U.S. patent application number 14/010149 was filed with the patent office on 2013-12-26 for shrouded sensor clip assembly and blood chamber for an optical blood monitoring system.
The applicant listed for this patent is Fresenius Medical Care Holding, Inc.. Invention is credited to Louis L. Barrett, Perry M. Law.
Application Number | 20130345529 14/010149 |
Document ID | / |
Family ID | 46719474 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130345529 |
Kind Code |
A1 |
Barrett; Louis L. ; et
al. |
December 26, 2013 |
SHROUDED SENSOR CLIP ASSEMBLY AND BLOOD CHAMBER FOR AN OPTICAL
BLOOD MONITORING SYSTEM
Abstract
An optical blood monitoring system includes a sensor clip
assembly and a blood chamber. The blood chamber has an internal
flow cavity for extracorporeal blood flow and viewing lenses to
enable the sensor clip assembly to monitor the blood when it is
mounted on the blood chamber. The sensor clip assembly includes an
annular shroud surrounding the LED emitters and another annular
shroud surrounding the photodetectors, both for the purpose of
blocking ambient light and limiting light piping. The blood chamber
includes separate, distinct shroud mating surfaces to engage the
shrouds on the sensor clip assembly.
Inventors: |
Barrett; Louis L.; (West
Point, UT) ; Law; Perry M.; (Centerville,
UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fresenius Medical Care Holding, Inc. |
Waltham |
MA |
US |
|
|
Family ID: |
46719474 |
Appl. No.: |
14/010149 |
Filed: |
August 26, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13034788 |
Feb 25, 2011 |
8517968 |
|
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14010149 |
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Current U.S.
Class: |
600/322 |
Current CPC
Class: |
A61B 5/14557 20130101;
A61M 2205/3306 20130101; A61M 1/367 20130101; A61M 39/10 20130101;
A61B 5/14535 20130101; A61B 2562/185 20130101; A61B 5/1455
20130101; A61M 2230/207 20130101; A61M 2230/205 20130101; A61M
2205/3313 20130101 |
Class at
Publication: |
600/322 |
International
Class: |
A61B 5/1455 20060101
A61B005/1455 |
Claims
1. A blood chamber for use in an optical blood monitoring system
having a sensor clip assembly with first shroud circumferentially
surrounding photoemitters on one side of the sensor clip assembly
and a second shroud circumferentially surrounding photodetectors on
the other side of the sensor clip assembly, the blood chamber
comprising: an inlet, an outlet and an internal blood flow cavity;
a first exterior side having a viewing lens and a separate,
distinct shroud mating surface located circumferentially around the
viewing lens, the shroud mating surface on the first exterior side
being adapted to engage a shroud on a sensor clip assembly when the
sensor clip assembly is clipped on to the blood chamber; a second
exterior side having a viewing lens and a separate, distinct shroud
mating surface located circumferentially around the viewing lens,
the shroud mating surface on the second exterior side being adapted
to engage a shroud on a sensor clip assembly when the sensor clip
assembly is clipped over the blood chamber; wherein each viewing
lens has a substantially flat exterior surface that is parallel to
and aligned with the other viewing lens, and further wherein the
viewing lenses provide a viewing area for the photoemitters and
photodetectors on the sensor clip assembly when it is clipped on to
the blood chamber.
2-28. (canceled)
Description
FIELD OF THE INVENTION
[0001] The invention relates to optical blood monitoring systems
used to monitor extracorporeal patient blood flow and take
real-time measurement of hematocrit, oxygen saturation levels
and/or other blood constituents. The invention is particularly
directed to improving the physical interface between the sensor
clip assembly and the mating, single-use blood chamber.
BACKGROUND
[0002] The type of blood monitoring systems to which the invention
pertains has been widely used to monitor a patient's hematocrit and
oxygen saturation levels during conventional hemodialysis
treatments. Patients with kidney failure or partial kidney failure
typically undergo hemodialysis treatment in order to remove toxins
and excess fluids from their blood. To do this, blood is taken from
a patient through an intake needle or catheter which draws blood
from an artery or vein located in a specifically accepted access
location (for example, a shunt surgically placed in an arm, thigh,
subclavian, etc.). The needle or catheter is connected to
extracorporeal tubing that is fed to a peristaltic pump and then to
a dialyzer that cleans the blood and removes excess water. The
cleaned blood is then returned to the patient through additional
extracorporeal tubing and another needle or catheter. Sometimes, a
heparin drip is located in the hemodialysis loop to prevent the
blood from coagulating. By way of background, as the drawn blood
passes through the dialyzer, it travels in straw-like tubes within
the dialyzer which serve as semi-permeable passageways for the
unclean blood. Fresh dialysate solution enters the dialyzer at its
downstream end. The dialysate surrounds the straw-like tubes and
flows through the dialyzer in the opposite direction of the blood
flowing through the tubes. Fresh dialysate collects toxins passing
through the straw-like tubes by diffusion and excess fluids in the
blood by ultra filtration. Dialysate containing the removed toxins
and excess fluids is disposed of as waste. The red cells remain in
the straw-like tubes and their volume count is unaffected by the
process.
[0003] It is known in the art to use an optical blood monitoring
system during hemodialysis, such as the CRIT-LINE.RTM. monitoring
system sold by the assignee of this application. The current
CRIT-LINE.RTM. blood monitoring system uses optical techniques to
non-invasively measure in real-time the hematocrit and the oxygen
saturation level of blood flowing through a hemodialysis system or
other systems involving extracorporeal blood flow. When the
CRIT-LINE.RTM. system is used with conventional hemodialysis
systems, a sterile, single-use blood chamber is usually attached
in-line to the extracorporeal tubing on the arterial side of the
dialyzer.
