Device for monitoring uterine contractions

Abstract

An apparatus (10) for use in monitoring uterine contractions. Means are provided for detecting (18) secure (e.g. flush) contact of at least part of a sensor unit (14) of the apparatus on the abdomen and for detecting (20) an initial starting pressure or baseline pressure between the sensor unit and the abdomen. A controller (24) is arranged to first sense contact of said at least part of the sensor unit on the abdomen and then, in response to the contact detection, to detect the starting pressure using an integrated pressure sensor. The same pressure sensor is preferably used to monitor uterine contractions. The starting pressure provides a direct or indirect measure or indication of the tension of a belt arranged to hold the apparatus against the abdomen of the subject in use. By sensing the starting pressure, for example directly in response to sensing contact of the abdomen, the initial pressure value or a derivative thereof can be used as a direct or indirect indication of the tension of the belt.

Description

TECHNICAL FIELD

[0001] The present invention relates to a device for monitoring uterine contractions and a method for initializing the device. BACKGROUND

[0002] Monitoring the uterine activity of a mother during labor and delivery is a standard measurement that is usually accompanied by the tracking of the fetal heart rate, which is usually measured using ultrasound Doppler. In obstetrics, information about uterine contractions, such as the duration of a contraction, the strength of a contraction, the waveform of a contraction, is important in assessing the health of the fetus during labor and delivery. For example, interpreting both uterine activity and fetal heart rate in chronological order can help medical personnel, such as a doctor or nursing staff, to provide the best treatment for the mother and the fetus.

[0003] A common technique for non-invasively deriving uterine contractions is the use of a tocodynamometer, which can also be referred to as a toco. The tocodynamometer is placed on the abdominal wall of the mother and held in place with an elastic belt that encircles the mother's abdomen. The tocodynamometer comprises a pressure sensor housed in a sensor housing. During a contraction of the uterus, changes in the tension of the uterine muscle occur and these changes are recorded as pressure changes on a sensitive area of the pressure sensor, which is placed in the middle of the sensor housing. The sensitive area is surrounded by a hard protective ring in order to reduce the influence of movement and breathing artifacts. A strain gauge element of the tocodynamometer converts the pressure into an electrical signal.

[0004] US 3945373 discloses another type of tocodynamometer for providing an electrical output related to displacement of a body surface of a patient. The tocodynamometer comprises a light interrupter extending into a space between an emitter and a detector to interrupt light passing from the emitter to the detector, wherein uterine contractions cause displacement of the light interrupter and change the amount of light from the emitter received by the detector.

[0005] US2012 / 277631 describes another example tocodynamometer. This example also uses an optical displacement sensor. A light emitter and an optical transducer are provided, as well as a reflector surface arranged to reflect at least a portion of the light emitted by the light emitter to the optical transducer. The reflector is coupled to a displacement member that, in use, contacts the mother's abdomen and moves in response to movements of the abdomen. The movements modify the intensity distribution of the light reflected to the optical transducer.

[0006] The measurement unit of the pressure changes is usually implemented using a pressure sensor that is mechanically coupled with the abdomen via a skin contact area at the base of the tocodynamometer device. The mechanical force (uterine activity, changes in tension of the muscle) is measured by the sensor, i.e. a strain gauge element, an optical sensor, etc.

[0007] For optimal performance of a tocodynamometer, the sensing part of the device should be held in place against the abdomen with a proper tension of the elastic belt. The belt tension should ideally fulfill the following criteria:

[0008] 1) The belt tension should not be too small, which would cause a loss of physical contact between the abdomen and the sensor element.

[0009] 2) The belt tension should not be too large, which would cause discomfort to the patient.

[0010] 3) The mechanical force measured by the Toco sensor is directly influenced by the belt tension. When the Toco sensor is first applied to the abdomen, the measured force is the baseline for all further measurements. It is important that the baseline is within the operating range of the measuring sensor. The operating range can be defined as the measurement range with optimal signal-to-noise performance, high linearity and / or other factors.

[0011] The belt tension can change over time due to:

[0012] - physical movements of the patient;

[0013] - degradation of the belt elasticity;

[0014] - medical personnel trying to increase the belt tension based on their experience;

[0015] - loss of belt tension due to moisture, e.g. because the belt gets wet in a shower or bath.

[0016] If a toco device is attached to the abdomen with an improper belt tension, this can lead to inaccurate measurements.

[0017] To illustrate, Figure 1 a sample measurement signal is illustrated that was acquired from a tocodynamometer that was applied to the abdomen with insufficient belt tension or in the absence of uterine contractions to be detected. It is not possible to determine from the signal alone which of the two reasons is responsible. Thus, a low belt tension can be confused with the absence of any contractions, which would have an adverse clinical impact on the patient.

[0018] Figure 2 a sample measurement signal is illustrated for the case that the belt tension has increased during the measurement (causing a step change of the baseline visible near the beginning of the signal trace) thus significantly reducing the measurement window. As a result, the uterine contraction measurement is clipped at the top of the plot. The baseline could be adjusted by post-processing to eliminate the clipping. However, the sensor under such high baseline pressure will not operate within its optimal range and thus the sensitivity can be reduced.

[0019] Figure 3A sample measurement signal as captured by a tocodynamometer having an optimal belt tension applied is illustrated. A strong signal is present in the measurement trace and there is no clipping of upper values.

