Fiber Optic Catheter

Abstract

A flexible fiber optic catheter insertable into the cardiovascular system for monitoring blood oxygen saturation. The catheter has a distal cage for preventing its end face from contacting vessel walls or the endocardium during use. The cage is terminated with a smoothly surfaced ball which is adapted to provide fixed reflections of light directed thereon from the catheter when in air or placed in a clear sterile solution for calibration prior to use.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

Fiber optic catheters with particular reference to catheters intended for insertion into the cardiovascular system.

2. Description of the Prior Art:

In-vivo fiber optic catheters which are sterilized before use require calibration in conjunction with their associated electro-optical equipment so that absolute values of oxygen saturation or dye concentration and/or accurate measurements of variations thereof with time are made possible in the performance of blood oxygen saturation determinations or dye dilution measurements with these catheters.

Heretofore, catheter calibration has required that the distel end of the catheter be placed in a sterile suspension medium such as milk-of-magnesia which will give a fixed ratio of reflections of wavelengths of light such as 805mu and 660mu or others which may be used for blood oxygen saturation or dye dilution testing. This method of calibrating in-vivo catheters, however, is potentially dangerous to patients since portions of the suspension medium clinging to the catheter may become introduced into the patients blood stream. These inclusions in not being isotonic with blood and embolic, are potentially dangerous to the patient and, leastwise, may adversely affect the accuracy of oxygen saturation determinations and/or other measurements taken with the in-vivo catheter and its associated equipment.

This invention makes it possible to calibrate in-vivo catheters without the subsequent danger of introducing extraneous matter into the blood stream and further provides an improved catheter tip design offering minimal obstruction and resistance to a flow of blood therethrough and maximum exposure of all of its external surfaces for cleaning and sterilization.

SUMMARY OF THE INVENTION

The objectives of this invention are accomplished by providing the fiber optic catheter in this case with a forwardly directed cage protecting its end face against coming into contact with or close enough relationship to the blood vessel walls or endocardium to cause problems of errors in oxygen saturation determination or other tests being conducted by intravascular and intracardiac fiber optic catherization. This cage uniquely comprises a dual pronged configuration, e.g., a single loop or wire, having a ball tip of a diametral size approximating the thickness of the catheter. The ball is formed of a substance which will provide a fixed ratio of reflections of wavelengths of light emitted from the catheter face when the catheter tip is in air or in a clear sterile solution after sterilization. By such means, the fixed ratio of reflections may be used to calibrate the catheter and its associated instrumentation so that absolute readings of oxygen saturation, for example, or other accurate measurements may be obtained. With calibration performed in a clean air environment or a clear saline solution which is isotonic with body fluids, such hazards as contamination of patient's blood or the creation of embolisms therein by residue of conventional calibrating suspension mediums is avoided.

Details of the invention will be more readily understood by reference to the following description taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration, in perspective, of a fiber optic catheter and system of a type useful in performing in-vivo testing of blood wherein the catheter incorporates a preferred embodiment of the invention;

FIG. 2 is a greatly enlarged fragmentary view, in perspective, of the distal end portion of the catheter of FIG. 1 showing the embodiment of the invention in greater detail; and

FIG. 3 is a fragmentary longitudinal cross-sectional view of the portion of the catheter shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fiber optic catheter 10 comprises a length of standard cardiac catheter tubing 12 containing a bundle 14 of efferent and afferent light-conducting fibers 16 (FIGS. 2 and 3).

Included with the bundle 14 of light-conducting fibers 16 is tube 18 which may be disposed centrally of bundle 16 or to one side thereof as illustrated in FIG. 2. Tube 18 which may be used for monitoring blood pressure or withdrawing samples of blood or introducing a medication is conventional. Also conventional in catheters of this type are optical fibers 16, some of which conduct light efferently through catheter 10 toward its distal end and others of which receive and conduct light afferently toward its proximal end. These fibers in bundle 14 may be randomly intermixed adjacent the distal end of catheter 10 and respectively individually separated into branches 20 and 22 at the proximal end of catheter 10 (FIG. 1). Alternatively, they may be retained in separately bundled relationship throughout the entire length of catheter 10. Those interested in greater details of fiber optic catheter constructions and/or the construction and function of individual fibers may refer to U.S. Pat. Nos. 3,068,742 and 3,068,739.

