GB2520487A - Blood-flow sensor apparatus - Google Patents

Blood-flow sensor apparatus Download PDF

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Publication number
GB2520487A
GB2520487A GB1320419.3A GB201320419A GB2520487A GB 2520487 A GB2520487 A GB 2520487A GB 201320419 A GB201320419 A GB 201320419A GB 2520487 A GB2520487 A GB 2520487A
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United Kingdom
Prior art keywords
blood
flow sensor
flow
sensor apparatus
housing
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GB1320419.3A
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GB201320419D0 (en
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Eduardo Mangieri
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Eduardo Mangieri
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Priority to GB1320419.3A priority Critical patent/GB2520487A/en
Publication of GB201320419D0 publication Critical patent/GB201320419D0/en
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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813Specially adapted to be attached to a specific body part
    • A61B5/6825Hand
    • A61B5/6826Finger
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/0059Detecting, measuring or recording for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/024Detecting, measuring or recording pulse rate or heart rate
    • A61B5/02416Detecting, measuring or recording pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infra-red radiation
    • A61B5/02427Details of sensor
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/02Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026Measuring blood flow
    • A61B5/0261Measuring blood flow using optical means, e.g. infra-red light
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/68Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813Specially adapted to be attached to a specific body part
    • A61B5/6822Neck
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/72Signal processing specially adapted for physiological signals or for diagnostic purposes
    • A61B5/7203Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2560/00Constructional details of operational features of apparatus; Accessories for medical measuring apparatus
    • A61B2560/04Constructional details of apparatus
    • A61B2560/0406Constructional details of apparatus specially shaped apparatus housings
    • A61B2560/0425Ergonomically shaped housings
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/04Measuring bioelectric signals of the body or parts thereof
    • A61B5/0402Electrocardiography, i.e. ECG

Abstract

The present invention relates to blood-flow sensors, in particular, to optical blood-flow sensors, such as photoplethysmographic sensors. In one aspect the present invention provides blood-flow sensor apparatus, comprising a blood-flow sensor probe 11 connected to signal processing apparatus, a housing, for receiving a body part of a subject, a light source 5 and a photodiode 6, mounted to the housing wherein the housing has a shaped surface 12, 13 which is shaped to conform, at least in part, to the shape of the body part. In embodiments the shaped surface can be an angled or curved surface, which can be shaped to receive a human digit. In other aspects the housing can form a clip. In other aspects the housing can provide a deformable pad 14 for cushioning the body part to be received. Further aspects provide blood flow sensor probes and methods for processing bloodflow data using a finite impulse response filter, such as a bandpass filter.

Description

BLOOD-FLOW SENSOR APPARATUS

FIELD OF THE INVENTION

The present invention relates to blood-flow sensors, in particular, to optical blood-flow sensors.

INTRODUCTION

Haemodynamic measurements using blood flow sensors can provide a large amount of information about the health of a subject, and allow the identification and characterisation of a wide range of medical conditions.

To be clinically useful, blood flow sensors should ideally provide reliable and accurate data, be non-invasive, relatively inexpensive and easy to use. The sensors should also allow reproducible data collection, i.e., repeat measurements for a patient in a given state (e.g., resting state) should be the same in the absence of a change in the state of the patient (e.g., absence of a change of positioning, or administration of a drug). A number of sensors are known for non-invasively measuring blood flow. However, these known sensors suffer from a number of drawbacks.

A widely used class of devices are oscillometric devices, which have an inflatable cuff which is placed around a patient's left arm and inflated gradually until the arteries within the arm are completely shut. During this operation, a pressure transducer is used to detect oscillations within the cuff caused by heart contractions and blood flowing through the arm.

Detection of these oscillations allows monitoring devices and physicians to identify systolic and diastolic blood pressure levels within the patient. However, such devices are not suitable for obtaining accurate haemodynamic and cardiovascular information, because the pressure within the cuff constantly varies during blood pressure measurements, and the pressure transducers which capture oscillations are situated distantly from the cuff. The poor reliability and reproducibility of data obtained by oscillometric devices means that multiple readings are commonly required for a diagnosis to be made.

It is also known to monitor blood pressure waveforms and blood flow velocity wavetorms using piezoelectric strips. However, the data obtained by such sensors is highly dependent on the location of the strips, meaning positioning of the sensor is crucial to obtaining reproducible data. This means that the strips must be applied by well-trained doctors over the arteries to obtain accurate results.

Ultrasound devices can also be used to extract blood flow and blood pressure waveform characteristics. Furthermore, they can visually display portions of the heart to diagnose heart irregularities and anomalies, and can display segments of an artery while providing blood flow and pulse wave signals. However, ultrasound devices are relatively expensive, and require technical training in order to obtain and display the correct information.

It is also known to use optical detection methods for monitoring blood flow. For example, photoplethysmographs measure blood flow by monitoring changes in light reflected by or transmitted through a body part (usually the finger) caused by blood flow. Traditionally, photoplethysmographs consist of a finger clip with a red light source and a photodetector mounted on an inner surface of the clip. Pulse oximeters are a commonly used type of photoplethysmograph which incorporate both a red light source and an infrared source, which allows the oxygenation level of the blood to be monitored by observing differences between the amount of red and infrared light absorbed by the blood.

However, there remains a need to develop sensors with improved sensitivity which are able to accurately, reliably and reproducibly measure blood flow characteristics.

Blood-flow data from photoplethysmographs are generally processed by differentiating the signal to give first and second derivatives of the signal, which medical professionals use to assess the condition of a subject. However, differentiation of the signal is relatively computationally expensive, as multiple derivative calculations have to be produced to extract accurate blood flow waveforms, and hence this method of signal processing is slow to carry out. In addition, differentiated blood pressure waveforms do not allow complete extraction of the true blood flow waveform. Therefore, there is also a need to develop apparatus and methods which simplify data processing of blood-flow data, and maximise the amount of data extracted from blood-flow data.

