U.S. patent application number 13/875500 was filed with the patent office on 2013-09-19 for assessing a subject's circulatory system.
This patent application is currently assigned to Dialog Devices Limited. The applicant listed for this patent is DIALOG DEVICES LIMITED. Invention is credited to Jody Brown, Vincent Crabtree.
Application Number | 20130245394 13/875500 |
Document ID | / |
Family ID | 40194739 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130245394 |
Kind Code |
A1 |
Brown; Jody ; et
al. |
September 19, 2013 |
Assessing a Subject's Circulatory System
Abstract
An apparatus comprising: an input interface configured to
provide signals from at least two sensors for at least two postures
including: signals, dependent upon blood presence, from a first
sensor when a subject is in a first posture; signals, dependent
upon blood presence, from the first sensor when the subject is in a
second posture; signals, dependent upon blood presence, from a
second sensor when the subject is in the first posture; and
signals, dependent upon blood presence. from the second sensor when
the subject is in the second posture; and processing circuitry
configured to determine and output a metric by combining, according
to pre-defined calibration data the provided signals.
Inventors: |
Brown; Jody; (Berkshire,
GB) ; Crabtree; Vincent; (Leicestershire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DIALOG DEVICES LIMITED |
Loughborrough Leicestershire |
|
GB |
|
|
Assignee: |
Dialog Devices Limited
Loughborrough Leicestershire
GB
|
Family ID: |
40194739 |
Appl. No.: |
13/875500 |
Filed: |
May 2, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12590930 |
Nov 17, 2009 |
8491486 |
|
|
13875500 |
|
|
|
|
Current U.S.
Class: |
600/301 |
Current CPC
Class: |
A61B 5/0261 20130101;
A61B 5/0295 20130101; A61B 5/0205 20130101 |
Class at
Publication: |
600/301 |
International
Class: |
A61B 5/0205 20060101
A61B005/0205 |
Claims
1-35. (canceled)
36. An apparatus comprising: an input interface configured to
provide signals from at least two sensors for at least two postures
including: signals, dependent upon blood presence, from a first
sensor when a subject is in a first posture; signals, dependent
upon blood presence, from the first sensor when the subject is in a
second posture; signals, dependent upon blood presence, from a
second sensor when the subject is in the first posture; and
signals, dependent upon blood presence from the second sensor when
the subject is in the second posture; and processing circuitry
configured to determine and output a metric by combining, according
to pre-defined calibration data the provided signals.
37. An apparatus as claimed in claim 36, wherein the provided
signals, for each combination of sensor and posture, comprises at
least one logarithm of detected light intensity.
38. An apparatus as claimed in claim 36, wherein the signals, for
each combination of sensor and posture, include a time varying
component of detected light intensity and a separated quasi static
component of detected light intensity.
39. An apparatus as claimed in claim 36, wherein the signals, for
each combination of sensor and posture, include separately a
logarithm of a time varying component of detected light intensity
and a logarithm of a quasi static component of the detected light
intensity.
40. An apparatus as claimed in claim 36, wherein the signals, for
each combination of sensor and posture, include a signal based upon
a light intensity signal detected at an optical reflectance sensor
and a signal based upon a light intensity signal detected at an
optical transmission sensor.
41. An apparatus as claimed in claim 36, wherein the signals, for
each combination of sensor and posture, include a signal based upon
a light intensity signal detected at a first wavelength but not at
a second wavelength and a signal based upon a light intensity
signal detected at, at least, the second wavelength but not the
first wavelength.
42. An apparatus as claimed in claim 36, wherein the calibration
data is used to assess divergence of the provided signals from an
expected average of a statistical model of expected signals to
produce the metric, wherein the provided signals comprise signals
that have been statistically manipulated to be averaged
signals.
43. An apparatus as claimed in claim 36, wherein the calibration
data is predetermined using machine learning.
44. An apparatus as claimed in claim 36, configured to emulate an
artificial neural network comprising a plurality of nodes each of
which has associated weights for inputs to the node, wherein the
calibration data provides said weights and wherein the artificial
neural network receives as inputs the provided signals wherein the
provided signals comprise signals that have been statistically
manipulated to be averaged signals.
45. An apparatus as claimed in claim 36, further comprising a
memory storing multiple sets of calibration data comprising a set
of calibration data for each of a plurality of predetermined
standard sequences of different body postures, wherein the
processing circuitry is configured to determine and output a metric
for a particular predetermined standard sequence of different body
postures by combining, according to calibration data for the
particular predetermined standard sequence of different body
postures, the provided signals.
46. An apparatus as claimed in claim 36, wherein at least one of
the sensors provide signals from optical reflection detectors.
47. An apparatus as claimed in claim 36, wherein at least the first
sensor is configured to be placed on the limb.
48. An apparatus as claimed in claim 36, wherein at least the first
sensor is configured to be placed on the subject's head.
49. An apparatus as claimed in claim 48, wherein the first sensor
provides signals from an optical transmission sensor.
50. An apparatus as claimed in claim 36, wherein the calibration
data is used to assess a divergence of the provided signals from an
expected pattern of signals that characterize an expected response
of a normalized circulation system to the predetermined sequence of
first, second and third postures.
51. An apparatus as claimed in claim 36, wherein the processing
circuitry is configured to perform pattern matching between
patterns produced by the provided signals during a kinematic
protocol involving at least a change between first, second and
third postures and normal circulatory response patterns.
52. An apparatus as claimed in claim 51, wherein the weightings are
determined by training.
53. An apparatus as claimed in claim 36, wherein the processing
circuitry is configured to combine, according to pre-defined
calibration data the provided signals, by using summation and
weightings.
54. A system comprising: at least a first sensor and a second
sensor; and an apparatus comprising: an input interface configured
to provide signals from at least the first sensor and the second
sensor for at least two postures including: signals, dependent upon
blood presence, from the first sensor when a subject is in a first
posture; signals, dependent upon blood presence, from the first
sensor when the subject is in a second posture; signals, dependent
upon blood presence, from the second sensor when the subject is in
the first posture; and signals, dependent upon blood presence from
the second sensor when the subject is in the second posture; and
processing circuitry configured to determine and output a metric by
combining, according to pre-defined calibration data the provided
signals.
55. A system as claimed in claim 54, wherein the first sensor is at
a first location and the second sensor is at a second, different,
location.
56. A system as claimed in claim 54, wherein the first sensor
detects light at a first wavelength but not at a second wavelength
and the second sensor detects light at the second wavelength but
not at the first wavelength.
57. A system as claimed in claim 54, wherein the first sensor is a
reflectance sensor and is attached without clamping using an opaque
adhesive collar that closely circumscribes the reflectance
sensor.
