WO2002015782A1

WO2002015782A1 - Side applied optical finger hematometer

Info

Publication number: WO2002015782A1
Application number: PCT/US2001/041718
Authority: WO
Inventors: Massi E. Kiani
Original assignee: Masimo Corporation
Priority date: 2000-08-18
Filing date: 2001-08-14
Publication date: 2002-02-28

Abstract

An optical probe is applied to a digit, such as, for example, a thumb, such that the optical probe includes an emitter and a detector on opposing sides of the digit perpendicular to the side having the nail portion in a manner that light travels through the finger in a plane parallel to the nail. Such side application of the optical probe advantageously provides a reduced change in optical path length during motion and an increased volume through which perfusion can be measured, resulting in the detector producing a signal having an increased signal-to-noise ratio.

Description

SIDE APPLIED OPTICAL FINGER HEMATOMETER

Field of the Invention

This invention relates in general to optical probes, and in particular to low-noise, disposable and reusable optical probes applied to the side of a digit. Description of the Related Art

Energy is often transmitted through or reflected from a medium to determine characteristics of the medium. For example, in the medical field, instead of extracting material from a patient's body for testing, light or sound energy may be caused to be incident to the patient's body, and transmitted or reflected energy may be measured to determine information about the material through which the energy is passed. This type of non-invasive measurement is more comfortable for the patient and can be performed more quickly.

Non-invasive measurements of bodily functions are often performed with optical probes. Typically, the optical probe is housed in an adhesive bandage, a reusable clip, a Velcro securing mechanism, or the like. Moreover, typically the optical probes are housed such that an emitter vertically opposes a detector over the nail of a digit, such as, for example, a finger or toe.

Drawbacks arise during the use of conventional optical probes during motion, or patient agitation, such as tapping or other physical depression of the digit being monitored. Such drawbacks relate to the strong reliance of optical probe technology on the optical path length. The optical path length is defined as the distance between the emitter and the detector, such as, for example, the thickness of the material through which the optical energy must pass before reaching the detector. Thus, when a patient moves in a manner that distorts or compresses the tissue of the digit through which measurement is being taken, the optical path length may change dramatically. Moreover, since patients may generally move in an erratic fashion, the compression of digits is often also erratic, resulting in an erratic change in the optical path length. Thus, patient movement often makes the absorption of optical energy erratic, resulting in difficulty with signal interpretation. In addition, the conventional attachment of the emitter and the detector such that the optical path length is defined through the nail of the digit, fails to optimize the volume through which perfusion may take place. For example, the placement of the emitter and the detector defines a volume of tissue through which some optical energy will pass, and it is the perfusion through that volume that is measured by the optical probe. When the volume is defined vertically through the nail portion of the digit, the perfusion is unnecessarily limited. The limited perfusion fails to optimize the eventual signal-to-noise ratio obtained. Similar to the erratic absorption of optical energy, lower signal- to-πoise ratios result in difficulty with signal interpretation.

Therefore, a need exists for an optical probe applied to a digit in a manner which reduces the change in optical path length during movement, increases the measured perfusion, and increases the eventual signal-to-noise ratio. Summary of the Invention Therefore, one aspect of the present invention is to apply an optical probe to a digit along a horizontal plane, or from the side. Such side-application dramatically decreases the chance of direct physical depression, thereby, reducing changes in optical path length. Moreover, side-application increases the volume through which perfusion can be measured, thereby advantageously increasing the signal-to-noise ratio.

Another aspect of the present invention is to apply the optical probe to the thumb of a patient. Use of the thumb provides increased perfusion and potentially less motion. As discussed in the foregoing, the advantages of increased perfusion and less motion include a more stable signal having an increased signal-to-πoise ratio.

Accordingly, one aspect of the invention is a method for producing an optical probe for measuring at least one characteristic of a digit. The method comprises positioning an emitter and a detector within an attachment mechanism such that the emitter and the detector substantially oppose one another along an axis substantially parallel to a nail portion of the digit when the attachment mechanism is attached to the digit.

Another aspect of the invention is a method of reducing a change in an optical path length caused by physical depression of a digit against an object. The optical path length is defined between an emitter and a detector in an optical probe. The method comprises attaching an emitter to a first side of a digit and attaching a detector to a second side of the digit. A vertical axis of the digit is defined as perpendicular to a nail portion of the digit. In addition, the first side and the second side substantially oppose one another and are approximately parallel to the vertical axis.

