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What happens between injury and our
perception of pain? This book is about the first unifying law of Pain that
explains the origin of all types of pain: from Arthritis to Fibromyalgia and
from Migraine to Sciatica.
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Designed for quick access to pain drugs
information, Sota Omoigui's Pain Drugs Handbook is a complete clinical guide
in a handy portable format
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As a synopsis of anesthetic pharmacology
it is a useful review for the beginning trainee and the advanced
practitioner. An all-time best seller, The Anesthesia Drugs Handbook has
been translated into Italian, Japanese, Malaysian, Polish and Portuguese.
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This booklet is written to guide those who
suffer or know someone suffering from pain. It provides the most current
information about the common painful syndromes, the right medications,
useful herbs and various treatments that can be utilized in the home, clinic
or hospital to successfully ease pain.
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One of the best books on Self Improvement
and Management ever published. Animals have been taking care of business
much longer than humans and they do it with an instinct few humans possess.
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The Universal
Drug Infusion Ruler
Drug Infusions Made Easy
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To obtain a phone consultation from pain
specialist, Dr. Sota Omoigui, click here.
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PATENTS
United States Patent
5,095,896
Audio-Capnometry Apparatus
Inventor: Sota Omoigui MD
Abstract
An apparatus for use in audio
monitoring of carbon dioxide concentration in general, and as an aid
in blind nasal intubation, as well as other procedures requiring the
monitoring of carbon dioxide in which carbon dioxide is measured by
a carbon dioxide monitor, the carbon dioxide monitors output is used
as the control voltage of a voltage controlled oscillator, and the
output of the voltage controlled oscillator is amplified, delivered
to a speaker, and thereby produces an audible tone whose pitch is
directly proportional to the level of carbon dioxide being
monitored.
L.A. Pain Clinic, Los Angeles, California, USA.
Read The Complete Patent
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United States Patent 5,833,602
Process of Continuous
Noninvasive Hemometry
Inventor: Sota Omoigui MD
Abstract
This invention relates to a process of determining continuously and
non-invasively (without the withdrawal of blood.) the concentrations
of hemoglobin. This is done by measurement of the path length and
analysis of the pulsatile component of absorbance of multiple wave
lengths of light transmitted through a tissue bed. This invention
also relates to the process of simultaneous direct or indirect
measurement of the pulsatile arterial width or arterial diameter
which is equivalent to the pulsatile path length of the light
transmitted across the tissue bed. Measurement of this arterial
diameter or pulsatile path length is a prerequisite for non invasive
determination of the hemoglobin, hematocrit or pigment
concentrations in blood.
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Inventors:
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Osemwota;
Omoigui
(1520 Manhatton Beach Blvd., Manhatton Beach, CA 90266)
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Appl. No.:
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327361 |
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Filed:
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October 11,
1994 |
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Current U.S.
Class: |
600/310;
600/322 |
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Intern'l Class:
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A61B 005/00 |
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Field of
Search: |
600/310,322-4,326,328,330,331 356/41
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References Cited
[Referenced By]
U.S. Patent
Documents
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4883055 |
Nov., 1989 |
Merrick |
128/633.
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4927264 |
May., 1990 |
Shiga et al. |
128/633.
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5111817 |
May., 1992 |
Clark et al. |
128/633.
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Primary Examiner: Nasser; Robert L.
Parent Case Text
This application is a continuation-in-part of the application entitled
PROCESS OF CONTINUOUS NONINVASIVE HEMOGLOBINOMETRY, Ser. No. 08/123,682,
filed on Sep. 20, 1993.
Claims
I claim:
1. A process to determine continuously, non-invasively a hemoglobin
concentration and hematocrit by analysis of a pulsatile component of
absorbance of an isobestic wavelength of light for oxygenated hemoglobin
and deoxyhemoglobin comprising the following steps:
a. attaching a pressure cuff to an extremity of a patient;
b. attaching a sensor probe from an isobestic wavelength oximeter to the
extremity of said patient;
c. inflating said pressure cuff above systolic arterial pressure, then
deflating to determine systolic pressure;
d. repeating steps a-c to determine the maximum systolic arterial
pressure;
d. determining the maximal arterial diameter from the maximum systolic
arterial pressure;
e. transmitting light at a predetermined isobestic wavelength from said
sensor probe across said extremity such that the light passes through
both venous blood, pulsatile arterial blood, and a tissue bed in said
extremity;
f. receiving light from said sensor probe that has passed through the
extremity;
g. determining the AC and DC components of the received light, AC and
DC;
h. determining said pulsatile component of absorbance PA of the received
light which is related to the hemoglobin concentration and independent
of the intensity of the received light from the formula PC=AC/DC;
i. determining the hemoglobin concentration THB using the equation:
THB=@PA/E*Ln;
where @ is a scalar coefficient
E is the extinction coefficient for light at the predetermined
wavelength
Ln is the path length of light at the predetermined wavelength; and
j. determining hematocrit from THB.
