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Description  |
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The present invention relates to instruments for determining chemical
concentrations by measuring light absorption at one or more selected
frequencies, and particularly relates to an apparatus and method for
making in-vivo measurement of chemical concentrations in a body fluid by
measuring the light absorption characteristics of the body fluid.
Laboratories have long used spectrophotometric measurements, including
absorbance measurements, as a method of analysis for body fluids in the
diagnosis and treatment of illness. Albumin, alcohol, calcium, total
bilirubin, cholestrol, chloride, glucose, lactic acid. Magnesium and
phosphorous are routinely assayed in the laboratory using
spectrophotometry. A bichromatic method is usually employed for the
absorption measurements in order to correct for interfering species.
Typically, spectrophotometric analysis are done in automated machines that
have increased the efficiency of the clinical laboratory, but there are
still several time consuming steps common to all such tests. Basically,
the patient must be moved to a special laboratory or procedure room for
the removal of a sample from his body, and the sample is generally picked
up and delivered to the clinical laboratory. The time delay in the
delivery of the sample to the clinical laboratory and any delays in the
laboratory may allow degregation of the sample so that the accuracy of the
analysis is compromised. To avoid the numerous problems associated with
the laboratory analysis of body fluids and to provide faster results, the
present invention provides an instrument for making in-vivo measurements
of chemical concentrations in body fluids.
A single optical fiber is used in the present invention to transmit light
from an exterior surface into the body to spectroscopically determine
chemical concentrations in body fluids. Fiber optic bundles have been used
for various clinical measurements and for the in-vivo observation of body
organs. However, these devices are generally too bulky to permit
site-specific, nontraumatic measurements in all body fluids, including the
interstitial fluids of soft tissue.
In accordance with the present invention, an apparatus for making in-vivo
determinations of the concentrations of light absorbing chemicals in the
body fluids of a body includes a needle with a needle point for
penetrating the body to a region of biological fluids to be tested. A
reflective surface is disposed within the needle and adjacent to the
needle point in an orientation generally perpendicular to the needle, and
a sample cavity is disposed within the needle for receiving and containing
samples of biological fluid. The reflective surface is positioned between
the needle point and at least a portion of the sample cavity.
An ingress pathway is provided from the biological fluids outside of the
needle to the sample cavity, and biological fluids are selectively
admitted through the ingress into the sample cavity. An optical fiber is
disposed within the needle and has first and second ends. The first end of
the optical fiber is disposed at the sample cavity in an opposed
relationship with the reflective surface in the sample cavity so that
light may be transmitted into the sample cavity and reflected back through
the sample cavity to the first end of the optical fiber. The distance
between the reflective surface and the first end of the optical fiber is
defined as one-half the distance of the sample cavity light path.
A light system transmits light into the second end of the optical fiber and
a detection system detects the intensity of the light eminating from the
second end of the optical fiber simultaneously with the transmission of
light into the second end of the optical fiber. Thus, the concentration of
a light absorbing chemical in the biological fluid within the sample
cavity may be determined by measuring the light guided into the sample
cavity through the optical fiber, transmitted through the sample twice,
and transmitted by the same fiber to the detector.
Preferably, the apparatus includes a second needle with a blunt end. The
second needle is disposed within the other needle and the blunt end is
disposed adjacent the needle point. The optical fiber is disposed within
the second needle and its first end is positioned at a distance of
one-half of the sample cavity light path distance from the blunt end of
the needle. The reflective surface is mounted on the blunt end of the
needle, and the sample cavity is defined by the reflective surface, the
second needle walls, and the first end of the optical fiber. An aspirating
port is connected to the second needle for selectively aspirating the
second needle to draw biological fluids from outside of the first needle
into the sample cavity through the ingress.
In the preferred embodiment, the ingress is at least one aperture in the
wall of the second needle between the reflective surface and the first end
of the optical fiber. In another embodiment, the reflective surface and
the ingress means are provided by a reflective mesh that is mounted on the
blunt end of the second needle. The reflective mesh will reflect at least
a portion of the light transmitted from the first end of the optical fiber
and will allow ingress of biological fluids into the sample cavity when a
negative pressure is created within the sample cavity by aspirating
through the aspiration port.
