WO2009091239A1

WO2009091239A1 - System and method for monitoring pressure within a living body

Info

Publication number: WO2009091239A1
Application number: PCT/NL2008/050027
Authority: WO
Inventors: Johannes Martinus Adrianus Mens; Hendrik Jan Stam; Johannes Bernardus Josephus Bussmann
Original assignee: Erasmus University Medical Center Rotterdam
Priority date: 2008-01-15
Filing date: 2008-01-15
Publication date: 2009-07-23

Abstract

A system for measuring intra-abdominal pressure in the body of a subject uses a pill with a pressure sensor for use inside the body. The system comprises an activity monitor with sensors to collect information about postures of the body of the subject, to classify activities of the subject. Information about the detected postures, such as activity code values, and information about pressures measured by the pressure sensor are recorded in temporal correlation with each other. This makes it possible to identify normal live activities wherein the subject has abnormal intra-abdominal pressure, and/or analyse pressure measurements during selected activities.

Description

Title: System and method for monitoring pressure within a living body

Field of the invention

The invention relates to a system and method for monitoring pressure within a living body, for example the intra-abdominal pressure of a human.

Background

High intra-abdominal pressure has been associated with various diseases. Accordingly, various methods have been proposed to measure intraabdominal pressures in living subjects. Unfortunately, the results of such methods are not always representative. Some of these methods require the subject to sit or lie down in a diagnostic apparatus, which may lead to unnatural results. Other methods involve requiring the subject to perform exercises while burdensome external sensor arrangements have been attached to his or her body, involving for example hoses entered through varies body orifices. This has also been found to produce unnatural results. An improvement over this was made when a pill was developed comprising a remotely readable pressure sensor. This made measurement of pressure less burdensome.

WO2005/096937 describes a system that uses a diagnostic pill that may contain a pressure sensor. In addition this document discloses the use of a number of sensors on the body of the subject to determine the position of the pill in the intestinal tract, in order to correlate pressure measurements with the location where the pressure is measured.

However, it has been found that straightforward measurement of pressure still does not provide representative results, even if an unobtrusive pill with a pressure sensor is used. Summary

Among others, it is an object to provide for a system and method for monitoring pressure within a living body with which representative measurements can be obtained of pressures in the body under normal circumstances.

A system according to claim 1 is provided. Herein information from pressure measurements from a pill in a body is recorded in temporal correlation with detected postures of the body. This enables pressure measurements in the body under natural circumstances. By recording information about the activities when the pressures are measured, meaningful measurements can be obtained.

Brief description of the drawing

These and other advantageous aspects will become apparent from a description of exemplary embodiments, using the following figures.

Figure 1 shows a pressure monitoring system Figure 2 shows a piece of clothing with sensors Figure 3 shows an analysis system

Detailed description

Figure 1 shows a pressure monitoring system, comprising a pill 10, a controller 12 and sensors 14. Pill 10 comprises a pressure sensor 100 and a wireless transponder 102 coupled to pressure sensor 100. Controller 12 comprises a processor 120, a transceiver 122 and a memory 124. Processor 120 is coupled to sensors 14, transceiver 122 and memory 124. As shown, memory 124 has an interface for external reading. Processor 120 and sensors 14 form an activity monitor, for detecting and classifying activities of a subject. Sensors 14 determine information about position and/or movement of body segments from which information about the posture of the body can be derived. As used herein, information about the posture comprises the value of any angle of at least one part of the body relative to a vertical direction, and/or at least one angle between different parts of the body, and/or or changes in such an angle or angles, such as its speed of change or acceleration of the angles. In various embodiments sensor 14 may include force sensors, position sensors, speed sensors, acceleration sensors, orientation sensors, angle sensors etc. In an embodiment, the system comprises one or more pieces of clothing for the subject, sensors 14 being included in or on the piece of clothing. Alternatively the sensors may be included directly on the body.

Figure 2 shows an example of such a piece of clothing 20, with sensors 14. Sensors 14 and controller 12 may be coupled to each other by electrical conductors to exchange information. Wireless communication connections (using RF or optical signals for example) may be used instead. Alternatively sensors 14 may be configured for direct attachment to the body of the subject, for example by means of straps, gluing etc. Processor 120 may be a programmable circuit, operating under control of a computer program loaded in a program memory (e.g. in memory 124 or in another memory (not shown)).

