U.S. patent application number 11/225295 was filed with the patent office on 2007-03-15 for medical sensor for reducing motion artifacts and technique for using the same.
Invention is credited to Carine Hoarau.
Application Number | 20070060808 11/225295 |
Document ID | / |
Family ID | 37667683 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070060808 |
Kind Code |
A1 |
Hoarau; Carine |
March 15, 2007 |
Medical sensor for reducing motion artifacts and technique for
using the same
Abstract
A sensor may be adapted to reduce motion artifacts by damping
the effects of outside forces and sensor motion. A sensor is
provided with a motion damping structure adapted to reduce the
effect of motion of a sensor emitter and/or detector. Further, a
method of damping outside forces and sensor motion is also
provided.
Inventors: |
Hoarau; Carine; (Lafayette,
CA) |
Correspondence
Address: |
FLETCHER YODER (TYCO INTERNATIONAL, LTD.)
P.O. BOX 692289
HOUSTON
TX
77269-2289
US
|
Family ID: |
37667683 |
Appl. No.: |
11/225295 |
Filed: |
September 12, 2005 |
Current U.S.
Class: |
600/323 |
Current CPC
Class: |
A61B 5/6838 20130101;
Y10T 29/49826 20150115; A61B 5/14552 20130101; A61B 5/6826
20130101; A61B 5/7207 20130101 |
Class at
Publication: |
600/323 |
International
Class: |
A61B 5/00 20060101
A61B005/00 |
Claims
1. A sensor comprising: a sensor body; an emitter and a detector
disposed on the sensor body; and a motion damping structure
associated with the sensor body, wherein the motion damping
structure is adapted to damp a force experienced by the sensor
body.
2. The sensor, as set forth in claim 1, wherein the sensor
comprises at least one of a pulse oximetry sensor or a sensor for
measuring a water fraction.
3. The sensor, as set forth in claim 1, wherein the emitter
comprises at least one light emitting diode.
4. The sensor, as set forth in claim 1, wherein the detector
comprises at least one photodetector.
5. The sensor, as set forth in claim 1, wherein the motion damping
structure comprises a dashpot.
6. The sensor, as set forth in claim 1, wherein the motion damping
structure comprises a foam.
7. The sensor, as set forth in claim 1, wherein the motion damping
structure comprises viscoelastic solid.
8. The sensor, as set forth in claim 1, wherein the motion damping
structure comprises a fluid.
9. The sensor, as set forth in claim 1, wherein the emitter is
disposed within a chamber comprising a fluid.
10. The sensor, as set forth in claim 1, wherein the detector is
disposed within a chamber comprising a fluid.
11. The sensor, as set forth in claim 1, wherein the motion damping
structure comprises a plurality of impact-absorbing chambers
connected by respective orifices, wherein the orifices are sized so
as to restrict the flow rate of a fluid between the plurality of
impact-absorbing chambers.
12. The sensor, as set forth in claim 1, wherein the sensor
comprises a bandage-type sensor.
13. The sensor, as set forth in claim 1, wherein the sensor
comprises a clip-type sensor.
14. 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; an emitter and a
detector disposed on the sensor body; and a motion damping
structure associated with the sensor body, wherein the motion
damping structure is adapted to damp a force experienced by the
sensor body.
15. The system, as set forth in claim 14, wherein the emitter
comprises at least one light emitting diode.
16. The system, as set forth in claim 14, wherein the detector
comprises at least one photodetector.
17. The system, as set forth in claim 14, wherein the motion
damping structure comprises a dashpot.
18. The system, as set forth in claim 14, wherein the motion
damping structure comprises a fluid.
19. The system, as set forth in claim 14, wherein the motion
damping structure comprises a foam.
20. The system, as set forth in claim 14, wherein the motion
damping structure comprises a viscoelastic solid.
21. The system, as set forth in claim 14, wherein the emitter is
disposed in a chamber comprising a fluid.
22. The system, as set forth in claim 14, wherein the detector is
disposed in a chamber comprising a fluid.
23. The system, as set forth in claim 14, wherein the motion
damping structure comprises a plurality of impact-absorbing
chambers connected by respective orifices, wherein the orifices are
sized so as to restrict the flow rate of a fluid between the
plurality of impact-absorbing chambers.
24. The system, as set forth in claim 14, wherein the sensor
comprises a bandage-type sensor.
