I II IIIIII Ill llll llll llll lllll Ill llll 111111111111111
`
`US005746206A
`[111 Patent Number:
`[451 Date of Patent:
`
`5,746,206
`*May 5, 1998
`
`United States Patent [19]
`Mannheimer
`
`[54]
`
`ISOLATED LAYER PULSE OXIMETRY
`
`[75]
`
`Inventor: Paul D. Mannheimer. Belmont. Calif.
`
`[73] Assignee: Nellcor Incorporated. Pleasanton.
`Calif.
`
`[ * ] Notice:
`
`The term of this patent shall not extend
`beyond the expiration date of Pat. No.
`5,524.617
`
`[21) Appl. No.: 662,439
`Jun. 10, 1996
`
`[22) Filed:
`
`Related U.S. Application Data
`
`[63) Continuation of Ser. No. 403,642, Mar. 14, 1995, Pat No.
`5,524,617.
`Int. Cl.6
`........................................................ A61B 5/00
`[51]
`[52] U.S. Cl . ............................................... 125/633; 356/39
`[58] Field of Search ..................................... 128/633. 664.
`128/665; 356/41
`
`[56]
`
`References Cited
`
`U.S. PATENf DOCUMENfS
`
`4,796,636
`5,057,695
`5,139,025
`5,188,108
`5,218,962
`5,226,417
`5,277,181
`5,285,783
`5,297,548
`5,372,135
`5,524,617
`
`.................... 128/633
`1/1989 Branstetter et al.
`10/1991 Hirao et al. ......... .................... 128/633
`8/1992 Lewis et al. ............................ 128/665
`2/1993 Secker ..................................... 128/633
`6/1993 Mannheimer et al .................. 128/633
`7/1993 Swedlow et al .....•.................. 128/633
`1/1994 Mendelson et al. .................... 128/633
`2/1994 Secker ........... ................ .......... 128/633
`3/1994 Pologe .................................... 128/633
`12/1994 Mendelson et al ..................... 128/633
`6/1996 Mannheimer ........................... 128/633
`
`FOREIGN P.IITENT DOCUMENTS
`
`8/1994 Germany .
`4304693 Al
`WO 92/21283 12/1992 WlPO.
`Primary Ewminer-Jennifer Bahr
`Assistant Examiner-Eric F. Winakur
`Attorney, Agent, or Firm-Nawrocki. Rooney & Sivertson
`ABSTRACT
`
`(57]
`
`An apparatus of and method for measuring arterial blood
`oxygen saturation at a particular tissue level of interest.
`Visible and near infrared radiation is emitted into a patient
`at the measurement site using two different wavelengths.
`Detection at two different detection sites permits rejection of
`oxygen saturation at undesired tissue levels.
`
`4,700,708 10/1987 New, Jr. et al.
`
`128/633
`
`6 Claims, 8 Drawing Sheets
`
`Petitioner Apple Inc. – Ex. 1008, p. 1
`
`

`

`U.S. Patent
`US. Patent
`
`May 5, 1998
`May 5, 1998
`
`Sheet 1 of 8
`Sheet 1 of 8
`
`5,746,206
`5,746,206
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`Petitioner Apple Inc. — Ex. 1008, p. 2
`
`Petitioner Apple Inc. – Ex. 1008, p. 2
`
`

`

`U.S. Patent
`US. Patent
`
`May 5, 1998
`May 5, 1998
`
`Sheet 2 of 3
`Sheet 2 of 8
`
`5,746,206
`5,746,206
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`Petitioner Apple Inc. — EX. 1008, p. 3
`
`Petitioner Apple Inc. – Ex. 1008, p. 3
`
`

`

`U.S. Patent
`US. Patent
`
`May 5, 1998
`May 5, 1998
`
`Sheet 3 of 8
`Sheet 3 of 8
`
`5,746,206
`5,746,206
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`Petitioner Apple Inc. — Ex. 1008, p. 4
`
`Petitioner Apple Inc. – Ex. 1008, p. 4
`
`