In accordance with another embodiment of the present invention, two sources
of light having two different wavelengths are used. An optical system is
provided for transmitting the two different wavelengths of light to and
into the second end of the optical fiber at different times, and a
detection system measures the intensity of the light of the light at the
two different wavelengths that is transmitted through the fiber and sample
cavity. In this construction the measured intensity at the two different
wavelengths can be used to simultaneously determine the concentration of
two chemicals in the body fluid, provided the molar absortivities of the
chemicals at the two wavelengths are known.
The instrumentation of the present invention provides a convenient in-vivo
analysis of body fluids and provides true absorbance values of body
fluids. Currently, the instrumentation used for remote absorbance
measurements is totally unsuitable for in-vivo measurements and the
equipment that is used for in-vivo measurements produces relative values,
that is, no true analytical values, such as light absorbance. In the
preferred embodiment of the invention, the sample cavity is contained
inside a hypodermic needle which makes it suitable for subcoutaneous
insertion and autoclaving. The probe is small and requires an extremely
small volume of fluid to fill the sample cavity, and after analysis, the
fluid may be expelled from the probe back into the patient. With the wide
use of lasers in the hospital today, existing layer equipment can be
adapted for use in this invention and would, thus, reduce the expense of
the overall system.
The present invention may best be understood by reference to the following
Detailed Description of preferred embodiments when considered in
conjunction with the Drawings in which:
FIG. 1 is a somewhat diagrammatical view of the in-vivo apparatus for
determining chemical concentrations in a body fluid;
FIG. 1a is a detailed cross-sectional view of the end of the interior and
exterior needles and fiber optic of FIG. 1.
FIGS. 2a; 2b and 2c show three alternate embodiments of the interior needle
of the present invention which defines a sample cavity for receiving
biological fluids;
FIG. 3 is a somewhat schematic diagram of the probe of the present
invention utilizing a micrometer to adjust the position of an optical
fiber;
FIG. 4 is a graph showing light absorbance versus methal orange
concentration in a sample cavity for three different sample cavity light
path distances;
FIG. 5 is a graph showing light absorbance versus bilirubin concentration
in a sample cavity for a preferred sample cavity size; and
FIG. 6 is a somewhat schematic diagram of the apparatus of the present
invention utilizing two lasers as light sources.
Referring now to the drawings in which like reference characters designate
like or corresponding parts throughout the several views, there is shown
in FIG. 1 a measuring apparatus 10 for making in-vivo determinations of
the concentrations of light absorbing chemical in biological fluids of a
body. Basically, the apparatus 10 includes two parts, a probe 12 and an
optics system 14, and the two parts are interconnected by an optical fiber
16.
The probe 12 includes an exterior needle 18 that is preferably a fifteen
gauge by two inch hypodermic needle. The base of needle 18 is attached to
needle mount 20 that is in turn affixed to a tuberculin syringe 22. At a
position on the lower end of the syringe 22, an aspiration port 24 is
formed in the syringe for providing aspiration as will be hereinafter
described in greater detail. The syringe 22 also includes a plunger 26,
and the optical fiber 16 is fixedly mounted through the center of the
plunger 26 and is positioned in an interior needle that is within the
needle 18. In this construction, the position of the optical fiber 16
within the needle 18 may be adjusted by moving the plunger 26 within the
barrell of the syringe 22.
FIG. 1 includes a detailed cross-sectional view, FIG. 1A, of the lower end
of the exterior needle 18. As shown in FIG. 1A, the exterior needle 18 has
a sharp needle point 19, and a blunt interior needle 28 is mounted within
the exterior needle 18. Preferably, the interior needle 28 is a nineteen
gauge by one and one-half inch hypodermic needle that were specially made
by Becton-Dickison, N.J., to have a smooth reflective inner wall that is
more reflective than conventional disposable hypodermic needle. The
specially made interior needles 28 were prepared by drawing stainless
steel tubing through dies, first with, then without, an internal mandrel
in decreasing gauges to the final gauge size. The tubing is then
straightened out and fibricated into needles. The increased reflectivity
of the interior needle 28 is needed in order to provide a greater
transmittance of light through a sample cavity as will be described
hereinafter.
The interior needle 28 is silver soldered and sealed within the exterior
needle 18 so that the aspiration port 24 is in fluid communication with
the interior needle, but not with the exterior needle directly. Thus,
aspiration using the aspiration port 24 is accomplished through the
interior needle 28. A blunt end is formed on the interior needle 28 and a
reflective surface 30 is mounted completely covering and sealing the blunt
end of the needle. In the embodiment shown, the reflective surface is
constructed a aluminum foil and is attached to the needle 28 using
optically transparent epoxy adhesive.