25. The system, as set forth in claim 14, wherein the sensor
comprises a clip-type sensor.
26. A method comprising: damping a mechanical force affecting a
sensor such that an effective force experienced by at least one of
a emitter or a detector is less than the mechanical force.
27. The method, as set forth in claim 26, wherein damping the
mechanical force comprises forcing ambient air through an orifice
at a controlled rate to dissipate mechanical energy.
28. The method, as set forth in claim 26, wherein damping the
mechanical force comprises forcing a fluid through a plurality of
impact-absorbing chambers connected by respective orifices, wherein
the orifices are sized so as to restrict the flow rate of the fluid
between the plurality of impact-absorbing chambers.
29. The method, as set forth in claim 26, wherein damping the
mechanical force comprises dissipating mechanical energy through a
fluid.
30. The method, as set forth in claim 26, wherein damping the
mechanical comprises dissipating mechanical energy through a
foam.
31. The method, as set forth in claim 26, wherein damping the
mechanical force comprises dissipating mechanical energy through a
viscoelastic solid.
32. A method of manufacturing a sensor, comprising: providing a
sensor body on which an emitter and a detector are disposed; and
providing a motion damping structure disposed on the sensor
body.
33. The method, as set forth in claim 32, wherein the sensor
comprises at least one of a pulse oximetry sensor or a sensor for
measuring a water fraction.
34. The method, as set forth in claim 32, wherein providing the
emitter comprises providing one or more light emitting diodes.
35. The method, as set forth in claim 32, wherein providing the
detector comprises providing one or more photodetectors.
36. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a dashpot.
37. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a chamber comprising a
fluid.
38. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a chamber comprising a
fluid within which the emitter is disposed.
39. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a foam disposed on the
sensor body.
40. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a chamber comprising a
fluid within which the detector is disposed.
41. The method, as set forth in claim 32, wherein providing the
motion damping structure comprises providing a plurality of
impact-absorbing chambers connected by respective orifices, wherein
the orifices are sized so as to restrict the flow rate of a fluid
between the plurality of impact-absorbing chambers.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to medical devices
and, more particularly, to sensors used for sensing physiological
parameters of a patient.
[0003] 2. Description of the Related Art
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] Pulse oximetry readings depend on pulsation of blood through
the tissue. Thus, any event that interferes with the ability of the
sensor to detect that pulsation can cause variability in these
measurements. Motion artifacts occur when a patient's movements
cause interference in the signal detected by the sensor. Motion
artifacts can also occur in response to outside forces acting on
the sensor. For example, a patient may be jostled by healthcare
workers in emergency room settings. The type of force acting on a
sensor will determine the nature of the motion artifact.
[0009] Generally, sensors are vulnerable to motion artifacts when
the optical distance, or path length, between a sensor's emitter
and detector varies due to an undesired mechanical change in the
conformation of the sensor while in use. The mechanical deformation
of the sensor may be in the form of a compression of the sensor,
causing a decrease in path length. Alternately, a sensor may flex
or move in a manner that increases the distance between an emitter
and detector, resulting in an increase in path length. In any case,
variability in the optical path length due to motion can cause
motion artifacts and obscure the desired pulse oximetry signal.
SUMMARY
[0010] 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.
[0011] There is provided a sensor that includes a sensor body, and
an emitter and a detector disposed on the sensor body. The sensor
also includes a motion damping structure associated with the sensor
body, whereby the motion damping structure is adapted to damp a
force experienced by the sensor body.
[0012] 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
includes a sensor body, and an emitter and a detector disposed on
the sensor body. The sensor also includes a motion damping
structure associated with the sensor body, whereby the motion
damping structure is adapted to damp a force experienced by the
sensor body.
[0013] There is also provided a method of operating a sensor that
includes damping a mechanical force affecting a sensor such that an
effective force experienced by at least one of a emitter or a
detector is less than the mechanical force.
