DETECTING INCREASING FLUID IN A LUNG OF A SUBJECT

A method of detecting increasing fluid in a lung of a subject, the method comprising: at a first time, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heart beat; at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and if the second difference is less than the first difference by more than a threshold value, producing a fluid detection alert.

TECHNOLOGICAL FIELD

Embodiments of the present invention relate to detecting increasing fluid in a lung of a subject.

BACKGROUND

It is desirable to be able to detect when fluid in a subject's lung is increasing so that, for example, medication may be provided to the subject.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising:

means for determining, at a first time, a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of a subject's heart beat;

means for determining, at a second later time, a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and

means for producing a fluid detection alert indicative of increasing fluid in a lung of the subject, if the second difference is less than the first difference by more than a threshold value.

In some but not necessary all examples, the apparatus comprises: an external electrode and a sensor configured to remain at the same positions between the first time and the second time, wherein the means for determining, at the first time, a first difference between a time of arrival of the first feature of a received electrical signal of the subject's heart beat and the time of arrival of the second feature of a received acoustic signal of the subject's heart beat is means for determining at the first time, the first difference between the time of arrival of a first feature of the received electrical signal of the subject's heart beat at the external electrode and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat at the sensor;

and wherein the means for determining, at the second time, the second difference between the time of arrival of the first feature of the received electrical signal of the subject's heart beat and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat is means for determining at the second time, the second difference between the time of arrival of the first feature of the received electrical signal of the subject's heart beat at the external electrode and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat at the sensor.

In some but not necessary all examples, the apparatus comprises multiple electrocardiogram (ECG) electrodes and a single acoustic sensor, all of which are configured to remain at the same positions between the first time and the second time, wherein the means for determining, at the first time, a first difference between a time of arrival of the first feature of a received electrical signal of the subject's heart beat and the time of arrival of the second feature of a received acoustic signal of the subject's heart beat is means for determining at the first time, a first difference between the time of arrival of a first feature of the received ECG electrical signal of the subject's heart beat at the ECG electrodes and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat at the single sensor;

and wherein the means for determining, at the second time, the second difference between the time of arrival of the first feature of the received electrical signal of the subject's heart beat and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat is means for determining at the second time, a second difference between the time of arrival of the first feature of a received ECG electrical signal of the subject's heart beat at the ECG electrodes and the time of arrival of the second feature of the received acoustic signal of the subject's heart beat at the single sensor.

In some but not necessary all examples, the sensor is configured to be placed on a lateral portion of the subject's thorax between a mid-clavicular line and one of the axillary lines and at or below the 5thintercostal space.

In some but not necessary all examples, the sensor is configured to be positioned with a lower portion of the subject's lung between the sensor and the subject's heart.

In some but not necessary all examples, the apparatus comprises means for detecting the first feature of the received electrical signal of a subject's heart beat and subsequent heart beat by detecting a recognizable part of an electrocardiogram.

In some but not necessary all examples, the apparatus comprises means for detecting the first feature of the received electrical signal of a subject's heart beat and subsequent heart beat by detecting rapid depolarization of the right and left ventricles and means for detecting the second feature of the received acoustic signal of a subject's heart beat and subsequent heart beat by detecting atrioventricular valves closure at beginning of systole.

In some but not necessary all examples, the apparatus comprises means for detecting the second feature of the received acoustic signal of a subject's heart beat and subsequent heart beat by detecting a first peak following an R peak of a QRS complex of the received electrical signal.

In some but not necessary all examples, the apparatus comprises means for detecting the first feature by detecting an inflection point, local maximum, local minimum, gradient of the received electrical signal amongst other inflection points, local maxima, local minima, gradients of the received electrical signal and wherein the second feature is an inflection point, local maximum, local minimum, gradient of the received acoustic signal amongst other inflection points, local maxima, local minima, gradients of the received acoustic signal.

In some but not necessary all examples, the apparatus comprises means for repeatedly determining over a first time interval of multiple heart beats, preceding the first time, a sample of first differences between a time of arrival of the first feature of a received electrical signal of a subject's heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's heart beat; means for processing the sample of first differences to produce the first difference at the first time; and means for repeatedly determining over a second time interval of multiple subsequent heart beats, preceding the second time, a sample of second differences between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat and means for processing the sample of second differences to produce the second difference at the second time.

