WO1989009566A1

WO1989009566A1 - Radiation sensor for monitoring a body condition

Info

Publication number: WO1989009566A1
Application number: PCT/US1989/001484
Authority: WO
Inventors: Thomas Mans
Original assignee: Datascope Corp.
Priority date: 1988-04-05
Filing date: 1989-04-05
Publication date: 1989-10-19

Abstract

An electromagnetic sensor including an emitter (12, 18), a detector (14, 36) and a reflector (26). The emitter is on the upper portion of a housing (10) and the detector is in the lower portion of the housing. The emitter faces the opposite direction from the detector. The sensor is adapted to be placed against the skin (28) of a patient, with the detector portion of the housing in contact with the skin. Also provided is an overlay (24) holding the reflector. The reflector redirects the electromagnetic radiation emitted by the emitter toward the skin. The overlay is of sufficient size to cover the area above and around the emitter and detector, while holding the reflector spaced from the opposite to the emitter. Also disclosed is a method comprising the steps of emitting electromagnetic radiation in a direction away from the skin, reflecting that radiation toward the skin, permitting some of that reflected radiation to pass through body tissue where some is absorbed, and detecting the radiation emanating from that tissue.

Description

- / - Title of the Invention:

"Radiation Sensor for lfonitoring a Body Condition"

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor and method suitable for use in monitoring a body condition, for example the oxygen saturation of the hemoglobin of arterial blood.

2. Description of Pertinent Information

It is important, in a variety of medical contexts, to closely monitor various body functions and/or conditions. In particular, it is especially useful during surgery for the medical personnel to be able to obtain an accurate reading of the oxygen saturation of the. arterial blood of a patient. Since the primary utility presently contemplated for the sensor and method of the instant invention is in arterial blood- oxygen content monitoring, the description hereinafter will be directed primarily " toward that utility. It should be understood, however, that this invention is not so limited in its application. Those of ordinary skill in the art will readily understand how to apply the principles herein disclosed to the monitoring of any body condition that is capable of being assessed through the use of reflected, transmitted or absorbed electromagnetic radiation.

One of the most common methods for determining blood-oxygen content requires the removal and analysis of a sample of the patient's blood. However, such invasive techniques are relatively time consuming, and have significant dr-awbacks during surgery, where continuous oxygen content monitoring is highly advantageous.

Non-invasive techniques have also been developed for monitoring the oxygenation of the patient's arterial blood. One common type of device for doing so is a pulse oximeter having a sensor and a processor for processing the signals from the sensor. The sensor usually includes two sources of radiation, one red and the other infrared, and a detector. The radiation passes through a part of a patient's body, such as a finger, before reaching the detector, and the detector, normally a photodetector, measures the radiation emerging from underlying tissues and blood vessels in the body part.

The radiation source and detector are typically housed separately from each other so that the source can be placed, on one side of the body part and the detector can be placed on the opposite side. Alternatively, the radiation source and detector may be housed in one flexible assembly that permits the source and detector to be positioned on different portions of the body part, although not necessarily directly opposite one another.

Another arrangement positions the radiation source and detector side-by-side, so that the source and detector are placed on adjacent portions of the skin surface, on the same side thereof. Such a side-by-side arrangement is shown, for example, in U.S. Patents Nos. 4,485,820; 4,537,197; 3,983,866; 4,380,240; 4,596,254; 4,621,643; and 4,714,080.

Sensors which are positioned on opposite sides of an^" appendage gnnerally work well on fingers and toes. However, the performance of this type of sensor may be less satisfactory in the presence of strong ambient light, which is not uncommon in an operating room. Further, such sensors will not function on other portions of the body which are not as thin as fingers and toes, through which light is not easily transmitted. In addition, if the emitter and detector are not aligned sufficiently precisely, performance suffers. On the other hand, sensors using a side-by-side arrangement often produce weak signals due to the small amount of tissue illuminated. These sensors also tend to be large and bulky and are usable on only a limited number of sites on the patient.

Thus, there is a need for a sensor, particularly an oximeter sensor, which can be used freely at many different positions on the body, which produces a strong signal, which does not require the user to align the emitter and the detector, and which can be used in the presence of strong ambient light.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an sensor which can be used on any site on the body.

It is another object of the present invention to provide a sensor which produces a strong signal with a high signal-to-noise ratio.

