(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY(PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`11 April 2002 (11.04.2002)
`
`
`
`PCT
`
`(10) International Publication Number
`WO 02/28274 Al
`
`(51) International Patent Classification’:
`
`A61B 5/00
`
`(21) International Application Number:
`
`=PCT/US01/26642
`
`(22) International Filing Date: 27 August 2001 (27.08.2001)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(81) Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM,DZ, EC, EE, ES, FI, GB, GD, GE, GH,
`GM,HR, HU,ID,IL,IN,IS, JP, KE, KG, KP, KR, KZ, LC,
`LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW,
`MX, MZ, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK,
`SL, TI, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA,
`ZW.
`
`(84) Designated States (regional); ARIPO patent (GH, GM,
`KE, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`(30) Priority Data:
`
`
`138884 5 October 2000 (05.10.2000)—IL patent (AM, AZ, BY, KG, KZ, MD,RU, TJ, TM), European
`patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR,IE,
`(71) Applicant (for all designated States except US): CYBRO
`OG Oy ae One naeNeen
`MEDICAL LTD. [ILL]; Matam Building 30, 31905
`oo
`>
`>
`»
`GQ,
`>
`>
`:
`>
`>
`>
`Haifa (IL).
`TG).
`
`(72) Inventor; and
`(for US only); MENDELSON,
`(75) Inventor/Applicant
`Yizhak [US/US]; 31 Whisper Drive, Worcester, MA
`01609 (US).
`
`Published:
`with international search report
`before the expiration of the time limit for amending the
`claims and to be republished in the event of receipt of
`amendments
`
`(74) Agents: YEE, James, R.et al.; Howard & Howard Attor-
`neys, P.C., Suite 101, The Pinehurst Office Center, 39400
`Woodward Avenue, Bloomfield Hills, MI 48304-5151
`(US).
`
`For two-letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes andAbbreviations" appearing at the begin-
`ning ofeach regular issue ofthe PCT Gazette.
`
`2/28274Al
`
`So
`
`S
`
`(54) Title: A PULSE OXIMETER AND A METHOD OFITS OPERATION
`
`(57) Abstract: A sensorfor use in an optical measurementdevice and a method for non-invasive measurementof a blood parameter.
`The sensor includes sensor housing, a source of radiation coupled to the housing, and a detector assembly coupled to the housing.
`The source ofradiation is adapted to emit radiation at predetermined frequencies. The detector assemblyis adapted to detect reflected
`radiation at least one predetermined frequency and to generate respective signals. The signals are use to determine the parameter of
`the blood.
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`1
`
`A PULSE OXIMETER AND A METHODOF ITS OPERATION
`
`BACKGROUND OF THE INVENTION
`
`Field of the Invention
`
`This invention is generally in the field ofpulse oximetry, andrelates to a sensor
`
`for use in a pulse oximeter, and a method for the pulse oximeter operation.
`
`Background ofthe Invention
`
`Oximetry is based on spectrophotometric measurements of changes in the
`
`10
`
`color of blood, enabling the. non-invasive determination of oxygen saturation in the
`
`patient’s blood. Generally, oximetry is based on the fact that the optical property of
`
`blood in the visible (between 500 and 700nm) and near-infrared (between 700 and
`
`1000nm) spectra dependsstrongly on the amount of oxygen in blood.
`
`Referring to Fig. 1, there is illustrated a hemoglobin spectra measured by
`
`15
`
`oximetry based techniques. Graphs G1 and G2 correspond,respectively, to reduced
`
`hemoglobin,
`
`or deoxyhemoglobin (Hb),
`
`and oxygenated hemoglobin,
`
`or
`
`oxyhemoglobin (HbO,), spectra. As shown, deoxyhemoglobin (Hb) has a higher optical
`
`extinction (i.e., absorbs more light) in the red region of spectrum around 660nm, as
`
`compared to that of oxyhemoglobin (HbO,). On the other hand, in the near-infrared
`
`20
`
`region ofthe spectrum around 940nm,the optical absorption by deoxyhemoglobin (Hb)
`
`is lowerthan the optical absorption of oxyhemoglobin (HbO.,).
`
`Prior art non-invasive optical sensors for measuring arterial oxyhemoglobin
`
`saturation (SaO,) by a pulse oximeter(termed SpO,) are typically comprised ofa pair
`
`of small and inexpensive light emitting diodes (LEDs), and a single highly sensitive
`
`25
`
`silicon photodetector. A red (R) LED centered on a peak emission wavelength around
`
`660nm and an infrared (IR) LED centered on a peak emission wavelength around
`
`940nm are used as light sources.