[0020] It can therefore be seen that belt tension has a significant impact on the quality and reliability of tocodynamometer measurement results. Since tocodynamometer measurements are taken over a medium to long period of time (e.g. several hours), an inappropriately applied Toco sensor can result in a loss of valuable patient information.

[0021] It would therefore be valuable to have a method to mitigate or eliminate this problem. SUMMARY

[0022] The invention is defined by the claims.

[0023] According to examples in accordance with an aspect of the invention, there is provided a device for monitoring uterine contractions of a subject, the device comprising:

[0024] a sensor unit for placement against an abdomen of the subject;

[0025] a belt component arranged for holding a contact surface of the sensor unit in place against the abdomen;

[0026] a contact sensing module adapted to detect engagement between the contact surface of the sensor unit and the abdomen of the subject;

[0027] a force or pressure sensing module adapted to detect a force or pressure between the abdomen and the sensor unit; and

[0028] a controller adapted to perform a procedure comprising:

[0029] detecting, by the contact sensing module, engagement between the contact surface of the sensor unit and the abdomen,

[0030] in response to the detection, acquiring, using the force or pressure sensing module, a measure of an initial pressure or force between the abdomen and the sensor unit, and

[0031] determining whether a tension or applied force of the belt component is within an optimal range by comparing the initial pressure to at least one predefined reference range.

[0032] The procedure can be referred to as an initialization or configuration or calibration procedure. It can be performed when the device is first installed to a user (i.e. at start-up) and optionally can be repeated during use of the device to check belt tension.

[0033] The predefined reference range can be a reference range for the initial pressure or a derivative thereof (e.g. a baseline for the initial pressure).

[0034] The measure of the initial pressure taken can be a pressure value or a pressure signal covering a time window.

[0035] Embodiments of the present invention are based on an indirect assessment of the belt tension based on initial pressure measurements taken as soon as the tocodynamometer device is attached to the abdomen. As soon as the device is mounted to the abdomen, it can be assumed that the initial pressure is indicative of the level of belt tension, rather than e.g. a contraction, because there has not been time for the abdomen to move the coupling to the pressure sensor. The timing of the initial attachment to the subject can be detected using a contact sensing module. Thus, by providing a sensing unit containing both a contact sensor and a pressure sensor and configured to take an initial pressure measurement in response to detecting skin contact, a reliable measure of the belt tension is obtained.

[0036] The pressure measurement or a derivative thereof can then be compared to a threshold or reference range to assess whether it falls within the optimal operating range of the tocodynamometer, e.g. the pressure sensor. This comparison of the initial pressure measure or a derivative thereof to a reference range is used to determine whether the belt tension is within its optimal range. If not, a responsive action can be triggered, e.g. alerting the user or interrupting the measurement until the tension is adjusted to an optimal level.

[0037] There can be a separate step of determining a measure of the belt tension based on the initial detected pressure (initial pressure), e.g. using an algorithm or a conversion equation. In some cases, the belt tension is considered to be e.g. equal to a baseline (i.e. offset) value of the taken pressure measurement. The reference range can be a reference range of the belt tension, and the determination is performed based on a comparison of the calculated belt tension to the reference range. The reference range can be a range of the initial pressure values of the measurement itself, and wherein e.g. the reference range has been pre-determined such that if the initial pressure is within the reference range, the belt tension can be known to be within its initial range. Thus, in such a case, the measured value of the initial pressure itself can be used for further analysis and comparison to the reference range. For example, the initial pressure can be considered to represent the initial belt tension.

[0038] Thus, it is not necessary to explicitly define a “best range” of the belt tension separate from the reference range; the determination of whether the belt tension falls within the best range is fully achieved by using the reference range and the initial pressure or force measurement. For example, the controller performs an evaluation or analysis of the initial pressure measurement based on the use of the reference range, and based on the evaluation derives a classification of whether the belt tension is within the best range or outside the best range. In some examples, the reference range defines the best range of the belt tension, or indirectly indicates it or is related to it.

[0039] The apparatus can further comprise an ultrasound transducer unit comprising one or more ultrasound transducers. This can be used to detect and monitor the fetal heart rate using Doppler ultrasound technology.

[0040] Here, the separate step of detecting contact has the additional benefit that it is important that any transducer is in good acoustic contact with the abdomen for accurate heart rate detection. A separate pressure sensor cannot always provide a reliable indication of firm contact with the abdomen.

[0041] In addition to the above, the controller can be configured to continuously monitor the belt tension even after the pressure measurement for contraction monitoring has started, and to produce a responsive action in case the tension moves outside the optimal range. This can for example be based on cyclically or continuously monitoring the pressure signal from the pressure sensing module and determining a baseline of the pressure signal, and considering the baseline value to be indicative of the belt tension.

[0042] The controller can further be adapted to generate an information output indicative of whether the belt tension is within the optimal range, and to communicate the output to a user output device.

[0043] The controller is preferably further adapted to monitor uterine contractions based on the output of the force or pressure sensing module. Preferably the same pressure sensing module (e.g. pressure sensor apparatus) is used to monitor uterine contractions as to gather initial pressure measurements for checking the belt tension.

[0044] In an advantageous embodiment, monitoring the uterine contractions can be conditionally performed in case the belt tension falls within the optimal range. In other words, the controller can be configured to perform the function of monitoring uterine contractions only if the belt tension is within a predefined optimal range. This avoids gathering contraction measurement information that can be inaccurate and thus can lead to incorrect clinical actions.

