Sept. 26, 1944.
`
`G. A. MILLIKAN
`
`OXYGEN METER
`
`2,358,992
`
`Filed June 28, 1941
`
`2 Sheets—Sheet l
`
`
`
`I
`INVENTOR
`676/27”? M[ZZA’CUZ
`“WM
`ATTORNEY
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`|PR2018—00294
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`Apple Inc. EX1015 Page 1
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`IPR2018-00294
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`SePt- 25, 1944-
`
`G. A. MILLIKAN
`OXYGEN METER
`
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`
`2,358,992
`
`Filed June 28, 1941
`
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`|PR2018—00294
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`Patented Sept. 26, 1944
`
`2,358,992
`
`UNITED STATES PATENT OFFICE
`
`2.353.992
`,
`OXYGEN METER
`
`Glenn A. Millikan, New York, N. Y.
`Application June 28, 1941; Serial: No. 400,285
`(01. 88—14)
`
`’11 Claims.
`
`10
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`15
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`2O
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`25
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`30
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`This invention relates to colorlmetry, and is
`particularly useful in determining the amount of
`oxygen in the blood.
`It provides a means by
`which the depletion of oxygen—as in the case 01"
`aviators flying at high altitudes or patients under
`anesthesia—can be continuously observed,
`so
`that appropriate measures may be taken before
`the danger point is reached. Various other appli-
`cations in calorimetry will become apparent to
`those skilled in the art. The objects of the inven-
`tion are to provide a simple and practical device
`for purposes such as those stated;
`to make it
`. applicable to persons having different physical
`characteristics;
`to permit frequent checking of
`the accuracy of the instrument; to protect the
`person being tested from pain or discomfort; to
`give greater ease and accuracy or operation; and
`in general to improve the performance, conven-
`ience and utility of such devices.
`The general principles upon which the appa-
`ratus is based are as follows.
`It has long been
`recognized that
`the hemoglobin of
`the blood
`changes color from red toward blue as the oxygen
`content diminishes.
`In recent years calorimeter
`tests involving light passing thru a specimen to
`fall on a light sensitive cell operating a galva-
`nometer have been developed, so as to give some
`means of determination independent of the mere
`judgment of the human eye. To calibrate the
`results laboratory analyses of blood samples in
`each instance were required. ‘ In order to produce
`a more direct reading method, and one adaptable
`to persons or various physical characteristics, the
`present device uses a system of readings and
`scales by which coordinated results of sufficient
`accuracy for most practical purposes can be
`quickly obtained.
`A beam of light can be passed thru a thin part
`of the body. such as the ear or the web of a
`finger, to fall upon a light sensitive cell operating
`a galvanometer.
`If all ears were alike. the prob-
`lem would present few dimculties. But. the varia-
`tions in thickness and texture of the tissues in
`different individuals introduce variations in the
`light transmitted quite independent of the color
`of the blood; so that difierent individuals with
`equal proportions of oxygen in their blood may
`produce quite different photo-electric readings.
`The problem then is to provide a. sound basis
`for calibration independent or such individual
`peculiarities.
`,
`In general the problem is solved in the present
`apparatus by providing a system which first de-
`termines a classification within which the indi-
`vidual subject falls, and selects a calibration
`
`scale. which will suit that subject within a prac-
`tical degree of accuracy; and then by direct read-
`ings indicates on that scale the percentage of
`oxygen content
`in the blood. The particular
`scientific principles by which this is accomplished
`will be described more in detail later in the speci-
`flcation.
`In the drawings forming part of this specifica—
`tion, Fig. 1 is a schematic view illustrating the
`general principles of a typical device.
`Fig. 2 is a side elevation view mostly in section
`of a light sensitive cell and lamp unit which may
`be clamped to the ear or other desired specimen.
`Fig. 3 is a front view of one form of the red
`and green filters used with the light sensitive
`cell.
`Fig. 4 is a chart showing the comparative light
`absorption of hemoglobin when high in oxygen
`and when reduced in oxygen, from which char—
`acteristics the function of the green filter is
`deduced.