In operation the pressure monitoring system records information about the pressures measured by pressure sensor 100 inside a subject in correlation with information about detected activities of the subject when the pressures where measured. The subject is asked to live his or her normal life, after swallowing pill 10 and while wearing sensors 14. The resulting record makes it possible to analyse the pressure measurements during normal life conditions, to detect exceptional pressure measurements that are due to special activities and/or to detect whether the subject has exceptional pressures when performing specific activities. Detection of exceptional pressures when performing specific activities may be used to generate a warning to the subject to instruct him or her to modify his or her behavior in order to avoid abnormal pressures. Detection of exceptional pressures when performing special activities may also be used to identify pressure peaks that are not abnormal, because they correspond to special activities where such pressures are unavoidable.

In operation pill 10 is swallowed orally by a subject, such as a human patient or an animal. Alternatively pill 10 may be entered into the body rectally or vaginally for example. Wireless transponder 102 and transceiver 122 may be configured to communicate by means of RF signals, transponder 102 responding to query signals by transceiver 122. Instead of a transponder 102, a transmitter may be used that periodically transmits data automatically. In this case transceiver may be a receiver.

Pill 10 may contain a battery (not shown) for powering sensor 100 and wireless transponder 102. Alternatively power may be provided to pill by RF signals. Controller 12 may contain a battery (not shown) to power operation.

Wireless transponder 102 reads pressure data from pressure sensor 100 and sends information about the pressure to transceiver 122. Sensors 14 are attached to the body of the subject, or in a piece of clothing of the subject. Processor 120 reads sensor data from sensors 14 and pressure data from transceiver 122. Processor 120 processes the data from sensors 14 and the pressure data and writes the results to memory 124.

Processor 120 uses the data from sensors 14 to detect and classify activities of the subject. Methods for detecting and classifying activities are known per se from the prior art, outside the context of measurement of abdominal pressure. Various alternative forms of activity monitoring may be used.

In an embodiment a sensor 14 comprises a force sensor, that is, a sensor for sensing an effect of gravitational plus inertial forces experienced by the sensor due to gravity and acceleration of the sensor in one or more directions. Such force sensors are well known per se. They are also called accelerometers, although it should be understood that they need not measure change in speed of any body part, but only some effect that is indicative of gravitational and inertial forces. In this sense a force sensor need not be a sensor that measures other forces, such as a force due to tightening of a belt around a user's body, due to blows inflicted on the body etc., but of course that type of force sensor may also be used as part of activity monitoring.

By way of example sensors 14 on the torso and thighs of a subject may be used. The sensor on the torso may be configured to sense forces in two directions (the head-groin and the front-back direction elative to the torso). The sensors on the thighs may each be configured to measure a force in one direction (the front back direction relative to the relevant thigh).

The time averaged force sensed by such a sensor represents the force of gravity. In addition an average of the forces sensed by sensors at different thighs may be used. The average forces may be used to classify activity into classifications such as standing-walking, sitting, lying. Any classification method may be used and schemes of classes may be used that allow for a greater or smaller degree of refinement. As a simple illustration of a class and its relation to forces, standing- walking may be taken to correspond to a non-zero force detected by the torso sensor in the head-groin direction and zero average forces in the front-back direction sensed by the torso sensor and the thigh sensors. Sitting may correspond to similar average forces, except that a non-zero forces is sensed by the thigh sensors in their front-back direction. Lying on the back corresponds to a non-zero average forces detected by the torso sensor and the thigh sensors zero in the front back direction and zero average force in the head groin direction sensed by the torso sensor. Lying on the belly corresponds to similar average forces, but with opposite sign. Lying on the side corresponds to zero average forces from all sensors. As will be appreciated, this illustration of classes and their relation to forces could already form the starting point for constructing a simple classification scheme, but of course more refined activity classes and more complex correspondences between classes and sensor outputs may be used. Also more refined or more gradual distinctions may be used than between zero and non-zero.