2. A process to determine continuously, non-invasively a hemoglobin
concentration and hematocrit by analysis of a pulsatile component of
absorbance of an isobestic wavelength of light for oxygenated hemoglobin
and deoxyhemoglobin comprising the following steps:
a. attaching an ultrasonic echo tracking device to an extremity of a
patient to allow continuous, non-invasive measurement of arterial
diameter;
b. attaching a sensor probe from an isobestic wavelength oximeter to
said extremity of said patient;
c. generating and detecting ultrasonic pulse with said ultrasonic echo
tracking device;
d. determining the maximal arterial diameter from the detected
ultrasonic pulses;
e. transmitting light of a predetermined isobestic wavelength from said
sensor probe across said extremity such that the light passes through
both venous blood, pulsatile arterial blood, and a tissue bed in said
extremity;
f. receiving light at said predetermined wavelength that has passed
through the extremity using said sensor probe;
g. determining the AC and DC components of the received light, AC and
DC;
h. determining said pulsatile component of absorbance PA of the received
light which is related to the hemoglobin concentration and independent
of the intensity of the received light from the formula PC=AC/DC;
i. determining the hemoglobin concentration THB using the equation:
THB=@PA/E*Ln;
where @ is a scalar coefficient
E is the extinction coefficient for light at the predetermined
wavelength
Ln is the path length of light at the predetermined wavelength; and
j. determining hematocrit from THB.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process by which existing technology may be
used by a health care provider in continuously measuring the hemoglobin
and hematocrit concentrations in a patients blood. This is done
non-invasively by analysis of the pulsatile component of absorbance of
selected wave lengths of light transmitted through a tissue bed. Devices
using the process of hemometry will enable continuous measurement of
hemoglobin and hematocrit without the withdrawal of blood. Patients will
no longer have to be subjected to the pain and trauma of repeated
withdrawal of blood. Over and under-transfusions will be avoided by
continuous non-invasive trending of the hemoglobin and hematocrit. By
not having to repeatedly withdraw blood with a needle and syringe,
health care providers will be spared the risks of blood transmitted
bacterial and viral infections.
DESCRIPTION OF THE PRIOR ART
The hemoglobin and hematocrit concentration is a measure of the amount
of red blood cells in the human body. The proper functioning of the body
is dependent on adequate amounts of red blood cells. Hemoglobin and
hematocrit measurements are the most frequently performed medical
laboratory tests. At present, these require withdrawal of a sample of
blood by needle stick or puncture. The sample of blood is then analyzed
by a laboratory oximeter and the hemoglobin concentration determined
based on curent methods of oximetry.
When light passes through matter, it is transmitted, absorbed, or
reflected. The Lambert-Bear Law, on which current methods of oximetry
are based, govern this phenomenon according to the following:
Law 1.: The intensity of light transmitted through a solution is related
to the concentration of a solute in suspension.
Equation: I.sub.trans =I.sub.in -(DC@)
where I.sub.trans =intensity of transmitted light
I.sub.in =intensity of incident light
D=distance light is transmitted through the liquid
C=concentration of solute (hemoglobin)
@=extinction coefficient of the solute a constant for a given solute at
a specific wavelength).
Extinction is the light absorption of a unit concentration and path
length of a substance.
SUMMARY OF THE INVENTION
In FIG. 1, the concentration of a solute dissolved in a solvent can be
calculated from the logarithmic relationship between the incident and
transmitted light intensity and the solute concentration.
Law 2: The total absorption of a system of absorbers is the sum of their
independent absorbances.
A total=E1C1L1=E2C2L2+. . . EnCnLn
where A total is the absorbance of a mixture of substances at a specific
wavelength
E1 is the extinction of a substance 1 at wavelength n
C1 is the concentration of substance 1
L1 is the path length of the light through substance 1 at wavelength n
E2 is the extinction of a substance 2 at wavelength n
C2 is the concentration of substance 2
L2 is the path length of the light through substance 2 at wavelength n
For Beer's Law to be valid, both the solvent and the container must be
transparent at the wavelength used, the light path length must be known
exactly and no other absorbing species can be present in the solution.
With empirical corrections to its calibrations, these requirements may
be fulfilled in laboratory devices, In clinical devices a limiting
factor has been the requirement to measure the path length of light
noninvasively in living tissue. Laboratory oximeters determine
hemoglobin concentration from a sample of blood by spectrophotometry.