[0004] In general, blood chambers along with the tube set and
dialyzer are replaced for each patient and the blood chamber is
intended for a single use. The blood chamber provides an internal
blood flow cavity, a substantially flat viewing region and two
viewing lenses. Blood chambers commonly used are molded from clear,
medical-grade polycarbonate. Typically, one of the viewing lenses
is integrally molded with the body of the polycarbonate blood
chamber, and the other viewing lens is molded into a separate lens
body that is sonically welded or otherwise fixed to the chamber
body. Alternatively, both lenses are molded into separate lens
bodies that may be welded or otherwise affixed into place on the
chamber body.
[0005] LED emitters and photodetectors for the optical blood
monitor are clipped into place onto the blood chamber over the
lenses. Multiple wavelengths of light may be directed through the
blood chamber and the patient's blood flowing through the chamber
with a photodetector detecting the resulting intensity of each
wavelength. The preferred wavelengths to measure hematocrit are
about 810 nm (e.g. 829 nm), which is substantially isobestic for
red blood cells, and about 1300 nm, which is substantially
isobestic for water. A ratiometric technique implemented in the
CRIT-LINE.RTM. controller, substantially as disclosed in U.S. Pat.
No. 5,372,136 entitled "System and Method for Non-Invasive
Hematocrit Monitoring", which issued on Dec. 13, 1999 and is
assigned to the assignee of the present application, uses this
information to calculate the patient's hematocrit value in
real-time. The hematocrit value, as is widely used in the art, is
the percentage determined by dividing the volume of the red blood
cells in a given whole blood sample by the overall volume of the
blood sample.
[0006] In a clinical setting, the actual percentage change in blood
volume occurring during hemodialysis can be determined, in
real-time, from the change in the measured hematocrit. Thus, an
optical blood monitor, such as the CRIT-LINE.RTM. monitor, is able
to non-invasively monitor not only the patient's hematocrit level
but also the change in the patient's blood volume in real-time
during a hemodialysis treatment session. The ability to monitor
real-time change in blood volume helps facilitate safe, effective
hemodialysis.
[0007] The mathematical ratiometric model for determining the
hematocrit (HCT) value can be represented by the following
equation:
HCT = f [ ln ( i .lamda. 2 I 0 - .lamda. 2 ) ln ( i .lamda. 1 I 0 -
.lamda. 1 ) ] Eq . ( 1 ) ##EQU00001##
where i.sub..lamda.2 is the infrared light intensity detected by
the photoreceiver at about 810 nm, i.sub..lamda.1 is the infrared
intensity detected at 1300 nm and I.sub.0-.lamda.2 and
I.sub.0-.lamda.1 are constants representing the infrared light
intensity incident on the blood accounting for losses through the
blood chamber. The function f[ ] is a mathematical function which
has been determined based on experimental data to yield the
hematocrit value. Preferably, the function f[ ] in the above
Equation (1) is a relatively simply polynomial, e.g. a second order
polynomial. The above Equation (1) holds true only if the distance
traveled by the infrared light radiation from the LED emitters to
the photodetectors at both wavelengths are constant distances and
preferably the same distance
[0008] The preferred wavelengths to measure oxygen saturation level
are about 810 nm and about 660 nm. The mathematical ratiometric
model for determining oxygen saturation level (SAT) can be
represented by the following equation:
SAT = g [ ln ( i .lamda. 3 I 0 - .lamda. 3 ) ln ( i .lamda. 1 I 0 -
.lamda. 1 ) ] Eq . ( 2 ) ##EQU00002##
where i.sub..lamda.3 is the light intensity of the photoreceiver at
660 nm, i.sub..lamda.1 is the detected intensity at 810 nm and
I.sub.0-.lamda.3 and I.sub.0-.lamda.1 are constants representing
the intensity incident on the blood accounting for losses through
the blood chamber. The function g[ ] is a mathematical function
determined based on experimental data to yield the oxygen
saturation level, again preferably a second order polynomial. Also,
like Equation (1) for the hematocrit calculation, Equation (2) for
the oxygen saturation level calculation holds true only if the
distance traveled by the visible and infrared light from the
respective LED emitter to the respective detector at both the 660
nm and 810 nm wavelengths are constant distances and preferably the
same distance.
[0009] In the art, the LED emitters and the photodetectors are
mounted on a sensor clip assembly. For accuracy of the system, it
is important that the LED photoemitters and the photodetectors be
located in a predetermined position and orientation each time the
sensor clip assembly is clipped into place over the blood chamber.
The optical monitor is in fact calibrated for the specific
dimensions of the blood chamber and the specific position and
orientation of the sensor clip assembly with respect to the blood
chamber. For this purpose, in the prior art, the heads of the
sensor clips are designed to mate in a fixed orientation with
non-circular, raised and stepped rims surrounding the viewing
lenses on the blood chamber (e.g. double-D configuration). More
specifically, the heads on both sides of the sensor clip assembly
are formed in a non-circular shape, e.g. a double-D configuration,
which matches the corresponding non-circular shape of the raised,
stepped rims surrounding the viewing lenses on the blood chamber so
that the sensor clip heads fit on the blood chamber in a fixed
orientation and are prevented from rotating relative to the blood
chamber. While the double-D configuration has proven to work well,
one drawback of the design is the additional amount of medical
grade polycarbonate material that is required to manufacture the
raised, stepped rims. In order to reduce the cost of manufacturing
the blood chambers which are single-use, disposable medical
devices, it is desirable to reduce the amount of medical grade
polycarbonate in the blood chambers.
[0010] If not addressed properly, stray ambient light and light
piping through the blood chamber can cause serious inaccuracies in
the measured hematocrit and/or oxygen saturation levels.