SUMMARY OF THE INVENTION

Accordingly, in a first aspect, the present invention provides blood-flow sensor apparatus, comprising a blood-flow sensor probe connected to signal processing apparatus, the blood-flow sensor comprising: a housing, for receiving a body part of a subject, the housing having a shaped surface which, in use, contacts the body part; a light source and a photodiode, mounted to the housing, for detecting blood flow in a body part received by the housing; wherein the shaped surface is shaped to conform, at least in part, to the shape of the body part.

The shaped surface is shaped so as to conform, at least in part, to the shape of the body part, in the absence of an applied force. By "conform" we mean that the shaped surface is shaped to fit/follow the shape (e.g., contours) of the body part. In other words, the shaped surface follows the anatomy of the body part. Thus, if the shaped surface contacts a body part with an angled surface, the shaped surface may have an angled shape to conform to the angled surface. Similarly, if the shaped surface contacts a curved body part, the shaped surface may have a curved shape to conform to the curvature of the body part. Suitably, the shaped surface is a continuous surface (i.e., it is not formed from distinct regions separated by gaps).

Advantageously, using a housing with a surface shaped to conform, at least in part, to the shape of the body part allows even pressure to be applied to the body part, minimising distortions in blood flow which would occur through uneven pressure application, and thus improving the accuracy and sensitivity of blood flow measurements. Having the shaped surface conform, at least in part, to the shape of the body part maximises the area of the body part in contact with the housing, thus spreading the force applied to the body part.

In some embodiments, the shaped surface has an angled shape. For example, the shaped surface may have a first section and a second section, with an angle between the first and second section. In this way, the shaped surface takes the form of an angled slope. The angle between the first section and second section may be smooth (i.e., rounded) or sharp (i.e., not rounded).

In some embodiments, the shaped surface has a curved shape. For example, the shaped surface may have a convex shape, such as a curved dip or recess (e.g., a "scooped" profile), to conform to the body.

In preferred embodiments, the housing is for receiving a digit, and the shaped surface is shaped to conform to the shape of the digit. Suitably, the digit is a finger or toe, preferably a human finger (thumb, index, middle, ring or little finger) or a human toe (hallux, long, third, fourth or fifth).

In such embodiments, it is preferred that the shaped surface is shaped to conform to the shape of the end of the digit. For example, the shaped surface may have an angled shape to conform to an angle at the tip of the digit. Additionally, or alternatively, the shaped surface may have a convex shape (e.g., a scooped profile) to conform to the contours of the underside of the tip of the digit.

In other preferred embodiments, the housing is for receiving a penis, and the shaped surface is shaped to receive the penis. In such embodiments, it is preferred that the shaped surface is shaped to closely conform to the shape of the end of the penis. For example, the shaped surface may have an angled shape to conform to an angle at the tip of the penis.

Additionally, or alternatively, the shaped surface may have a convex shape (e.g., a scooped profile) to conform to the contours of the underside of the tip of the penis.

Advantageously, a sensor probe for detecting blood flow through a penis can provide important information about the health of a male subject. For example, blood flow restrictions and stenosis within the pudendal artery can cause erectile dysfunction, and can be indicative of conditions such as diabetes. Currently, it is only possible to monitor and detect the blood pulse wave within the pudendal artery using expensive and complex ultrasound devices. This is in contrast to the relatively cheaper and easier to use probe of the present invention. Since the human penis is, on average, bigger than human digits, it is generally desirable to use a bigger sensor probe than that used for measurements of digits.

In other embodiments, the housing is for receiving a neck, and the shaped surface is shaped to receive the neck. In such embodiments, it is preferred that the shaped surface is shaped to closely conform to the shape around the carotid arteries of the subject.

The housing may be suitable for use with a wide range of animals, including mammals.

However, in preferred embodiments the housing is for receiving a body part of a human.

Suitably the housing is a clip. Preferably, the clip comprises a first member and a second member, connected by a hinge (i.e., the clip is a pair of hinged jaws).

In some embodiments, the first member has the shaped surface shaped to conform, at least in part, to the shape of the body part (e.g., the underside or topside of the tip of a digit or penis).

In some embodiments, the first and second members have shaped surfaces, shaped to conform, at least in part, to the shape of the body part.

Preferably, the first member and second member are resiliently biased together by biasing means, such as a spring. Advantageously, resiliently biasing the first and second members together facilitates easy attachment and removal from a body part of a subject. In addition, a resiliently biased clip allows the light source and/or photodiode to be brought into close contact with a body part, to maximise the sensitivity of the sensor probe.

Preferably, the housing is configured to apply a pressure of 8 kPa or less to the body part, in use. Advantageously, applying a pressure of 8 kPa or less in conjunction with the shaped surface increases the reliability and versatility of the sensor when taking measurements in humans, because the minimum blood pressure in the human body is, on average, 8 kPa (60 mmHg). If a higher pressure is applied the housing will potentially distort measurement values, introducing artefacts which could result in an incorrect diagnosis. For example, a higher pressure may eliminate the signal from certain waveforms which appear during diastole.

The housing optionally has a deformable pad (e.g., a foam pad), for cushioning a body pad received by the housing. Advantageously, including a deformable pad provides increased comfort to a subject, and helps to evenly distribute pressure on the body part received by the probe. In some embodiments, the deformable pad provides the shaped surface. In such embodiments, the shaped surface is present in the absence of an applied force (i.e., the shaped surface does not conform to the body pad solely due to forces applied by the body part).

The light source and photodetector are mounted to the clip to allow optical detection of blood flow, as in known photoplethysmographs. In some embodiments, the light source is mounted opposite to the photodiode so that, in use, the photodiode detects light which is transmitted through the body pad of the subject. In some embodiments, the light source is mounted adjacent to the photodiode such that, in use, the photodiode detects light from the light source which is reflected by the body pad of the subject.

In some embodiments, the blood-flow sensor probe has only one light source and one photodiode. Advantageously, using only one light source and one photodiode simplifies construction of the probe.

Preferably, the light source is a red light source. Advantageously, blood absorbs red light, and therefore allows the blood-flow sensor probe to have good sensitivity. Preferably, the light source is a light-emitting diode (LED). Most preferably, the light source is a red LED.

