GB1595206A

GB1595206A - Apparatus for photometric analysis of a fluid

Info

Publication number: GB1595206A
Application number: GB3398877A
Authority: GB
Original assignee: Oximetrix Inc
Current assignee: Oximetrix Inc
Priority date: 1976-10-18
Filing date: 1977-10-18
Publication date: 1981-08-12
Also published as: FR2371203B1; DE2741913B2; DE2741913C3; FR2371203A1; JPS5353191A; DE2741913A1; CH620108A5; NL7709209A; CA1089252A

Abstract

Catheter device having fibre optical waveguides (T and R, respectively) which transmit light into the interior of living bodies to be examined and out of these bodies again for the photometric analysis of a flow agent which makes it superfluous to calibrate each individual catheter in a multiplicity of catheters. For this, the distance between the central points of the light emergence surface of each fibre optical wave guide (T) transmitting light into the body and of each fibre optical wave guide (R) receiving light inside the body of an individual catheter within each bundle of fibre optical wave guides is chosen to be identical. Moreover, the size and shape of all light emergence surfaces of the fibre optical waveguides (T) transmitting light into the body are generally chosen to be identical in the same way as the size and shape of the light admission surfaces of all fibre optical waveguides (R) receiving light in the body in each catheter and from catheter to catheter, and the alignment of all fibre optical waveguides (T) transmitting light into the body is virtually identical with regard to all fibre optical waveguides (R) receiving light in the body. <IMAGE>

Description

(54) APPARATUS FOR PHOTOMETRIC ANALYSIS OF A FLUID (71) We, OXIMETRIX, INC., of 1215A Terra Bella Avenue, Mountain View, California 94043, United States of America, a corporation organized and existing under the laws of the State of California, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to apparatus for photometric analysis of a fluid.

Optical catheters for performing in-vivo spectrophotometric measurements in the blood stream or elsewhere within living organisms are well-known in the art. (See for example U.S. Patent No. 3,847,483).

These have most commonly been used for the performance of oximetry, i.e., measuring the relative amount of the total hemoglobin within the blood stream that is in the oxygenated form. While prior art optical catheters can be used successfully for performing oximetry, they have a shortcoming which is of major importance to the medical practioner in the care of critically-ill patients. The catheters of the prior art require that an individual calibration be performed for each and every individual catheter that is to be used, in order to obtain accurate oxygen saturation measurements.

To perform this calibration, commonly a sterile optical catheter is inserted through the wall of a blood vessel of interest and advanced so that its tip is at a position within the flowing blood stream where it is desired that oxygen saturation measurements be made. The patient is frequently given a particular gas mixture to breathe, commonly a mixture enriched in oxygen or depleted of oxygen, or two such mixtures sequentially, which causes the patient's blood to attain an oxygen saturation level in the regions of interest. Then, as blood samples are withdrawn (most commonly through an open lumen of the optical catheter) measurements are made of the relative light reflectances or transmissions at the catheter tip for the various optical wavelengths used by the catheter oximeter system.

The blood samples must then be taken to a separate instrument (for example, a transmission spectrophotometer located in a central laboratory) where an independent measurement of the oxygen saturation of the one or more blood samples is made. The results of this independent measurement are then returned to the catheter oximeter at the patient's bedside, so that appropriate changes may include changes in bias levels and/or gains of various amplifiers in order to correct for the deviation between the initial oxygen saturation measurement made at the time of blood sampling and the oxygen saturation measurement independently determined by the separate instrument.

This requirement for individual calibration of catheters has obvious and important disadvantages. One such disadvantage is the delay between the time of catheter placement and the time at which accurate measurements of oxygen saturation utilizing the optical catheter can be obtained. This delay deprives the physician of important information at a time when such information is often of the utmost importance in caring for the patient. For example, at the time of delivery of a newborn infant with severe respiratory distress because of prematurity, or severe Rh Hemolytic Disease or with other disorders, the resuscitation of these sick infants (who may weigh only two to three pounds) is frequently a precarious and difficult problem. This resuscitation must be instituted immediately upon birth and the various therapeutic manipulations completed within a very short time period.

Unfortunately, the time required to perform calibration procedures on prior art optical catheters interferes with these catheters being used to furnish blood oxygen measurements during the course of resuscitation to guide the physician in the resuscitation procedure.

A second disadvantage associated with calibrating the optical catheters of the prior art relates to the uncertainties associated with the resultant calibration. Changes in blood oxygen level occur continuously and often very rapidly, making it difficult to be certain that the blood sample and the oximeter readings are truly correlated.