`
`Pulse oximetry relies on the detection of a photoplethysmographic signal
`
`caused by variations in the quantity of arterial blood associated with periodic
`
`30
`
`contraction and relaxation ofa patient’s heart. The magnitudeofthis signal depends on
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`2
`
`the amount ofblood ejected from the heart into the peripheral vascular bed with each
`
`systolic cycle, the optical absorption of the blood, absorption by skin and tissue
`
`components, and the specific wavelengthsthat are used to illuminate the tissue. SaO,
`
`is determined by computing the relative magnitudes of
`
`the R and IR
`
`photoplethysmograms. Electronic circuits inside the pulse oximeter separate the R and
`
`IR photoplethysmogramsinto their respective pulsatile (AC) and non-pulsatile (DC)
`
`signal components. An algorithm inside the pulse oximeter performs a mathematical
`
`normalization by which the time-varying AC signal at each wavelength is divided by
`
`the corresponding time-invariant DC component which results mainly from thelight
`
`10
`
`absorbed and scattered by the bloodlesstissue, residual arterial blood whenthe heart is
`
`in diastole, venous blood and skin pigmentation.
`
`Since it is assumed that the AC portion results only from the arterial blood
`
`component, this scaling process provides a normalized R/IR ratio (i.e., the ratio of
`
`AC/DC values corresponding to R- and IR-spectrum wavelengths, respectively), which
`
`15
`
`is highly dependent on SaO., but is largely independent ofthe volumeofarterial blood
`
`entering the tissue during systole, skin pigmentation, skin thickness and vascular
`
`structure. Hence, the instrument does not needto be re-calibrated for measurements on
`
`different patients. Typical calibration of a pulse oximeteris illustrated in Fig. 2 by
`presenting the empirical relationship between SaO, and the normalized R/IR ratio,
`which is programmed by the pulse oximeters' manufacturers.
`
`20
`
`Pulse oximeters are of two kinds operating, respectively, in transmission and
`
`reflection modes.In transmission-modepulse oximetry, an optical sensor for measuring
`
`SaO, is usually attached across a fingertip, foot or earlobe, such that the tissue is
`
`sandwiched between the light source and the photodetector.
`
`25
`
`In reflection-mode or backscatter type pulse oximetry, as shownin Fig, 3, the
`
`LEDsand photodetector are both mounted side-by-side next to each other on the same
`
`planar substrate. This arrangement allows for measuring SaO, from multiple convenient
`
`locations on the body (e.g. the head, torso, or upper limbs), where conventional
`
`transmission-mode measurements are not feasible. For this reason, non-invasive
`
`30
`
`reflectance pulse oximetry has recently become an important new clinical technique
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`3
`
`with potential benefits in fetal and neonatal monitoring. Using reflectance oximetry to
`
`monitor SaO, in the fetus during labor, where the only accessible location is the fetal
`
`scalp or cheeks, or on the chest in infants with low peripheral perfusion, provides
`
`several more convenient locations for sensor attachment.
`
`Reflection pulse oximetry, while being based on similar spectrophotometric
`
`principles as the transmission one, is more challenging to perform and has unique
`
`problemsthat can not always be solved by solutions suitable for solving the problems
`
`associated with the transmission-mode pulse oximetry. Generally, comparing
`
`transmission and reflection pulse oximetry, the problems associated with reflection
`
`10
`
`pulse oximetry consist of the following:
`
`In reflection pulse oximetry, the pulsatile AC signals are generally very small
`
`and, depending on sensor configuration and placement, have larger DC components as
`
`compared to those of transmission pulse oximetry. Asillustrated in Fig. 4, in addition
`
`to the optical absorption and reflection due to blood, the DC signal of the R and IR
`
`15
`
`photoplethysmogramsin reflection pulse oximetry can be adversely affected by strong
`
`reflections from a bone. This problem becomes more apparent when applying
`measurements at such body locations as the forehead and the scalp, or when the sensor
`is mounted on the chest over the ribcage. Similarly, variations in contact pressure
`
`between the sensor andthe skin can cause largererrorsin reflection pulse oximetry (as
`
`20
`
`compared to transmission pulse oximetry) since some of the blood near the superficial
`
`layers of the skin may be normally displaced away from the sensor housing towards
`
`deeper subcutaneousstructures. Consequently, the highly reflective bloodless tissue
`
`compartment near the surface of the skin can cause large errors even at body locations
`
`where the boneis located too far away to influencethe incident light generated by the
`
`25
`
`sensor.