In some embodiments, the blood-flow sensor apparatus comprises a second blood-flow sensor probe (the blood-flow sensor probe being as defined above), connected to the signal processing apparatus. Advantageously, this embodiment allows the blood-flow sensor probes to be placed on different body parts, which allows a comparison of the blood flow through those body parts. This allows the location of a circulation problem in a subject's body to be identified. For example, when a first probe is applied to a finger on the left hand and a second probe is applied to a finger on the right hand, the difference between the signal from the fingers can be used to distinguish between arterial blockages in the left and right side of the body (e.g., the left and right arm). Advantageously, such apparatus may allow both the type and the location of a circulation problem in a subject's body to be identified.

In some embodiments, the blood-tlow sensor apparatus further comprises an electrocardiograph (EGG) machine connected to the signal processing apparatus.

Advantageously, an ECG machine provides information which is complementary to that obtained by the blood-flow sensor probe. For example, the ECG signal can be used as a reference signal by clinicians to compare against the signal from the blood-flow sensor apparatus, e.g., such apparatus allows the study of time differences between an electro-cardiovascular signal (e.g.. the start of a heartbeat) and blood flow in a particular body part of a subject (e.g., the start of a pulse of blood through the body part).

The signal processing apparatus may comprise one or more of the following elements: amplifying means, for amplifying the signal from the blood-flow sensor probe; noise-filtering means, for reducing noise in the signal from the blood-flow sensor probe; converting means, for converting an analogue signal from the blood-flow sensor probe into a digital signal.

The amplifying means, noise-filtering means and/or converting means may be separate hardware, or may be computer software.

In one embodiment, the noise-filtering means is a bandpass filter which passes signals between 0.1 to 40 Hz.

Preferably, the blood-flow sensor apparatus further comprises a display, for displaying data from the signal processing apparatus.

The signal processing apparatus preferably comprises a computer. In preferred embodiments, the computer is programmed with software to apply a finite impulse response (FIR) filter to data obtained by the blood-flow sensor probe.

Advantageously, using a FIR filter to filter blood-flow data allows the extraction of large amounts of information.

To be processed using a FIR filter, the blood-flow data should be a digital signal. Therefore, in embodiments in which the blood-flow data is initially an analogue signal, the apparatus includes converting means, for converting the analogue signal from the blood-flow sensor probe into a digital signal.

Suitably, the finite impulse response (FIR) filter is a bandpass filter. Suitably, the FIR filter is a windowed linear phase FIR digital filter. Preferably, the FIR filter is a Hamming-window based, linear-phase FIR digital filter.

The filter coefficients of the FIR filter are calculated based on cutoff frequencies for the filter, using methods well-known in the art. The cutoff frequencies used to calculate the filter coefficients are calculated as follows: = A -Nth (Equation 1)

N

= A2 + tabs (Equation 2) with NbS (Equation 3) where f3 is the sampling frequency in Hz (i.e., the number of data points per second). NbS is the number of tabs (sometimes referred to as "taps") used in the FIR filter. The computer program may include pre-programmed filter coefficients based on the above equations.

Advantageously, the above equations allow the fidelity of the blood-flow signal to be retained. In addition, the equations allow the signal processing to work over a wide range of sampling frequencies, because Ntabs adjusts according to the sampling frequency.

Preferably, X = 2.5 to 3, most preferably 2.8.

In one embodiment, the following values are used in Equations ito 3: A1 = 0 to 15; B1 = 35 to 45; A2 = 5 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000.

In one preferred embodiment, the following values are used in Equations 1 to 3: A1 = 5 to 15; B1 = 35 to 45; A2 = 10 to 25; B2 = 35 to 45; X = 2.5 to 3.5; and f5 = 100 to 1000.

Advantageously, this choice of cutoff frequencies allows extraction of information about the opening and closing of the aortic valve, and ventricular contractions.

In this embodiment, it is preferred that A1 = 10; A2 = 22; and B1 = B2 = 38.8, because these values allow extraction of particularly useful information about the opening and closing of the aortic valve, and ventricular contractions.

In another preferred embodiment, the following values are used in Equations 1 to 3: A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000.

Advantageously, this choice of cutoff frequencies allows extraction of information about pulse waves flowing from the heart through the arteries.

In this embodiment, it is preferred that A1 = 3; A2 = 30; and B1 = B2 = 38.8, because these values allow extraction of particularly useful information about pulse waves flowing from the heart through the arteries.

In some embodiments, the signal processing apparatus includes a computer program programmed to filter blood-flow data using two or more different FIR filters (the filters both being applied to the same raw data). For example, in preferred embodiments, the computer program is programmed to: filter the blood-flow data using a first finite impulse response filter; and separately filter the blood-flow data using a second finite impulse response filter; wherein the first finite impulse response filter has A1 = 5 to 15; B1 = 35 to 45; A2 = 10 to 25; B2 = 35 to 45; X = 2.5 to 3.5; and f3 = 100 to 1000; and the second finite impulse response filter has A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and L = 100 to 1000.

Advantageously, processing the blood4low data using two or more FIR filters (in particular, the two specific filters given above) allows a large amount of information to be extracted from the blood-flow data.

In a second aspect, the present invention provides a blood-flow sensor probe, comprising: a housing, for receiving a body part of a subject, the housing having a shaped surface which, in use, contacts the body pad; a light source and a photodiode, mounted to the housing, for detecting blood flow in a body part received by the housing; wherein the shaped surface is shaped to conform, at least in part, to the shape of the body part.

The blood-flow sensor probe may have any of the preferred and optional features mentioned for the blood-flow sensor probe of the first aspect.

In a third aspect, the present invention provides a blood-flow sensor probe, comprising: a housing, for receiving a body part of a subject; a light source and a phototiode, mounted to the housing, for detecting blood flow in a body part received by the housing; wherein the housing is configured to apply a pressure of B kPa or less to the body part.

The blood-flow sensor probe may have any of the preferred and optional features mentioned for the blood-flow sensor probe of the first aspect.