It is another object of the present invention to provide such a sensor in which it is not necessary for the user to align the emitter and detector. It is still another object of the present invention to provide such a sensor whose performance is not degraded in the presence of strong ambient light.

These and other objects of the present invention are achieved by providing a sensor adapted to be placed in contact with the skin of a patient. The sensor comprises an emitter, a reflector and a detector. The emitter may itself generate electromagnetic radiation or alternatively, it may merely emit radiation generated elsewhere. The radiation from the emitter is directed away from the patient and the reflector redirects it toward the skin of the patient. The reflected electromagnetic radiation diffuses through the patient's skin surrounding the detector and then emerges from the skin beneath the sensor. The detector senses the electromagnetic radiation which has emerged from the skin, i.e. _r that which has not been absorbed.

The sensor preferably also includes a support or housing having top and bottom opposed sections. The emitter is in the top section of the support or is within the upper portion of the housing and the detector is in the bottom section or is within the lower portion of the housing. The emitter faces away from the skin and the detector faces toward the skin. Thus, the emitter and detector face away from one another.

These and other objects, features, and advantages of the present invention will become more apparent upon a consideration of the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic side view, partly in section, of the preferred embodiment of the sensor of the present invention in contact with the skin of the patient;

Figure 2 is a schematic bottom view of the sensor of Figure 1, showing the sensor electrically connected to a processor;

Figure 3 is a schematic side view of the sensor of Figure 1;

Figure 4 is a schematic top view of the sensor of Figure 1; and

Figure 5 is a schematic transverse view of the housing containing the emitter and detector of the sensor of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 is a partial cross-sectional view of the preferred embodiment of the sensor of the present invention. The sensor comprises a housing 10 supporting an emitter 12 and a detector 14. Emitter 12 is positioned in the top portion of housing 10 and detector 14 in the bottom, the two being in a "back-to-back" arrangement. Emitter 12 comprises, as illustrated in Fig. 4, a plurality of light emitting diodes (LED's) 16 which emit electromagnetic radiation of two wavelengths. One of the wavelengths is preferably in the red region of the electromagnetic spectrum, and the other in the infrared region. The LED's 16 preferably generate radiation having wavelengths of 660nm and 930nm, although it should be understood that it is within the scope of the invention to use other wavelengths. For example, other wavelengths or combinations of wavelengths may enable monitoring of blood components other than oxygen. It should be understood that other applications may need only one kind of emitter, i.e. radiation of only one wavelength, still others may employ more than two and some may not need light of well defined discreet wavelengths at all, but may use "white" light made up of a mix of wavelengths from one end of the spectrum to the other.

The radiation of both wavelengths in the preferred embodiment is directed from emitter 12, via reflector 26, to the skin 28 of the patient. This radiation is transmitted through the surface of the skin 28 to the blood vessels in the underlying tissue. The blood in the arteries beneath the illuminated portion of the skin as well as in the skin and tissue, absorbs part of the radiation in each region of the spectrum. Some of the radiation is also absorbed by the skin and tissue. Some of the radiation, however, is not absorbed and emerges from skin 28 under detector 14 where it is detected by the detector.

Emitter 12 also has a light-scattering translucent cover 18 in which the LED's 16 are encapsulated. Cover 18 scatters the light substantially uniformly over the reflector. Cover 18 can be composed of a translucent silicon or other material.

Detector 14, as shown in Figure 2, is comprised of a photodetector for producing electric signals in response to the electromagnetic radiation incident thereon. In the preferred embodiment, detector 14 is sensitive to the two wavelengths of radiation generated by emitter 12 and can m i for exam le a sin le silicon cr st l photodetector. Also provided is a wire mesh noise shield 36 for filtering out electromagnetic noise (this term is used herein to include both electrical and electronic noise) such as that generated by electrosurgical units. A wire (not shown) is provided for grounding shield 36. The strands of the shield are coated with an insulator, for example a polyester.

When used as an oximeter probe, the two wavelengths are chosen because, as is well known, one wavelength is absorbed approximately equally by hemoglobin and oxyhemoglobin in the blood, and the other is absorbed differently by hemoglobin and oxyhemoglobin. This difference in absorption permits a processor 22, according to known techniques and formulae, to compute the oxygen saturation of arterial blood in response to electrical signals generated by detector 14.

