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`and Mirimei L. Lrwiire, PhD
`
`olmne 7 Number 1 January 1991
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`23
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`CLINICAL SCIENCES cemen Liam
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`s. K. C'2n.i:ifirf,.1\.vI"Di,-I*'F.:'-’ii‘i2CS, Cimmi A. Matrisili, MD,
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`Knowing Your Monitoring Equipment
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`68 Corresponcfence
`70 Books
`Workshop
`.
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`john
`iE'ii‘iiiioru, MD, cmri Drwiri W. Erisoii, MD
`Abstracts of Scientific Papers
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`U.S. Patent No. 8,989,830
`U.S. Patent No. 8,989,830
`
`I
`
`

`
`JOURNAL OF GL|NIBAL_MOH|T0ill|llli
`
`Volume 7 Number 1 January 1991
`
`JAN17 1391
`
`Hrrnclat Jounmn at THE socltrr F[fH_fEEHl0l{|fiY HI Auasrursn
`ELI
`iliiii
`N. Ty Smith, MD
`University of California. San Diego
`VA Medical Center
`San Diego. California
`
`J-.['Il'fl]lil.~'J.l_ lll]ilFli'I
`Paul G. Barash, MD. New Haven, Connecticut
`Charlotte Bell. MD. New Haven, Connecticut
`
`jan E. W. Bertcl-ten, PhD, Eindhovcn, The Netherlands
`Casey D. Blitt, MD, Tucson, Arizona
`jetty M. Calkins. MD, PhD, Phoenix, AZ
`Henry Casson. MD. Portland. Oregon
`Jeffrey B. Cooper, PhD. Boston. Massachusetts
`D. Daub, MD, Karlsruhe. Germany
`Edward Dclatid, MD, Los Angeles. California
`Peter C. Duke, MD. Winnipeg, Manitoba, Canada
`john H. Eichhorn, MD, Boston, Massachusetts
`Erich Epple, PhD, Tiibingcn, Germany
`A. Dean Forbes. Palo Alto, California
`
`Wesley T. Frazier, MD. Atlanta. Georgia
`Yasuhiro Fukui, PhD, Hatoyama, japan
`Leslie A. Geddes. ME. PhD. FACC. West Lafayette, Indiana
`Nikolaus Gravenstein, MD. Gainesville, Florida
`A. Gerson Greenbutg, MD. PhD, Providence, Rhode Island
`Betty L. Grundy, MD, Gainesville. Florida
`H. _l. Hartung, MD. Mannheim, Germany
`Carl C. Hug, jr. MD, Atlanta. Georgia
`Kazuyuki Ikeda, MD, PhD, I-laman1atsu._]apan
`_]oel Karlincr, MD, San Francisco. California
`John D. Michenfclder, MD, Rochester, Minnesota
`P. M. Osswald, PhD, Mannheim. Germany
`Tsutomu Oyama, MD, Hirosaki, japan
`Carlos Parsloe, MD, Sao Paulo, Brazil
`jan Pefiaz, MUDr, CSc, Brno. Czechoslovakia
`james H. Philip, ME{E). MD. Boston, Massachusetts
`Richard E. Piazza, PhD, Bcllcvuc, Washington
`Ellison C. Pierce, jr, MD, Boston, Massachusetts
`Cedric Prys-Roberts. MA. DM. PhD, FFARCS. Bristol, UK
`Michael L. Quinn, PhB, San Diego, California
`Ira]. Rarnpil, MD, San Francisco. California
`Maynard Ramsey III. MD. Tampa, Florida
`Charles L. Rice. MD. Seattle. Washington
`Michael F. Roizen, MD, Chicago. Illinois
`Helmut Schwilden, MD, PhD, Bonn, Germany
`john W. Severinghaus, MD, San Francisco, California
`Lewis B. Sheiner, MD. San Francisco, California
`
`David B. Swedlow, MD, Hayward, California
`Richard Tcplick. MD. Boston. Massachusetts
`Kevin K. Tremper, PhD. MD. Orange, California
`Max I-I. Weil, MD, Chicago, Illinois
`Arnold M. Wei-ssler, MD, Denver, Colorado
`
`Karel H. Wesseling. PhD. Amsterdam. Holland
`
`_|. S. Gravenstcin. MD
`University of Florida College of Medicine
`Gainesville, Florida
`
`Allen K. Ream, MD
`Stanford University School of Medicine
`Stanford, California
`31
`.. ['!E'd'lliW lllill 'fEl.lilJfllltllVlUllil3i\TlfiPiS ftflllflil
`Frank E. Block. _]r, MD. Columbus, Ohio
`In .'IL"l55i'l‘lil3.'llllE lil‘-lffifl
`Robert K. Kalwinsky
`Fl.