Sophisticated signal processing techniques have been used in the
art to remedy most of the issues pertaining to ambient light. In
addition, prior art blood chambers are molded with a moat around a
relatively thin, flat viewing area in the blood flow cavity between
the viewing lenses. This internal moat within the blood flow cavity
fills with blood and blocks light from the silicon and gallium
indium arsenide photodetectors on the sensor clip assembly unless
the light propagates on a direct path from the respective LED
emitter, through the blood in the blood flow cavity, to the
respective photodetector. The effectiveness of the moat depends on
many factors including the patient's hematocrit level and the
wavelength spectrum of the light that is sought to be blocked from
the photodetectors. In practice, the above-mentioned signal
processing techniques have been found necessary to cope with most
ambient light issues, whereas the moat has been found useful to
reduce inaccuracies due to light piping in most circumstances.
Co-pending patent application Ser. No. 12/876,572, entitled "Blood
Chamber for an Optical Blood Monitoring System", by Barrett et al,
assigned to assignee of the present application and incorporated
herein by reference, discloses the use of an opaque chamber body in
order to prevent inaccuracies when measuring oxygen saturation
levels due to light ducting which can occur at low oxygen
saturation levels and low hematocrit levels. Both the use of the
moat and the opaque chamber body physically block piped and/or
ambient light. The present invention is directed to providing
another way to physically block ambient light from the
photodetectors.
SUMMARY OF THE INVENTION
[0011] The invention pertains to the use of an optical blood
monitoring system having a sensor clip assembly and a blood chamber
designed to physically block ambient light from the photodetectors
on the sensor clip assembly. The sensor clip assembly includes an
emitter subassembly to which the LED photoemitters are mounted and
a photo detector subassembly to which the photo detectors are
mounted. As known in the art, the emitter subassembly and the
detector subassembly are arranged to face one another and to be
clipped onto a blood chamber when the monitoring system is in use.
A first aspect of the invention is directed to the use of a shroud
on the emitter subassembly and another shroud on the detector
subassembly to prevent ambient light from entering the blood
chamber. In the preferred of the invention, the heads on the sensor
clip each include a shroud in the form of circular a wall that
encircles the LED emitters and photodetectors, respectively. It is
known in art that the LED photoemitters direct light through a
diffusing lens mounted on the head of the emitter subassembly, and
that the photodetectors receive light through a diffusing lens
mounted on the head of the detector subassembly. The purpose is to
distribute light energy across the volume of blood in the lens
areas of the blood chamber to avoid hot spots of concentrated light
from the emitters for consistency in calibrations. In accordance
with the invention, it is preferred that the emitter shroud be
spaced apart from the diffusing lens related to the emitter
subassembly and also extend away from the emitter subassembly
toward the detector subassembly to a distance beyond the emitter
diffusing lens. Similarly, it is preferred that the detector shroud
be spaced apart from the diffusing lens related to the detector
subassembly and also that the detector shroud extend away from the
detector subassembly to a distance beyond the detector diffusing
lens. Thus, when the sensor clip is clipped on the blood chamber,
the shrouds effectively surround the viewing lenses on both sides
of the blood chamber and block ambient light. The incident angle of
light rays from the LED emitters into the wall of the blood chamber
is also limited by the shroud geometry thereby minimizing possible
light piping.
[0012] Another aspect of the invention is directed to the design of
the blood chamber to enable the use of the shrouded sensor clip
assembly. In this regard, the blood chamber includes a first and
second exterior side each having a viewing lens and a separate,
distinct shroud mating surface located circumferentially around the
viewing lens. Preferably, on one exterior surface of the blood
chamber, the first viewing lens is raised above the circumferential
shroud mating surface such that a sunken annular well is formed
around the raised viewing lens. The floor of the sunken annular
well corresponds to the shroud mating surface on that side of the
blood chamber. It is preferred that the shrouds on the clip
assembly when mounted on the blood chamber substantially fill the
area of the floor of the sunken annular well in order to maximize
the amount of ambient light blocked by the shroud. It is preferred
that the other exterior surface of the blood chamber include an
upstanding wall that surrounds the second viewing lens and
separates the second viewing lens from the shroud mating surface on
that side of the blood chamber. In this way, an annular well is
formed around the second viewing lens, although this annular well
is preferably at substantially the same depth as the viewing lens
on that side of the blood chamber. Again, the floor of the annular
well corresponds to the shroud mating surface on the exterior side
of the blood chamber, and has dimensions substantially the same as
the dimensions of the floor of the sunken annular well on the other
side of the blood chamber so that the shroud will fill the surface
area of the floor of the well.
[0013] The improved design with the shrouds on the sensor clip
assembly not only reduces the influx of ambient light, but also
enables the use of less molded material (e.g. medial grade
polycarbonate) in the manufacture of the blood chamber over
previous designs. As mentioned, prior art blood chambers have
non-circular (e.g. double-D configuration), raised, stepped rims
surrounding the viewing lenses to fix the relative position and
orientation of the LED emitters and photodetectors with respect to
the blood chamber. The present invention eliminates the need for
such a non-circular, raised, stepped rims surrounding the viewing
lenses. Instead, the blood chamber preferably has one or more
anti-rotation tabs to fix the position of the sensor clip assembly
and prevent rotation relative to the blood chamber. In one
embodiment, a pair of extending tabs is formed on an exterior
surface on one side of the blood chamber. The anti-rotation tabs
may take on any reasonable geometric shape, but are designed to
inter-engage with the shroud. In the preferred embodiment, the
shrouds on the sensor clip assembly contain mating slots which are
shaped to receive the anti-rotation tabs. The engagement of the
tabs, fixes the orientation of the sensor clip assembly with
respect to the blood chamber. The shroud with the tab receiving
slot eliminates the need for the non-circular raised, stepped rims
surrounding the viewing lenses on the blood chamber, and therefore
reduces the amount of molded material needed to manufacture the
blood chamber. One skilled in the art will understand that placing
anti-rotation tabs on the shrouds and including mating detents or
slots on the blood chamber, while not preferred, may be a suitable
alternative to carry out this aspect of the invention. Either
arrangement is likely to reduce the amount of material needed to
mold the blood chamber.