`
`Another problem with currently available reflectance sensorsis the potential
`
`for specular reflection caused by the superficial layers of the skin, when an air gap
`exists betweenthe sensorandthe skin, or by direct shunting oflight between the LEDs
`and the photodetector through a thin layer of fluid which may be due to excessive
`
`30
`
`sweating or from amniotic fluid present during delivery.
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`4
`
`It is important to keep in mind the two fundamental assumptions underlying
`
`the conventional dual-wavelength pulse oximetry, which are as follows:
`
`(1) the path of light rays with different illuminating wavelengthsin tissue are
`
`substantially equal and,
`
`therefore, cancel each other; and (2) each light source
`
`illuminates the same pulsatile changein arterial blood volume.
`
`Furthermore,
`
`the correlation between optical measurements and tissue
`
`absorptions in pulse oximetry are based on the fundamental assumption that light
`
`propagation is determined primarily by absorbance due to Lambert-Beer’s law
`neglecting multiple scattering effects in biological tissues. In practice, however, the
`
`10
`
`optical paths of different wavelengths in biological tissues is known to vary more in
`
`reflectance oximetry compared to transmission oximetry, sinceit strongly depends on
`
`the light scattering properties ofthe illuminated tissue and sensor mounting.
`
`Several human validation studies, backed by animal investigations, have
`
`suggested that uncontrollable physiological and physical parameters can cause large
`
`15
`
`variations in the calibration curve of reflectance pulse oximeters primarily at low
`
`oxygen saturation values below 70%. It was observed that the accuracy of pulse
`
`oximeters in clinical use might be adversely affected by a numberofphysiological
`
`parameters when measurements are made from sensors attached to the forehead, chest,
`
`or the buttock area. While the exact sources ofthese variations are not fully understood,
`
`20
`
`it is generally believed that there are a few physiological and anatomical factors that
`
`may be the major source oftheseerrors.It is also well known for examplethat changes
`
`in the ratio ofblood to bloodless tissue volumes may occur through venous congestion,
`
`vasoconstriction/vasodilatation, or through mechanical pressure exerted by the sensor
`
`on theskin.
`
`25
`
`Additionally, the empirically derived calibration curve of a pulse oximeter can
`
`bealtered by the effects of contact pressure exerted by the probe on the skin. This is
`associated with the following. The light paths in reflectance oximetry are not well
`
`defined (as compared to transmission oximetry), and thus may differ between the red
`
`and infrared wavelengths. Furthermore, the forehead and scalp areas consist of a
`
`30
`
`relatively thin subcutaneous layer with the cranium bone underneath, while the tissue
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`5
`
`of other anatomicalstructures, such as the buttock and limbs, consists of a much thicker
`
`layer of skin and subcutaneous tissues without a nearby bony support that acts as a
`
`strong light reflector.
`
`Several in vivo and in vitro studies have confirmed that uncontrollable
`
`physiological and physical parameters (e.g., different amounts of contact pressure
`
`applied by the sensor on the skin, variation in the ratio of bloodless tissue-to-blood
`
`content, or site-to-site variations) can often causelarge errors in the oxygensaturation
`readings of a pulse oximeter, which are normally derived based onasingle internally-
`
`programmed calibration curve. The relevant in vivo studies are disclosed in the
`
`10
`
`following publications:
`
`1. Dassel, et al., “Effect of location of the sensor on reflectance pulse
`
`oximetry”, British Journal of Obstetrics and Gynecology, vol. 104, pp. 910-916, (1997);
`
`2. Dassel, et al., “Reflectance pulse oximetry at the forehead of newborns: The
`
`influence ofvarying pressure on the probe”, Journal of Clinical Monitoring, vol. 12, pp.
`
`15
`
`421-428, (1996).]
`
`The relevant in vitro studies are disclosed, for example in the following
`
`publication:
`
`3. Edrichetal., “Fetal pulse oximetry: influenceoftissue blood content and
`
`hemoglobin concentration in a new in-vitro model”, European Journal of Obstetrics and
`
`20
`
`Gynecology and Reproductive Biology, vol. 72, suppl. 1, pp. S29-S34, (1997).