`'
`‘.i'il"lEH
`Little, Brown and Company. Boston, Massachusetts
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`The authors. editors. and publisher have exerted every effort to ensure that
`drug selection and dosage. as well as the description of instruments and rec-
`ommendations for their use. set forth in all articles appearing in the Jaimie!‘ of
`Cfiitirttl tlafniiitnrirtg are in accord with current reconunendations and practice
`at the time of publication. However. many considerations necessitate caution
`in applying in practice information reported in any article appearing in the
`Jnunirll. These include ongoing research. changes in government regulations.
`variations in standards among different countries. the possibility that original
`research as reported in thejolmlel may differ from standard practice. and the
`constant flow of information relating to drug therapy and drug reactions. as
`well as the principles of monitoring. application of instruments. and differ-
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`The Jottrttal afCliniral' Moitftnring is indexed in hltfrx M'etlfrItr, Cmrent
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`Biological Sriritrrs.
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`l l l I I
`
`II
`
`

`
`JOURNAL OF CLINICAL MONITORING
`
`Volume 7 Number 1 January 1991
`
`Ortgmal Articles
`IN IIITRO EIAIRLUETIOII OF HELITIVE PEIIFOFINIIIIII PUTENTIIII.
`OF OENTIUIL VENOUS CIITIIETEH31 CONIPDRISON UF
`MDTEIIIDLS, SELECTED HUI}-EL5. NUIIIBEII OF LUMENS, MID
`fiN{iI.E5 [IF INCIDENCE TU SIMIJIJTEO MEMBIIDNE
`Nikolaus Cravertstefll, MD, and Robert H. Bfadesllear, MD
`SKIN HEFLECTANBE PULSE OXIMETBY:
`IN FWD MEASUREHENT5
`FHDM THE FDHEAIIM AND CALF
`
`Y. Mendelson, PhD, and M. J. Mr:Gr'rm. MS:
`
`_
`THE FIEIJITWE ACCUMCIES OF TWO AUTDHRTEO
`NONIIIWASIIIE ARTERIAL PHESSIIIIE MEASUREMENT DEVICES
`Michael S. Gorback, MD, Tfmotlay J. Quill, MD,
`and Michael L. Lauine, PhD
`
`ELECTFIDENCEPIIALOGRJIPHIC MIIPPIIIG DURING ISOFIMRANE
`AIIESTHESIA FOII TREHTMENT OF MENTAL DEPRESSION
`
`W. EugeIIIara'r, Dr med, C. Can‘, Dr Med,
`T. Dierks, Dr med, and K. Maurer, Prof Dr med
`
`Case Reports
`IISEFUUIESS OF EPIIJUIIALLY EUOKED GDHTICAL PDTEIITIM.
`MONITORING DURING CEHUICOMEOIILLAIW CLIOMD SURGERY
`Tafearo Moriolea, MD, Kiyotaka Fqjfi, MD,
`Sfrazo Tobfalatsts, MD, MHMSIII Fukui, MD,
`and Yoshiro SaIeagueIu', MD
`CAPNDGRAPHY FOR DETECTION [IF ENDDBRDNCHIAJ.
