CA1094341A

CA1094341A - Sterilizable, disposable optical scattering reference medium

Info

Publication number: CA1094341A
Application number: CA284,617A
Authority: CA
Inventors: Robert F. Shaw; John M. Sperinde
Original assignee: Oximetrix Inc
Current assignee: Oximetrix Inc
Priority date: 1976-10-18
Filing date: 1977-08-12
Publication date: 1981-01-27
Also published as: FR2368032A1; NL7709499A; GB1595207A; FR2368032B1; JPS5350878A; CH626171A5; DE2741914B2; JPS6120806B2; DE2741914C3; DE2741914A1

Abstract

STERILIZABLE DISPOSABLE OPTICAL- SCATTERING
REFERENCE MEDIUM

ABSTRACT OF THE DISCLOSURE

An optical scattering reference medium is formed of a plurality of scattering particles substantially uniformly dispersed in a solid medium which is an incompressible body having a surface which is sufficiently compliant to effect intimate optical coupling with the end of a light guide, whereby to provide the interfacing properties of a liquid and the static dispersal of particles, as within a solid. The combination provides a sterilizable disposable package for performing repeatable photometric measurements to standardize the performance of the photo-metric measuring instrument.

Description

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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 unknowll 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 - 10 intensities received after transmission throuyil 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 mknown concentrations of the substànces being quantified can then be utilized relative to the cali-bration 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 blcod stream oE a patient and the blood oxygenation OL the patient varied by having the patient breathe mixtures enriched with or depleted of oxygen.
While light intensity measurements are made, blood samples are ~ ldrawn, usually through the catheter. The oxygen saturation of these blood samples are then independently measured Oll a separate instrument, often in a central laboratory. After these measurements have been completed, , : . ' ' ~a39~3~ .
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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 satur~tion. Such a calibration curve may be introduced electronically into the catheter oximeter system so that automatic computed o~gen satur-ation may be displayed.
This technique has several disadvantacJes. First, blood o~ygen 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 measure-ments utilizing the catheter oximeter can be obtained.
Third, challges in blood oxygen level occur continuously lS and often very rapidly, making it difEicult to be certain that the blood sample and the actual light intensity reading are truly correla-ted.
In order to eliminate the first and second dis-advantages referred to above, efforts have been made to precalibrate the catheters in flood samples or suspensiotls of othel- materials such as milk of ma~nesia combined with ~yes or ~ilters which are believed to produce light intensity measurements equivalent to blood of known o~gen saturations. (See Taylor et al., Journal of the American ~ledical ~ssociation, ~ugust 14, 1972, page 669;

Frommer et al., The American Journal of Cardiolo~, May 1965, page 672; Gamble et al., Circulation, March 1965, page 331).
Ih~se calibration techniques have many disadvantages.

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In all of them, sterility of tlle catheter and of the liquid sample is difficult to maintain. In all of them, the materials in suspensioll (e.g. red blood cells or magnesium o~ide 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 differellt measurement sites within the sample and the flo~ profile and the resultant orientation of red blood cells or chemical particles is usually not similar to tllat 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 ~echnique commonly used to relate actual light intensity measurements to the concentration of known substrates ~Ider test may be referred to as the "Differen-tial Spectrophotometric Technique". In this technique, "Reference" light intensity measurements Io (ei~ler transmission or reflectance) are made on a material havlng op~ical properties similar to the material to be tested but lacking the specific substances to be quantified. Thereafter, actual light-intensity measure-ments Is may be made on the material under test including the substances to be quantified, and`these light intensity measurements [s are referenced against such "Reference" ligllt intensity measurements Io previously obtained. The substance of interest can then be quantified ~ro~ the known relationship between th con-:. . .
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centrations of the substances and the actual lightintensity meàsurements Is normalized to the reference light intensity measurements Io~
Summary of the Invention In accordance with the present invention, a solid reference element having optical proporties similar to those of blood, is used to provide Reference light intensity measurements Io for normalizing actual light intensity measurements Is 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 standard-ized prior to use and in which the catheter can remain ; in sterile condition until its use is desired.
In accordance with on~ aspect of this invention there is provided apparatus for providing a calibration refer~
ence for use with a photometric measuring device which operates with radiation at a number of selected wavebands, the apparatus including 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 effectively optically coupling its surface to the end of a light guide by intimate physical contact with the end of the light guide.

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Description of the Drawing Figure 1 is a cross-section~l view of the reference element contained within a housing wh.ich receives the end of an optical catheter to be calibrated; and Figure 2 is a plan vi.ew showing enclosures disposed about the optical catheter and reference element illustrated =5a-,~. .