Further, during the process of blood sampling through the catheter tip, significant variations in flow profile of the red blood cells in the region where the optical measurements are being made may introduce errors into the optical measurements. In addition the manipulations of the blood sample required to perform oxygen saturation measurement with an independent instrument can introduce errors in the calibration procedure.

It is therefore highly desirable to provide catheters which do not require individual calibration, at the time of use, so that each catheter of a whole population of catheters can be used to obtain blood oxygen measurement immediately upon introduction of the catheter into a blood vessel of interest.

The present invention provides apparatus comprising (a) a catheter, selected from a population of a plural number of optical catheters for photometric analysis of a fluid wherein the catheters within the population do not require individual calibration; each catheter of said population comprising one or more transmitting optical fibers and one or more receiving optical fibers; each optical fiber having end surfaces providing an aperture at each end of the fiber; each aperture of each transmitting and each receiving optical fiber at the distal end thereof having a centroid of area; the distance of the centroid of area of the aperture of the or each and every receiving optical fiber at the distal end of each and every catheter being a constant value for all catheters of the population; and (b) an associated photometric measuring device for the photometric analysis of a fluid, the apertures of the transmitting and receiving optical fibers at the proximal end of each being disposed to mate in abutting and optical engagement with end surfaces, respectively, of transmitting and receiving optical channels of the associated measuring device; the optical fibers being of substantially different hardness and compliance from the material of the end surfaces of the optical channels of the measuring device to allow deformation of either the optical fibers or the optical channels in response to longitudinally applied force to provide intimate optical coupling between the optical fibers and the optical channels.

In apparatus as set forth in the last preceding paragraph, the catheter may comprise a single transmitting or receiving fiber surrounded by a plurality of receiving or transmitting fibers.

In apparatus as set forth in the last preceding paragraph, or the last preceding paragraph but one, it is preferred that said one or more transmitting fibers is/are contiguous with said one or more receiving fibers. Alternatively, said one or more transmitting fibers is/are spaced from said one or more receiving fibers.

In apparatus as set forth in the last preceding paragraph but two, the catheter may comprise two transmitting fibers and two receiving fibers only, the two transmitting fibers being located such that their centroids at their distal ends are located at two diagonally opposite corners of a square and the two receiving fibers being located such that their centroids at their distal ends are located at the two other corners of the square, with adjacent fibers in contiguous relationship.

The fibers may be of circular or square cross-section.

In an alternative apparatus according to the invention, the catheter may comprise a single transmitting optical fiber and a single receiving optical fiber.

There now follows a detailed description which is to be read with reference to the accompanying drawings of apparatus and catheters according to the present invention; it is to be clearly understood that this apparatus and these catheters have been selected for description to illustrate the invention by way of example and not by way of limitation.

In the accompanying drawings: Figures 1 and 2 are sectional views of the distal ends of catheters for an apparatus according to the present invention in which a plurality of receiving optical fibers (R) are disposed contiguous to the transmitting optical fiber (T) and in which the centroid of area of each receiving optical fiber (R) is equidistantly spaced from the centroid of area of the single transmitting optical fiber; and Figure 3 is a sectional view of the distal end of another embodiment of a catheter for an apparatus according to the present invention in which each of the transmitting or receiving optical fibers is positioned remotely from a single receiving (or transmitting, respectively) optical fiber, with the centroid of area of each of the remotelypositioned optical fibers disposed equidistantly from the centroid of area of the single, centrally-located optical fiber; and Figures 4 and 5 are sectional views of the distal ends of still other embodiments of catheters for an apparatus according to the present invention in each of which the centroid of area of each of a pair of receiving optical fibers (R) is equidistantly disposed from the centroid of area of each of a pair of transmitting optical fibers (T); and Figure 6 is a sectional view of the distal end of another embodiment of a catheter for an apparatus according to the present inven tion in which the centroid of area of each of a plurality of rectangular receiving optical fibers (R) is equidistantly disposed from the centroid of area of a single, square transmitting optical fiber (T); and Figure 7 is a graph showing the distribution of light flux at different wavelengths and blood conditions as a function of distance from the centroid of area of a round transmitting optical fiber at the distal end of the catheter; and Figure 8 is a sectional view of a further embodiment of a catheter for an apparatus according to the present invention in which a pair of substantially cylindrical optical fibers are contiguously disposed at the distal end of the catheter; and Figure 9 is a side view of an apparatus according to the present invention comprising a catheter engaged with a photometric oximeter at an optically-coupled interface.