Using interference filters on an emitted light beam, monochromatic light
at four specific wavelengths (535.0, 582.2, 594.5 and 626.5 nm) is
produced. The light beam is split with one beam transmitted through a
cuvette filled with a solution of lysed blood to a sample photo-detector
to generate a sample absorbance. The other beam is imaged through a
cuvette filled with a zeroing solution onto a reference photo-detector
to generate a blank absorbance. The absorbance of the blood A at each
wavelength is represented by the equation:
A (sample)-A(blank)=A(blood)
where A is the absorbance at each wave length
A coefficient matrix is determined by oximeter analysis of 100% content
for each of thefour Hemoglobin species (Reduced Hb, Oxygenated Hb, COHb
and Meth Hb). Utilizing this matrix, the following equations are solved
to determine the concentrations of the four measured Hb species in the
blood sample.
Equations:
C.sub.(RHb) =K(E.sub.535RHb A.sub.535 +E.sub.585RHb A.sub.585
+E.sub.594RHb A.sub.594+ +E.sub.626RHb A.sub.626)
C.sub.(O2Hb) =K(E.sub.535O2Hb A.sub.535 +E.sub.585O2Hb A.sub.585
+E.sub.594O2Hb A.sub.594+ +E.sub.626O2Hb A.sub.626)
C.sub.(COHb) =K(E.sub.535COHb A.sub.535 +E.sub.585COHb A.sub.585
+E.sub.594COHb A.sub.594+ +E.sub.626COHb A.sub.626)
C.sub.(MetHb) =K(E.sub.535MetHb A.sub.535 +E.sub.585MetHb A.sub.585
+E.sub.594MetHb A.sub.594+ +E.sub.626MetHb A.sub.626)
where
C=concentration of each Hb species
K=a scalar constant set by the THb calibration procedure
E=each coefficient in the matrix (4 Hb species at 4 wavelengths)
A=the absorbance value of the blood at each wavelength
The Total hemoglobin (THb) value (g/dl) is the sum of the four
concentrations
THb=C.sub.(RHb) +C.sub.(O2Hb) +C.sub.(COHb) +C.sub.(MetHb)
Calibrations are performed using blood samples with known hemoglobin
concentrations assayed by laboratory spectrophotometry.
Pulse oximeters analyze the pulsatile component of absorbance and
determine continuously and noninvasively hemoglobin oxygen saturation.
Pulse oximeters measure the pulsatile component of red (660 nm) and
infra-red light (940 nm) absorbance after transmission through a tissue
bed (e.g. finger or ear). These wavelengths are used because they
maximize the differences in absorbance of deoxy and oxygenated
hemoglobin. At the red wavelength of 660 nm, deoxyhemoglobin absorbs
approximately 10 times as much light as does oxygenated hemoglobin. At
the infra-red wavelength of 940 nm, the absorption coefficient of
oxygenated hemoglobin is greater than that of deoxyhemoglobin. The
output light at each wavelength consists of two components. The baseline
or DC component is a large constant light output level and represents
the absorbances of the tissue bed, including venous blood, capillary
blood and nonpulsatile arterial blood. The pulse-added, or AC component
varies with pulsation of the arterial blood (FIG. 2). The amplitude of
both the DC and AC levels are directly dependent on the incident light
intensity. Dividing the AC level by the DC level (at each wavelength)
gives a corrected AC level (Equation 1) that is no longer a function of
the incident intensity. This corrected AC level is a function only of
the extinction of the two species of hemoglobin (FIG. 3) and the path
length of arterial blood through which the light has passed. The AC
light is only a function of arterial blood since essentially only the
arterioles are pulsating in the lights path. The transmitted light at
each wavelength is converted to an electronic signal by means of a
silicone photodiode. The signals are amplified, filtered, converted to
digital values by an analog-to-digital converter and then fed into a
microprocessor. The oximeter then calculates the ratio R of the pulse
added absorbance at 660 nm (AC660) to the pulse added absorbance at 940
nm (AC940). This ratio (Equation 2) is empirically related to the
hemoglobin oxygen saturation (SaO2).
Equation 1
PAn=ACn/DCn
where PAn=Pulsatile absorbance at wavelength n
ACn=AC component at wavelength n
DCn=DC component at wavelength n
Equation 2
R=(AC660/DC660)/(AC940/DC940).
where R=Ratio of Pulsatile absorbance at wavelength 660 nm and 940 nm
In FIG. 2., is a schematic representation of the absorption of constant
intensity light by living tissues. The output light consists of a
constant light level with a small amount of modulation caused by the
pulsating arterial blood. The constant output light (the DC component)
represents all of the non pulsatile absorbers. The pulsatile output
light (the AC component) is from the arterial blood which is the only
pulsatile component in the series of light absorbers in living tissue.