[0045] According to one or more embodiments, in response to a determination that the belt tension is not within the optimal range, an output can be generated for communication to a user output device to alert the user. The user output device can comprise for example a display unit and / or one or more other sensory output devices.

[0046] There are different ways in which contact sensing can be performed.

[0047] According to one or more embodiments, the contact sensing module can be provided by the same component as the force or pressure sensing module (e.g. a pressure sensor such as a strain gauge or an optical based pressure sensor), and wherein engagement with the abdomen is detected based on detecting a change in the measured force or pressure that exceeds a predefined threshold.

[0048] According to another set of embodiments, the sensor unit can comprise additional components for detecting contact.

[0049] For example, according to one set of embodiments, the sensor unit can comprise an optical sensor arrangement comprising a light source arranged to direct light output from the contact surface into the skin of the subject and a light detector arranged to detect the light output at the contact surface after passing through the skin, and wherein the contact sensing module is provided by the optical sensor arrangement, contact being detected based on the output of the light detector.

[0050] In an advantageous embodiment, the optical sensor element can be a PPG sensor, and wherein the controller is adapted to use the output of the PPG sensor to determine the pulse of the subject. In other words, the sensor unit can incorporate an integrated PPG sensor comprising a light source arranged to direct light output from the contact surface into the skin of the subject and a light detector arranged to detect the light output at the contact surface after passing through the skin, and wherein the controller is adapted to use the components of the PPG sensor to detect contact. In this way, the number of parts can be minimized.

[0051] Furthermore, there are different ways of using the optical sensor arrangement to detect engagement with the abdomen.

[0052] For example, in one set of embodiments, contact can be detected based on detection of the light output generated by the light source at the light detector. When this is detected, it means that the optical sensor arrangement must be in optical communication with the skin for light to have coupled to the light detector through the tissue of the subject, and thus it can be assumed that contact with the abdomen has occurred.

[0053] According to another set of embodiments, contact can be detected based on detection of a drop in detected light intensity from: the light detector being exposed to ambient light to: the surface of the abdomen covering the light detector.

[0054] In this example, the light source does not need to be activated for contact detection. Engagement with the abdomen can be detected based on a change in the light detector output only. The controller is effectively configured to detect engagement with the abdomen based on detection of a drop in detected light level.

[0055] For example, in one or more embodiments, the light detector can be tuned to saturate when exposed to ambient light, and wherein engagement with the abdomen is detected based on a change in the output of the light detector from a saturated state to a non-saturated state.

[0056] Examples in accordance with another aspect of the application provide a method for initializing or configuring a device for monitoring uterine contractions of a subject, the device comprising:

[0057] a sensor unit for placement against an abdomen of the subject; and

[0058] a belt component arranged for holding a contact surface of the sensor unit in place against the abdomen;

[0059] a contact sensing module adapted to detect an engagement between the contact surface of the sensor unit and the abdomen of the subject;

[0060] a force or pressure sensing module adapted to detect a force or pressure between the abdomen and the sensor unit;

[0061] the method comprising:

[0062] detecting an engagement between the contact surface of the sensor unit and the abdomen,

[0063] acquiring a measure of a starting pressure or force between the abdomen and the sensor unit using a force or pressure sensing module (e.g. comprised in the sensor unit) in response to the detection, and

[0064] determining whether a tension or applied force of the belt component is within an optimal range by comparing the starting pressure to at least one predefined reference range.

[0065] The predefined reference range can be a reference range of the starting pressure or a derivative thereof, e.g. a reference range of a baseline of the starting pressure.

[0066] The controller is further adapted to monitor uterine contractions based on the output of the force or pressure sensing module, and preferably wherein monitoring uterine contractions is conditionally performed in case the belt tension falls within the optimal range.

[0067] According to at least one set of embodiments, detecting an engagement between the contact surface of the sensor unit and the abdomen can comprise:

[0068] sensing light received at the contact surface using a light detector, and

[0069] detecting the engagement based on an output of the light detector.

[0070] According to another aspect of the application, there is also provided a computer program product comprising code means configured, when run on a processor, to cause the processor to perform a method according to any of the examples or embodiments outlined above or described below or according to any of the claims of the present application.

[0071] These and other aspects of the application will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0072] For a better understanding of the present application, and to show how it can be put into effect, there will now be described, by way of example only, the application with reference to the accompanying drawings in which:

[0073] Figure 1 An example pressure signal output from a tocometer that has been applied with insufficient belt tension is shown;

[0074] Figure 2 An example pressure signal output from a tocometer that has been applied with excessive belt tension is shown;

[0075] Figure 3 An example pressure signal output from a tocometer that has been applied with optimal belt tension is shown;

[0076] Figure 4 A block diagram showing parts of an example device according to one or more embodiments is shown;

[0077] Figure 5 An example of an optimal belt tension range as an intersection of a plurality of parameters is illustrated;

[0078] Figure 6 A plan view showing the exterior of a sensor unit housing according to one or more embodiments is shown;

[0079] Figure 7 A perspective view of a device in a position on the abdomen of a subject according to one or more embodiments is shown;

[0080] Figure 8 And 9 An example device containing optical sensing means for detecting contact with the abdomen is shown;

[0081] Figure 10 An example device containing capacitive sensing elements for detecting contact with the abdomen is shown; and

[0082] Figure 11 An example workflow according to one or more embodiments is outlined in block diagram form. DETAILED DESCRIPTION

[0083] The application will be described with reference to the accompanying drawings.