[0014] There is also provided a method of manufacturing a sensor
that includes providing a sensor body on which an emitter and a
detector are disposed. The method also includes providing a motion
damping structure disposed on the sensor body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Advantages of the invention may become apparent upon reading
the following detailed description and upon reference to the
drawings in which:
[0016] FIG. 1A illustrates a perspective view of an exemplary
embodiment of a clip-style pulse oximetry sensor featuring a
dashpot;
[0017] FIG. 1B illustrates a cross-sectional view of the pulse
oximetry sensor of FIG. 1A applied to a patient digit that is
pressing against an object;
[0018] FIG. 2 illustrates a cross-sectional view of an exemplary
embodiment of a bandage-style pulse oximetry sensor applied to a
patient's digit, whereby the sensor includes an impact-absorbing
chamber at one end of the sensor;
[0019] FIG. 3 illustrates a perspective view of an alternate
exemplary embodiment of a bandage-style pulse oximetry sensor with
a fluid-filled impact-absorbing chamber disposed along the body of
the sensor;
[0020] FIG. 4 illustrates a perspective view of an exemplary
embodiment of a forehead pulse oximetry sensor whereby the emitter
and detector are disposed within impact-absorbing chambers;
[0021] FIG. 5A illustrates a cross-sectional view of an exemplary
embodiment of a bandage-style pulse oximetry sensor having a series
of interconnected impact-absorbing chambers;
[0022] FIG. 5B illustrates a cross-sectional view of the pulse
oximetry sensor of FIG. 5A applied to a patient digit that is
flexed at the first finger joint;
[0023] FIG. 6A illustrates a perspective view of an embodiment of
an exemplary clip-style pulse oximetry sensor with an
impact-absorbing foam disposed on the surface that does not contact
a patient's tissue during normal use according to the present
invention;
[0024] FIG. 6B illustrates a cross-sectional view of the pulse
oximetry sensor of FIG. 6A; and
[0025] FIG. 7 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
[0026] 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.
[0027] In accordance with the present technique, sensors for pulse
oximetry or other applications utilizing spectrophotometry are
provided that reduce motion artifacts by damping the effects of
patient movement or outside forces. For example, sensors are
provided that have various motion damping mechanisms adapted to
reduce the effect of motion or outside forces on a pulse oximetry
measurement.
[0028] Motion artifacts in pulse oximetry are often generated by
the movement of the pulse oximetry sensor relative to the optically
probed tissue, which is typically caused by patient movement.
Because pulse oximetry is often used in settings where it is
difficult to prevent patient motion, it is desirable to provide a
mechanism for reducing the effects of motion on the pulse oximetry
measurement. For example, a squeezing motion by a patient may
mechanically deform a sensor, causing the sensor's emitter and
detector to change position relative to one another, resulting in a
motion artifact. The squeezing motion may be damped by converting
the mechanical energy of patient movement into thermal energy by
damping the force with an impact-absorbing fluid or solid, thus
dissipating the force and reducing mechanical deformation of the
sensor. The force of squeezing may be damped such that the
effective force experienced by the sensor's emitter and/or detector
is reduced, and the relative change in the position of the emitter
relative to the detector is also reduced. Similarly, outsides
forces, such as the mechanical force of an object pressing against
a sensor, can be damped by absorbing the force such that the
effective force experienced by the sensor components is
reduced.
[0029] Mechanical forces, including those caused by translational
and/or kinetic energy of an object, may be impeded by opposing
forces. Specifically, as a force acts on a pulse oximetry sensor,
it is opposed by the inertia of the sensor as well as the opposing
force of a damper. The amplitude of the mechanical energy of
movement is attenuated through energy lost to inertia and damping.
For example, energy may be lost to viscous damping with a fluid, or
by yielding or plastic straining of a damping material.
Additionally, some energy will be converted to thermal energy
through frictional forces.
[0030] Sensors are disclosed herein having a motion damping
mechanism to reduce the effect of motion or outside forces on the
measurements of physiological parameters, such as pulse oximetry
measurements. FIG. 1A illustrates an exemplary clip-type sensor 10A
appropriate for use on a patient's digit 12. The sensor 10A has a
dashpot 14 disposed on the sensor body 16, a cross-sectional view
of which is illustrated in FIG. 1B. A dashpot 14 is a mechanical
device used to damp motion that includes a piston 18 that moves
through a cylinder 20 containing a fluid 22. The dashpot 14 is
partially embedded in the sensor body 16 such that the piston 18
protrudes from the sensor body 16 on a surface 24 that does not
contact the sensor site of the patient's tissue during normal use.