In FIG. 3, extinction coefficients are plotted against the transmitted
light absorbance spectra in the wavelength range of interest (red and
infra red range) for four species of hemoglobin. Any point in which two
species have the same extinction coefficient is known as the isobestic
point. An isobestic point occurs for oxygenated hemoglobin and
deoxyhemoglobin at 805 nm.
Calibration curves developed from experimental studies in human
volunteers are used to calculate arterial oxygen saturation (SaO2) from
the ratio (R) of the light absorbed (A) by the tissue being monitored.
In FIG. 4., is a calibration curve used by the oximeter to calculate
arterial oxygen saturation (SA02) from the ratio (R) of the light
absorbed (A) by the tissue being monitored.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a light transmitted through a solute
dissolved in a solvent. The concentration of the solute can be
calculated from the logarithmic relationship between the incident and
transmitted light intensity and the solute concentration.
FIG. 2 is a diagram showing the two components of a transmitted
wavelength of light. The baseline or DC component is a large constant
light output level and represents the absorbances of the tissue bed,
including venous blood, capillary blood and nonpulsatile arterial blood.
The pulse-added, or AC component varies with pulsation of the arterial
blood. The amplitude of both the DC and AC levels are directly dependent
on the incident light intensity.
FIG. 3 is a diagram showing extinction coefficients plotted against the
transmitted light absorbance spectra in the wavelength range of interest
(red and infra red range) for four species of hemoglobin. Any point in
which two species have the same extinction coefficient is known as the
isobestic point. An isobestic point occurs for oxygenated hemoglobin and
deoxyhemoglobin at 805 nm.
FIG. 4 is a calibration curve used by an oximeter to calculate arterial
oxygen saturation (SAO2) from the ratio (R) of the two wavelengths of
light absorbed (A660 nm and A940 nm) by the tissue being monitored.
FIG. 5 is a diagram of the apparatus used to carry out the process. A
pressure cuff (2) with a microprocessor controlled oscillotonometer (A)
is attached to the arm of the patient. A sensor probe (6) from the
single to four wavelength oximeter (4) is attached to a finger (5) of
the patient on the same arm. Light from the pulse oximeter sensor is
transmitted across the finger. The oximeter (4) communicates with the
pressure instrument (3) through a communication link (8).
FIG. 6 is another diagram of the same apparatus used to carry out the
process. However the pressure cuff (2) with a microprocessor controlled
oscillotonometer (A) is attached to the arm of the patient. A sensor
probe (6) from the single to four wavelength oximeter (4) is attached to
said finger of the patient on the same arm. Light (5) from the pulse
oximeter sensor is transmitted across the finger. The oximeter (4)
communicates with the pressure instrument (3) through a communication
link (8).
FIG. 7 is a diagram of the second apparatus used to carry out the
process. An ultrasound device (13) is attached to the arm of the
patient. A sensor probe (6) from the single to four wavelength oximeter
(4) is attached to said finger (5) of the patient on the same arm. Light
from the pulse oximeter sensor is transmitted across the finger. The
oximeter (4) communicates with the ultrasound device (13) through a
communication link (8).
FIG. 8 is another diagram of the second apparatus used to carry out the
process. The ultrasound device (3) is attached to the arm of the
patient. A sensor probe (6) from the single to four wavelength oximeter
(4) is attached to a finger (5) of the patient on the same arm. Light
from the pulse oximeter sensor is transmitted across the finger. The
oximeter (4) communicates with the ultrasound device (3) through a
communication link (8).
FIG. 9 is a description of different diameter-pressure relationships
proposed in the literature.
Specifically, FIG. 9 shows a comparison between following different
diameter-pressure relationships proposed in the literature, with the
number of the article corresponding tot he number on the table in FIG.
