U.S. patent application number 11/361304 was filed with the patent office on 2007-05-03 for portable co-oximeter.
This patent application is currently assigned to Stat-Chem, Inc.. Invention is credited to Michael H. Burnam, James Huntington Dabney, Martin J. Patko, Lisa A. Tam.
Application Number | 20070098595 11/361304 |
Document ID | / |
Family ID | 25026575 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070098595 |
Kind Code |
A1 |
Tam; Lisa A. ; et
al. |
May 3, 2007 |
Portable co-oximeter
Abstract
The invention discloses a system, method and medical device for
measuring various hemoglobin derivatives, such as oxyhemoglobin,
reduced hemoglobin, partial hemoglobin, carboxyhemoglobin,
methemoglobin and sulfhemoglobin in whole or in hemolyzed blood.
The novel method uses a statistical approach to enable the design
of a portable co-oximeter. This portable co-oximeter utilizes
compact light sources, such as light emitting diodes or light
emitting lasers, to emit light in the visible region. Being
portable, the device is a point-of-care device that can be used in
emergency situations by paramedics, in the emergency room, and in a
physicians office to detect and measure the concentrations and/or
percentages of functional and non-functional hemoglobin derivatives
in a patient's blood.
Inventors: |
Tam; Lisa A.; (Lake Forest,
CA) ; Dabney; James Huntington; (Irvine, CA) ;
Burnam; Michael H.; (Calabasas, CA) ; Patko; Martin
J.; (Anaheim Hills, CA) |
Correspondence
Address: |
Curtis L. Harrington;Suite 250
6300 State University Drive
Long Beach
CA
90815
US
|
Assignee: |
Stat-Chem, Inc.
Orange
CA
|
Family ID: |
25026575 |
Appl. No.: |
11/361304 |
Filed: |
February 23, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09752502 |
Dec 28, 2000 |
7029628 |
|
|
11361304 |
Feb 23, 2006 |
|
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|
Current U.S.
Class: |
422/82.05 |
Current CPC
Class: |
G01N 21/3151
20130101 |
Class at
Publication: |
422/082.05 |
International
Class: |
G01N 21/00 20060101
G01N021/00 |
Claims
1. A medical device for measuring the concentration and/or
percentages of one or more hemoglobin derivatives in a blood sample
taken from a patient comprising; a) a housing; b) a holder for the
blood sample contained within the housing; c) a light generating
apparatus contained within the housing comprising at least one
compact light source emitting light in the visible region of the
spectrum or at least one polychromatic light source and at least
one light filter for separating the light from the polychromatic
light source into distinct bandwidths along the visible spectrum;
wherein the number of light sources or filters in the visible
region of the electromagnetic spectrum is less than or equal to the
number of hemoglobin derivatives to be measured; d) a light
receiving apparatus contained within the housing comprising at
least one light detector receiving light for determining one or
more absorbance values of the blood sample at one or more
wavelengths within the bandwidth of each light source or filter in
the visible region of the spectrum; and e) a microprocessor for
determining the concentration of each hemoglobin derivative from
the measured absorbance values.
2. The medical device of claim 1 wherein the compact light
source(s) or light filter(s) have bandwidths of about 7-50
nanometers.
3. The medical device of claim 1, wherein the optimal wavelength
for determining the absorbance value(s) for a hemoglobin derivative
depends on the characteristics of the compact light source and/or
optical filter used in the device.
4. The medical device of claim 1, wherein the overall size of the
device is sufficiently small so as to be hand-held.
5. The medical device of claim 1, wherein the portable device
weighs less than about 50 pounds.
6. The medical device of claim 1, wherein at least one light source
emits light ranging from about 450 nanometers to about 700
nanometers.
7. The medical device of claim 1, wherein the compact light sources
comprise light emitting diodes, light emitting lasers, a
polychromatic light or combinations thereof.
8. The medical device of claim 1, wherein the light receiving
source(s) comprise photo detectors, photo diodes, pin diodes, photo
transistors, CCD arrays, photo multiplier tubes or combinations
thereof.
9. The medical device of claim 1, wherein the blood sample
comprises hemolyzed blood.
10. The medical device of claim 1, further comprising at least one
light source emitting light in the high visible to infra red region
of the electromagnetic spectrum.
11. The medical device of claim 10, wherein the blood sample
comprises non-hemolyzed blood.
12. The medical device of claim 10, wherein the light source emits
light in the range of about 650 nanometers to about 1000
nanometers.
13. The medical device of claim 10, wherein the light receiving
detector lies on the same plane as the plane used to measure the
reflectance of the blood sample.
14. The medical device of claim 10, wherein the absorbance and/or
reflectance is used to measure and/or calculate the hematocrit
and/or to measure all hemoglobin derivatives as total hemoglobin of
non-hemolyzed blood sample.
15. The medical device of claim 1, comprising at least two compact
light sources for distinguishing two or more hemoglobin
derivatives.
16. The medical device of claim 1, comprising at least three
compact light sources for distinguishing three or more hemoglobin
derivatives.
17. The medical device of claim 1, comprising at least five compact
light sources for distinguishing five or more hemoglobin
derivatives.
18. The medical device of claim 1, comprising at least three
compact light sources for distinguishing two or more hemoglobin
derivatives, wherein one light source emits light in the high
visible to infra red region of the electromagnetic spectrum.
19. The medical device of claim 1, wherein the hemoglobin
derivatives to be measured are oxyhemoglobin, reduced hemoglobin,
partial hemoglobin, carboxyhemoglobin, methemoglobin, fetal
hemoglobin and/or sulfhemoglobin.
20. The medical device of claim 1, wherein the device further
yields values for total hemoglobin, hematocrit, oxygen saturation,
fractional oxygen saturation, oxygen content and/or oxygen
capacity.
21. The medical device of claim 1, wherein the microprocessor
comprises software capable of validating and/or adjusting the
measured concentrations and/or percentages of hemoglobin
derivatives by use of one or more ratiometric curves.
22. The medical device of claim 1, wherein the device is battery
powered.
23. The medical device of claim 21, wherein the ratiometric
calibration curves comprise known ratios of absorbance values taken
from absorbance spectra comprising more than one hemoglobin
derivative.
24. The medical device of claim 21, wherein the ratiometric curves
comprise spectral data for combinations of two or more hemoglobin
derivatives at various known concentrations.
25. A method for determining concentrations and/or percentages of
hemoglobin derivatives from a blood sample of a patient comprising;
a) selecting the medical device or system of claim 1; b) obtaining
a blood sample from a patient; and c) determining the concentration
and/or percentage of at least one hemoglobin derivative.
26. The method of claim 25, further comprising determining a value
for total hemoglobin, hematocrit, oxygen saturation, fractional
oxygen saturation, oxygen content and/or oxygen capacity.
27. The method of claim 2.5, further comprising validating and/or
adjusting the measured concentration and/or percentages of any
hemoglobin derivative by use of one or more ratiometric calibration
curves.
28. The method of claim 25, wherein the optimal wavelength or
wavelengths for measuring the concentration and/or percentages of
the varipus hemoglobin derivatives depends on the compact light
source or light filter used in the medical device.
29. The medical device of claim 25, wherein the ratiometric curves
comprise known ratios of absorbance values taken from absorbance
spectra comprising more than one hemoglobin derivative.
30. The medical device of claim 25, wherein the ratiometric curves
comprise spectral data for combinations of two or more hemoglobin
derivatives at various known concentrations.
31. A method of determining the concentration and/or percentages of
hemoglobin derivatives in a blood sample taken from a patient using
compact light sources and/or a polychromatic light source with
filters comprising: a) selecting certain bandwidths of light
sources or filters to be used to measure the visible absorption
spectrum of the blood sample, wherein the peak wavelength for each
light source or light filter selected overlaps with the peak areas
and/or areas of peak overlap for the known spectra of the
hemoglobin derivatives to be measured; b) performing a calculation
that normalizes the distribution of the absorption coefficients of
each hemoglobin derivative across the wavelength, wherein the
normalized data yields a calculated weighted absorption spectrum
for each hemoglobin derivative; c) locating at least one optimal
wavelength, or near optimal wavelength, for each hemoglobin
derivative to be measured from each calculated absorption spectrum;
d) detecting an actual absorbance measurement at or near the
optimal, or near optimal, wavelength or wavelengths selected for
each hemoglobin derivative determined in step (d); and e) using the
measured absorbance for each wavelength to determine the
concentration and/or percentage of each hemoglobin derivative in
the blood sample.
32. The method of claim 31, wherein the normalization is based on
characteristics of the light source or light sources.
