(15)
`United States Patent
`5,024,226
`[11] Patent Number:
`Jun, 18, 1991
`[45] Date of Patent:
`Tan
`
`[54] EPIDURAL OXYGEN SENSOR
`
`{75}
`
`Inventor:
`
`Josef K. S. Tan, Tampa, Fla.
`
`[73] Assignee: Critikon, Inc., Tampa, Fla.
`
`{21] Appl. No.: 394,997
`[22] Filed:
`Aug, 17, 1989
`[5D] Ut, CRS vecccseescccsscsssssecsscsssecasensessssevesses A61B 5/00
`[52] U.S. Ch ow“seeessssucsessssesesseeee 128/633; 128/666
`[58] Field of Search .......ss 128/632, 633, 634, 665,
`128/666; 356/40
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`
`4,621,643 11/1986 New Sr. et al. cece 128/666
`4,623,789 11/1986 Ikeda et ab. w.ceseeeeseneees 604/175
`
`4,714,080 12/1987 Edgar Jr. et al. ccs 128/666
`
`4,784,150 11/1988 Voorhies et al. ou. 128/664
`
`5/1989 Tun et ab. oc
`eseeenes 128/665
`4,825,872
`
`9/1984 Rich et al. wccsceesesesereenes 128/665
`4,865,038
`
`
`oe 356/41
`4,867,557
`9/1989 Takataniet al.
`5/1990 Nicolson et al... 128/633
`4,928,691
`4,938,218
`7/1990 Goodmanetal... 128/633
`
`FOREIGN PATENT DOCUMENTS
`
`0094749 11/1983 European Pat. Off. ........ 128/633
`0135840 4/1985 European Pat. Off. .......... 128/633
`3152963 10/1983 Fed. Rep. of Germany...... 128/633
`
`OTHER PUBLICATIONS
`
`“Cerebral Oxidative Metabolism and Blood Flow Dur-
`ing Acute Hypoglycemia and Recovery in Unaesthe-
`tized Rate’, Journ. of Neurochem., 1982 p. 397.
`“Regional Acetylcholine Metabolism in Brain During
`Acute Hypoglycemia and Recovery”, Journ. Neuro- .
`chem., 1985 at p. 94 et seq.
`Yee, Sinclair et al., “A Proposed Minature Red/Infra-
`
`red Oximeter .. .”, IEEE Trans, Biomed. Eng. (USA),
`vol. BME-24 NO. 2 (Mar. 1977).
`
`Primary Examiner—Lee S. Cohen
`Assistant Examiner—John D. Zele
`Attorney, Agent, or Firm—Paul A. Coletti
`
`ABSTRACT
`[57]
`A sensor for measuring the oxygen availability of blood
`flow within the skull is described. In a first embodiment
`the sensor comprises a photodetector anda pair oflight
`emitting diodes surface mounted near the end of a
`length of flexible printed wiring. The sensoris sealed by
`a coating of rubber or polymeric material which has an
`optical window over the photodetector and light emit-
`ting diodes. The sensor is inserted through a burr hole
`drilled in the skull and slides between the skull and the
`dura of the drain. The light emitting diodes are pulsed
`to illuminate blood flow in the brain beneath the dura
`with light, and light reflected by the blood is received
`by the photodetector and converted to electrical sig-
`nals. The signals are processed by a pulse oximeter to
`provide an indication of blood availability. In a second
`embodiment the photodetector and light emitting di-
`odes are mounted at the end of a core of compressible
`foam extending from the end of a hollow bone screw.
`As the bone screw is screwed into a burr hole in the
`skull the photodetector and light emitting diodes will
`contact the dura and the foam will compress to maintain
`optical contact between the electrical components and
`the dura. Light from the diodesis reflected by blood in
`the dura and brain, received by the photodetector, and
`the resultant electrical siganls are processed by the
`pulse oximeter.
