OPTICAL OXIMETER APPARATUS AND METHOD

• US 3,847,483 A
• Filed: 09/24/1973
• Issued: 11/12/1974
• Est. Priority Date: 02/01/1972
• Status: Expired due to Term

• Current Assignee: David P. Sidlauskas, Donn D. Lobdell, Robert F. Shaw
• Original Assignee: David P. Sidlauskas, Donn D. Lobdell, Robert F. Shaw
• Inventors: Sidlauskas, David P., Lobdell, Donn D., Shaw, Robert F.
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US05/400,085
• Time in Patent Office: 414 Days
• Field of Search: 356/39,41 128/2L 250/573,574,227
• US Class Current: 356/41
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G02B 6/4416 Heterogeneous cables

Abstract

An improved oximeter operates at two radiation wavelengths, neither of which need be an isosbestic wavelength, to provide direct and accurate indications of oxygen saturation of blood substantially independently of variation in blood flow velocities, hematocrits and hemoglobin concentrations. Fiber optic light guides are arranged within a double-lumen catheter of improved design and reduced diameter for convenient insertion into a blood vessel of a patient. Dual detection and computing circuitry for use with a pair of catheters permits direct determination of arterial-venous oxygen difference as a useful indication of the adequacy of cardiac output.

Claims

1. Apparatus for determining the oxygen saturation of blood, comprising:

a plurality of electromagnetic radiation sources operable alternately and cyclically in selected timed sequence to produce electromagnetic radiation in a plurality of different wave bands;

means coupled to said sources for providing a first optical path between said sources and an optical outlet port remote from said sources which is disposed to communicate with blood;

detector means for producing electrical signals in response to electromagnetic radiation of each of said different wave bands applied thereto;

means coupled to said detector means for providing a second optical path between said detector means and an optical inlet port which is disposed to communicate with the blood at a location in close proximity to said optical outlet port;

signal means coupled to said detector means for producing an electrical signal for each of said radiation wave bands which is representative of the intensity of the radiation received by said detector means at the corresponding wave band;

source means of first and second reference signals;

first circuit means connected to receive said electrical signals and said first reference signal for producing a first electrical output as the combination of said electrical signals and first reference signal, each selectively weighted by a first set of coefficients;

second circuit means connected to receive said electrical signals and said second reference signal for producing a second electrical output as the combination of said electrical signals and said second reference signal, each selectively weighted by a second set of coefficients; and

means coupled to said first and second circuit means for producing a first output indicative of oxygen saturation of blood as the ratio of the first and second electrical outputs from said first and second circuit means.

2. Apparatus as in claim 1 wherein all said sources produce electromagnetic radiation at non-isosbestic wavelengths.

3. Apparatus as in claim 1 wherein:

said first optical path includes a portion of optical path of fixed geometry and a portion of flexible optical path terminating at said optical outlet port;

said portion of fixed geometry includes an optical element having a plurality of inlets, each optically coupled to receive radiation from a corresponding one of said radiation sources, and having a single outlet for transmitting radiation therethrough from said sources along said first optical path; and

said sources are electrically actuatable to produce said wave bands of electromagnetic radiation in said timed sequence.

4. Apparatus as in claim 3 wherein said first optical path includes an optical integrator disposed intermediate said flexible portion and said element, said optical integrator including a light guide having a length-to-diameter ratio which produces radiation at the outlet of the optical integrator that is uniformly distributed over the area of the outlet substantially independently of spatial separation of radiation present over the area of the inlet of the optical integrator.

5. Apparatus as in claim 3 wherein said first optical path includes an optical connector disposed intermediate the flexible portion and said element for selectively disconnecting the flexible portion from the portion of fixed geometry.

6. Apparatus as in claim 1 wherein said optical outlet port and said optical inlet port for optically communicating with blood are substantially coplanarly disposed in immediately adjacent relationship.

7. Apparatus as in claim 1 comprising:

at least another pair of electromagnetic radiation sources operable alternately and cyclically in selected timed sequence to produce electromagnetic radiation in a plurality of different wave bands;

means coupled to said other sources for providing a third optical path between said other sources and an additional optical outlet port remote from said sources which is disposed to communicate with blood;

second detector means for producing electrical signals in response to electromagnetic radiation of the different wave bands applied thereto from said other sources;

means coupled to said second detector means for providing a fourth optical path between said detector means and an additional optical inlet port which is disposed to communicate with blood at a location in close proximity to said additional optical outlet port;

second signal means coupled to said second detector means for producing an electrical signal for each of said radiation wave bands which is representative of the intensity of the radiation received by said second detector means at the corresponding wave band;

additional source means of reference signals;

third circuit means connected to receive said electrical signals from said second signal means and an additional reference signal for producing a third electrical output as the combination of said electrical signals and additional reference signal selectively weighted by a third set of coefficients;

fourth circuit means connected to receive said electrical signals from said second signal means and an additional reference signal for producing a fourth electrical output as the combination of said electrical signals and additional reference signal selectively weighted by a fourth set of coefficients;

means coupled to said third and fourth circuit means for producing a second output indicative of oxygen saturation of blood as the ratio of the third aNd fourth electrical outputs from said third and fourth circuit means; and

means coupled to receive said first and second outputs for providing an output indication of oxygen difference as the algebraic combination of said first and second outputs.