An optical fiber 16 is positioned in a spaced-apart substantially coaxial
relationship with the interior needle 28. In the preferred embodiment, the
optical fiber 16 has a diameter of 600 micrometers, and, thus, the size of
the optical fiber is such that it will not interfere with aspiration
through the interior needle 28. The lower end 34 of the optical fiber 16
is positioned at a selected distance from the reflective surface 30,
within the range of 0.25 mm to 2.5 mm, and preferably a distance of 0.9
mm. The distance between the end 34 of the optical fiber 16 and the
reflective surface 30 is one-half the sample cavity light path distance.
Four apertures 32 are drilled in the interior needle 28 having a diameter
of 0.015 inches and being positioned approximately 0.045 inches from the
reflective surface 30. The holes 32 provide an ingress and egress pathway
from the exterior of the needle 18 to the interior of the needle 28. The
volume of defined between the end 34 of the optical fiber 16, the
reflective surface 30 and the interior walls of the interior needle 28 is
the sample cavity 36. The distance between the optical fiber end 34 and
the reflective surface 30 will be defined as one-half the sample cavity
light path distance, although it is recognized that the average light path
distance is somewhat greater since the light will be transmitted and
reflected at angles and will be reflected from the interior walls of the
interior needle 28.
The probe 12 is connected to an optics system 14 which includes a laser 40,
for example an argon ion laser producing radiation of 0.025 watts at 4579
angstroms manufactured by Spectra-Physics, Model 171. A laser beam is
transmitted to a beam splitter 44 which transmits fifty percent of the
light and reflects fifty percent of the laser beam toward a 35 mm focal
length quartz lens 46 which focuses the laser beam onto the end of the
optical fiber 16 which is mounted and positioned by a fiber postioner 48.
Light is also transmitted out of the optical fiber 16 in the fiber
positioner 48 and is transmitted through the lens 46 to the beam splitter
44. Fifty percent of this light is reflected and fifty percent of the
light is transmitted to the monochromator and optical filter system 50.
The system 50 includes an entrance slit and an iris which spacially reject
reflected radiation from the surface of the lens and the input end of the
optical fiber and, thus, minimize the detection of stray radiation.
Neutral density filters are placed within the monochromator and optical
filter system 50 to obtain the desired magnitude of light which is then
fed into a photomultiplier tube, for example, the photomultiplier tube
manufactured by RCA, Model No. IP28-A. The voltage from the
photomultiplier tube 52 is supplied to a meter 54 which provides output
information.
In operation, the probe 12 is inserted into a body so that the needle point
19 is positioned in the region of biological fluids to be tested. A
suction is then placed on the aspiration port 24 and the biological fluids
are drawn into the sample cavity 36. A laser beam having a power level of
about 20 milliwatts is transmitted from the laser 40, reflected by the
reflective surface 42 and the beam splitter 44, focused by the lens 46 and
transmitted by the optical fiber 16 to the optical fiber end 34. The light
then travels through the fluid in the sample cavity 36, against the
reflective surface 30 and back through the biological fluid to the optical
fiber 16 and back to the fiber positioner 48. The light that was reflected
back into the optical fiber end 34 was a combination of reflected light
from the reflective surface 30, the inner walls of the needle 28 and the
reflection of the body fluid itself within the cavity 36. Once the light
that is reflected back to the fiber positioner 48, it passes through the
lens 46 and fifty percent of it is passed through the beam splitter 44 and
into the monochromator and optical filter system 50. The photomultiplier
52 then creates a signal that corresponds to the magnitude of the light
intensity that it receives which is indicated on the meter 54. Thus, the
reading of the meter 54 will correspond to the light that is received by
the photomultiplier tube 52 which corresponds to the amount of light that
was reflected through the optical fiber 16 after it passed through the
sample cavity 36.
The apparatus 10 may be calibrated using a transparent substance in the
sample cavity 36 so that when biological fluid is placed in the cavity 36,
the reading on the meter 54 will correspond to the light absorbed by the
biological fluid. That is, the logarithim of the ratio of the reading of
the meter 54 when nothing is present in the sample cavity and a reading
when body fluid is contained in the sample cavity will correspond to the
absorbance by the chemical contained in the body fluid within the sample
cavity.