`
`12 Claims, 3 Drawing Sheets
`
`
`
`MASIMO 2011
`MASIMO2011
`Apple v. Masimo
`Apple v. Masimo
`IPR2020-01526
`IPR2020-01526
`
`

`

`U.S. Patent
`
`5,024,226
`
`June 18, 1991
`
`"Sheet 1 of 3
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`

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`U.S. Patent
`
`June 18, 1991
`
`Sheet 2 of 3
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`5,024,226
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`
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`BLFIG-oa
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`FiG-4a
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`FIG-4b_
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`FIG-4c
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`FIG-3b
`FIG-oC
`3022" re 22" 224
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`FIG-6a
`30 £22
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`

`

`U.S. Patent
`
`June 18, 1991
`
`Sheet 3 of 3
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`5,024,226
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`FIG-8a
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`FIG-8b —
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`
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`FIG-8c_
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`-©-
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`22
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`

`

`1
`
`5,024,226
`
`EPIDURAL OXYGEN SENSOR
`
`2
`FIGS. 4a-4c, 5a-5c and 6a-6c are plan viewsofdif-
`ferent placements of LED’s and photodiodes of epidu-
`ral oxygenation sensors ofthe present invention;
`FIG.7 is an electrical schematic of the components of
`This invention relates to sensors for determining the
`the epidural oxygenation sensor of FIG. 2; and
`oxygen availability of tissues within the skull and, in
`FIGS. 8a-8c¢ are cross-sectional,
`top, and bottom
`particular, to such sensor which are placed: epidurally
`views of an epidural oxygenation sensor mounted in a
`through the skull to measure oxygen availability.
`hollow bone screw.
`During neurological and neurologically related surgi-
`Referring first to FIG. 1, a skull is shown in which a
`cal procedures it is oftentimes desirable to continuously
`burr hole 12 has been drilled. Underlying the skull is the
`monitor the oxygenation of blood which is supplied to
`dura 16 which encasesthe brain, and beneath the durais
`the brain. Frequently access is gained to the brain
`the cerebrum 14. An epidural oxygenation sensor 20is
`through a borehole in the skull, and a sensor which
`inserted through the burr hole 12 for measurement of
`optically measures oxygenation can then be inserted
`the oxygenation of blood flowing in the brain. The
`through such a borehole. An optical sensor should then
`sensor 20 is inserted through the burr hole andslides
`exhibit numerous design and performancecriteria in
`between the skull 10 and the dura 16, where it
`is
`orderto operate satisfactorily in this environment. The
`shielded from ambient light entering the burr hole. At
`sensor must be capable of insertion through the bore-
`the distal end of the sensor 20 is a photodetector 24 and
`hole so as to contacttissue where oxygen availability is
`LED’s 22 which face the dura through optical windows
`to be measured The sensor must be soft so that it does
`in the sensor. The photodetector and LED’s are
`not damage neurological tissue, yet be sufficiently rigid
`mounted on flexible printed wiring which is connected
`in certain dimensionsso that it can be maneuvered from
`to a sensor cable 26. The sensor cable is connected to a
`outside the skull. It also must be sized to fit inside the
`pulse oximeter
`(not shown), which provides drive
`borehole and in the location where measurementsare to
`pulses for the LED’s, receives electrical signals from
`be taken. Furthermore, the sensor must be designed so
`the photodetector, and processes the received electrical
`as to eliminate detection of ambient light which will
`signals to producean indication of the oxygen availabil-
`interfere with detection of the desired optical signals
`ity of blood in the brain. The sensor is operated in a
`The sensor must also prevent the detection of directly
`reflective mode, whereby light of different wavelengths
`emitted by the LED’sis reflected by the blood in the
`transmitted light from the light source of the sensor.
`brain and the reflected light is received by the photode-
`In accordance with the principles of the present in-
`tector.
`vention, an optical sensor is provided for epidural mea-
`As shownin FIG.2, the sensor 20 comprises a photo-
`surement of blood oxygenation In a first embodiment
`detector 24 and an adjacent pair of LED’s 22a and 226
`the sensor comprises a pair of light emitting diodes
`which are surface mountedto leads of flexible printed
`(LED’s) which emit light at two predetermined wave-
`wiring 28 such as 0.001 inch Kapton TM based printed
`lengths. The sensor also includes a photodetector for
`wiring. The use of surface mounted componentsand the
`receiving light emitted by the LED’s which has been
`printed wiring provide a thin sensor which minimizes
`reflected from adjacent blood perfused tissue. The
`cerebral compression. Separating the LED’s and the
`LED’s and the photodetector are mounted on flexible
`photodetectoris a light barrier 25 which prevents the
`printed wiring which transmits signals to the LED’s
`direct transmission oflight from the LED’sto the pho-
`and from the photodiode. The components are encapsu-
`todetector. The light barrier may be provided by an
`lated in a soft polymer which is biocompatible. The
`opaque epoxy material, but in a preferred embodiment
`resultant sensoris thus capable of operation in an epidu-
`the light barrier is formed of a thin sheet of copperfoil.
