Lingual oximeter probe

Abstract

A non-invasive, electro-optical sensor probe and a method for its use are disclosed. The sensor probe measures light extinction during transillumination of a portion of blood-perfused tissue. A malleable layer makes the sensor particularly well-suited for attachment to a central site, such as the patient's tongue, cheek, gum or lip, to provide accurate oxygen saturation and pulse rate readings for patients with lowered or inconsistent peripheral circulation.

Description

BACKGROUND OF THE INVENTION

This invention relates to an electrooptical oximeter sensor probe. More particularly, this invention relates to a sensor probe with rigid but malleable attachment means for attachment to a central site such as the tongue, gum, cheek or lip, to provide accurate readings for patients with poor peripheral circulation.

Oximeters which measure blood oxygenation levels and pulse by transilluminating blood-perfused tissue and measuring the light extinction at different wavelengths are known. One type of sensor or probe which can be used with such an oximeter is described in commonly-assigned U.S. Pat. No. 4,685,464 issued Aug. 11, 1987. Another suitable sensor conforms to and with the cutaneous layer of the blood perfused portion of flesh upon which the sensor is placed, preferably a fingertip. A light source is mounted to the first end portion of a single substrate and a photosensor is mounted to the second end portion. The single flexible substrate may be elongated, and it may be provided with adhesive. The sensor is suitably windowed so that light is allowed to take an optical path through the finger.

Although these sensors perform well under most conditions, it has been found that because they are usually attached to peripheral areas of a patient, they may yield inaccurate or no readings for patients with poor circulation. This is particularly so in cases of shock or hypothermia (whether intentionally induced or otherwise), or other conditions of lowered or inconsistent circulation. Thus, it would be desirable to provide a sensor which would yield more precise pulse and oxygen saturation readings for those patients whose lowered or inconsistent circulation produces inaccurate readings in sensors located at peripheral sites.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a method and an apparatus for accurately measuring oxygen saturation and pulse rate for patients with poor peripheral circulation.

It is a further object of this invention to provide a sensor which is more reliable under conditions of low blood perfusion, for example with patients suffering from hypothermia, trauma, shock, decreased cardiac output, or increased systemic vascular resistance, or with patients experiencing hypothermic cardiopulmonary bypass with circulatory arrest for cardiac surgery.

In accordance with this invention a method and apparatus are disclosed for accurately measuring light extinction during transillumination of a portion of blood-perfused tissue. The method includes the steps of attaching a rigid but malleable sensor probe to the tissue to be transilluminated, placing a light source and photo sensor embedded in the probe in a position such that they directly oppose each other across the tissue, emitting light from the light source and detecting it at the photosensor, and calculating the oxygen saturation and pulse rate from changes in absorption of the light detected. It has been determined that placement of the apparatus at a central site such as the tongue, cheek, gum or lip of the patient provides more reliable and continuous assessment of arterial hemoglobin oxygen saturation and pulse rate, particularly in patients with poor peripheral circulation or minimal cardiopulmonary reserve.

The apparatus of the invention includes strip member for attachment to and close conformance with the tissue to be transilluminated. A light source and a photosensor, to detect light emitted by the light source, are mounted on the strip member. Rigid but malleable attachment means are provided so that the apparatus may be attached to the tissue by bending it around the tissue without restricting blood flow. The light source and photosensor are placed in opposed positions with respect to each other on opposite sides of the tissue so that light from the light source may pass through the tissue and be detected by the photosensor.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects and advantages of this invention will be apparent after consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

FIG. 1 is a perspective view of the sensor of this invention looking towards the photosensor, light emitting diodes and adhesive surface;

FIG. 2 is a view of the sensor of FIG. 1 illustrating various layers peeled back to expose the inner construction;

FIG. 3 is a perspective view of the photosensor and light source of the sensor of FIG. 1;

FIG. 4 is an enlarged detailed view of a portion of the light source of FIG. 3 showing a substrate having light emitting diodes thereon;

FIG. 5 is an enlarged view of the photosensor of FIG. 3 showing a substrate supporting the photosensitive surface; and