[0084] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of apparatuses, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the present application. These and other features, aspects, and advantages of the apparatuses, systems and methods of the present application will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the drawings are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings for like or similar items.

[0085] The present application provides an apparatus for use in monitoring uterine contractions, and wherein there is provided a module for detecting stable (e.g. flush) contact of at least part of a sensor unit of the apparatus on the abdomen and for detecting an initial starting pressure or baseline pressure detected by a pressure sensor of the sensor unit, respectively. A controller is arranged to first sense contact of said at least part of the sensor unit on the abdomen, and then to detect a starting pressure using the integrated pressure sensor in response to said contact detection. The same pressure sensor is preferably used to monitor uterine contractions. The starting pressure can be used to provide a direct or indirect measure or indication of belt tension, the belt being arranged to hold the apparatus against the abdomen of the subject in use. By sensing the starting pressure, e.g. directly in response to sensing abdominal contact, the initial pressure value or a derivative thereof can be considered to be a direct or indirect indication of belt tension (rather than e.g. caused by uterine contraction activity).

[0086] Figure 4 Functional components of an apparatus according to one or more embodiments of the present application are schematically illustrated in block diagram form.

[0087] The apparatus 10 comprises a sensor unit 14 for placement against the abdomen of the subject.

[0088] The apparatus 10 further comprises a belt component 16 arranged for holding a contact surface of the sensor unit 14 in place against the abdomen.

[0089] The apparatus 10 further comprises a contact sensing module 18 for detecting engagement between the contact surface of the sensor unit and the abdomen of the subject.

[0090] The apparatus 10 further comprises a force or pressure sensing module 20 adapted to detect force or pressure between the abdomen and the sensor unit 14.

[0091] The apparatus 10 further comprises a controller 24 adapted to perform an initialization procedure comprising:

[0092] detecting engagement between the contact surface of the sensor unit and the abdomen,

[0093] collecting, using the force or pressure sensing module, a measure of the initial pressure or force between the abdomen and the sensor unit in response to the detection, and

[0094] determining, based on the initial pressure and based on at least one predefined reference range, whether the tension or applied force of the belt component is within an optimal range.

[0095] In advantageous embodiments, the contact sensing module, the pressure sensing module and the controller can all be integrated in the sensor unit.

[0096] The predefined reference range can be a reference range for the initial pressure or a derivative thereof, e.g. a reference range for a baseline of the measure of the initial pressure.

[0097] The collected measure of the initial pressure can be a pressure value, or a pressure signal captured over a time window.

[0098] This pressure measurement or a derivative thereof can then be compared to a threshold or reference range to assess whether it falls within an optimal operating range of the tocometer, e.g. the pressure sensing module. This comparison of the initial pressure measure or a derivative thereof to a reference range is used to determine whether the belt tension is within its optimal range.

[0099] The determined initial pressure can be used to provide a direct or indirect indication of the tension of the belt. There can be a separate step of determining the belt tension based on the measured initial pressure, e.g. using an algorithm or a conversion equation, or the initial pressure itself can simply be used as a surrogate measure for further analysis. For example, the belt tension can be considered to be a baseline of the pressure measurement. This can optionally be processed using one or more conversion equations to convert it to a tension value. If there is a separate step of determining the belt tension, in some examples this belt tension can be compared to the reference range, rather than the initial pressure measurement itself.

[0100] According to some embodiments, therefore, the belt tension can be determined indirectly from the pressure measurement from the pressure sensing module. Preferably, this pressure sensing module is the same pressure sensing module used by the device to measure uterine contractions. A measure of the belt tension can be derived, for example, from a baseline of the pressure signal values of the pressure measurement (which is indicative of the mechanical force applied to the sensor in the absence of uterine contractions).

[0101] The predefined reference range can for example correspond to an optimal range of the belt tension, so that the pressure sensing module 20 operates at its optimal sensing range (e.g. where the sensitivity is maximised).

[0102] To illustrate this, reference will now be made to Figure 5An example configuration is discussed including an example parameter set, Figure 5 The intersection between the parameters is illustrated.

[0103] For example, the pressure measurement sensor 20 can be capable of measuring mechanical forces between 0 N and 15 N. Its optimal range (e.g. where the sensitivity is greatest) can be 1 N to 10 N. In this case, the optimal strap tension can be in the range of 2 N to 9 N. Furthermore, the optimal measurement window (to enable the systolic pressure variation to be fully captured) can be a pressure measurement window spanning 4 N. This would mean that the baseline of the pressure measurement must be at least 4 N below the upper limit of the optimal strap tension range.

[0104] The intersection of the ranges is shown in Figure 5 In this specific example, the intersection is in the range of 2 N to 5 N. This intersection can be used as the predefined optimal (reference) range used by the controller 20.

[0105] The above represents only one example setup. The exact span and magnitude of the reference range will depend on the specific pressure sensor 20 and strap 16 used. It can be predetermined and pre-stored on the controller 20. The controller can have different reference ranges stored for different devices it is connected to, and where the reference range can be selected by the user during setup using a user interface.