`ral environment,and is further capable of being maneu-
`The copper foil not only effectively blocks light from
`vered into the desired position for epidural measure-
`the LED’s, butis also connected to a groundedlead of
`ments.
`the flexible printed wiring. The copperfoil thus shields
`In a second embodiment the LED’s and photodetec-
`the photodetector from radio frequency interference
`tor are located in a hollow bone screw, with the compo-
`such as that emanated during pulsing of the LED's.
`nents opposing thetissue from which measurementsare
`The foregoing components are encapsulated byasoft
`to be taken. The components are backed bya resilient
`coating 30 ofsilicone rubber or polyurethane material.
`membersuch as a spring or soft polymeric foam which
`Thesoft coating smoothly rounds the corners and edges
`will compress under gentle pressure within the bone
`of the sensor which prevents injury to the dura by the
`screw to cause the components to contact the dura and
`sensor. The coating also seals the components from
`maintain optical contact with the dura as it moves with
`moisture and other environmental factors. The coating
`the patient’s respiration.
`30 is optically transmissive to light at the wavelengths
`In the drawings:
`of the LED’s whereit overlies the lower surfaces of the
`FIG.1 illustrates a cross-sectional view of the use of
`photodetector and the LED’s from which lightis trans-
`an epidural oxygenation sensor constructed in accor-
`mitted and received by these components.
`dance with the present invention;
`FIG.2a is a perspective view of the sensor 20 of FIG.
`FIG. 2 is a side cross-sectional view of an epidural
`2, referenced to x, y, and z axes. As mentioned above,
`oxygenation sensor constructed in accordance with the
`the coating 30 provides the sensor with a smooth,
`gently rounded profile such as the rounded distal end
`principles of the present invention;
`27. The sensoris relatively stiff along the portion of the
`FIG.2a is a perspective view of an epidural oxygena-
`printed wiring where the components are mounted to
`tion sensor constructed in accordance with the princi-
`maintain their relative alignment. In the x dimension the
`ples of the present invention;
`sensoris fairly stiff so that it may be inserted and guided
`FIGS. 3a-3c are cross-sectional views of different
`beneath the skull and in contact with the dura. In the z
`embodiments of epidural oxygenation sensors of the
`dimension the sensoris stiff to provide maneuverability
`present invention;
`
`we 5
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`3
`during placement of the sensor. In the y dimension the
`sensor proximal the components is flexible to curve
`through the burr hole and underthe skull, which may
`have a thickness of 2 to 20 mm depending upon the
`patient.
`In order to be capable of sliding between the skull
`and the dura the sensor should be thin in the y dimen-
`sion so as not to injure the patient. Preferably the sensor
`thickness in this dimension should be not greater than 4
`mm, and most preferably not greater than 2.5 mm. The
`sensor should also be not less than about one millimeter
`in thickness to maintain continuous contact with the
`dura. This will reduce the occurrence of motion arti-
`facts, as the dura can move as much as } mm or more
`away from the skull during hyperventilation of the
`patient, for instance.
`In the embodiment of FIG. 2 the photodetector 24 is
`located toward the distal end 27 of the sensor with
`respect to the LED’s 22. This distal placement of the
`photodetector keeps the photodetector well removed
`from the burr hole and ambient light passing through
`the burr hole. FIGS. 3¢-3c show other component
`orientations which may be employedin different sensor
`embodiments. In FIG. 3a the LED’s 22’ are canted
`toward the dura where the dura overlies the photode-
`tector 24, which improvesthe efficiency oflight reflec-
`tance. The canted LED’sare supported bya filler of the
`coating material 30. In FIG. 34 two pairs of LED’s 22”
`are located on either side of the phototdetector 24 to
`illuminate the dura from both sides of the photodetec-
`tor. In FIG. 3c the pair of LED’s 22is centrally located
`between a pair of photodetectors 24’, the latter being
`canted toward the area of the dura illuminated above
`the LED’s.