Advantageously, applying a pressure of B kPa or less increases the reliability and versatility of the sensor when taking measurements in humans, because the minimum blood pressure in the human body is, on average, B kPa (60 mmHg). If a higher pressure is applied the clip will potentially distort measurement values, which could result in an incorrect diagnosis. For example, a higher pressure may eliminate the signal from certain waveforms which appear during diastole.

In a fourth aspect, the present invention provides blood-flow sensor apparatus comprising a blood-flow sensor probe of the third aspect connected to a signal processing apparatus.

In a fifth aspect, the present invention provides blood-flow sensor apparatus comprising two blood-flow sensor probes connected to a signal processing apparatus. Advantageously, this embodiment allows the blood-flow sensor probes to be placed on different body parts, which allows a comparison of the blood flow through those different body parts (as discussed above).

In a sixth aspect of the present invention, the present invention provides blood-flow sensor apparatus, comprising a blood-flow sensor probe and an electrocardiograph (ECG) machine connected to signal processing apparatus. Advantageously, an ECG machine provides information which is complementary to that obtained by the blood-flow sensor probe. For example, the ECG signal can be used as a reference signal by clinicians to compare against the signal from the blood4low sensor apparatus, e.g., such apparatus allows the study of time differences between an electro-cardiovascular signal (e.g., the start of a heartbeat) and blood flow in a particular body part of a subject (e.g., the start of a pulse of blood through the body part).

Suitably, in the fifth and sixth aspects the blood-flow sensor probe is a photoplethysmograph, such as a pulse oximeter. In preferred embodiments, the blood-flow sensor probe is according to the second or third aspect of the present invention.

In a seventh aspect, the present invention provides a method of processing blood-flow data, comprising filtering blood-flow data using a finite impulse response filter. The FIR filter is as described for the first aspect. Advantageously, using a FIR filter to filter blood-flow data allows the extraction of large amounts of information.

In an eighth aspect, the present invention provides a method of monitoring blood flow in a subject, comprising: obtaining blood-flow data using blood-flow sensor apparatus; and processing the blood-flow data according to the seventh aspect of the present invention.

Suitably, in this eighth aspect the blood-flow sensor apparatus is a photoplethysmograph, such as a pulse oximeter. In preferred embodiments, the blood-flow sensor apparatus is according to the first aspect of the present invention. Advantageously, obtaining blood-flow data using the apparatus of the first aspect of the present invention and processing that data using the method of the seventh aspect allows extremely sensitive detection, and extraction of large amounts of information from the blood-flow data. In some embodiments of this eighth aspect, monitoring blood flow involves monitoring the opening and/or closing of one or more valves of the heart (e.g., opening and/or closing of the aortic valve).

In a ninth aspect, the present invention provides a method of detecting a condition in a subject, comprising: obtaining blood-flow data using blood-flow sensor apparatus; processing the blood-flow data according to the seventh aspect of the present invention, to produce filtered data; and studying the filtered data for markers of the condition.

In certain embodiments, the step of studying the filtered data involves comparing the filtered data with reference data, and the markers of the condition correspond to differences between the filtered data and reference data.

In this ninth aspect, the blood-flow sensor apparatus is preferably a photoplethysmograph, such as a pulse oximeter. In preferred embodiments, the blood-flow sensor apparatus is according to the first aspect of the present invention. Advantageously, obtaining blood-flow data using the apparatus of the first aspect of the present invention and processing that data using the method of the seventh aspect allows extremely sensitive detection, and extraction of large amounts of information from the blood-flow data.

In some embodiments, the condition is a disease (e.g., cardiovascular disease) or infection.

In one embodiment, the condition is selected from arterial stiffness, stenosis, reduction in blood flow (for example, due to swollen infections), cardiac dysrhythmia (sometimes known as irregular heartbeat or arrhythmia), heartbeat variation during bradypnea, heartbeat variation due to chemicals (e.g., adrenaline, noradrenaline, tobacco), heartbeat variations due to exercise, pacemaker activation/deactivation.

In a tenth aspect, the present invention provides a method of treating a medical condition in a subject, comprising: detecting a medical condition in a subject according to the ninth aspect of the present invention; and treating the subject for the medical condition, based on that diagnosis.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a side section of a conventional prior art blood-flow sensor probe.

Figure 2 is a side section of a blood-flow sensor probe of the present invention.

Figure 3 is a schematic view of blood4low sensor apparatus of the present invention.

Figure 4 is a schematic view of blood-flow sensor apparatus of the present invention.

Figure 5 shows five different readings (a)-(e) obtained from the same patient using the blood-flow sensor apparatus of the present invention. Data has been processed with FIR filters according to the seventh aspect of the present invention, with "1" and "2" indicating use of the parameters defined for "Filter 2" and "Filter 1" below, respectively.

Figure 6 shows blood-flow data obtained using blood-flow sensor apparatus of the present invention, processed with FIR filters according to the seventh aspect of the present invention using the parameters defined for "Filter 1".

Figure 7 shows blood-flow data obtained using blood-flow sensor apparatus of the present invention, processed according to the seventh aspect of the present invention using the parameters for "Filter 2". The figure has been labelled to indicate signal attributable to (1) opening of the aortic valve, (2) ventricular contraction, (3) closure of the aortic valve, and (4) a reflective wave.

Figure 8 shows the first derivative of the data in Figure 6.

Figure 9 shows the second derivative of the data in Figure 6.

Figure 10 shows blood-flow data obtained using blood-flow sensor apparatus of the present invention for subjects with flexible arteries ((a) and (b)) and relatively stiffer arteries ((c) and (d)). The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1".

Figure 11 shows blood-flow data obtained using blood-flow sensor apparatus of the present invention from the left foot (a) and right foot (b) of a patient suffering from stenosis. Data has been processed according to the seventh aspect of the present invention, with "1" and "2" indicating use of the parameters defined for "Filter 1" and "Filter 2" below, respectively.

Figure 12 shows blood-flow data obtained using blood-flow sensor apparatus of the present invention from the left foot (a) and right foot (b) of a patient having a cellulitis infection in the left ankle. The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 2".

Figure 13 shows blood4low data from a patient with coronaropathy obtained using blood-flow sensor apparatus of the present invention. The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1" (Figure 13a) and "Filter 2" (Figure 13b).