FIG. 6 is an exploded side view of the sensor taken from line 6--6 of FIG. 2 wherein each of the composite elements of the preferred embodiment of the substrate are individually shown and identified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The ability to monitor continuous arterial hemoglobin oxygen saturation and pulse rate noninvasively using a sensor placed on a hand, finger or toe has been shown to result in prompt recognition and treatment of desaturation in a variety of clinical settings. However, peripheral sensors may not function reliably under a variety of conditions, including hypothermia, shock, increased systemic vascular resistance, and decreased cardiac output. Therefore, an alternative sensor location providing more reliable and continuous assessment of arterial hemoglobin oxygen saturation during such conditions is desirable. The arterial pulsations in the tongue, cheek, gum or lip are less influenced by intraoperative conditions, or by other factors which can induce poor peripheral circulation. In addition, the relatively protected intraoral site is less influenced by motion of the surgical team than a peripheral site. Monitoring arterial oxygen saturation and pulse rate via a non-invasive lingual sensor shows promise for application in cardiac surgery and in other settings where conventional sites prove unreliable.

However, presently available sensors cannot readily be used at sites such as the tongue, which is much less structured than, e.g., a finger or other typical peripheral sites. The present invention allows a sensor to be used at sites such as the tongue. A number of design variations can be used to provide other means of attachment (e.g., spring clamps) and to further stabilize sensor position (e.g., material choices or designs to increase friction between the sensor and tongue). A further design variation of this sensor would allow monitoring of oxygen saturation in patients by transillumination of the cheek, gum, or lip.

Advantages of this sensor design include: more reliable performance under conditions of low perfusion (e.g., hypothermia, cardiopulmonary bypass, shock), extended monitoring duration, less susceptibility to electromagnetic interference from electrocautery devices, and reduced susceptibility to ambient light and surgical field motion.

The sensor probe 10 of the present invention is depicted in FIG. 1 in a partially shaped position. A rigid but malleable layer 30 allows the sensor to be shaped for close conformance with the tongue or other relatively unstructured site without constricting blood vessels. In FIG. 2, the sensor 10 is shown flattened and partially peeled back to expose the various layers comprising the sensor.

In FIG. 3, the photosensor 21 and light source 11 are illustrated. FIGS. 4 and 5 are, respectively, detailed illustrations of photo sensor 21 and the light source 11 of the present invention.

Referring to FIG. 4, the photosensitive portion of sensor 10 can be seen. This photosensitive portion includes a substrate 14, electrical connections 15 and a photosensitive surface 13 adhesively fastened to substrate 14. Dimensions are provided which give the apparatus a low profile and a low aspect ratio.

In FIG. 5, light emitting diodes (LEDs) 22 and 23 are adhesively fastened to a substrate 24 as by gluing with electrically conductive epoxy adhesive. Very small dimensional LEDs with micro-circuitry can be utilized. By way of example, substrate 24 is typically 4 mm.times.6 mm, although other dimensions may be used. Electrical connections 25 are used and include paired light emitting diode driving conductors with a common ground.

It should be apparent that the electrical connections herein disclosed can be made in other configurations. For instance, an integrated chip or thin film construction may be desirable for mass production of the element herein disclosed.

In the preferred embodiment, the elements are covered on their photoactive side with a transparent epoxy layer. A clear layer of epoxy 26 is placed over the LEDs 22, 23 of FIG. 5 for insulation and light transmission and a second clear layer of epoxy 16 is placed over the substrate 14 of FIG. 4. Alternatively, this layer can be red to shield the photosensor 21 from ambient spectra outside of the desired red and infrared wavelengths.

The sequential construction of the preferred embodiment of this invention can best be illustrated with respect to FIG. 6. Referring to FIG. 6, it can be seen that the photoactive elements of the sensor substrate 11, 21 are fastened with their inactive sides down to a rigid but malleable strip 30, e.g., a strip of aluminum, preferably soft aluminum, having a thickness of preferably under 2 mm, and having an adhesive surface 32. Strip 30 is attached to a strip of tape 34 having an adhesive surface 35.