In determining oxygen saturation of blood in-vivo with catheter 10, for example, light from lamp 24 is introduced into the optical fibers contained in one branch 20 of the catheter for conductance through the catheter and emission outwardly thereof at its face 26 directly into blood within a vessel or heart chamber of the cardiovascular system into which the catheter is inserted for this purpose. This light, upon entering the blood becomes diffusely reflected thereby back toward and partially into face 26 for reception by afferent fibers therein which convey the reflected light back through catheter 10 to and outwardly of branch 22. It is then received by a photodetector 28 from which a measurement of its intensity may be made.

To the extent that catheter 10 and its function in determining oxygen saturation of blood have been thus far described, the catheter and its associated light source and photoelectric detector 28 are conventional and explained in detail in the aforementioned U.S. Pat. Nos. 3,068,742 and 3,068,739. As is also explained in these patents, typical wavelengths of light useful in performing in-vivo oxygen saturation determinations are 805mu and 660mu which may be alternately or intermitently supplied to branch 20 of catheter 10 by positioning suitable light filters 30 and 32 in the path of light from lamp 24. Filters 30 and 32 may be supported in a rotating disc 34 as illustrated in FIG. 1 or in a sliding mechanism as shown and described in the aforementioned U.S. patents. Alternatively, the filters 30 and 32 may be replaced by a suitable dichroic beam splitter placed so as to receive the light returned by catheter through branch 22 and direct preselected individual wavelengths of this light along separate paths to two or more photoelectric detectors similar to detector 28 from which interpretation of the ratio of intensities of the different wavelengths of light may be accomplished for determination of blood oxygen saturation. This latter arrangement of beam splitting and individual photoelectric detection of different wavelengths of light may be found in U.S. Pat. No. 3,296,922.

In order to render catheter 10 and its associated electro-optical system capable of affording absolute and/or accurate measurement of oxygen saturation or dye dilution in-vivo with each application of catheter 10 to the body, calibration of the catheter and its associated electro-optical instrumentation is required as is explained in U.S. Pat. Nos. 3,068,742; 3,068,739; and 3,296,922. This calibration, accordingly, requires that a portion of light directed through and emitted from face 26 of catheter 10 be returned therethrough with a fixed ratio of reflections, e.g., 805mu/ mu. This, has been accomplished heretofore by placing face 26 of catheter 10 in a suspension medium of, for example, milk-of-magnesia whereupon a zero or other preselected meter reading of an electro-optical measuring system used in conjunction with catheter 10 may be established as a reference for interpreting readings of blood oxygen saturation or dye concentration in-vivo.

According to the present invention, a fixed ratio of reflections of light emitted from face 26 of catheter 10 is accomplished in air or in a clear saline solution or the like, i.e., without contamination of the catheter by non-isotonic mediums such as milk-of-magnesia, as follows: Catheter tubing 12 is longitudinally slotted adjacent face 26 at diametrically opposite sides to receive each of the free ends 36 of a two pronged, hairpin-like cage 38 which extends forwardly from the slotted catheter tubing 12 beyond face 26. A ball 40 at the end of cage 38 is grooved and set into place or previously molded over the looped end 42 of cage 38. The ball 40 may be formed of metal and cemented or soltered in place or, preferably, molded of a white pigmented epoxy which will not degrade or deteriorate when exposed to gas sterilization, e.g., ethylene oxide gas. In either case, ball 40 is highly polished or otherwise smoothly finished and is preferably of a diameter approximately equal to the diametral thickness of catheter tubing 12. Ends 36 of cage 38 are permanently fixed to catheter 10 preferably with a binding wire or cord 44 wrapped therearound in a circumferential slot extending about catheter tubing 12. Once ends 36 of the cage are secured in place, the slots are filled with a suitable cement preferably of the epoxy type which forms a smooth outer surface flush and continuous with the main outer surface of catheter tubing 12. All potentially sharp edges of the catheter are removed by rounding and/or polishing and all corners between face 26 and cage 38 as well as between ball 40 and the wire legs of the cage are open and readily accessible for cleaning and sterilization.

In use, the distal end of the catheter is inserted into the cardiovascular system with the smoothly finished ball 40 functioning to guide the catheter thereinto with minimal friction and/or irritation to vascular walls of the endocardium while keeping face 26 of the catheter sufficiently spaced therefrom to permit a free flow of blood across face 26 at all times.