33. The method of claim 31, wherein the normalization is based on
characteristics of the filter or filters.
34. The method of claim 31, wherein the absorbances at each optimal
wavelength are used to calculate the total hemoglobin, hematocrit,
oxygen saturation, fractional oxygen saturation, oxygen content
and/or oxygen capacity.
35. The method of claim 31, wherein the compact light sources are a
light emitting diodes, light emitting lasers, a polychromatic light
source and filters, and/or combinations thereof.
36. The method of claim 31, wherein the light receiving sources are
photo detectors, photo diodes, pin diodes, photo transistors, CCD
arrays, photo multiplier tubes or combinations thereof.
37. The method of claim 31, wherein the blood sample comprises
non-hemolyzed blood.
38. The method of claim 37, further comprising measuring and/or
calculating the absorbance and/or reflectance of the blood sample
in the high visible to near infra red region of the optical
spectrum and correcting the determined concentration of each
hemoglobin derivative using the measured absorbance or reflectance
value of the blood sample in the high visible to near infra red
region of the spectrum.
39. The method of claim 37, further comprising measuring or
calculating the hematocrit using the absorbance and/or reflectance
of the high visible to near infra red range of the optical
spectrum.
40. The method of claim 31, further comprising validating and/or
adjusting the measured concentration and/or percentages of any
hemoglobin derivative by use of one or more ratiometric curves.
41. The medical device of claim 28, wherein the ratiometric curves
comprise known ratios of absorbance values taken from absorbance
spectra comprising more than one hemoglobin derivative.
42. The medical device of claim 28, wherein the ratiometric curves
comprise spectral data for combinations of two or more hemoglobin
derivatives at varying known concentrations.
43. The method of claim 28, wherein the number of light sources or
light filters in the visible region of the electromagnetic spectrum
is less than or equal to the number of hemoglobin derivatives to be
measured.
44. A medical system for measuring the concentration and/or
percentages of one or more hemoglobin derivatives in a blood sample
taken from a patient comprising; a) a housing; b) a light
generating subsystem contained within the housing comprising at
least one compact monochromatic light source emitting light in the
visible region of the spectrum or at least one polychromatic light
source and at least one light filter for separating the light from
the polychromatic light source into distinct bandwidths along the
visible spectrum; wherein the number of light sources or filters in
the visible region of the electromagnetic spectrum is less than or
equal to the number of hemoglobin derivatives to be measured; c) a
light receiving subsystem contained within the housing comprising
at least one light detector receiving light for determining one or
more absorbance values of the blood sample at one or more
wavelengths within the bandwidth of each light source or filter in
the visible region of the spectrum; d) an emitter subsystem
contained within the housing providing a constant current source;
e) a detector subsystem contained within the housing comprising a
PIN diode; f) a sensor optics subsystem contained within the
housing comprising a block configured to hold a holder for the
blood sample so that the holder is in optical communication with
the emitter subsystem, the light receiving subsystem and the
detector subsystem; and g) a microprocessor subsystem contained
within or outside of the housing for determining the concentration
of each hemoglobin derivative from the measured absorbance
values.
45. The system of claim 44, further comprising an external
interface contained within the housing or outside of the housing
for linking the system to other medical systems and/or devices.
46. The system of claim 44, wherein the microprocessor subsystem
further comprises a microcontroller.
47. The system of claim 44, further comprising a data acquisition
subsystem contained within the housing or outside of the
housing.
48. The medical device of claim 44, wherein the microprocessor
comprises software capable of validating and/or adjusting the
measured concentrations and/or percentages of hemoglobin
derivatives by use of one or more ratiometric curves.
49. The medical device of claim 45, wherein the medical device is
linked to a pulse oximeter.
50. A method of improving the accuracy of a determination of the
concentration or percentage of a mixture of unknown hemoglobin
derivatives comprising: a) preparing a series of known mixtures
comprising two or more hemoglobin derivatives such that each
mixture in the series differs in the percentage of each hemoglobin
derivative; b) observing the optical behavior of the series of
mixtures; c) selecting from the optical behavior of the series of
mixtures, a wavelength, or wavelengths, where the optical behavior
of series of mixtures appears different and a wavelength, or
wavelengths, where the optical behavior of the series of mixtures
appears similar, wherein optically determined values can be
determined for each mixture at these selected wavelengths; d)
taking a ratio of the optically determined values for each mixture
at the wavelength, or wavelengths, where the optical behavior
appears different and at the wavelength, or wavelengths, where the
optical behavior appears similar, to yield the ratiometric behavior
of the series of mixture; and f) using the ratiometric behavior of
the series of known mixtures to improve the accuracy of optically
determined values of an unknown mixture of hemoglobin derivatives
by a comparison to the ratiometric behavior of the series of known
mixtures.
51. The method of claim 50, wherein the ratiometric behavior of the
series known mixtures is linearly related.
52. The method of claim 50, wherein the ratiometric behavior of
known mixtures is observed for one or more separate mixtures where
COHb, rHb and/or O.sub.2HB is, or are, the dominating hemoglobin
derivative, or derivatives, in each series of known mixtures.
Description
BACKGROUND
[0001] Hemoglobin derivatives are an important clinical parameter
for diagnosis of the oxygen carrying capability of blood
hemoglobin. The functional hemoglobin derivatives are known as
oxygenated hemoglobin (O.sub.2Hb) and deoxy- or reduced hemoglobin
(rHb). In many cases, the presence of other, non-functional
hemoglobin derivatives, such as carboxyhemoglobin (COHb),
methemoglobin (metHb) and/or sulphhemoglobin (sHb) may affect the
measurement and/or calculation of oxygen-related parameters, such
as oxygen saturation. Indeed, information regarding the presence of
other hemoglobin derivatives is important, as these derivatives are
non-functional, i.e., they do not have any significant capability
to carry oxygen.
[0002] Traditionally, hemoglobin derivative measurements are
performed using hemoglobin analyzers known as co-oximeters. Current
models of tabletop co-oximeters use various numbers of wavelengths
to measure and distinguish various hemoglobin derivatives. Some
examples of these are the Radiometer ABL700 Series (manufactured by
Radiometer Medical A/S, DK-2700 Bronshoj) using 128 wavelengths,
the AVL912 CO-OXYLITE (manufactured by AVL Scientific Corporation),
which is one of the few co-oximeters that measures sHb, uses 17
wavelengths. The AVL912 utilizes a modified spectrophotometer in
bandwidths of 6 to 10 nm. The ABL700 uses a typical high-resolution
spectrophotometer with a 11/2 nm bandwidth. The type of technology
utilized in the ABL700, and other co-oximeters as well, entails
large and highly controlled optical components which results in the
tabletop instrument weighing about 75 pounds. In addition, both the
AVL912 and ABL700 ultrasonically lyse the red blood cells (RBC) to
measure released hemoglobin in plasma. This ultrasonic portion of
the system adds size and power requirements to the overall
device.
[0003] Despite the presence in the art of these large co-oximeters,
there is a need, for a point-of-care co-oximeter that is smaller
and portable. Such a co-oximeter would enable the direct
measurement of functional and/or non-functional hemoglobin
derivatives by paramedics, doctors and other health care providers,
in the field, in the emergency room or in the medical office.
SUMMARY
[0004] In accordance with the invention, an optical device for
measurement of hemoglobin derivatives including and not limited to
oxygenated hemoglobin, deoxy-hemoglobin, carboxyhemoglobin,
methemoglobin and sulphhemoglobin is described. The measurement may
take place on diluted and undiluted, hemolyzed or non-hemolyzed
blood, and at room or body temperature. This device has several
advantages over the current co-oximeters in that it is compact,
portable, and may be battery operated.
[0005] Also, in accordance with the invention, the portable
co-oximeter utilizes reduced size optical components, such as light
emitting diodes (LEDs). LEDs are available in various sizes,
bandwidths and peak wavelengths.
[0006] Further, the portable co-oximeter of the present invention
may be used to measure or calculate hematocrit, and also to
calculate total hemoglobin, oxygen saturation (SaO.sub.2),
fractional oxygen saturation (SaO.sub.2frac), oxygen content and
oxygen capacity.
[0007] In accordance with the invention, another method leading to
a reduction in size of the co-oximeter is to take measurements on a
whole blood sample, thus eliminating the size and power
requirements of currently available lysing devices that accompany
prior art co-oximeters. Yet another method for the reduction of the
size of the medical device of the invention is to perform the
measurements on a blood sample without temperature
compensation.