[0014] Other advantages and features of the invention may be
apparent to those skilled in the art upon reviewing the drawings
and the following description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Prior Art
[0015] FIG. 1 is a perspective view of a patient undergoing
hemodialysis treatment with a non-invasive, optical blood monitor
monitoring the patient's blood in real-time as it passes through
extracorporeal tubing in the hemodialysis system utilizing a prior
art blood chamber and sensor clip assembly.
[0016] FIG. 2 is a perspective view showing a prior art sensor clip
assembly for the optical blood monitor clipped on to a prior art
blood chamber connected in the extracorporeal tubing of the
hemodialysis system.
[0017] FIG. 3A is a detailed view of the prior art blood chamber
shown in FIG. 2.
[0018] FIG. 3B is a detailed view of the prior art sensor clip
assembly shown in FIG. 2.
[0019] FIG. 4 is a cross-sectional view taken along line 4-4 of the
prior art blood chamber shown in FIG. 2.
[0020] FIG. 5 is a schematic drawing illustrating the detection of
light and infrared light at various wavelengths through the blood
chamber in order to monitor the hematocrit and oxygen saturation of
the blood passing through the blood chamber.
[0021] FIG. 5A is a schematic drawing similar to FIG. 5 further
illustrating the effect of ambient or ducted light that does not
pass through the direct path through the blood in the blood flow
chamber.
EMBODIMENTS OF THE INVENTION
[0022] FIG. 6 is a perspective view of one side of a blood chamber
constructed in accordance with an embodiment of the invention.
[0023] FIG. 7 is a perspective view of the other side of the blood
chamber shown in FIG. 6.
[0024] FIG. 8 is a front elevation view of the blood chamber shown
in FIG. 6.
[0025] FIG. 9 is a is a longitudinal sectional view taken along
line 9-9 in FIG. 6.
[0026] FIG. 10 is a perspective view showing a sensor clip assembly
constructed in accordance with an embodiment of the invention.
[0027] FIG. 11 is a perspective view showing the sensor clip
assembly of FIG. 10 engaged with the blood chamber of FIG. 6.
[0028] FIG. 12 is a longitudinal sectional view of taken along line
12-12 in FIG. 11.
DETAILED DESCRIPTION
Prior Art
[0029] FIG. 1 illustrates a patient 10 undergoing hemodialysis
treatment with a conventional hemodialysis system 12, and also
illustrates a non-invasive, optical blood monitor 14. A typical
hemodialysis clinic will have several hemodialysis systems 12 for
treating patients.
[0030] An input needle or catheter 16 is inserted into an access
site of the patient 10, such as shunt in the arm, and is connected
to extracorporeal tubing 18 that leads to a peristaltic pump 20 and
then to a dialyzer or blood filter 22. The dialyzer 22 removes
toxins and excess fluid from the patient's blood. The dialysized
blood is returned from the dialyzer 22 to the patient through
extracorporeal tubing 24 and a return needle or catheter 26. The
extracorporeal blood flow in the United States generally receives a
heparin drip to prevent clotting although that is not shown in FIG.
1. Excess fluids and toxins are removed by clean dialysate liquid
which is supplied to the dialyzer 22 via tube 28 and removed for
disposal via tube 30. A typical hemodialysis treatment session in
the United States takes about 3 to 5 hours. In a typical
hemodialysis treatment as described in FIG. 1, the access site
draws arterial blood from the patient. If no arterial access is
available then a venous catheter may be used to access the
patient's blood. As mentioned, other dialysis applications such as
low flow Continuous Renal Replacement Therapy (CRRT) sometimes used
in the Intensive Care Unit and perfusion measurements during
cardiac surgery can measure venous blood from the patient. Current
art indicates that oxygen saturation levels in venous blood
correlate to the cardiac output for the patient. The typical blood
monitor 14 shown in FIG. 1 can be used in these other applications
as well.
[0031] The optical blood monitor 14 includes a blood chamber 32, a
sensor clip assembly 34, and a controller 35. The blood chamber 32
is preferably located in line with the extracorporeal tubing 18
upstream of the dialyzer 22. Blood from the peristaltic pump 20
flows through the tubing 18 into the blood chamber 32. The
preferred sensor assembly 34 includes LED photoemitters that emit
light at substantially 810 nm (e.g. 829 nm), which is isobestic for
red blood cells, substantially 1300 nm, which is isobestic for
water, and at substantially 660 nm, which is sensitive for
oxygenated hemoglobin. The blood chamber 32 includes lenses so that
the sensor emitters and detector(s) can view the blood flowing
through the blood chamber 32, and determine the patient's real-time
hematocrit value and oxygen saturation value using ratiometric
techniques generally known in the prior art.
[0032] Referring to now FIGS. 2-4, the body of a prior art blood
chamber 32 is made of molded, medical grade, clear polycarbonate.