Figure 14 shows blood-flow data from a patient with atrial fibrillation obtained using blood-flow sensor apparatus of the present invention. The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1" (Figure 14a) and "Filter 2" (Figure 14b).

Figure 15 shows blood-flow data from a patient with ventricular premature beats obtained using blood-flow sensor apparatus of the present invention. The data has been processed according to the seventh aspect of the present invention using the parameters defined for Filter 1" (Figure 15a) and "Filter 2" (Figure 15b).

Figures 16 and 17 show blood-flow data from a subject during spells of normal breathing and bradypnea breathing obtained using blood-flow sensor apparatus of the present invention.

The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1".

Figure 18 shows blood-flow data from a patient (a) before smoking tobacco, (b)whilst smoking tobacco and (c) five minutes after smoking tobacco, obtained using blood-flow sensor apparatus of the present invention. Data has been processed according to the seventh aspect of the present invention, with "1" and "2" indicating use of the parameters defined for "Filter 1" and "Filter 2" below, respectively.

Figure 19 shows blood-flow data from a patient fitted with a pacemaker, obtained using blood-flow sensor apparatus of the present invention. The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1".

Figure 20 shows zoomed data from Figure 19 during (a) a period when the patient's pacemaker is activated and (b) a period when the patient's pacemaker is deactivated.

Figure 21 shows the first derivative of blood4low data from a patient fitted with a pacemaker, obtained using blood-flow sensor apparatus of the present invention.

Figure 22 shows the second derivative of blood-flow data from a patient fitted with a pacemaker, obtained using blood4low sensor apparatus of the present invention.

Figure 23 shows blood-flow data from the pudendal artery of a healthy subject, obtained using blood-flow sensor apparatus of the present invention. The data has been processed according to the seventh aspect of the present invention using the parameters defined for "Filter 1".

Figure 24 shows blood-flow data obtained when the blood-flow sensor probe applies a pressure of: (a) 8 kPa to the body pad; (b) less than 8 kPa to the body pad; and (c) more than 8 kPa to the body part. Data has been processed according to the seventh aspect of the present invention, with "1" and "2" indicating use of the parameters defined for "Filter 1" and "Filter 2" below, respectively.

DETAILED DESCRIPTION

Figure 1(a) shows a prior art blood-flow sensor probe 1. The blood-flow sensor probe 1 includes a clip, formed from an upper jaw 2 and lower jaw 3 attached at a hinge 4 and biased towards one another by a spring. The lower jaw 3 includes a photodiode Sand red LED 6, which are configured so that, in use, a portion of the light emitted by the red LED 6 is reflected onto the photodiode 5 by a body part held between the jaws. Changes in the intensity of light detected by the photodiode are related to the volume of blood passing through the body part, which allows measurement of blood flow through the body part.

The upper jaw 2 and lower jaw 3 include flat surfaces which, in use, contact a subject's finger, as shown in Figure 1(b). The surfaces are not shaped to conform to the subject's finger, which means that uneven pressure is applied to the finger, resulting in interference with the blood flow.

Figure 2(a) shows a blood-flow sensor probe 11 according to the present invention. The probe 11 includes the same components as the prior art probe 1, but in this case the lower jaw has an angled surface formed from first section 12 and second section 13. The second section 13 is also slightly concave to adapt to the subject's finger. In addition, the upper member includes a foam pad 14. As shown in Figure 2(b), the angled surface of the lower jaw conforms to the tip of a subject's finger so as to more evenly distribute the pressure applied by the clip.

Figure 3 shows blood-flow sensor apparatus according to the present invention. In this embodiment, the analogue signal obtained by blood-flow sensor probe 11 is passed to an analogue band pass filter (0.1-40 Hz)to reduce noise in the signal, and is subsequently amplified by an analogue amplifier. The amplified signal is then digitised using a microcontroller unit, to give data with a sampling frequency of between 100 to 1000 Hz. The digitised signal is passed to a computer where it is processed using two bandpass FIR filters according to the seventh aspect of the present invention, with the resulting filtered signals being displayed on the computer screen.

Figure 4 schematically shows blood-flow sensor apparatus of the present invention. In the embodiment shown in (a), the apparatus comprises a first blood-flow sensor probe 21 and a second blood-flow sensor probe 22, the probes being according to the second aspect of the present invention, with shaped surfaces which conform to the finger of subject 23. The apparatus also includes ECG probes 24. The blood-flow sensor probes and ECG probes are connected to signal processing apparatus 25, which displays results on display screen 26. The embodiment shown in (b) is analogous to that in the embodiment shown in (a), except the blood-flow sensor probes 27 and 28 have shaped surfaces which conform to the big toe (hallux) of subject 23. The embodiment shown in (c) is analogous to that shown in embodiment (a), but only a single blood-flow sensor probe 29 is used, having a shaped surface shaped to conform to the penis of subject 23.

Exoerimental Data The performance of the blood-flow sensor probes, apparatus, and signal processing techniques of the present invention were assessed experimentally.

Blood-flow sensor apparatus was constructed using a blood4low sensor probe connected to signal processing apparatus. The blood-flow sensor probe incorporated a sprung-loaded clip as shown in Figure 2, having an angled, concave surface on the lower jaw and a foam pad on the upper jaw. The blood-flow sensor probe was connected to signal processing apparatus, having an analogue filter, analogue amplifier and microcontroller MCU, which subsequently fed data to an oscilloscope, as shown in Figure 3. The blood-flow sensor probe was applied to the body pad of a subject so that the clip applied a pressure of 8 kPa, and data were recorded at a sampling frequency of 100 Hz.

Unless indicated otherwise, data were processed according to the seventh aspect of the present invention. Specifically, data were processed using an Hamming-window based, linear-phase FIR bandpass filter with Ntabs = 35, and filter coefficients calculated using the following cutoff frequencies: Filter 1 -1 and 35 Hz; Filter 2-10 and 25Hz; Reliability and recroducibility To demonstrate the reliability and reproducibility of signals obtained using the apparatus and signal processing methods of the present invention, five separate readings were taken for the same patient using the blood-flow sensor probe, with the probe being removed and re-attached between readings. As shown in Figure 5(a)-(e), the amplitudes of the waveforms for each reading are approximately the same, despite the removal and re-attachment of the probe, indicating that the apparatus and signal processing methods of the present invention produce reliable and reproducible signals.

