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Claims  |
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We claim:
1. Apparatus for providing a calibration reference for use with a light
guide that cooperates with a photometric measuring device in making light
intensity measurements at a number of selected wavebands, the apparatus
comprising (a) a plurality of light-scattering particles substantially
uniformly dispersed throughout a solid medium that has a substantially
incompressible body which is sufficiently compliant at its surface for
intimate physical contact with the end of the light guide; and (b) means
for urging and maintaining intimate physical contact between the end of
the light guide and the compliant surface.
2. Apparatus as in claim 1 wherein said medium is sufficiently transparent
at the selected wavebands of a photometric measuring device to transmit
light that is scattered from within the body to the compliant surface in
contact with the light guide.
3. Apparatus as in claim 1 for providing a light-scattering reference means
for operation with a photometric measuring device which measures oxygen
saturation of blood, wherein the light-scattering particles have
dimensions within the range of from about 0.02 to 20 microns.
4. Apparatus as in claim 1 for providing a light-scattering reference means
for operation with a photometric measuring device which measures oxygen
saturation of blood, wherein the density of light-scattering particles
within said medium ranges from about 0.001% to 1.0% by weight.
5. Apparatus as in claim 1 wherein said light-scattering particles are
materials selected from the group consisting of oxides, carbonates,
sulphates of titanium, magnesium, calcium and barium.
6. An assembly adapted for use with an optical catheter which has a light
guide and which is capable of cooperating with a photometric measuring
device in making light intensity measurements comprising:
clamp means disposed to receive the optical catheter near an end of the
catheter and to restrain the optical catheter against movement in a
direction substantially along the length thereof,
resilient means disposed to urge a reference surface into intimate physical
engagement with the end of the light guide of the optical catheter
restrained by the clamp means for providing a medium for reference
measurements at the end of the light guide, and
actuating means supported on said clamp means for causing said clamp means
to restrain the optical catheter received by said clamp means and to cause
said resilient means to urge said reference surface into engagement with
the end of the optical catheter received by said clamp means in response
to manual manipulation of said actuating means.
7. Apparatus for providing a calibration reference for use with a light
guide that cooperates with a photometric measuring device in making light
intensity measurements at a number of selected wavebands, the apparatus
comprising (a) a plurality of light-scattering particles substantially
uniformly dispersed throughout a solid medium that has a substantially
imcompressible body which is sufficiently compliant at its surface for
intimate physical contact with the end of the light guide; and (b) means
for urging and maintaining intimate physical contact between the end of
the light guide and the compliant surface, said means for urging and
maintaining comprising (i) clamp means disposed to restrain said light
guide against movement in a direction substantially along the length of
the light guide; and (ii) resilient means disposed to urge said compliant
surface into intimate physical engagement with the end of said light guide
when the light guide is clamped by said clamp means, said resilient means
urging with a force which is substantially constant and reproducible in
said assembly and in each assembly within a population of such assemblies.
8. An assembly for use with an optical catheter which has a light guide and
which is capable of cooperating with a photometric measuring device in
making light intensity measurements comprising
apparatus for providing a reference means for operation with a photometric
measuring device which operates on radiation at selected wavebands, the
apparatus including a plurality of light-scattering particles dispersed
within a solid medium having a substantially incompressible body,
clamp means disposed to receive the optical catheter near an end of the
catheter and to restrain the optical catheter against movement in a
direction substantially along the length of the catheter,
resilient means disposed to urge a reference surface of said reference
means into intimate physical engagement with the end of the light guide of
the optical catheter restrained by said clamp means for providing a medium
for reference measurements at the end of the light guide,
housing means disposed to receive the optical catheter near one end of the
catheter and to support said clamp means near said one end to selectively
engage the optical catheter received by the housing means,
said housing means supporting said resilient means for movement relative
thereto to selectively engage said reference surface with the end of the
optical catheter received by said housing means, and
actuating means supported on said housing means for actuating said clamp
means to restrain the optical catheter received by said housing means and
to actuate said resilient means to resiliently urge said reference surface
into intimate physical engagement with the end of the optical catheter
received by said housing means in response to manual manipulation of said
actuating means.
9. In combination with the assembly of claim 8:
an optical catheter having a light guide extending therethrough from a
distal end to a proximal end thereof, said optical catheter having its
distal end received by the assembly and having a proximal end which forms
an optical coupler;
inner enclosure means disposed about the assembly having the optical
catheter to form an enclosure thereabout with a region thereof having a
flexible portion adjacent the actuating means to facilitate manual
manipulation of the actuating means supported on said housing means, the
inner enclosure means having an opening through which the proximal end and
optical coupler formed thereon protrude; and
outer enclosure means disposed about the inner enclosure means having the
optical coupler and forming an enclosure thereabout.
