U.S. patent application number 13/868794 was filed with the patent office on 2013-11-14 for clip-style medical sensor and technique for using the same.
The applicant listed for this patent is Covidien LP. Invention is credited to Rodney P. Chen.
Application Number | 20130303864 13/868794 |
Document ID | / |
Family ID | 38662022 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130303864 |
Kind Code |
A1 |
Chen; Rodney P. |
November 14, 2013 |
CLIP-STYLE MEDICAL SENSOR AND TECHNIQUE FOR USING THE SAME
Abstract
A clip-style pulse sensor may be adapted to apply limited, even
pressure to a patient's tissue. A clip-style sensor is provided
that reduces motion artifacts by exerting limited, uniform pressure
to the patient tissue to reduce tissue exsanguination. Further,
such a sensor provides a secure fit while avoiding discomfort for
the wearer.
Inventors: |
Chen; Rodney P.; (Carson
City, NV) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Covidien LP; |
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|
US |
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|
Family ID: |
38662022 |
Appl. No.: |
13/868794 |
Filed: |
April 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13290957 |
Nov 7, 2011 |
8437826 |
|
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13868794 |
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11415717 |
May 2, 2006 |
8073518 |
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13290957 |
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Current U.S.
Class: |
600/306 ;
600/340 |
Current CPC
Class: |
A61B 5/443 20130101;
A61B 5/6838 20130101; A61B 5/6819 20130101; A61B 2090/034 20160201;
A61B 5/14552 20130101; A61B 5/6816 20130101; A61B 5/6826
20130101 |
Class at
Publication: |
600/306 ;
600/340 |
International
Class: |
A61B 5/1455 20060101
A61B005/1455; A61B 5/00 20060101 A61B005/00 |
Claims
1. A sensor adapted to be applied to a patient's tissue comprising:
a sensor body having a first portion and a second portion biased
towards one another; a first substrate disposed on the first
portion; a second substrate disposed on the second portion, wherein
the first substrate and the second substrate are each configured to
tilt relative to the sensor body; and at least one sensing element
disposed on at least one of the first substrate or the second
substrate.
2. The sensor, as set forth in claim 1, wherein the first substrate
and the second substrate are adapted to pivot on respective
pins.
3. The sensor, as set forth in claim 1, wherein the first substrate
is connected to the first portion by a hinge.
4. The sensor, as set forth in claim 1, wherein the sensor is
adapted to apply a spring force to the patient's tissue adapted to
overcome a blood pressure of about 35 mm Hg or less.
5. The sensor, as set forth in claim 1, further comprising a
resilient material disposed on at least one of the first portion or
the second portion.
6. The sensor, as set forth in claim 6, wherein the resilient
material is disposed on one or both of the first substrate or the
second substrate.
7. The sensor, as set forth in claim 6, wherein the resilient
material comprises a foam.
8. The sensor, as set forth in claim 1, comprising an adhesive
material disposed on at least one of the first substrate or the
second substrate.
9. The sensor, as set forth in claim 1, wherein the sensing element
comprises an emitter and a detector.
10. The sensor, as set forth in claim 9, wherein the emitter
comprises a light-emitting diode and the detector comprises a
photodetector.
11. The sensor, as set forth in claim 9, wherein the emitter is
disposed on the first portion and the detector is disposed on the
second portion such that the emitter and the detector are not
opposite each other.
12. The sensor, as set forth in claim 1, wherein the sensor
comprises at least one of a pulse oximetry sensor, a sensor for
measuring a water fraction, or a combination thereof.
13. The sensor, as set forth in claim 1, comprising at least one
integrated circuit device.
14. The sensor, as set forth in claim 1, comprising a cable
comprising one or more integrated circuits.
15. A pulse oximetry system comprising: a pulse oximetry monitor;
and a pulse oximetry sensor adapted to be operatively coupled to
the monitor, the sensor comprising: a sensor body having a first
portion and a second portion biased towards one another; a first
substrate disposed on the first portion; a second substrate
disposed on the second portion, wherein the first substrate and the
second substrate are each configured to tilt relative to the sensor
body; and at least one sensing element disposed on at least one of
the first substrate or the second substrate.
16. The pulse oximetry system, as set forth in claim 15, wherein
the sensing element comprises an emitter and wherein a detector is
disposed on the second portion.