[0008] To accomplish the foregoing, a portable system, device and
method for measuring/detecting various hemoglobin derivatives in a
non-hemolyzed, or hemolyzed, blood sample taken from a patient are
provided. The system/device/method comprise subjecting the sample
to radiation of at least one wavelength for each hemoglobin
derivative to be measured, .lamda..sub.1, .lamda..sub.2,
.lamda..sub.3, .lamda..sub.4 . . . .lamda..sub.n, where n is
defined as the number of desired hemoglobin derivatives. However,
when using whole blood, non-hemolyzed samples, an additional
wavelength is needed for adjustment of turbidity resulting from the
presence of intact red blood cells in the non-hemolyzed blood
sample. Thus, for a whole blood non-hemolyzed sample the sample is
subjected to radiation at n+1 wavelengths for all hemoglobin
derivatives of interest.
[0009] In accordance with the invention, a measurement of
absorbance, transmittance or reflectance may be used to perform the
measurement of hemoglobin derivative. These determined values
further may be used to measure the hematocrit of the non-hemolyzed
sample. Reflectance may be used when measuring whole blood due to
the scattering effects of the cell walls of the red blood
cells.
[0010] Generally, in the system, device and method of the
invention, the absorbance and/or reflectance of the blood sample at
each wavelength is measured, and then this measured value is used
to solve for the concentration and/or percentage of each hemoglobin
derivative of interest. This method is readily described in the
literature, e.g., Zwart, et al. (Clinical Chemistry, Vol. 32, No.
6, 1986) and is incorporated herein by reference in its
entirety.
[0011] One embodiment of the invention utilizes compact light
sources with bandwidths in the range of 7-100 nm without the use of
narrow bandwidth bandpass filters and/or complex diffraction
gratings. Another embodiment can utilize a compact broadband light
source with bandpass filters. Still, another embodiment can utilize
bandwidth compact light sources in the range of 10-60 nm along with
bandpass filters.
[0012] Thus, the novel system, device and method are developed to
utilize existing and future technology in compact light sources to
create a portable co-oximeter. Some examples of the type of light
sources suitable for use in the present invention include, but are
not limited to, light emitting diodes, laser diodes or small
monochromatic light sources. Monochromatic light sources, as well
as light emitting diodes and laser diodes are readily available in
various wavelengths of light, sizes, intensities and power
requirements. Heretofore, the difficulty in using compact light
sources for the measurement of hemoglobin derivatives was that
differentiating between the optical characteristics of the various
hemoglobin derivatives heretofore required the use of tightly
controlled diffraction gratings or very narrow bandwidth bandpass
filters due to the overlapping visible absorption spectra of the
various hemoglobin derivatives. This difficulty is now overcome by
the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of preferred embodiments of the invention. As
illustrated in the accompanying drawing in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention.
[0014] FIG. 1 represents a spectral of various hemoglobin
derivative plots empirically obtained by Zwart, et al. (Clinical
Chemistry, Vol. 32, No. 6, 1986) illustrating optical absorbance
spectra of O.sub.2Hb, rHb, COHb, metHb and sHb in the visible
wavelength range. This data is plotted in 2 nm bandwidth
increments.
[0015] FIG. 2 shows representative output spectra for typical LED
light sources in the visible region of the electromagnetic
spectrum. The bandwidths (center wavelength) range from 12-36
nm.
[0016] FIG. 3 is a plot of the calculated absorbance spectra of
O.sub.2Hb, rHb, COHb, metHb and sHb in the visible wavelength
range, which essentially represents a superimposition of
theoretical 40 nm bandwidth LEDs of peak wavelengths as
labeled.
[0017] FIG. 4 is a plot of the calculated absorbance spectra of
O.sub.2Hb, rHb, COHb, metHb and sHb which essentially represent a
superimposition of actual bandwidth data of LEDs of peak
wavelengths as labeled.
[0018] FIG. 5 is a representation of the results for measurements
of various hemoglobin derivatives using AVL Confitest ff.TM.
solutions, which are standardized solutions that mimic the behavior
of the various hemoglobin derivatives. Results from the product
insert range for each hemoglobin species is charted along with the
results using five distinct wavelengths taken from the spectra
generated in FIG. 1 at 2 nm bandwidths using an HP8451A
spectrophotometer. FIG. 5 also represents the results for various
hemoglobin derivatives using whole bovine blood. In addition,
results from the AVL912 Co-Oxylite using 17 distinct wavelengths is
charted along with the results for various hemoglobin derivatives
using five distinct wavelengths taken from the spectra generated in
FIG. 1 at 2 nm bandwidths and the measurements from an HP8451A
spectrophotometer.
[0019] FIG. 6 is a representation of the results for measurements
of various hemoglobin derivatives using AVL Confitest ff.TM.
solutions, which are standardized solutions that mimic the behavior
of the various hemoglobin derivatives. Results from the product
insert range for each hemoglobin species is charted along with the
results using five distinct wavelengths taken from the spectra
generated in FIG. 3 using the theoretical 40 nm bandwidth LEDs and
the measurements from an HP8451A spectrophotometer. FIG. 6 also
represents the results for various hemoglobin derivatives using
whole bovine blood. In addition, results from the AVL912 Co-Oxylite
using 17 distinct wavelengths is charted along with the results for
various hemoglobin derivatives using five distinct wavelengths in
the same manner as in FIG. 5.
[0020] FIG. 7 is a plot of absorbance at 722 nm taken from an
HP8451A spectrophotometer vs. hematocrit of whole bovine blood.
Wavelengths in the visible range to the near infrared range are
similar in shape and can be described by similar equations. 722 nm
is plotted here for clarity.
[0021] FIG. 8 is a plot of hematocrit vs. calculated hematocrit in
the high visible to near infrared wavelengths (722 nm) using whole
bovine blood. This information is used for turbidity adjustment for
all data presented.
[0022] FIG. 9 illustrates a schematic of an embodiment of the
system of the present invention.
[0023] FIG. 10 illustrates an embodiment of the device of the
present invention.
[0024] FIG. 11 is a plot of absorbance of a theoretical 40 nm
bandwidth as a function of percentage of O.sub.2Hb in combination
with COHb and rHb. The amount of metHb and sHb are calculated to be
negligible in this plot.
[0025] FIG. 12 is a plot of the ratio of absorbance of the
theoretical 40 nm bandwidth as a function of percentage of
O.sub.2Hb in combination with COHb & rHb. The amount of metHb
and sHb are calculated to be negligible in this plot. There are two
ratiometric relationships shown in this plot. One relationship may
be more accurate than the other depending on the environmental
factors.
[0026] FIG. 13 is a representation of the results for measurements
of O.sub.2Hb, rHb and COHb in a mixture of Confitest solution and
whole bovine blood. The results from the AVL912 are charted along
with the results of the spectrophotometer placed through the 40 nm
program and Beer-Lambert Law calculations, as well as the same 40
nm data placed through the ratiometric relationship, as described
by FIG. 12.
[0027] FIG. 14 is a representation of the results for measurements
of various hemoglobin derivatives using AVL Confitest Level 1
ff.TM. solutions (low clinical tHb levels), which are standard
solutions that mimic the behavior of the various hemoglobin
derivatives, as well as results from real LEDs of the peak
wavelengths as labeled on FIG. 2, the results using five distinct
wavelengths taken from the spectra generated as in FIG. 4 at 12-36
nm bandwidths of theoretical LEDs using an HP8451A
spectrophotometer along with the range for each hemoglobin species
from the Confitest Product Insert Datasheet (PID).
[0028] FIG. 15 is a representation of the results for measurements
of various hemoglobin derivatives using AVL Confitest Level 1 .mu.m
solutions (mid clinical tHb levels), which are standard solutions
that mimic the behavior of the various hemoglobin derivatives, as
well as results from real LEDs of the peak wavelengths as labeled
in FIG. 2, the results using five distinct wavelengths taken from
the spectra generated as in FIG. 4 at 12-35 nm bandwidths of
theoretical LEDs using an HP8451A spectrophotometer along with the
range for each hemoglobin species from the Confitest Product Insert
Datasheet (PID).
[0029] FIG. 16 is a representation of the results for measurements
of various hemoglobin derivatives using AVL Confitest Level 3 .mu.m
solutions (high clinical tHb levels), which are standard solutions
that mimic the behavior of the various hemoglobin derivatives, as
well as results from real LEDs o the peak wavelengths labeled on
FIG. 2, the results using five distinct wavelengths taken from the
spectra generated in FIG. 4 at 12-35 nm bandwidths of theoretical
LEDs using an HP8451 spectrophotometer along with the range for
each hemoglobin species from the Confitest Product Insert Datasheet
(PID).