As can best be seen in figure 5, emitter 12 and detector 14 are located in housing 10. The housing has an upper portion with a cover 18 defining the face thereof and a lower portion with shield 36 defining a portion of its face. It has been found that a domed detector, as is shown in Figure 5, is more efficient than a flat detector. The shield 36 is therefore also domed to conform to the shape of the detector. Around shield 36 and defining the remainder of the bottom face of housing 10 is periphery 40. Periphery 40 is opaque and its lower face is flush with the domed shape of shield 36. Separating the upper and lower portions of the housing is partition 20. Emitter 12, which is located above partition 20, and detector 14, which is below partition 20, face in opposite directions. Thus, when housing 10 is placed on the patient with the face of the lower portion against the patient's skin, as shown in Figure 1, the radiation from emitter 12 is directed away from the patient's skin.

In order to redirect the radiation toward the patient's skin a reflector 26 is provided on the inner surface of an overlay 24. Overlay 24, which may take the form of a tape or membrane or the like, preferably is of sufficient size to cover the entire area surrounding the emitter, detector and the adjacent skin of the patient. Overlay 24 should, preferably, also be of sufficient size, or be attached to another element, for example, a flexible band or adhesive tape, to be attached to the skin 28 of the patient around housing 10, while holding the lower face of housing 10 against skin 28 as seen in Fig. 1. The several elements of the device are preferably arranged to hold reflector 26 so that it is spaced from and opposed to emitter 12, as seen in Figure 1. The overlay should most advantageously be flexible, non-elastic and opaque. It is also within the scope of the present invention to replace overlay 24 or a portion of overlay 24 with an inflexible support for holding reflector 26.

Reflector 26 may be composed of polyester etalized, for example, with aluminum. Reflector 26 redirects the electromagnetic radiation from emitter 12 toward the skin of the patient, and also substantially reduces, and in the preferred embodiment virtually eliminates, the amount of ambient light that is incident on the skin immediately adjacent housing 10. Reflector 26 thus ensures that only light from emitter 12 is directed to the skin of the patient immediately surrounding the detector. It also ensures that the light from emitter 12 is directed to a sufficiently large area of the skin to produce a strong signal from detector 14. This may be accomplished by making the surface area of reflector 26 substantially larger (e.g., five, ten, twenty, or even forty or more times larger) than the area of the emitting face of emitter 12. A large reflector promotes a large signal from detector 14, and at the same time prevents ambient light from reaching the skin around detector 14. Alternatively, it may be the overlay 24 or, if employed, the band to which it is attached, which functions to shield the detector and the area surrounding it from ambient light. In yet another alternative embodiment, a large reflector can be employed and the overlay can be eliminated, in which case a band or other means can be employed to hold the sensor against skin 28 and reflector 26 above and around emitter 12.

It is highly desirable, especially in oxi eter applications, but not absolutely essential, that none of the light impinging upon detector 14 come directly from emitter 12, from reflector 26 or from overlay 24, and that none of it (or essentially none of it) be reflected from the surface of skin 28. This kind of screening can be accomplished by insuring that in use, the periphery 40 of housing 10 which surrounds detector 14 is against skin 28. To further insure against stray light striking detector 14, housing 10 can be made with a raised rim around detector 14. Alternatively, the same might be accomplished by having detector 14 recessed below the surface of periphery 40.

While, as presently contemplated, it is most advantageous to prevent any light reflected directly from the skin surface from striking the detector, that may not be an absolute requirement in all applications. Indeed, it is possible, particularly in non-oximeter applications, that maximum scraening of this type may be unnecessary or perhaps even undesirable. In order to facilitate uniform dispersion and maximum reflection of the electromagnetic radiation generated by emitter 12, a raised open lattice-like structure or a glass ring may be provided around the face of emitter 12 or around cover 18.

Partition 20 is preferably rigid and emitter 12 and detector 14 are rigidly attached to the partition. In such a structure the geometrical relationship between emitter and detector is both fixed and known. However, such a fixed relationship, while believed to be most desirable, is not essential. The shape of the reflector may be so designed that, within certain limits, the orientation of the emitter relative to the detector would have substantially no (or only very minimal) effect on the signal generated by the detector.

Reflector 26 may be preformed or it may be flexible. If flexible, it will conform, at least i part, to the shape of the upper face of emitter 12 or cover 18 or any structure protuding from the top of housing 10. Alternatively, if preformed it may touch the upper face of housing 10 at only a few points or not at all. For example, a preformed reflector could take the shape of a hollow hemisphere similar to a bell jar, with its edge resting on the skin around the sensor.