17. The pulse oximetry system, as set forth in claim 16, wherein
detector is disposed on the second portion such that the emitter
and the detector are not opposite each other.
18. The pulse oximetry system, as set forth in claim 15, wherein
the sensor is configured to be applied to an ear.
19. The pulse oximetry system, as set forth in claim 15, wherein
the sensor is configured to be applied to a finger.
20. The pulse oximetry system, as set forth in claim 15, wherein
the sensor comprises a spring that biases the first portion and the
second portion towards one another.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/290,957, filed Nov. 7, 2011, which is a
continuation of U.S. patent application No. Ser. 11/415,717, now
U.S. Pat. No. 8,073,518, filed May 2, 2006, the specifications of
which are incorporated by reference in their entireties herein for
all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to medical devices
and, more particularly, to sensors used for sensing physiological
parameters of a patient.
[0004] 2. Description of the Related Art
[0005] This section is intended to introduce the reader to various
aspects of art that may be related to various aspects of the
present invention which are described and/or claimed below. This
discussion is believed to be helpful in providing the reader with
background information to facilitate a better understanding of the
various aspects of the present invention. Accordingly, it should be
understood that these statements are to be read in this light, and
not as admissions of prior art.
[0006] In the field of medicine, doctors often desire to monitor
certain physiological characteristics of their patients.
Accordingly, a wide variety of devices have been developed for
monitoring many such physiological characteristics. Such devices
provide doctors and other healthcare personnel with the information
they need to provide the best possible healthcare for their
patients. As a result, such monitoring devices have become an
indispensable part of modern medicine.
[0007] One technique for monitoring certain physiological
characteristics of a patient is commonly referred to as pulse
oximetry, and the devices built based upon pulse oximetry
techniques are commonly referred to as pulse oximeters. Pulse
oximetry may be used to measure various blood flow characteristics,
such as the blood-oxygen saturation of hemoglobin in arterial
blood, the volume of individual blood pulsations supplying the
tissue, and/or the rate of blood pulsations corresponding to each
heartbeat of a patient. In fact, the "pulse" in pulse oximetry
refers to the time varying amount of arterial blood in the tissue
during each cardiac cycle.
[0008] Pulse oximeters typically utilize a non-invasive sensor that
transmits light through a patient's tissue and that
photoelectrically detects the absorption and/or scattering of the
transmitted light in such tissue. One or more of the above
physiological characteristics may then be calculated based upon the
amount of light absorbed or scattered. More specifically, the light
passed through the tissue is typically selected to be of one or
more wavelengths that may be absorbed or scattered by the blood in
an amount correlative to the amount of the blood constituent
present in the blood. The amount of light absorbed and/or scattered
may then be used to estimate the amount of blood constituent in the
tissue using various algorithms.
[0009] Conventional pulse oximetry sensors are either disposable or
reusable. In many instances, it may be desirable to employ, for
cost and/or convenience, a reusable pulse oximeter sensor. Reusable
sensors are typically semi-rigid or rigid devices that may be
clipped to a patient. Unfortunately, reusable sensors may be
uncomfortable for the patient for various reasons. For example,
sensors may have angled or protruding surfaces that, over time, may
cause discomfort. In addition, reusable pulse oximeter sensors may
pose other problems during use. For example, lack of a secure fit
may allow light from the environment to reach the photodetecting
elements of the sensor, thus causing inaccuracies in the resulting
measurement.
[0010] Because pulse oximetry readings depend on pulsation of blood
through the tissue, any event that interferes with the ability of
the sensor to detect that pulsation can cause variability in these
measurements. A reusable sensor should fit snugly enough that
incidental patient motion will not dislodge or move the sensor, yet
not so tight that normal blood flow to the tissue is disrupted. As
sensors are worn for several hours at a time, an overly tight fit
may cause local exsanguination of the tissue around the sensor.
Exsanguinated tissue, which is devoid of blood, shunts the sensor
light through the tissue, resulting in increased measurement
errors.
SUMMARY
[0011] Certain aspects commensurate in scope with the originally
claimed invention are set forth below. It should be understood that
these aspects are presented merely to provide the reader with a
brief summary of certain forms that the invention might take and
that these aspects are not intended to limit the scope of the
invention. Indeed, the invention may encompass a variety of aspects
that may not be set forth below.