`Fig. 5 shows the logarithmic curves of trans-
`mitted light and oxygen saturation for various
`types of ears, labelled “thick ear.” “medium ear”
`and “thin ear"; from which the necessity for
`different scales for different types of cars will be
`seen.
`Similar reference numerals refer to similar
`parts thruout the various views.
`.
`Referring first to Fig. 1, a light sensitive cell
`I embodying separate units capable or respond-
`ing to diflerent selected colors is placed in prox—
`imity to the specimen to be analyzed, such as the
`human ear 2, thru which light from the electric
`light bulb 3 passes to energize the light sensitive
`cell I. To control the color of the light which is
`to energize the cell
`i. color filters 4 and 4’, la-
`belled R for red and G for green respectively, are
`interposed between the light 3 and the cell
`i.
`The light sensitive cell i
`is of the compound or
`multiple type, so that part of it responds only to
`the light falling on it thru the green filter, and
`another part responds only to the light falling on
`it thru‘the red filter. These parts are labelled
`R for red and G for green, and these letters are
`also applied to switch terminals, indicator lights,
`rheostats, and similar parts to be later described,
`so that the red and green circuits can be readily
`traced.
`'
`'
`The cell l is therefore really two light sensitive
`cells having a common ground wire 6 but other—
`wise operating independently, one portion being"
`sensitive to green light and the other portion
`being sensitive to red light.
`It is the well known
`property of any light sensitive cell that when
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`ight falls upon it an electro-motive force is gen-
`erated, which is usually capable of operating a.
`measuring instrument such as a galvanometer.
`When the light thru the green filter 4' falls on
`the corresponding portion of the cell
`|, the cir-
`cuit is thru the conductor 6 to the terminal of
`the switch 1 marked G, then thru the conductor
`8 to the galvanometer 3, and back thru the
`ground wire 5 to the cell I.
`When the red portion or the cell I is in action,
`the light after passing thru the red filter I ialls
`on the corresponding portion of the cell |, gener-
`ating an electro-motive force in accord with the
`intensity of the red light. When the switch 1 is
`turned to the terminal R, for the red circuit, the
`current flows thru the conductor m, switch 1, and
`conductor 8 to the galvanometer 9, and back thru
`the ground wire 5 to the cell |. There are thus
`two simple alternative circuits, one energized by
`red light and the other by green light, either of
`which may be read on the galvanometer 9. by
`throwing the switch 1 to the appropriate position.
`The point marked Z on the switch 1 is used for
`setting the zero reading of the galvanometer 9;
`and the point marked 0 (for “ofl") is used when
`the apparatus is entirely shut oil. Since the cur-
`rent is generated by the direct action of the light
`falling on the light sensitive cell, no battery or
`other external power source is required for this
`part of the apparatus, these reading circuits being
`self-contained and independent of the supple-
`mentary circuits now to be described.
`‘
`'
`To assist the operator in using the apparatus,
`indicator lights |2 and |3 are provided, the light
`|2 being on when the green circuit is in use and
`the light I: being on when the red circuit is in
`use. These lights are operated by the switch M,
`which has four switch points. 0 (off), R (red),
`Z (zero set), and G (green), similar to the switch
`
`circuit must be provided for the electric light
`2| that shines on the galvanometer mirror. This
`circuit is controlled by the switch 22, which really
`has only two positions, on and oil; but for con-
`Venience of manufacture it may be provided with
`contact points similar to the switches 1, M and
`IS, so that it may be operated by the same shaft:
`but in the case or the switch 22 all the points
`O, z, and. R are connected together so that the
`light 2| remains on regardless of the position of
`the switch 22, unless it is in the “01!” position.