`

`U.S. Patent
`
`May 5, 1998
`
`Sheet 4 of 8
`
`5,746,206
`
`MyE'ti.l\
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`Petitioner Apple Inc. – Ex. 1008, p. 5
`
`
`

`

`U.S. Patent
`US. Patent
`
`May 5, 1998
`May 5, 1998
`
`Sheet 5 of 8
`Sheet 5 of 8
`
`5,746,206
`5,746,206
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`Petitioner Apple Inc. — Ex. 1008, p. 6
`
`Petitioner Apple Inc. – Ex. 1008, p. 6
`
`

`

`U.S. Patent
`US. Patent
`
`May 5, 1998
`May 5, 1998
`
`Sheet 6 of 3
`Sheet 6 of 8
`
`5,746,206
`5,746,206
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`Petitioner Apple Inc. — EX. 1008, p. 7
`
`FIG.5
`
`. . . . . . . .
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`
`Petitioner Apple Inc. – Ex. 1008, p. 7
`
`

`

`U.S. Patent
`
`May 5, 1998
`
`Sheet 7 of 8
`
`5,746,206
`
`0.B ....... ---t---+-----+----+-------.--
`0.7---e-"t----t---+-----+-----+----t--i--
`-2: 0.5-t--~ .......... --+-_ _., _ __.,_----_ _ . _ _
`~ 0.6 ....... -.....--t---+-----+---+---t------1i---(cid:173)
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`
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`FIG_ 6
`
`Petitioner Apple Inc. – Ex. 1008, p. 8
`
`

`

`U.S. Patent
`
`May 5, 1998
`
`Sheet 8 of 8
`
`5,746,206
`
`ol:..10
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`FIG. 7
`
`Petitioner Apple Inc. – Ex. 1008, p. 9
`
`