It includes a raised, stepped rim 33 having a double-D
configuration surrounding the substantially flat viewing lens 35
(see FIG. 3A). It also includes two viewing windows 36, 38 (see
FIG. 4). The inlet 40 and outlet 42 are designed to be compatible
with standard medical industry connecting devices, conventionally
known as luer lock connectors. In the blood chamber 32 shown in
FIGS. 2-4, the inlet 40 is integrally molded with the blood chamber
32, whereas the outlet 42 consists of a suitable off-the-shelf
connection adapter bonded to the body of the blood chamber 32
(alternatively, tubing can be attached directly to the body in
place of connector 42). The sensor assembly 34 includes an emitter
subassembly 44 and a detector subassembly 46. Referring to FIG. 3B,
the emitter and detector heads (see, reference no. 45) both have a
double-D configuration which corresponds to the double-D
configuration of the blood chamber 32. The interlocking double-D
configuration serves to fix the sensor clip 34 in a predetermined
orientation when it is clipped into place over the blood chamber
32. Fixing the sensor clip 34 in a predetermined position is
important for measurement accuracy because the system is calibrated
for that predetermined position.
[0033] The housings 44 and 46 for the sensor clip assembly 34
include an inner housing frame 45, 47 which connects to the outer
housing shells 44, 46. Each side of the inner housing frame 45, 47
provides an opening into which the molded diffusion lenses 50, 54
are mounted. The sensor assembly 34 is a spring-loaded clip
assembly adapted to be removably mounted to the blood chamber 32,
as shown in FIG. 2. Both sides of the blood chamber 32 are molded
such that the clip 34 will reside in a predetermined position when
mounted to the blood chamber 32. As mentioned, blood chamber 32 is
a single-use clear polycarbonate component. Between patient
treatments, the blood chamber 32 is replaced along with the
extracorporeal tubing 18, 24, and blood filter 22.
[0034] As best shown in FIG. 4, an emitter circuit board 48
containing LEDs emitting light at substantially 660 nm, 810 nm and
1300 nm is mounted within the housing for the sensor subassembly
46. The photoemitters on the LED circuit board 48 emits visible and
infrared light through a molded lens 50 that is mounted in the clip
loop housing 45, and direct visible and infrared light through the
viewing window 36 for the blood chamber 32. The controller 35 (FIG.
1), controls the operation of the respective LED emitters and
detector(s) in order to multiplex the independent wavelength
measurements so that the emitter and respective detector
measurements remain correlated. Another circuit board 52 contains
photo detectors, at least one made of silicon to detect light
intensity at substantially 810 nm and 660 nm, and at least one made
of InGaAs to detect light intensity at 1300 nm. The detector
circuit board 52 is mounted within the housing for the detector
subassembly 44. A molded lens 54 is mounted in the clip loop
housing 47 on the detector side of the clip covered by housing 44.
The controller 35 includes data acquisition hardware and software
which receives signals proportional to the intensities detected by
the InGaAs and Si detector diodes. The viewing window 38 in the
blood chamber 32 facilitates transmission of visible and infrared
light at the respective wavelengths to the detectors on the circuit
board 52 of the detector subassembly 44. Note that the viewing
window 38 is molded into a separate insert 58 (referred to as the
lens body 58) that is sonically welded to the body of the blood
chamber 32. Blood flows from the inlet 40 through the passageway 60
to a central viewing region 62, also referred to herein as an
internal blood flow cavity 62. The internal blood flow cavity
provides a substantially flat, thin (e.g. less than 0.1 inches)
viewing region for the blood flowing through the blood chamber 36.
The multiplexed visible or infrared light at the three selected
wavelengths, namely about 810 nm, 1300 nm and 660 nm, are
transmitted through the blood flowing through the flat viewing
region provided by internal blood flow cavity 62, as well as
through the viewing windows 36, 38 in the chamber 32. A moat 64
surrounds the flat viewing region 62. The moat 64 is somewhat
deeper than the flat viewing region 62. The moat helps distribute
non-laminar flow evenly and steadily through the viewing region and
provides a thicker region of blood which under most normal
operating conditions optically isolates the detectors from
detecting ambient or ducted light that does not pass through the
direct path through the blood in the blood flow chamber. One or
more turbulence posts 66 are located immediately upstream of the
viewing region 62 to create steady eddy currents in the flow across
the viewing region 62.
[0035] FIG. 5 is a schematic illustration of a prior art blood
chamber 32 with a patient's blood 82 flowing through the chamber
32. As described above, the blood 82 enters the blood chamber
through an inlet 40 and then flows into a moat 64 surrounding the
flat viewing area 62. The distance across the viewing area 62 is
given by the arrow labeled d.sub.b, which signifies the thickness
of the blood flowing through the flat viewing area 62. After the
blood leaves the flat viewing area 62, it flows into the moat 64
located on the other side of the viewing area 62 and out of the
chamber through the outlet 42. FIG. 5 shows three LED emitters 84,
86 and 88. LED 84 emits infrared light at substantially 1300 nm,
LED 86 emits infrared light at substantially 810 nm, and LED 88
emits red light at substantially 660 nm. As mentioned, each of the
LEDs 84, 86, 88 emits light at a fixed average intensity. The LEDs
are pulsed on for a time period such that it is on at a time when
the other LEDs are not on (i.e., timed-based multiplexing),
although other methods of multiplexing are possible. As shown in
FIG. 5, light from each LED emitter 84, 86, 88 is first transmitted
through the clear polycarbonate transmission window 90 in the blood
chamber 32, then through the blood flowing through the flat viewing
region 62, and finally transmitted through the clear polycarbonate
receiving window 92 on the other side of the blood chamber 32. An
indium gallium arsenide detector 93 detects the intensity of the
1300 nm light wave that is transmitted through the walls of the
blood chamber 32 and the blood flowing through the flat viewing
region 92. A silicon detector 95 detects the intensity of the light
at 810 nm and at 660 nm transmitted through the walls of the blood
chamber 32 and the blood flowing through the flat viewing region
62.
[0036] The intensity of the light at each of the various
wavelengths is reduced by attenuation and scattering from the fixed
intensity of the light emitted from each of the LEDs 84, 86, 88.