[0012] There is provided a sensor that includes: a sensor body
having a first portion and a second portion; a spring adapted to
bias the first portion towards the second portion; a stopping
element adapted to establish a minimum distance between the first
portion and the second portion; and at least one sensing element
disposed on the sensor body.
[0013] There is provided a sensor that includes: a sensor body
having a first portion, a second portion; a spring adapted to bias
the first portion towards the second; a substrate disposed on at
least one of the first portion or the second portion, wherein the
substrate is adapted to move with at least one degree of freedom
relative to the sensor body; and at least one sensing element
disposed on the substrate.
[0014] There is also provided a pulse oximetry system that
includes: a pulse oximetry monitor and a pulse oximetry sensor
adapted to be operatively coupled to the monitor, the sensor
comprising: a sensor body having a first portion and a second
portion; a spring adapted to bias the first portion towards the
second portion; a stopping element adapted to establish a minimum
distance between the first portion and the second portion; and at
least one sensing element disposed on the sensor body.
[0015] There is also provided a method of operating a sensor that
includes: biasing a first portion and a second portion of a sensor
body towards one another with a spring; and establishing a minimum
distance between the first portion and the second portion with a
stopper disposed on the sensor body.
[0016] There is also provided a method of manufacturing a sensor
that includes: providing a sensor body having a first portion and a
second portion; providing a spring adapted to bias the first
portion towards the second portion; providing a stopping element
adapted to establish a minimum distance between the first portion
and the second portion; and providing at least one sensing element
disposed on the sensor body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Advantages of the invention may become apparent upon reading
the following detailed description and upon reference to the
drawings in which:
[0018] FIG. 1A illustrates a perspective view of an exemplary
sensor with a stopper and a flat spring according to the present
invention;
[0019] FIG. 1B illustrates the sensor of FIG. 1A applied to a
patient earlobe according to the present invention;
[0020] FIG. 2A illustrates a perspective view of an exemplary
sensor with a rigid bar according to the present invention;
[0021] FIG. 2B illustrates a cross-sectional view of the open
sensor of FIG. 2A;
[0022] FIG. 2C illustrates a cross-sectional view of the sensor of
FIG. 2A applied to a patient's earlobe;
[0023] FIG. 2D illustrates a view of an exemplary sensor with an
adjustable bar according to the present invention;
[0024] FIG. 3A illustrates a cross-sectional view of an open
exemplary sensor with a stopper within a hinge according to the
present invention;
[0025] FIG. 3B illustrates a cross-sectional view of the sensor of
FIG. 3A applied to a patient's earlobe;
[0026] FIG. 4A illustrates a cross sectional view of an exemplary
sensor with a strap according to the present invention;
[0027] FIG. 4B illustrates a cross-sectional view of the sensor of
FIG. 4A applied to a patient's earlobe;
[0028] FIG. 4C illustrates a view of an alternative embodiment of
the sensor of FIG. 4A;
[0029] FIG. 4D illustrates a view of an alternative embodiment of
the sensor of FIG. 4A with an offset emitter and detector;
[0030] FIG. 5A illustrates a cross sectional view of an exemplary
sensor with pivoting heads according to the present invention.
[0031] FIG. 5B illustrates a cross-sectional view of the sensor of
FIG. 5A applied to a patient's earlobe; and
[0032] FIG. 6 illustrates a pulse oximetry system coupled to a
multi-parameter patient monitor and a sensor according to
embodiments of the present invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0033] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, not all features of an actual
implementation are described in the specification. It should be
appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0034] In accordance with the present technique, motion-resistant
pulse oximetry sensors are provided that reduce measurement error
by applying limited and uniform pressure to the optically probed
tissue. A clip-style sensor for pulse oximetry or other
spectrophotometric uses is provided that has a compliant material
disposed on the sensor to distribute the spring force of the clip
to the tissue evenly when the sensor is applied to a patient. The
clip-style sensor may also have a stopper that prevents the two
portions of the clip from applying an excess of pressure to the
patient's tissue. Alternatively, the clip-style sensor may allow
the light emitting and detecting components of the sensor to tilt
or otherwise move to accommodate the patient's tissue and to
prevent overly tight gripping at the sensor placement site.