DESCRIPTION
I. Developing Methodology of The Invention
[0030] The starting point for the development of the system, device
and method used to measure the presence of various hemoglobin
derivatives is the use of small readily available light sources.
For the sake of clarity LEDs will be used as the light source with
the understanding that laser diodes and monochromatic light
sources, as well as LEDs in combination with bandpass filters or
bandpass filters in combination with broadband light sources may be
used. When referring to a light receiving source, photodetectors
will be used with the understanding that photo transistors, photo
diodes, PIN diodes, CCD arrays, photo multipliers and the like may
be used.
[0031] LEDs are available in various peak wavelengths and
bandwidths. A statistical evaluation is typically performed by the
manufacturer to describe or specify the LED light source, and these
characteristics of LEDs are often used in the evaluation of test
data when verifying a product against its performance
specification. This type of evaluation is also performed to
describe the performance of a bandpass filter. An example of a LED
characteristic output may be described as a peak wavelength of 612
nm, for example, with a 50% intensity bandwidth or center
wavelength (CWL) of 12 nm. The output of this specific LED may be
described by a 3.sup.rd order polynomial with 98% confidence along
a 12 nm bandwidth.
[0032] In the present invention an evaluational statistical
approach was taken to develop a methodology that enables the use of
larger bandwidth light sources, such as LEDs for instance, for use
in a portable co-oximeter.
[0033] As a starting point in the invention, consideration is given
to the shape of the curves developed in FIG. 1, as well as the
maxima in wavelengths and extinction coefficients of the various
derivatives. This is the starting point of the methodology that
enables the use of compact light sources in the portable
co-oximeter of the invention. In this method, it is assumed that
the typical, and probably the worst case LED may be described by a
peak wavelength with a 50% intensity bandwidth or center wavelength
(CWL) of 40 nm. Thus, 99% of the 50% and greater intensity output
of the LED is within 20 nm above the peak and 20 nm below the peak
wavelength. FIG. 2 shows examples of the output spectra of typical
LEDs in the 12-36 nm range provided by a supplier.
[0034] FIG. 3 is a description of the calculated optical behavior
of hemoglobin derivatives where the output spectrum of a 40 nm
bandwidth LED essentially has been superimposed onto the spectra
described in FIG. 1. In essence, the data shown in FIG. 3,
represent the empirical data shown in FIG. 1, where data points are
generated at every 2 nm, averaged across 40 nm surrounding each
peak of interest. Specifically, each data point shown in FIG. 3 was
developed by taking a weighted average of 20 data points (a data
point at every 2 nm across 40 nm). For example, in order to get a
data point at 500 nm, the average was taken across the wavelength
range of 480 nm to 520 nm with 500 nm being given the maximum
weight. A typical arithmetic average may be performed by adding all
20 data points and dividing the sum by 20. In order to more closely
estimate the performance of a typical LED light source with a 40 nm
bandwidth, the curves were weighted based on the typical spectral
response of a 40 nm light source.
[0035] It is noteworthy that the calculated spectra depicted in
FIG. 3 show greatly differing maxima and isobestic points as
compared to those of FIG. 1. For example, the dual peak maxima of
the O.sub.2Hb residing at 542 nm and 576 nm normalizes into a
single peak at about 560 nm. Interestingly, the normalization of
the rHb may be described very similarly with a single maxima at
about 556 nm. It is interesting to note, however, that the
normalized plots of these two derivatives and that of COHb, show
greatly differing absorption coefficients at about 534 nm. This
wavelength has not been considered in any literature reference as a
potential measuring wavelength. Thus, from the inventive
methodology, different maxima and isobestic points are revealed in
FIG. 3 which can be used as measuring wavelengths to determine the
concentration and/or percentage of the hemoglobin derivatives of
interest using compact light sources, such as LED light
sources.
[0036] After determining the absorbance of the light generated from
a typical LED for the hemoglobin derivatives of interest,
simultaneous, or near simultaneous, linear equations are used to
calculate the concentration of each hemoglobin derivative. The sum
of these concentrations are calculated and reported as total
hemoglobin. From this total, the percentage of each hemoglobin
derivative can be calculated along with other clinically relevant
parameters, such as saturation (SaO.sub.2), fractional oxygen
saturation (SaO.sub.2frac), oxygen content and oxygen capacity.
[0037] For greater accuracy in these measured values, a ratio of
the absorbance at certain specified wavelengths can be performed,
called a ratiometric calculation, to yield more precise values with
respect to the percentages of each hemoglobin derivative, as these
percentages relate to the total hemoglobin content. Finally, a
measurement of the absorbance and/or reflectance of a turbid,
non-hemolyzed blood sample at wavelengths in the high visible to
near infra red region of the spectrum is taken to adjust for
turbidity and to measure the hematocrit of the blood sample.
[0038] In addition, the relationship between total hemoglobin and
hematocrit may also be used to validate the measurement of total
hemoglobin, e.g., hematocrit is equal to 3 times the total
hemoglobin in g/dL in non-hemolyzed blood, except in diabetic coma
in hyperlipidemia and altered viscosity, as well as other states
where the 1:3 relationship for hematocrit is invalid.
[0039] The hematocrit also may be measured ratiometrically to bring
the measurement into even greater accuracy. Ratiometric
calculations improve accuracy particularly for embodiments of the
medical devices of the present invention which do not include a
thermal device to compensate for temperature effects. Ratiometric
calculations also compensate for other environmental effects such
as flow rate, presence of air, etc.
[0040] From the plots shown in FIG. 1, the peak wavelengths
.lamda..sub.1, .lamda..sub.2, .lamda..sub.3, .lamda..sub.4 . . .
.lamda..sub.n are about 500, 556, 568, 578, and 622 nm with a 2 nm
bandwidth for each hemoglobin derivative of interest, namely
O.sub.2Hb, rHb, COHb, sHb and metHb. For the experimental work
leading to the invention, 722 nm was chosen as the excitation
wavelength for the adjustment for turbidity with a 2 nm bandwidth.
The absorbances and/or reflectances at each wavelength are then
determined substantially simultaneously using broadband light split
into 2 nm bandwidths using a diffraction grating.
[0041] Alternatively, from the data developed in FIG. 3, the
optimal wavelengths .lamda..sub.1, .lamda..sub.2, .lamda..sub.3,
.lamda..sub.4 . . . .lamda..sub.n are about 500, 536, 554, 566,
616, and 722 nm for measurement of turbidity, using a typical LED
with a 40 nm bandwidth. These wavelengths represent the shifts of
the optical absorbance spectra resulting from the spectral output
of a LED, along a bandwidth of 40 nm.
[0042] FIG. 4 shows the optimal wavelengths .lamda..sub.1,
.lamda..sub.2, .lamda..sub.3, .lamda..sub.4 . . . .lamda..sub.n are
about 506, 526, 556, 570, 610 and 800 nm for adjustment of
turbidity using a typical LED with a 20 nm bandwidth. The empirical
absorbances and/or reflectances at each of these wavelengths may be
measured substantially simultaneously, or in an alternating
fashion, using light emitting diodes or diode lasers operable at
these wavelengths
[0043] It is noteworthy that in the invention the optimal
wavelengths may be chosen by inspection of the calculated
absorption spectrum generated for a given light source. The optimal
measuring wavelength, or wavelengths, are those wavelength(s)
capable of best distinguishing each hemoglobin derivative of
interest. These optimal wavelengths can be determined from the
calculated absorption spectra by visual inspection or with the aid
of computer software directed to yield the optimal wavelengths for
distinguishing among the hemoglobin derivatives. Thus, the optimal
wavelengths ultimately will depend on the light source or light
sources, or filters selected to be used in an embodiment of the
system and device of the invention.
II. Experimental Verification of the Invention
[0044] Optical measurements in blood rely on the difference in the
optical extinction or absorbance/reflectance coefficient of
different hemoglobin derivatives, as illustrated in the plot of
FIG. 1. Traditionally, co-oximeters, such as AVL912, utilize a
large number of specific wavelengths in the visible region of the
optical spectrum. In particular, the AVL912 utilizes 17 wavelengths
in the visible region at 530, 536, 542, 548, 554, 560, 566, 572,
578, 584, 590, 604, 612, 622, 630, 640 and 648 nm to measure five
hemoglobin derivatives. Selection of the proper wavelengths is
achieved by a stepper motor driven monochromator.