Referring now to FIGS. 2a, 2b, and 2c there is shown three different
embodiments, 60, 62 and 64, of the interior needle 28. In the embodiment
60, a gold foil 36 is mounted on the blunt end of the needle 28 to
function as the reflective surface and as a means for allowing ingress and
egress of body fluids between the needle 28 and the body of the subject.
The gold mesh 36 may be chosen to provide a desired reflectivity and the
mesh will also act as a filter of the body fluids entering the needle 28.
Thus, the mesh size may also be chosen to provide a desired filtering
action.
The second embodiment 62 shown in FIG. 2b retains the use of a solid
reflective surface 30 and apertures 32, and a reflective coating 66 is
applied to the interior walls of the needle 28 to improve the transmission
of light through the needle 28. The reflective coating 66 extends at least
partially into the sample cavity area 36 and would, thus, improve the
light transmission within the cavity. It is understood that the reflective
coating 66 is shown in an exaggerated size for purposes of clarity of
illustration. The composition of the reflective coating is not critical,
but is preferably a metal, such as aluminum, deposited on the interior of
the needle 28, or an inserted sleeve.
The embodiment 64 shown in FIG. 2c also includes a solid reflective surface
and holes 32, but further includes a blackened interior coating 68 on the
needle 28. The coating 68 will absorb radiation that strikes the interior
of the needle 28 and, thus, the light path between the optical fiber end
34 and the reflective surface 30 includes only direct light paths and
would not include light paths where light impinged on the interior walls
of the needle 28.
A critical dimension of the probe 12 is the distance between the optical
fiber end 34 and the reflective surface 30 because this distance defines
the sample cavity light path length. As the distance between the
reflective surface 30 and the optical end 34 increases, the sensitivity of
the apparatus will increase, but the limit of detection decreases. Thus,
for most biological fluids, there is an optimum position for the optical
fiber end 34 and there is a range of positions within which the probe 12
will work well.
This optimum position and range is discussed with regard to FIG. 3 in which
there is shown yet another embodiment of the invention. Both a micrometer
70 and the probe 12 are mounted in a bracket 72 with the micrometer 70
connected to move the plunger 26 of the probe. Since the plunger 26 is
fixedly connected to the optical fiber 16, the micrometer 70 may be used
to move the fiber 16 axially within the needle 18 and, thus, is operable
to move the optical fiber end 34 relative to the reflective surface 30.
Once the micrometer is calibrated, the readings of the micrometer 70 will
correspond to the distance between the optical fiber end 34 and the
reflective surface 30, and a desired distance may be obtained by simply
rotating the micrometer and observing the micrometer readings which
correspond to sample cavity light path distances.
To illustrate the relationship between sensitivity and limits of detection,
FIG. 5 depicts three graphs of light absorbance versus methal orange
concentration in the sample cavity. The graphs in FIG. 4 were determined
empirically by placing methal orange in different concentrations into the
absorbance probe and measuring the light absorbance for three different
path lengths. Line 74 was obtained using a path length of 0.5 mm, line 76
using a path length of 1.8 mm and line 78 using a path length of 4.3 mm.
It will be recalled that the light path length is twice the distance
between reflective surface 30 and optical fiber end 34.
Using the apparatus 10 shown in FIG. 1, it was empirically determined that,
assuming a limit of detection at a signal to noise ratio of two, the
limits of detection using a path length of 4.3 mm was 0.009 absorbance
units. Using a path length of 1.8 mm, the limit of detection was found to
be 0.005 absorbance units. With a path length of 0.5 mm, the limit of
detection was 0.011 absorbance units. Based on these and other
experimental results, it was determined that for most body fluids, the
optimum path length is about 1.8 mm and that the probe would operate well
only within a light path length range of about 0.5 mm to about 5.0 mm. The
optimum path length was chosen to obtain a balance between sensitivity and
limits of detection.
To illustrate the use of apparatus 10 for measuring concentrations of
biological fluids, the apparatus was used to measure bilirubin
concentration. In FIG. 5, graph 80 plots bilirubin concentrations versus
absorbance in the sample cavity 36 using a light path of 1.8 mm. The
bilirubin concentration was first determined using apparatus 10 and the
results were verified by standard laboratory techniques. The graph of
absorbance versus bilirubin concentration is shown in FIG. 6 by way of an
example, but it will be understood that the probe may be used to determine
concentrations of most any chemical in body fluids that may be detected
spectroscopically based on the chemical's light absorption.