`MIGFIMIDN DF AN ENDDTRACHEILL TUBE
`S. K. Gandhi, MD, FFARCS, Charm‘ A. Mmishi, MD,
`Robert Coon, PIID, and Am: Bardeen-Heusdael, MD
`OXYGEN PIPEUIIE SUPPLY FMLURE:
`£4 COPIIIG STMTEGY
`
`Wayne R. Anderson, MD, and Jofm C. Brock-Ume, FFA(SA,I
`
`Technical Notes
`A TARGET FEEDBDCK DEVICE FOR VENTILMOIW MUSCLE
`TRAINING
`
`Michael _I. Behuan, MD, and Reza Shadmehr, MS
`49 REDUCTION OF FRESH [HIS FLOW IIEIJUIFIEIIIENTS BI‘ A
`CIRCLE-MODIFIED BMII BIIEIITIIIIIG CIRCUIT
`
`_,Io.Im Bernard Voldnlghi, MD, and Patrick Newfand Nance, MD
`
`Knowing Your Monitoring Equipment
`55 moan enessune Mnmroamn: AUTOMATED nscluomermc
`DEVICES
`
`Maynard Ramsey III, MD, PIID
`Correspondence
`68 LOW PEHFIJSIDII PIIIESS-‘DRE OH IHTERIIIIPIIDN {IF BLDIJD FLDIT
`SUPPIIESSES ELECTROENCEPHALDSHAPHIC ACTIVITY?
`forge Urzrm, MD
`68' HEPLY
`
`Mark S. ScI':eIIer and Brian R. Jones
`68 HEASUFIEMENT UF MITEHIIIL UIWUEN TENSION IN THE
`HTPEFIBI-IRIS ENVIRONMENT
`Lindefl K. Weaver, MD
`
`HEP-L9
`Dr. G. Litseher
`
`Books
`70 CM-‘IIO’J8.APHY IN CLIIIICIII. PIIACTICE
`
`]. S. Gravcnstein, MD, David A. Paulus, MD. MS, and
`Thomas j. Hayes. BS
`B. Smafhour, MD, PIID
`
`C'omems rormimed on page 21-4
`
`III
`
`

`
`Cements :onn':medjPam page A-2
`
`Workshop
`71 OOHPIITERIIQHDR OF MIESTHESIA IIIFBHMJFHDII
`MMIAGEHEHT
`
`john H. Efchhorn, MD, and David W. Edsalf, MD
`Abstracts of Scientific Papers
`33 mun MEDICAL HDIIITIIIIIIIII TEE!-IIIIJLIJBY BHFEBEIICE
`
`1192 HRS? Mlllllhl MEETING (IF THE SOCIETY FOR TECHNOLOGY Ill
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`A-I6 Announcements
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`34 name man In: EBITIJBS
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`A-16 musx Tn nnvsnnsaas
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`IV
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`

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`This material may be protected by Copyright law (Title 17 U.S. Code)
`
`

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`OPTICM. SHIELD
`
`R ‘
`
`IR LED‘
`
`PBOTODIODE5
`BRASS RING
`
`PHOTODIODES
`OP'1'ICh.l'..LX
`CLEAR E9 OX!
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`TEEEMOFOIL
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`RUBBER
`B
`
`..
`
`Fig 1. (A) Fnmral and (B) side rriews u_f'.'lrr' lrrared slain rr3‘irr—
`tame pulse oximeter sensor. See rexrfur rxplanan'un. ll 8: IR
`LEDs = red mid in_fim‘en‘ lr'gliI-eriiirrfiig diodes.
`
`eludes an array of six identical photodetectors arranged
`symmetrically in a hexagonal configuration surround-
`ing two pairs of red (peak emission wavelength, 660
`nm) and infrared (peak emission wavelength, 930nm)
`light-emitting diodes (LEDS)
`In another related
`study, we showed that by locally heating the skin under
`the sensor to a temperature above 40°C, it is possible to
`achieve a four- to fivefold increase in the magnitude of
`the pulsatile component detected from the forearm, and
`thus significantly improve the detection reliability ofthe
`reflectance photoplethysmograms
`The new optical
`reflectance sensor designed for this study combines the
`two features described above.
`
`SEIISIIH DESIGN
`
`reflectance sensor
`The teniperature-controlled optical
`used in this study is shown in Figure 1. The major fea-
`ture of the optical layout design is the multiple photo-
`diode array, which is arranged concentric with the
`LEDs. This arrangement maximizes the amount of
`backscattered light that is detected by the sensor. The
`technical details related to the design and geometric
`
`8 joirrnal o_,I"Clr'm'ml Mnm’mrr'n_Q Vol 7 Nu Ijanmiry 1991'
`
`company, are better reliability in critical care situations
`such as peripheral circulatory shutdown, less interfer-
`ence from ambient light, and better accuracy because
`measurement from the forehead is relatively unsuscep-
`tible to motion artifacts.