58. A system as claimed in claim 54, wherein the first sensor and
second sensor are attached to a flexible substrate comprising
interconnects that are connectable to the apparatus via an
interface, wherein a portion of the flexible substrate, underlying
one or more of the interconnects, has a manufactured structural
weakness and wherein, in use, the portion of the flexible substrate
having the structural weakness connects with the interface which
retains the substrate against removal such that on attempted
removal of the flexible substrate from the interface the
manufactured structural weakness breaks the one or more
interconnects.
59. A system as claimed in claim 58, wherein the interface
additionally detaches a portion of the flexible substrate to reveal
an indicator.
60. A system as claimed in claim 54, wherein the first sensor and
second sensor are attached to a flexible substrate for application
to a subject and are connectable to the processing circuitry via a
first set of interconnects embedded in the flexible substrate,
wherein an ordering of the interconnects embedded in the substrate
is dependent upon whether the flexible substrate is for use on a
right limb or a left limb and wherein the ordering of the
interconnects embedded in the substrate, in use, is indicative to
the processing circuitry of whether the flexible substrate is
applied to a right limb of the subject or a left limb of the
subject.
61. A system as claimed in claim 54, wherein the first sensor and
second sensor are attached to a first side of a flexible reversible
substrate and are connectable to the processing circuitry via a
first set of interconnects on the first side of the flexible
substrate and wherein a third sensor and a fourth sensor are
attached to a second side of the flexible substrate and are
connectable to the processing circuitry via a second set of
interconnects on the second side of the flexible substrate, wherein
an ordering of the first set of interconnects across the first side
of the flexible interconnect, when the first side of the flexible
substrate is upwards facing, is different to an ordering of the
second set of interconnects across the first side of the flexible
substrate when the second side of the flexible substrate is upwards
facing thereby enabling the processing circuitry to determine which
side of the reversible flexible substrate is operational.
62. A system as claimed in claim 54, wherein first signals detected
by the first sensor are processed to produce parallel signals that
have different frequency components before combination at the
processing circuitry and wherein second signals detected by the
second sensor are processed to produce parallel signals that have
different frequency components before combination by the processing
circuitry.
63. A method comprising: attaching at least a first optical sensor
and a second optical sensors to a subject; and connecting the
optical sensors to an apparatus comprising: an input interface
configured to provide signals from at least the first sensor and
the second sensor for at least two postures including: signals,
dependent upon blood presence, from the first sensor when a subject
is in a first posture; signals, dependent upon blood presence, from
the first sensor when the subject is in a second posture; signals,
dependent upon blood presence, from the second sensor when the
subject is in the first posture; and signals, dependent upon blood
presence from the second sensor when the subject is in the second
posture; and processing circuitry configured to determine and
output a metric by combining, according to pre-defined calibration
data the provided signals; and moving the subject through a
predetermined ordered sequence of different postures including the
first and second postures.
64. A method as claimed in claim 63, wherein the optical sensors
are attached by attaching a disposable flexible substrate to the
subject.
65. A method as claimed in claim 64, wherein the disposable
flexible substrate is attached to a limb and comprises at least one
optical reflectance sensor.
66. A method as claimed in claim 65, wherein the flexible substrate
is attached using adhesive only and without the use of a clamping
force.
67. A method as claimed in claim 63, wherein the disposable
flexible substrate is attached to a subject's head and comprises at
least one optical transmission sensor.
68. A method as claimed in claim 63, wherein moving the subject
through a predetermined ordered sequence of different postures
comprises moving the subject between postures to cause a local, as
opposed to systemic, circulatory reaction.
69. A method as claimed in claim 63, wherein moving the subject
through a predetermined ordered sequence of different postures
comprises moving the subject between postured to cause, for the
subject, a relative vertical displacement with respect to the
subject's heart of a subject's peripheral limb without relative
vertical displacement with respect to the subject's heart of the
subject's head.
70. A method as claimed in claim 63, wherein moving the subject
through a predetermined ordered sequence of different postures
comprises moving the subject between postured to cause a systemic
circulatory reaction.
71. A method as claimed in claim 63, wherein moving the subject
through a predetermined ordered sequence of different postures
comprises moving the subject between postures to cause, for the
subject, a relative vertical displacement, with respect to the
subject's heart, of the subject's head.
72. A method as claimed in claim 63, moving the subject through a
predetermined ordered sequence of different postures including the
first, the second posture and a third posture.
Description
FIELD OF THE INVENTION
[0001] Embodiments of the present invention relate to assessing a
subject's circulatory system.
BACKGROUND TO THE INVENTION
[0002] The response of a subject's circulation system to a
subject's posture change may depend upon characteristics of the
blood such as its viscosity, characteristics of the circulation
system such as its resistance and how the autonomous nervous system
responds to maintain homeostasis.
[0003] Blood perfusion at a periphery may, for example, be
dependent upon one or a combination of the following factors:--
[0004] 1. vascular disease such as for example Raynaud's disease
[0005] 2. genetic problems such as for example scleroderma [0006]
3. an abnormal vaso-constriction or vaso-dilation response from the
autonomous nervous system instigated by for example diabetic
neuropathy or alcoholism [0007] 4. drug treatments such as for
example Beta blockers [0008] 5. auto-immune diseases such as for
example Lupus
[0009] It will therefore be appreciated that there may be many
reasons why a subject's circulatory system response to a postural
change may be "abnormal". Different pathologies may have the same
or different effects on circulation.
[0010] It would be desirable to provide an interim clinical
indicator that characterizes a response of the circulation system
to a series of postural changes and provides a clinician with
information which in combination with other information and the
clinician's skill and knowledge may be used to assess whether or
not pathology may be present. The medical practitioner can then,
using his own medical knowledge, conduct independent investigations
before identifying any pathology.
BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION
[0011] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising:
an input interface configured to provide signals from at least two
sensors for at least two postures including: [0012] signals,
dependent upon blood presence, from a first sensor when a subject
is in a first posture; [0013] signals, dependent upon blood
presence, from the first sensor when the subject is in a second
posture; [0014] signals, dependent upon blood presence, from a
second sensor when the subject is in the first posture; and [0015]
signals, dependent upon blood presence. from the second sensor when
the subject is in the second posture; and processing circuitry
configured to determine and output a metric by combining, according
to pre-defined calibration data the provided signals.
[0016] The signals, for each combination of sensor and posture, may
comprises at least one logarithm of detected light intensity.
[0017] The signals, for each combination of sensor and posture, may
include separately a time varying component of detected light
intensity and a quasi static component of detected light
intensity.
[0018] The signals, for each combination of sensor and posture, may
include separately a logarithm of a time varying component of
detected light intensity and a logarithm of a quasi static
component of the detected light intensity.
[0019] The signals, for each combination of sensor and posture, may
include a signal based upon a light intensity signal detected at an
optical reflectance sensor and a signal based upon a light
intensity signal detected at an optical transmission sensor.