[0106] In a preferred embodiment, after the initialization procedure, the controller 24 can be configured to continue to monitor the pressure measurement cyclically or continuously, and thus cyclically or continuously monitor the strap tension. For example, the strap tension can be determined as the baseline of the pressure measurement.

[0107] Preferably, the controller 24 is configured to detect when the strap tension or the baseline of the pressure sensor measurement moves outside the predefined optimal range. A pre-warning alarm can be implemented by the controller 24, where it cyclically detects the trend of the strap tension or the baseline of the pressure measurement, and when it detects that this will move outside the reference optimal range in a predefined time interval in the future (based on the trend), provides an alarm output, e.g. for communication to a user interface.

[0108] The force or pressure sensing module 20 can take different forms. For example, it can comprise a strain gauge sensor. It can comprise an optical pressure sensing module, for example comprising a light probe and a light sensor, arranged in optical communication and arranged movable relative to each other, and wherein the optical path therebetween varies in dependence on pressure applied by the abdomen. For example, one of the light source and light probe can be arranged fixed relative to the abdomen, and the other can be arranged on a cantilever member arranged to pivot or flex based on pressure applied to it directly or indirectly from the patient's abdomen. Any other example of pressure sensor can be used, and various options will be apparent to the skilled person.

[0109] Figure 6 A plan view showing the exterior of an example implementation of the sensor unit 14 is shown. Figure 7 A perspective view of the sensor unit 14 attached to the patient's abdomen 32 by a belt 16 wrapped around the patient's abdomen and extending over the top of the housing of the sensor unit to exert a constant pressure on the sensor unit 14 inwardly towards the abdomen 32, thereby maintaining the lower contact surface of the sensor unit in firm contact with the abdomen, is shown (left). The belt can be elastic, for example. Figure 6 A cross-sectional view of the sensor unit 14 in position on the abdomen, with the belt 16 holding it in position, is shown (right). Thus, the sensor unit is positioned for measuring uterine contraction activity.

[0110] The sensor unit 14 can also contain one or more ultrasound transducer elements. These can be used to detect one or more physiological parameters of the fetus, such as the fetal heart rate. For example, the use of Doppler ultrasound to detect the fetal heart rate is a well-known technique in the art.

[0111] The controller 24 is also adapted to generate an information output indicative of whether the belt tension falls within an optimal range. For example, it can pass or send this output to a user output device. The user output device can for example comprise a display unit and / or one or more other sensory output devices.

[0112] Once the initialization procedure is complete, the controller can also be adapted to monitor uterine contractions of the subject based on the output of the force or pressure sensing module 20.

[0113] Monitoring uterine contractions based on pressure measurements from pressure sensors in a tocodynamometer type device is a well-known procedure in the art, and the skilled person will know methods for implementing this.

[0114] In an advantageous embodiment, the monitoring of uterine contractions is conditionally performed only if the belt tension is determined to be within the optimal range. If not, the uterine contraction monitoring can not be activated or can be deactivated until the belt tension is detected to be within the optimal range. In this way, potentially inaccurate and thus clinically misleading uterine contraction information is avoided from being generated.

[0115] In some embodiments, in response to the belt tension not being within the optimal range, an information output is generated for delivery to the user output device to alert the user. This can be an on-screen message for display on a display unit of, for example, the user interface device. It can additionally or alternatively comprise an audible alert, such as an alarm sound.

[0116] There are different ways of implementing the contact sensing module 18, which can be used individually or in combination in different embodiments. Reference will now be made to Figures 8-10 the selection of these options is discussed.

[0117] In summary, there are two broad approaches to detecting contact. The first is to use the same pressure sensor integrated in the sensor unit 14 that is used to detect pressure measurements for monitoring uterine contractions and for detecting the onset pressure (to determine the belt tension) to detect engagement of the sensor unit with the abdomen. Engagement can be detected, for example, based on detecting a change in the measured force or pressure (output of the pressure sensing module) that exceeds a predefined threshold. Engagement can be detected based on detecting a change in the baseline of the measured force or pressure that exceeds a predefined threshold.

[0118] For example, when the sensor unit is applied to the abdomen, there will be a relatively sudden positive shift in the baseline (or offset) of the pressure signal. This can be, for example, a step change or a steep incline in the baseline that exceeds a certain gradient. Thus, detection of contact with the abdomen can be detected based on detecting this shift in the baseline. The baseline can be explicitly extracted, or its change can simply be detected by a sudden (e.g. occurring within a defined short time window) positive shift in the magnitude of the measured pressure signal values.

[0119] A threshold can be defined for the change in the baseline. The threshold can be a threshold for the magnitude of the baseline shift and / or the gradient of the baseline shift (i.e. how steep or how quickly the baseline change occurs). One or either or both of these give an indication that contact is being made, where the change in the baseline corresponds to the initial pressure exerted by the abdomen on the bottom of the sensor unit 14. For example, if the baseline shift is higher than x Newtons, where x is a predefined value, the sensor unit can be considered to be “detected on the abdomen”. The threshold can be predetermined and pre-stored on the sensor unit controller 24, for example, based on empirical measurements or analytical calculations.

[0120] A second method of detecting engagement with the abdomen is to include a separate sensor device in the sensor unit 14 that detects contact. With respect to this method, again there are different options.