Beers Law, for each wavelength of light, describes attenuation and
scattering as follows:
i.sub.n=I.sub.o-ne.sup.-.epsilon..sup.p.sup.X.sup.p.sup.d.sup.pte.sup.-.-
epsilon..sup.b.sup.X.sup.b.sup.d.sup.be.sup.-.epsilon..sup.p.sup.X.sup.p.s-
up.d.sup.pr Eq. (3)
where i.sub.n=received light intensity at wavelength n after
attenuation and scattering; I.sub.o-n=transmitted light intensity
at wavelength n incident to the measured medium; e=the natural log
exponential term; .epsilon.=the extinction coefficient for the
measured medium (p--polycarbonate, b--blood); X=the molar
concentration of the measured medium (p--polycarbonate, b--blood);
and d=the distance through the measured medium (pt--transmitting
polycarbonate, b--blood, pr--receiving polycarbonate).
[0037] Since the properties of the polycarbonate blood chamber do
not change, the first and third exponential terms in the above
Equation (3) are normally assumed in the prior art to be constants
for each wavelength. Mathematically, these constant terms are
multiplicative with the initial constant term I.sub.o-n which
represents the fixed intensity of the radiation transmitted from
the respective LED emitter 84, 86, 88. For simplification purposes,
Equation (3) if often rewritten in the following form using bulk
extinction coefficients and a modified initial constant as as
follows:
i.sub.n=I'.sub.o-n*e.sup.-.alpha..sup.b.sup.d.sup.d Eq. (4)
where i.sub.n=received light intensity at wavelength "n" after
attenuation and scattering as though the detector were at the
receive blood boundary; .alpha.=the bulk extinction coefficient for
blood; .alpha..sub.b=.epsilon..sub.bX.sub.b; and I'.sub.o-n equals
the equivalent transmitted radiation intensity at wavelength n
boundary accounting for losses through the blood chamber walls.
[0038] Using the approach defined in Equation (4) above, the 810 nm
wavelength which is isobestic for red blood cells and the 1300 nm
wavelength which is isobestic for water can be used to determine
the patient's hematocrit. The ratio of the normalized amplitudes of
the measured intensity at these two wavelengths produces the ratio
of the composite extinction values .alpha. for the red blood cells
and the water constituents in the blood chamber, respectively.
Therefore, the following mathematical function defines the measured
HCT value:
HCT = f [ ln ( i 810 I 0 - 810 ) ln ( i 1300 I 0 - 1300 ) ] Eq . (
5 ) ##EQU00003##
where i.sub.810 is the detected infrared intensity of the
photoreceiver 95 (FIG. 5) at 810 nm, i.sub.1300 is the detected
infrared intensity of the photodetector 93 (FIG. 5) at 1300 nm and
I.sub.0-810 and I.sub.0-1300 are constants representing the
infrared light intensity incident on the blood accounting for
losses through the blood chamber at 810 nm and 1300 nm
respectively. The above equation holds true assuming that the flow
of blood through the blood chamber 32 is in steady state, i.e.
steady pressure and steady flow rate. The preferred function fn is
a second order polynomial having the following form:
HCT = f = A [ ln ( i 810 I 0 - 810 ) ln ( i 1300 I 0 - 1300 ) ] 2 +
B [ ln ( i 810 I 0 - 810 ) ln ( i 1300 I 0 - 1300 ) ] + C . Eq . (
6 ) ##EQU00004##
[0039] A second order polynomial is normally adequate as long as
the infrared radiation incident at the first and second wavelengths
is substantially isobestic.
[0040] The oxygen saturation level, or the oxygenated hemoglobin
level, is determined using a ratiometric equation for the intensity
of red light at 660 nm detected by detector 95, FIG. 5 and the
intensity of infrared light at 810 nm detected by detector 95, FIG.
5. The form of the ratiometric model for determining oxygen
saturation level is as follows:
SAT = g [ ln ( i 660 I 0 - 660 ) ln ( i 810 I 0 - 810 ) ] Eq . ( 7
) ##EQU00005##
where i.sub.660 is the detected intensity of the photoreceiver at
660 nm, i.sub.810 is the detected intensity of the photodetector at
810 nm and I.sub.0-660 and I.sub.0-810 are constants representing
the light intensity incident on the blood accounting for losses
through the blood chamber. The function g[ ] is a mathematical
function based on experimental data to yield the oxygen saturation
level, again preferably a second order polynomial
SAT = g = A [ ln ( i 660 I 0 - 660 ) ln ( i 810 I 0 - 810 ) ] 2 + B
[ ln ( i 660 I 0 - 660 ) ln ( i 810 I 0 - 810 ) ] + C . Eq . ( 8 )
##EQU00006##
[0041] FIG. 5A is a schematic drawing similar to FIG. 5 further
illustrating the effect of ambient ducted light that does not pass
through a direct path through the blood in the blood flow chamber.
In this regard, ray 96 is illustrative of ambient or ducted light.
If ambient or ducted light is sensed by the detectors 93, 95,
measurement inaccuracies can occur if not appropriately accounted
for by signal processing. In accordance with the invention, it has
been found desirable to physically eliminate the effect of ambient
light that might otherwise be detected by the photo detectors 93,
95. As mentioned, this is done in accordance with the invention by
providing shrouds on the sensor clip assembly and providing a
single-use blood chamber with a mating configuration. It may also
be desirable to construct the chamber body of an opaque material to
further attenuate ambient light.
PRESENT INVENTION
[0042] FIGS. 6 through 9 illustrate a blood chamber 100 constructed
in accordance with a preferred embodiment of the present
invention.