[0035] Pulse oximetry sensors are typically placed on a patient in
a location that is normally perfused with arterial blood to
facilitate measurement of the desired blood characteristics, such
as arterial oxygen saturation measurement (SpO.sub.2). The most
common sensor sites include a patient's fingertips, toes, earlobes,
or forehead, and clip-style sensors are most commonly used on
patient digits, earlobes, or nose bridges. Regardless of the
placement of the sensor 10, the reliability of the pulse oximetry
measurement is related to the accurate detection of transmitted
light that has passed through the perfused tissue. Hence, a sensor
10 that fits a patient securely may reduce movement of the sensor
and/or infiltration of light from outside sources into the sensor,
which may lead to more accurate pulse oximetry measurements.
[0036] There are several factors that may influence the tightness
with which a sensor may grip a patient's tissue. It is desirable to
affix the sensor 10 to the patient in a manner that does not
exsanguinate the tissue, but that provides sufficient pressure to
squeeze out excess venous blood. Excess venous blood congestion in
the optically probed tissue may influence the relationship between
the modulation ratio of the time-varying light transmission signals
of the wavelengths transmitted and SpO.sub.2. As venous blood has
an increased concentration of deoxyhemoglobin as compared to
arterial blood, its contribution to the pulse oximetry measurement
may shift the wavelength of the detected light. Thus, the pulse
oximetry sensor may measure a mixed arterial-venous oxygen
saturation and detect differences in signal modulations unrelated
to the underlying SpO.sub.2 level. It is therefore desirable to
reduce the contribution of excess venous blood to the pulse
oximetry measurement by clipping a sensor to a patient's tissue
with enough spring force to squeeze out excess venous blood.
[0037] On the other hand, a patient's tissue may suffer if clipped
too tightly by a pulse oximetry sensor. In addition to causing
patient discomfort, a sensor with excess gripping force in a hinge
spring or other closing mechanism may squeeze both arterial and
venous blood from a patient's tissue, causing the tissue to become
exsanguinated. Light from a sensor's emitter that passes through
such exsanguinated tissue may not be modulated by arterial blood,
which may cause the resulting SpO.sub.2 measurements to be
artificially low. Thus, it is desirable to clip a sensor 10 to a
patient's tissue tightly enough to reduce the amount of venous
blood congestion, but not so tightly as to interfere with arterial
blood perfusion.
[0038] In accordance with the present techniques, examples of
clip-style sensors that apply limited, uniform pressure to a
patient's tissue are disclosed. An exemplary sensor 10A adapted for
use on a patient's earlobe is illustrated in FIG. 1A. The sensor
has a first portion 12 and a second portion 14 that are applied to
opposite sides of an earlobe. The sensor body 16 includes a flat
spring 18 that may be used to connect the first portion 12 and the
second portion 14. The first portion 12 and the second portion 14
may have a rigid outer layer 20.
[0039] The sensor 10A may also include a stopper 22 that limits the
distance that the first portion 12 and the second portion 14 may
move towards one another. Generally, it is envisioned that the
stopper 22 be configured to allow the first portion 12 to move
towards the second portion 14 such that they are not able to move
past a minimum distance from one another that permits the sensor
10A to securely grip a patient's tissue. Such a minimum distance
may generally be determined by the desired sensor placement site
(e.g. nose, earlobe, or digit) and the size of the patient (e.g.
child or adult). As the sensor 10A is applied to the patient's
earlobe 24, the stopper 22 absorbs part of the spring force of the
flat spring 18 to prevent the sensor 10A from gripping the tissue
so tightly as to cause exsanguinations or discomfort. The stopper
22 may be permanently attached to the sensor body 16, or may be
removable.
[0040] In an alternate embodiment, FIG. 2A depicts a perspective
side view of a sensor 10B with a permanently attached rigid bar 30
acting as a stopper between a first portion 32 and a second portion
34 of a sensor body 36. An emitter 26 is disposed on the first
portion 32 and a detector 26 is disposed on the second portion 34.