`
`Improved sensors for application in dual-wavelength reflectance pulse
`
`oximetry have been developed. As disclosed in the following publication: Mendelson,
`
`et al., “Noninvasive pulse oximetry utilizing skin reflectance photoplethysmography”,
`
`IEEE Transactions on Biomedical Engineering, vol. 35, no. 10, pp. 798-805 (1988), the
`
`25
`
`total amount of backscattered light that can be detected by a reflectance sensor is
`
`directly proportional to the number of photodetectors placed around the LEDs.
`
`Additional improvements in signal-to-noise ratio were achieved by increasing the active
`
`area of the photodetector and optimizing the separation distance between the light
`
`sources and photodetectors.
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`6
`
`Another approach is based on the use of a sensor having six photodiodes
`
`arranged symmetrically around the LEDsthatis disclosed in the following publications:
`
`4, Mendelson, et al., “Design and evaluation of a new reflectance pulse
`
`oximeter sensor”, Medical Instrumentation, vol. 22, no. 4, pp. 167-173 (1988); and
`
`5. Mendelson,et al., “Skin reflectance pulse oximetry: in vivo measurements
`
`from the forearm and calf’, Journal of Clinical Monitoring,vol. 7, pp. 7-12, (1991).
`
`According to this approach, in order to maximize the fraction of backscattered
`
`light collected by the sensor, the currents from all six photodiodes are summed
`
`electronically by internal circuitry in the pulse oximeter. This configuration essentially
`
`10
`
`creates a large area photodetector made ofsix discrete photodiodes connected in parallel
`
`to producea single current that is proportional to the amountof light backscattered from
`
`the skin. Several studies showed that
`
`this sensor configuration could be used
`
`successfully to accurately measure SaO, from the forehead, forearm and the calf on
`
`humans. However, this sensor requires a means forheating the skin in order to increase
`
`15
`
`local blood flow, which haspractical limitations since it could cause skin burns.
`Yet another prototype reflectance sensor is based on eight dual-wavelength
`LEDsand a single photodiode,andis disclosed in the following publication: Takatani
`
`et al., “Experimental and clinical evaluation of a noninvasivereflectance pulse oximeter
`
`sensor”, Journal of Clinical Monitoring, vol. 8, pp. 257-266 (1992). Here, four R and
`
`20
`
`four IR LEDsare spaced at 90-degree intervals around the substrate and at an equal
`radial distance from the photodiode.
`|
`
`A similar sensor configuration based on six photodetectors mounted in the
`
`center of the sensor around the LEDsis disclosed in the following publication: Konig,
`et al., “Reflectance pulse oximetry — principles and obstetric application in the Zurich
`system”, Journal of Clinical Monitoring, vol. 14, pp. 403-412 (1998).
`
`25
`
`According to the techniques disclosed in all of the above publications, only
`
`LEDsof two wavelengths, R and IR,are usedaslight sources, and the computation of
`
`SaO,is based onreflection photoplethysmograms measured bya single photodetector,
`
`regardless of whether one or multiple photodiodes chips are used to construct the
`
`30
`
`sensor. This is because of the fact that the individual signals from the photodetector
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`7
`
`elements are all summedtogether electronically inside the pulse oximeter. Furthermore,
`
`while a radially-symmetric photodetector array can help to maximize the detection of
`
`backscattered light from the skin and minimize differences from local
`
`tissue
`
`inhomogeneity, human and animal studies confirmed that this configuration can not
`
`completely eliminate errors caused by pressure differences and site-to-site variations.
`
`The use of a nominal dual-wavelength pair of 735/890nm wassuggested as
`
`providing the best choice for optimizing accuracy, as well as sensitivity in dual-
`
`wavelength reflectance pulse oximetry, in US 5,782,237 and 5,421,329. This approach
`
`minimizes the effects of tissue heterogeneity and enables to obtain a balance in path
`
`10
`
`length changesarising from perturbationsin tissue absorbance. Thisis disclosed in the
`
`following publications:
`
`6. Mannheimerat al., “Physio-optical considerations in the design offetal
`pulse oximetry sensors”, European Journal of Obstetrics and Gynecology and
`
`Reproductive Biology, vol. 72, suppl. 1, pp. S9-S19, (1997); and
`
`15
`
`7. Mannheimer at al., “Wavelength selection for low-saturation pulse
`
`oximetry”, IEEE Transactions on Biomedical Engineering, vol. 44, no. 3, pp. 48-158
`
`(1997)].