A force applied to the piston 18, such as tapping against an object
26, causes the piston 18 to move through the fluid 22 in the
direction shown by arrow 28. As the piston 18 pushes through the
fluid 22, the mechanical energy of the force acting on the piston
18 is converted into thermal energy. The damping force is
proportional to the velocity of the piston 18 and the viscosity of
the fluid 22 through which the piston moves. Thus, the dashpot 14
damps motion caused by tapping or pressing the sensor 10A against
an object 26.
[0031] In other embodiments (not shown), the sensor 10A may have
multiple dashpots 14 disposed on the sensor body 16 on the surface
24 that does not contact the sensor site of the patient's tissue
during normal use. It may be advantageous to provide motion damping
mechanisms on multiple sides of the sensor 10A, as it is difficult
to predict the types of motion that the sensor 10A may experience.
For example, dashpots 14 may be distributed on the sensor body 16
in locations directly opposing each other across the digit 12.
Further, it should be understood that a dashpot 14 according to the
present technique may be adapted to damp forces applied at various
angles. The piston 18 may be adapted move through the fluid 22 at
an angle that corresponds to the angle with which the force was
applied.
[0032] In certain embodiments, a fluid may used to damp mechanical
energy by other techniques. For reasons related to total sensor
weight, it may be desirable to employ a lightweight motion damping
device in conjunction with disposable sensors. For example, FIG. 2
illustrates a bandage-type sensor 10B applied to a patient digit
30. The sensor 10B has an impact-absorbing chamber 32 that contains
a fluid 34. As depicted, the impact-absorbing chamber 32 is
disposed on the sensor 10B such that it correlates with the
fingertip region of the digit 30. The fluid 34 in the
impact-absorbing chamber 32 damps energy caused by pressing or
tapping a fingertip against an object. The impact-absorbing chamber
32 is flexible and not completely filled with fluid, and is thus
compressible in response to an applied force. The mechanical energy
of the pressing or tapping is damped through conversion to thermal
energy and/or absorbed by the physical deformation of the fluid in
an amount proportional to the force applied. Thus, the motion is
damped and the effective force experienced by the emitter 36 and
the detector 38 is reduced as a consequence.
[0033] In another embodiment, as shown in FIG. 3, an
impact-absorbing chamber 42 may be disposed on a sensor 10C such
that the impact-absorbing chamber 42 covers the surface 40 of the
sensor body 44 that does not contact the tissue during normal use.
The fluid 46 in the impact-absorbing chamber 42 will physically
impede a finger squeezing motion as well as damp the mechanical
energy associated with the motion. As the energy of squeezing is
absorbed by the fluid 46, the sensor 10C remains substantially
stable. As a consequence, the emitter 48 and the detector 50 also
remain substantially unaffected by the motion.
[0034] It is also contemplated that a fluid may damp mechanical
energy to reduce its direct action on an emitter 52 or a detector
54. FIG. 4 illustrates a reflectance-type sensor 10D adapted for
use on a patient's forehead. The sensor 10D has impact-absorbing
chambers 56 and 58 containing a fluid 60. The impact-absorbing
chambers 56 and 58 enclose an emitter 52 and a detector 54,
respectively. The emitter 52 and the detector 54 are surrounded by
the fluid 60, which absorbs outside forces, thereby reducing the
transmission of outside forces to the emitter 52 and the detector
54. The impact-absorbing chambers 56 and 58 also protect the
emitter 52 and the detector 54 from damage during the period of use
of the sensor 10D. Such an arrangement may be advantageous in
outpatient situations in which it is contemplated that a patient
may be ambulatory, and the sensor 10C may be subject to
higher-than-normal outside forces.
[0035] In another embodiment, FIG. 5A illustrates an exemplary
bandage-style sensor 10E adapted for use on a digit 62. The sensor
10E has a plurality of impact-absorbing chambers 64 connected by
respective orifices 66, wherein the orifices 66 are sized so as to
restrict the flow rate of a fluid 68 between the impact-absorbing
chambers 64. As shown in FIG. 5B, as the digit 62 moves in a
squeezing motion, the fluid 68 passes through the orifices 66 and
is redistributed through the impact-absorbing chambers 64 in
response to the movement. The impact-absorbing chambers 64 are
partially full of the fluid 68. The redistribution of the fluid 68
serves to damp the energy generated by the digit 62 moving in
space. Specifically, the force of the digit 62 movement is opposed
by the force required to push the fluid 68 through the orifices 66.
