Blood Oxygenation And Pulse Rate Monitoring Apparatus

Abstract

An ear oximeter functioning as a transducer for monitoring blood oxygen saturation and pulse rate comprising an ear clamp having a pair of opposed jaws between which body tissue may be clamped for transillumination by light emitted from one jaw into the clamped tissue. Thermostatically controlled heating means arterializes the transilluminated tissue and light emitter from the tissue is monitored by a photoelectric light-intensity meter for indication of percent oxygen in blood within the arterialized tissue.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Tissue oximeters with particular reference to improvements in means for arterializing relevant portions of body tissue under observation.

2. Description Of The Prior Art

The determination of oxygen saturation of the circulating blood without extracting a sample of the blood can be accomplished by transilluminating the pinna of the ear, or another suitable portion of the body, and measuring the light transmitted at a wavelength of about 650 .mu. against a reference wavelength of about 805 m.mu.. The ear oximeter, in general, is a well-known instrument and is described in U.S. Pat. No. 2,706,927.

In this manner of measuring oxygen saturation, it is common to heat the skin in the area under observation so as to dilate arterioles with the intent of increasing the blood flow to the point where very little deoxygenation occurs in the capillaries so that the measurement becomes essentially that of arterial oxygen saturation which in most instances is of greater clinical value than a measurement of oxygen saturation in venus blood.

Heretofore, a small incandescent lamp has been used both for illumination and for heating of the skin. However, when the blood circulation is abundant, heat from a lamp is quickly dissipated and the skin may not become sufficiently heated for arterialization. On the other hand, when circulation is poor and little or no dissipation of heat occurs, serious discomfort or harm to the patient may result from excessive heating by the lamp.

It has also been determined that in cases where the optical path length of light in an ear oximeter is varied according to the thickness of ear tissue being transilluminated, difficulty in obtaining absolute measurements of blood oxygen saturation is encountered.

The aforesaid drawbacks in prior art ear oximetry and others which may become apparent hereinafter are overcome by the present invention which is directed more particularly to a system wherein a fixed optical path length of light is used to transilluminate portions of bodies under test and heating is kept within a narrow range of a temperature which is comfortable and harmless to the patient, yet optimum in effecting arterialization.

SUMMARY OF THE INVENTION

The optimum in arterialization without discomfort or harm to the patient and the corollary of greater accuracy and dependability of oxygen saturation measurements performed according to principles of this invention are accomplished by directing cold light to the portion of tissue under observation and heating that portion with a heating pad kept within a narrow range of temperature (e.g. 41.degree. C.) which is optimum for arterialization of the skin.

The term "cold light" as used herein is intended to include any light which is rendered substantially unaccompanied by appreciable amounts of heat such as light emitted from fiber optic conductors, or light-emitting diodes which, when directed upon tissue under observation will produce minimal heating of the tissue.

The present invention features a system having a fixed path length of light into which portions of the body (e.g. the ear) may be positioned for transillumination whereby measurements of blood oxygen saturation obtained by such means are substantially independent of thickness of the body under test. Furthermore, greater precision in the measurement of blood oxygen saturation is accomplished by directing light into the transilluminated portion of the body specimen from points equally radially spaced a few millimeters from the axis along which light from the specimen is received for analysis. Also, an arrangement for receiving light from the transilluminated specimen at points equally radially spaced from the axis of a bundle of light rays directed into the specimen will produce similar results.

Details of this invention will become more fully understood by reference to the following description and the accompanying drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic illustration of a system and apparatus for performing oximetry and pulse rate monitoring according to principles of this invention; and

FIG. 2 is an enlarged cross-sectional view of the apparatus shown in FIG. 1 wherein portions thereof pertinent to the present inventive concept are shown in greater detail and modifications thereof are shown with dot-dash outline; and

FIG. 3 is a view taken along line 3--3 of FIG. 2 looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 of the drawing there is illustrated an oxygen saturation and pulse rate monitoring system 10 incorporating an ear oximeter 12 functioning as a transducer in the system. Amounts of oxygen in blood flowing through an ear 14 and/or changing amounts of blood present in the ear are converted by oximeter 12 into corresponding variations in intensity of particular wavelengths of light caused to pass through the pinna of the ear.