`The switches 1, H, l5 and 22, being or similar
`mechanical construction, are readily moved in
`unison by a single shaft 24 indicated by the broken
`line, which is operated by the handle 25. When
`this handle 25 moves the switches 1, M, It and 22
`from the “oil” position to G (green), the gal-
`vanometer l is put in circuit with that portion of
`the light sensitive cell i which is under the green
`color filter I’;
`the green indicator light
`I2 is
`turned on; the light source 3 is turned up to a
`higher intensity; and the galvanometer reading
`light 2| is turned on. When the handle 25 moves
`the switches 1, N, Is and 22 to the “zero” posi-
`tion, the light sensitive cell circuits are discon-
`nected, as is the light source 3, but the gal-
`vanometer light 2| remains on. so that the gel-
`vanometer can be set for zero reading, to give it
`the proper preliminary adjustment. When the
`handle 25 moves the switches 1, ll, l! and 22'to
`the R (red) position, the galvanometer is con—
`nected to that portion of the light sensitive cell
`energized by the light thru the red color filter I:
`the light source 3 is dimmed to a degree previ-
`ously set .by the resistance Is: and the galvanom-
`eter light 2| remains on to provide the reading
`spot or indicator. Thus the zero setting, and the
`readings produced by either the red or the green
`light are conveniently obtained, and their pres-
`ence indicated, by simultaneous switch movements
`all operated by a single handle.
`The electricity for the indicator lights l2, II,
`the light source 3, and the galvanometer light 2|,
`may be obtained from any suitable source indi-
`cated conventionally by the reference numeral an,
`ordinary electric light lines being generally used
`when available.
`The light sensitive cell | and color filters I and
`4' have been described as simply red and green
`units set close together so as to utilize the same
`light source 3. The green filter and cell are made
`larger in area than the .red filter and cell, be-
`cause of the fact that red light activates the light
`sensitive cell much more strongly than green, as
`previously stated; and this difference in the green
`and red areas helps to bring the galvanometer
`readings into the same general order of magni-
`tude and avoids the necessity for changing the
`galvanometer scale or
`resistance, particularly
`when this is combined with the alteration of the
`light source intensity above described.
`,
`The diiference between the red and green
`areas will best be seen in Fig. 2, and Fig. 3 which
`show in greater detail a light cell unit more
`simply shown in Fig. 1. Referring now to Fig. 2.
`the housing 3| contains the color filters 4 and l'
`and the light sensitive cell
`i, which is conven-
`tionally shown in Fig. 2 and in somewhat greater
`detail in the front view of Fig. 3. The housing
`3| is preterably made of hard rubber, plastic or
`similar smooth material so that it may beplaced
`It the galvanometer or other reading instru-
`against the car without discomfort; and is pro-
`ment 9 is of the type using a spot of light as its
`vided with an opening 32 to admit light from
`indicator point, as is generally the case, then a 75 the electric light bulb I. This bulb I is sup-
`
`1 t
`
`The light source 3 which supplies the light to '
`he specimen 2 and light can I, is preferably an
`ordinary light bulb of the miniature type, and
`is controlled by the switch l5, which has four
`contact points similar to those of switches 1 and
`N, that is, marked 0 (01!), G (green), Z (zero
`set) , and R (red). Light sensitive cells are gener-
`ally much more responsive to red rays than to
`green, and this would normally necessitate chang-
`ing the scale or resistance of the galvanometer or
`other measuring instrument.
`In order to take
`readings from both the red and green circuits
`without changing the galvanometer, means are
`provided to reduce the intensity of the light source
`3 when the red screen is in use; or conversely, to
`increase the relative intensity of the light source
`3 when the green screen is in use.
`For this purpose, adjustable resistances I1 and
`N are provided in the circuit of the light bulb
`3, and are arranged so that the resistance ll,
`connected to the green circuit terminal G of the
`switch Is is less than the resistance IB, which is
`connected to the red circuit terminal R of the
`switch I5. This gives a brighter light at a when
`the switch l5 is at the point G of the green side,
`and a dimmer light when the switch Is is on the
`point R of the red side. Conductors |9 lead to
`the light bulb 2. A voltmeter 20 is connected
`across the circuit of the light bulb I as an addi-
`tional means of checking the setting of that light
`if desired.
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`ported on a hollow arm 33 extending from the
`housing 3|. thru which the wires l9 pass to
`supply electricity to the bulb 3. The end of the
`arm 3! extends back toward the housing ti and
`is provided with a threaded neck 35 on which
`is screwed a knurled ring It having smoothly
`rounded surfaces. on the side adjacent the hous-
`ing 3|, so that it may be clamped on the human
`ear or other thin part of the body without dis-
`comfort.