Sensitivity To demonstrate the improved sensitivity achievable using signal processing methods of the present invention, the method was compared with conventional signal processing methods.

Raw blood-flow data from a healthy subject was obtained using the blood-flow sensor apparatus of the present invention, with the blood-flow sensor probe attached to the left-hand thumb of the subject.

Figures 6 and 7 show the signal from the patient after the raw blood-flow data is processed according to the present invention. Figure 7 shows that the processing method of the present invention allows clear identification of different phases of the blood flow, including (1) opening of the aortic valve, (2) ventricular contraction, (3) closure of the aortic valve, and (4) a reflective wave.

Known methods for processing ultrasound and photoplethysmographs data extract information using algorithms which are relatively complex compared to the FIR filtering methods of the present invention. For example, conventional methods for processing data from photoplethysmographs involve taking first and second derivatives of the blood-flow data, as shown in Figures 8 and 9 (which were obtained by differentiating the waveform shown in Figure 6). In Figures 8 and 9, ventricular contractions, closure of the aortic valve and the reflective wave are visible, but there is no evidence of the waveform which represents the opening of the aortic valve ("l"in Figure 7). Further information could be obtained with this methodology by taking further derivatives, but the signal would then deteriorate to a point where additional digital filters are necessary to display the signals of interest; meaning that a large amount of additional signal processing would be required.

Thus, the signal processing method of the present invention allows the identification of haemodynamic waves which are not detectable with conventional signal processing methods. Furthermore, the apparatus of the present invention is sufficiently sensitive to accurately detect different phases of a blood pulse wave.

Monitoring the state of the arteries The blood-flow sensor apparatus of the present invention can very accurately capture signal corresponding to pulse waves originating from head ventricular contractions. This high sensitivity allows precise monitoring of the state of the arteries, for example, monitoring of the flexibility/stiffness of the arteries. This is demonstrated in Figure 10, which shows data from four different patients. The data for Patients 1 and 2 are indicative of healthy flexible arteries. In contrast, the data for Patients 3 and 4 are indicative of stiffer arteries.

Monitoring artery blockage and stenosis The high reliability and sensitivity of the apparatus and methods of the present invention allow the detection of blockage and stenosis within arteries. To demonstrate this, readings were taken from the hallux of the left and right foot of a middle-aged patient with stenosis along his left leg. As shown in Figure 11, the signal from the left foot (a) is dramatically reduced compared to the signal from the right foot (b), due to stenosis in the left leg [N.B. the axes in (a) and (b) have the same scale]. In particular, when the blood-flow data is processed using Filter 2 (shown in Figure 11(a2) and (b2)) a large difference in blood flowing through the right and the left leg is clearly detectable, allowing the doctor to diagnose a stenosis within the left lower limb.

Monitoring reduction of blood flow due to infection The high reliability and sensitivity of the apparatus and methods of the present invention allow the detection of blood flow variations arising from infection. To demonstrate this, readings from both the left foot and right foot of a patient having a cellulitis infection just above her left ankle were taken. As shown in Figure 12, the signal from the left foot (Figure 12(a)) has a reduced amplitude compared to the signal from the right foot (Figure 12(b)), due to a reduction in blood flow by the swollen infection.

Monitoring heart beat anomalies and aortic valve anomalies The apparatus and methods of the present invention allow the detection of heartbeat anomalies (cardiac dysrhythmias, or arrhythmias), along with irregular aortic valve movements. To demonstrate this, three subjects having different heart conditions were monitored according to the present invention: specifically, a subject with coronaropathy (data shown in Figure 13), a subject with atrial fibrillation (data shown in Figure 14), and a subject with ventricular premature beats (sometimes referred to as premature ventricular contraction -data shown in Figure 15).

Figures 13 to 15 show data captured for the three different conditions during heart beat anomaly events. Figures 13(a), 14(a) and 15(a) show the cardio pulse wave captured by the sensor [data processed according to FIR Filter 1]; while Figures 13(b), 14(b) and 15(b) show the extracted waveforms, showing opening of the aortic valve, ventricular contraction, closure of the aortic valve and the reflective wave within the arteries [data processed according to FIR Filter 2].

These data show that the sensor can easily detect heart beat variations through monitoring changes in the pulse wave, such as changes in the part of the pulse wave attributable to opening of the aortic valve, ventricular contraction, closure of the aortic valve and reflective waves. For example, Figures 13 to 15 show that the device is able to detect abnormal opening of the aortic, and detect instances where the amplitude and rate of ventricular contractions is abnormal.

Monitoring effects of bradygnea The apparatus and methods of the present invention allow the effects of breathing variation on the cardio pulse wave to be monitored. Consequently, it is possible to detect and observe variations in heart contractions due to bradypnea (abnormally slow breathing), which arise due to reduced oxygen absorption.

A healthy subject was picked and asked to slow his breathing in order to achieve bradypnea.

Figure 16 shows a continuous reading where the subject breathed naturally (Figure 16(a)), slowed their breathing to achieve bradypnea (Figure 16(b)), and then returned to breathing naturally (Figure 16(c)). The data in Figure 16 show that the apparatus and methods of the present invention accurately captures differences between normal breathing activity and bradypnea.

Figure 17 (a-c) shows in greater detail how the cardio pulse wave varies during normal and bradypnea activity, and demonstrate again that the apparatus and methods of the present invention allow doctors/physicians to monitor and observe different phenomena and variations in the haemodynamics of the subject/patient.

Monitoring effects of tobacco Smoking can have a large influence on blood flow through causing deterioration of the heart and arteries. To demonstrate that the accuracy and sensitivity of the apparatus and methods of the present invention allows the effects of tobacco on the state of the heart and arteries to be monitored, readings were taken on a healthy subject (a) before smoking tobacco, (b) whilst smoking tobacco and (c) five minutes after smoking tobacco. Figure 18 shows that the signal varies due to the absorption of tobacco. In particular, Figures 18 (a2), (b2) and (c2) show changes in the signal corresponding to opening/closure of the aortic valve, ventricular contraction, and reflective wave.