`
`However, replacing the conventional R wavelength at 660nm, which coincides
`
`with the regionof the spectrum wherethe difference between the extinction coefficient
`
`20
`
`of Hb and HbO,is maximal, with a wavelength emitting at 735nm, not only lowers
`
`considerably the overall sensitivity of a pulse oximeter, but does not completely
`
`eliminate errors due to sensor placement and varying contact pressures.
`
`Pulse oximeter probes of a type comprising three or more LEDsforfiltering
`
`noise and monitoring other functions, such as carboxyhemoglobin or variousindicator
`
`25
`
`dyes injected into the blood stream, have been developed and are disclosed, for.
`
`example, in WO 00/32099 and US 5,842,981. The techniques disclosed in these
`
`publications are aimed at providing an improved method for direct digital signal
`
`formation from input signals produced bythe sensor andforfiltering noise.
`
`Noneofthe above prior art techniques provides a solution to overcome the
`
`30
`
`mostessential limitation in reflectance pulse oximetry, which requires the automatic
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`8
`
`correction of the internal calibration curve from which accurate and reproducible
`
`oxygen saturation values are derived, despite variations in contact pressure or site-to-
`
`site tissue heterogeneity.
`
`In practice, most sensors used in reflection pulse oximetry rely on closely
`
`spaced LED wavelengthsin order to minimize the differencesin the optical path lengths
`
`of the different wavelengths. Nevertheless, within the wavelength range required for
`
`oximetry, even closely spaced LEDs with closely spaced wavelengths mounted on the
`
`same substrate can lead to large random errorin the final determination of SaO,.
`
`10
`
`SUMMARYOF THE INVENTION AND ADVANTAGES
`
`Theobject of the inventionis to provide a novel sensor design and method that
`
`functions to correct the calibration relationship of a reflectance pulse oximeter, and
`
`reduce measurement inaccuracies in general. Another object of the invention is to
`
`provide a novel sensor and methodthat functions to correct the calibration relationship
`
`15
`
`of a reflectance pulse oximeter, and reduce measurement inaccuracies in the lower
`
`range of oxygen saturation values (typically below 70%), which is the predominant
`
`range in neonatal and fetal applications.
`
`Yet another object of the present inventionis to provide automatic correction
`
`20
`
`of the internal calibration curve from which oxygen saturation is derived inside the
`oximeter in situations where variations in contact pressure or site-to-site tissue
`heterogeneity may cause large measurement inaccuracies.
`
`Another object of the invention is to eliminate or reduce the effect of
`
`variations in the calibration of a reflectance pulse oximeter between subjects, since
`
`perturbations caused by contact pressure remain one of the major sourcesof errors in
`
`25
`
`reflectance pulse oximetry. In fetal pulse oximetry, there are additional factors, which
`
`must be properly compensated for in order to produce an accurate and reliable
`
`measurement of oxygen saturation. For example,the fetal head is usually the presenting
`
`part, and is a rather easily accessible location for application of reflectance pulse
`
`oximetry. However, uterine contractions can cause large and unpredictable variations
`
`30
`
`in the pressure exerted on the head and by the sensor on the skin, which can lead to
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`9
`
`large errors in the measurement ofoxygen saturation by a dual-wavelength reflectance
`
`pulse oximeter. Another object of the invention is to provide accurate measurement of
`
`oxygen saturation in the fetus during delivery.
`
`The basis for the errors in the oxygen saturation readings of a dual-wavelength
`
`pulse oximeteris the fact that, in practical situations, the reflectance sensor applications
`
`affect the distribution ofblood in the superficial layers of the skin. This is different from
`
`an ideal situation, when a reflectance sensor measures light backscattered from a
`
`homogenous mixture of blood and bloodless tissue components. Therefore, the R and
`
`IR DC signals practically measured by photodetectors contain a relatively larger
`
`10
`
`proportion of light absorbed by andreflected from the bloodless tissue compartments.
`
`In these uncontrollable practical situations, the changes caused are normally not
`
`compensated for automatically by calculating the normalized R/IR ratio since the AC
`
`portions of each photoplethysmogram, and the corresponding DC components, are
`
`affected differently by pressure or site-to-site variations. Furthermore, these changes
`
`15
`
`depend not only on wavelength, but depend also on the sensor geometry, and thus
`
`cannotbe eliminated completely by computing the normalized R/IR ratio, as is typically
`
`the case in dual-wavelength pulse oximeters.