Referring now to Figures 1 to 6, there is shown in each Figure the end sectional view of the optical fiber position at the distal ends of optical catheters for an apparatus according to the present invention. In these Figures, there is at least one optical fiber designated with a "T" to indicate a fiber which transmits radiation to blood under test and the end sectional view of at least one optical fiber designated with the letter "R" to indicate a fiber which receives radiation from the blood under test. It should be understood that, with respect to Figures 1 to 6, the transmitting fibers and receiving fibers may be transposed in which case each "R" would represent an optical fiber which transmits radiation to blood under test and each letter "T" would indicate an optical fiber which receives radiation from the blood under test.

Where more than one waveband of radiation is transmitted to the blood under test, there may be a number of transmitting fibers at least equal to the number of wavebands of radiation being transmitted to the blood under test; or alternatively, and preferably, all wavebands of radiation used may be transmitted sequentially down each transmitting fiber.

Radiation that is transmitted down the transmitting fiber illuminates the blood, and the intensity of this radiation falls off with distance because of scattering and absorption. Some portion of that light which illuminates the blood is back-scattered by the red blood cells and is collected by receiving fibers which guide this collected light back to a measuring instrument (not shown) where the light intensity is measured by a photodetector element. It is the total light collected by the entire portion of each and every receiving fiber that is measured by the photodetector. To a usable approximation, for radiation of wavelengths in the optical portion of the electro-magnetic spectrum used, and for optical fibers having dimensions of the order of ten thousandths of an inch, the centroids of the areas of the apertures of the transmitting and receiving fibers substantially correspond with the centroids of the illuminating and the receiving light fluxes merging from and being collected by the apertures of the optical fibers. For circular fibers, as shown in Figures 1 to 4, the centroid of the cross-sectional area of each fiber is the center of the circle. However, fibers having apertures with cross-sectional shapes other than circular also have centroids of cross-section and can be used. For example, for fiber apertures having rectangular cross-sectional shape at the distal end, as shown in Figures 5 and 6, the centroid of such cross-section is located at the intersection of the diagonals through the corners thereof. Similarly, if the fiber apertures have a triangular cross-sectional shape (not shown), the centroids of such cross-sections are located at the intersection of the bisectors of the sides thereof. Of course, the fibers may have other more complex crosssectional shapes at their apertures, and it should be understood that such apertures also have centroids of cross-section.

Referring now to Figure 7, the graph portion illustrates the intensity of received light as a function of distance from the centroid of a transmitting fiber for two different wavelengths and two different conditions of oxygenation of blood under test.

Specifically, in curve 17 the intensity (or light flux) measured at the 800 nanometer waveband is substantially the same for hemoglobin and oxy-hemoglobin and decays with distance away from the centroid 10 of the transmitting optical fiber 11.

Curves 21 and 19 illustrate that the radiation intensity (or light flux) measured at the 670 nanometer waveband falls off with distance measured from the centroid 10 of the transmitting optical fiber 11 at a more rapid rate for reduced hemoglobin (Curve 21) than for oxyhemoglobin (Curve 19). From these curves it can be shown that the integral of light flux received by a receiving optical fiber 13 over the total cross-section area at a given wavelength will be the same for all equidistantly-spaced locations from the transmitting optical fiber 11. These curves also illustrate that for a receiving optical fiber 13' which is placed at a greater distance from the transmitting optical fiber 11 than the receiving optical fiber 13, the integral of light flux received at a given wavelength will be less for the optical fiber 13' than for the optical fiber 13. Further, the light flux received by the fiber 13' compared with the optical flux received by the fiber 13 will be relatively different for different wavelengths, thereby introducing a wavelength-dependent aspect to the change in the optical properties of the catheter.

Returning now to Figure 1, it can be seen that if light at all the optical wavebands used for the measurement is transmitted down the single optical fiber 12, the received light intensities of each waveband relative to each other waveband will be unchanged whether one receiving fiber 14 is used, or the entire array of receiving fibers 14 to 24 are used, or if some number of receivers between these two cases is selected, as long as the center-to-center spacing from the transmitting fiber to each of the receiving fibers 14 to 4 remains identical.

As a practical matter, individual fibers in a group of, say, receiving fibers may break or may have poorer or better optical transmission properties than the average. As long as the center-to-center spacing between the transmitting and receiving fibers remains constant, the loss of one of a group of such receiving fibers (unless it is the only one) and the concomitant variation in the transmitting properties of such group of receiving fibers will not influence the relative lightintensities measured at the various wavelengths.