Prior to use or reuse of catheter 12 it must, in either case, be sterilized, e.g., by exposure to ethylene oxide gas, and then calibrated in conjunction with the electro-optical system with which it may be used for performing oxygen saturation or dye dilution measurements. This calibration, with the cage 38 of the present invention may be performed simply in a clean air environment by directing light of wavelengths intended to be used for testing through afferent fibers 16 of bundle 14 which light becomes emitted from face 26 and reflected from ball 40 as shown by arrows in FIG. 3 reversely upon face 26. All directions of reflection being fixed and constant, calibration of the catheter and its associated instrumentation according to the ratio of light wavelengths (e.g., 805mu and 660mu) returned through the catheter may be accomplished. The instrument measuring meter may be set to read zero at this time or, alternatively, set to read a percentage of blood oxygen saturation, e.g., 85 percent which is known to reflect the same ratio of light wavelengths.

This calibration, in either case, is performed without contamination of the catheter by the heretofore requirement that it be placed in a non-isotonic medium. It should be understood that calibration of catheter 10 with ball 40 of cage 38 may be accomplished within a clear isotonic liquid such as a saline solution if desired.

When the catheter is inserted into the cardiovascular system wherein the space between ball 40 and face 26 is filled with blood, ball 40 has no effect upon the reflection of light from the blood back into face 26. The density of blood prevents light, especially 805 and 660mu wavelengths, from penetrating appreciably thereinto before diffuse reflection. The spacing between face 26 and ball 40 is considerably greater than a distance in blood capable of being penetrated by light and especially, even greater than a distance through which light might be directed and returned by reflection in blood.

In addition to catheter 10 being adaptable to calibration without immersion of its distal end in an extraneous calibrating medium, its cage 38 construction, having only two posts 48, uniquely renders this catheter relative to conventional catheters, more readily adaptable to cleaning and complete sterilization and less resistant to the circulation of blood through its cage with a corresponding lessening of tendencies for clotting.

Claims

We claim:

1. A fiber optic catheter for use in measuring amounts of diffuse reflection of light in blood, said catheter having a multiplicity of light-conducting fibers and a catheter tubing surrounding said fibers, the fibers all being intimately juxtaposed adjacent the distal end of said catheter with corresponding end faces thereof exposed at said distal end and separated into a pair of branches adjacent the opposite proximal end of said catheter, corresponding fibers of each branch being intimately juxtaposed and respective end faces thereof exposed; wherein the improvement comprises;

a rigid ball disposed forwardly of said exposed faces of said fibers at said distal end of said catheter and spaced away therefrom a distance greater than a maximum distance of penetration of light into blood whereby light emitted from said exposed faces of said fibers will be prevented from reaching said ball when said distal end of said catheter is placed in blood, said ball further being formed of a substance which characteristically reflects a fixed ratio of at least two preselected wavelengths of light directed thereupon from said exposed faces of said fibers at said distal end of said catheter when said distal end including said exposed faces and said ball is disposed in air and clear liquids; and

a pair of slender posts supporting said ball in said spaced relationship with said fiber faces, said posts respectively extending from approximately diametrically opposed sides of said ball in a direction longitudinally of said catheter tubing and being secured to said distal end of said catheter for completing the configuration of a cage permitting a free flow of blood between said ball and adjacent fiber faces when said catheter distal end is placed in said blood for testing thereof, said cage further preventing contact of said exposed fiber ends with walls of means containing said blood.

2. A fiber optic catheter according to claim 1 wherein said fibers of each of said branches are randomely intermixed adjacent said distal end of said catheter.

3. A fiber optic cather according to claim 1 wherein said fibers in said branches are maintained in correspondingly separated relationship throughout the length of said catheter.

4. A fiber optic catheter according to claim 1 wherein said pair of slender posts comprise oppositely disposed extensions of a looped length of wire and said ball is affixed to the intermediate looped portion of said wire.

5. A fiber optic catheter according to claim 1 wherein said ball is formed of a white pigmented plastic material.

6. A fiber optic catheter according to claim 1 wherein said ball is formed of metal.

7. A fiber optic catheter according to claim 4 wherein said ball is molded over said looped intermediate portion of said length of wire.

8. A fiber optic catheter according to claim 1 wherein said slender posts are at least partially imbedded in said catheter tubing and said tubing is smoothly finished thereover.

9. A fiber optic catheter according to claim 1 in combination with means for introducing light into said exposed end faces of one of said branches and photoelectric means for receiving light emitted from said exposed faces of the other of said branches.

10. A fiber optic catheter in the combination according to claim 9 further including means for determining ratios of amounts of light of two preselected wavelengths returned through said catheter from said distal end to one of said branches at said proximal end.