Referring now to FIG. 6, there is shown another embodiment of the apparatus
10. A second laser 82, and a dichroic filter 84 have been added along with
a recorder 86. The dichroic filter 84 is chosen to transmit the beam of
laser 40 and reflect the beam of laser 82. The dichroic filter 84 is
interposed in the laser beam path between reflective surface 42 and beam
splitter 44 so that the filter 84 transmits the light from laser 40 to the
beam splitter 42. The splitter 84 is oriented so that it also receives
light from the new laser 82 and reflects it along the same light path as
the laser beam from laser 40. The filter 84 also reflects the light from
laser 82 toward splitter 44, and both laser beams from lasers 40 and 82
are reflected by splitter 44 toward the lens 46 and into the optical fiber
16 as previously described.
The recorder 86 is a standard strip chart recorder interconnected with the
meter 54. The recorder 86 simply provides a printout of the meter readings
over a period of time so that subsequent calculations may be performed to
determine the concentrations of various chemicals in body fluids.
In operation, laser 40 is first energized and readings are taken to
determine the amount of light absorption taking place in the sample cavity
at the wavelength of the laser beam produced by laser 40. Next, laser 40
is turned off and laser 82 is turned on. Then, measurements are again
taken to determine the amount of light absorption taking place within the
sample cavity at the wavelength of the laser 82. By using two different
lasers at two different light wavelengths, information about the chemical
concentration is obtained in accordance with standard spectroscopy
procedures. For example, if it is known that the chemical to be tested
will absorb light having a wavelength of laser 40 but it will not absorb
light having a wavelength of laser 82, and an interfering chemical will
absorb light of both wavelengths by the same amount then the difference in
absorption obtained when using laser 40 as compared to laser 82 will
correlate to the absorption of the chemical being studied. The difference
between the absorption at one wavelength and the absorption at another
wavelength should correspond to the absorption of the chemical being
studied, and in this manner, compensation is made for the interfering
chemical. It will be understood that other optical arrangements may be
used to obtain different wavelengths and multiple lasers may be used to
achieve greater variations in the wavelengths. Also, so long as the
absorption characteristics of both the chemical to be studied and the
interfering chemicals are known, corrections to compensate for the
absorption of these interfering chemicals can be made using radiation of
two or more wavelengths.
Referring again to FIG. 1, and particularly FIG. 1A, it will be appreciated
that a reagent may be immobilized within the sample cavity 36 so that the
reagent is inserted along with the probe into the region of the biological
fluids to be tested. When the biological fluids are aspirated into the
sample cavity 36, the reagents will react with the chemical to be tested
and will change the light absorption characteristics of the chemical so
that it absorbs light at a different wavelength. In this manner, if a
chemical to be tested is found in the presence of an interfering chemical
that absorbs light at the same wavelength, the absorption characteristics
of the chemical to be tested are changed to avoid the interfering
chemical. It will be understood that most any reagent may be used if it is
not toxic so that an inadvertent release of any of the reagent will not
harm the patient. If toxic reagents are used, a filter or semipermiable
membrane should be placed over the holes 32 to permit biological fluids to
enter the sample cavity but to prevent reagents from escaping the sample
cavity.
As an example of reagents that may be used, in testing for bilirubin, a
commonly used reagent for changing the light absorption characteristics of
bilirubin is a combination of a caffine reagent, a diazio reagent and a
tartrate solution. The caffine reagent is typically made of caffine,
sodium benzoate, sodium acetate, and sodium. The diazoe reagent is
composed of sulfanilic acid, hydrochloric acid, sodium nitrate and water.
The tartrate solution is composed of sodium hydroxide and sodium tactrate.
The caffine reagent can be immobilized within the sample cavity 36 to
react with bilirubin when it is aspirated into the cavity.
Although particular embodiments of the invention have been discussed, it
will be understood that these are examples that were described for the
purposes of illustration and the invention is capable of numerous
rearrangements, modifications and substitutions of parts without departing
from the spirit of the invention. In particular, it is noted that the
probe could be constructed of other tubular materials, such as a flexible
pointed cylinder. The term needle, as it is used herein, will be
understood to have a broad meaning encompassing tubular structures of
varying lengths, widths and flexibility.
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