Another aspect of the invention is a housing for an optical probe used to noninvasively measure at least one characteristic of a digit. The housing comprises a first portion configured to position an emitter along a first side of a digit, wherein the first side is substantially perpendicular to a nail portion of the digit. The housing includes a second portion configured to position a detector along a second side, wherein the second side substantially opposes the first side. In addition, the housing includes a third portion configured to position a flexible circuit within the housing, wherein the flexible circuit connects the emitter and the detector to an oximeter connector. Another aspect of the invention is an optical probe that comprises an emitter configured to cause light energy incident to a patient's thumb, a detector configured to detect the light energy, a housing configured to position an emitter on a first side of the thumb and to position a detector on a second side of the thumb, wherein the first side substantially opposes the second side and both sides are substantially perpendicular with a plane of a thumbnail. The optical probe also comprises a flexible circuit electrically connected to the emitter and the detector for communicating a drive signal to the emitter, and communicating a detected signal from the detector.

Another aspect of the invention is a method of applying an optical probe to a patient's thumb, the method comprising applying an optical probe to a patient's thumb such that an emitter is positioned on a first side of the patient's thumb and a detector is positioned to detect light energy emitted from the emitter.

According to another aspect, the invention includes an oximetry system comprising an optical probe having an emitter substantially secured to a first side of a digit and a detector substantially secured to a second side of the digit, the first side and the second side being substantially perpendicular to a nail portion of the digit. The oximetry system also includes an oximeter configured to interpret signals from the optical probe and a connector connecting the optical probe to the oximeter.

Brief Description of the Drawings The present invention is described in more detail below in connection with the attached drawings, which are meant to illustrate and not to limit the invention and in which:

FIGURE 1 illustrates a simplified frontal view (in partial cross section) of a typical optical probe attached to a digit;

FIGURE 2 illustrates a simplified frontal view (in partial cross section) of the optical probe of FIGURE 1 being physically depressed against an object;

FIGURE 3 illustrates a simplified frontal view (in partial cross section) of an optical probe according to aspects of an embodiment of the invention;

FIGURE 4 illustrates a simplified frontal view (in partial cross section) of the optical probe of FIGURE 3 being physically depressed against an object; FIGURE 5 illustrates a simplified top plan view of an optical probe according to aspects of an embodiment of the invention;

FIGURES 6A and 6B illustrate a simplified top view of the optical probe of FIGURE 5 attached to a thumb; and

FIGURE 7 illustrates a simplified top view of another optical probe attached to a digit, according to aspects of another embodiment of the invention.

Detailed Description of the Preferred Embodiment The inventions are described in detail below with reference to the figures, wherein like elements are referenced with like numerals throughout.

Examination of a material is often advantageous, especially when difficult or expensive to procure and test a sample of the material. For example, in physiological measurements, it is often desirable to monitor a patient without drawing blood or tissue from the patient. The known properties of energy absorption as energy propagates through a material may be used to determine information about the material through which the energy is passed. Energy is made incident on a material, and a measurement is made of energy either transmitted by, or reflected from, the material.

The amplitude of the measured signal is highly dependent on the thickness of the material through which the energy passes, or the optical path length, as well as other properties such as erratic movement of venous blood during motion.

For example, U.S. Patent l\lo. 5,782,757, issued to Diab, et al., on July 21, 1998, assigned to the assignee of the present application, and incorporated by reference herein, discloses that energy transmitted through a medium having ll constituents is approximately attenuated according to the following equation:

Wherein l_D is the energy transmitted from the emitter, S_j is the absorption coefficient of the i^th constituent, X; is the thickness of the i^th constituent through which light energy passes, or the optical path length of the i^t constituent, and C_| is the concentration of the i^th constituent in the thickness X,. As indicated in the forgoing equation, absorption is strongly dependent upon the thickness of the constituents that make up the medium through which the energy passes. For example, when the thickness of the medium changes due to motion, the thickness of the individual constituents change. This causes the absorption characteristics of the medium to change.

For example, FIGURE 1 illustrates a simplified frontal view of a typical optical probe 100 attached to a digit 105. The typical optical probe 100 includes an emitter 1 10 and a detector 1 15. In addition, the digit 105 includes a nail portion 120, such as a fingernail. As discussed above, the emitter 110 is typically positioned above the nail portion 120 of the digit 105. Moreover, the detector 115 is typically positioned substantially opposite the emitter 110, for example, underneath the digit 105.

As shown in FIGURE 1, an optical path length XI can be defined between the emitter 110 and the detector 115. The optical path length X1 defines both the thickness of the tissue of the digit 105, and the volume of the tissue through which perfusion may be measured. FIGURE 2 illustrates a simplified frontal view of the typical optical probe 100 being depressed against an object 200. As shown in FIGURE 2, the object 200 contacts the optical probe 100, for example at the detector 1 15, and depresses the tissue of the digit 105 toward the nail portion 120. Such physical depression can be caused by a wide number of patient movements, including, for example, a patient tapping the digit 105 against the object 200.