8. Apparatus as in claim 5 wherein:

said optical connector comprises alignment means including a plurality of V-shaped grooves;

a pair of cylindrically shaped housings disposed in each of said V-shaped grooves, one of the pair of housings in a V-shaped groove being attached to the portion of the respective optical path of fixed geometry; and

the other of the pair of housings in a V-shaped groove being attached to the portion of the respective optical path of flexible geometry.

9. Apparatus as in claim 8 wherein the flexible and fixed geometry portions of each of the first and second optical paths are disposed substantially coaxially within the respective cylindrical housings for axial alignment of corresponding pairs thereof disposed within a common V-shaped groove.

10. Apparatus as in claim 9 comprising clamping means disposed with respect to said alignment means and the corresponding pairs of cylindrical housings in the V-shaped grooves for exerting forces thereon in axial and lateral directions for maintaining said corresponding pairs of cylindrical housings in aligned, abutting relationship.

11. Apparatus as in claim 3 wherein said portion of flexible optical path comprises a tube containing a pair of flexible, continuous optical light guides positioned therein along the length thereof.

12. Apparatus as in claim 11 wherein said tube includes a septum therein for separating the tube along the length thereof into first and second separated conduits;

said pair of light guides is contained within the first conduit along the length thereof; and

the second conduit is disposed to conduct liquid therethrough, out of contact with the light guides in said first conduit.

13. Apparatus as in claim 11 comprising at least one continuous filament disposed in one of the first and second conduits along the length of the tube and having a higher modulus of elasticity than the modulii of elasticity of the combined pair of light guides and tube.

14. Apparatus as in claim 11 wherein said outlet port and said inlet port are each formed at the end of a light guide which includes at least one optical fiber and which has a diameter not greater than 15 mils.

15. Apparatus as in claim 11 wherein the total combined areas of the light guide outlet port and inlet port are not greater than 360 square mils.

16. Apparatus as in claim 11 wherein the flexible optical light guides are formed of radiation-transmissive plastic and the first one of said conduits contain liquid in contact with said light guides.

17. Apparatus as in claim 11 wherein said light guides are clad throughout their length with an opaque optical barrier.

18. Apparatus as in claim 16 wherein said optical barrier is impervious to fluid.

19. Apparatus as in claim 18 wherein said optical barrier is metal.

20. Apparatus as in claim 11 comprising:

an inflatable member surrounding the wall of the tube at its distal tip;

a fluid aperture through the wall of said tube near the distal end thereof communicating with the conduit containing the light guides and with the interior of the inflatable member; and

connection means to the conduit containing the light guides near the proximal end thereof for introducing fluid under pressure to inflate the inflatable member.

21. Method of determining oxygen saturation comprising the steps of:

producing electromagnetic radiation in a plurality of different wave bands;

coupling the radiation in the plurality of different wave bands alternately to blood under test;

detecting radiation in each of the plurality of wave bands received back from the blood under test for producing a corresponding plurality of electrical signals representatIve of the intensities of radiation received from the blood under test at the respective wave bands;

altering by a first set of coefficients the plurality of electrical signals and a first reference signal for producing therefrom a first electrical output as a selected combination of said altered first and second electrical signals and first reference signal;

altering by a second set of coefficients the plurality of electrical signals and a second reference signal for producing therefrom a second electrical output as a selected combination of said altered first and second electrical signals and second reference signal; and

producing a first output indication of oxygen saturation of the blood under test as the ratio of said first and second electrical outputs.

22. The method as in claim 21 wherein in the step of producing electromagnetic radiation, each of the plurality of wave bands contain only non-isosbestic wavelengths.

23. The method according to claim 21 wherein in the step of coupling the radiation, the electromagnetic radiation in the plurality of wave bands are alternately transmitted to the blood under test along a first common optical transmission path;

and in the step of detecting radiation, the radiation in the plurality of wave bands is received from the blood under test and is transmitted along a second common optical transmission path from an inlet port disposed within the blood under test adjacent an outlet port of the first common optical transmission path.

24. Method as in claim 21 comprising the additional steps of:

producing electromagnetic radiation in a plurality of auxiliary different wave bands;

coupling the radiation in the auxiliary wave bands alternately to the blood under test along an additional auxiliary coupling path;

detecting radiation in said auxiliary wave bands received back from the blood under test for producing third and fourth electrical signals representative of the intensities of radiation received back from the blood under test at the respective ones of said auxiliary wave bands;

altering by a third set of coefficients the third and fourth electrical signals and a first additional reference signal for producing therefrom a third electrical output as a selected combination of said altered third and fourth electrical signals and first additional reference signal;

altering by a fourth set of coefficients the third and fourth electrical signals and a second additional reference signal for producing therefrom a fourth electrical output as a selected combination of said altered third and fourth electrical signals and second additional reference signal;

producing a second output indication of oxygen saturation of the blood under test as the ratio of the third and fourth electrical outputs; and

providing an output indication of oxygen difference as the algebraic combination of said first and second outputs.