9:
(1) Langewouters G. J, Wesseling K. G. and Goedhard W. J. A 1984: The
static elastic properties of 45 human thoracic and 20 abdominal aortas
in vitro and the parameters of a new model, J. Biomech, 17, 425-35;
(2) van loon P., Klip W. and Bradley E.L. 1977, Length-force and
volume-pressure relationships of arteries, J. Biorheology 14, 181-201;
(3) Vander werff T. J. 1974, Significant parameters in arterial pressure
and velocity development, J. Biomech 7, 437-47;
(4) Powaloski T. and Pensko B., 1985, A non-invasive ultrasonic method
for blood flow and pressure measurements to evaluate hemodynamic
properties of the cerebro-vascular system, Arch. Accoust. 10, 303-14;
(5) Kivity Y. and Collins R. 1974, Non linear wave propagations in visco-elastic
tubes: applications to aortic rupture, J. Biomech 7, 67-76; and
(6) Hayashi K., Handa H., Nagasawa S., and Okumura A. 1980, Stiffness
and elastic behaviour of human intracranial and extracranial arteries,
J. Biomech 13, 175-84.
FIG. 10 is a model of an arterial diameter-pressure curve.
FIG. 11 is an example of an ultra sound echo reflected from the anterior
and posterior walls of an artery.
DETAILED DESCRIPTION
Like the Laboratory oximeter, the continuous noninvasive hemometer will
determine hemoglobin concentrations. Unlike the laboratory oximeter,
hemoglobin concentrations will be determined continuously and
noninvasively by a probe attached to the tissue (e.g. finger) rather
than one single measurement from a sample of blood. Unlike the
Laboratory oximeter, the hemometer will have to measure noninvasively,
variable path lengths of light in order to determine hemoglobin
concentrations.
Like the Pulse oximeter measurements will be determined continuously by
a probe attached to the tissue (e.g. finger). Unlike the Pulse oximeter,
this will determine continuous hemoglobin concentrations in absolute
amounts rather than continuous hemoglobin oxygen saturation's derived
frrom ratios. Unlike the Pulse oximeter, the hemometer will need to
measure the path length of the light through the pulsating artery.
NON INVASIVE MEASUREMENT OF HEMOGLOBIN CONCENTRATION--THE SINGLE
WAVELENGTH METHOD THIS REQUIRES THE PATH LENGTH OF LIGHT TO BE MEASURED
(SEE BELOW)
At a wavelength of 805 nm (the isobestic point), the optical extinction
coefficient of reduced and oxygenated hemoglobin are the same (FIG. 3).
The hemometer would measure the pulsatile absorbance (PA=AC/DC) of this
wavelength of light after transmission through a tissue bed (e.g.
finger). Use of the pulsatile absorbance takes into account the effect
of absorption of light by skin, soft tissue, venous and capillary blood.
Use of the isobestic wavelength ensures that the absorption of light is
independent of the degree of oxygenation of the blood. The pulse added
absorbance at the isobestic wavelength will thus be directly related to
the concentration of oxygenated and deoxyhemoglobin irrespective of
their saturation or oxygen content. The Concentration of oxygenated
hemoglobin (C1) and deoxyhemoglobin (C2)) may be derived as follows:
Beer's Law 2 relates absorbance (A) to extinction coefficient En and
path length Ln at wavelength n
A=EnCnLn
Extrapolating Beer's Law with the use of pulsatile absorbance (PAn) in
which path length is measured (see page 9), the modified equation is:
PAn=EnCnLn
and Cn=PAn/EnLn
The sum of the concentration (C1+C2) of oxygenated and deoxyhemoglobin
is obtained at the isobestic wavelength of 805 nm
Therefore C1+C2=@PA805/E805Ln805
Now PA805=AC805/DC805
Thus C1+C2=@AC805/DC805E805Ln805
where
AC=absorbance of tissue bed including venous blood
DC=absorbance of pulsatile arterial blood
PA=Pulsatile Absorbance at a wavelength of 805 nm
C1=Concentration of oxygenated hemoglobin
C2=Concentration of deoxyhemoglobin
@=scalar coefficient
E805=extinction coefficient at a wavelength of 805 nm
Ln805=is the path length of the light at a wavelength of 805 nm
The scalar coefficient @ will be determined by Calibration curves from
experimental studies in human volunteers (plotting PA/E805 against known
hemoglobin concentrations determined by laboratory spectrophotometry).
In the absence of COHb and MetHb or their presence in negligible
amounts:
Total Hb=C1+C2=@PA/E805Ln805
Other derivatives that may be calculated from Total Hb (THb) are:
1. Hematocrit (HCT)
HCT=THb.times.3
substituting for THb
HCT=@PA/E805Ln805.times.3
2. Arterial Oxygen Content (CA02)
CAO2 (vol% O2)=1.39.times.THb.times.%O2Hb/100
substituting for THb
CAO2(vol% O2)=1.39.times.@PA/E805Ln805.times.%O2Hb/100
THREE METHODS TO MEASURE THE PATHLENGTH OF LIGHT THROUGH A PULSATING
ARTERY (OR THE PULSATING WIDTH OF THE ARTERY)
Measurement of the pathlength of light through a pulsating artery (or
the pulsatile width) is based on the following laws;
OMOIGUI'S LAW 1: The pathlength of light through a
pulsating artery (or the pulsatile width) is equivalent to the pulsating
distance of the artery which is equivalent to the maximal arterial
diameter.