Housing 10 also has a partition 20, (see Fig. 5) which separates emitter 12 from detector 14 and which is opaque t© the electromagnetic radiation emanating from emitter 12. This partition 20 is preferably composed of or is covered on its upper face with reflective material. For example, it may be the same reflective material as reflector 26 is made of. Partition 20, in cooperation w:.th he remaining structure of housing 10, shields detector 14 from receiving light which has not passed through skin and tissue. Partition 20 also acts as a back reflector sending radiation toward reflector 26.

Emitter 12 and detector 14 are connected by suitable connections, such as wires, to a source of power. The power source causes emitter 12 to generate electromagnetic radiation. The wire connection also transmits electrical signals from detector 14, to processor 22. In addition, means are provided for isolating- and insulating shield 36, emitter 12 and detector 14 from contact with the patient when housing 10 is against the skin.

In one embodiment, the dimensions are approximately as follows: housing 10, including area 40, is 0.313 inch wide 0.5 inch long by 0.156 inch thick; the face of cover 18 over emitter 12 is 0.3 inch by 0.35 inch; screen 36 is 0.2 inch by 0.25; the reflector 26 is 2.25 inches by 1.25 inches.

Such a sensor is easy to manufacture and to clean, and can be made very thin and small so that it can be applied easily to any site on the body. This is important because during surgery it is common for blood flow to the patient's peripheral appendages, such as the fingers and/or toes, to decrease. Such a decrease in blood flow can prevent or substantially interfere with the taking of a reading of the oxygen saturation in the blood. When this occurs, the sensor of the present invention can be moved to the patient's face or ear, both of which areas are more likely to remain well perfused with blood, even during decreased blood flow.

Further, because in the preferred embodiment the emitter and detector are integral with the housing, alignment between the emitter and detector is ensured. In addition, the use of a reflective material on or as part of the housing and in the reflector improves the signal-to-noise ratio of the signal produced by the detector by increasing the area that is illuminated by the emitted light, by increasing the amount of emitter radiation reaching the skin surrounding detector 14 and by reducing the amount of ambient light reaching the detector. As will readily be appreciated by those familiar with the field, the sensor of the present invention can be integrated into a wide variety of different housing structures depending upon the nature of the application to which it is put.

Although the invention has been described with respect to specific examples and embodiments, it should be understood that the invention is not limited thereto, but extends to all equivalents within the scope of the claims.

Claims

WHAT IS CLAIMED IS:

1. A sensor adapted to be placed in proximity to the skin of a patient, said sensor comprising: an emitter for emitting electromagnetic radiation directed away from the skin of the patient; a reflector for redirecting at least some of said radiation toward the skin, so that at least some of the reflected electromagnetic radiation passes through the skin, underlying tissue and blood vessels; and a detector for detecting electromagnetic radiation emerging from the underlying skin of the. patient.

2. The sensor defined by Claim 1, wherein said emitter has an emitting face and said detector has a detecting face, said sensor further comprises a housing having top and bottom opposed sections wherein said emitter is positioned in said top section of said housing and said detector is positioned in said bottom section of said housing such that said detecting face faces generally in the opposite direction from said emitting face.

3. The sensor of Claim 1, wherein said reflector surrounds substantially the entire space around and above the housing down to the skin of the patient.

4. The sensor defined by Claim 2, further comprising an overlay which supports said reflector.

5. The sensor defined by Claim 2, wherein said housing comprises a partition which is opaque to the electromagnetic radiation emitted by said emitter.

6. The sensor defined by Claim 5, wherein said partition is reflective, for redirecting electromagnetic radiation emitted by said emitter. - 14 -

7. The sensor defined by Claim 1, wherein said electromagnetic radiation emitted by said emitter is such that the electromagnetic radiation emerging from the underlying skin can be used to determine the oxygen saturation of the hemoglobin in the blood of the patient.

8. The sensor of Claim 1 wherein said emitter emits radiation of substantially only one wavelength.

9. The sensor of Claim 1 wherein said emitter emits radiation of at least two different wavelengths.

10. The sensor defined by Claim 7, wherein said emitter comprises a plurality of light emitting diodes, and wherein said detector comprises a photodetector.

11. The sensor of Claim 10, further comprising a housing in which said emitter is held and wherein said housing has structure to ensure separation between said diodes and said reflector.