`

`5,746,206
`
`1
`ISOLATED LAYER PULSE OXIMETRY
`
`This is a continuation application of U.S. application Ser.
`No. 08/403,642, filed Ma.r 14. 1995 now U.S. Pat. No.
`5.524,617.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention generally relates to instruments
`which operate on the principal of pulse oximetry and more
`particularly relates to instruments which non-invasively
`measure oxygen saturation of arterial blood in vivo.
`2. Description of the Prior Art
`Light in the visible and near infrared region of the
`electromagnetic spectrum has been used for the in vivo
`measurement of oxygen saturation levels of a patient's
`blood. Lewis et al. in U.S. Pat. No. 5.139,025 and Lewis et
`al. in International Publication (PCT) Number WO
`92/21283 discuss spectrophotometric instruments whereby
`the oxygen saturation of blood. both venous and arterial
`combined, is estimated using at least three electromagnetic
`sensor areas. A disadvantage of such instruments is that the
`accuracy of the oxygen saturation calculation is limited due
`to such calculation• s sensitivity to varying parameters of the
`tissue other than blood saturation, for example a change in
`concentration. Rall. et al. in German Patent No. DE 43 04
`693 teaches the use of a plurality of light sensors with a
`single light detector as the best means for oximetry mea(cid:173)
`surement in the particular shape of the device of the
`invention. primarily intended for connection to a fetus.
`New, Jr. et al. in U.S. Pat. No. 4,700,708, the disclosure
`of which is incorporated by reference, calculates arterial
`oxygen saturation by isolating the change in detected light
`intensities during a cardiac cycle in an attempt to minimize 35
`and even eliminate the light scattering and absorption effects
`of non-arterial blood tissue of a patient. Though this
`technique, known as pulse oximetry, is effective in elimi(cid:173)
`nating many of the artifacts introduced by bone, skin,
`muscle, etc. a disadvantage exists in that the signal acqui- 40
`sition and computation circuits must be very robust since the
`useful part of the signal is the relatively small change in
`detected intensities, as opposed to the total detected inten(cid:173)
`sity. Another disadvantage is that the calculated oxygen
`saturation value is influenced by pulsatile signal contribu- 45
`tions from many differing tissue layers, including the skin or
`surface tissue layer. It is often desirable to know the arterial
`oxygen saturation of a particular tissue layer or range of
`tissue layers as opposed to knowing only a general average
`arterial oxygen saturation value for all layers, because the 50
`oxygen saturation value of the multiple layers may differ
`from one another. Some clinical conditions. such as stasis,
`may continue to provide a pulsatile signal in the absence of
`flow. particularly near the outer surface.
`U.S. Pat. No. 5.188.108 issued to Secker, suggests the use
`of a plurality of emitters and/or receivers to provide multiple
`emitter/receiver combination. The emitter/receiver spacing
`for each combination is selected to provide equivalent
`optical path lengths between combinations using different 60
`wavelengths of emission.
`
`2
`limitations induced in the prior art systems. Specifically. the
`present invention allows for pulsed oximetry measurement
`which isolates arterial saturation levels for particular ranges
`of tissue layers which rejects saturation levels of the tissue
`5 above or below the tissue of interest by utilizing multiple
`spaced detectors and/or emitters.
`According to one embodiment of the invention. a sensor
`for use with a pulse oximeter monitor comprises a patient
`interface housing for coupling to a patient; at least three
`10 sensor areas for emitting electromagnetic radiation which
`penetrates tissue of the patient and detects that electromag(cid:173)
`netic radiation scattered by the tissue. a spacing between a
`first pair of electromagnetic emitter and electromagnetic
`detector being different than that of a spacing between a
`15 second pair of electromagnetic emitter and electromagnetic
`detector; and means for calculating an arterial oxygen satu(cid:173)
`ration level of the patient in response to the detected
`electromagnetic radiation.
`According to two preferred embodiments. the sensor
`20 areas comprise first and second separated and spaced apart
`emitter areas each capable of generating light of at least two
`distinct wavelengths. and a detector. the first emitter area
`and the detector corresponding to a first pair of emitter and
`detector, the second emitter area and the detector corre-
`25 sponding to the second pair of emitter and detector; or the
`sensor areas comprise first and second detector areas each
`capable of detecting light of at least two separate wavelength
`values. and an emitter area capable of generating said light
`having the at least two separated wavelength values.
`
`30
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`Other objects of the present invention and many of the
`attendant advantages of the present invention will be readily
`appreciated as the same becomes better understood by
`reference to the following detailed description when con(cid:173)
`sidered in connection with the accompanying drawings. in
`which like reference numerals designate like parts through(cid:173)
`out the figures thereof and wherein:
`FIG. lA is a schematic diagram showing the basic prin(cid:173)
`ciples of the present invention using a single emitter and
`. multiple detectors;
`FIG. lB shows an alternative approach using multiple
`emitters and a single detector;
`FIG. 2 is a closeup perspective view of a portion of the
`patient contact element;
`FIG. 3 is a partially sectioned view showing the operation
`of the present invention in vivo;
`FIG. 4 is an overall block diagram showing the major
`components of an operational system employing the present
`invention;
`FIG. 5 is a timing diagram for the operation of the
`embodiment of FIG. 4;
`FIG. (i is a graph of absorptivity vs. wavelength for
`various different oxygen saturation levels within the range of
`operation of the present invention; and
`FIG. 7 is a graph comprising calculated oxygen saturation
`values using the principles of the invention for deep and
`shallow tissue measurements. and values obtained without
`using the principles of the invention.
`
`55
`
`SUMMARY OF THE INVENTION
`The present invention overcomes the disadvantages found
`in the prior art by providing a pulse oximetry system for the 65
`determination of arterial blood oxygen saturation level at a
`particular depth of tissue which readily compensates for
`
`DEfAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`FIG. 1A is a schematic diagram showing the principles of
`operation of the present invention. In this example. it is
`
`Petitioner Apple Inc. – Ex. 1008, p. 10
`
`