`
`there are no commercially available re-
`Currently,
`flectance pulse oximeters for monitoring SaO2 from lo-
`cations other than the forehead. Therefore. the objective
`of this work was to investigate the feasibility of moni-
`toring S303 with a skin reflectance pulse oximeter from
`two alternative and convenient locations on the body:
`the ventral side ofthe forearm and the dorsal side ofthe
`
`calf. Besides extending the clinical application of pulse
`oximetry, it appears also that reflectance pulse oximetry
`from peripheral tissues may have potential advantage in
`the assessment of local blood oxygenation after skin
`transplantation and regeneration Following microvascu—
`lat surgery.
`In this article, we describe preliminary in vivo evalua-
`tion ofa new optical reflectance sensor for noninvasive
`monitoring of SaO3 with a modified commercial trans»-
`mittance pulse oximeter. We present the experimental
`evaluation of this sensor in a group of 10 healthy adult
`volunteers and compare 8302 measured with the reflec-
`tance pulse oximeter sensor, SpO3(r), with SaO3 mea-
`sured noninvasively from the finger by a standard trans-
`mittance pulse oximeter sensor. SpO3(t).
`
`IIEFLEBTAHBE PULSE I|X|ME'l'llY
`
`The principle of reflectance, or backscatter, pulse ox-
`imetry is generally similar to that of transmittance pulse
`oximetry. Both techniques are based on the change in
`light absorption oftissue caused by the pulsating arterial
`blood during the cardiac cycle. The pulsating arterioles
`in the vascular bed, by expanding and relaxing, mod-
`ulate the amount of light absorbed by the tissue. This
`rhythmic change produces characteristic photoplethys—
`Inographic waveforms, two of which are used to mea-
`sure SaO2 noninvasively.
`Recently, we showed that accurate noninvasive mea-
`surements of SaO2 from the forehead can be made with
`an unheated reflectance pulse oximeter sensor
`The
`major practical limitation of reflectance pulse oximetry
`is the comparatively low-level photoplethysmograms
`recorded from low-density vascular areas of the skin.
`Therefore,
`the feasibility of reflectance pulse oximetry
`depends on the ability to design an optical reflectance
`sensor that can reliably detect sufficiently strong reflec-
`tance photoplethysmograms from various locations on
`the skin.
`
`In order to partially overcome this limitation, we
`have developed an optical
`reflectance sensor that
`in-
`
`

`
`Mriitieisoia and MrCi‘mi: Sim! Rt:flt‘Ca'rI.|h‘t‘ Pulse Oacfim-try
`
`9
`
`configuration ofthe optical components were described
`rccentiy by Mendelson et al
`The heater consists of a ring-shaped (dimensions:
`30-min outside diameter;
`"l5-mm inside diameter)
`thermofoil resistive heating element (Ocean State Ther-
`motics, Smithfleld, RI). The thermofoil heater was
`mounted between the surface of the optically clear
`epoxy, which was tised to seal the optical components
`ofthe reflectance sensor, and a thin (0.005 mm) match-
`ing brass ring. which facilitates better thermal condL1c—
`tion to the skin. A miniature (dimensions: 2 X 5
`X I mm) solid—state ternperature transducer (AD 590,
`Analog Devices, Wilmington, MA) was mounted on
`the outer surface of the brass ring with the thermally
`sensitive surface facing the skin. The entire sensor as-
`sembly was potted in room-temperature vulcanizing
`silicorie rubber to minimize heat losses to the sur1'ot1nd-
`
`ing environment. The assembled sensor weighs approx-
`imately 65 g. The sensor measures approximately 38
`mm in diameter and is 15 mm thick. The heater assem-
`
`bly was separately interfaced to a temperature controller
`that was used to vary the temperature of the skin be-
`tween 35 and 45°C in ] : 0. 1°C steps.
`
`SUBJECTS Mill METHODS
`
`Dam Arqm'si(ien
`
`Each of the two heated optical reflectance sensors were
`separately interfaced to a temperature controller and a
`commercially available ACCUSAT (Datascope Corp,
`Paramus, NJ) pulse oximeter [3].