[0121] One option is to use an optical contact sensing module. Figure 8 and 9 A cross-sectional view of an example device 10 containing such an optical sensing device 18 is schematically illustrated. Note that for simplicity, the controller 24 is not shown, but is also included in the sensor unit 14 operatively coupled with the pressure sensing module 20 and the contact sensing module 18.

[0122] In both embodiments of the device 10, the contact sensing module 18 comprises an optical sensor device comprising a light source 44 arranged to direct a light output from the (lower) contact surface of the sensor unit 14 into the skin of the abdomen 32 of the subject, and a light detector 42 arranged to detect said light output at the contact surface after passing through the skin, and wherein the contact sensing module is provided by the optical sensor device, detecting contact based on the output of the light detector 42. Figure 8 and 9 In both embodiments of the device 10, the contact sensing module 18 comprises an optical sensor device comprising a light source 44 arranged to direct a light output from the (lower) contact surface of the sensor unit 14 into the skin of the abdomen 32 of the subject, and a light detector 42 arranged to detect said light output at the contact surface after passing through the skin, and wherein the contact sensing module is provided by the optical sensor device, detecting contact based on the output of the light detector 42.

[0123] By way of example, the light source can be an infrared light (IR) source, and the light detector can be an infrared light detector. However, visible light can alternatively be used.

[0124] In some examples, the light source 44 can be an LED, but this is not essential. The light detector 42 can comprise one or more photodiodes.

[0125] In an advantageous embodiment, the same optical sensor device 18 can be used to measure the maternal pulse rate. The sensor unit 14 may, for example, contain an integrated optical sensor device for the purpose of detecting the pulse rate, and the controller 24 can be arranged to utilize this same sensor for the secondary or dual purpose of detecting contact. This will minimize the parts in the device, and thus reduce the overall size and manufacturing complexity of the device.

[0126] For example, the optical sensor device can be a PPG sensor integrated in the unit for determining the pulse, the PPG sensor comprising a light source 44 arranged to direct a light output from the contact surface into the skin of the subject, and a light detector 42 arranged to detect said light output at the contact surface after passing through the skin 32.

[0127] For example, the optical sensor arrangement can comprise an infrared (IR) emitter 44 and receiver 42 pair that can be used to determine the maternal pulse. The emitter can comprise, for example, an LED. The receiver can be or comprise, for example, a photodiode. The IR light source 44 illuminates the skin of the abdomen 32 and the photodiode 42 receives light reflected from the skin, thereby measuring changes in light absorption corresponding to blood volume changes. These blood volume changes (e.g. the frequency of blood volume changes) are indicative of the maternal pulse.

[0128] In some embodiments, for example, the detection of contact with the abdomen can be based on the controller detecting the maternal pulse with the optical sensor arrangement. Thus, the detection of the maternal pulse can be a criterion for detecting Toco sensor contact on the abdomen.

[0129] There are different ways of using an optical sensing module, such as the one outlined above, to detect contact.

[0130] In one set of embodiments, contact can be detected based on detecting at the light detector 42 the light output generated by the light source 44. When this is detected, it means that the optical sensor element must be in optical communication with the skin in order for the light to have coupled to the light detector through the subject's tissue, and thus it can be assumed that contact with the abdomen has occurred. This example is illustrated in Figure 8 .

[0131] In another set of embodiments, contact can be detected based on the use of the output of a separate light detector 42. For example, contact can be detected based on detecting a drop in the light intensity detected at the light detector, and wherein, for example, the drop has a magnitude indicative of the change from the light detector being exposed to ambient light to the light sensor being covered by the surface of the abdomen.

[0132] For example, the light detector 42 can be tuned to saturate when exposed to ambient light, and wherein contact is detected based on a change in the output of the light detector 42 from a saturated state to a non-saturated state.

[0133] According to another set of embodiments, the contact sensing module can comprise a capacitive sensor 18 element arranged to capacitively detect contact between the lower contact surface of the sensor unit 14 and the surface of the abdomen. This example is illustrated in Figure 10 .

[0134] By way of non-limiting example, further methods of detecting contact with the abdomen can include: a mechanical switch (detecting contact by mechanical pressing of an integrated switch or button exposed at the contact surface), a temperature sensor (detecting contact based on a certain amount or detected temperature increase to a certain value or range), an electrical conductivity sensor, and / or an optical proximity sensor. In each case, the sensor can have a sensitive portion exposed at the contact surface of the sensor unit 14. Combinations of different contact sensing methods are also possible.

[0135] According to another aspect of the present application, a user interface unit for providing a sensory output of the result of the initial pressure detection and / or belt tension can also be provided. This can take the form of a monitoring unit or monitoring station, for example, comprising at least a display device for displaying information related to the detected initial belt tension and / or the analysis performed by the controller. Preferably, it can also comprise a user input module for user input of control commands, such as re-checking the belt tension, and / or overriding various functions of the controller, or adjusting parameters used by the controller, such as a predefined optimal range of the detected belt tension.

[0136] The monitoring unit can be a fetal monitoring unit, for example, which in some examples can be configured to display a plurality of measurement information related to the fetus and the mother (e.g. fetal and maternal heart rate, blood pressure, temperature, and / or contraction activity, as well as the belt tension), and can receive sensor inputs from a range of different physiological sensor sources.