In some but not necessary all examples, the means for processing the sample of first differences to produce the first difference at the first time comprises means for averaging the sample of first differences; and the means for processing the sample of second differences to produce the second difference at the second time comprises means for averaging the sample of second differences.

According to various, but not necessarily all, embodiments of the invention there is provided a method of detecting increasing fluid in a lung of a subject, the method comprising: at a first time, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heart beat;

at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and if the second difference is less than the first difference by more than a threshold value, producing a fluid detection alert.

According to various, but not necessarily all, embodiments of the invention there is provided a method comprising: at a first time, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of a subject's heart beat;

at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and if the second difference is less than the first difference by more than a threshold value, producing a fluid detection alert indicative of increasing fluid in a lung of the subject.

According to various, but not necessarily all, embodiments of the invention there is provided a computer program that when run on a processor enables the processor to: at a first time, determine a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of a subject's heart beat;

at a second later time, determine a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and

produce a fluid detection alert indicative of increasing fluid in a lung of the subject, if the second difference is less than the first difference by more than a threshold value.

According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising:

at least one processor; and

at least one memory including computer program code

at a first time, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heart beat;

at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and

if the second difference is less than the first difference by more than a threshold value, producing an alert.

According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

The following portion of this ‘Brief Summary’ section, describes various features that may be features of any of the various embodiments described in the foregoing portion of the ‘Brief Summary’ section. The description of a function should additionally be considered to also disclose any means suitable for performing that function.

In some but not necessarily all examples, at the first time and the second time, the electrical signal is received at the same external electrode at the same location on an exterior of the subject and, at the first time and the second time, the acoustic signal is received at the same sensor at the same location on an exterior of the subject. At the first time and the second time, the electrical signal is received, in some but not necessarily all examples, at the same external ECG electrodes at the same location on an exterior of the subject. The sensor is placed, in some but not necessarily all examples, on a lateral portion of the subject's thorax between a mid-clavicular line and one of the axillary lines and at or below the 5thintercostal space. The sensor is positioned, in some but not necessarily all examples, with a lower portion of the subject's lung between the sensor and the subject's heart.

In some but not necessarily all examples, the first feature of the received electrical signal of a subject's heart beat and subsequent heart beat is associated with a recognizable part of an electrocardiogram.

In some but not necessarily all examples, the first feature of the received electrical signal of a subject's heart beat and subsequent heart beat is associated with rapid depolarization of the right and left ventricles and wherein the second feature of the received acoustic signal of a subject's heart beat and subsequent heart beat is associated with atrioventricular valves closure at beginning of systole.

In some but not necessarily all examples, the second feature of the received acoustic signal of a subject's heart beat and subsequent heart beat is associated with a first peak following an R peak of a QRS complex of the received electrical signal.

In some but not necessarily all examples, the first feature is an inflection point, local maximum, local minimum, gradient of the received electrical signal amongst other inflection points, local maxima, local minima, gradients of the received electrical signal and wherein the second feature is an inflection point, local maximum, local minimum, gradient of the received acoustic signal amongst other inflection points, local maxima, local minima, gradients of the received acoustic signal.

In some but not necessarily all examples, the method comprises: detecting a time of arrival of a first feature of a received electrical signal of a subject's heart beat by sampling the received electrical signal at a sampling rate greater than 10 khz; and detecting a time of arrival of a second feature of a received acoustic signal of a subject's heart beat by sampling the received acoustic signal at a sampling rate greater than 10 khz

In some but not necessarily all examples, at the first time, determining the first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heartbeat, comprises:

repeatedly determining over a first time interval of multiple heart beats, preceding the first time, a sample of first differences between a time of arrival of the first feature of a received electrical signal of a subject's heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's heart beat and processing the sample of first differences to produce the first difference at the first time; and wherein, at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; comprises: repeatedly determining over a second time interval of multiple subsequent heart beats, preceding the second time, a sample of second differences between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat and processing the sample of second differences to produce the second difference at the second time. Processing the sample of first differences to produce the first difference at the first time comprises, in some but not necessarily all examples, averaging the sample of first differences. Processing the sample of second differences to produce the second difference at the second time comprises, in some but not necessarily all examples, averaging the sample of second differences. In some but not necessarily all examples, iteration is used. In some but not necessarily all examples the time difference between the first time and the second time is significantly greater than the duration of the first interval or the second interval. In some but not necessarily all examples the time difference between the first time and the second time is a period when a lower power consumption mode or a lower sampling rate mode is operational and wherein the first interval and the second interval are periods when a higher power consumption mode or a higher sampling rate mode is operational.