`Two of the three ACCUSAT pulse oximeters were
`modified to function as reflectance pulse oxiineters. The
`modification, which was described in a separate study
`[1], included the adjustment ofthe red and infrared LED
`intensities in the reflectance sensors so that the reflec-
`
`tance photoplethysmograms were approximately equal
`to transmittance photoplethysmograms measured by a
`standard transmittance sensor from an average size adult
`finger tip.
`The third ACCUSAT transmittance pulse oximeter
`was used as a reference to measure SpO3(t) from the
`finger tip. The specified accuracy of this transmittance
`pulse oximeter is $2.00/o and t4.0°/1 for 5210; values
`ranging between 70 and 100% and 60 and 70%, respec-
`tively
`The three pulse oximeters were adapted to
`provide continuous digital rcadouts of the AC and DC
`components of the red and infrared photoplethysrno-
`grams.
`
`Readings from each ofthe three pulse oximeters were
`acquired every 2 seconds through a standard RS—232C
`
`serial port interface using an AT&T 6300 personal com-
`puter. The conversions of the reflectance redfinfrared
`(IUIR) ratios measured by the two reflectance pulse ox-
`imeters to SpO3(r) were performed by using the cali-
`bration algorithm obtained in a previous calibration
`study in which measurements were made with a similar
`nonheated sensor from the forehead [1].
`
`In Vivo Study
`
`The ability to measure SpO2(r) from the forearm and
`calf was investigated in vivo during progressive steady-
`state hypoxia in humans.
`Measurements were acquired from 10 healthy non-
`smoking male adult volunteers ofdifferent ages and skin
`pigmentations. The study was performed in compliance
`with the University of Massachusetts Medical Center’s
`review guidelines on human experimentation. Each
`volunteer was informed of the complete procedure as
`well as the possible risks associated with breathing hy-
`poxic gas levels. Each volunteer received monetary
`compensation for participation in this study. The sub-
`ject distribution included 1 East Indian, 3 Asians, and 2
`darkly tanned and 4 lightly tanned Caucasians. Their
`ages ranged from 22 to 37 years old {mean 1 SD, 27.5
`: 4.9 years). Measured blood hematocrits were in the
`range of 40 to 50.5% (mean 1 SD, 45.7 1 3.2%).
`All instruments were allowed to warm up for at least
`30 minutes before the study. The transmittance sensor
`of the pulse oximetcr was attached to the index finger.
`The rcfiectance sensors were attached to the ventral side
`
`of the forearm and the dorsal side of the calf by using a
`double—sided transparent adhesive ring. In cases where
`an abundance of hair prevented intimate contact be-
`tween the sensors and the skin,
`the contact was im-
`
`proved by loosely wrapping the sensor and the limb
`with an elastic strap. The temperature of each reflec-
`tance sensor was set to 40°C and remained unchanged
`throughout the entire study.
`A standard lead—l electrocardiogram and end-tidal
`carbon dioxide levels were continuously monitored by
`a Hewlett-Packard '/8345A patient monitor (Hewlett-
`Packard, Andover, MA). Each subject was placed in a
`supine position. A face mask was tightly fitted over the
`subject’s nose and mouth, and the subject was instructed
`to breathe spontaneously while we administered differ-
`ent gas mixtures of nitrogen and oxygen. The inspired
`gas mixture was supplied by a modified Heidbrink anes-
`thesia machine (Ohio Medical Products, Madison, WI).
`The breathing circuit of the anesthesia machine was
`equipped with a carbon dioxide scrubber (soda lime).
`The inspired oxygen concentration was adjusted be-
`tween 12 and 100% and was monitored continuously
`
`

`
`]0 jonrmrl ofCh'm’m! Monr’rarr'ng Vol’ 7 Na Ifinnmry I991
`
`throughout the study with an IL 408 (Instrumentation
`Laboratories, Lexington. MA) oxygen monitor, which
`was inserted in the inspiratory limb of the breathing
`circuit.