[0043] FIG. 7 illustrates a first exterior side of the blood
chamber 100. The blood chamber 100 is constructed from a molded
chamber body 101 which includes an inlet and an outlet as well as a
first viewing lens 103. In accordance with the invention, the
chamber body 101 may be molded entirely of clear, medical grade
polycarbonate material or other suitable material. Alternatively,
it may be desirable to use a lens insert 102 made of entirely
clear, medical grade polycarbonate, and over mold the remaining
parts of the chamber body 101 with an opaque material such as a
blue-tinted medical grade polycarbonate. In either case, the
preferred chamber body 101 includes a circular viewing lens 103 and
a separate, distinct shroud mating surface 104 located
circumferentially around the viewing lens 103. The shroud mating
surface 104 is sunken with respect to the surface of the viewing
lens 103, and is adapted to receive a shroud on a sensor clip
assembly as will be discussed in more detail below. FIG. 7 also
illustrates two anti-rotation tabs 107, 108 formed on the exterior
surface of the blood chamber 100. The anti-rotation tabs 107, 108
are raised above the surface of the lens 103.
[0044] FIG. 6 illustrates the other exterior side of the blood
chamber 100. This side of the blood chamber 100 includes a second
circular viewing lens 200. The region between the second viewing
lens 200 in FIG. 6 and the first viewing lens 103 in FIG. 7
consists of lens material (e.g. clear, medical grade polycarbonate)
and the blood flowing through the internal blood flow cavity within
the blood chamber 100. The lenses 103, 200 thus provide a viewing
window for the sensor clip assembly to monitor the blood flowing
through the blood chamber 100. Referring still to FIG. 6, an
upstanding annular wall 206 surrounds the second viewing lens 200.
An annular well 204 is formed between the upstanding, annular wall
206 and a peripheral wall 210 on the blood chamber 100. The floor
of this annular well 204 is another shroud mating surface which
again is separate and distinct from the viewing lens 200. In
accordance with the preferred embodiment of the invention, a lens
body 202 containing the viewing lens 200, the upstanding wall 206,
and the surrounding annular well 204, is molded of a clear
polycarbonate material and is attached via sonic welding or other
means to the chamber body 101 during the manufacturing process.
[0045] FIG. 9 shows the cross section of the blood chamber 100. The
chamber body 101 including a substantially flat internal wall 110
that forms part of the internal blood flow cavity 120. The lens
body 202 attached to the chamber body 101 also includes a
substantially flat internal wall 112 that is substantially parallel
to the substantially flat internal wall 110 on the chamber body
101. The flat internal wall 112 on the lens body 202 is separated
from the flat internal wall 100 on the chamber body 101 by a
predetermined fixed distance. The first viewing lens 103 on the
chamber body 101 and the second viewing lens 200 on the lens body
202 serve as viewing windows 136 and 138 (FIG. 12) for blood
flowing through the internal blood flow cavity 120. The chamber
body 101 (FIG. 9) includes a first port 122 and a channel 124
(inlet) that are in fluid communication through a first opening 126
in the internal blood flow cavity 120. The chamber body 101 also
includes a second port 128 and channel 130 (outlet) that are in
fluid communication through a second opening 132 in the internal
blood flow cavity 120.
[0046] FIG. 10 illustrates a sensor clip assembly 134 configured in
accordance with a preferred embodiment of the invention. The sensor
clip assembly 134 is used to monitor the patient's blood flowing
through the blood chamber 100. As depicted in the embodiment
illustrated in FIG. 11, the LED emitter arm 144 and the
photodetector arm 146 are affixed into place around a blood chamber
100 in order to monitor the hematocrit, hemoglobin, change in blood
volume and oxygen saturation level, and/or other blood constituents
of blood flowing through the blood chamber 100. Accordingly, the
sensor clip assembly 134 preferably includes a spring biased bridge
148 or equivalent structure to attach a sensor clip assembly 134 to
a blood chamber 100.
[0047] The sensor clip assembly 134 includes an LED emitter arm 144
and a photodetector arm 146, which are connected via a spring
biased bridge 148. The LED emitter arm 144 contains an emitter
subassembly with at least two LED emitters, one emitting infrared
light or radiation at a first wavelength (.lamda..sub.1) of about
1300 nm and another emitting infrared light or radiation at a
second wavelength (.lamda..sub.2) of about 810 nm (e.g. 829 nm).
The LED emitter preferably also includes a third LED emitter for
emitting infrared light or radiation at a third wavelength
(.lamda..sub.3) of about 660 nm. Other wavelengths could be
substituted or added to measure additional blood constituents or
properties of other fluids. The detector arm 146 contains
preferably two types of photodetectors: a silicon photo detector to
detect the approximate 660 and 810 nm wavelengths, and an indium
gallium arsenide photo detector to detect the approximate 1300 nm
wavelength. As configured in the embodiment depicted in FIGS.
10-12, the sensor clip assembly 134 emits infrared light or
radiation through the viewing lenses 103 and 200 and through the
viewing windows 136 and 138 and through the blood flowing through
the internal blood flow cavity 120 of the blood chamber 100.
[0048] The sensor clip assembly 134 preferably includes a shroud
140 on the inner housing piece of the emitter arm 144 subassembly
to prevent ambient light from entering the blood chamber through
the viewing lenses or the lens bodies and a shroud 142 on the inner
housing piece of the detector arm 146 subassembly to prevent
ambient light from entering the blood chamber through the viewing
lenses or the lens bodies.
[0049] Referring now to FIGS. 10-12, the shrouds 140 and 142 are
preferably mirror images of one another. The description of shroud
140 on the emitter arm 144 therefore is representative and applies
equally to the description of the shroud 142 on the detector arm
146. Referring in particular to FIG. 10, it can be seen the shroud
142 contains an outer annular ledge or step surface 150 and an
inner annular ledge or step surface 152. The difference in the
heights of the step surfaces 150, 152 corresponds to the height of
the annular wall 206 on the second exterior side of the blood
chamber 100 (see, FIG. 6), and also to the height at which the lens
surface 103 is raised above the sunken well 104 on the first side
of the blood chamber 100 (see, FIG. 7). Preferably, the shape and
surface area of the outer annular step surface 150 is substantially
equal to the shape and surface area of the respective shroud mating
surfaces 104, 204 on the blood chamber 100, see FIGS. 11 and 12, in
order to maximize the blocking of ambient light.