OMOIGUI'S LAW 2: The maximal arterial diameter due to
pulsation of the arterial wall is a function of the distending pressure
on the arterial wall which is measured as the systolic arterial
pressure.
The maximal arterial diameter may be derived from the systolic arterial
pressure by statistical analysis and non linear regression of the
arterial diameter and arterial pressure curves. Values to plot these
curves are obtained by measuring simultaneously at the same site, the
arterial diameter and arterial pressure of an artery.
MEASUREMENT OF PATHLENGTH OF LIGHT (ARTERAL DIAMETER) AND HEMOGLOBIN
CONCENTRATION--METHOD 1
The relationship between arterial pressure and arterial diameter
(pulsating width) may be characterized by measuring simultaneously at
the same site, the arterial diameter and arterial pressure of an artery
in a large number of human volunteers of various ages. Such measurements
may be obtained by utilizing synchronized ultrasonic (e.g. Asulab SA)
and photoplethysmographic (e.g. Finapres.TM.) devices. Statistical
analysis and non linear regression of the arterial diameter against
arterial pressure curves derived from these actual measurements will
determine the relationship. The arterial pressure-diameter relationship
has been described by several non-linear mathematical expressions (FIG.
9).sup.1234 some of which utilize pressure-diameter equations
(arctangent function and three optimal fit parameters) in the form:
##EQU1## where: S=arterial cross-sectional area
d=arterial diameter
a=optimal fit parameter characterizing the arterial diameter-pressure
curve.
.beta.=optimal fit parameter characterizing the arterial
diameter-pressure curve.
y=optimal fit parameter characterizing the arterial diameter-pressure
curve.
.sup.1 van Loon P., Klip W. and Bradley E.L. 1977: Length-force and
volume-pressure relationships of arteries: Biorheology 14: 181-201
.sup.2 Vander Werff T. J. 1974: Significant parameters in arterial
pressure and velocity development: J. Biomech. 7:437-47
.sup.3 Tardy Y., Meister J. J. et al: Non invasive estimate of the
mechanical properties of peripheral arteries from ultrasonic and
photoplethysmographic measurements: Clin. Phys. Physiol. Meas., 1991,
Vol 12, No 1, 39-54.
.sup.4 Langewouters G. J. Wesseling K. H. and Goedhard W. J. A. 1984:
The static elastic properties of 45 human thoracic and 20 abdominal
aortas in vitro and the parameters of a new model: J. Biomech. 17 425-35
To measure the pulsatile pathlength of light which is equivalent to the
pulsatile arterial width or maximal arterial diameter, it will be
necessary to determine the systolic arterial pressure of the artery
adjacent or at the site of the pulse oximeter sensor.
In order to carry out the above described processes (FIG. 6), a pressure
cuff (2) for an automatic oscillometric blood pressure instrument (3)
with a microprocessor controlled oscillotonometer (A) is attached to the
arm or finger of the patient. A sensor probe (6) from the single to four
wavelength oximeter (4) is attached to said finger (5) of the patient on
the same arm. The cuff pressure is first increased above the expected
systolic blood pressure value, then it is slowly and automatically
decreased while pressure oscillations in the cuff are measured
electronically by the microprocessor controlled oscillotonometer (A) and
systolic blood pressures are determined. The process will be done
continuously with deflation and reinflation of the cuff to determine the
maximum systolic arterial pressure. The maximal arterial diameter
(pulsatile width) will be calculated using an arterial pressure diameter
equation (see FIG. 9), such as
S=.SIGMA.d.sup.2 /4=a›.SIGMA./2+tan.sup.-1 (p-.beta./y)!
where:
S=arterial cross-sectional area
d=arterial diameter
a=optimal fit parameter characterizing the arterial diameter curve
.beta.=optimal fit parameter characterizing the arterial diameter curve
y=optimal fit parameter characterizing the arterial diameter curve
p=pressure
The oximeter (4) communicates with the automatic oscillometric blood
pressure device (3) through a communication link p=pressure (8) and
light from the pulse oximeter sensor is transmitted across the finger
during deflation of the cuff. The absorbance of the isobestic wavelength
of light transmitted through the pulsating artery will be determined by
the amount of light detected by the sensor probe on the opposite side of
the finger. The pulse added absorbance at the isobestic wavelength will
be directly related to the concentration of oxygenated and
deoxyhemoglobin irrespective of their saturation or oxygen content. The
Concentration of each species of hemoglobin (Chb) will be empirically
determined using the equations described above. A correction coefficient
k is determined by plotting derived hemoglobin concentrations with known
hemoglobin concentrations in human volunteers of various ages will then
be determined below.