`
`Steady-state hypoxia was gradually induced by low-
`ering the inspired fraction of oxygen in the breathing
`gas mixture. Initially,
`the inspired oxygen concentra-
`tion was changed in step decrements. each step pro-
`ducing approximately a 5% decrease in SpO2(t) as
`determined from the display of the ACCUSAT
`transmittance pulse oximeter. The inspired oxygen was
`m_aintained at each level for at least 3 minutes until the
`
`pulse oximeter readings reached a steady level (i.e..
`SaO2 fluctuations ofless than 1-3%). When the inspired
`oxygen level reached 12%,
`the process was reversed.
`Thereafter, the inspired oxygen level was increased in a
`similar stepwise manner to 100%. Data were recorded
`during both desaturation and reoxygenation.
`All subjects tolerated the procedure well without ad-
`verse reactions. None ofthe subjects showed electrocar-
`diographic abnormalities before or after the study. Each
`subject was studied for approximately 1 hour.
`
`Data Analysis
`
`To avoid operator biases, the data from each pulse ox-
`imeter were acquired automatically by the computer
`and later subjected to the same statistical tests.
`For each step change in inspired oxygen, readings
`from the three pulse oximeters were averaged consecu-
`tively over a period of 20 seconds. Averaged readings
`from the 10 subjects were pooled and 3 least—squarcs
`linear regression analysis was performed. Student's r test
`determined the significance of each correlation; p <
`0.001 was considered significant.
`Although the correlation coefficient of the linear re-
`gression (r) provides a measure of association between
`the SPOg(l') and SpO2(t) measurements, it does not pro-
`vide an accurate measure ofagreement between the two
`variables. Therefore, the measurement accuracy was es-
`timated on the basis ofthe mean and standard deviations
`
`of the difference between the readings from the trans-
`mittance and reflectance pulse oximeters. The mean of
`the difference between the pulse oximeter measure-
`ments, which is often referred to as the bias, was used to
`
`assess whether there was a systematic over— or underes-
`timation of one method compared with the other. The
`standard deviation of-the bias, which is often referred to
`as the precision. represents the variability or random
`error. Finally, we computed the mean errors and stan-
`dard deviations of each measurement. The mean error
`
`is defined as the absolute bias divided by the corre-
`sponding SpO3(t) values.
`
`
`
`R/IRRzrmcrmcsRATIO E‘-":"(DRJ
`
`+—s-—
`
`FORLRM
`Y = 1.02K - 0.05
`CAL?
`Y = 0.373 + 0.04
`
`0. 4
`
`-
`
`D. 8
`
`1. 2
`
`1. 5
`
`R/IR Tannsura-mines ruvuo
`
`Fig 2. Cornpmfson afred/irrflnred (RI IR) mrfos measured by {in
`nmdffied refiernmte pnise oxiinrrrr (y axis) and tin: srrrnnhrri trans-
`nn’rmm'e pnisr oxinlerer (x :1.\'fs) during prqgrrssiw steady-smrr
`liypo.\'r'rr in 10 iieriifiry sirigiecrs. The snhri iine J'£’pl'£’$'£.’Hl'S the lies!-
`‘fitted ifnmr regrrssfrnr .'nrr_,*'or n':t-fn'earrir measnrrrneu.'s. The (inn-
`leen line f'£'pf‘£*S[’lIi‘S the best-fiffeti linear regression linefor the rail"
`nieasnremem's.
`
`RESULTS
`
`Normalized IUIR ratios and SpO2(r) values measured
`by the reflectance pulse oxinieters from the forearm and
`calf of the 10 subjects were compared with the nor-
`malized RIIR ratios and SpO2(t) values measured simul-
`taneously by the transmittance pulse oximeter from the
`finger. A total oF9'l and 93 pairs ofdata points measured
`simultaneously from the Forearm and calf, respectively.
`were used in the regression analysis, which provided the
`estimated slopes and intercepts of the linear regression
`lines. Each pair of data points represents a different hy-
`poxic levei.
`Regression analysis of the normalized RHR ratios
`measured from the reflectance pulse oximeters from the
`forehrm and calf (y axis) versus the normalized RHR
`ratios measured simultaneously by the tmnsniittancc
`pulse oximeter from the finger tip (x axis) is shown in
`Figure 2. The equations for the best—fitted linear regres-
`sion lines were y = — 0.05 + 1.02): (r = 0.94. SEE =
`0.08, p d 0.001) for the Forearm and y -= 0.04 + [).87x
`(r = 0.88, SEE = 0.11. p < 0.001) for the calf.