Monitoring activation/de-activation of an internal ijacemaker The apparatus and methods of the present invention also allow the effects of internal pacemakers on the cardio pulse wave to be monitored. To demonstrate this, studies were carried out on a patient suffering from several heart conditions (coronaropathy, ischemic heart disease and left-sided head failure) who had been fitted with a wirelessly activated pacemaker to keep their heartbeat regular. Data were recorded using the apparatus of the present invention, with the blood-flow sensor probe applied to the left thumb of the patient.

As shown in Figure 19, the apparatus and methods of the present invention were able to detect differences in signal when the pacemaker was activated compared to when the pacemaker was de-activated. In particular, the differences in amplitude of the signal show that the pacemaker allows the heart to pump blood more effectively, allowing a slightly higher volume of blood flowing through the arteries.

Figure 20(a) and (b) show zoomed-in regions of Figure 19 corresponding to periods when the pacemaker is activated and deactivated respectively. These figures show in greater detail the haemodynamics and head movements related to the activation and deactivation of the pacemaker. Indeed, during pacemaker activation, it is possible to observe the presence of the dicrotic waves in the signal (indicated by arrows in Figure 20(a)); while such waves do not appear when the pacemaker is deactivated.

To compare the performance of the signal processing method of the present invention with conventional signal processing methods, first and second derivatives of the blood-flow data were taken and compared to the signal in Figures 20(a) and (b). Figure 21 and 22 show the first and second derivatives of the blood-flow data where the pacemaker was activated and then deactivated. These figures show that differences in amplitude are detected, but the shape of the waveforms does not vary significantly. This demonstrates again that the level of accuracy and sensitivity of the apparatus and signal processing methods of the present invention are greater than the conventional technologies and mathematical algorithms.

Monitoring the pudendal artery The apparatus and methods of the present invention are sufficiently sensitive to allow blood flow through the pudendal artery (the artery which branches off the iliac artery and provides blood to the penis) to be monitored. This is demonstrated in Figure 23, which shows an example of a pudendal artery pulse wave captured in a healthy subject.

Monitoring the effect of pressure applied by the blood-flow sensor probe To demonstrate that the pressure applied by a blood-flow sensor probe can impact the signal obtained by that probe, data were obtained from the same body part at different applied pressures.

Figure 24(a) shows that the different features of the blood-flow waveform discussed above are clearly visible at 8 kPa applied pressure. Figure 24(b) shows that at low pressure (below 8 kPa) the waveforms have a number of additional features, which can be attributed to noise. Figure 24(c) shows that at high pressure (above 8 kPa) some of the features present in the waveforms of Figures 24(a) and (b) are suppressed (particularly those obtained using Filter 2), introducing artefacts into the data and limiting the amount of information that can be obtained.

The skilled person will appreciate that the probes, apparatus and methods illustrated in the figures and described above are examples embodying inventive concepts described herein and that many and various modifications can be made without departing from the invention.

Claims (52)