`
`The inventor has found that the netresult of this nonlinear effect is to cause
`
`large variationsin the slope ofthe calibration curves. Consequently, if these variations
`
`20
`
`are not compensated automatically, they will cause large errors in the final computation
`
`of SpO,, particularly at
`
`low oxygen saturation levels normally found in fetal
`
`applications.
`
`Another object of the present invention is to compensate for these variations
`
`and to provide accurate measurement of oxygen saturation. The invention consists of,
`
`25
`
`in addition to two measurement sessionstypically carried out in pulse oximetry based
`
`on measurements with two wavelengths centered around the peak emission values of
`
`660nm (red spectrum) and 940nm + 20nm (IR spectrum), one additional measurement
`
`sessionis carried out with an additional wavelength. At least one additional wavelength
`
`is preferably chosen to be substantially in the IR region of the electromagnetic
`
`30
`
`spectrum,i.e., in the NIR-IR spectrum (having the peak emission value above 700nm).
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`10
`
`In a preferred embodimentthe useofat least three wavelengths enables the calculation
`
`of an at least one additional ratio formed by the combination of the two IR wavelengths,
`
`which is mostly dependent on changesin contact pressure or site-to-site variations. In
`
`a preferred embodiment, slight dependenceoftheratio on variationsin arterial oxygen
`
`saturation that may occur, is easily minimizedor eliminated completely, by the proper
`
`selection and matching of the peak emission wavelengths and spectral characteristics
`
`of the at least two IR-light sources.
`
`Preferably, the selection of the IR wavelengths is based on certain criteria. The
`
`IR wavelengths are selected to coincide with the region of the optical absorption curve
`
`10
`
`where HbO,absorbsslightly morelight than Hb. The IR wavelengths are in the spectral
`
`regions where the extinction coefficients of both Hb and HbO,are nearly equal and
`
`remain relatively constant as a function of wavelength, respectively.
`
`In a preferred embodiment, tracking changes in the ratio formed by the two
`
`IR wavelengths, in real-time, permits automatic correction of errors in the normalized
`
`15
`
`ratio obtained from the R-wavelength and each of the IR-wavelengths. The term “ratio”
`
`signifies the ratio oftwo values of AC/DCcorresponding to two different wavelengths.
`This is similar to adding another equation to solve a problem with at least three
`unknowns(i.e., the relative concentrations ofHbO, and Hb, which are usedto calculate
`
`SaO,, and the unknown variable fraction of blood-to-tissue volumes that effects the
`
`20
`
`accurate determination of SaO,), which otherwise must rely on only two equations in
`
`the case of only two wavelengths used in conventional dual-wavelength pulse oximetry.
`
`In a preferred embodiment,a third wavelength provides the added ability to compute
`SaO, based on the ratio formed from the R-wavelength and either of the IR-
`wavelengths. In a preferred embodiment, changes in these ratios are tracked and
`
`25
`
`compared in real-time to determine which ratio produces a more stable or less noisy
`
`signal. That ratio is used predominantly for calculating SaO,.
`
`The present
`
`invention utilizes collection of light reflected from the
`
`measurement location at different detection locations arranged along a closed path
`
`aroundlight emitting elements, which can be LEDsorlaser sources. Preferably, these
`
`30
`
`detection locations are arranged in two concentric rings, the so-called “near” and “far”
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`11
`
`rings, aroundthe light emitting elements. This arrangementenables optimal positioning
`
`of the detectors for high quality measurements, and enables discrimination between
`
`photodetectors receiving “good” information (i.e, AC and DC values which would
`result in accurate calculations of SpO,) and “bad”information (i.e., AC and DC values
`
`which would result in inaccurate calculations of SpO,).
`
`There is thus provided according to one aspect of the present invention, a
`
`sensor for use in an optical measurement device for non-invasive measurements of
`
`blood parameters, the sensor comprising:
`
`(1) alight source for illuminating a measurement location with incident light
`
`10
`
`of at least three wavelengths,the first wavelength lying in a red (R) spectrum, and the
`
`at least second and third wavelengths lying substantially in the infrared (IR) spectrum;
`
`and
`
`(2) a detector assembly for detecting light returned from the illuminated
`
`location, the detector assembly being arranged soas to define a plurality of detection
`
`15
`
`locations along at least one closed path aroundthe light source.