As shown in FIGURE 2, a new optical path length X2 is defined between the emitter 1 10 and the now depressed detector 115. Comparing FIGURE 2 to FIGURE 1, a change between the optical path lengths X1 and X2 can be recognized. The change in optical path length of the prior art optical probe, or X_PΛ, is equal to X1-X2. As is shown by comparing FIGURE 1 and FIGURE 2, the change in optical path length X_PA may be quite significant, and therefore, may significantly affect the ability of an oximeter to interpret the measured signal from the detector 1 15.

FIGURE 3 illustrates a simplified frontal view of an optical probe 300 according to aspects of an embodiment of the invention. As shown in FIGURE 3, the optical probe 300 is attached to a digit 305. According to one embodiment of the invention, the digit 305 comprises a patient's thumb. The optical probe 300 further comprises an emitter 310 and a detector 315. Moreover, the digit 305 includes a nail portion 320, such as a thumbnail. As shown in FIGURE 3, the optical probe 300 is preferably configured such that the emitter 310 and the detector 315 are on substantially opposing sides of the digit 305. Moreover, the emitter 310 and the detector 315 are preferably positioned at sides of the digit 305 substantially perpendicular to the side of the digit 305 having the nail portion 320. Thus, as shown in FIGURE 3, the optical probe 300 advantageously positions the emitter 310 and the detector 315 in a manner rotated approximately ninety degrees from that of the conventional optical probe 100.

Although the optical probe 300 is disclosed with reference to a preferred embodiment, the invention is not intended to be limited thereby. Rather, a skilled artisan will recognize that the emitter 310 and the detector 315 may advantageously switch positions relative to the digit 305. For example, while the preferred embodiment includes the emitter 310 positioned on the ulnar side of the digit 305, alternative embodiments may advantageously position the emitter 310 on the radial side of the digit 305. As mentioned in the foregoing, according to one embodiment, the detector 315 is positioned to oppose the emitter 310 regardless of which side of the digit 305 the emitter 310 occupies. According to another embodiment, the detector 315 is positioned to detect energy emitted from the emitter 310, such as, for example, to detect reflective or direct energy emissions.

According to an embodiment of the invention, the optical probe 300 includes adhesive material for attaching the emitter 310 and the detector 315 to the digit 305. According to alternative embodiments, a skilled artist will recognize from the disclosure herein a wide number of attachment mechanisms for the optical probe 300. For example, the attachment mechanism may advantageously comprise a spring-tension based reusable clip, a hook-and-loop material, other adhesive-type bandages, or the like. In addition, the attachment mechanism may advantageously substantially secure the emitter 310 and the detector 315 to the digit 305 and block excessive ambient light from interfering with the transmitted energy sensed at the detector 315.

Also as shown in FIGURE 3, the optical probe 300 has an optical path length X3 defined as the length between the emitter 310 and the detector 315 when the optical probe 300 is attached to the digit 305. Similar to XI in FIGURE 1 and X2 in FIGURE 2, the optical path length X3 determines the volume of tissue through which perfusion is measured. As shown in FIGURE 3, the optical path length X3 is greater than the optical path lengths X1 and X2. Accordingly, the volume of tissue through which perfusion is measured is increased. By increasing the volume of tissue through which the perfusion is measured, the eventual signal produced by the detector 315 will advantageously include an increased signal-to-noise ratio. Moreover, because the preferred embodiment includes positioning of the optical probe over a thumb, the thumb advantageously increases the available perfusion.

FIGURE 4 illustrates the optical probe 300 being physically depressed against an object 400 according to aspects of an embodiment of the invention. As shown in FIGURE 4, the digit 305 expands horizontally along an axis parallel to that of the nail portion 320 when depressed against the object 400. Such depression may be caused by patient or caregiver agitation, such as for example, tapping of the digit against the object 400. As shown in FIGURE 4, as the digit 305 is compressed vertically, the tissue of the digit 305 expands horizontally. However, the horizontal expansion is significantly less than the vertical depression for several reasons. For example, the tapping typically occurs on the underside of the digit 305, as opposed to one of the sides. Accordingly, such tapping depresses the malleable digit 305 as opposed to the rigid detector 315. Also as shown in FIGURE 4, a new optical path length, X4 is defined as the distance between the emitter 310 and the detector 315 during the physical depression of the digit 305 against the object 400. Thus, a new change in optical path length, X, is equal to X4-X3. As is shown by comparing FIGURE 3 and FIGURE 4, the change in optical path length X is much smaller than the change in optical path length X_PA, illustrated by the differences between X1 in FIGURE 1 and X2 in FIGURE 2. Therefore, by applying the optical probe 300 in a manner that positions the emitter 310 and the detector 315 on sides substantially opposite one another and substantially perpendicular to the side having the nail portion 320, the present invention advantageously reduces the change in optical path length during motion. This reduction in optical path length change advantageously reduces erratic absorption of optical energy by the tissue, thereby providing less erratic optical energy levels sensed by the detector 315, resulting in easier signals for the oximeter to interpret.