3~1 in ~igure 1.
., D lptiOII of the ~referred ~mbodimcllt Referring now to Figure 1, there is shown a body 9 of a housing which includes an aperture l0 at one end thereof.for receiving an optical catheter 12, and having a lon~itudinal bore 13 therein aligned with the apertùre 10. A plunger element 15 is disposed within the bore.l3 and has attached thereto a reference element 17 which is described in detail thereinafter. The plunger element lS and the reference element 17 attached thereto are disposed to move longitudinally within the bore 13 in a direction to~ard the end 21 of catheter 12 that is disposed ithin the bore 13.. ~ spring 19 is positioned between the end of the body 9 and the plunger element lS to urge the reference element 17 in a direction toward the end 21 oE ca~heter 12. The plunger element 15 is restrained from moving toward the end 21 o~ 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 ~lhich 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 Figure 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 witll the end 21 of optical catheter 12.
This is accomplished by manually depressing region 33 of ; -6 . ~ :
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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 eauses step 54 of latch mechanism 25 to engage a retaining eatch 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 suxface 53 to indieate when the plunger element 15 is in the proper axial position for the standardization process. Thus, the apparatus illustrated in Figure 1 may be manually actuated to establish the requisite ; conditions for standardizing the performance of an associated photom0tric measuring dev.ice 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 Figure 2 and as more fully described in copending Canadian applieation 284,615, filed August 12, 1977.
After the reference photometric measurements are performed and the performance characteristics of the photo-metric 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, ~9~34~
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which is provided with a recess which resiliently engages cxtension 29, to move sufficiently to permit removal of thc catheter 12. The catheter 12, in cooperation with the photo-metric measuring device 35 is then ready for use in a patient.
S Tile reference element 17 shown in ~igure 1 may b.e formed by uni.formly dispersing particles 36 into a liquid medium which may be cured to form a substantially ~
solid mass. The particles 36 should have dimensions wlthin the range 0.02 to 20 micrometers, 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. populat:ion of reference elements, and should be of a magnitude to produce signals during reference ~hotometric measurements made therewi.th tllat are of the same order oE ma~3nl-tude as signals produced during measur~ment 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 .001% and 1.0% by weight. Other light-scattering particles such as oxides, sulphates and carbon-: 25 ates 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 ~ ..

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suit,able for use as the vehicle to retain the particlçs in substantially unifonll dispersion~ .The mass of the reference element 17 should exhibit compliant character-~-~' istics at least at the surface ~ 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 dispèrs~ed particles 36 withln the mass.

ALso, the substantial transparency of the mass is desirable to ensure that the intensity of liyht bac~-scatter'ed from ' .
the ~iformly-dis3,ersed particles 36 is not differentially influenced by photometric signals of different waveballds. ' The transparency desired for the mass of reference elements 17 that are to be used ~ith optical catheters wllicll aid in measuring oxygen saturation of 'blood under -test,should be about the order of magnitude of optical transparency as that o~ blood under test.
: 20 Referring now to Figure 2, there is shown a pictoral diayram of the cathe~er 12 having its distal end 21 disposed ,within the body 9 of the assembly shown in Figure 1, and having a proxima.l 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 an~ enseals the optical catheter 12 except for the optical coupler 37'. The entire assembly including the envelope 39 and the optical coup~er 37' and a supporting tray 43 therefor is enclosed within a second envelope 45 which is ~, '' _g~

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completcly sealed to provide an impervious barrier to micro-organisms. 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 tech-niques such as irradiation or ethylene oxide gas sterili-zation.
To prepare a catheter 12 for use, the outer envelo~e 45 i5 removed to eY~pose the optical coupler 37'. Without disturbing the bacterioloyical sterility of the rest of the assembly, the optical coupler 37' is attached to its mating optical coupler 37 whicll 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.
l~fter the requisite standardizatioll procedures for device 35 ca~heter 12 are completed, the catheter 12 and photometric measuring system including the catheter 12 and device 35 are ready for use. The cathe-ter 12 may remain within the envelope 39 until it is required to make a measurement, at wllicil time the catheter 12 may be aseptically xemoved from the envelope 3-9. The catheter 12 may then be pulled from the body 9, as described above, and the distal -` end 21 of the catlleter 12 may be introduced into the material under test~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for providing a calibration reference for use with a photometric measuring device which operates with radiation at a number of selected wavebands, the apparatus including a plurality of light-scattering particles substantially uniformly dispersed throughout a solid medium that has a sub-stantially incompressible body which is sufficiently compliant at its surface for effectively optically coupling its surface to the end of a light guide by intimate physical contact with the end of the light guide.

2. Apparatus as in Claim 1 wherein said medium is substantially transparent at the selected wavebands of a photometric measuring device which is operable therewith.

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 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 .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 apparatus as in Claim 1 comprising:
clamp means disposed to restrain said light guide against movement in a direction substantially along the length of the light guide, and resilient means disposed to urge said compliant surface into intimate optical engagement with the end of said light guide when the light guide is clamped by said clamp means, said urging with a force which is substantially constant and reproducible in said assembly and in each assembly within a population of such assemblies.

7. Apparatus for calibrating a photometric measuring device which may be connected to light guides and which operates with radiation at a number of selected wavebands, comprising:
the apparatus for providing a calibration reference as claimed in Claim 1, and means for urging together the compliant surface of said incompressible body of the apparatus claimed in Claim 1 and the end of a light guide to achieve intimate optical engagement therebetween.

8. Apparatus as in Claim 7 wherein said means for urging together the compliant surface of said incompressible body and the end of a light guide includes (i) clamp means adapted to restrain the light guide against movement in a direction sub-stantially 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 optical engagement therewith.

9. An apparatus as claimed in Claim 6 further comprising:
actuating means connected to said clamp means for causing said resilient means to urge said compliant surface of said incompressible body into intimate optical engagement with the end of the light guide in response to manual manipulation of said actuating means.