[0020] The signals, for each combination of sensor and posture, may
include a signal based upon a light intensity signal detected at a
first wavelength but not at a second wavelength and a signal based
upon a light intensity signal detected at at least the second
wavelength but not the first wavelength.
[0021] The calibration data may be used to assess divergence of the
provided signals from an expected average of a statistical model of
expected signals to produce the metric.
[0022] The calibration data may define a non-linear combination of
the signals.
[0023] The calibration data may be predetermined using machine
learning.
[0024] The apparatus may be configured to emulate an artificial
neural network comprising a plurality of nodes each of which has
associated weights for inputs to the node, wherein the calibration
data provides said weights.
[0025] The apparatus may further comprise a memory storing multiple
sets of calibration data comprising a set of calibration data for
each of a plurality of predetermined standard sequences of
different body postures.
[0026] At least one of the sensors may provide signals from optical
reflection detectors.
[0027] A change from the first posture to the second posture may be
expected to cause a local, as opposed to systemic, circulatory
reaction
[0028] A change from the first posture to the second posture may
cause, for the subject, a relative vertical displacement with
respect to the subject's heart of a subject's peripheral limb
without relative vertical displacement with respect to the
subject's heart of the subject's head. At least the first sensor
may be on the limb.
[0029] A change from the first posture to the second posture may be
expected to cause a systemic circulatory reaction.
[0030] A change from the first posture to the second posture may
cause, for the subject, a relative vertical displacement with
respect to the subject's heart of the subject's head.
[0031] At least the first sensor may be on the subject's head. This
first sensor may provide signals from an optical transmission
sensor.
[0032] The metric may record a divergence of the signals from an
expected pattern of signals that characterize an expected response
of a normalized circulation system to the predetermined sequence of
first and second postures.
[0033] A system may comprising: the apparatus and at least a first
sensor and a second sensor. The first sensor may be at a first
location and the second sensor may be at a second, different,
location. The first sensor may detect light at a first wavelength
but not at a second wavelength and the second sensor may detect
light at the second wavelength but not at the first wavelength. The
first sensor may be a reflectance sensor and may be attached
without clamping using an opaque adhesive collar that closely
circumscribes the reflectance sensor. The first sensor and second
sensor may be attached to a flexible substrate comprising
interconnects that are connectable to the apparatus via an
interface, wherein a portion of the flexible substrate, underlying
one or more of the interconnects, has a manufactured structural
weakness and wherein, in use, the portion of the flexible substrate
having the structural weakness connects with the interface which
retains the substrate against removal such that on attempted
removal of the flexible substrate from the interface the
manufactured structural weakness breaks the one or more
interconnects. The interface may additionally detach a portion of
the flexible substrate to reveal an indicator. The first sensor and
second sensor may be attached to a flexible substrate for
application to a subject and may be connectable to the processing
circuitry via a first set of interconnects embedded in the flexible
substrate, wherein an ordering of the interconnects embedded in the
substrate is dependent upon whether the flexible substrate is for
use on a right limb or a left limb and wherein the ordering of the
interconnects embedded in the substrate, in use, is indicative to
the processing circuitry of whether the flexible substrate is
applied to a right limb of the subject or a left limb of the
subject. The first sensor and second sensor may be attached to a
first side of a flexible reversible substrate and may be
connectable to the processing circuitry via a first set of
interconnects on the first side of the flexible substrate and
wherein a third sensor and a fourth sensor may be attached to a
second side of the flexible substrate and may be connectable to the
processing circuitry via a second set of interconnects on the
second side of the flexible substrate, wherein an ordering of the
first set of interconnects across the first side of the flexible
interconnect, when the first side of the flexible substrate is
upwards facing, is different to an ordering of the second set of
interconnects across the first side of the flexible substrate when
the second side of the flexible substrate is upwards facing thereby
enabling the processing circuitry to determine which side of the
reversible flexible substrate is operational. First signals
detected by the first sensor may be processed to produce parallel
signals that have different frequency components before combination
at the processing circuitry and wherein second signals detected by
the second sensor are processed to produce parallel signals that
have different frequency components before combination by the
processing circuitry.
[0034] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
system for assessing a subject's blood circulation a first detector
configured to detect signals dependent upon blood presence when the
subject is in a first posture and when the subject is in a second
posture; at least one other detector configured to detect signals
dependent upon blood presence when the subject is in the first
posture and when the subject is in the second posture; and
processing circuitry configured to determine a metric by combining
the detected signals from the first and second detectors for the
first and second postures according to calibration data.
[0035] According to various, but not necessarily all, embodiments
of the invention there is provided a method comprising: attaching
optical sensors to a subject; connecting the optical sensors to the
apparatus; and moving the subject through a predetermined ordered
sequence of different postures including the first and second
postures. The optical sensors may be attached by attaching a
disposable flexible substrate to the subject. The disposable
flexible substrate may be attached to a limb and may comprise at
least one optical reflectance sensor. The flexible substrate may be
attached using adhesive only and without the use of a clamping
force. The disposable flexible substrate may be attached to a
subject's head and comprises at least one optical transmission
sensor.
[0036] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
method comprising: processing light intensity signals received from
optical sensors positioned on a subject when the subject is moved
through a predetermined sequence of at least three different
postures according to a kinematic protocol to provide input
signals; combining the input signals to produce and output a metric
that quantitatively defines a response of the subject's circulatory
system to the predetermined sequence of at least three different
postures of the kinematic protocol.
[0037] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
flexible substrate; a first optical sensor at a first location on
the flexible substrate arranged in a reflectance configuration
and
a first adhesive collar closely circumscribing the first optical
sensor, a second optical sensor at a second location on the
flexible substrate; and a second adhesive collar closely
circumscribing the second optical sensor, wherein the first
adhesive collar is configured to position the first sensor adjacent
a subject's body for physiological sensing and wherein the second
adhesive collar is configured to position the second sensor
adjacent the subject's body for physiological sensing.
[0038] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
flexible substrate comprising a manufactured structural weakness;
at least a first sensor and a second sensor attached to the
flexible substrate; interconnects connected to the first and second
sensors; and an interface for connecting the interconnects to a
cable, wherein the manufactured structural weakness underlies one
or more of the interconnects adjacent the interface.
[0039] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
reversible flexible substrate having a first side and an opposing
second side; a first sensor and a second sensor attached to the
first side of the reversible flexible substrate; a first set of
interconnects, on the first side of the reversible flexible
substrate, connected to the first and second sensors in a first
order; a third sensor and a fourth sensor attached to the first
side of the reversible flexible substrate; a second set of
interconnects, on the second side of the reversible flexible
substrate, connected to the third and fourth sensors in a second
order; wherein the first order of the first set of interconnects
across the first side of the flexible interconnect, when the first
side of the flexible substrate is upwards facing, is different to
the second order of the second set of interconnects across the
second side of the flexible substrate when the second side of the
flexible substrate is upwards facing.