In an embodiment angles defined by the ration of forces measured for different directions may be used to refine the classification. Thus for example a zero and non-zero tilt angle of the torso derived from the forces measured by the torso sensor in the head-groin and front -back directions may be used to distinguish walking and climbing stairs.

Classification may be performed for example by defining vectors of reference forces from different sensors for different classes of activity and computation of distance measures between sets of average sensed forces and the sets of reference forces. In this case a vector of average sensed forces may be assigned to a class by selecting the class with a vector of reference forces at smallest distance to the set of average sensed forces. An example of a measure of distance between sets is a sum of squares of differences between pairs forces from the sets, but many similar distance measures may be used. Respective activity code values may be associated each with a group of one or more reference vectors, the code of the reference vector that is closest to a vector of measurements for a time point being recorded in correlation with a pressure measurement for that time point. In another embodiment classification may be performed by providing a table indexed by sets of quantized average force measurements, the table containing codes of classes corresponding to the sets of average force measurements.

The classifications may be refined by additionally using a measure of variability of the forces, such as the variance of deviations from the average force and/or the detection whether the frequency spectrum of a force has more than a threshold amount of content in a predetermined frequency band characteristic for an activity and/or the frequency spectrum has a peak with a size that exceeds a threshold value. Thus for example standing and walking can be distinguished, by zero and non-zero variability of the forces measures on the thighs respectively. Running can be distinguished from walking by a larger variability of thigh forces and/or a peak at higher frequency. Cycling and sitting may be distinguished by a peak of the frequency spectrum of thigh forces. Information about the variability and/or size and/or position of the peaks may be added to the sets of average force measurements for the purpose of classification. In another embodiment, the angle between the torso and a thigh of the subject may be measured, or speed or acceleration of change in the angle, as well as its temporal variation, and used to classify activities into bending over , sitting (angle in a range that includes 90 degrees plus or minus, say, 45 degrees) lying, standing (angle in a range that includes a 180 degrees plus or minus, say, 45 degrees), cycling or walking (angle in range that includes 180 degrees with periodic variations in a range including 1 Hz). The changes in such an angle may be computed from differences between speeds or acceleration sensed by speed or acceleration sensors at different positions on the body, or from distances between sensors measured by distance sensors. The angle may also be measured directly using sensors that extend along different parts of the body. A measurement of an angle between the torso and the vertical may be used to discriminate upright and lying positions, bending over and sitting. Angle speed or acceleration measurements may be used to discriminate between static and dynamic activity. In addition to sensors 14 controller 12 may be provided with a user interface to enable the user to indicate activities. The user interface may include a keyboard and an alarm, to signal the user when a code for an activity should be entered on the keyboard. Thus for example, processor 120 may identify unrecognized activities, or acquire training data that adds a classification to a pattern of sensor measurements detected before the alarm. Processor 120 may subsequently use such patterns as reference patterns in comparisons with other measured patterns. In this case processor may copy classification of the other measured patterns from the classification of the closest reference pattern. A user interface may also be used to replace sensors 14 altogether, when the user is asked to encode all his or her activities. Although usable, it is preferred to use sensors 14 to avoid burdening the user to such an extent that pressures are affected.

Instead of angle sensors, or in addition to such sensors, other sensors may be used, such as speed or acceleration sensors. From sensing results of combinations of such sensors on the torso and/or different limbs, relative motion can be determined, which processor 120 may use to classify activities. Individual speeds or acceleration measurements may also be used to distinguish activities like stationary activities, driving, walking, running etc. Furthermore, other types of sensors, such as a heart-rate sensor and/or a temperature sensor may be added to enable refinement of classification of activities.

Processor 120 writes a code indicating the detected activity into memory 124 in temporal correlation with information about the measured pressure of pressure sensor 100 in pill 10 inside the body at the time of measurement. "In (temporal) correlation" denotes any way of recording that allows the determination of pairs of measured pressure and detected activity that occurred at a same time point associated with the pair, or within a time distance of each other wherein no change of activity has occurred. This may be done for example by writing the code indicating the detected activity and information about the co-temporally measured pressure together in a common record, or in records at the same index in different tables.