Figure 4 illustrates an embodiment a catheter for apparatus according to the invention involving multiple-transmitting and multiple-receiving optical fibers. In this catheter, as long as the center-to-center spacing between all transmitting and all receiving-optical fibers remains constant, the relative light-intensities measured at the various wavelengths utilized will be unchanged, despite fiber breakage and variations in fiber transmissivity.

Figures 2 and 3 illustrate catheters for apparatus according to the invention in which the transmitting optical fibers and the receiving optical fibers are not the same size. However, in these catheters, it is only necessary that all of the transmitting optical fibers be identical in size to each other and all of the receiving optical fibers be identical in size to each other, and that the center-tocenter spacing between each of the transmitting optical fibers and each of the associated receiving optical fibers remains constant.

Figures 5 and 6 illustrate other catheters for apparatus according to the invention in which all of the fibers are not circular in shape. Rather, it is only necessary that the transmitting fibers be similar in size and shape, and that the receiving fibers be similar in size and shape and that the orientation of all transmitting fibers relative to all receiving fibers be similar to maintain the advantages noted above.

Figure 3 illustrates another catheter in which the transmitting and receiving fibers are not contiguous to each other. However, all of the operating advantages noted above may be retained by making the center-tocenter spacing between each transmitting optical fiber and each receiving optical fiber substantially the same and by making the sizes and shapes of the transmitting optical fibers substantially the same within the group thereof and by making the sizes and shapes of the receiving optical fibers substantially the same within the group thereof.

Figure 8 illustrates the simplest, most economic, and most readily manufacturable optical catheter for an apparatus according to the present invention. In this embodiment, a single transmitting optical fiber 11 and a single receiving optical fiber 13 of identical size are placed contiguous to each other. This configuration minimizes the amount of fiber material required, reduces the number of processes required to make the fibers, simplifies the sorting required of fibers, and readily assures the relationship between optical fibers discussed above.

Referring now to Figure 9, an optical catheter 26 typically operates in conjunction with a photometric measuring device 28 which furnishes one or more wavebands of light for transmission down a transmitting optical fiber or fibers 30 and which has a photodetector means for measuring the intensity of light collected by a receiving optical fiber or fibers 32. Thus, at the proximal end 34 of the optical catheter, the optical fibers must be conveniently couplable to such a measuring device 28. To produce reliable accurate photometric measurements, a repeatable stable optical relationship between the proximal ends 34 of the transmitting and receiving optical fibers 30, 32 of the catheter 28 and the corresponding optical channels 36 and 38 of such a measuring device 28 must be attained.

While both the optical channels 36, 38 of such a measuring device and the proximal end surfaces or apertures 34 of the corresponding optical fibers 30, 32 of the catheter 28 are nominally flat and perpendicular to the axis of light transmission, certain variations in geometric normality can occur and these surfaces may be irregular and imperfect. If the coupling between the optical channels 36, 38 of such a measuring device and the proximal end surfaces of the optical fibers 30, 32 is less than intimate, specular reflections will occur wherever an air/surface interface occurs, and this introduces undesirable extraneous light-intensity variations in the signals being measured by such measuring device. In addition, less than intimate optical coupling between the optical channels of such a measuring device and the proximal end surfaces of the corresponding optical fibers may produce optical interference patterns which are wavelength dependent and which therefore can produce spurious changes in the relative lightintensities measured at the various wavebands being used.

To avoid the error introduced by specular reflections and by interference patterns at the optical coupling interface 34 between a measuring device and the optical fibers 30, 32, it is important that intimate surface contact be attained and maintained, even during use where patient motion and other extraneous factors may introduce undesirable forces which tend to misalign and disengage the optical coupling at this interface 34. In accordance with the present invention intimate contact between optical channels 36, 38 and optical fibers 30, 32 at the interface 34 is attained and maintained by using a material in the optical fibers 30, 32 which is softer and more compliant than the material in the optical channels 36, 38 of the measuring device 28 with which they engage. In addition, the housing 40 for the optical fibers 30, 32 may be made of a material that is softer and more compliant than the material of the housing 42 which surrounds the optical channels 36, 38. Further, to attain and maintain this intimate optical contact between the proximal ends 34 of the optical fibers 30, 32 and the optical channels 36, 38 of the measuring device 28, it is desirable to employ means to apply an axially-aligned force 44 to the optical catheter housing 40 which will establish an axial force at the mating surfaces between the proximal ends 34 of the optical fibers 30, 32 and the optical channels 36, 38. One suitable material to use in the optical fibers 30, 32 for interfacing with optical channels 36, 38 made of glass having the properties referred to above is polystyrene.