`In use, the thin upper portion or shell
`of the ear is slipped between the housing 3i and
`the ring 36, and the latter is then screwed up
`until it is gently clamped on the ear. The pres-
`sure should not be enough to impede the circu-
`lation, but only enough to hold the device lightly
`in place and exclude light other than that from
`the bulb. 3. A gentle pressure is sufficient and
`is not uncomfortable.
`While the apparatus may be constucted with
`only one green light area and one red light area,
`it is generally desirable to construct the green
`light area in two parts connected together, with
`’the relatively small red light area located in
`between, as shown in Fig. 3. where the green
`filter and cell areas are labelled G and the red
`filter and cell area is labelled R. This provides
`a more uniform distribution and guards against
`errors which might be indie-5.1 by local varia-
`tions in brightness on one side. While such an
`arrangement is mechanically made up of three
`or more parts, in principle they are the equiva—
`lent of but tw0 regions, since all the green areas
`are connected to the same conductor 6' and so
`act as one; and similarly, the red areas, if they
`were divided. would all act as one by being con-
`nected to the same conductor Ill.
`The apparatus and the principles which have
`been described would suffice to determine blood
`color and thereby oxygen content under most
`conditions were it not for the fact that varia-
`tions in the thickness and tissue of the ear in
`different individuals cause wide variations in the
`light transmitted thru the ear,
`irrespective of
`whether the blood in the ear is the same color.
`If all ears had the same thickness and texture,
`But '
`relatively simple readings would suffice.
`that not being the case, it is necessary to pro-
`vide means to overcome errors induced by such
`individual peculiarities.
`The present solution to this portion of the
`problem involves the following general, steps.
`(1) Providing a means for classifying the speci-
`mens or cars according to their physical char-
`acteristics of thickness and texture and other
`individual peculiarities affecting the transmis-
`sion of light, independent of the color of the
`blood, so that, the classifications would not be
`afiected by the oxygen content of the moment.
`(2) Having then segregated the ears into groups
`which act alike, the present invention provides
`separately calibrated scales for each group,
`‘on
`which can be correctly read the oxygen content
`of any individual in that group, at any particu-
`lar moment.
`The scientific principles on which this solution
`is based will be better understood after referring
`to Fig. 4, which is a typical chart showing the
`light absorption of oxyhemoglobin, or blood high
`in oxygen—indicated in solid lines— as compared
`with reduced hemoglobin, or blood low in oxygen,
`shown in broken lines. both curves being plotted.
`with light absorption as the ordinates and light
`wave length, A., that is color, as the abscissae.
`In the chart the spectrum runs from red on the
`right to the blue violet on the left.
`It will be
`
`2,358,992
`seen that on the right the red light is absorbed
`much more by the reduced hemoglobin than by
`the oxyhemoglobin, as would be expected from .
`. the fact that the blood with more oxygen is
`redder in color and so transmits red light more
`freely. On the other hand, the left portions of
`the curves indicate that with the bluer light
`the oxyhemoglobin absorbs more, that is, is more
`resistant to the passage of blue light than blood
`reduced in oxygen, which is bluer; While these
`characteristics are naturally to be expected, the
`interesting fact appears in the«middle of the
`curves that the two curves repeatedly cross each
`other, with the oxyhemoglobin sometimes. above
`and sometimes below. Where they cross, the two
`curves have of course the same value; which-
`means that there are certain coldrs or wave
`lengths which are- absorbed equally by either
`oxyhemoblogin or reduced hemoglobin; that is,
`that light of a certain color will be absorbed to
`the same degree regardless of whether the blood
`is high or low in oxygen; Since 'with light of
`that color the oxygen content does not enter
`into the problem, that particular color can be
`used to measure the various other physical char-
`acteristics or peculiarities that retard the pass—
`age of light, such as thickness, texture of the
`tissues, color of the skin, etc.
`In general it may
`be said that the amount of the selected green
`light transmitted is determined almost entirely
`by the amount of blood in the ear, independent
`of how much oxygen it contains.” The green
`light thus measures what may be termed the
`“blood thickness" of the ear.