The damped force experienced by the sensor 10E is thus reduced by
roughly the amount of the opposing force provided by the damping
mechanism.
[0036] The fluid (e.g. fluid 22, fluid 34, fluid 46, fluid 60, or
fluid 68) described in the above embodiments may be any suitable
fluid with the appropriate rheological properties for damping
mechanical energy, such as a viscoelastic fluid or gel. In certain
embodiments, the fluid may be air or other gases and gas mixtures.
In other embodiments, the fluid may be an oil or liquid, such as
mineral oil. Other examples of suitable fluids include, but are not
limited to, polyethylene glycol, liquid silicone,
magnetorheological fluids, and polyurethane polymer gels. It is
contemplated that the fluid may be a mixture of liquid and gas. In
certain embodiments, it may be desirable employ a gas or gas
mixture for reasons related to cost, manufacturing convenience, and
total sensor weight. In situations where a sensor may be exposed to
more extreme outside forces, it may be desirable to employ a
viscoelastic oil, as oils generally provide more efficient damping
than gases.
[0037] In certain embodiments, impact-absorbing solids and/or foams
with viscoelastic properties may be appropriate for mechanical
damping of motion to reduce motion artifacts in a pulse oximetry
sensor. For example, a clip-style sensor 10F is illustrated in FIG.
6A that has an impact-absorbing foam 70 disposed over a
non-tissue-contacting surface 72 of the sensor body 74. FIG. 6B is
a cross-sectional view of the sensor 10F. The impact-absorbing foam
70 dissipates the effect of an outside force on the sensor 10F. In
another embodiment (not shown), the impact absorbing foam 70 is
disposed on the tissue-contacting surface of the sensor 10F.
Impact-absorbing solids and foams according to the present
invention include, but are not limited to, neoprene, silicone,
rubber, Sorbothane.RTM. (available from Sorbothane, Incorporated),
and ISODAMP.RTM. SD or CONFOR.RTM. foams (available from E-A-R
Specialty Composites).
[0038] A sensor, illustrated generically as a sensor 10, may be
used in conjunction with a pulse oximetry monitor 76, as
illustrated in FIG. 7. It should be appreciated that the cable 78
of the sensor 10 may be coupled to the monitor 76 or it may be
coupled to a transmission device (not shown) to facilitate wireless
transmission between the sensor 10 and the monitor 76. The monitor
76 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 76 to provide additional
functions, the monitor 76 may be coupled to a multi-parameter
patient monitor 80 via a cable 82 connected to a sensor input port
or via a cable 84 connected to a digital communication port.
[0039] The sensor 10 includes an emitter 86 and a detector 88 that
may be of any suitable type. For example, the emitter 86 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
88 may be a photodetector selected to receive light in the range or
ranges emitted from the emitter 86. 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.
[0040] The emitter 86 and the detector 88 may be disposed on a
sensor body 90, which may be made of any suitable material, such as
plastic, foam, woven material, or paper. Alternatively, the emitter
86 and the detector 88 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 78 that is
responsible for transmitting electrical and/or optical signals to
and from the emitter 86 and detector 88 of the sensor 10. The cable
78 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.
[0041] The sensor 10 may be a "transmission type" sensor.
Transmission type sensors include an emitter 86 and detector 88
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 86
and detector 88 lie on either side of the patient's nail bed. In
other words, the sensor 10 is positioned so that the emitter 86 is
located on the patient's fingernail and the detector 88 is located
180.degree. opposite the emitter 86 on the patient's finger pad.
During operation, the emitter 86 shines one or more wavelengths of
light through the patient's fingertip and the light received by the
detector 88 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 86 and the detector 88 may be exchanged. For example, the
detector 88 may be located at the top of the finger and the emitter
86 may be located underneath the finger. In either arrangement, the
sensor 10 will perform in substantially the same manner.
[0042] Reflectance type sensors generally operate under the same
general principles as transmittance type sensors. However,
reflectance type sensors include an emitter 86 and detector 88 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 86 and detector 88 lie
side-by-side. Reflectance type sensors detect light photons that
are scattered back to the detector 88.
[0043] 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. For example, using the same, different, or additional
wavelengths, the present techniques may be utilized for the
measurement and/or analysis of carboxyhemoglobin, met-hemoglobin,
total hemoglobin, intravascular dyes, and/or water content. 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.
* * * * *