The rigid bar 30 is permanently attached to the first portion 32
and moves away from the second portion 34 during the opening of the
sensor 10B, as shown in the cross-sectional view of the open sensor
10B in FIG. 2B. However, it should be understood that the rigid bar
30 may alternatively be disposed on the second portion 34 in other
embodiments. The rigid bar 30 as depicted is disposed on the first
portion 32 of the sensor 10B in a region of the sensor body 36 that
is free of intervening tissue when the sensor 10B is applied an
earlobe 38, as shown in FIG. 2C. As the sensor 10B is closed, the
rigid bar 30 contacts the second portion 34 and prevents further
biasing of the first portion 32 towards the second portion 34. The
first portion 32 and the second portion 34 may be connected by a
hinge 40 with a spring 42. Thus, the rigid bar 30 restricts the
range of motion of the hinge 40, such that the hinge 40 may only
move the first portion 32 and the second portion 34 toward one
another to a certain degree. Thus, the maximum spring force applied
to the tissue is limited because the rigid bar 30 limits the force
that the first portion 32 and the second portion 34 may exert
against the earlobe 38.
[0041] When the sensor 10B is applied to the patient's earlobe 38,
as shown in FIG. 2C, a resilient pad 44 absorbs part of the force
of the spring 42 and distributes the remaining spring force to the
earlobe 38 along the tissue-contacting surface of the sensor 10B.
Thus, the total compression resistance of the resilient material is
generally less than the force of the spring 42. The resilient pad
may be any shock-absorbing material, including foam, silicone, or
rubber. The sensor 10B thereby evenly distributes a limited force
to the patient's tissue through use of a resilient pad 44, which
spreads the force along the tissue-contacting surface.
[0042] In an alternate embodiment, depicted in FIG. 2D, the sensor
10B may include an adjustable bar 31 that may be threaded through
an opening (not shown) in the sensor body 36. Thus, the length of
the adjustable bar 31 may be increased by threading more length of
the adjustable bar 31 through the sensor body 36. In such an
embodiment, the minimum distance between the first portion 32 and
the second portion 34 may be increased to accommodate the tissue of
larger patients. Alternatively, smaller patients may require
adjustment of the adjustable bar 31 such that more of the
adjustable bar is threaded outside the sensor body 36 (i.e. not in
the region between the first portion 32 and the second portion 34).
Additionally, the sensor 10B may be applied to the patient, and a
healthcare worker may adjust the length of the adjustable bar 31
until a desired amount of pressure on the tissue is achieved. In
certain embodiments, the adjustable bar may be further secured by a
nut 33 or other holding mechanism.
[0043] It is also envisioned that spring force of a hinge may be
restricted by other mechanical structures. For example, in an
alternative embodiment shown in FIG. 3A and FIG. 3B, a sensor 10C
has a stopper 46 that is disposed within the mechanism of a hinge
48 to restrict rotational motion, thus preventing the hinge 48 from
exerting maximum pressure to the tissue when sensor 10C is applied
to a patient's earlobe 58. The stopper 46 may be a rigid material
that is designed to mechanically block the motion of the hinge
48.
[0044] As depicted, the emitter 50 and the detector 52 are disposed
on a thin substrate 54. The substrate 54 may be any suitable
material, including plastic or woven cloth, and may be rigid or
flexible. The substrate 54 may be disposed on the tissue-contacting
side of a resilient pad 56. In certain embodiments, it may be
advantageous to employ a flexible substrate 54, which may conform
more closely to a patient's tissue when the sensor 10C is applied.
In other embodiments, a more rigid substrate 54 may absorb more of
the spring force of the hinge 48, and thus may prevent the sensor
10C from exerting excess pressure on the tissue.
[0045] Alternatively, as shown by the embodiment illustrated in
FIGS. 4A-D, a sensor 10D may have a flexible but inelastic strap
60, such as a plastic or metal strap, disposed on the handle end 62
of the sensor body, connecting the first portion 64 and the second
portion 66. When the sensor 10D is open, the strap 60 is slack.
When the sensor 10D is closed, such as when the sensor 10D is
applied to a patient, as shown in FIG. 4B, the strap 60 is drawn
taut, thus preventing the hinge 68 from moving the first portion 64
and the second portion 66 closer than a distance dictated by the
length of the strap 60.