`'
`While any one of
`the cross-over points of
`the two curves might be used, it is preferable
`with human subjects to use the cross-over point
`at about 5900 A., which we have called the
`, "green” light. Using this color, which is absorbed
`40
`in the same degree with any oxygen content of
`the blood, we test out various individual ears
`and find some transmit the light rather freely,
`and others not so freely, according generally as
`they are thin or thick or vary in texture. The
`transmission of the green light, as indicated by
`the action of the light sensitive cell 1 on the
`galvanometer 9, shows the general resistance to
`light attributable to the personal characteristics
`of the individual, aside from the, oxygen content
`of his blood; and we use such a determination
`of the “blood thickness” of the ear to select the
`proper scale suitable for that type of person.
`Referring now to Fig. 5, which shows the oxy-
`gen saturation plotted against the logarithm of
`the transmitted light, for various types of ears
`labelled “Thick ear,” “Medium ear,” and “Thin
`ear”—-it will be seen that the curves are not only
`spaced from each other, but are not parallel, that
`is, have different slopes. This means that the
`calibration curVes for such different types of cars
`will be quite different; and any single scale on the
`galvanometer reading directly in terms of percent
`oxygen in the blood would not be accurate for all
`types of people.
`In practice it has been found
`that by using a reasonable number of scales, pref-
`erably four, the oxygen content can be directly
`read with a suflicient degree of accuracy for most
`practical purposes.
`Accordingly the galvanometer 9 is provided
`with four separately calibrated scales labelled
`“Wafer," “Thin,” , “Medium,” and “Heavy," as
`shown in Fig. 1, with curves running from 50% to
`100% oxygen content crossing them in a generally
`diagonal direction.
`In operating the apparatus
`these are used in the following manner.
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`_ 2,358,992
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`changes in the lamp, voltage, lamp luminosity,
`and sensitivity of the light Sensitive cell.
`It is
`advisable to check this incident “green" light
`reading at the beginning and end of a run to see
`that it has not changed by more than a few per-
`cent.
`.
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`5
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`First to warm up and properly dilate the blood
`vessels‘ln the ear, the switches are turned to the
`green position, which it will be recalled makes
`the lamp 3 hotter than in the red position. This
`green position is usually too hot for comfort if
`left on continuously, and therefore during the
`initial warming up period of from five to fifteen
`minutes, the light is turned on intermittently and
`left on each time until the ear begins to feel un-
`comfortable. Once the ear is properly vasodi-
`lated, as indicated by a steady reading on the gal-
`vanometer, the dimmer red light should be warm ‘
`enough to keep it so, and the green need only be
`flashed on occasionally—say at one minute to five
`minute intervals—to see that the blood thickness
`of the ear has not changed. This reading with
`the switch on “green” shows how much blood
`there is between the lamp 3 and the photo-cell I.
`that is, the “blood thickness" of the ear.
`When this green reading has arrived at a steady
`value, we find it within one or another of the
`heavy black blocks shown staggered along the
`four scales of the galvanometer. For example, if
`it were in the region of the figures 60—90 on the
`upper scale, it would fall within the block of the
`scale labelled ”Wafer”; if the green reading were
`in the region of 50—60 on the upper scale. it would
`fall within the block on the scale labelled “Thin":
`if in the region of 60—70 on the lower scale it would
`lie in the block of the scale labelled “Medium";
`and if in the region of 50—60 on the lower scale, it
`would lie in the block of
`the scale labelled
`“Heavy.” With fewer or more scales the blocks
`would be different but the principle would be the
`same.
`.
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`Since the blocks do not overlap, the galvanom-
`eter indicationon the “green” setting is always
`within one block or another, and a glance at the
`scales suffices to select
`the scale to ‘be used.
`Whichever scale has the block in which the
`“gree ” reading falls is the scale on which the
`percent oxygen is read when the “red” setting is
`used.
`
`Beer’s law, as applied to a mixture of two sub-
`stances, such as hemoglobin and oxyhemoglobln,
`states that for a monochromatic light which is
`difierently absorbed by them, the logarithm of the
`transmitted light is linearly related to the frac-
`tion of one substance in the mixture. Beer's law
`has been found to hold adequately even for the
`optically complex system of blood in the human
`car, so long as the amount of blood in the ear
`remains fairly constant, as determined by the
`“green” reading.