`It is desirable for the optical windowsof the compo-
`nents which face the dura to be as large as possible so as
`to maximize optical transmission efficiency. Opposing
`this desire is the constraint that the sensor must be sized
`to fit through the burr hole in the skull. To determine
`the largest components which mayfit through a given
`burr hole diameter, rectangular configurations of com-
`ponents may be calculated which are capable offitting
`through the burr hole. FIGS. 4a-6¢ show component
`configurations which can fit through a 14 mm diameter
`burr hole. FIGS. 4a—4c show plan views of component
`layouts for the single photodetector and pair of LED’s
`employed in the sensors of FIGS. 2 and 3a. In FIG. 4a
`the LED’s 22’ and the photodetector are arranged in a
`layout which measures 8.2 mm by 6.3 mm. In FIG. 45
`the rectangular layout measures 10.5 mm by 5.3 mm,
`and in FIG. 4c the rectangular layout measures 9.3 mm
`by 5.7 mm. In each layout the coating material 30 is
`shownin the area outside the boundaries of the electri-
`cal components.
`FIGS. 5a-5¢e show component layouts for a 14 mm
`diameter burr hole using two pairs of LED’s 22” and
`one photodetector 24, In FIG. 5a the rectangular layout
`measures 10.8 mm by 7.0 mm; in FIG. 50 the layout
`measures 13.0 mm by 5.5 mm; and in FIG.5c the layout
`measures 8.2 mm by 7.3 mm.Ina similar manner, FIGS.
`6a-6c show componentlayouts using two photodetec-
`tors 24’ and one or two pairs of LED’s 22 or 22". In
`FIG. 6a the rectangular layout measures 8.1 mm by 6.8
`mm; in FIG. 66 the layout measures 11.5 mm by 6.8 mm;
`and in FIG. 6c the layout measures 8.6 mm by 7.5 mm.
`In FIGS. 4a-6c¢ each LED pair had an area of 3.0 mm
`by 4.2 mm. The photodetectors in FIGS. 6a and 6c had
`an area of 2.25 mm by 6.25 mm. In the remaining lay-
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`6.25 mm.
`FIG.7 is an electrical schematic of the sensor 20 of
`FIG. 2. The two LED’s 22a and 226 emitlight at a red
`wavelength and are connected in parallel. These two
`LED’s are paralleled by LED's 23a and 23), which
`emit light at an infrared wavelength. The LED's are
`connected in series with respective resistors 25, 25’ of
`values chosen in correspondence with the drive current
`to be supplied to the LED’s. The LED’sare also cou-
`pled to a biasing resistor 27. The resistors may be
`mountedin line with the flexible printed wiring, such as
`the points 32¢-32d at which the wiring joins the cable to
`the pulse oximeter monitor. Points 32c¢, 32d are con-
`nected to leads from photodetector 24. Alternatively
`the resistors can be functionally incorporated into the
`printed wiring by proper selection of materials and’
`dimensions.
`FIGS. 8a-8c illustrate a further embodiment of an
`epidural sensor in which the sensor components are
`located in a hollow bone screw 40. The screw 40 is
`threaded as indicated at 44 to screw into the skull, and
`the head of the screw has a slot 42 to turn the screw
`with an adjustment instrument as more clearly shown in
`the top plan view of FIG. 8b. A photodetector 24 anda
`pair of LED’s 22 are located at the bottom of a core of
`soft, compressible foam material 52 in the center of the
`screw, as shownin the bottom plan view of FIG. 8c. A
`resilient member 50 is located above the compressible
`foam 52 in the center of the screw. Theresilient member
`may comprise a metallic spring or a core ofsilicone
`rubber or polyurethane. The electrical leads 26’ from
`the LED’s and photodetector pass through the foam
`material §2 and theresilient member 50 and exit through
`the top of the hollow screw as shown in FIG. 8c.
`In use of the sensor embodiment of FIGS. 8a-8c, a
`hole is drilled in the skull into which the bone screw 40
`is screwed. As the bone screw is screwed into the skull,
`the oximeter monitor is continuously monitored for the
`onset of oxygen availability readings. When the bottom
`of the screw with the sensor components contacts the
`dura, oxygen readings will commence,and willinitially
`occurerratically. As the bone screw is slowly turned
`the sensor components will make better contact with
`the dura and the signal quality will
`improve The
`contact between the sensor components and the dura is
`induced in a gentle manner by the compressible foam
`§2, which will readily compress as the components
`make contact with the dura to prevent damage to the
`dura. Theresilient member acts to maintain the com-
`pression of the foam 52, When consistent readings occur
`no further turning of the screw is necessary, as the
`sensor componentsare in good surface contact with the
`dura and will gently ride on the dura due to the com-
`pressibility of the foam 52.