  1. CLAIMS1. Blood-flow sensor apparatus, comprising a blood-flow sensor probe connected to signal processing apparatus, the blood-flow sensor comprising: a housing, for receiving a body pad of a subject, the housing having a shaped surface which, in use, contacts the body pad; a light source and a photodiode, mounted to the housing, for detecting blood flow in a body pad received by the housing; wherein the shaped surface is shaped to conform, at least in part, to the shape of the body pad.
  2. 2. Blood-flow sensor apparatus according to claim 1, wherein the shaped surface has an angled shape.
  3. 3. Blood-flow sensor apparatus according to claim 1 or 2, wherein the shaped surface has a curved shape.
  4. 4. Blood-flow sensor apparatus according to claim 3, wherein the curved shape is a curved dip.
  5. 5. Blood-flow sensor apparatus according to any one of claims 1 to 4, wherein the housing is for receiving a digit, and the shaped surface is shaped to conform to the shape of the digit.
  6. 6. Blood-flow sensor apparatus according to any one of claims 1 to 4, wherein the housing is for receiving a penis, and the shaped surface is shaped to conform to the shape of the penis.
  7. 7. Blood-flow sensor apparatus according to any one of claims 1 to 4, wherein the housing is for receiving a neck, and the shaped surface is shaped to conform to the shape of the neck.
  8. 8. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the housing is for receiving a body part of a human.
  9. 9. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the housing is a clip.
  10. 10. Blood-flow sensor apparatus according to claim 9, wherein the clip comprises a first member and a second member, connected by a hinge.
  11. 11. Blood-flow sensor apparatus according to claim 10, wherein the first member has the shaped surface.
  12. 12. Blood-flow sensor apparatus according to claim 11, wherein the second member also has a shaped surface, shaped to conform, at least in part, to the shape of the body part.
  13. 13. Blood-flow sensor apparatus according to any one of claims 10 to 12, wherein the first member and second member are resiliently biased together by biasing means.
  14. 14. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the housing is configured to apply a pressure of 8 kPa or less to the body part, in use.
  15. 15. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the housing has a deformable pad, for cushioning a body part received by the housing.
  16. 16. Blood-flow sensor apparatus according to any one of the preceding claims, comprising a second blood-flow sensor probe, connected to the signal processing apparatus.
  17. 17. Blood-flow sensor apparatus according to any one of the preceding claims, comprising an electrocardiograph machine connected to the signal processing apparatus.
  18. 18. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the signal processing apparatus comprises one or more of the following elements: amplifying means, for amplifying the signal from the blood-flow sensor probe; noise-filtering means, for reducing noise in the signal from the blood-flow sensor probe; converting means, for converting an analogue signal from the blood-flow sensor probe into a digital signal.
  19. 19. Blood-flow sensor apparatus according to any one of the preceding claims, wherein the signal processing apparatus comprises a computer.
  20. 20. Blood-flow sensor apparatus according to claim 19, wherein the computer is programmed with software to apply a finite impulse response filter to data obtained by the blood-flow sensor probe.
  21. 21. Blood-flow sensor apparatus according to claim 20, wherein the finite impulse response filter is a bandpass filter.
  22. 22. Blood-flow sensor apparatus according to claim 21, wherein the cutoff frequencies for the bandpass filter are calculated according to the following equations: = A1 -(Equation 1) tabs 2 = 2 + (Equation 2) Li2 with Ntabs = L_ (Equation 3) where A1 = 0 to 15; B1 = 35 to 45; A2 = 5 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f is the sampling frequency of the apparatus.
  23. 23. Blood-flow sensor apparatus according to claim 22, wherein A1 = 5 to 15; B1 = 35 to 45;A2= 10to25; B2= 35to45; X=2.5to3.5; andf3= lOOto 1000.
  24. 24. Blood-flow sensor apparatus according to claim 23, wherein A1 = 10; A2 = 22; and B1 = B2 = 38.8.
  25. 25. Blood-flow sensor apparatus according to claim 22, wherein A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000.
  26. 26. Blood-flow sensor apparatus according to claim 25, wherein A1 = 3; A2 = 30; and B1 = B2 = 38.8.
  27. 27. Blood-flow sensor apparatus according to claim 22, wherein the computer program is programmed to: filter the blood-flow data using a first finite impulse response filter; and separately filter the blood-flow data using a second finite impulse response filter; wherein the first finite impulse response filter has A1 = 5 to 15; B1 = 35 to 45; A2 = 10 to 25; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000; and the second finite impulse response filter has A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and t3 = 100 to 1000.
  28. 28. A blood-flow sensor probe, comprising: a housing, for receiving a body part of a subject, the housing having a shaped surface which, in use, contacts the body part; a light source and a photodiode, mounted to the housing, for detecting blood flow in a body part received by the housing; wherein the shaped surface is shaped to conform, at least in part, to the shape of the body part.
  29. 29. A blood-flow sensor probe, comprising: a housing, for receiving a body part of a subject; a light source and a photodiode, mounted to the housing, for detecting blood flow in a body part received by the housing; wherein the housing is configured to apply a pressure of 8 kPa or less to the body part.
  30. 30. Blood-flow sensor apparatus comprising a blood-flow sensor probe of claim 29 connected to a signal processing apparatus.
  31. 31. Blood-flow sensor apparatus comprising two blood-flow sensor probes connected to a signal processing apparatus.
  32. 32. Blood-flow sensor apparatus comprising a blood-flow sensor probe and an electrocardiograph machine.
  33. 33. A method of processing blood-flow data, comprising filtering blood-flow data using a finite impulse response filter.
  34. 34. A method of processing blood-flow data according to claim 33, wherein the finite impulse response filter is a bandpass filter.
  35. 35. A method of processing blood-flow data according to claim 34, wherein the cutoff frequencies are calculated according to the following equations: = A1 -(Equation 1)N= A2 + (Equation 2) with = -(Equation 3) where A1 = 0 to 15; B1 = 35 to 45; A2 = 5 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f3 is the sampling frequency of the apparatus.
  36. 36. A method of processing blood-flow data according to claim 35, wherein A1 = 5 to 15; B1 = 35 to 45; A2 = 10 to 25; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000.
  37. 37. A method of processing blood-flow data according to claim 36. wherein A1 = 10; A2 = 22; and B1 = B2 = 38.8.
  38. 38. A method of processing blood-flow data according to claim 35, wherein A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f3 = 100 to 1000.
  39. 39. A method of processing blood-flow data according to claim 38, wherein A1 = 3; A2 = 30; and B1 = B2 = 38.8.
  40. 40. A method of processing blood-flow data according to claim 35, comprising filtering the blood-flow data using a first finite impulse response filter; and separately filtering the blood-flow data using a second finite impulse response filter; wherein the first finite impulse response filter has A1 = S to 15; B1 = 35 to 45; A2 = 10 to 25; B2 = 35 to 45; X = 2.5 to 3.5; and f = 100 to 1000; and the second finite impulse response filter has A1 = 0 to 6; B1 = 35 to 45; A2 = 25 to 35; B2 = 35 to 45; X = 2.5 to 3.5; and f8 = 100 to 1000.
  41. 41. A method of monitoring blood flow in a subject, comprising: obtaining blood-flow data using blood-flow sensor apparatus; and processing the blood-flow data according to any one of claims 33 to 40.
  42. 42. A method of monitoring blood flow in a subject according to claim 41, wherein the blood-flow sensor apparatus is according to any one of claims 1 to 27 or 30 to 32.
  43. 43. A method of detecting a condition in a subject, comprising: obtaining blood-flow data using blood-flow sensor apparatus; processing the blood-flow data according to any one of claims 33 to 40; and studying the filtered data for markers of the condition.
  44. 44. A method of detecting a condition in a subject according to claim 43, wherein the blood-flow sensor apparatus is according to any one of claims 1 to 27 or 30 to 32.
  45. 45. A method of detecting a condition in a subject according to claim 43 or 44, wherein the step of studying the filtered data involves comparing the filtered data with reference data, and the markers of the condition correspond to differences between the filtered data and reference data.
  46. 46. A method of detecting a condition in a subject according to any one of claims 43 to 45, wherein the condition is a disease or infection.
  47. 47. A method of treating a medical condition in a subject, comprising: detecting a medical condition in a subject according to any one of claims 43 to 46; and treating the subject for the medical condition, based on that diagnosis.
  48. 48. Blood-flow sensor apparatus substantially as described herein with reference to Figures 2 to 4.
  49. 49. A blood-flow sensor probe substantially as described herein with reference to Figures 2 to 4.
  50. 50. A method of processing blood-flow data, substantially as described herein with reference to Figures 2 to 24.
  51. 51. A method of monitoring blood flow in a subject, substantially as described herein with reference to Figures 2 to 24.
  52. 52. A method of detecting a condition in a subject, substantially as described herein with reference to Figures 2 to 24.
GB1320419.3A 2013-11-19 2013-11-19 Blood-flow sensor apparatus Withdrawn GB2520487A (en)

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