`It should be emphasized that
`there are many reasons why Beer’s law should not
`hold in a system so far removed from that of a
`clear solution of pigment in a parallel sided
`trough, and the happy validity of the law for the
`human ear within the desired degree of accuracy
`does not Justify its extension to other tissues
`without independent check.
`~
`It follow from Beer’s law that there is a
`straight line relationship between the logarithm
`of the transmitted light and the percent satura-
`tion. This, however, is only true if both the in-
`tensity of the incident light and the total pigment. i‘
`concentration (hemoglobin plus oxyhemdglobin)
`remain unchanged.
`If the light intensity is in-
`creased, this straight line is shifted to the right
`in Fig. 5 without change of slope, while if the pig-
`ment becomes more‘concentrated its slope is de-
`creased. The position of the line can be uniquely
`determined if its slope is known and if one point
`on it is determined experimentally. The first
`quantity Can be predicted from the “green” read-
`ing, while the second datum can be obtained either
`by forcing the saturation up to 100% by breathing
`oxygen oreby assuming the saturation is 96%
`when air is breathed normally.
`The effective wavelengths depend both upon
`the transmission characteristics of
`the filters
`used and upon the spectral sensitivities of the
`light sensitive cell. The choice of the color ill-
`ters therefore depends to some extent on the par—
`ticular photocell used. For the red light an ef.
`fective wave length is desired which is very dif—
`ferently absorbed by reduced hemoglobin than by
`oxyhemoglobin. A number or regions might be
`used, but for‘ measurements on man the most
`suitable region is from 6200 A. to 6600 A. For
`example, a “Wratten No. 29” filter. having a con-
`trol wave length of 6400 A. was found to be sat-
`isfactory. For the green light an effective wave
`length is desired which is equally absorbed by
`oxyhemoglobin or reduced hemoglobin. Such a
`region lies between 5200 A. and 6000 A” and vari-
`ous other points as indicated in Fig. 4. A band
`in the neighborhood of 5900 A., obtained with
`“Wratten No. 61” filter has been found satisfac-
`tory. By keeping in mind the principles above
`outlined various suitable selections can be made.
`The apparatus has been described in the form
`of a single unit capable of handling one person
`at a time. Where it is desired to test a number
`of persons simultaneously, multiple types can
`be made by the mere duplication or multiplica-
`tion of the corresponding parts.
`-
`While I have in the foregoing described certain
`particular embodiments of the invention, it will
`be understood that they are merely for purposes
`of illustration to make clear the principles there-
`of, and that the invention is not limited to the
`
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`The proper scale having been so determined, the.
`switch is then moved to the “red" position. The
`four scales are so arranged that in each case 100%
`saturation corresponds to the full scale deflection
`of the measuring instrument. The adjustment
`of the chosen Scale is obtained by varying the in—
`' cident, “red” light intensity by means of the rheo-
`- stat l8 until the correct reading for a known oxy-
`gen content (100% with oxygen or 96% with air)
`is obtained for one point on the scale. Any other
`degree of oxygen can then be read directly on
`that scale. The reading is quick, almost instan-
`taneous; and by holding one’s breath, can be seen
`to drift down from a normal content of about
`96% to say 80%, 70% or lower, depending on the
`depletion of oxygen occurring. This rapid and
`continuous reading of the oxygen content of the
`blood, without taking blood samples, is the chief
`advantage of the instrument.
`Care should be taken that carbon monoxide is
`not present, as its effect on the color of the blood
`is similar to oxygen.