DETAILED DESCRIPTION

FIG. 1illustrates an example of a method100of detecting increasing fluid in a lung of a subject, the method comprising:

at a first time, at block102, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heart beat;

at a second later time, at block104, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and

at block106, if the second difference is less than the first difference by more than a threshold value, producing a fluid detection alert.

FIG. 2illustrates an example of an apparatus200that provides means for performing the method ofFIG. 1. The apparatus200comprises circuitry210configured to perform the method100ofFIG. 1. An electrical signal222measured by an electrode220is received at the circuitry210. An acoustic signal232measured by a sensor230is received at the circuitry210. The sensor230transduces the received pressure waves to an electrical signal. The sensor230may, for example, be a microphone. The circuitry210produces an alert238.

The circuitry210is configured, at a first time, to determine a first difference between a time of arrival of a first feature (F1) of a received electrical signal222of a subject's heartbeat and a time of arrival of a second feature (F2) of a received acoustic signal232of the subject's heartbeat. The circuitry is configured, at a second later time, to determine a second difference between a time of arrival of the first feature (F1) of a received electrical signal222of a subject's subsequent heartbeat and time of arrival of the second feature (F2) of a received acoustic signal232of the subject's subsequent heartbeat.

The circuitry210is configured, if the second difference is less than the first difference by more than a threshold value, to produce a fluid detection alert238.

In some examples, the apparatus200is configured to provide the alert238as an alert to the subject. In other examples, the apparatus200is configured to provide the alert238to an apparatus that causes automatic medication of the subject.

In some, but not necessarily all, examples, the apparatus200may be a personal device that is worn or carried by the subject.

In some, but not necessarily all, examples, the apparatus200may be configured to provide additional functionality. For example, it may produce a visual display of the received electrical signal222.

FIG. 3illustrates an example of a received electrical signal222of a subject's heartbeat and an example of a received acoustic signal232of the subject's heartbeat.

In this example, the electrical signal222is an electrocardiogram (ECG) signal. An ECG signal has a number of distinct characteristics commonly referred to as PQRST. The P-wave precedes the QRS complex which precedes the T-wave.

Any distinctive feature of the electrical signal222may be used as the first feature (F1). The most distinctive feature is the R-peak of the QRS complex. Consequently, the first feature (F1) of the received electrical signal222of a subject's heartbeat and the subsequent heartbeat is associated with a recognisable part of an electrocardiogram. For example, it may be associated with rapid depolarisation of the right and left ventricles (R-peak).

In this example, the acoustic signal232is a phonocardiogram signal. The phonocardiogram signal232has a distinctive maximum amplitude pulse labelled S1.

Any distinctive feature of the acoustic signal232may be used as the second feature (F2). The maximum amplitude feature S1is easily detected.

The second feature of the received acoustic signal232of a subject's heartbeat and subsequent heartbeat may be associated with atrioventricular valves closure at beginning of systole.

In some examples, the second feature (F2) of the received acoustic signal232of a subject's heartbeat and subsequent heartbeat is associated with the first peak following the R-peak of a QRS complex of the received electrical signal222.

The first feature and/or second feature may be an inflection point, a local maximum, a local minimum, a gradient of the received signal particularly located amongst other inflection points, local maxima, local minima, gradients of the received signal.

FIGS. 4A and 4Billustrate an example of a subject240.FIG. 4Aillustrates a front (anterior) view andFIG. 4Billustrates a side (lateral) view. The position of the subject's heart242and lungs244are schematically illustrated inFIG. 4A. The heart242is centrally located, slightly to the subject's left. The left lung244is posterior to the heart242.

The ECG electrode220may be placed in any suitable position. It may for example be placed in one of the standard positions for obtaining a standard ECG vector.