[0046] As depicted, the sensor 10D has resilient pads 70 disposed
on the tissue-contacting sides of the first portion 64 and the
second portion 66 of a sensor. The use of a resilient pad 70 on
both the first portion 64 and the second portion 66 provides
greater compression resistance against the spring force of the
hinge 68 than only a single resilient pad. Additionally, the spring
force is evenly distributed along the tissue-contacting surface
that holds both the emitter 72 and the detector 74 against the
tissue. Thus, a sensor 10D may be used in conjunction with a
relatively strong spring. This may be advantageous in situations in
which an ambulatory patient may require the sensor 10D to fit
securely enough to withstand dislodgement in response to everyday
activity.
[0047] In an alternate embodiment, FIG. 4C illustrates a sensor 10D
with an adjustable strap 61. The adjustable strap 61 may be
threaded through an opening (not shown) in the sensor body. When an
appropriate length of the adjustable strap is disposed between the
first portion 64 and the second portion 66 to provide the desired
pressure on a patient's tissue, the adjustable strap 61 may be held
in place by a clamp 63. As more length of the adjustable strap 61
is released into the region between the first portion 64 and the
second portion 66, the sensor 10D is able to close more tightly
over the tissue. Alternatively, a healthcare worker may pull the
adjustable strap 61 through the sensor body such that the length of
adjustable strap 61 between the first portion 64 and the second
portion 66 is decreased, and as a result the sensor 10D would exert
less pressure on the tissue.
[0048] Clip-style sensors as provided herein are often used on a
patient's earlobes, which may have fewer vascular structures as
compared to a digit. To maximize the transmission of light through
well-perfused capillary structures, an alternative embodiment of
the sensor 10D is depicted in which the emitter 72 and detector 74
are offset from each other, so that they are not directly opposite.
This causes the light emitted by the emitter 72 to pass through
more blood-perfused tissue to reach the detector 74. As such, the
light has a greater opportunity to be modulated by arterial blood
in a manner which relates to a blood constituent. FIG. 4D
illustrates that the configuration of the sensor 10D provides a
longer light transmission path through the tissue, as indicated by
arrow 75.
[0049] FIG. 5A and FIG. 5B depict an embodiment of a sensor 10E in
which part of the spring force of a hinge 76 is absorbed by
pivoting heads 78, upon which an emitter 80 and a detector 82 are
disposed. The pivoting heads 78 are disposed on a first portion 84
and a second portion 86 of the sensor 10E. The first portion 84 and
the second portion 86 are connected by the hinge 76. Pivoting heads
are disposed on the tissue-contacting side of the first portion 84
and the second portion 86. As FIG. 5B illustrates, the pivoting
heads 78 may tilt relative to the sensor body 88 in order to
accommodate the contours of the patient's tissue. In certain
embodiments, the pivoting heads 78 may also include resilient pads
(not shown) that distribute the spring force of the hinge 76 along
the tissue-contacting surface of the sensor 10E. In other
embodiments, the sensor 10E may also include a stopper or stopping
mechanism as described herein.
[0050] In an alternate embodiment (not shown), an adhesive material
is applied to the tissue-contacting surface of the sensor 10 to
enhance the securing of the sensor 10 to the tissue. The use of an
adhesive material may improve the contact of the sensor to the
appendage, and limit the susceptibility to motion artifacts. In
addition, the likelihood of a gap between the sensor body and the
skin is avoided.
[0051] In certain embodiments, it is contemplated that the spring
force of the hinge (e.g. 40, 48, 68, or 78) or other closing
mechanism, such as a flat spring (e.g. flat spring 18), has
sufficient pressure so that it exceeds the typical venous pressure
of a patient, but does not exceed the diastolic arterial pressure.
A sensor 10 that applies a pressure greater than the venous
pressure will squeeze excess venous blood from the optically probed
tissue, thus enhancing the sensitivity of the sensor to variations
in the arterial blood signal. Since the pressure applied by the
sensor is designed to be less than the arterial pressure, the
application of pressure to the tissue does not interfere with the
arterial pulse signal. Typical venous pressure, diastolic arterial
pressure and systolic arterial pressure are less than 10-35 mmHg,
80 mmHg, and 120 mmHg, respectively. These pressures may vary
because of the location of the vascular bed and the patient's
condition. In certain embodiments, the sensor may be adjusted to
overcome an average pressure of 15-30 mmHg. In other embodiments,
low arterial diastolic blood pressure (about 30 mmHg) may occur in
sick patients. In such embodiments, the sensor 10 may remove most
of the venous pooling with light to moderate pressure (to overcome
about 15 mmHg). It is contemplated that removing venous blood
contribution without arterial blood exsanguination may improve the
arterial pulse signal.