`A comparison of SpO3(r) readings from the reflec-
`tance pulse oximeter (y axis) and SpO2(t) readings mea-
`
`

`
`t\rlt’urieisott ami .r".«irGr'nn: Skin Reflectance Pulse Oxt‘metry
`
`11
`
`UD C3
`
`CD CD
`
`nasnacrauceS902(a)
`
`FORIRRH
`3 - 1.09: — 7.06
`CRLT
`Y I 0.93x + T.TB
`
`80
`
`90
`
`100
`
`an
`
`rnansurrrauca SPO2 (s)
`
`1-nnusurnmucn 51:02 (at)
`
`Fig 3. Comparison afpereent arteriai lretaagiohitt oxygen satm'a-
`tion (SpO2) measurements abtafm-dfitom the modified rtflettrmre
`pulse oximeter ()1 axis) and SpO;» vaittes measnreri hy a standard
`transmittamte pttise aximeter {x axis) dtrritig progressive steady-
`state hypoxia in 10 itealthy stthjetts. The solid line represents the
`hrst-fitted linear t'egressian line for the forearm ttteasttremettts. The
`braieen line represents the best-fitted linear regression line fin the
`wit measurements.
`
`Fig 5. Mean ritflerehces between arterial. hetttaglohhi oxygen sat-
`uration (S1302) measured from the caifhy the tttaritfied reflectattre
`pulse oxfttteter rmri the standard transmittance pulse aximeter mea-
`sitremettts fiam the finger tip.
`
`Statistical Analysis ofArterr'ai Oxygen Saturation (SaO2) Levels
`Measured flom the Forearm and Cal)‘ by the Modified Reflectante
`Pulse Oxittteters
`
`Location!
`‘/a S202
`
`Forearm
`90-100
`80~89
`70-79
`
`Calf
`90-100
`80-89
`70-79
`
`No. of
`Data Points
`
`Mean Value (SD)
`
`Difference
`
`% Error
`
`12
`
`43
`33
`17
`
`2.47 (1.66)
`2.35 (2.45)
`2.42 (1.20)
`
`1.57 (4.00)
`2.22 (4.00)
`1.95 (2.42)
`
`3.36 (3.06)
`3.45 (4.12)
`2.97 (2.75)
`
`sured simultaneously from the transmittance pulse ox-
`irneter (x axis) is shown in Figure 3. The equations for
`the best—f1tted linear regression lines were y = — 7.06
`+ 1.09): (r = 0.95, SEE = 2.62, p < 0.001) for the
`forearm and y = 7.78 + 0.93): (r = 0.88, SEE = 3.73,
`p < 0.001) for the calf.
`Figures 4 and 5 show the percent differences between
`SpO2(r) and SpO2(t), that is, SpO2(r) - SpO2(t). ob-
`tained from the forearm and calf data plotted in Figure
`3, respectively. The corresponding means and standard
`deviations of the differences and errors for the forearm
`and calf measurements are summarized in the Table.
`
`DIFFERENCES
`
`Q0
`
`IUU
`
`TRANSMITTANCE S1302 Ht)
`
`Fig 4. Meat: dt_'fli?t'entes between arterial hemoglobin oxygen sat-
`ttratiott (SFIO2) ttteautredfrom the fisrearm by the rttadtfied refle€-
`tanee pulse oximeter and the startdarri trattstrtittanre pulse oximeter
`rm-asuremeuts float the finger tip.
`
`

`
`I2 _,lrmrm1l o_,fClim'rrll Arlaiiitiiriiig Vol 7 No 1' _,l:1um1i'y 1991
`
`Data were summarized for three different ranges of
`SpO3(t) values between 70 and 100%.