[0045] The concentrations of oxyhemoglobin (O.sub.2Hb), reduced
hemoglobin (rHb), carbooxylhemoglobin (COHb), methemoglobin
(metHb), and sulphhemoglobin (sHb) may be determined by solving at
least five independent equations derived from Beer-Lambert's Law.
Beer-Lambert's Law may be described by the following equation:
A=.epsilon.(.lamda.)*c*I.
[0046] Where A=absorbance or optical density [0047]
.epsilon.(.lamda.)=extinction coefficient (L/mmol*cm) at A
wavelength (nm) [0048] c=concentration of hemoglobin derivative
(mmol/L) and I=pathlength (cm)
[0049] These results are expressed in concentration of units of
either mmol/L or gram % (g/dL) and in percentage of the tHb,
calculated from division by the sum of each individual hemoglobin
derivative. Oxygen saturation (SaO.sub.2), fractional oxygen
saturation (SaO.sub.2frac), oxygen content and oxygen capacity may
be calculated by the following equations:
SaO.sub.2=O.sub.2Hb/O.sub.2Hb+rHb)]*100%,
SaO.sub.2frac-[O.sub.2Hb/THb]*100%, oxygen content=O.sub.2Hb,
oxygen capacity=O.sub.2Hb+rHb.
[0050] In selecting suitable light sources for the portable
co-oximeter of the invention, light emitting diodes (LED) were
considered as the compact light source. Light emitting diodes are
available in various peak wavelengths, bandwidths and cost. They
are available in small packages that are smaller in size compared
to any diffraction grating associated with a broadband light
source. The HP8451A spectrophotometer (manufactured by
Hewlett-Packard now Agilent Technologies) was used for the initial
experimentation, which utilized a diffraction grating that splits
polychromatic light into 2 nm bandwidths.
[0051] To develop the system, device and method of the present
invention, standard quality control liquids were used. AVL provides
three levels of QC liquids, Confitest 1, 2 and 3 resulting in
similar percentages of each hemoglobin derivative but at different
total hemoglobin levels. These standard solutions are used in
conjunction with the AVL912 co-oximeter and compared with the
product insert and the printed result for the AVL912 instrument. In
addition, absorbance measurements were performed with an HP8451A
spectrophotometer, and placed into equations of the Beer-Lambert
Law for calculations of hemoglobin concentrations. The results with
whole blood compared with the results from the AVL912 and are shown
in FIG. 5.
[0052] One important challenge that LEDs present are realized in
their spectral emission. The emission of a LED is specified as its
peak wavelength and bandwidth. The bandwidth of the emission of a
LED is a major component in the cost of the LED. An important
aspect of the reduction in size is the determination of potential
bandwidths that may prove to be feasible to distinguish between the
various hemoglobin derivatives, as many of the derivatives have
similar and overlapping optical spectra.
[0053] The extinction coefficients of each of the hemoglobin
derivatives were normalized among a 40 nm bandwidth and the
resulting plot is shown in FIG. 3. The results depicted in FIG. 3
were obtained by normalizing the absorption coefficients of each of
the hemoglobin derivatives across the wavelength spectrum. The
normalization used can be described as a normal distribution across
a 40 nm wide bandwidth including 3 standard deviations. Five
wavelengths were used in the solution of the Beer-Lambert Law for
the five hemoglobin derivatives of interest. As discussed above,
the output weighting equation taken along 40 nm shifted the spectra
some and therefore the maxima of the O.sub.2Hb shifted from a dual
peak at 542 nm and 576 nm to a single maxima at 560 nm very closely
resembling and overlapping the maxima of the rHb at 558 nm. For
this reason, a wavelength at about 536 nm was chosen to distinguish
between O.sub.2Hb and rHb and also COHb for use with a 40 nm LED
light source.
[0054] The wavelength at about 536 nm shows a large disparity and
significant amplitude in the optical spectra of the O.sub.2Hb, rHb
and COHb. The lowest amplitude is expressed in the spectra of rHb
where the extinction coefficient is about 7.97 which is much
greater than those in the near infrared, where the extinction
coefficient is about 0.3. The wavelength at about 566 nm is
representative of an isobestic point for the three derivatives. The
maxima of the COHb shifted from a dual peak at 540 nm and 568 nm to
a single maximum at about 554 nm. The maxima of sHb shifts slightly
from 622 nm to about 616 nm.
[0055] The results with AVL Confitest Quality Control fluids and
whole blood are shown in FIG. 6.
[0056] The weighted optical spectra among 40 nm was plotted with
theoretical various mixtures of O.sub.2Hb, rHb and COHb as these
derivatives overlap each other in the wavelength ranges of 530-580
nm. In this example, the contributions of metHb and sHb are
minimal.
[0057] In order to verify the percentages of O.sub.2Hb, rHb and
COHb it is assumed that the amounts of MetHb and sHb do not affect
the absorbances a high degree in the area of 534 to 566 nm. FIG. 3
shows this to be a valid assumption as even when 100% present, the
extinction coefficients are about 50% or less than that of the
hemoglobin derivatives of interest. The optical density of each of
the wavelengths of 534 nm, 554 nm and 566 nm may be calculated as
resulting from only the O.sub.2Hb, rHb and COHb by using
Beer-Lambert's Law and subtracting the contribution of MetHb and
sHb using the measured concentrations from the previous portion of
the program.
[0058] These calculated absorbances may then be taken as a ratio
and related to the percentages of O.sub.2Hb, rHb and COHb. The
ratiometric measurement has an advantage in that environmental
factors may similarly affect absorbances in similar manners and may
be cancelled out when taking the ratio. Some examples of these
environmental factors are, but are not limited to temperature, pH,
hematocrit, air bubbles, cuvette factors, etc.
[0059] After the absorbances and calculated concentrations and
percentages of the five hemoglobin derivatives are obtained,
ratiometric curves may be used to validate and/or fine tune the
percentages of hemoglobin derivative. The result can then be
mathematically iterated into the original absorbances for
adjustment. In this manner, the environmental factors such as
temperature, air bubbles and slight disparities in cuvette
thickness, pathlength and position may be compensated.
[0060] Measurement of turbidity can take place at any wavelength of
the visible to near infrared range. The extinction coefficients of
the hemoglobin derivatives is about 10 times lower in this
wavelength range, and therefore, does not absorb a great amount of
light in this wavelength range. It is, therefore, advisable to work
in the near infrared wavelength ranges in order to eliminate the
sensitivity to hemoglobin type. The verifying experimentation was
performed at 722 nm as the HP8451 measures quite adequately at this
wavelength. Measurement of turbidity may be used for the adjustment
for the presence of the RBC's and may also be used to provide
information of the hematocrit. Hematocrit or the volume percent of
RBC's in a blood sample is also an important parameter to monitor.
The method, system and device of the present invention may also be
used to measure hematocrit directly, in addition to permitting the
calculation of the hematocrit indirectly based on the sum of all
hemoglobin derivatives.
[0061] Those well acquainted in the art understand that turbidity
and hematocrit are related in the field of blood chemistry and that
total hemoglobin is also related to hematocrit. The turbidity
relates to the hematocrit in that it is the cell membrane of the
red blood cells that effectively scatter light, and therefore,
inhibit its transmission of light radiation. Thus, it is important
to make an adjustment in absorbance measurements, as it is the
light transmission that is measured, while the absorbance is
indirectly measured with the assumption that all light that is not
transmitted is absorbed from the sample. Absorbance is related to
transmission by the relationship of: Abs=log(100%/% T) Where:
Abs=absorbance
[0062] % T=percent transmittance.
[0063] If in fact some of the light is scattered, this mathematical
relationship is invalid and scattering must be accounted for. The
scattering of red blood cells is similar across the visible and
near infrared ranges. It is for this reason that the recommendation
of turbidity measurement be performed in the near infrared
range.
[0064] As discussed above, a method for the reduction in size of
the portable co-oximeter is the use of LEDs as the light source. It
is assumed for the development that the distribution of the
wavelength output is normal around the peak wavelength. Also, as
stated above, FIG. 3 is the data of FIG. 1 with a 40 nm bandwidth
"filter." This "filtering" of the data was performed with
mathematical software. The population of the extinction
coefficients of each 2 nm from 480 nm to 650 nm was weighted along
40 nm with an assumed polynomial equation of 3.sup.rd order. It is
assumed that 100% of the output of intensity greater than 50% (CWL)
is captured in this equation. A 40 nm bandwidth is representative
of current LED sources in the red to near infrared range, and about
20 nm bandwidth is representative for the lower visible
wavelengths. It is noted that these bandwidths represent typical
values. LEDs are available in tighter bandwidths by selection at a
premium price.