[0050] Still referring to FIG. 10, the shroud 142 illustrated in
FIG. 10 includes slots 154, 156 that are adapted to receive the
anti-rotation tabs 107, 108 on the blood chamber 100 (see FIG. 7).
The shroud 140 on the emitter arm 144 includes identical slots so
that the sensor clip assembly 134 may be clipped on to the blood
chamber 100 in either direction. In either direction, however, the
sensor clip assembly will be fixed in a predetermined position and
rotational orientation corresponding to the factory calibration for
the optical monitoring system. As mentioned previously, the shape
of the anti-rotation tabs 107, 108 and the corresponding slots 154,
156 may take on any reasonable shape, and furthermore as previously
mentioned aspects of the invention may be implemented using
alternative anti-rotation configurations.
[0051] FIG. 12 shows a cross-sectional view of sensor clip assembly
134 clipped on to the blood chamber 100. Referring specifically to
the blood chamber 100 as shown in FIG. 12, the blood chamber 100
includes two viewing windows 136 and 138. Surface 103 of the first
viewing lens 136 is exposed on the first exterior side of the blood
chamber 100 (see FIG. 7). The exterior surface 206 of the other
viewing window 138 is exposed on the first side of the blood
chamber 100 (see FIG. 6). The blood chamber 100 includes an inlet
140 and outlet 142 that are designed to be compatible with standard
medical industry connecting devices conventionally known as lure
lock connectors. In the blood chamber 100 shown in FIG. 12, the
inlet 140 is integrally molded with the blood chamber 100, whereas
the outlet 142 consists of a suitable off-the-shelf connector
adapter bonded to the body of the blood chamber 100. Alternatively,
tubing can be attached directly to the body of the blood chamber
100 in place of the connector 142.
[0052] The LED emitter subassembly 144 as shown in FIG. 12 contains
an emitter circuit board 152 containing LEDs emitting light at
substantially 660 nm, 810 nm and 1300 nm. The LEDs radiate light
through the molded diffusing lens 154. As shown in FIG. 12, the
shroud 140 on the emitter sub-housing 144 is spaced apart from the
molded diffusing lens 154. In addition, the shroud 140 extends
towards the detector subassembly 146 beyond the location of the
diffusing lens 154.
[0053] The photodetector subassembly 146 includes a circuit board
148 to which the silicon photodetector can detect intensity at 810
nm and 660 nm, and the indium gallium arsenide photodetector to
detect light intensity at 1300 nm are mounted. Again, the
photodetectors are mounted to receive light energy through a molded
diffusing lens 150. FIG. 12 shows that the shroud 142 is spaced
apart from the diffusing lens 150 and also that the shroud 142
extends beyond the diffusing lens 150 toward the emitter
subassembly 144. In FIG. 12, the anti-rotation tabs 107, 108 are
shown in cross-section as taken along the line 12-12 in FIG.
11.
[0054] The viewing window 136 as shown in the embodiment in FIG. 12
is either part of a separate lens insert which is then over molded
to the remainder of the chamber body 101 if an opaque body is
desired or this lens can be molded as part of the chamber body 101
as one piece. The viewing window 138 on the other side of the blood
chamber 100 is part of a separately molded lens body, which is
sonically welded or otherwise adhered to the chamber body.
[0055] Further referring to FIG. 12, blood flows from the inlet
into the central viewing region which has been referred to
previously as the internal blood flow cavity 162. The internal
blood flow cavity provides a substantially flat, thin (e.g. less
than 0.1 inches) viewing area for the blood flowing through the
blood chamber 100. The multiplexed visible or infrared light at the
selected wavelengths are transmitted through the blood flowing
through the flat viewing region as well as through the viewing
windows 136 and 138. A moat 164 surrounds the flat viewing region
162. The moat 164 is somewhat deeper than the flat viewing region
162, and servers in part to distribute non-laminate flow evenly and
steadily through the viewing region. Though optional, when used the
moat 164 also provides a thicker region of blood which under most
normal operating conditions optically isolates the detectors from
ducted or ambient light that does not pass through the direct path
from the emitters through the blood to the detectors.
[0056] The viewing lenses 103, 200 are preferably made of clear,
medical grade polycarbonate material which is molded with a
polished finish in order to facilitate reliable light transmission,
e.g. Bayer Makrolon FCR 2458-5515 (no re-grind allowed), which is
blood contact approved, USPXX11 class VI. It is expected that the
material be certified as to grade number, lot number and date of
manufacture. Moreover, the viewing lenses should contain splay,
bubbles or marks when looking through the display window viewed
from twelve inches with the normal eye. The molded parts should be
produced with no lose foreign material greater than 0.1 mm.sup.2
and no embedded foreign material greater than 0.2 mm.sup.2 and no
mold release should be use, and any lubrications should be food
grade and not silicon based. The mold finish is preferably SPIA3
(scale) except along the surfaces for the viewing windows which the
finish should preferably be at least SPIA1. Parts should be cleaned
and free and dirt, oils and other foreign matter before use.
[0057] While the lens portions 103 and 200 should be made of clear
material, it may be desirable to tint the remaining portions of the
chamber body. For example, it may be desirable to use a blue-tinted
polycarbonate material for the remaining portions of the chamber
body.
[0058] The described use and embodiment of the invention is to be
considered in all respects as only illustrative and not
restrictive.
* * * * *