Based on the forgoing, the preferred and alternative embodiments of the side-applied optical probe 300 advantageously increase the measured volume of tissue available for perfusion while decreasing the level of erractness in the transmitted optical energy sensed by the detector 315. Therefore, the eventual signal interpreted by the oximeter includes an increased signal-to-noise ratio. FIGURE 5 illustrates a top plan view of an optical probe 500 according to aspects of an embodiment of the invention. The optical probe 500 includes a pair of adhesive flaps 502 and a pair of adhesive flanges 504 extending from a central portion 506. The pair of adhesive flanges 504 preferably house an emitter 510 and a detector 515, both electrically connected to a flexible circuit 520. According to the preferred embodiment, the emitter 510 comprises at least one light-emitting diode, while the detector 515 comprises a photodetector. As shown in FIGURE 5, the emitter 510 and the detector 515 are preferably positioned near the centers of each adhesive flange 504, respectively.

According to a preferred embodiment, the central portion 506 comprises an accordion-like stretchable material such that the distance between the adhesive flaps 502 and the adhesive flanges 504 may be advantageously increased or decreased to better fit differing sizes of digits. The optical probe 500 also includes a connector portion 525. The connector portion 525 preferably comprises accordion-like stretchable material similar to that of the central portion 506. According to one embodiment of the invention, the connector portion 525 is preferably two to six inches in length. Moreover, the connector portion 525 preferably includes an exposed portion 530 of the flexible circuit 520, such that the connector portion 525 may advantageously connect to an oximeter or oximeter cable (not shown), as is known in the art.

Although the optical probe 500 is disclosed with reference to its preferred embodiment, the invention is not intended to be limited thereby. Rather, a skilled artisan will recognize from the disclosure herein a wide number of alternatives for the shape and structure of the optical probe 500. For example, the emitter 510 and the detector 515 may advantageously interchange their respective positions on the adhesive flanges 504. For example, according to one embodiment, the optical probe 500 attaches to a patient's thumb and the detector 515 is positioned on the radial side of the thumb such that the detector 515 does not contact the index finger. According to this embodiment, the optical probe 500 may advantageously include left-hand and right-hand sensors such that the detector is always on the radial side. Alternatively, a skilled artisan will recognized from the disclosure herein that a left-hand or right-hand thumb sensor may advantageously be attached to the thumb on the opposing hand by rotating the sensor 180 degrees around the opposing thumb, thereby avoiding contact between the detector 315 and the index finger.

According to another embodiment, the emitter 510 and the detector 515 may advantageously be positioned on the adhesive flaps 502 as opposed to the adhesive flanges 504. According to another embodiment, the central portion 506 and the connector portion 525 may advantageously comprise nonstretchable material similar to that of the adhesive flaps 502 and the adhesive flange 504. In addition, the optical probe 500 may advantageously comprise a reusable portion and a disposable portion. For example, the reusable portion may comprise the emitter 510, the detector 515, and the flexible circuit 520, while the disposable portion may comprise the adhesive flaps 502, the central portion 506, and the adhesive flanges 504. In such an embodiment, the reusable portion may be withdrawn from the disposable portion, preferably sterilized, and then reused in a new disposable portion.

FIGURES 6A and 6B illustrate a simplified frontal and side view of the optical probe 500 of FIGURE 5 attached to the digit 305. According to the preferred embodiment, the digit 305 comprises the left-hand thumb. As shown in

FIGURES 6A and 6B, the emitter 510 is advantageously positioned on the side of the digit 305 perpendicular to the side having the nail portion 320. As shown in FIGURE 6, the optical probe 500 folds at the central portion 506 around the end of the tip of the digit 305 such that the emitter 510 and the detector 515 are substantially secured to the digit 305.

Although not depicted specifically in FIGURE 5 and FIGURE 6, the optical probe 500 is preferably fabricated from multiple layers, including a preferred flex circuit layer, a preferred MYLAR™ layer, a preferred facestock tape layer, and other tape layers, as is known in the art.