`A preferred technique for using the embodiment of
`FIGS. 8a-8cis to drill a hole in the skull and screw the
`bone screw into the hole before locating the sensor in
`the screw. After the bone screw is in place the sensor
`with its foam backing material 52 slides into the hollow
`bone screw,followed by insertion of the resilient mem-
`ber 50. The foam is gently compressed by theresilient
`memberto cause the sensor to make good contact with
`the dura, a condition which is detected by monitoring
`the signal quality of the monitor. This technique obvi-
`ates problems of entangling the sensor wires as the bone
`screw is screwed into the skull with the sensor already
`positioned within the bone screw. Only after the bone
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`

`5
`screw is emplaced is the sensor with its backing and
`filling materials inserted into the screw, which can then
`be done without twisting the sensor components and
`the wiring to the sensor.
`This hollow bone screw embodimentis desirable for
`its ability to completely block ambient light from the
`sensor components, and by plugging the burr hole with
`the bone screw infection of the dura is retarded. The
`sensor can be safely left in place in the burr hole for
`extended periodsoftime.
`Whatis claimed is:
`1. A sensor for measuring cerebral oxygen availabil-
`ity through a burr hole in the skull by optical reflec-
`tance comprising:
`a length offlexible wiring having (a) a distal end and
`(b) a proximal end which is to be connected to an
`oximeter;
`a photodetectorelectrically connectedto said flexible
`wiring in the proximity of said distal end;
`a pair of light emitting diodes connected tosaid flexi-
`' ble wiring adjacent to said photodetector; and
`a coating encapsulating said photodetector,said light
`emitting diodes, and said flexible wiring in the
`proximity of said photodetector andsaidlight emit-
`ting diodes, said coating including optical windows
`wheresaid coating overlies the optical windowsof
`said photodetector and said light emitting diodes
`whichis transmissive to light at the wavelengths of
`said light emitting diodes, said encapsulated photo-
`detector and said light emitting diodes having a
`width less than about 20 mm to fit through the
`diameter of said burr hole and a thickness less than
`about 4 mm to slide between the skull and dura.
`2. The sensor of claim 1, further including a light
`barrier positioned between said photodetector and said
`light emitting diodes which shields said photodetector
`from the direct reception of light from said light emit-
`ting diodes.
`_3. The sensor of claim 2, wherein said light barrier
`comprises opaque epoxy.
`4. The sensor of claim 2, wherein said light barrier
`comprises metalfoil.
`
`6
`5. The sensor of claim 1, wherein said flexible wiring
`comprises flexible printed wiring.
`6. The sensor of claim 1, wherein said coating issili-
`cone rubber.
`7. The sensor of claim 1, wherein said coatingis poly-
`urethane.
`8. The sensor of claim 1, wherein the optical window
`of said light emitting diodes is canted toward the area
`abovesaid photodetector.
`9. The sensor of claim 1, further comprising a second
`pair of light emitting diodes located adjacent said pho-
`todetector and on the opposite side of said photodetec-
`tor as said first-named pair of light emitting diodes.
`10. The sensor of claim 1, further comprising a sec-
`ond photodetector located adjacent said light emitting
`diodes on the opposite side of said light emitting diodes
`as said first-named photodetector.
`11. The sensor of claim 10, wherein said photodetec-
`tors are canted toward the area abovesaid light emitting
`diodes.
`12. A methodof epidurally sensing oxygen availabil-
`ity comprising the steps of:
`drilling a burr hole in a skull;
`inserting a length of flexible wiring connected to a
`photodetector and a pair of light emitting diodes
`mounted in the proximity of the distal end ofsaid
`wiring, said wiring, said photodetector, and said
`light emitting diodes encapsulated in a coating
`through said burr hole and between the skull and
`the dura, said encapsulated photodetector and said
`light emitting diodes having a width less than about
`20 mm to fit through the diameter of said burr hole
`and a thickness less than about 4 mm toslide be-
`tween the skull and dura, with the optical windows
`of said photodetector andsaid light emitting diodes
`opposing the dura;
`energizing said light emitting diodes, and receiving
`electrical signals from said photodetectorresulting
`from the reception of reflected light emanating
`from said diodes, by way of said flexible wiring;
`and
`processing said electrical signals to produce an indi-
`cation of blood oxygen availability.
`*
`*
`*
`*
`*
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