60 Hz for the electrical noise.

LMS adaptive filtering

The LMS adaptive filtering is used to help extract the FECG from the composite abdominal signal, by removing an abdominal MECG estimate from the abdominal signal. The thoracic MECG is the input signal (x(n)) to the LMS adaptive filter. The adaptive filter calculates an estimate of the abdominal MECG (y(n)) by comparing between the thoracic MECG and the abdominal composite signal (d(n)), according to: y(n) = W*X, wherein W is a row vector of L (filter length) filter coefficients, and X is a buffer column vector of length L of the L last input signals (X=(x(n),x(n-1),...x(n-L+l))').

The adaptive filter coefficients (W) are updated at each iteration according to:

W = W + mu*e(n)*X'.

wherein mu is the filter step size, and e(n) is the estimated FECG (plus unwanted residual noise). e(n) is calculated as the difference between d(n) and y(n) for the n-th sample.

To optimize the filter performance, the filter length and step-size are determined according to the values that reduce the error between the input signal and the desired signal.

The LMS step size is normalized according to the power of the thoracic MECG signal, with its value chosen as, e.g., (10/power (thoracic MECG)). It was found that this normalization provides better convergence of the thoracic MECG to the desired, abdominal MECG (with a different amplitude, shape and phase). The optimal filter length in testing was 30.

FECG enhancement

The FECG signal enhancement may be done by using all the different abdominal channels (e.g., 9) with PC A, wavelet de -noising, averaging, etc.

QRS detection and FHR Calculation

The absolute value of the FECG is computed.

An initial threshold is set based on the first seconds from the beginning of data acquisition. The time frame is not long after measurement starts, but usually the LMS filter has converged by that time. The threshold can be initially set as, e.g., the mean + 3 times the standard deviation of the data. The threshold is dynamically adapted according to the detected peaks.

Peak detection starts after e.g. 3.5 seconds from data acquisition.

Peak Detection

Local maxima search is run when the data values are above the dynamic threshold. A peak is searched in the next 140 milliseconds (a normal QRS interval length is typically less than 120 milliseconds). The peak is defined as the data point with the largest local maxima in the peak search area.

If there are less than 3 points above the threshold, a peak is not detected and those 140 milliseconds of data are skipped.

If the peak is abnormally wide (more than 140 milliseconds, this may mean that a P wave was detected instead of the QRS complex), the threshold is increased by multiplying it by 1.1, and the peak search is repeated with the new threshold. If after 3 such iterations the peak is still abnormally wide, it is skipped.

Once a peak is detected, a 200 millisecond "refractory period" is set after the detected peak. A new peak can be discovered only after that period, thus reducing false negative detections for times when a QRS peak does not occur.

Dynamic Threshold

A running threshold buffer of a number of the last peaks, e.g., 5 last peaks, is used to determine the adaptive threshold. When a new peak is discovered, the oldest peak in the buffer is discarded and the new peak is added to the first place of the threshold buffer. If the new peak is 1.5 times larger than the "oldest" peak in the buffer, the new peak value in the buffer is set to 1.1 times the "oldest" peak in the buffer.

If the new peak is 0.6 times smaller that the "oldest" peak in the buffer, the new peak value in the buffer is set to 0.9 times the "oldest" peak in the buffer.

The dynamic threshold is first set as the 0.8 times the mean of the threshold buffer. However it is dynamically changed according to the data and the time that passed since the last peak detection.

Between 0.2 to 1.2 seconds after the last peak was detected the dynamic threshold is decreased by (0.2/Fs) times the current dynamic threshold for each data point.

From 1.2 seconds after the last peak was detected the dynamic threshold remains 0.8 times the dynamic threshold, i.e., a total of 0.64 times the mean threshold buffer.

If more than 4 seconds have passed without peak detection, the threshold buffer is re-initialized according to the last 2 seconds of data, and the dynamic threshold is set to 0.8 times the threshold buffer mean. Alternatively, the threshold is adapted and a repeated search of the missed peaks is performed.

FHR calculation

To compensate for false positives or false negative QRS peak detections, the FHR is calculated from the median of the last 4 R-R intervals. It is calculated as:

60*Fs/(R-R interval median in counts) = 60/(R-R interval median in sec)

It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.

Claims

CLAIMS What is claimed is:
1. An electrical uterine monitor (EUM) electrode (10) characterised by:
one or more uterine activity sensors (12) mounted on a substrate (14); and at least one fiduciary mark (18) that has repeatable positioning capability relative to an anatomic feature of a woman for repeatable positioning of said EUM electrode (10).
2. The EUM electrode (10) according to claim 1, wherein said at least one fiduciary mark (18) is located on said substrate (14).
3. The EUM electrode (10) according to claim 1, wherein said at least one fiduciary mark (18) is an opening formed in said substrate (14) corresponding to a position of a navel of the woman.
4. The EUM electrode (10) according to claim 1, wherein said one or more uterine activity sensors (12) comprise electromyogram (EMG) electrodes.
5. The EUM electrode (10) according to claim 1, wherein a combination of said at least one fiduciary mark (18) and another portion (38) on said substrate (14) defines a repeatable orientation of said EUM electrode (10).
6. The EUM electrode (10) according to claim 1, wherein an area near, at or around each said uterine activity sensor (12) is at least partially covered with an adhesive (22).
7. The EUM electrode (10) according to claim 1, wherein said uterine activity sensor (12) is placed in a cutout (26) formed in said substrate (14).
8. The EUM electrode (10) according to claim 1, wherein said substrate (14) comprises branches (36) that extend from a trunk (38), and wherein said uterine activity sensor (12) is mounted on a portion of said branches (36).
9. The EUM electrode (10) according to claim 1, wherein said substrate (14) is formed with non-symmetrical identification elements (40) in order to prevent incorrect mounting of said EUM electrode (10).
10. The EUM electrode (10) according to claim 1, wherein said substrate (14) comprises a flexible printed circuit board (PCB), and said uterine activity sensor (12) is connected to a processor (34) by connectors (32), and wherein connections of said connectors (32) to said processor (34) uniquely correspond to different sensor statuses.
11. The EUM electrode (10) according to claim 1, wherein said uterine activity sensor (12) is marked with unique alphanumeric characters or colors or shapes.
12. The EUM electrode (10) according to claim 1, wherein said uterine activity sensor (12) is assigned a unique position code.
13. An electrical uterine monitoring system characterised by:
one or more electrical uterine monitor (EUM) electrodes (10) comprising one or more uterine activity sensors (12) mounted on a substrate (14), and at least one fiduciary mark (18) that has repeatable positioning capability relative to an anatomic feature of a woman for repeatable positioning of said EUM electrode (10); and
an electrical uterine monitoring (EUM) unit (34) in communication with said one or more EUM electrodes (10), operative to communicate data sensed by said one or more EUM electrodes (10) to a remote site.
14. The electrical uterine monitoring system according to claim 13, wherein said EUM unit (34) comprises an EMG amplifier (36) for amplifying signals received from said one or more EUM electrodes (10), an A/D (analog-to-digital) unit (38) for sampling data, a DSP (digital signal processing) module (40) for extracting fetal heart and uterine activity, a transmitter (42), and a memory (44) for storing data until transmitted.
15. The electrical uterine monitoring system according to claim 14, wherein said EUM unit (34) is in communication with a clinical hub receiver unit (46) which is in communication with a computer (48) for collecting data, performing analysis and/or presenting results/data to medical staff.
PCT/US2012/023060 2011-01-31 2012-01-30 Monitoring of uterine contraction intensity and fetal heart rate WO2012106219A1 (en)

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