Correlation may also be realized by writing the code of the detected activity and the information about the measured pressure each in correlation with a time stamp (e.g. at a entry for a specific time in a table). A clock circuit may be added to controller 12 for this purpose, coupled to processor 120. In this case the code and the information can be associated later, on the basis of corresponding time stamps. It should be noted that this may be used to split controller 12 into separate devices, each with its own clock circuit, one device for recording information about pressure and another for recording codes of activities. In this case these different devices may later be placed in communication with each other, or with a third device of the system, to read out the information about the pressure and the activity codes and to associate them on the base of the time stamps. One of the devices may be pill 10, in which case pill would not need a transponder 102, provided that pill 10 is recovered after use to read out information.

It may be noted that processor 120 may use memory 124 to record actual measurements from sensors 14 in correlation with information about measured pressure, without first classifying the activity. In this case, classification may be performed later.

After collection of data controller 12 coupled to an analysis computer to analyse the measurements.

Figure 3 shows an analysis system comprising controller 12 and analysis computer 30. Analysis computer 30 is programmed to read out correlated information about the pressure and activity codes from controller 12 and to analyse the correlated data. Various forms of analysis may be provided for. In one embodiment, standard ranges of pressure are defined for each activity code. In this embodiment analysis computer 30 tests for each pair of a correlated activity code and pressure information whether the pressure is within the standard range for the activity code or not. Analysis computer 30 reports incidents where the pressure is out of range on a display screen or prints them. In other embodiments, analysis computer 30 may perform statistical analysis of the correlated data, to signal the average pressures for different activities. It should be appreciated that a different embodiment is possible wherein analysis computer 30 is part of controller 12. As another alternatively, controller 12 may also comprise sensor data to analysis computer 30 to record it as it comes in. In this case analysis computer 30 may perform classification of activities.

As will be realized the system makes it possible to perform internal pressure measurements with a minimum of perturbation of the normal activity pattern of the subject. Representative measurements are obtained because the pressure measurements are automatically correlated with activities. Measurements are possible during daily life. It is made unnecessary to place the subject in a test situation, which will always cause the subject to behave abnormally. It is made possible to perform measurements during activities that cannot be simulated in a test set-up for reasons of privacy and practicality.

Claims

1. A system for measuring pressure in a living body, comprising

- a pill comprising a pressure sensor, for use inside the body;

- an activity monitor configured to detect information about postures of the body; - a recording arrangement configured to record information about the detected postures and information about pressures measured by the pressure sensor in temporal correlation with each other.

2. A system according to claim 1, wherein the activity monitor comprises at least one sensor for mounting on the body and configured to measure an angle or angles between at least one part of the body and a vertical direction and/or changes of that angle or those angles.

3. A system according to claim 1, wherein the activity monitor comprises at least one sensor for mounting on the body and configured to measure an angle or angles between different parts of the body and/or changes of that angle or those angles.

4. A system according to claim 1, wherein the activity monitor is configured to determine measure of variability of an angle between a first part of the body and a vertical direction or a second part of the body.

5. A system according to claim 1, comprising a processor configured to determine activity classification codes from the detected postures, the recording arrangement being configured to record the activity classification codes and the information about the pressures in temporal correlation with each other.

6. A method of measuring pressure in a living body, the method comprising

- reading pressures measured by a pressure sensor in a pill ingested in the body; - detecting information about postures of the body;

- recording the detected information about postures and information about pressures measured by the pressure sensor in temporal correlation with each other.

7. A method according to claim 6, comprising measuring an angle or angles between at least one part of the body and a vertical direction and/or changes of that angle or angles and determining the information about postures of the body using said angle or angles.

8. A method according to claim 6, comprising measures an angle or angles between different parts of the body and/or changes of that angle or angles and determining the information about postures of the body using said angle or angles.

9. A device for use in a system for measuring pressure in a living body, the device comprising - a receiver for wireless reception of pressure signals from a pressure sensor;

- a sensor input for receiving signals about posture of the body or changes thereof;

- a recording arrangement configured to record information postures derived from the signals about the posture or changes thereof and information about pressures measured by the pressure sensor, in temporal correlation with each other.

10 A device according to claim 9, comprising at least one sensor coupled to the sensor inputs.