10. An apparatus for providing an optical reference element adapted for use
with a light guide comprising,
clamp means disposed to restrain said light guide against movement in a
direction substantially along the length thereof,
resilient means disposed to urge the optical reference element into
intimate physical engagement with the end of said light guide when said
light guide is restrained by the clamp means, and
actuating means connected to said clamp means for causing said clamp means
to restrain said light guide and for causing said resilient means to urge
said reference element into intimate physical engagement with said light
guide in response to manual manipulation of said actuating means.
11. Apparatus for providing a calibration reference for use with a light
guide that cooperates with a photometric measuring device in making light
intensity measurements at a number of selected wavebands, the apparatus
comprising (a) a plurality of light-scattering particles substantially
uniformly dispersed throughout a solid medium that has a substantially
incompressible body which is sufficiently compliant at its surface for
intimate physical contact with the end of the light guide; and (b) means
for urging and maintaining intimate physical contact between the end of
the light guide and the compliant surface, said means for urging and
maintaining comprising (i) clamp means adapted to restrain the light guide
against movement in a direction substantially along the length thereof,
and (ii) resilient means adapted to urge the compliant surface of said
incompressible body against the end of the light guide to achieve intimate
physical engagement therewith.
12. Apparatus for providing a calibration reference for use with a light
guide that cooperates with a photometric measuring device in making light
intensity measurements at a number of selected wavebands, the apparatus
comprising (a) a plurality of light-scattering particles substantially
uniformly dispersed throughout a solid medium that has a substantially
incompressible body which is sufficiently compliant at its surface for
intimate physical contact with the end of the light guide; and (b) means
for urging and maintaining intimate physical contact between the end of
the light guide and the compliant surface, said means for urging and
maintaining comprising (i) clamp means disposed to restrain said light
guide against movement in a direction substantially along the length of
the light guide; and (ii) resilient means disposed to urge said compliant
surface into intimate physical engagement with the end of said light guide
when the light guide is clamped by said clamp means, said resilient means
urging with a force which is substantially constant and reproducible in
said assembly and in each assembly within a population of such assemblies;
and (c) actuating means connected to said clamp means for causing said
resilient means to urge said compliant surface of said incompressible body
into intimate physical engagement with the end of the light guide in
response to manual manipulation of said actuating means.
13. A method for calibrating a photometric measuring device having a light
guide comprising the steps of:
(a) selecting a calibration reference comprising a plurality of
light-scattering particles substantially uniformly dispersed throughout a
solid medium that has a substantially incompressible body which is
sufficiently compliant at its surface for intimate physical contact with
the end of the light guide; and
(b) urging and maintaining intimate physical contact between the end of the
light guide and the compliant surface during calibration of the
photometric measuring device. |
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Claims |
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Description |
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RELATED APPLICATIONS
The subject matter of this application relates to the subject matter of
U.S. Pat. No. 4,114,604, entitled Improved Catheter Oximeter Apparatus,
filed Oct. 18, 1976, and to the subject matter of pending application Ser.
No. 733,279, now abandoned, entitled Improved Optical Catheter Not
Requiring Individual Calibrations, filed Oct. 18, 1976, the disclosures of
which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
In determining the unknown concentration of known substances by photometric
measurements, two techniques are available to relate the actual light
intensities received from the sample under test to the unknown
concentrations of the substances being quantified in the sample under
test.
One of these techniques is the "Calibration Technique". In this technique,
the actual light intensities received after transmission through or
reflectance from a sample having known concentrations of the substances
being quantified are utilized to produce a "calibration curve".
Thereafter, actual light intensity measurements obtained from a sample
having unknown concentrations of the substances being quantified can then
be utilized relative to the calibration curve to quantify the
concentrations (S) of such substances.
The "calibration technique" has been commonly used in catheter oximetry. An
optical catheter may be inserted into the blood stream of a patient and
the blood oxygenation of the patient varied by having the patient breathe
mixtures enriched with or depleted of oxygen. While light intensity
measurements are made, blood samples are withdrawn, usually through the
catheter. The oxygen saturation of these blood samples are then
independently measured on a separate instrument, often in a central
laboratory. After these measurements have been completed, oxygen
saturation can be determined, by comparison of actual light intensities
measurements relative to the calibration curve which was derived from the
two known conditions of oxygen saturation. Such a calibration curve may be
introduced electronically into the catheter oximeter system so that
automatic computed oxygen saturation may be displayed.