[0040] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising: a
flexible substrate for application to a subject, the flexible
substrate comprising at least a first sensor and a second sensor; a
set of interconnects supported by the flexible substrate and
connected to the sensors; an interface for connecting the
interconnects to remote processing circuitry; wherein an ordering
of the interconnects is dependent upon whether the flexible
substrate is for use on a right limb or a left limb and wherein the
ordering of the interconnects is indicative, when the apparatus is
in use, to the processing circuitry of whether the flexible
substrate is applied to a right limb of the subject or a left limb
of the subject.
[0041] According to various, but not necessarily all, embodiments
of the invention there is provided a collection of flexible
substrates wherein each flexible substrate is ergonomically
configured to be applied to a different body part of a subject, and
comprises: [0042] at least a first sensor and a second sensor;
[0043] a set of interconnects supported by the flexible substrate
and connected to the sensors; [0044] an interface comprising a
common fixed physical configuration of interface connectors for
connecting the interconnects to remote processing circuitry;
wherein an ordering of the interconnects with respect to the common
fixed physical configuration of interface connectors is dependent
upon the body part to which a flexible substrate is to be applied
and wherein the ordering of the interconnects with respect to the
common fixed physical configuration of interface connectors is
uniquely indicative, when the flexible substrate is in use, to the
processing circuitry of the body part to which the flexible
substrate is attached.
[0045] According to various, but not necessarily all, embodiments
of the invention there is provided an apparatus comprising:
an input interface configured to provide signals dependent upon
blood presence at at least two locations for at least two postures
including signals dependent upon blood presence at a first location
when a subject is in a first posture, signals dependent upon blood
presence at the first location when the subject is in a second
posture, signals dependent upon blood presence at a second location
when the subject is in the first posture, and signals dependent
upon blood presence at the second location when the subject is in
the second posture; processing circuitry configured to determine
and output a metric by combining, according to pre-defined
calibration data the provided signals.
[0046] According to various, but not necessarily all, embodiments
of the invention there are provided methods, systems, apparatuses
and computer programs as claimed as the appended claims.
[0047] According to various, but not necessarily all, embodiments
of the invention there is provided a system and method for
assessing a subject's circulatory system using optical sensors and
multiple postural changes.
[0048] This provides the advantage of low cost, rapid pain free
assessment of subject physiology by assessment of disturbances to
the circulatory system.
[0049] It should therefore be appreciated that the present
invention does not diagnose a disease but provides an interim
clinical indicator which is of a type that is not dissimilar to
body temperature, blood pressure, heart rate etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] For a better understanding of various examples of
embodiments of the present invention reference will now be made by
way of example only to the accompanying drawings in which:
[0051] FIG. 1 schematically illustrates a system comprising:
optical sensors and an apparatus;
[0052] FIG. 2 illustrates the apparatus in more detail;
[0053] FIG. 3 schematically illustrates an artificial neural
network for producing a metric;
[0054] FIGS. 4A and 4B illustrate different implementations of a
flexible substrate for sensors:
[0055] FIGS. 5A, 5B and 5C schematically illustrate safety features
for flexible substrates.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION
[0056] Functional tests are used to provoke changes in the
circulatory system of a subject. Functional test involves placing
the subject into different postures and recording data at those
postures. The exact number, type, order, frequency of postures used
in a particular functional test protocol is predetermined and
depends upon the subject's physiology and pathology under
investigation.
[0057] A kinematic protocol (or test) is a sequence of three or
more different postures. The sequence is typically carried out in a
single continuous session. The sequence may be carried out as an
uninterrupted sequence that does not have significant hiatus
between postural changes.
[0058] The different postures adopted during a kinematic protocol
may for example include at least three of: a reference posture,
none, one or more `local` (or `limb`) postures, none, one or more
`orthostatic` (or `torso`) postures, and none, one or more
`systemic` (or `whole body`) postures.
[0059] In a `local` (or `limb`) posture, a limb has been moved
through a gravitational field relative to a stationary body
torso.
[0060] In a `orthostatic` (or `torso`) posture, the body torso has
been moved through a gravitational field relative to a stationary
limb or limbs (e.g. legs).
[0061] In a `systemic` (or `whole body`) posture, the whole body
has been moved within a gravitational field but without relative
movement between the body torso and limbs. This may be achieved by
inclining a stationary subject.
[0062] The at least three different postures result in at least two
different postural changes. The postural changes are changes of the
whole or parts of the body relative to a gravitational field. The
different postural changes therefore result in different `impulses`
to the subject's circulatory system.
[0063] It may be desirable to have a first type of impulse such as
a `local` (or `limb`) impulse by changing to a `local` (or `limb`)
posture or an `orthostatic` (or `torso`) impulse by changing to an
`orthostatic` (or `torso`) posture or a `systemic` (or `whole
body`) impulse by changing to a `systemic` (or `whole body`)
position. It may be desirable to also have a different second type
of impulse. Therefore if the first type of impulse was `local` (or
`limb`) the second type of impulse may be `orthostatic` (or
`torso`) or `systemic` (or `whole body`) but not `local` (or
`limb`).
[0064] The following kinematic protocol can be used to assess a
local response of a capillary bed i.e. vaso-dilation and
vaso-contraction. A local postural change is followed by a systemic
postural change.
[0065] First the local postural change is performed. An initial
reference posture in which a subject is supine and an arm is level
with the heart may be followed by a local posture in which the
subject is supine and the arm is vertically displaced below the
heart.
[0066] Then a systemic postural change is performed. An initial
reference posture in which a subject is supine and an arm is level
with the heart may be followed by a systemic posture in which the
angle of incline of the body is changed without independent
movement of the arm relative to the torso so that the head is
vertically displaced below the heart.
[0067] A sensor may be located on an index finger of the arm. This
sensor may be an optical transmission sensor which is sensitive to
the arterial blood volume.
[0068] A sensor may be located on the forearm or the back of the
hand. This sensor may be an optical reflection sensor which is
sensitive to skin venous blood volume changes. The skin reflection
sensor also permits normalizing of the digit transmission sensor
caused by venous blood volume changes.
[0069] The outputs from the sensors have characteristics that
produce different patterns as the kinematic protocol is performed.
The patterns for a normal circulatory response share a common
distinctive pattern. This distinctive pattern may be determined
theoretically or empirically and then used to pattern match the
outputs from the sensors for a subject during the same kinematic
test. A metric may be output that indicates whether or the degree
of pattern matching. A pattern match indicates a normal circulatory
response for the given kinematic test. A pattern mismatch indicates
an abnormal circulatory response that merits further
investigation.