MEASUREMENT OF PATHLENGTH OF LIGHT AND HEMOGLOBIN CONCENTRATION--METHOD
2
Measurement of the pathlength of light through a pulsating artery (or
the pulsatile width/diameter of the artery) may occur by use of an
ultrasonic echo tracking device (or pulsed doppler ultrasound) that
allows continous non-invasive recording of the internal diameter of
peripheral arteries. Short ultrasonic pulses are generated and detected
by a piezoelectric transducer. The timed displacement of the signal
waveform (echo) reflected by the interface between blood and the inner
and outer arterial walls and identified on an RF mode display
corresponds to the arterial diameter (FIG. 11). The maximum difference
between the two waveforms is proportional to the maximal arterial
diameter which is equivalent to the pulsatile arterial width of the
arterial wall.
In order to carry out the above described processes (FIG. 7, 8), an
ultrasonic echo tracking device (13) is attached to the arm or finger of
the patient. A sensor probe (6) from the single to four wavelength
oximeter (4) is attached to said finger (5) of the patient on the same
arm. The arterial diameter will be determined by the ultrasonic echo
tracking device (13). The oximeter (4) communicates with the ultrasonic
echo tracking device (13) through a communication link (8). The
ultrasonic echo tracking device (13) and pulse oximeter sensor (6) are
synchronized to enable simultaneous measurements of arterial diameter
and pulsatile absorbances respectively. Light from the pulse oximeter
sensor is transmitted across the finger simultaneous with generation of
short ultrasonic pulses by the ultrasonic echo tracking device (13). The
diameter of the pulsating artery will be determined by the ultrasonic
echo tracking device (13). The absorbance of the isobestic wavelength of
light transmitted through the pulsating artery will be determined by the
amount of light detected by the sensor probe on the opposite side of the
finger. The pulse added absorbance at the isobestic wavelength will be
directly related to the concentration of oxygenated and deoxyhemoglobin
irrespective of their saturation or oxygen content. The Concentration of
each species of hemoglobin (Chb) will be empirically determined using
the equations described above. A correction coefficient k is determined
by plotting derived hemoglobin concentrations with known hemoglobin
concentrations in human volunteers of various ages.
NON INVASIVE MEASUREMENT OF HEMOGLOBIN CONCENTRATION, HEMOGLOBIN SPECIES
CONCENTRATION AND BLOOD PIGMENT CONCENTRATION--MULTIPLE WAVELENGTHS
METHOD THIS REQUIRES THE PATH LENGTH OF LIGHT TO BE MEASURED (SEE ABOVE)
According to Beer's Law, at least n wavelengths are required to identify
any one absorber of light out of a system of n absorbers. To determine
the concentrations of all or any of the species of hemoglobin, the
hemometer will measure the pulsatile absorbance of four hemoglobin
species at four wavelengths. At each wavelength, the extinction
coefficient for one of the species is optimal (e.g. 940 nm for
oxygenated hemoglobin, 660 nm for deoxyhemoglobin, 535 nm for
carboxyhemoglobin and 626.6 nm for methemoglobin). The pulsatile
absorbance at each of the selected wavelengths will be a function of the
concentration of the species of hemoglobin. Four linear equations of
absorbance are solved simultaneously for four independent variables. The
path length of light will be determined as measured above. The
Concentration of each species of hemoglobin (Chb) will be empirically
determined by the equation:
AC/DC=PA
C(RHb)=@(PA535RHb/E535L535+PA585RHb/E585L585+
PA594RHb/E594L594+PA626RHb/E62
6L626)
C(O2Hb)=@(PA535O2Hb/E535L535+PA585O2Hb/E585L585+
PA594O2Hb/E594L594+PA626O2H
b/E626L626)
C(COHb)=@(PA535COHb/E535L535+PA585COHb/E585L585+
PA594COHb/E594L594+PA626COH
b/E626L626)
C(MetHb)=@(PA535MetHb/E535L535+PA585MetHb/E585L585+
PA594MetHbE594L594+PA626
MetHb/E626L626)
where AC=absorbance of tissue bed including venous blood
DC=absorbance of pulsatile arterial blood
PA=Pulsatile Absorbance
Chb=concentration of hemoglobin species
@=scalar coefficient
En=extinction coefficient at wavelength n
Ln=pathlength of light at wavelength n
The scalar coefficient @ will be determined by Calibration curves from
experimental studies in human volunteers (plotting PA/EnLn against known
concentrations of the hemoglobin species as determined by laboratory
spectrophotometry).