This technique has several disadvantages. First, blood oxygen saturation
levels are imposed upon the patient which may be deleterious to his
health. Second, there is an undesirable delay between the time of catheter
placement and the time at which oxygen saturation measurements utilizing
the catheter oximeter can be obtained. Third, changes in blood oxygen
level occur continuously and often very rapidly, making it difficult to be
certain that the blood sample and the actual light intensity reading are
truly correlated.
In order to eliminate the first and second disadvantages referred to above,
efforts have been made to precalibrate the catheters in blood samples or
suspensions of other materials such as milk of magnesia combined with dyes
or filters which are believed to produce light intensity measurements
equivalent to blood of known oxygen saturations. (See Taylor et al.,
Journal of the American Medical Association, Aug. 14, 1972, page 669;
Frommer et al., The American Journal of Cardiology, May 1965, page 672;
Gamble et al., Circulation, March 1965, page 331).
These calibration techniques have many disadvantages. In all of them,
sterility of the catheter and of the liquid sample is difficult to
maintain. In all of them, the materials in suspension (e.g. red blood
cells or magnesium oxide particles) tend to be non-uniform and tend to
settle. If settling is prevented by stirring the samples, the flow
patterns are highly variable at different measurement sites within the
sample and the flow profile and the resultant orientation of red blood
cells or chemical particles is usually not similar to that found in vivo.
Lastly, manipulations utilizing liquid suspensions and dyes or filters to
simulate the changes produced in actually measured light intensities
measured as a function of changes in blood oxygen saturation have not been
satisfactory.
Another technique commonly used to relate actual light intensity
measurements to the concentration of known substrates under test may be
referred to as the "Differential Spectrophotometric Technique". In this
technique, "Reference" light intensity measurements I.sub.o (either
transmission or reflectance) are made on a material having optical
properties similar to the material to be tested but lacking the specific
substances to be quantified. Thereafter, actual light-intensity
measurements I.sub.s may be made on the material under test including the
substances to be quantified, and these light intensity measurements
I.sub.s are referenced against such "Reference" light intensity
measurements I.sub.o previously obtained. The substance of interest can
then be quantified from the known relationship between the concentrations
of the substances and the actual light intensity measurements I.sub.s
normalized to the reference light intensity measurements I.sub.o.
SUMMARY OF THE INVENTION
In accordance with the present invention, a solid reference element having
optical properties similar to those of blood, is used to provide reference
light intensity measurements I.sub.o for normalizing actual light
intensity measurements I.sub.s in the differential spectrophotometric
technique. The reference element is contained within an apparatus which is
disposable and sterilizable and which automatically couples the reference
element to the distal tip of an optical catheter in a convenient,
repeatable fashion and within a sterile environment. This apparatus
including the reference element and an optical catheter are assembled
within a dual-envelope sterilizable package which permits the catheter
oximeter system to be standardized prior to use and in which the catheter
can remain in sterile condition until its use is desired.
DESCRIPTION OF THE DRAWING
FIG. 1 is a cross-sectional view of the reference element contained within
a housing which receives the end of an optical catheter to be calibrated;
and
FIG. 2 is a plan view showing enclosures disposed about the optical
catheter and reference element illustrated in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown a body 9 of a housing which
includes an aperture 10 at one end thereof for receiving an optical
catheter 12, and having a longitudinal bore 13 therein aligned with the
aperture 10. A plunger element 15 is disposed within the bore 13 and has
attached thereto a reference element 17 which is described in detail
hereinafter. The plunger element 15 and the reference element 17 attached
thereto are disposed to move longitudinally within the bore 13 in a
direction toward the end 21 of catheter 12 that is disposed within the
bore 13. A spring 19 is positioned between the end of the body 9 and the
plunger element 15 to urge the reference element 17 in a direction toward
the end 21 of catheter 12. The plunger element 15 is restrained from
moving toward the end 21 of catheter 12 under the influence of spring 19
by a manually-operable latch mechanism 25 which is pivoted for movement
about an axis 27 and which has a clamp block 31 attached at the other end
of latch mechanism 25.
In operation, the optical catheter 12 is positioned within the body 9, as
shown in FIG. 1, and is held lightly clamped in position by the clamp
block 31. In order to perform the reference photometric measurement, the
reference element 17 must be brought into intimate optical contact with
the end 21 of optical catheter 12. This is accomplished by manually
depressing region 33 of latch mechanism 25 which simultaneously tips the
end 32 of the latch mechanism 25 out of engagement with a detent 34 in the
plunger element 15 to allow the reference element 17 to be urged into
intimate optical contact with the distal end 21 of the optical catheter 12
by the spring 19.