[0070] The following kinematic protocol can be used to assess
arterial blood supply to the brain. An orthostatic (or body)
postural change is followed by a systemic postural change.
[0071] First the orthostatic (or body) postural change is
performed. The subject is initially in a supine reference position
to record a baseline. The subject sits up or is sat up to an
orthostatic (or body) posture, which would cause blood flow to the
brain to initially reduce due to orthostatic pressure changes.
[0072] Then the systemic postural change is performed. The subject
is returned to the supine reference position to record a baseline.
The subject in the supine position is tilted so that the angle of
incline of the body is changed so that the head is vertically
displaced below the heart.
[0073] A sensor may be located on the subject's forehead. This
sensor may be an optical reflection sensor which is sensitive to
localized venous blood volume caused by pooling.
[0074] A sensor may be located across the nose. This sensor may be
an optical transmission sensor which is sensitive to the arterial
blood volume which is dependent upon the interior carotid artery
via the ophthalmic and ethmoidal arteries.
[0075] A sensor may be located on an ear lobe. This sensor may be
an optical transmission sensor which is sensitive to the arterial
blood volume which is dependent on the external carotid artery via
the temporal artery.
[0076] The sensors are preferably at approximately the same height
to avoid orthostatic compensation.
[0077] The outputs from the sensors have characteristics that
produce different patterns as the kinematic test is performed. The
patterns for a normal circulatory response share a common
distinctive pattern. This distinctive pattern may be determined
theoretically or empirically and then used to pattern match the
outputs from the sensors for a subject during the same kinematic
test. A metric may be output that indicates whether or the degree
of pattern matching. A pattern match indicates a normal circulatory
response. A pattern mismatch indicates an abnormal circulatory
response that merits further investigation such as a Magnetic
Resonance Imaging (MRI) Scan if compromised blood supply to the
brain is a possibility.
[0078] FIG. 1 schematically illustrates a system 10 comprising:
optical sensors 2A, 2B, 2C and an apparatus 20.
[0079] The sensors 2A, 2B and 2C are positioned at respective
locations 4A, 4B, 4C of a subject's body. In the example
illustrated, the sensors 2A and 2B are attached to a substrate 6
and the substrate 6 is attached to the subject's body 8.
[0080] The sensors are non-invasive sensors typically photo sensors
such as optical transmission sensors and/or optical reflection
sensors. The sensors are for sensing physiological attributes such
as, for example, changes in the volume of the body
(plethysmography). An optical sensor comprises a light emitter and
photo-detector. In a transmission sensor, in use, the
photo-detector is positioned to receive light from the light
emitter that has passed through the subject's body 8. In a
reflection sensor, in use, the photo-detector is positioned to
receive light from the light emitter that has been reflected by the
subject's body 8.
[0081] It should be appreciated that the sensors 2A, 2B provide
inputs to the apparatus 20 throughout the kinematic protocol i.e.,
for each posture of the subject.
[0082] Although only a single sensor is illustrated at each
location, it should be appreciated that multiple sensors may be
implemented at each location. For example, combinations of
reflectance and transmission sensors may be provided in the same
location. Also sensors that operate at different wavelengths of
light may also be positioned at the same location. A sensor
operating in near infrared of around 850 nm would be weakly
affected by absorption in tissue but strongly affected by
absorption by blood and could for example be used to monitor the
reaction of a capillary bed during a kinematic test. Whereas a
sensor operating around 650 nm would be strongly affected by
absorption in tissue and could for example be used to monitor the
reaction of skin tone during a kinematic test. The signal from the
850 nm sensor would have a much larger arterial component than the
650 nm sensor as it would penetrate deeper into tissue.
[0083] The sensors communicate with the apparatus 20 either using
wireless methods (ZigBee, Bluetooth, UHF radio etc) or cables.
[0084] The apparatus 20 comprises an input interface 22 that
pre-processes signals received from the sensors 2A, 2C and provides
signal 23 to processing circuitry 24. The processing circuitry 23
is configured to determine and output a metric 25 by combining,
according to pre-defined calibration data 28 the provided signals
23.
[0085] In the example illustrated, the provided signals 23
dependent upon blood presence at a first, second and third
locations 4A, 4B, 4C when a subject is in the different postures of
the kinematic protocol.
[0086] The interface 22 may also perform some signal processing
before providing the signals 23 to the processing circuitry 24.
[0087] For example, the interface may separate an intensity signal
from a sensor into two distinct signals having different frequency
components. For example, it may produce an `ac signal` that relates
to the time varying intensity recorded at a sensor and a `dc
signal` that measures the quasi-static intensity recorded at the
sensor.
[0088] As another example, the interface 22 may apply a non-linear
function such as a logarithmic function to the signals 23 before
they are provided to the processing circuitry 24.
[0089] The processing circuitry 24 may be implemented in any
suitable manner. It may, for example, be a programmable computer or
dedicated hardware. The interface 22 may be implemented in any
suitable manner. It may, for example, comprise a programmable
computer or dedicated hardware.
[0090] It should be appreciated that the interface 22 and
processing circuitry may not be discrete physical components but
may be functional modules implemented by common circuitry such as a
processor executing different software modules.
[0091] The calibration data 28 is used to assess divergence of the
provided signals 23 from an expected pattern of signals that
characterize an expected response of a normalized circulation
system to the kinematic protocol. The expected response may be an
average of a statistical model of expected signals produced for
example using machine learning.
[0092] The calibration data defines a non-linear combination of the
signals. There will typically be different non-linear combinations
of the signals 23 required for different kinematic tests as any
pattern to be matched will vary with the location and type of
sensors used and with the kinematic test performed. There will
therefore be different calibration data 28 for each kinematic
test.
[0093] Referring to FIG. 2, the interface 22 comprises interface
components 22A etc for one of the sensors 2A, however only the
interface component 22A for the sensor 2A is illustrated. It should
be appreciated that there will be an equivalent interface
component.
[0094] The interface component 22A comprises analogue front end
signal processing circuitry 32 for processing the intensity signal
received from the sensor 2A and at least one Analogue to Digital
converter 34.
[0095] There may be multiple front ends intended for simultaneous
continuous monitoring of multiple sensors, or a single front end
with an appropriate multiplexor switch. The front end circuitry may
provide for constant control of the current provided to the
sensors, trans-impedance amplification of the received signals 30,
compensation for ambient light interference. This may be achieved
using time division multiplexing (TDM), in which the periods where
a light source is not illuminated, allows monitoring of ambient
light interference. This may alternatively be achieved using
frequency division implemented by employing a modulated light
source and a frequency locking or demodulation system.
[0096] The front end circuitry 32 may initialize the sensors by
configuring itself for a mid-scale value of the semi-static signal
component by varying the LED intensity so the resultant signal
would be mid way between a desired range, again for example unity.