Total Hb=C1+C2+C3+C4
where C1=concentration of oxygenated hemoglobin
C2=concentration of deoxyhemoglobin
C3=concentration of carboxyhemoglobin
C4=concentration of methemoglobin
If C3+C4 are negligible
Total Hb=C1+C2
C2 (the concentration of reduced or unoxygenated hemoglobin) may also be
derived as a function of the oxygen saturation and the concentration C1
of oxygenated hemoglobin.
C2=K(SaO2)C1
where K is a coefficient derived by Calibration curves from experimental
studies in human volunteers plotting known oxygen saturations at known
concentrations of oxygenated hemoglobin against known concentrations of
deoxyhemoglobin as determined by laboratory spectrophotometry
Thus
Total Hb=C1+KSaO2C1
As derived previously
C1=@PA/E940L940
where PA=Pulsatile Absorbance
C1=concentration of oxygenated hemoglobin
@=scalar coefficient
En=extinction coefficient at wavelength 940 nm (selected for oxygenated
hemoglobin)
L940=pathlength of light at wavelength 940 nm
Therefore
Total Hb=@PA/E940Ln940+KSaO2@PA/E940L940
The multiple wavelength method may also be used to determine the
concentration of any hemoglobin species or blood pigment e.g. bilirubin.
An additional equation using the optimal wavelength of absorbance for
the blood pigment (e.g. 450 nm for bilirubin) will be added to the four
equations for the four species of hemoglobin. The pulsatile absorbance
of the blood pigment and the four hemoglobin species at five wavelengths
will be determined. Five linear equations of absorbance are solved
simultaneously for five independent variables. Using the measured path
length of light the concentration of the blood pigment and each species
of hemoglobin will be determined by solving the equations:
C(Bil)=@(PA450Bil/E450L450+PA535Bil/E535L535+
PA585Bil/E585L585+PA594Bil/E59
4L594+PA626Bil/E626L626)
C(RHb)=@(PA450RHb/E450L450+PA535RHb/E535L535+
PA585RHb/E585L585+PA594RHb/E59
4L594+PA626RHb/E626L626)
C(O2Hb)=@(PA450O2Hb/E450L450+PA535O2Hb/E535L535+
PA585O2Hb/E585L585+PA594O2H
b/E594L594+PA626O2Hb/E626L626)
C(COHb)=@(PA450COHb/E450L450+PA535COHb/E535L535+
PA585COHb/E585L585+PA594COH
b/E594L594+PA626COHb/E626L626)
C(MetHb)=@(PA450MetHb/E450L450+PA535MetHb/E535L535+
PA585MetHb/E585L585+PA59
4MetHb/E594L594+PA626MetHb/E626L626)
where AC=absorbance of tissue bed including venous blood
DC=absorbance of pulsatile arterial blood
PA=Pulsatile Absorbance
Cbil=concentration of bilirubin
Chb=concentration of hemoglobin species
@=scalar coefficient
En=extinction coefficient at wavelength n
Ln=pathlength of light at wavelength n
The scalar coefficient @ will be determined by Calibration curves from
experimental studies in human volunteers (plotting PA/EnLn against known
concentrations of bilirubin and the four hemoglobin species as
determined by laboratory spectrophotometry).
Total Hb=C1+C2+C3+C4
where C1=concentration of oxygenated hemoglobin
C2=concentration of deoxyhemoglobin
C3=concentration of carboxyhemoglobin
C4=concentration of methemoglobin
If C3+C4 are negligible
Total Hb=C1+C2
C2 (the concentration of reduced or unoxygenated hemoglobin) may be
derived as a function of the oxygen saturation and the concentration Cl
of oxygenated hemoglobin.
C2=k(SaO2)C1
where k is a coefficient derived by calibration curves from experimental
studies in human volunteers plotting known oxygen saturations at known
concentrations of oxygenated hemoglobin against known concentrations of
deoxyhemoglobin as determined by laboratory spectrophotometry
Thus
Total Hb=C1+KSaO2C1
As derived previously
C1=@PA/E940Ln940
where PA=pulsatile absorbance
C1=concentration of oxygenated hemoglobin
@=scalar coefficient
En=extinction coefficient at wavelength 940 nm (selected for oxygenated
hemoglobin)
Ln=pathlength of light at wavelength 940 nm
Therefore
Total Hb=@PA/E940Ln940+KSaO2@PA/E940L940
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