`

`3
`assumed desirable to measure the percentage of oxygen
`saturation within the arterial blood of patient 10 at subder(cid:173)
`rnal tissue level 12 having light absorption properties ub.
`Interposed between the non-invasive monitoring and mea(cid:173)
`surement system (not shown) and subdermal tissue level 12. 5
`is skin or surface tissue level 14 having light absorption
`properties ua. It is deemed desirable to measure arterial
`oxygen saturation in the tissue layer 12 or the tissue layer 14
`independently.
`According to a first preferred embodiment, ·emitter 16 10
`transmits electromagnetic radiation in the visible and near
`infrared region at two predetermined wavelengths (e.g. 660
`nm and 905 nm). Emitter 16 is shown as a single entity in
`this example. However. different emitters may be used for
`the different predetermined wavelengths. if desired. If more l5
`than one emitter is used, it is most convenient that they be
`co-located to simulate a single point source. LED's are a
`preferred type of emitter. The signals from emitter 16 travel
`generally along path 18 to a first detector 20 and along path
`22 to a second detector 24 as shown. The length of path 18 20
`within layer 12 (with absorption ub) is shown as L 1 and the
`length of path 22 within layer 12 is shown as L 2 •
`Detector 20 is spaced a distance of r1 from emitter 16 and
`detector 24 is spaced at a distance of r 2 •
`As can be seen in the drawing, both path 18 and path 22
`traverse skin layer 14 twice. Furthermore. because paths 18
`and 22 traverse skin layer 14 using approximately the same
`angle. the primary difference between paths 22 and 18 is the
`difference between length L2 and length L1 traversing sub- 30
`dermal layer 12, which is the tissue layer of interest
`Therefore, it can be assumed that the difference in absorp(cid:173)
`tion between path Li and path L 1 is directly attributable to
`subderrnal layer 12. the tissue layer of interest, correspond(cid:173)
`ing to the different spacings r2 and r 1 •
`The path length through skin layer 12 may be represented
`by 1 and the deeper path through the subdermal tissue by L 1
`and L 2, depending on which detector is considered. Note
`that multiple emitters may transmit to a single detector as
`discussed below in relation to FIG. lB. Following the 40
`formalism of Beer's Law. the signal detected at D 1 20 is
`given by:
`
`5,746,206
`
`4
`layers vary with time following the cardiac cycle, and that
`the two layers may additionally have different pulse ampli(cid:173)
`tudes. Assume the background venous blood concentration
`does not vary with the cardiac cycle. Taken at any conve(cid:173)
`nient point in time ( e.g. maxima or minima of the cardiac
`cycle), the logarithm of equation 2, considering equation 3,
`becomes:
`
`ln(I, (t,) FI..-2(J\0 ,..,., [ c.,(t,) ]...,+JI •. ,_( c 0 J,,..n)l-{Jl6,o,.,( cb(t,) 1,..,+Jl.,
`(4)
`-[c.J,_)1,1
`Subtracting the signal observed at a second point in time.
`this expression simplifies:
`
`(5)
`
`where ll.[clart=lc(t 1)larr-lc(ti)larr Recalling that we assume
`the contribution of the skin layer has the same influence on
`both detectors, we can write a similar expression for the