[0065] FIG. 4 is an example of this same type of weighting taken
over a 12-36 nm bandwidth of real or actual LEDs. It may be
understood by those in the art that any type of statistical
distribution describing the light source may be applied to this
data of extinction coefficients and may represent the performance
of many types of light sources, including those using bandpass
filters and fiberoptics. To develop this plot, five distinct LEDs
with associated peak wavelengths are used that are available as off
the shelf items. In this case the supplier is the distribution
network, PRP Optoelectronics Inc. Data sheets received from PRP
Optoelectronics gave about a 12-36 nm bandwidth that may be
described by polynomial equations of 93-98% confidence.
[0066] FIG. 5 shows a bar graph of the results of the Confitest
solutions. These solutions mimic the behavior of COHb only. The
product insert included with the Confitest solutions gives a range
of expected results that indicate the AVL 912 Co-Oxylite is in
calibration. Results from the data of this same fluid measured in
the HP8451A and data placed into a proprietary software program
using the Beer-Lambert Law gives the results graphed as the second
from the left to right bar. Note that the values calculated for
this second bar are trending appropriately but somewhat slightly
lower than the expected values for PID low and PID high as these
related to tHb.
[0067] Whole blood was used in addition to the Confitest solutions
and also plotted in FIG. 5. In this case, as well the data taken
from the HP8451A, trends in the same manner as the AVL912. These
deviations are acceptable as the objective was to demonstrate
feasibility of measurement and only the five wavelengths specified
in FIG. 1 were used. Current devices measure at more wavelengths,
e.g., 17-128 wavelengths.
[0068] FIG. 6 shows the results of the same Confitest fluid
information plotted with the data of the same fluid measured from
the HP8451A and proprietary software using the 40 nm filter as
described and charted in FIG. 3. Note that the results of the 40 nm
program trend with the expected results of the Confitest
solutions.
[0069] Note that the results for FIG. 6 of the 40 nm program trend
with the expected results of the Confitest solutions and also fall
within the expected range of the Confitest solutions. Also, in FIG.
6, whole blood was used in addition to the Confitest solutions and
trends in the same manner as the AVL912.
[0070] FIG. 7 shows the relationship between the high visible to
near infrared wavelength light sources and the mathematical
relationship between that and the hematocrit (volume % of red blood
cells in a blood sample). A similar equation/relationship exists
between any wavelength and bandwidth in this region. It is
noteworthy that the extinction coefficients in this wavelength
range are on the order of 40 times less than in the low visible
wavelength range. Therefore, the absorbance and/or reflectance in
this range may be less sensitive to concentration of hemoglobin
derivatives. It may also be noted that just as a ratiometric
relationship may not be affected by environmental factors, this
measurement too may be best expressed as a ratiometric
relationship.
[0071] FIG. 8 is a chart of calculated hematocrit from the
relationship shown and described in FIG. 7. This figure covers the
entire biological hematocrit range. The hematocrit used as the
control is the results from the AVL 912 Co-Oxylite total hemoglobin
multiplied by 3. This work has also been verified by performing
hematocrit measurements using a hematocrit centrifuge.
III. An Example of a System and a Device of the Invention
[0072] FIGS. 9 and 10 illustrates the system and device of the
present invention. Functionally, the system is a dedicated purpose
spectrophotometer system utilizing a number of fixed wavelength
emitters to provide for a means of measuring absorbance of those
frequencies. These emitters are optically combined to result in,
essentially, a point source emitter capable of any of six available
output wavelengths. The emitters are optically coupled though the
sample cuvette to a photo detector (PIN diode) and suitable
recovery electronics. While a number of different approaches are
also possible, a goal is to utilize the approach which also will
result in the most cost-effective and reliable product design.
[0073] FIG. 9 illustrates a schematic design of the system of the
present invention. An emitter is energized at a known output level
generating light of specific wavelength(s), which is passed through
the sample onto the corresponding detector. The resulting detected
current (light) is read by the computer and converted to
appropriate units of transmittance, absorbance and/or reflectance.
The results are further manipulated in conjunction with the
requirements of the application to render results of hemoglobin
concentration, % hemoglobin and other results in accordance with
the requirements of the application. The schematic shown in FIG. 9
is meant to be illustrative for the use of a multitude of suitable
components and product families from which to implement in specific
embodiments of the present invention.
[0074] The system shown in FIG. 9 is comprised of a processor
platform which provides support for a user interface of display and
keypad, system control and interface capability to external
devices. Interfaced to the control computer are control and data
acquisition system devices. These provide selection and control of
the light emitters as well as control over the sensitivity of the
recovery (detector) system and the ability to convert the detected
light to numerical values useful in calculations by the computer.
Common to all of these are a power supply system. The following is
a detailed discussion of each of the components of the system shown
in FIG. 9.
[0075] CPU SYSTEM: The control computer subsystem 40 is comprised
of an embedded microcontroller which supports the computation
requirements of the device. It provides timing, interrupt service
control, memory management and control of all peripheral devices
under program control. Storage of calibration constants and other
non-volatile data is supported via a small EEPROM.
[0076] EXTERNAL INTERFACE: A serial interface is provided for
establishing connection with other subsystems, as well as for
testing and manufacturing support. In particular, an embodiment of
the present invention can be linked to a pulse oximeter so that the
measurement of the various hemoglobin derivatives can be determined
independently of co-oximetry and pulse oximetry. The information
obtained from the multi-component system of the present invention
may be used to further improve the accuracy of the medical device
and system of the invention as described in U.S. Ser. No.
09/460,251, which is incorporated by reference herein in its
entirety.
[0077] Portable and hand-held pulse oximeters are well known in the
art. Examples of such pulse oximeters are found in U.S. Pat. No.
4,733,422, U.S. Pat. No. 5,490,523 and U.S. Pat. No. 5,792,052, all
issued to Isaacson et al., and U.S. Pat. No. 5,575,284 issued to
Athan and Scharf, which are incorporated herein by reference.
Currently marketed hand-held pulse oximeters are produced by BCI
International, such as Model BCI 3301, and Model BCI 3303. Other
marketed portable pulse oximeters are available from Nonin, such as
the Onyx Finger Pulse Oximeter Model, and PaceTech, Inc., such as
the Vitalmax 800 plus Model. These patented devices and products
are all suitable for use as linked pulse oximeters in the medical
device and system of the present invention.
[0078] DATA ACQUISITION SUBSYSTEM: The sensor system interfaces to
the computer through a number of data acquisition components.
Interfaces for analog input (ADC, or analog to digital conversion),
analog output (DAC, or digital to analog conversion) and digital IO
(input/output) are contained in the subsystem. These subsections
connect to the emitter and detector electronics as well as
providing support for self diagnostics and system status testing.
They are discussed further with their corresponding subsystems.
[0079] EMITTER SUBSYSTEM: Light emitting diodes produce output
which is essentially proportional to the current through the diode.
The emitter drive system provides a precision, high performance
bipolar constant current source whose output current is determined
by an input reference voltage, which is provided by a digital to
analog converter (DAC). Setting the DAC to a given value results in
a very precise current being sourced to a LED.
[0080] An embodiment of the system of the present invention
utilizes six LEDs as emitters. These may be combined via a
light-pipe assembly, or through optical fibers, or all dies may be
bonded onto one hybrid with a single lens. Whether a LED is active,
and at what output level, is determined by program control. Any one
of the six emitters of the emitter subsystem may be activated at a
precise operating current and for a period determined by the
control system.
[0081] SENSOR OPTICS: The sensor optics system consists of a block
of opaque material 10 which is machined or molded to provide for
retention of a sample cell 18 (cuvette) containing the specimen to
be analyzed 17 (blood). The block is configured to allow for
optical communication with the various emitters and optical
detector(s), which are maintained in optical alignment and project
through the active proportion of the sample cell.
[0082] DETECTOR SUBSYSTEM: The detector subsystem utilizes a blue
enhanced low noise PIN diode as its detector. These devices have
been selected as they are known to have good linearity and
appropriate characteristics in the visible to near infrared
wavelength range. Light falling onto the die of a PIN diode results
in a current proportional to the incident luminance. The position
of the LED to the PIN diode may be arranged to result in the
transmittance, absorbance, reflectance measurement. The PIN diode
is connected to a transimpedance amplifier, which has been designed
for very high sensitivity, low noise and fast response.)
[0083] PROGRAMMABLE GAIN AMPLIFIER: The transimpedance amplifier is
connected to a programmable gain amplifier, then to one channel of
the ADC input multiplexer, from which it is routed to a sample and
hold circuit and finally to the analog to digital converter (ADC).