[0137] In some examples, a belt tension indicator can be displayed on a display unit of the monitoring device, which can be a graphical or textual indicator in different examples. This can indicate a real-time estimated value of the belt tension, for example. The belt tension indicator can graphically display the belt tension in the form of a linear graphical scale, which is marked within the scale with an optimal range of the belt tension, so that an operator (e.g. a clinician) can easily see when the belt tension is approaching to move outside the optimal range.

[0138] In some examples, the sensor unit 14 can comprise a visual indicator arranged to be visible at an outer surface of the housing of the sensor unit 14, and configured to provide a visual indication of the current belt tension and / or whether the belt tension is within the optimal range. The visual indicator can comprise a plurality of colored lights (e.g. LEDs), for example. Different colors can be used to indicate different levels or levels of the belt tension, such as a first color (tension too low), a second color (tension within optimal range), a third color (tension too high). The first, second and third colors can be blue, green and red, for example. This represents only one example of the present application, which is not limiting.

[0139] The monitoring unit or sensor unit can be adapted to generate an acoustic or visual signal to alert a user when the belt tension moves outside the optical range and thus needs to be adjusted. For example, an alarm can be sounded.

[0140] Examples in accordance with another aspect of the application provide a method for initializing a device for monitoring uterine contractions of a subject, the device comprising:

[0141] a sensor unit for placement against an abdomen of the subject; and

[0142] a belt component arranged for holding a contact surface of the sensor unit in place against the abdomen;

[0143] The method comprises:

[0144] detecting an engagement between the contact surface of the sensor unit and the abdomen,

[0145] acquiring, using a force or pressure sensing module, a measure of an initial pressure or force between the abdomen and the sensor unit in response to the detecting, and

[0146] determining, based on the initial pressure and based on at least one predefined reference range, whether a tension or applied force of the belt component is within an optimal range.

[0147] The predefined reference range can be a range of the initial pressure or a derivative thereof, e.g. a range of a baseline of the initial pressure.

[0148] Implementation options and details of each of the above steps can be understood and interpreted in accordance with the explanations and descriptions provided above for the device aspect of the application, i.e. the device aspect.

[0149] Any examples, options or embodiment features or details described above in relation to the device aspect of the application (in relation to the device) can be applied or combined or incorporated into the present method aspect of the application mutatis mutandis.

[0150] The method can further comprise monitoring uterine contractions based on an output of the force or pressure sensing module, wherein monitoring uterine contractions is conditionally performed upon determining that the belt tension is within the optimal range.

[0151] Detecting an engagement between the contact surface of the sensor unit and the abdomen can comprise:

[0152] sensing light received at the contact surface using a light detector,

[0153] detecting the engagement based on an output of the light detector.

[0154] By way of illustration, in Figure 11One example workflow according to one or more embodiments is outlined in the summary.

[0155] The contact sensing module 18 is arranged to detect 62 contact between the sensor unit 14 and the abdomen, for example using one or more of the methods outlined above. The controller can monitor the signal from the contact sensing module cyclically or continuously and check 64 whether contact has been made. As soon as contact is made, the belt tension is determined 66 based on an initial or starting measurement taken from the pressure sensing module integrated in the contact sensing face of the sensor unit. For example, the belt tension can be taken as a baseline of the pressure signal output from the pressure sensing module in immediate response to detecting contact. Additionally or alternatively, an algorithm or conversion equation can be applied to convert the measured pressure or baseline pressure to a belt tension value.

[0156] A determination 68 is made as to whether the belt tension falls within a defined belt tension range. This can be done in different ways. The value of the belt tension can be calculated from the initial pressure measurement and this is compared to a predefined reference range for the belt tension. Alternatively, a reference range can be predefined for the initial pressure measurement itself or the baseline of the initial pressure measurement, where the reference range has been pre-calculated such that an initial pressure falling within that range is indicative of the belt tension being within its optimal range.

[0157] If the belt tension is determined 68 to be outside the optimal range, the measurement of contractions of the device is stopped 74 and an alert message (e.g. visual or audible) can be generated to change the user that they need to adjust the belt tension. The belt tension can be displayed on a display unit for observation by an operator. The workflow then returns to the start step in which contact with the sensor unit is re-detected 62 before another starting measurement of pressure is re-taken to again check the belt tension.

[0158] The cycle continues until a determination 68 is made that the belt tension is within the optimal range. At this point, the measurement and monitoring of uterine contractions using the pressure sensing module 20 in the sensor unit 14 can continue. A check 70 is made as to whether the contraction measurements have been performed, in which case they can continue and the workflow returns to the steps of checking contact and re-checking the belt tension. If not, the contraction measurements are activated 72 and at this point the workflow returns to the start 62. In this way, in either case, the workflow re-checks the belt tension cyclically or continuously even after the measurement has been initiated to determine whether it is still within the optimal range. If at any point falls outside this range, the measurement is stopped 74 until the tension is adjusted.

[0159] Optionally, an early function can be included such that an early warning is issued if the belt tension is close to the edge of the optimal tension range, for example within a predetermined proximity or threshold of the upper or lower boundary of the optimal tension range.

[0160] Examples in accordance with another aspect of the application also provide a computer program product comprising code means, which when operating on a processor, causes the processor to carry out a method in accordance with any of the examples or embodiments outlined above or described below or in accordance with any of the claims of this application.