`signals observed at detector D 2 :
`
`ln(l,(1 1) )-ln(l,(t,) F-2(Jl • ..,..A[ c 0 )-)l-{Jl._,'1[c•L,..,)L,
`Subtracting equation 6 from equation 5, we find:
`
`(6)
`
`[ln(I1 (t1 ))-ln(I1 (t,)) ]-[ln(l,(t 1) )-ln(l,(t2 )) ]=Jl6..,,,.i[c6 1.,,,(L,-L1) (7)
`Notice that the contribution of the skin layer has been
`eliminated. Finally, the measurements are repeated at a
`second wavelength. Taking the ratio of equation 7 evaluated
`at two wavelengths gives:
`
`25
`
`R=([ln(I1 (t1 ))-ln(I1 (t,)) ]-[ln(L.,(t1) )-ln(l,(t,) )fo,/([ln(l1 (t1 ))-ln(l1,
`(t,))]-[ln(l,(t,))-ln(l,(t,))lh..=Jlb,orl).l(L, -L,),..,!Jlb,orl.).2(1,,-
`(8)
`L,)u
`Equation 8 is equivalent to conventional pulse oxirnetry if
`the second detector is eliminated. In the conventional.
`nonscattering. model of oximetry, it is assumed that the
`35 average path lengths are equal at the two wavelengths-and
`they would simply drop out of equation 8. The model is
`improved, however, if the ratio of the average path lengths.
`or in this case the ratio of the difference lengths, is kept as
`an empirically determined correction factor:
`
`where M.-=L2-L1• In conventional pulse oximetry, the ratio
`of average path lengths is stable over a useful (but limited)
`saturation range. With the proper choice of wavelengths. this
`useful range can be engineered to cover specific meaningful
`clinical windows (e.g., 70-100% saturation or 40-60%
`saturation).
`The extinction coefficient can be rewritten in oxygen
`50 saturation terminology as:
`Jl=S. Jl...,,+(l-S).Jl,.4
`
`(9)
`
`(10)
`
`45
`
`11=I.,exp(-u,.1).cxp(-u,,L 1).exp(-u,,I)
`which describes the attenuation of the signal traveling twice
`through the skin layer 14 and once through the subdermal
`tissue 12 where:
`11=the detected light intensity at D 1
`l 0 =the emitted light intensity of emitter E
`u,,=the characteristic absorption of layer 14
`ub=the characteristic absorption of layer 12
`l=the path length through layer 14
`L1=the path length through layer 12
`The absorption coefficients can be rewritten as the product 55
`of the concentration of an absorbing constituent, [ c ]. and its
`extinction coefficient ~- In this case, [ c] is the concentration
`of total hemoglobin in the tissue. Allowing for different
`concentrations in the two layers, equation 1 becomes:
`
`(1)
`
`(2)
`
`Where
`S=[O2Hb]/([O 2Hb]+[Hbl) and where
`~oxy refers to oxygenated hemoglobin (O 2Hb) and
`~- refers to reduced hemoglobin (Hb)
`From this point on in the derivation. everything follows
`the conventional approach to pulse oximetry, applying equa-
`60 tion 10 to 9, and solving for S(SP,O:i) in terms of the
`observation R:
`
`To include the venous contribution, ~[ c] expands as follows:
`
`(3) 65
`Jl[c] becomes ~~c]°" +Jl-[c]...,
`Next is added the feature of pulse oximetry. Consider that
`the arterial blood concentration in both upper and lower
`
`(11)
`SPO,=[J\...,ru-R. Jl..-1]/[R.(Jl...,,M-Jl...ru)-Jl...,,u+Jl,..,d
`In equation 11, the ratio of M.,' s has been absorbed into the
`appropriate W s as these will ultimately be determined
`empirically according to a preferred embodiment of the
`invention.
`
`Petitioner Apple Inc. – Ex. 1008, p. 11
`
`