The ADC converts the voltage resulting from the detector subsystem
to a numerical value, which is then suitable for use by the
computer program.
OTHER: In addition to the core functionality described above, there
is support for internal test and validation of data, power supply
functionality, emitter drive system test circuitry and program data
validation.
[0084] FIG. 10 illustrates the optical layout of an embodiment of a
microspectrophotometer 10 of the invention. This device consists of
six compact light sources, namely six LEDs 11, 12, 13, 14, 15, and
16, a sample cell/cuvette 18, six photodetectors 26, 26, 27, 28, 29
and 30, a microprocessor 40 of the CPU system and display 42. The
LEDs and photodetectors are mounted inside an opaque black housing.
The LEDs are controlled by a programmable constant current source
and selection logic which communicate with the microprocessor. The
light generated by the LEDs is directed onto the cuvette 18. The
cuvette is filled with the sample to be measured. The cuvette is
inserted into the housing 10 adjacent the emitters. The light
transmitted through the sample filled cuvette to the photodetectors
25, 26, 27, 28, 29 and 30 with peak emission wavelengths at about
500, 525, 555, 568, 612 and 810 nm.
[0085] The photodetectors are comprised of PIN photodiodes (such as
a Photonic Detectors Inc. PDB-V104). Each photodiode is coupled in
the detector subsystem 6 to a corresponding high-speed
transimpedance amplifier. The resulting output voltages from each
transimpedance amplifier are then connected to the microprocessor
40 via an analog multiplexer and analog to digital converted (ADC)
and further calculations are performed.
[0086] The following further details the enabling method yielding
the portable co-oximeter of the present invention.
[0087] 1. Summary of the Enabling Technology
[0088] a) Overall Design and Results
[0089] Thus, the co-oximeter of the present invention is generally
enabled to be portable by three design characteristics. These may
be defined as:
[0090] a) using small optical components that do not require tight
controls;
[0091] b) performing the measurement on whole blood; and
[0092] c) using ratiometric calculations.
[0093] Of these three design characteristics, it is specifically
the use of small optical components that allow the mechanical
design and electronics of the co-oximeter to be small enough to be
portable. Use of whole blood allows the design to be smaller still.
Typical hemolyzing methods include ultrasonic devices that are
large and have high power requirements. If hemolyzing the blood was
deemed necessary, a small pump with water and/or other chemicals
might be used to lyse the blood and still allow the instrument to
be portable.
[0094] Temperature control can be designed into embodiments of the
co-oximeter within a small amount of real estate but designing
methods for temperature compensation allows for a simpler and even
smaller mechanical design.
[0095] In this device, the procedures for measurement have been
developed to accommodate the performance characteristics of the
smaller optical components utilized. The method continues to use
the laws of optics and the Beer-Lambert Law as do all existing
co-oximeters.
[0096] It is clear that small optical components alone, such as
LEDs having bandwidths from about 7 to 100 nm, would not allow
accurate measurements or even have the capability of distinction
between hemoglobin derivatives. It is for this reason that
co-oximeters of the past have relied upon tightly controlled
optical components requiring diffraction gratings, tight bandpass
filters, tightly controlled laser diodes and the like as the
optical components of choice.
[0097] With an understanding of the capabilities of LED technology,
however, the current method, device and system were developed by
going further back into the history of co-oximetry and looking at
the extinction coefficients through a wider bandwidth "filter", in
particular a 40 nm bandwidth "filter."
[0098] This filter was devised with mathematical equations.
Starting with a possible worst case of 40 nm bandwidth light
source, an equation was developed to simulate the performance of a
40 nm bandwidth LED. Very simply summarized, the data of the
extinction coefficients plotted above were averaged over a 40 nm
range. In a linear averaging each point of the new plot would
consist of an average of 20 data points from the above plot. This
would, of course, be performed by taking a sum of the values at
each of the 20 wavelengths totaling the 40 nm bandwidth and
dividing the sum by 20. This linear averaging, however, does not
simulate the performance of a LED. An LED radiates light at a
certain peak wavelength and around that peak wavelength to varying
degrees. The point(s) or wavelength range at which 50% of the peak
output is known as the center wavelength (CWL) and may be
considered the bandwidth of the LED. The shape of the curve
dictates the confidence that all the radiated light above 50%
intensity will be modeled by a 3.sup.rd degree polynomial around
the peak.
[0099] An example of the performance curve of an LED in the 612 nm
peak wavelength shows that at 50% intensity the wavelength range is
12 nm. This data was provided by PRP Optoelectronics DIS 390 series
612 nm peak wavelength LED. It should be noted that any peak
wavelength, with associated bandwidth and standard deviation may be
reduced into an equation and further devised into a "filter" or
weighting table to establish working extinction coefficient spectra
consistent with the optical components of interest. This may also
be accomplished by creation of a "look-up" table.
[0100] Superimposing the LED characteristic curves shown in FIG. 2,
over the plot of the extinction coefficients of Zwart, et al.,
yields the plot of FIG. 3. The characteristics of each LED are
slightly different, however, the curves seem to overlap even at the
ends of their output spectra.
[0101] These changes are reflected in the optical spectra shown in
FIG. 3. The curves of the above plots shown in the figure greatly
differing maxima and isobestic points from those measured by Zwart
at a 2 nm bandwidth. These new and different maxima and isobestic
points are then used to determine the concentration of the
hemoglobin derivatives of interest using larger bandwidth light
sources.
[0102] A sixth wavelength was also used in order to adjust for the
turbidity of a whole blood sample. The wavelength of 722 nm was
initially used. Further investigation in the area of turbidity and
hematocrit showed that the near infrared wavelengths gave results
that were more favorable with respect to hematocrit only over a
longer bandwidth. For this reason, 810 nm is now preferred.
[0103] It is noteworthy that the invention is developed with a 40
mm bandwidth as an illustration of the worst case scenario. LEDs
are readily available in tighter bandwidths of 12-35 nm in the
blue, green, yellow and orange ranges and approach 30-50 nm when
entering the red to near infrared range as is shown in FIG. 2.
[0104] The results rendered from the solution of five simultaneous
equations adjusted for turbidity using the 6th wavelength gives
good estimation of each concentration of hemoglobin derivative.
These same wavelengths may be used in a ratiometric calculation to
verify and/or adjust the percentages of each hemoglobin derivative
and allow the compensation for environmental factors such as sample
temperature, air bubbles and pH.
[0105] b) The Ratiometric Refinement
[0106] The ratiometric portion of this measurement was developed in
the following manner. It was assumed that the effects of any
present metHb and sHb would be of low significance. In the case
where the metHb and sHb derivatives are low, this is a valid
assumption on its own. In addition, the presence of any amount of
these derivatives may also be taken into account by using Beer's
Lambert's Law:
[0107] Using this equation, the contribution of the metHb and sHb
may be adjusted for by subtracting the .epsilon.(.lamda.)*c*I for
each of the two derivatives.
[0108] The sum of all Hb derivatives may be calculated and
representative of the total amount of Hb, both functional and
nonfunctional in the blood sample. Physiologically, the tHb is
related to the volume percent of red blood cells in the blood
sample, hematocrit, by a factor of three when tHb is presented in
units of gram % or g/dL. The equation is known as tHb[g/dL]*3=Hct.
This may serve as an estimate of hematocrit.
[0109] In addition, the measurement of turbidity may directly be
related to the amount of red blood cells present in the sample or
Hct. Red blood cells act as diffuse reflectors in the visible to
near infrared wavelength ranges. By measurement of the
transmittance of a blood sample the indirect measurement of
absorbance and scattering is accomplished. The absorbance of Hb
derivatives in the wavelength ranges of 650 nm to the near infrared
(1000 nm) is very low. In this range the measurement of
transmittance would then be an indirect measurement of scattering
reflectance only. With the direct measurement of HCT and the
calculated HCT based on the tHb measurement, both measurements may
serve as verification or validation for increased confidence of the
measurements of tHb, each Hb derivative or HCT.
[0110] The ratiometric method applied to the co-oximeter of the
present invention can be used for verification of initial results
using 5 distinct absorbance measurements to distinguish 5 distinct
hemoglobin derivatives. Specifically the Hb derivatives are COHb,
metHb, O.sub.2Hb, rHb and sHb. The corresponding peak wavelengths
to measure these derivatives are about: 534 nm, 500 nm, 568 nm, 554
nm and 616 nm as shown calculated weighted spectra of FIG. 3. This
is based on a methodology that looks at the spectrum of each
specific derivative with respect to wavelength assuming a 40 nm
bandwidth.