WHAT WE CLAIM IS: 1. Apparatus comprising (a) a catheter, selected from a population of a plural number of optical catheters for photometric analysis of a fluid wherein the catheters within the population do not require individual calibration; each optical fiber having end surfaces providing an aperture at each end of the fiber; each aperture of each transmitting and each receiving optical fiber at the distal end thereof having a centroid of area; the distance of the centroid of area of the aperture of the or each and every receiving optical fiber at the distal end of each and every catheter being a constant value for all catheters of the population; and (b) an associated photometric measuring device for the photometric analysis of a fluid, the apertures of the transmitting and receiving optical fibers at the proximal end of each being disposed to mate in abutting and optical engagement with end surfaces, respectively, of transmitting and receiving optical channels of the associated measuring device; the optical fibers being of substantially different hardness and compliance from the material of the end surfaces of the optical channels of the measuring device to allow deformation of either the optical fibers or the optical channels in response to longitudinally applied force to provide intimate optical coupling between the optical fibers and the optical channels.

2. Apparatus according to claim 1 wherein the catheter comprises a single transmitting or receiving fiber surrounded by a plurality of receiving or transmitting fibers.

3. Apparatus according to claim 1 wherein said one or more transmitting fibers is/are contiguous with said one or more receiving fibers.

4. Apparatus according to claim 1 wherein said one or more transmitting fibers is/are spaced from said one or more receiving fibers.

5. Apparatus according to claim 1 wherein two transmitting fibers and two receiving fibers only are provided, the two transmitting fibers being located such that their centroids at their distal ends are located at two diagonally opposite corners of a square and the two receiving fibers being located such that their centroids at their distal ends are located at the two other corners of the square, with adjacent fibers in contiguous relationship.

6. Apparatus according to any one of claims 1 to 5 wherein the fibers are of circular cross-section.

7. Apparatus according to any one of claims 1 to 5 wherein the fibers are of square cross-section.

8. Apparatus according to claim 1 wherein the catheter comprises a single transmitting optical fiber and a single receiving optical fiber.

9. Apparatus for photometric analysis of blood or other spectrally-absorbing, optically scattering fluids substantially as hereinbefore described with reference to Figure 9 in conjunction with any one of Figures 1 to 6 and 8 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. wavebands being used. To avoid the error introduced by specular reflections and by interference patterns at the optical coupling interface 34 between a measuring device and the optical fibers 30, 32, it is important that intimate surface contact be attained and maintained, even during use where patient motion and other extraneous factors may introduce undesirable forces which tend to misalign and disengage the optical coupling at this interface 34. In accordance with the present invention intimate contact between optical channels 36, 38 and optical fibers 30, 32 at the interface 34 is attained and maintained by using a material in the optical fibers 30, 32 which is softer and more compliant than the material in the optical channels 36, 38 of the measuring device 28 with which they engage. In addition, the housing 40 for the optical fibers 30, 32 may be made of a material that is softer and more compliant than the material of the housing 42 which surrounds the optical channels 36, 38. Further, to attain and maintain this intimate optical contact between the proximal ends 34 of the optical fibers 30, 32 and the optical channels 36, 38 of the measuring device 28, it is desirable to employ means to apply an axially-aligned force 44 to the optical catheter housing 40 which will establish an axial force at the mating surfaces between the proximal ends 34 of the optical fibers 30, 32 and the optical channels 36, 38. One suitable material to use in the optical fibers 30, 32 for interfacing with optical channels 36, 38 made of glass having the properties referred to above is polystyrene. WHAT WE CLAIM IS:

1. Apparatus comprising (a) a catheter, selected from a population of a plural number of optical catheters for photometric analysis of a fluid wherein the catheters within the population do not require individual calibration; each optical fiber having end surfaces providing an aperture at each end of the fiber; each aperture of each transmitting and each receiving optical fiber at the distal end thereof having a centroid of area; the distance of the centroid of area of the aperture of the or each and every receiving optical fiber at the distal end of each and every catheter being a constant value for all catheters of the population; and (b) an associated photometric measuring device for the photometric analysis of a fluid, the apertures of the transmitting and receiving optical fibers at the proximal end of each being disposed to mate in abutting and optical engagement with end surfaces, respectively, of transmitting and receiving optical channels of the associated measuring device; the optical fibers being of substantially different hardness and compliance from the material of the end surfaces of the optical channels of the measuring device to allow deformation of either the optical fibers or the optical channels in response to longitudinally applied force to provide intimate optical coupling between the optical fibers and the optical channels.