System 10 further includes a remote light source 16, at least one elongated fiber optical light pipe 18 for receiving and conducting light from source 16 to ear 14 and a number of bandpass filters 20 adapted to be selectively interposed between light source 16 and end 22 of light pipe 18 for filtering all but selected wavelengths of light caused to enter light pipe 18. Filters 20 are conventionally so preselected as to have one transmissive to substantially only light of a wavelength of 650 m.mu., another transmissive to substantially only light of a wavelength of 805 .mu. and a third transmissive to substantially only light of a wavelength of 910 m.mu.; the latter wavelength being used for dye dilution testing wherein 910 m.mu. light is readily absorbed by dyes commonly used in dye dilution testing.

With light of a preselected wavelength (e.g. 650 m.mu. ) directed into ear 14, a measurement of the amount of such light transmitted through the ear, which is a function of oxygen saturation, is made by directing the light into a measuring and indication photoelectric system represented by block 24 in FIG. 1.

Fiber optic light pipe 26, FIGS. 1 and 2, receives light transmitted through ear 14 and conducts the same to the measuring and indicating means 24. The measuring and indicating means 24 is calibrated to measure oxygen saturation independently to tissue pigmentation by rendering the portion of ear 14 under observation temporarily bloodless. An inflatable diaphragm 18, FIGS. 1 and 2, is provided for this purpose. Compressed air directed through conduit 30 inflates diaphragm 28 whereby the adjacent portion of ear 14 is squeezed against a fixed platen 32 stopping the circulation of blood in the area between diaphragm 28 and platen 32. Those interested in further details of blood monitoring systems such as that thus far described may refer to U.S. Pat. Nos. 3,068,739; 2,706,927 and 3,412,729.

In connection with the matter of supplying cold light to body tissue (e.g. ear 14) under observation, it should be understood that the arrangement of lamp 16, filters 20 and light pipe 18 may be replaced by light-emitting diodes having peak emission wavelengths corresponding to the wavelengths of light transmitted by band-pass filters 20. Such diodes, also referred to as "visible diodes" are well known to the artisan and readily commercially available. In this instance, light-emitting diodes 19a, shown in dot-dash outline (FIG. 2) would be located behind diaphragm 28 at a position corresponding to or near the location of the emitting end 19 of the full line of illustration of light pipe 18. In this latter case, light pipe 18 would be omitted. Diaphragm 28 is transparent to light emitted from light pipe 18 and, accordingly, would be similarly transmissive to light emitted by diodes 19a. It is also pointed out that photoelectric detectors having the same general appearance as diodes 19a may be positioned adjacent to platen 32 (e.g. in the vicinity of the light-receiving end 27 of light pipe 26) in which case light pipe 26 would be replaced by electrical connections extending from such photoelectric detectors to the measuring and indicating means 24.

Preferably, either the light-emitting end 19 or the light-receiving end 27 of light pipes 18 and 26 respectively are formed with corresponding ends of fibers of the particular bundle thereof arranged annularly about the axis A-A(FIG. 1) of the light path through ear 14 as illustrated in FIG. 3. This arrangement of fibers has been found to produce greater precision in the measurement of blood oxygen saturation. Alternatively, either one or the other of the light-emitting and light-receiving ends 19 and 27 respectively may have corresponding ends of their fibers similarly spaced from each other in two or more groups respectively disposed at approximately equal distances from each other (e.g. 4 millimeters) from the axis A-A of the light path through ear 14.

With the light transmitted through ear 14 being of a temperature substantially below that of incandescence, ear 14 is heated to arterialize the portion thereof under observation by heating coil 34 (FIG. 2) which heats platen 32, keeping ear 14 to within a narrow range of optimum temperature for arterialization of about 41.degree. C.

Heating coil 34 is operated by proportional temperature controller 36 (FIG. 1) which includes thermistor 38 located in platen 32 adjacent the surface thereof contacted by the portion of ear 14 under observation. Electrical leads 40 connect heating coil 34 and thermistor 38 to controller 36 which, in turn, is connected to a suitable source of current SC.

Platen 32 and diaphragm 28 are supported by jaws 42 and 44 respectively of oximeter 12. Jaw 42 is slidable toward and away from jaw 44 along a supporting hollow post 46 to which jaw 44 is fixed by clamp nut 48. Jaw 42, accordingly, may be moved away from jaw 44 sufficiently to permit insertion of ear 44 between platen 32 and diaphragm 28. Release of jaw 42 will automatically nonsubjectively clamp ear 14 in oximeter 12 with an optimum holding force normally permitting free circulation of blood through the ear. Spring 50 provides the nonsubjective holding force. Clam nut 52, when tightened, prevents accidental displacement of oximeter 12 during use and prevents displacement of jaw 42 when diaphragm 28 is inflated to render the portion of ear 14 under observation bloodless.