The movement of region 33 of latch mechanism 25 also causes step 54 of
latch mechanism 25 to engage a retaining catch 55 attached to the body 9
for maintaining force on the resilient clamp block 31 to securely hold the
catheter 12 in place against the longitudinal force exerted thereon by
spring 19, the plunger element 15 and reference element 17. A suitable
marking may be carried on surface 53 to indicate when the plunger element
15 is in the proper axial position for the standardization process. Thus,
the apparatus illustrated in FIG. 1 may be manually actuated to establish
the requisite conditions for standardizing the performance of an
associated photometric measuring device 35 which may be attached to the
proximal end of the catheter 12. In practice, optical coupling of a
catheter 12 to a photometric measuring device 35 may be accomplished
through optical connectors 37 and 37', as shown in FIG. 2 and as more
fully described in Application Ser. No. 733,279, now abandoned.
After the reference photometric measurements are performed and the
performance characteristics of the photometric measuring system are
standardized, the catheter is ready to use and may be withdrawn from the
aperture 10 in the body 9. This is accomplished by pulling the catheter 12
outwardly from the body 9, causing clamp block 31, which is provided with
a recess which resiliently engages extension 29, to move sufficiently to
permit removal of the catheter 12. The catheter 12, in cooperation with
the photometric measuring device 35 is then ready for use in a patient.
The reference element 17 shown in FIG. 1 may be formed by uniformly
dispersing particles 36 into a liquid medium which may be cured to form a
substantially solid mass. The particles 36 should have dimensions within
the range 0.02 to 20 microns, and should be uniformly dispersed within the
solid mass. The solid mass should be substantially transparent, compliant
at the surface 14 and noncompressible. The concentration of particles
within the mass should be the same from mass to mass for all reference
elements 17 in a population of reference elements, and should be of a
magnitude to produce signals during reference photometric measurements
made therewith that are of the same order of magnitude as signals produced
during measurement of the materials to be tested.
For reference elements 17 that are to be used with optical catheters which
aid in measuring the oxygen saturation of blood under test, the particles
36 may be titanium dioxide in a range of particle concentrations between
about 0.001% and 1.0% by weight. Other light-scattering particles such as
oxides, sulphates and carbonates of magnesium, barium and calcium, or the
like, may also be used. Silicone resins which cure to a substantially
transparent, compliant and incompressible solid mass are suitable for use
as the vehicle to retain the particles in substantially uniform
dispersion. The mass of the reference element 17 should exhibit compliant
characteristics at least at the surface 13 to assure intimate optical
engagement of the surface 14 of the reference element 17 with the ends or
apertures of the optical fibers that are exposed at the distal tip 21 at
the catheter 12. The incompressible characteristic of the mass is
desirable to prevent changes in concentration of the uniformly dispersed
particles 36 within the mass. Also, the substantial transparency of the
mass is desirable to ensure that the intensity of light back-scattered
from the uniformly-dispersed particles 36 is not differentially influenced
by photometric signals of different wavebands. The transparency desired
for the mass of reference elements 17 that are to be used with optical
catheters which aid in measuring oxygen saturation of blood under test
should be about the order of magnitude of optical transparency as that of
blood under test.
Referring now to FIG. 2, there is shown a pictorial diagram of the catheter
12 having its distal end 21 disposed within the body 9 of the assembly
shown in FIG. 1, and having a proximal end which is attached to one
section 37' of an optical coupler. This assembly is disposed within a
flexible and transparent first envelope 39 which encloses and enseals the
optical catheter 12 except for the optical coupler 37'. The entire
assembly including the envelope 39 and the optical coupler 37' and a
supporting tray 43 therefor is enclosed within a second envelope 45 which
is completely sealed to provide an impervious barrier to microorganisms.
The envelopes 39 and 45 may be formed of a suitable material such as
polyethylene film, or the like. This entire assembly may be sterilized by
standard techniques such as irradiation or ethylene oxide gas
sterilization.
To prepare a catheter 12 for use, the outer envelope 45 is removed to
expose the optical coupler 37'. Without disturbing the bacteriological
sterility of the rest of the assembly, the optical coupler 37' is attached
to its mating optical coupler 37 which forms a part of the photometric
measuring device 35. To initiate the reference measurement procedure,
latch mechanism 25 is depressed in the region 33 by applying force thereto
through the envelope 39.
After the requisite standardization procedures for device 35 catheter 12
are completed, the catheter 12 and photometric measuring system including
the catheter 12 and device 35 are ready for use. The catheter 12 may
remain within the envelope 39 until it is required to make a measurement,
at which time the catheter 12 may be aseptically removed from the envelope
39. The catheter 12 may then be pulled from the body 9, as described
above, and the distal end 21 of the catheter 12 may be introduced into the
material under test.
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Description |
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