[0052] The exemplary sensors described above, illustrated
generically as a sensor 10, may be used in conjunction with a pulse
oximetry monitor 90, as illustrated in FIG. 6. It should be
appreciated that the cable 92 of the sensor 10 may be coupled to
the monitor 90 or it may be coupled to a transmission device (not
shown) to facilitate wireless transmission between the sensor 10
and the monitor 90. The monitor 90 may be any suitable pulse
oximeter, such as those available from Nellcor Puritan Bennett Inc.
Furthermore, to upgrade conventional pulse oximetry provided by the
monitor 90 to provide additional functions, the monitor 90 may be
coupled to a multi-parameter patient monitor 94 via a cable 96
connected to a sensor input port or via a cable 98 connected to a
digital communication port.
[0053] The sensor 10 includes an emitter 100 and a detector 102
that may be of any suitable type. For example, the emitter 100 may
be one or more light emitting diodes adapted to transmit one or
more wavelengths of light in the red to infrared range, and the
detector 102 may be a photodetector selected to receive light in
the range or ranges emitted from the emitter 100. For pulse
oximetry applications using either transmission or reflectance type
sensors, the oxygen saturation of the patient's arterial blood may
be determined using two or more wavelengths of light, most commonly
red and near infrared wavelengths. Similarly, in other
applications, a tissue water fraction (or other body fluid related
metric) or a concentration of one or more biochemical components in
an aqueous environment may be measured using two or more
wavelengths of light, most commonly near infrared wavelengths
between about 1,000 nm to about 2,500 nm. It should be understood
that, as used herein, the term "light" may refer to one or more of
infrared, visible, ultraviolet, or even X-ray electromagnetic
radiation, and may also include any wavelength within the infrared,
visible, ultraviolet, or X-ray spectra.
[0054] The emitter 100 and the detector 102 may be disposed on a
sensor body 104, which may be made of any suitable material, such
as plastic, foam, woven material, or paper. Alternatively, the
emitter 100 and the detector 102 may be remotely located and
optically coupled to the sensor 10 using optical fibers. In the
depicted embodiments, the sensor 10 is coupled to a cable 92 that
is responsible for transmitting electrical and/or optical signals
to and from the emitter 100 and detector 102 of the sensor 10. The
cable 92 may be permanently coupled to the sensor 10, or it may be
removably coupled to the sensor 10--the latter alternative being
more useful and cost efficient in situations where the sensor 10 is
disposable.
[0055] The sensor 10 may be a "transmission type" sensor.
Transmission type sensors include an emitter 100 and detector 102
that are typically placed on opposing sides of the sensor site. If
the sensor site is a fingertip, for example, the sensor 10 is
positioned over the patient's fingertip such that the emitter 100
and detector 102 lie on either side of the patient's nail bed. In
other words, the sensor 10 is positioned so that the emitter 100 is
located on the patient's fingernail and the detector 102 is located
180.degree. opposite the emitter 100 on the patient's finger pad.
During operation, the emitter 100 shines one or more wavelengths of
light through the patient's fingertip and the light received by the
detector 102 is processed to determine various physiological
characteristics of the patient. In each of the embodiments
discussed herein, it should be understood that the locations of the
emitter 100 and the detector 102 may be exchanged. For example, the
detector 102 may be located at the top of the finger and the
emitter 100 may be located underneath the finger. In either
arrangement, the sensor 10 will perform in substantially the same
manner.
[0056] Reflectance type sensors generally operate under the same
general principles as transmittance type sensors. However,
reflectance type sensors include an emitter 100 and detector 102
that are typically placed on the same side of the sensor site. For
example, a reflectance type sensor may be placed on a patient's
fingertip or forehead such that the emitter 100 and detector 102
lie side-by-side. Reflectance type sensors detect light photons
that are scattered back to the detector 102.
[0057] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Indeed, the present techniques may not only be applied to
measurements of blood oxygen saturation, but these techniques may
also be utilized for the measurement and/or analysis of other blood
constituents using principles of pulse oximetry. Rather, the
invention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the following appended claims.
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