Once the photoactive elements 11, 21 are attached, a second opaque vinyl tape 37 is placed over the photoactive elements. This tape has a downwardly exposed adhesive layer 38, holding the light source substrate 24 and the photosensor substrate 14 between strip 30 and opaque strip 37.

Tape 37 is apertured (40, 41) to allow light to pass. A layer of clear polyester 45, having an adhesive coating 46, is placed over the length of the strip 37. Clear polyester layer 45 may also have an adhesive layer 47 on its opposite side, in which case a protective layer of release tape (not shown) could be provided to protect the entire article during manufacture and before use.

Strip 30 may be shaped by the user so that attachment can be made to either the front or side of the tongue, providing close conformance without restricting blood flow. It should be noted that while this preferred configuration is designed for use with the tongue, strip 30 can be shaped to be suitable for use with cheek, gum, or lip. Similarly, the configuration of the sensor might be varied at the time of manufacture to make it more adaptable to an alternate site.

Thus, a method and apparatus are provided for measuring light extinction in patients with poor peripheral circulation. One skilled in the art will recognize that the inventive principles disclosed herein can be practiced by other than the embodiments described.

Claims

1. A non-invasive, electro-optical sensor probe for attachment to a patient for use in measuring light extinction during transillumination of a portion of blood-perfused tissue of the patient's body part, comprising:

a light source for directing light through the tissue portion to be transilluminated;

a photosensor for receiving light directed through the tissue portion transilluminated by the light source; and

malleable, flexible, non-resilient, shape retentive

attachment means for securing the light source and the photosensor to a cutaneous layer of the tissue portion such that the probe is held in conformance with said tissue portion, wherein said attachment means can be shaped to the body part being transilluminated.

2. The sensor probe of claim 1 wherein:

said light source, said photosensor and said attachment means are of small dimensions in relation to said tissue portion so as to allow the probe to be held in conformance with said tissue portion; and

wherein said attachment means is adaptable to place the light source and the light source in opposed positions with respect to each other on opposite sides of the portion of tissue to be transilluminated to provide a light path therethrough when the probe is in place on the patient.

3. The sensor probe of claim 1 further comprising adhesive means for affixing the attachment means to said cutaneous layer.

4. The sensor probe of claim 1 wherein the attachment means comprises a metal strip.

5. The sensor probe of claim 4 wherein the metal strip is aluminum.

6. The sensor probe of claim 1 adapted for placement on one of a patient's tongue, cheek, gum or lip, wherein said attachment means further comprises:

first and second end portions for molding around the tongue, cheek, gum or lip; and

a medial portion connecting the first and second end portions; and wherein:

said light source and said photosensor are mounted on said first and second end portions, respectively.

7. A non-invasive, electro-optical sensor probe for removable attachment to a convex portion of the skin of a patient for use in measuring light extinction during transillumination of the blood-perfused tissue beneath said skin, comprising:

a flexible substantially planar support structure having substantially parallel, spaced, oppositely facing upper and lower surfaces;

a light source mounted in said support structure, said light source having a light-emitting surface for directing light outward from the plane of said lower surface;

a photosensor mounted in said support structure, said photosensor having a light-responsive surface for receiving light directed onto the plane of said lower surface, said photosensor being spaced from said light source in the plane of said support structure; and

a malleable, flexible, non-resilient, shape retentive layer means within said support structure for removably securing said lower surface to said convex skin portion in conformance with said skin portion, said layer means being moldable also to conform said planar support structure to said skin portion without stressing either of said skin portion or the underlying tissue, the convexity of said skin portion causing said light-emitting and light-responsive surfaces to be inclined toward one another so that light from said light source transilluminates the tissue between said light source and said photosensor and said light-responsive surface receives at least a part of said light.

8. The apparatus of claim 7 wherein:

said lower surface is relatively opaque except at the locations of said light source and said photosensor, where said lower surface is relatively transparent;

said layer means forms the upper surface of said support structure; and

means are included for securing said upper and lower surfaces together with said light source and said photosensor captured therebetween.