The sensor230for detecting received acoustic signal232is preferably positioned with a lower portion of the subject's lung244between the sensor230and the subject's heart242.

For example, the sensor230may be placed on a lateral portion of the subject's thorax246between a mid-clavicular line251and one of the axillary lines253and at or below the fourth or fifth intercostal space252. The axillary lines253may be any one of the posterior, middle or anterior axillary lines253p,253m,253a.

As previously described, the production of the alert238is dependent upon the threshold value. If the second difference is less than the first difference by more than the threshold value then the fluid detection alert238is produced. The second difference being less than the first difference may occur because the acoustic signal232will propagate through liquid fluid faster than trough air. Therefore when the second difference is less than the first difference by more than the threshold value, the fluid detection alert238is likely indicative that there is an increased build-up of liquid fluid at the second time t2relative to the first time t1. The build-up of liquid fluid may be located within one or both of the subject's lungs244and/or in a region of the subject's chest cavity that surrounds the lungs244.

The threshold value may be subject-dependent. Typically it is of the order 0.2 ms, however, it may vary for different subjects. For example, the threshold value may be based upon the difference between the speed of sound in water/body tissue and speed of sound in air, and the estimated size of the subject's thorax246. Therefore by measuring the subject's thorax246it may be possible to produce a threshold value for that subject. A thorax size may be estimated from a person's height and weight or from chest circumference measurements. Alternatively, it may be desirable to calibrate the apparatus200for each subject. For example, calibration may occur by measuring propagation delay of sound through the chest by providing an audio source e.g. a tap (strike) on the outer chest or back.

FIG. 5illustrates an example of the apparatus200performing the method100.

At a first time t1, at block102, the method100determines a first difference between a time on arrival of a first feature (F1) of a received electrical signal222of a subject's heartbeat and a time of arrival of a second feature (F2) of a received acoustic signal232of the subject's heartbeat.

At a second later time t2, at block104, the method100determines the second difference between a time of arrival of the first feature (F1) of a received electrical signal222of a subject's subsequent heartbeat and a time of arrival of the second feature (F2) of a received acoustic signal232of the subject's subsequent heartbeat.

Then, at block106, if the second difference is less than the first difference by more than a threshold value, the method100produces a fluid detection alert238.

At the first time t1and the second time t2, the electrical signal222is received at the same external electrode220at the same location on an exterior of the subject240.

At the first time t1and the second time t2, the acoustic signal232is received at the same sensor230at the same location on an exterior of the subject240.

In some, but not necessarily all, examples, only a single sensor230for receiving an acoustic signal232is required to produce a fluid detection alert238for a lung.

In some, but not necessarily all, examples, multiple ECG electrodes220may be used.

The time of arrival of a first feature (F1) of a received electrical signal222of a subject's heartbeat may be detected by sampling the received electrical signal222at a sampling rate greater than 10 khz. A time of arrival of a second feature (F2) of a received acoustic signal232of a subject's heartbeat may be detected by sampling the received acoustic signal232at a sampling rate greater than 10 khz.

In some, but not necessarily all, examples, the received electrical signal222and the received acoustic signal232may be sampled using the same clock or synchronised clocks.

There may be a considerable amount of time between the first time t1and the second time t2compared to the sample period (100 μs). For example, the time difference may be more than one hour (equivalent to 36 million samples).

In order to improve the accuracy of the method and to avoid the impact of noise, it may be desirable to perform statistical averaging at the first time and to perform, separately, statistical averaging at the second time.

For example, at the first time, at block102the method may comprise determining at block102a first difference between a time of arrival of a first feature (F1) of a received electrical signal222of a subject's heartbeat and a time of arrival of a second feature (F2) of a received acoustic signal of the subject's heartbeat by repeatedly determining over a first time interval T1of multiple heartbeats, preceding the first time t1a sample of first differences between the first time of arrival of the first feature (F1) of a received electrical signal222of the subject's heartbeat and a time of arrival of the second feature (F2) of a received acoustic signal of the subject's heartbeat and processing the sample of first differences to produce as an average the first difference at the first time. Thus the method of block102is applied repeatedly for different heartbeats within the first interval T1and the resulting first time differences are averaged, although other processes may be used, such as integration, for example.