12. The sensor of Claim 10, wherein said diodes emit electromagnetic radiation of at least two different wavelengths.

13. The sensor of Claim 12, wherein one of said wavelengths is in the infrared region and another is in the red region.

14. The sensor defined by Claim 10, further comprising a radiation-scattering cover, covering said emitter, for scattering the radiation emitted by said light emitting diodes.

15. The sensor defined by Claim 1, further comprising a wire mesh noise shield covering said detector for filtering out electromagnetic noise.

16. An oximeter sensor comprising: a housing having top and bottom opposed portions; an electromagnetic radiation emitter having an emitting face in said top portion of said housing; a reflector; and an electromagnetic radiation detector having a detecting face in said bottom portion of said housing, wherein said emitter face and said detecting face, face in generally opposite directions.

17. The sensor defined by Claim 16, wherein said housing has a partition between said emitter and said detector, which partition is opaque to the electromagnetic radiation emitted by said emitter.

18. The sensor defined by Claim 17, wherein said partition is at least partially reflective, for redirecting electromagnetic radiation emitted by said emitter.

19. The sensor defined by Claim 16, wherein said reflector is arranged so as to redirect electromagnetic radiation emitted by said emitter in the direction in which said detector face faces.

20. The sensor defined by Claim 19, wherein at least some of the reflected electromagnetic radiation passes through the surface of the skin of the patient and emerges therefrom, and said detector is adapted to sense the radiation emerging from the underlying skin of the patient, wherein said sensor further comprises an overlay having an inner surface supporting said reflector, and wherein said overlay is of sufficient size to cover a portion of the skin of the patient around the periphery of said housing, while holding said reflector spaced from and opposite to said emitter.

21. The sensor defined by Claim 20, wherein the electromagnetic radiation emitted by said emitter is such that the electromagnetic radiation emerging from the skin can be used to determine the oxygen saturation of the hemoglobin in the blood of the patient.

22. The sensor defined by Claim 20, wherein said emitter comprises a plurality of light emitting diodes, and wherein said detector comprises a photodetector.

23. The sensor of Claim 22, wherein said diodes emit electromagnetic radiation of at least two different wavelengths.

24. The sensor of Claim 23, wherein one of said wavelengths is in the infrared region and another is in the red region.

25. The sensor defined by Claim 22, further comprising a radiation scattering cover, covering said emitter, for scattering radiation emitted by said light emitting diodes.

26. The sensor defined by Claim 16, further comprising a , wire mesh noise shield covering said detector to filter out electromagnetic noise.

27. The sensor of Claim 22, further comprising a housing in which said emitter is held and wherein said housing has structure to ensure separation between said diodes and said reflector.

28. The sensor of Claim 20, wherein said overlay surrounds substantially the entire space around and above the housing down to the skin of the patient.

29. The sensor of Claim 19, wherein said reflector surrounds substantially the entire space around and above the housing down to the skin of the patient.

30. The sensor of Claim 1 or 16, further comprising means for retaining said sensor with said detector facing generally toward the patient's skin and the emitter facing generally away from the patient's skin.

31. The sensor of Claim 2 or 16, wherein said housing maintains a fixed and predetermined geometric relationship and orientation between said emitter and said detector.

32. The sensor of Claim 1 or 16, further comprising means for preventing ambient electromagnetic radiation from reaching said detector.

33. The sensor of Claim 1 or 16, further comprising means for ensuring that the only electromagnetic radiation reaching said detector is radiation which has passed through at least some body tissue.

34. A sensor for passing electromagnetic radiation through the surface of the skin of a patient, underlying which skin is body tissue and blood vessels, comprising: an emitter for emitting electromagnetic radiation directed generally away from said skin; a reflector for reflecting at least some of said emitted radiation toward said skin; and a detector for detecting said radiation not absorbed by said skin, tissue, blood vessels or blood.

35. The sensor of Claim 34, wherein at least some of said radiation from said reflector passes through some body tissue before reaching said detector.

36. The sensor of Claim 34, wherein said detector detects at least some of said radiation which has passed through some body tissue.

37. A method for evaluating a body condition comprising the steps of: emitting electromagnetic radiation in a direction generally away from said body; reflecting at least some of said radiation in order to redirect it toward said body; detecting the radiation not absorbed by said body.

38. The method of Claim 37, wherein at least some of said redirected radiation passes through body tissue before being detected.