`
`The term “closed path” used herein signifies a closed curve, like a ring,
`
`ellipse, or polygon, and thelike.
`
`The detector assembly is comprised ofat least one array of discrete detectors
`
`(e.g., photodiodes) accommodated along at least one closed path, or at least one
`
`20
`
`continuous photodetector defining the closed path.
`
`The term “substantially IR spectrum”used herein signifies a spectrum range
`
`including near infrared and infrared regions.
`
`According to another aspect ofthe present invention, there is provided a pulse
`
`oximeter utilizing a sensor constructed as defined above, and a control unit for
`
`25
`
`operating the sensor and analyzing data generated thereby.
`
`According to yet another aspect of the present invention, there is provided a
`
`method for non-invasive determination of a blood parameter, the method comprising
`
`the steps of:
`
`illuminating a measurementlocation with at least three different wavelengths
`
`30
`
`A1, 2 and 13, the first wavelength 41 lying in a red (R) spectrum, andtheat least
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`12
`
`second andat least third wavelengths 42 and 43 lying substantially in the infrared (IR)
`
`spectrum;
`
`detecting light returned from the measurementlocationat different detection
`
`locations and generating data indicative of the detected light, wherein said different
`
`detection locations are arranged so as to define at least one closed path around the
`
`measurement location; and
`
`analyzing the generated data and determining the blood parameter.
`
`10
`
`_ BRIEF DESCRIPTION OF THE DRAWINGS
`Other advantages of the present invention will be readily appreciated as the
`
`same becomesbetter understood by reference to the following detailed description when
`
`considered in connection with the accompanying drawings wherein:
`
`Fig. 1 illustrates hemoglobin spectra as measured by oximetry based techniques;
`
`Fig. 2 illustrates a calibration curve used in pulse oximetry as typically
`
`15
`
`programmedby the pulse oximeters manufacturers;
`
`Fig. 3 illustrates the relative disposition of light source and detector in
`
`reflection-modeor backscatter type pulse oximetry;
`Fig.4 illustrates light propagationin reflection pulse oximetry;
`
`Figs. 5A and 5B illustrate a pulse oximeterreflectance sensor operating under
`
`20
`
`ideal andpractical conditions, respectively;
`
`Fig. 6 illustrates variations of the slopes of calibration curves in reflectance
`
`pulse oximetry measurements;
`
`Fig. 7 illustrates an optical sensor according to the invention;
`
`Fig. 8 is a block diagram of the main components ofa pulse oximeter utilizing
`
`25
`
`the sensorofFig. 7;
`
`Fig. 9 is a flow chart of a selection process used in the signal processing
`
`technique accordingto the invention; and
`
`Figs. 10A to 10C are flow charts ofthree main steps, respectively, ofthe signal
`
`processing method according to the invention.
`
`30
`
`MASIMO2059
`
`Apple v. Masimo
`IPR2022-01466
`
`MASIMO 2059
`Apple v. Masimo
`IPR2022-01466
`
`

`

`WO 02/28274
`
`PCT/US01/26642
`
`13
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
`
`Referring to the Figures, wherein like numerals indicate like or corresponding
`
`parts throughout the several views, Figs. 1 and 2 illustrate typical hemoglobin spectra
`
`and calibrations curve utilized in the pulse oximetry measurements.
`
`The present invention provides a sensor for use in a reflection-mode or
`
`backscatter type pulse oximeter. The relative disposition of light source and detector in
`
`the reflection-mode pulse oximeterareillustrated in Fig. 3.
`
`Fig. 4 showslight propagationin the reflection-mode pulse oximeter where,
`
`in addition to the optical absorption and reflection due to blood, the DC signal of the
`
`10
`
`R and IR photoplethysmogramscan be adversely affected by strong reflections from the
`
`bone.
`
`Figs. 5A and 5Billustrate a pulse oximeterreflectance sensor operating under,
`
`respectively, ideal and practical conditions. Referring now to Fig. 5A,it is shown that,
`
`under ideal conditions, reflectance sensor measures light backscattered from a
`
`15
`
`homogenous mixture of blood and bloodless tissue components. Accordingly, the
`
`normalized R/IR ratio in dual-wavelength reflection type pulse oximeters, whichrelies
`
`on proportional changes in the AC and DC components in the photoplethysmograms,
`
`only reflect changes in arterial oxygen saturation.
`