`
`IIIISIIIJSSIIIII
`
`Commercially available transmittance sensors can be
`used on only a limited number of peripheral locations of
`the body. Brinkman and Zijlstra [4] and Cohen and
`Wadsworth [5] showed that instead of tissue transil-
`lumination, noninvasive monitoring of SaO2 can be
`performed based on
`skin
`reflectance
`spectropho-
`tometry. More recently, we described an improved
`optical reflectance sensor that was used for measuring
`SaO2 from the forehead with a modified commercial
`
`transmittance pulse oximeter
`Measuring large reflectance photoplethysmograms
`from sparsely vascularized areas ofthe skin is challeng-
`ing. Differences in capillary densities between various
`locations on the body are known to affect the magnitude
`and quality of the reflected photoplethysmograms. For
`example, estimated average capillary density of the hu-
`man forehead is approximately 127 to 149 loopsr"mm2,
`whereas the capillary densities of the forearm and calf
`are approximately 35 to 51 and 41 loopsfmmz, respec-
`tively [6,7]. Furthermore, the frontal bone of the fore»
`head provides a highly reflective surface that signifi-
`cantly increases the amount of light detected by the
`reflectance sensor. Therefore,
`reflected photoplethys-
`mograms recorded from the forehead are normally
`larger than those recorded from the forearm and calf.
`Local skin heating could be used as a practical method
`for improving the signal-to-noise ratio of the reflected
`photoplethysmograms from the forearm or calf areas
`and thus reduce the measurement errors in reflectance
`
`pulse oximetry.
`The approach presented in this article demonstrated
`that $302 can be estimated by using a heated skin
`reflectance sensor from the forearm and calf over a rela-
`
`tively wide range of S303 values. This technique may
`provide a clinically acceptable alternative to currently
`available transmittance pulse oxirneters. In a previous
`study [2}, we found that the ability to measure accurate
`SaO2 values with a reflectance skin oximeter is indepen-
`dent of the exact skin temperature. We noticed, how-
`ever,
`that a minimum skin temperature of approxi-
`mately 40°C is generally sufficient to detect adequately
`stable photoplethysmograms. Furthermore, our experi-
`ence in healthy adults also has shown that at this skin
`temperature, the heated sensor can remain in the same
`location without any apparent skin damage.
`Note that despite the proven advantage of local skin
`heating to increase skin blood flow.
`reflected photo-
`plethysmograms recorded from the forearm and the calf
`are considerably weaker than those recorded from the
`
`the mean errors for the SpO3(r)
`forehead. Therefore,
`measurements from the forearm and calfare higher than
`the corresponding errors for similar SpOg(r) measure-
`ments made with an unheated reflectance sensor from
`
`the forehead. For comparison, relative to 5:103 mea-
`sured with a noninvasive transmittance pulse oximeter,
`the SEE for SpO2(r) measurements obtained from the
`forehead using a similar unheated optical
`reflectanee
`sensor were 1.82% [1]. The SEE obtained in this study
`using the heated reflectance sensor were 2.62% for the
`forearm and 3.73% for the calf measurements. Despite
`those differences, it is apparent that the degree ofcorre-
`lation obtained i11 this preliminary study is encouraging
`and in selected clinical applications may be acceptable.
`We conclude that reflectance pulse oximetry from the
`forearm and calf may provide a possible alternative to
`conventional transmittance pulse oximetry and retice-
`tance pulse oximetry from the forehead. Further stud-
`ies, however, are needed in order to compare our
`reflectance pulse oximeter against SaO2 measurements
`obtained directly from arterial blood samples. Addi-
`tional work to investigate the source of variability in
`reflectance pulse oximetry is i11 progress.
`
`Financial support for this study was provided in part by the
`Datascope Corporation and NIH Grant R15 GM36l l l-UIAI.
`
`The authors would like to acknowledge the clinical assistance
`of Albert Shahnarian, PhD, Gary W. Wclch MD, PhD, and
`Robert M. Giasi, MD, Department of Anesthesiology, Uni-
`versity of Massachusetts Medical Center, Worcester, MA.
`We also thank Paul A. Nigroni, Datascope Corporation.
`Paramus, NJ, and Kevin Hines, Semiconductor Division,
`Analog Devices, Wilmington, MA, for technical assistance.
`The skillful art work by Yi Wang is also greatly appreciated.
`
`REFERENCES
`
`. Mendelson Y, Kent _]C, Yocmn BL, Birle M]. Design and
`evaluation of a new reflectance pulse oximeter sensor.
`Biomed lnstrum Techno] 1988;22(4):l67—]73
`