`

`5,746.206
`
`5
`This result differs from the conventional single detector
`pulse oximetry algorithm in that the skin layer signals are
`excluded from the measurement. regardless if the skin
`pulses or is non-pulsatile (e.g .• vasoconstriction or
`exsanguination). Within the limitations of the assumptions 5
`made. as long as the upper skin layer does not create a shunt,
`and the deeper layer continues to pulse. this algorithm gives
`a result related only to the arterial blood saturation of the
`deeper tissue.
`The separation of the first emitter/detector pair 16,20 (i.e. 10
`r 1 ) and the second emitter/detector pair 16.24 (i.e. r2) should
`be larger than several times the skin thickness (i.e. r 1 .r2
`much greater than d) so that the four occurrences of are all
`approximately equal, or at least have equivalent counterparts
`influencing the two detectors. The detector separation from 15
`the emitter should also be large enough to probe "deep"
`enough, the probed depth somewhat less than the separation.
`The two detectors should not be too far separated from one
`another, however. or else the assumption of equivalent skin
`thickness may be violated. If the detectors are too close to 20
`each other, M., becomes O and the measurement becomes
`unstable (see equation 9).
`It is also possible to solve for the skin's saturation
`explicitly. excluding the contribution of deeper pulsating
`tissues. Instead of subtracting equation 6 from 5. multiply 25
`equation 5 by L 2 and equation 6 by L 1• then subtract to form:
`
`L,.[ln(I,(t,))-ln(I,(½))}-L,.[ln(l,(t,))-ln(l,(½))J=2(L,-L,)lll~
`(12)
`[c0 ] , . .
`The quotient of equation 12. evaluated at the two wave- 30
`lengths becomes:
`
`(L,.ln[I1(t1yI1(½)]-L1 .ln[I2 ) (½Ylo(½)l)u/(L,.ln{I1(t1yI1(½)]-L1 .In
`(13)
`[l,(t,Yl:,(½)l)u=[(IM.,)u/(IM.,)u-(lla,artA,/I!..,...,.>.,)
`
`Now, utilizing the concept of the path length multiplier.
`defined as Ur. M will refer to the subdermal tissue and m for
`the skin layer. If M.. is much less than r 1, one can approxi(cid:173)
`mate that the path length multipliers are the same for the two
`detectors. This leaves us with:
`
`(14a)
`
`(14b)
`
`6
`mechanical means known in the art. Further. if desirable,
`surface 28 may have a curvature, and may be either flexible
`or rigid.
`During the time that planar surface 28 is in position,
`emitter 16. detector 20. and detector 24 are in direct contact
`with the skin of the patient ( see also F1G. 1 ). The spacing of
`emitter 16. detector 20. and detector 24 are as previously
`discussed.
`Wiring, not shown in this view. electrically couples emit(cid:173)
`ter 16. detector 20. and detector 24 to the circuitry which
`performs the monitoring functions.
`F1G. 3 is a partially sectioned view showing patient
`interface device 26 in operational position. Cable 32 con(cid:173)
`ducts the electrical signals to and from the monitoring
`circuitry as described below. All other elements are as
`previously described.
`F1G. 4 is a block diagram showing the entire monitoring
`and measurement system employing the present invention.
`According to a first preferred embodiment. multiplexer 36
`and two wavelength driver 34 alternately turn on the red and
`infrared LED's 16 at a desired chop frequency (e.g. 1.600
`hz). These red and infrared signals are detected by detectors
`20 and 24 and amplified by current-to-voltage amplifiers 38
`and 40. The outputs of transconductance amplifiers 38 and
`40 are demultiplexed by DMUX 42 so as to generate a first
`and second wavelength signal for each of detectors D 1 (20)
`and D 2 (24). which generated signals are sent through