The method100at block104may comprise, at the second later time t2, determining a second difference between a time of arrival of the first feature (F1) of a received electrical signal222of a subject's subsequent heartbeat and a time of arrival of the second (F2) of a received acoustic signal232of the subject's subsequent heartbeat by repeatedly determining over a second time interval T2of multiple subsequent heartbeats, preceding the second time t2, a sample of second differences between a time of arrival of the first feature (F1) of a received electrical signal222of a subject's subsequent heartbeat and a time of arrival of the second feature (F2) of a received acoustic signal232of the first subject's subsequent heartbeat and processing the sample of second differences to produce as an average the second difference at the second time. Thus the method of block102is applied repeatedly for different heartbeats within the second interval T2and the resulting second time differences are averaged, although other processes may be used such as integration, for example.

It will be appreciated that, at block106, the method100produces an alert when a difference between the first time of arrival and the second time of arrival decreases, on average, below a threshold.

FIG. 6illustrates an example of the electrical signal222and the acoustic signal232over the first interval T1and the second interval T2.

The time difference between the first time t1and the second time t2is significantly greater than the duration of the first interval T1or the second interval T2.

The apparatus200may be operated in low power mode between the end of the first interval T1and the beginning of the second interval T2and operated at a higher power mode during the first interval T1and during the second interval T2. Consequently, there is significant power saving compared to continuous operation of the apparatus200in the high power mode.

The apparatus200may be power downed fully between the end of the first interval T1and the beginning of the second interval T2

The low power mode may be a mode in which a lower sampling rate is used compared to the higher power mode. The sampling rate of the higher power mode may be above 1 kHz. The sampling rate of the lower power mode may be below 1 kHz.

It will be appreciated that the methods described may be continuously iterated producing comparisons between time of arrival differences determined at any two different times and determining whether or not to produce an alert based on the comparisons. At any arbitrary time t0the current time may be considered to be the second later time and the immediately preceding time tn-1when the method was performed may be considered to be the first time. It will therefore be appreciated that the method operates continuously.

The averaging over the first time interval and the second time interval is preferably over a time that is long compared to the respiratory cycle. This then normalises the results with respect to the respiratory cycle and results in a consistent comparison of like with like.

Implementation of the circuitry210may be as a controller. The controller may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated inFIG. 7Asuch a controller260may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program266in a general-purpose or special-purpose processor262that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor262.

The processor262is configured to read from and write to the memory264. The processor262may also comprise an output interface via which data and/or commands are output by the processor262and an input interface via which data and/or commands are input to the processor262.

The memory264stores a computer program266comprising computer program instructions (computer program code) that controls the operation of the apparatus200when loaded into the processor262. The computer program instructions, of the computer program266, provide the logic and routines that enables the apparatus to perform the methods illustrated inFIGS. 1 and 5. The processor262by reading the memory264is able to load and execute the computer program266.

at least one processor262; and

at least one memory264including computer program code

the at least one memory264and the computer program code configured to, with the at least one processor262, cause the apparatus200at least to perform:

at a first time, determining a first difference between a time of arrival of a first feature of a received electrical signal of a subject's heart beat and a time of arrival of a second feature of a received acoustic signal of the subject's heart beat;

at a second later time, determining a second difference between a time of arrival of the first feature of a received electrical signal of a subject's subsequent heart beat and a time of arrival of the second feature of a received acoustic signal of the subject's subsequent heart beat; and

if the second difference is less than the first difference by more than a threshold value, producing a fluid detection alert.

As illustrated inFIG. 7B, the computer program266may arrive at the apparatus200via any suitable delivery mechanism270. The delivery mechanism270may be, for example, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a compact disc read-only memory (CD-ROM) or digital versatile disc (DVD), an article of manufacture that tangibly embodies the computer program266. The delivery mechanism270may be a signal configured to reliably transfer the computer program266. The apparatus200may propagate or transmit the computer program266as a computer data signal.

Although the processor262is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor262may be a single core or multi-core processor.

As used in this application, the term ‘circuitry’ refers to all of the following:

(b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

(c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

As used here ‘module’ refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user.