[0161] As noted above, embodiments utilize a controller 20. The controller can be implemented in numerous ways, with software and / or hardware, to perform the various functions required. A processor is one example of a controller which employs one or more microprocessors that can be programmed using software (e.g., microcode) to perform the required functions. A controller can however be implemented with or without employing a processor, and also can be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0162] Examples of controller components that can be employed in various embodiments of the disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0163] In various implementations, a processor or controller can be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media can be encoded with one or more programs that, when executed on one or more processors and / or controllers, perform at least some of the required functions. Various storage media can be fixed within a processor or controller or can be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement the functions described herein.

[0164] modifications to the disclosed embodiments can be understood and implemented by those skilled in the art upon the reading of the drawings, which, together with the disclosure and claims, disclose the disclosed embodiments. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality.

[0165] A single processor or other unit can implement the functions of several items recited in the claims.

[0166] Although specific measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used effectively.

[0167] A computer program can be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state storage medium supplied together with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0168] If the term "adapted to" is used in the claims or specification it should be noted that the term "adapted to" is intended to be equivalent to the term "configured to".

[0169] No reference signs in the claims should be construed as limiting the scope.

Claims

1. An apparatus (10) for monitoring uterine contractions of a subject, the apparatus comprising: a sensor unit (14) for placement against an abdomen of the subject; a belt member (16) arranged for holding a contact surface of the sensor unit in place against the abdomen; a contact sensing module (18) adapted to detect engagement between the contact surface of the sensor unit and the abdomen of the subject; a force or pressure sensing module (20) adapted to detect a force or pressure between the abdomen and the sensor unit; and a controller (24) adapted to perform a procedure comprising: detecting, by the contact sensing module (18), engagement between the contact surface of the sensor unit and the abdomen, in response to the detection, acquiring, using the force or pressure sensing module, a measure of a starting pressure or force between the abdomen and the sensor unit, and determining, by comparing the starting pressure to at least one predefined reference range, whether a tension or applied force of the belt member is within an optimal range.

2. The apparatus (10) of claim 1, the controller (24) being further adapted to generate an information output indicative of whether the tension of the belt member is within the optimal range, and to communicate the output to a user output device. The controller (24) is further adapted to monitor uterine contractions based on an output of the force or pressure sensing module (20).

3. The apparatus (10) of claim 1, wherein, Monitoring the uterine contractions is conditionally performed in case the tension of the belt member is within the optimal range.

4. The apparatus (10) of claim 3, wherein An output for communication to a user output device to alert the user is generated in response to a determination that the tension of the belt member is not within the optimal range.

5. The apparatus (10) according to any one of claims 1-4, wherein, The sensor unit (14) comprises an optical sensor arrangement comprising a light source (44) arranged to direct a light output from the contact surface into skin of the subject, and a light detector (42) arranged to detect the light output at the contact surface after passing through the skin, and wherein the contact sensing module is provided by the optical sensor arrangement, the engagement with the abdomen is detected based on an output of the light detector.

6. The apparatus (10) according to any one of claims 1-4, wherein, The engagement with the abdomen is detected based on detection of the light output generated by the light source (44) at the light detector (42).

7. The apparatus (10) of claim 6, wherein Contact is detected based on a drop in detected light intensity indicative of a change from:

8. The apparatus (10) of claim 6, wherein, exposure of the light detector (42) to ambient light, to coverage of the light detector (42) by a surface of the abdomen. The light detector (42) is tuned to saturate when exposed to ambient light, and wherein contact is detected based on a change of the output of the light detector from a saturated state to a non-saturated state.

9. The apparatus (10) of claim 8, wherein The optical sensor arrangement is a PPG sensor, and wherein the controller (24) is adapted to determine a pulse of the subject using an output of the PPG sensor.

10. The apparatus (10) of claim 6, wherein, ​ 11. The apparatus (10) according to any one of claims 1-4, wherein, The contact sensing module (18) is provided by the same component as the force or pressure sensing module (20), and wherein engagement is detected based on detecting that a change in the measured force or pressure exceeds a predetermined threshold.

12. A method for initializing or configuring an apparatus (10) for monitoring uterine contractions of a subject, the apparatus comprising: a sensor unit (14) for placement against an abdomen of the subject; and a belt component (16) arranged for holding a contact surface of the sensor unit in place against the abdomen; a contact sensing module (18) adapted to detect engagement between the contact surface of the sensor unit and the abdomen of the subject; a force or pressure sensing module (20) adapted to detect a force or pressure between the abdomen and the sensor unit; and a controller (24) adapted to perform the method, the method comprising: detecting engagement between the contact surface of the sensor unit and the abdomen, acquiring a measure of a starting pressure or force between the abdomen and the sensor unit using the force or pressure sensing module in response to the detection, and determining whether a tension or applied force of the belt component is within an optimal range by comparing the starting pressure to at least one predefined reference range.

13. The method of claim 12, further comprising monitoring uterine contractions based on the output of the force or pressure sensing module, wherein, Monitoring uterine contractions is conditionally performed in case it is determined that the belt tension is within the optimal range.

14. The method of claim 12 or 13, wherein, Detecting engagement between the contact surface of the sensor unit and the abdomen comprises: sensing light received at the contact surface using a light detector, detecting the engagement based on an output of the light detector.

15. A computer program product comprising code means configured to, when run on a controller of an apparatus according to any of claims 1 to 11, cause the controller to perform the method according to any of claims 12-14.

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