Any signal increases or decreases would be accommodated within the
signal ranges, reducing the likelihood of signal saturation or
diminishment.
[0097] In the example illustrated, the interface component 22A
separates the received signal 30, after pre-processing, into two
distinct signals 35, 36 having different frequency components.
[0098] It may produce an ac signal 36 by passing the received
signal 32 through a high pass filter 38. The ac signal 36 relates
to the time varying intensity recorded at a sensor. It may also
produce a dc signal 35 by passing the received signal 32 through a
low pass filter 42 that integrates, typically with a time constant
of several seconds. The dc signal 35 relates to a quasi-static
intensity recorded at the sensor. Filtering could be performed
either in hardware using conventional linear time invariant filters
or after digitization within a microprocessor using digital filters
such as Finite impulse response designs. Digital filtering has the
advantage of being able to change the filter parameters via
software update if required.
[0099] The signal or signals (if high and low pass filtering has
occurred) would then be fed to an analogue to digital converter
(ADC) 35 before being provided to the processing circuitry 24. The
ADC may be a discrete item or may be contained in a
microprocessor.
[0100] A logarithmic function may be applied to signals before they
are processed by the processing circuitry 24 to produce the metric
25. This logarithmic function may be applied in the analogue or
digital domain. If applied in the digital domain, it may be applied
by the interface 22 or the processing circuitry 24.
[0101] Optical absorption spectroscopy can be modeled using the
Lambert-Beer Law, in which received optical intensity is
proportional to an exponential function that has as its argument
the product of a one dimensional optical path length and an
absorption coefficient. Taking the natural logarithm of the
received intensity produces a result that is linear in the optical
path length. The optical path length may be assumed to vary
depending on tissue blood volume, which is affected by posture and
arterial dilation responses.
[0102] The processing circuitry in the illustrated example
comprises a processor 40, a memory 42, a display 44 and a network
interface 46. The processor 40 is configured to read from and write
to the memory 42, to provide output commands to the display 44 and
to communicate using the network interface 46.
[0103] The processor 40 would typically execute a program 48 from a
memory 42 to calculate a metric 25 and then display the metric 25
on display 44.
[0104] The computer program may arrive at the apparatus via any
suitable delivery mechanism. The delivery mechanism may be, for
example, a computer-readable storage medium, a computer program
product, a memory device, a record medium such as a CD-ROM or DVD,
an article of manufacture that tangibly embodies the computer
program. The delivery mechanism may be a signal configured to
reliably transfer the computer program.
[0105] The exact form of the algorithm for a multi sensor, multi
posture kinematic test is typically a summation of non-linear
weighted input signals S 23. Some statistical manipulation may
occur on the signals 23 before input to the algorithm. For example
the median of a dc signal 35 may be calculated whereas a root mean
squared value may be calculated for the ac signal 36.
[0106] The algorithm weights may be set using a-priori knowledge,
or training using a teaching pattern and altering the weights
according to the error.
[0107] If there are multiple postures i, multiple sensor sites j
and multiple sensor wavelengths k at each sensor site, then the
metric y could be defined as:
y = k j i c ijk log s ijk ##EQU00001##
where S.sub.ijk is the input signal 23 for posture i, at site j for
wavelength k.
[0108] Calculation of the weights c is possible using regression
analysis. A multi posture kinematic test would be performed on a
range of subjects who would also undergo independent clinical
assessment. Then a least squares regression analysis of the
recorded inputs against an idealized metric permits the algorithm
weights to be defined.
[0109] Alternatively the metric could be defined as an arbitrary
weighted summation of non-linear functions of the input signals
S.sub.ijk using an artificial neural network 50 such as, for
example, schematically illustrated in FIG. 3.
[0110] Artificial Neural Networks (ANN) are a class of non-linear
weighting algorithms. The feed forward representation as
illustrated in FIG. 3 consists of a directed acyclic graph of
interconnected nodes 52 arranged in layers 54A, 54B, 54C.
[0111] The feed forward network 50 illustrated in FIG. 3 with three
layers of neurons. Each input signal 23A, 238, 23C, 23D is sent to
every neuron 52 in an input layer 54A. Each neuron 52 in the input
layer 54A forms its own weighted sum of its inputs 23A-D and
provides the sum as an output. Each neuron 52 in the input layer
54A has its output connected to every neuron 52 in a hidden layer
54B. Each neuron 52 in the hidden layer 54B forms its own weighted
sum of its inputs and provides the sum as an output. Each neuron 52
in the hidden layer 54B has its output connected to every neuron 52
in an output layer 54C. Each neuron 52 in the output layer 54C
forms its own weighted sum of its inputs and multiplies the
weighted sum by an activation function to produce the metric
25.
[0112] The metric 25 may be constrained to be a continuous value
between 0 and 1 using a sigmoid function as the activation
function, or between -1 and 1 using a hyperbolic tangent (Tan h)
function as the activation function. If the metric is to be
discrete, then a signum or step function could be used as the
activation function.
[0113] In some implementations two layers 54 of neurons 52 may
suffice.
[0114] The various weights applied in the weighted summations may
be determined using supervised learning and back propagation.
Alternatively optimum weights may be found using a genetic
algorithm. The weights are comprised in the calibration data
28.
[0115] If there are i input nodes, j hidden nodes and only a single
output node, the metric may be defined as
f ( x i ) = f j w g 1 j ( g v j i w h 1 i ( h v i i w i x i ) )
##EQU00002##
Wherein h.sub.v.sub.i, g.sub.v.sub.i, x.sub.i are:--
g.sub.v.sub.i=(g.sub.1,g.sub.2, . . . ,g.sub.j),
h.sub.v.sub.i=(h.sub.1,h.sub.2, . . . ,h.sub.i),
x.sub.i(AC(.lamda..sub.1 . . . n,P.sub.1 . . . q).sub.S.sub.1,
DC(.lamda..sub.1 . . . n,P.sub.1 . . . q).sub.S.sub.1, . . . ,
AC(.lamda..sub.1 . . . n,P.sub.1 . . . q).sub.S.sub.m,
DC(.lamda..sub.1 . . . n,P.sub.1 . . . q).sub.S.sub.m)
[0116] Note that x.sub.i represents a vector of statistic for the
corresponding Sensor (S.sub.1 . . . m) pulsatile component (AC) and
quasi-static (DC) signal components for the different wavelengths
(.lamda..sub.1 . . . n) for each posture (P.sub.1 . . . q).
[0117] The weights are defined using a training algorithm.
Training, like in the simple algorithm above, requires known
training data to be fed to the ANN, and the weights are modified
using an error function or learning rule.
[0118] The network 50 would be trained by providing it with the
input signal values for the postures obtained from a kinematic test
and then matching using back propagation would be used to reduce an
error between the output metric and an expected metric.