[0111] The ratiometric portion of the program was initiated
focusing on the three derivatives that have similar optical
spectra, specifically COHb, O.sub.2Hb and rHb.
[0112] A set of theoretical mixtures of COHb, O.sub.2Hb and rHb
were made up consisting of 100% O.sub.2Hb, 90% O.sub.2Hb with 5%
COHb and 5% rHb, 80%/10%/10% down to 0/50/50. The same was repeated
when starting with 100% COHb and again with 100% rHb. These were
plotted as a function of wavelength. FIG. 11 shows the resulting
plot of percentage of O.sub.2Hb mixtures against wavelength.
[0113] It is noteworthy that for mixtures of various percentages of
O.sub.2Hb derivative, there is good separation at 554 nm and no
separation and good amplitude at 534 nm and 566 nm. In this case,
566 nm or 534 nm may provide information as a reference wavelength
absorbance measurement with good amplitude optical spectra but not
affected by changing percentages of O.sub.2Hb.
[0114] FIG. 12 represents the ratiometric relationships of the
percentages of O.sub.2Hb in combination with rHb and COHb. In all
these representations, metHb and sHb have been calculated to be 0%.
It is interesting to note that when O.sub.2Hb is the dominating Hb
derivative, the most representative in a clinical sense, either
ratiometric relationship (abs566 nm/abs554 nm) or (abs534 nm/abs554
nm) will suffice as a measurement. When rHb is high, however, it is
preferred to use the (abs566 nm/abs554 nm) as the rHb has a large
response in the 534 nm range. This measurement is less important
during clinical use as high concentrations of rHb do not occur in
live human blood samples.
[0115] In addition, 554 nm may provide information as a measuring
wavelength absorbance measurement with good amplitude optical
spectra and is highly affected by Hb derivative that is dominating.
The absorbance at 554 nm may be described as a function of (Hb
derivative mixture, temperature, pH, turbidity, hematocrit, air
bubbles, etc.) The absorbance at 566 nm or 534 nm may be described
as a function of (temperature, pH, turbidity, hematocrit, air
bubbles, etc.)
[0116] Therefore when calculating the ratiometric measurement of a
measured absorbance/reference absorbance, the values resulting are
a function of the Hb derivative mixture only. It should also be
noted that this relationship may also be described by polynomial
equations of various orders.
[0117] By the same methods, evaluations of rHb and COHb may be
performed.
[0118] The plots of rHb and COHb derivatives also have a linear
relationship between a ratiometric measurement and percentage of
each derivative.
[0119] By using these ratiometric measurements, the percentage of
derivative may be calculated and compared to the results received
from the original solution using 5 distinct wavelengths. The
hemoglobin derivatives of lower percentages may also be calculated
using the same equations, however, care must be taken to
distinguish which ratiometric relationship to use. The selection of
the appropriate ratiometric relationship may be performed in
software as part of the electronics.
[0120] This comparison may serve as a verification of the initial
results and may be further served as an adjustment to run through
one or more "iterations" of calculations to increase the accuracy
and/or confidence of the calculated derivative concentrations and
percentages.
[0121] 2. Specific Example Using Weighted Spectrophotometric
Data
[0122] The following is an example of how the method of the present
invention can be used to determine the concentration and/or
percentages of hemoglobin derivative in a blood sample from a
patient. The data from the spectrophotometer is input into a
Mathsoft Mathcad program and the resulting calculations compared to
the results and printout of the AVL912 Co-Oximeter.
[0123] An example of the order in which the measurements are
performed and calculated may be done in the following manner.
[0124] Choose LED components to be used. Obtain associated output
data with respect to peak wavelength and output along its bandwidth
(this is usually provided by the manufacturer of the LED)
[0125] Using this function or using a look-up table, calculate the
extinction coefficient associated with the peak wavelength and
bandwidth.
[0126] Measure the absorbance at each of the wavelengths.
[0127] In the case of whole blood, adjust the absorbance for the
turbidity.
[0128] Solve simultaneous linear equations using the pathlength of
the cuvette, the calculated extinction coefficients and measured
adjusted absorbances. This gives the concentration of each
hemoglobin derivative.
[0129] Sum the individual Hb derivatives resulting in tHb.
[0130] Divide each concentration by the tHb resulting in % Hb
derivative.
[0131] Determine if the resulting percentages are in the High
O.sub.2Hb, High COHb or High rHb.
[0132] Adjust the absorbances of the appropriate wavelengths to
subtract the contribution of any metHb and sHb present using
Beer-Lambert Law.
[0133] Calculate the appropriate ratiometric value based on the
dominating Hb derivative.
[0134] Solve the linear or polynomial equation resulting in % of
dominating Hb derivative.
[0135] Repeat, making appropriate adjustments absorbance and/or
ratiometric values until the ratiometric and linear equations fall
within the desired accuracy.
[0136] A mixture of whole bovine blood and AVL Confitest 2
solutions was prepared. This was done in order to attain a turbid
sample with a high % of COHb near to a high clinical level. The AVL
Confitest solution has an absorbance that simulates a 95% COHb,
which is not clinically relevant.
[0137] The results are plotted in FIG. 13. The data taken from the
AVL912 is plotted with the data from the HP8451A spectrophotometer
and placed through the software program simulating a theoretical 40
nm bandwidth LED and through the Beer-Lambert Law. The ratiometric
data is calculated using the 40 nm weighted data and taken as a
first pass through the ratiometric relationships as described by
FIG. 12 and similar. For further refinement, this data may be
placed into a feedback loop to repeat until a specified confidence
is found.
[0138] 3. Specific Example Using LED Data
[0139] Light Emitting Diodes were received from PRP
Optoelectronics. The relative intensity was taken across 100 nm at
1 nm and used to create a weighted lookup table. LEDs were received
in the following peak wavelengths: 506, 525, 555, 568, 612 and 810
nm. The LEDs ranged in CWL bandwidth from 12-36 nm as is shown in
FIG. 2. 3.sup.rd degree polynomials were generated that estimated
the output of the LEDs that gave 93-99% confidence factors.
[0140] Measurements of the AVL Confitest solutions were placed into
a sample cuvette and into the device described above, where each
LED was mechanically placed on the opposite side of a photodiode.
Measurements of transmittance were taken, transferred into
absorbance and placed through the Beer-Lambert Law using the
weighted extinction coefficients corresponding to the peak
wavelengths.
[0141] The results were compared to results of the same fluid
placed into a similar cuvette and measured with the HP8451
Spectrophotometer. A proprietary software program incorporating the
weighted extinction coefficients of the LEDs and Beer-Lambert Law
was used and represented as HP8451A with weighted LED program in
FIGS. 14, 15 and 16. The same software program replacing the
measurements of transmittance from the device for the weighted
measurements of the spectrophotometer and are represented as Real
LED Data in FIGS. 14, 15 and 16. The results show similar trending
with tHb measurements within the expectation of accuracy stated by
the AVL product insert datasheet.
[0142] 4. Conclusion:
[0143] a) The method of starting with the performance of the
optical components to adjust the extinction coefficient data can be
used to perform the Beer-Lambert Law solving 5 simultaneous
equations to result in concentration data of Hb derivatives in a
whole blood sample.
[0144] b) Using a near infrared absorbance can be used as an
adjustment for turbidity.
[0145] c) A ratiometric relationship with % Hb derivative can be
used to verify or increase confidence and accuracy of the
concentrations arrived at using the Beer-Lambert law.
[0146] All features disclosed in the specification, including the
claims, abstracts, and drawings, and all the steps in any method or
process disclosed, may be combined in any combination, except
combinations where at least some of such features and/or steps are
mutually exclusive. Each feature disclosed in the specification,
including the claims, abstract, and drawings, can be replaced by
alternative features serving the same, equivalent or similar
purpose, unless expressly stated otherwise. Thus, unless expressly
stated otherwise, each feature disclosed is one example only of a
generic series of equivalent or similar features.
[0147] The above description of the invention applies to
embodiments of the system, device and methods of the invention
whether or not explicitly stated.
[0148] Any element in a claim that does not explicitly state
"means" for performing a specified function or "step" for
performing a specified function, should not be interpreted as a
"means" or "step" clause as specified in 35 U.S.C. .sctn. 112.
[0149] The abstract is submitted only to comply with 37 C.F.R.
1.72. The language in the abstract should not be used to interpret
the scope of the claims. Further, the abstract is not to be used in
any manner other than to assist the Patent and Trademark Office and
the general public in determining the gist of the invention.
* * * * *