FIGURE 7 illustrates a side view of an optical probe 700 attached to the digit 305, according to another embodiment of the invention. The optical probe 700 preferably includes an optical probe as is conventionally known in the art. For example, the optical probe 700 may advantageously comprise an optical probe similar to that disclosed in the above-referenced U.S. Patent No. 5,782,757. As shown in FIGURE 7, the optical probe 700 includes an emitter 710 and a detector 715 positioned on opposite sides of the digit 305 substantially perpendicular to the nail portion 320. Thus, the conventional optical probe 700 may be applied to the digit 305 such that an optical path length between the emitter 710 and the detector 715 includes the advantages disclosed in the forgoing with reference to side-application of the optical probes 300 and 500, respectively.

Although the forgoing invention has been described in terms of certain preferred embodiments, other embodiments will be apparent to those of ordinary skill in the art from the disclosure herein. For example, the optical probes 300, 500, and 700 may be advantageously applied to a finger or toe. In addition, the optical probes 300, 500, and 700 may advantageously be housed in a spring-tension-based clip, a hook-and-loop bandage, such as Velcro, disposable, reusable, or differing shaped adhesive attachment mechanisms.

Additionally, other combinations, omissions, substitutions and modifications will be apparent to the skilled artisan in view of the disclosure herein. Accordingly, the present invention is not intended to be limited by the reaction of the preferred embodiments, but is to be defined by referenced to the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for producing an optical probe for measuring at least one characteristic of a digit, the method comprising: positioning an emitter and a detector within an attachment mechanism such that the emitter and the detector substantially oppose one another along an axis substantially parallel to a nail portion of a digit when the attachment mechanism is attached to the digit.

2. The method of Claim 1, wherein the attachment mechanism is configured to attach to a thumb.

3. A method of reducing a change in an optical path length caused by physical depression of a digit against an object, wherein the optical path length is defined between an emitter and a detector in an optical probe for measuring at least one characteristic of the digit, the method comprising: attaching an emitter to a first side of a digit; and attaching a detector to a second side of the digit; wherein a vertical axis of the digit is defined as perpendicular to a nail portion of the digit, and wherein the first side and the second side substantially oppose one another and are approximately parallel to the vertical axis.

4. The method of Claim 3, wherein the digit comprises a thumb.

5. An housing for an optical probe used to non-invasively measure at least one characteristic of a digit, the housing comprising: a first portion configured to position an emitter along a first side of a digit, wherein the first side is substantially perpendicular to a nail portion of the digit; a second portion configured to position a detector along a second side, wherein the second side substantially opposes the first side; and a third portion configured to position a flexible circuit within the housing, wherein the flexible circuit connects the emitter and the detector to an oximeter connector.

6. The housing of Claim 5, wherein the third portion includes a flexible accordion-like structure.

7. The housing of Claim 5, wherein the first and second portions include an adhesive material for attaching the housing to the digit.

8. The housing of Claim 5, wherein the first and second portions are configured to substantially secure the emitter and the detector to a thumb.

9. The housing of Claim 5, wherein the first and second portions each comprise a flange extending outwardly from the third portion.

10. A oximetry system comprising: an optical probe having an emitter substantially secured to a first side of a digit and a detector substantially secured to a second side of the digit, the first side and the second side being substantially perpendicular to a nail portion of the digit; an oximeter configured to interpret signals from the optical probe; and a connector connecting the optical probe to the oximeter.

11. The oximetry system of Claim 10, wherein the digit comprises a thumb.

12. The oximetry system of Claim 10, wherein the first side corresponds to the ulnar side of the digit and the second side corresponds to the radial side of the digit.

13. The oximetry system of Claim 10, wherein the first side corresponds to the radial side of the digit and the second side corresponds to the ulnar side of the digit.

14. The oximetry system of Claim 10, wherein the optical probe includes a positioning portion having flanges, and wherein the emitter is housed in a first flange and the detector is housed in a second flange.

15. An optical probe comprising: an emitter configured to cause light energy incident to a patient's thumb; a detector configured to detect the light energy; a housing configured to position an emitter on a first side of the thumb and to position a detector on a second side of the thumb, wherein the first side substantially opposes the second side and both sides are substantially perpendicular with a plane of a thumbnail; and a flexible circuit electrically connected to the emitter and the detector for communicating a drive signal to the emitter, and communicating a detected signal from the detector.

16. A method of applying an optical probe to a patient's thumb, the method comprising applying an optical probe to a patient's thumb such that an emitter is positioned on a first side of the patient's thumb and a detector is positioned to detect light energy emitted from the emitter.

17. The method of Claim 16, wherein the first side is substantially perpendicular to a nail portion of the patient's thumb.