`integrating amplfiers 49, 51. 53 and 55 to be placed on,
`respectively. lines 50. 52. 54 and 56. These first and second
`wavelength signals are digitized by Analog/Digital Con(cid:173)
`verter 46. The digitized signals are transmitted to CPU 48 for
`calculating arterial oxygen saturation. A preferred architec(cid:173)
`tural implementation of the control electronics is disclosed
`in PCT/US94/03546. the disclosure of which is incorporated
`35 herein by reference. Alternate control electronics are known
`in the art and could be used. if desired.
`As previously described, if deep tissue properties are
`desired. CPU 48 calculates R using equation 8 and SPO2
`using equation 11 with constants ~re.t.)..2•~nod.).l•~oxy.M• and
`40 ~ 0 %)'.A.2 being stored in CPU memory. having been previously
`determined empirically. If shallow tissue properties are
`desired. CPU 48 calculates R using equation 15 and SPO2
`using equation 11.
`According to a preferred embodiment. CPU 48 identifies
`and qualifies arterial pulses from the signals D 1• A1; D 1, ½;
`D2 , A.1• D 2, ½ using any of the signal processing techniques
`described in U.S. Pat. Nos. 4,869.254; 5,078.136; 4.911.167;
`4,934.372; 4,802,486; and 4.928,692, the disclosures of
`which are all incorporated herein by reference.
`In addition, though R is determined in equations (8). ( 15)
`using maximum and minimum intensities occurring during
`the cardiac cycle. other points in the cardiac cycle could be
`utilized as well. including adjacent digital points using
`derivative signal processing techniques described in PCf/
`ss US94/03546 cited above.
`According to a preferred embodiment. one wavelength is
`chosen from the red portion of the electromagnetic spectrum
`( e.g. 660 nm) and the other wavelength is chosen from the
`near infrared portion of the electromagnetic spectrum (e.g.
`60 900 nm). The precise wavelength values are a matter of
`design choice depending on the application. For sensors for
`detecting fetal arterial oxygen saturation. a preferred wave(cid:173)
`length pair is 735 nm, 905 nm, as disclosed in U.S. patent
`application Ser. No. 08/221.911, the disclosure of which is
`65 incorporated herein by reference.
`F1G. 5 is a timing diagram for the apparatus of F1G. 4. The
`clock signal. containing pulses 58, 60, 62, and 64, is
`
`Substituting these definitions into equation 13 simplifies the 45
`result into a more useful form:
`
`R=(r2.ln[l,(t1yI1(½)]-r1.ln[I2(t1)11,(½)DA,/(r2.ln(I1(t,(t1Y11(½)]-
`(15)
`r,.ln[l,(t1Yle,(t,)]),.,=mA1/mu.fl..,...,,ull!0,..,..l2
`
`As with the subdermal calculation. the ratio of m)..ifmA-2 can 50
`be absorbed into the empirically determined constants. And
`just as in the previous calculation. the path-length-multiplier
`ratio is adequately stable over limited, but useful. windows
`of saturation. The positioning of the two detectors takes on
`more importance here, and thus would need to be reproduc(cid:173)
`ible in a preferred sensor embodiment. Calculation of SP02
`follows in the same manner as in equations 9 through 11.
`F1G. 1B is a schematic diagram. similar to F1G. IA,
`showing the present invention employing multiple emitters
`16 and 17 and a single detector 24. Those of skill in the art
`will appreciate that the operation is similar to that described
`above.
`F1G. 2 is a perspective view of the preferred mode of
`patient interface device 26 employing the present invention.
`Planar surface 28 is placed into contact with the skin of the
`patient during monitoring and measurement. If desirable,
`this position may be maintained via adhesive or other
`
`Petitioner Apple Inc. – Ex. 1008, p. 12
`
`