Jaw 42, in its movement toward and away from jaw 44, is guided by pin 54 fixed in support 56 which, in turn, is fixed to post 46. Pin 54 thus maintains platen 32 and diaphragm 28 in aligned relationship with each other at all times. Light pipe 26 having its end 27 fixed in support 56 at a given distance from the light-emitting end or ends 19 of one or more light-emitting light pipes 18, established the above-mentioned fixed optical path length of light into which portions of body tissue of varying thickness may be placed by adjustment of jaw 42 relative to jaw 44 independently of support 56.

In its application as a pulse monitor, system 10 measures variations in amounts of transmitted light resulting from changing amounts of blood perfusing ear 14 due to pulsatile characteristics of the blood flow. The controlled heating of ear 14 to the optimum temperature of about 41.degree. C. increases the normal pulsatile flow by a factor of approximately three with a corresponding increase in intensity of light transmitted through the ear.

With the ear being held continuously within a narrow range of optimum temperature the monitoring of pulsatile characteristics in the ear with the aforesaid increase in light intensities provides an accurate indication of actual pulse rate, even in cases of poor peripheral circulation.

Claims

We claim:

1. An oximeter device comprising:

a main supporting member;

a pair of parallel clamping jaws extending laterally from said member, said jaws being movable at least one toward the other along said member for clamping a section of body tissue between their corresponding terminal ends;

light-emitting means in a first of said jaws of said pair adjacent its terminal end and a light-receiving platen adjacent the terminal of the second of said jaws between which said section of body tissue is adapted to be received for said clamping thereof and is adapted to be transilluminated by light emitted from said emitting means;

an electrical heating element adjacent said platen for heating same;

a thermistor in said platen;

temperature control means in electrical circuit with said heating element and thermistor, said control means being responsive to variations in electrical resistance of said thermistor for maintaining the temperature of said platen and said section of tissue substantially constant during said transillumination of the tissue;

means adjacent said terminal end of said jaw for receiving light transmitted through said tissue and;

light intensity measuring means operatively associated with said light-receiving means for measuring the intensity of light received thereby.

2. An oximeter device according to claim 1 wherein said light-emitting means comprises one end of an elongated bundle of light-conducting fibers having a source of light adjacent its opposite end.

3. An oximeter device according to claim 1 wherein said light-emitting means comprises at least one light-emitting diode.

4. An oximeter device according to claim 1 wherein said thermistor in said platen is positioned adjacent the surface thereof against which said tissue is adapted to be clamped.

5. An oximeter device according to claim 1 wherein said movable jaw is biased toward the other jaw of said pair thereof by spring means whereby said tissue may be clamped nonsubjectively.

6. An oximeter device according to claim 5 including means for releasably fixing said jaws against separation from a clamped relationship with said section of body tissue.

7. An oximeter device according to claim 6 further including an inflatable transparent membrane extending over said light-emitting means and means through which an inflating medium may be directed into said membrane to distend same.

8. An oximeter device according to claim 1 wherein said light-receiving means comprises one end of an elongated bundle of light-conducting fibers and said light-intensity measuring means includes a photoelectric transducer system.

9. An oximeter device according to claim 1 wherein said light-receiving means comprises at least one photoelectric detector for converting light received thereby into electrical energy and said light-intensity measuring means includes electrical energy measuring and intensity indicating means electrically connected to said detector.

10. An oximeter device according to claim 2 wherein portions of said light-conducting fibers adjacent said one end of said bundle are spaced a preselected radial distance away from the principal axis of the bundle.

11. An oximeter device according to claim 10 wherein said portions of said light-conducting fibers are disposed annularly about said principal axis of said bundle.

12. An oximeter device according to claim 8 wherein portions of said light-conducting fibers adjacent said one end of said bundle are spaced a preselected radial distance away from the principal axis of the bundle.

13. An oximeter device according to claim 13 wherein said portions of said light-conducting fibers are disposed annularly about said principal axis of said bundle.