[0119] The steps for back propagation of ANN supervised learning
may include:-- [0120] 1. Present known training inputs to the ANN.
[0121] 2. For each output neuron in the output layer, compare the
ANN output metric to the expected metric for that known training
sample and calculate the local error. [0122] 3. For each output
neuron adjust the weights to lower the local error. [0123] 4.
Assign different contributions for the local error to the neurons
in the hidden layer, giving greater responsibility to neurons
connected by stronger weights. [0124] 5. Repeat the steps 3 and 4
for the neurons in the hidden layer using each one's responsibility
as its error.
[0125] It will be appreciated from the above that the metric is
sensitive to the location of a sensor and the order and nature of
the postures in a kinematic test.
[0126] To enable the correct order and nature of the postures to be
performed for a kinematic test corresponding to the current
calibration data 28, the apparatus 20 may give instructions either
via a display 44 or by synthesizing a voice. The instructions would
indicate when and how a posture of a subject should be changed.
[0127] There will be different sets of calibration data for
different kinematic tests. A menu may be provided to select a
particular test. The correct calibration data 28 would then be
loaded for use by the apparatus 20 along with the instructions
telling the operative how to perform the kinematic test.
[0128] It is also important that the sensors are located accurately
and applied to a subject in a manner that does not arbitrarily
interfere with the signals 23.
[0129] FIGS. 4A and 4B illustrate two different examples of
apparatus 60 having flexible substrates 62 that are suitable for
applying sensors to a subject 8.
[0130] The apparatus 60 illustrated comprises an ergonomically
shaped flexible substrate 62.
[0131] At one end 64 of the flexible substrate 62 are located light
emitter(s) and photo-detector(s) in an adjacent configuration in
order to act as a reflection sensor 66.
[0132] An adhesive collar 68 that surrounds and closely
circumscribes the reflectance sensor 66 is used to attach the end
64 of the flexible substrate 62 to the subject. The collar 68 is
preferably substantially opaque at the wavelengths at which the
photo-detector operates so that it acts to isolate the
photo-detector from ambient light. The adhesive collar may be
shaped like an annulus. The adhesive collar 68 may be formed from
hydrogel.
[0133] A second portion 70 of the flexible substrate 62 is folded
to act as a transmission sensor 72--a light emitter(s) 72A is
applied to one side of a protuberance and a photo-detector(s) 72B
is applied on the other side of the protuberance.
[0134] An adhesive collar 68 that surrounds and closely
circumscribes the light emitter 72A and an adhesive collar 68 that
surrounds and closely circumscribes the photo-detector 72B are used
to attach the end 70 of the flexible substrate 62 to the subject.
The adhesive collar circumscribes in the sense that it surrounds
but it does not necessarily touch. The collars 68 are preferably
substantially opaque at the wavelengths at which the photo-detector
operates so that it acts to isolate the photo-detector from ambient
light. The adhesive collar may be shaped like an annulus. The
adhesive collar 68 may be formed from hydrogel.
[0135] The adhesive collars 68 adhere sensors in the correct
strategic place and they avoid the use of a mechanical clip system,
which would compress the arteries and veins in the bridge of the
nose. This is especially important for reflectance sensors as they
are sensitive to a vasodilatory response that would be masked by
mechanical compression.
[0136] Conductive interconnects feed from an edge connector 74
(where the embedded contacts are exposed from within the flexible
substrate and are inserted into a spring leaf type metal contact,
one for each connector) to the ends 64, 70 of the flexible
substrate 62, communicating with the light sources and
photo-detectors.
[0137] Referring to FIG. 4A the flexible substrate 62 has a `Y` or
`T` shape. The end 62 is located at the forehead of the subject.
The end 70 is folded over the bridge of the nose to act as a
transmission sensor.
[0138] The distance between the bridge of the nose and the
reflection sensor on the head may be adjusted using a buckle (not
shown), typically located between the eye brows which is only
possible using a flexible substrate that will conform around the
buckle. Alternatively the flexible substrate may be allowed to arch
in order to accommodate excess length, as the hydrogel annulus
adhesive should firmly affix the active components of the
non-invasive optical sensors against the skin. The flexible
substrate would typically be disposed of after use on a single
subject to maintain hygiene and avoid subject cross
contamination.
[0139] Referring to FIG. 4B the flexible substrate 62 has a `Y` or
` T` shape. The end 62 is located over the extensor digitorum
brevis muscle, located over the region of the third cuneiform,
cuboid and metatarsal bones of the foot. The end 70 of the
substrate 62 would wrap over the end of the locating toe (typically
second toe). The transmission light emitter 72A is applied to the
nail matrix and the transmission photo-sensor 72B is applied to the
pad of the second toe, diametrically opposite the emitter 72A.
[0140] During application of the sensor to the subject, the
flexible substrate is designed to conform to the subject's foot,
naturally following the contours of the foot in order to locate
over the second toe. The flexible substrate is shaped to follow the
curvature of the foot, approximating a `Z` shape which is easily
achieved by stamping and laminating in conductive elements.
[0141] The advantages of the adhesive fixation method are that
hydrogel adhesion locates the sensors in the correct strategic
places on the foot rather than using mechanical clip systems or
loops around the diameter of the toe. The arteries feeding the pulp
of the toe pass alongside the side of the toe; therefore any method
of securing the toe sensor which employs fastenings around the toe
could compress the arteries and veins, spoiling the effects of the
postural test. This is especially important if a vasodilatory
response is to be observed as these mechanical effects would mask
the homeostasis response.
[0142] In addition, adhesive pads may be located at strategic
points along the flexible substrate to stabilize the substrate and
reduce sensor movement and resultant motion artifact.
[0143] The flexible substrate 62 illustrated in FIG. 5B can with
minor modification be made suitable for use with a hand. The
reflectance sensor is located on the back of the hand and the
transmission sensor is located on the index finger.
[0144] An alternative embodiment of this flexible substrate sensor
would employ sensor elements on both sides of the substrate,
permitting the substrate to be utilized on either foot.
Handedness Detection
[0145] A connecting cable connects with the edge conductor 74. The
connecting cable has a series of contacts which are connected
(perhaps semi-permanently) through the cable to particular parts of
the front end circuitry 32. Consequently, the arrangement of the
contacts at the interface of the connecting cable has, at least
initially, a specific, predefined dedicated order. Thus a dedicated
contact is always used to energize a first sensor and a dedicated
contact is always used to receive.
[0146] Thus for example the following simplified table may
illustrate a first correspondence between the contacts of the cable
and those of the edge connector.
TABLE-US-00001 TABLE 1 Cable Contact Connector Contact 1 Output LED
1 Sensor 1 2 Input LED 2 Sensor 1 3 Output LED 3 Sensor 2 4 Input
LED 4 Sensor 2
[0147] The following simplified table may illustrate a second
correspondence between the contacts of the cable and those of the
edge connector.