`

`5,746,206
`
`7
`produced by Pattern Generator 44 (see also FIG. 4). The
`clock pulses are preferably produced at a rate of about 1600
`hz. Each of the clock pulses triggers an output of emitter 16
`as shown by pulses 66, 68. 70, and 72. The first wavelength
`is emitted twice corresponding to timing signals 74 and 76. 5
`Thereafter. the second wavelength is emitted twice corre(cid:173)
`sponding to timing signals 78 and 80.
`The signal from the first wavelength as received by
`detector 20 is gated to Analog/Digital converter 46 by
`DMUX 42 via line 50 during times 82 and 83. The signal 10
`produced by the first wavelength as received by detector 24
`is gated over line 54 at times 81 and 86. Similarly. the signal
`from the second wavelength emission is gated over lines 52
`and 54 from detectors 20 and 24 at times 84 and 85, and
`times 87 and 88, respectively. The received signals are 15
`converted to digital form and transferred to CPU 48 for
`calculation of the oxygen saturation level.
`FIG. 6 is a graphical representation of the absorptivities of
`the various saturation levels of arterial blood as a function of
`wavelength of emitter 16. The wavelengths preferred in the 20
`instant invention are about 660 nm and about 905 nm.
`However. those of skill in the art will readily appreciate that
`the present invention may be satisfactorily practiced using
`other wavelengths.
`FIG. 7 is a graph illustrating data obtained from computer 25
`models of arterial oxygen saturation calculated using tradi(cid:173)
`tional techniques for a single detector, and using first and
`second detectors as described in FIG. 1. As can be seen, the
`ratios of the Deep track very closely with the ratios from the
`conventional system.
`Though the invention has been primarily described by
`reference to an apparatus having a single emitter area 16
`which emits light of at least two differing and known
`wavelengths. and first and second separated detector areas
`20. 24. it will be appreciated that the three sensor areas could 35
`also be achieved by having a single detector area and first
`and second separated emitter areas, each of which emit light
`at first and second differing and known wavelengths, as
`illustrated in FIG. 1B. According to a preferred embodiment,
`the signals are transmitted by the emitters and detected by 40
`the detectors using standard time signal multiplex
`techniques. though other signal multiplex techniques could
`alternately be used if desired (e.g. frequency multiplex). In
`addition, increased resolution between differing tissue layers
`is achievable if increased number of sensor areas is utilized. 45
`For example, a half dozen or more detector areas could be
`utilized in combination with a single emitter area, or half
`dozen or more dual wavelength emitter areas could be
`utilized in combination with a single detector area. In
`addition. the sensor areas could be aligned in a linear array, 50
`either straight or curved, or could be disposed in a two(cid:173)
`dimensional array. Each different emitter/detector spacing
`pair could be used to calculate an oxygen saturation using
`different pulse oximetry signal processing methodologies as
`disclosed. and these multiple saturation values could be 55
`processed to image the tissue layers beneath the sensor areas
`or to reveal other desired information regarding these tissue
`layers.
`Having thus described the preferred modes of the present
`invention, those of ordinary skill in the art will be readily 60
`able to think of yet other embodiments within the scope of
`the claims hereto attached and wherein:
`I claim:
`1. An apparatus comprising:
`a. a patient interface adapted to be coupled to a patient; 65
`b. an emitter of electromagnetic radiation coupled to said
`patient interface;
`
`30
`
`8
`c. a first detector coupled to said patient interface at a first
`distance from said emitter;
`d. a second detector coupled to said patient interface at a
`second distance from said emitter;
`e. means for synchronizing an oxygen saturation mea(cid:173)
`surement to a predetermined portion of a cardiac cycle
`of said patient; and
`f. means coupled to said first and said second detectors
`and said synchronizer for computing an oxygen satu(cid:173)
`ration level of arterial blood of said patient. at a
`predetermined tissue level of interest. with an algo(cid:173)
`rithm that filters out pulsatile signal contributions from
`a second predetermined tissue level.
`2. An apparatus according to claim 1 wherein said emitter
`emits a plurality of predetermined wavelengths of electro(cid:173)
`magnetic radiation.
`3. An apparatus according to claim 2 wherein said emitter
`emits two predetermined wavelengths of electromagnetic
`radiation.
`4. A pulse oximeter apparatus for calculating arterial
`oxygen saturation, comprising:
`a. a patient interface adapted to be coupled to a patient and
`including at least three sensor areas for emitting elec(cid:173)
`tromagnetic radiation which penetrates tissue of the
`patient and detects that electromagnetic radiation scat(cid:173)
`tered by the tissue, a first spacing being between a first
`combination of electromagnetic emitter which emits at
`least two wavelengths and electromagnetic detector a
`second spacing being between a second combination of
`electromagnetic emitter which emits at least two wave(cid:173)
`lengths and electromagnetic detector, the first spacing
`being different from the second spacing; and
`b. means for calculating an arterial oxygen saturation
`level of the patient in response to the detected electro(cid:173)
`magnetic radiation, at a predetermined tissue level of
`interest. with an algorithm that filters out pulsatile
`signal contributions from a second predetermined tis(cid:173)
`sue level.
`5. A method of measuring oxygen saturation level of
`arterial blood at a measurement site of a patient comprising:
`a. determining a time of arrival of an arterial pulse
`wavefront at the measurement site of the patient;
`b. emitting a first wavelength of electromagnetic radiation
`at the measurement site of the patient;
`c. measuring an amplitude of the first wavelength of
`electromagnetic radiation at a first detector located at a
`first distance from the measurement site;
`d. measuring an amplitude of the first wavelength of
`electromagnetic radiation at a second detector located
`at a second distance from the measurement site;
`e. emitting a second wavelength of electromagnetic radia(cid:173)
`tion at the measurement site of the patient;
`f. measuring an amplitude of the second wavelength of
`electromagnetic radiation at the first detector located at
`the first distance from the measurement site;
`g. measuring an amplitude of the second wavelength of
`electromagnetic radiation at the second detector located
`at the second distance from the measurement site;
`h. computing an arterial oxygen saturation level, at a
`predetermined tissue level of interest, with an algo(cid:173)
`rithm that filters out pulsatile signal contributions from
`a second predetermined tissue level, using the ampli(cid:173)
`tudes of the first wavelength measured at the first
`detector