TABLE-US-00002 TABLE 2 Cable Contact Connector Contact 1 Output LED
1 Sensor 1 2 Input LED 2 Sensor 2 3 Output LED 3 Sensor 2 4 Input
LED 4 Sensor 1
[0148] It is possible for the front end circuitry 32 to determine
which of these configurations is used by applying an output LED
control signal on only cable contact 1. If an input is received at
the front end circuitry 32 on connector contact 2 then the first
configuration is in use whereas if an input is received at the
front end circuitry 32 on connector contact 4 then the second
configuration is in use.
[0149] The different configurations may be used to identify
different substrates 62.
[0150] Alternatively, the same substrate may be reversible with the
first configuration used on one side and the second configuration
used on the other side. This would enable the front end circuitry
to determine the handedness of the substrate i.e. whether it is
applied to a left or right foot. The front-end circuitry may then
for example change how it provides signals to the substrate and how
it interprets signals from the substrate.
[0151] It would also be possible to add redundant and/or degenerate
contacts to create different configurations.
[0152] It is therefore possible to have a collection of flexible
substrates where each substrate is ergonomically configured to be
applied to a different body part of a subject. Each substrate may
comprise the same (or different) sensors and will have a set of
interconnects supported by the flexible substrate that connect to
the sensors. Each substrate will also have an interface comprising
a common fixed physical configuration of interface connectors
(connector contacts) for connecting the interconnects to remote
processing circuitry via the cable. An ordering of the
interconnects with respect to the common fixed physical
configuration of interface connectors is dependent upon the body
part to which a flexible substrate is to be applied. The ordering
of the interconnects with respect to the common fixed physical
configuration of interface connectors is uniquely indicative, when
the flexible substrate is in use, to the processing circuitry of
the body part to which the flexible substrate is attached.
Safety Control
[0153] Referring to FIGS. 5A, 5B and 5C, the flexible substrate 62
may have a score or partial cut 90 (kiss-cut) through close to the
designated edge connector 74. The width of the score may be across
the whole of a tab supporting the edge connector 74 or more
typically across 90% the width, leaving some of the substrate
un-scored. The scoring produces a localized structural weakness
controlled by the depth of the score, the cross section of the
substrate and the tensile strength of the substrate material.
[0154] The interconnects 80 connecting the edge connector 74 to
sensors may be formed from conductive ink, the thickness of the ink
is tightly controlled, so the cross sectional area is less in the
width of the score, but still sufficient to carry the appropriate
current.
[0155] The design of the connecting cable's distal end female edge
connector 94 includes a spring loaded retainer 92 which engages
with a notch 83 on the side of the substrate male edge connector
74, or alternatively the cable edge connector includes a spring
loaded detent pin which engages with a hole in the substrate close
to the exposed edges of the connector tab. These features are
designed into an edge connector shroud and are inaccessible by the
user. The preferred method would use a small section of Printed
Circuit Board (PCB) as a chassis, with the edge connector mounted
and soldered to the PCB with through hole pins, where a piece of
spring steel formed to act as the retaining lever is also soldered
to the PCB. The cable shroud then serves to protect and form a
substantial, rigid enclosure which can accept the force of the
retainer and force of the operator.
[0156] When the kinematic test is complete, the operator removes
the substrate 62 from the subject in the conventional way. The
sensor is removed from the subject as normal, but for the substrate
62 to be removed from the cable edge connector, the substrate must
be firmly grasped and pulled in order to overcome the spring loaded
retainer 92 located in the edger connector shroud. At this moment
the substrate section with the score will break, fracturing the
interconnects 80. The score 90 runs transversely across some or all
of the interconnects 80.
[0157] As the substrate is only partially scored, a section of the
substrate will still remain intact, holding the tab to the
remaining substrate. This prevents the substrate from breaking into
two and the edge connector tab from getting stuck in the female
edge connector.
[0158] To further facilitate this, the substrate is formed as a
laminate of two layers 81A and 81B that are folded about join 83
and adhered together (FIG. 5A). Less or no adhesive glue is applied
between the layers where the layer 81A has a score 90. In this
embodiment, the score is made only in the laminate layer 81A
supporting the interconnects. The portion of this laminate layer
81A demarcated by the score breaks away and may detach (FIG. 5C).
The retainer is however now no longer in effect, and the retained
portion may be easily removed from the female edge connector.
[0159] The other laminated layer 81B underlying the detachable
portion 87 of the laminate layer 81A may be colored 89 e.g. red.
When the portion 87 of the laminate layer 81A detaches severing the
interconnects 90, the underlying colored layer 89 is exposed. This
would indicate to the user that the substrate 62 has been used and
should be disposed.
[0160] This method of fracturing the conductive ink conductors is
far superior to the accidental, possibly intermittent, fractured
conductor produced by material fatigue reuse, since the proposed
method for producing the fractured electrical conductor is defined
and reliable. Attempting to reuse a substrate with fractured
conductors would be detected by the front end circuitry 32 when it
performs the standard self tests when initializing for a kinematic
test. For example, detecting insufficient power being consumed by
the LEDs indicates fracture in the LED conductor lines.
[0161] For additional security, a programmable component such as a
fusible link may also be incorporated as part of the conductive ink
inside the sensor, which permits a sensor to be marked as `used` by
the system after the test. The fusible link can be effected by
carefully controlling the screen printing process to deliver a
conductive ink section with a known cross sectional area for a
given maximum power dissipation. A short electrical pulse
substantially exceeding this maximum power dissipation would
controllably disrupt the fusible link, leaving it open circuit. The
fusible link would be brought out to an additional edge connector
conductor, or would be part of the existing tracking inside the
sensor.
[0162] The blocks illustrated in the Figs may represent steps in a
method and/or sections of code in the computer program. The
illustration of a particular order to the blocks does not
necessarily imply that there is a required or preferred order for
the blocks and the order and arrangement of the block may be
varied. Furthermore, it may be possible for some steps to be
omitted.
[0163] Although embodiments of the present invention have been
described in the preceding paragraphs with reference to various
examples, it should be appreciated that modifications to the
examples given can be made without departing from the scope of the
invention as claimed.
[0164] Features described in the preceding description may be used
in combinations other than the combinations explicitly
described.
[0165] Although functions have been described with reference to
certain features, those functions may be performable by other
features whether described or not.
[0166] Although features have been described with reference to
certain embodiments, those features may also be present in other
embodiments whether described or not.
[0167] Whilst endeavoring in the foregoing specification to draw
attention to those features of the invention believed to be of
particular importance it should be understood that the Applicant
claims protection in respect of any patentable feature or
combination of features hereinbefore referred to and/or shown in
the drawings whether or not particular emphasis has been placed
thereon.
* * * * *