`In order to compare one ear with another, the
`incident light,
`in. the “green” position of the
`switch, must always be the same. This is secured
`by initially placing a neutral filter of constant
`transmiSsion in the position of the ear and then
`adjusting the brightness of the lamp until the in-
`strument comes to a predesignated mark on the
`calibration scale, determined by the original cali-
`bration from known data. This method of ad—
`Justment automatically compensates for slow
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`Apple Inc. EX1015 Page 6
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`IPR2018-00294
`Apple Inc. EX1015 Page 6
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`strument operable by either or said cells, said in-
`strument having different- scales with marks at
`different locations thereon to indicate which type
`scale is to be used, said indication being made by
`operation or the first mentioned filter and cell,
`and difi'erent oxygen calibrations on said scales
`whereby the oxygen content may be directly
`read by operating the instrument by the second
`color filter and cell and reading the oxygen con-
`tent on the scale previously indicated, means for
`increasing the' brightness of the light source when
`the first color filter and cell is used and means
`for reducing the brightness when the second
`filter and cell is used, a switch selectively con—
`nected to either light sensitive‘cell and the meas-
`uring instrument, a second switch connected to
`the means for rendering operative the brightness
`control means of the light source according to
`which filter and cell is used, and means for op—
`erating said switches simultaneously.
`5. In an oxygen meter, means for obtaining
`electrical indications‘comprislng in combination
`a light source, a red light filter and light sensi-
`tive cell, a green light filter and light sensitive
`cell, said green filter and cell being of greater
`area than the red filter and cell whereby efiects
`of the same general order of magnitude are ob-
`tained when applied to oxygen determination in
`the blood, means lor attaching said light source,
`filters and cells to the ear, whereby they may re-
`spond to the color of the blood in the ear, and a
`measuring instrument operable by either of said
`cells.
`6. In an oxygen meter, means for obtaining
`electrical indications comprising in (combination
`a light source, a red light filter and light sensi—
`tive cell. a green light filter and light sensitive
`cell, said green filter and cell being of greater
`area than the red filter and cell, a measuring in-
`strument operable by either of said cells, and
`means for increasing the brightness of the light
`source when the green filter and cell is used and
`for reducing the brightness when the red filter
`and cell is used. whereby the same general scale
`of measurement may be used with either the red
`or the green light indications when applied to
`oxygen determination in the blood.
`'1. In an oxygen meter, the combination of a
`light source, a color filter and light sensitive cell
`for the selection of types operable by said light
`source and responsive to wave lengths which are
`equally absorbed by oxyhemoglobin and reduced
`hemoglobin, a second color filter and light sensi—
`tive cell for oxygen determination responsive to
`wave lengths which are absorbed differently by
`reduced hemoglobin than by oxyhemoglobin,
`means for clamping said light source, filters and
`cells on the ear of the subject to be measured, a
`measuring instrument operable by either of said
`cells, said instrument having diflerent scales with
`marks at different locations thereon to indicate
`which type or scale is to be used, said indications
`being made by operation of the first mentioned
`filter and cell, and different oxygen calibrations
`on said scales, whereby the oxygen content may
`be directly read by operating the instrument by
`the second color filter and cell and reading the
`oxygen content on the scale previously indicated,
`means for increasing the brightness of the light
`source when the first color filter and cell is used
`and means for reducing the brightness when the
`second filter and cell is used. a switch selectively
`. connected to either one of the light sensitive cells
`and the measuring instrument. a second switch
`connected to the means for rendering operative
`75
`
`particular form described, but is subject to vari-
`ous modifications and adaptations in difi’erent
`installations as will be apparent to those skilled
`in the art without departing from the scope or
`the invention as stated in the following claims.
`I claim:
`.
`1. In an oxygen meter, the combination of a ‘
`light source, a color filter and light sensitive cell
`for the selection of types operable by said light
`source and responsive to wave lengths which
`are equally absorbed by oxyhemoglobin and re-
`duced hemoglobin, a second color filter and light
`sensitiVe cell for oxygen determination operable
`by said light source and responsive to wave
`lengths which are absorbed differently by reduced
`hemoglobin than by oxyhemogiobin, - a measur-
`ing instrument, a switch for connecting the
`measuring instrument
`to either light sensitive
`cell so that it is operable by either of said cells,
`said instrument having diiferent scales with
`marks at different locations thereon to indicate
`which type scale is to be used, said indication be- ,
`ing made by operation of the first mentioned
`filter and cell, and different oxygen calibrations
`on said scales, whereby the oxygen content may
`be directly read by operating the instrument by
`the second color filter and cell and reading the
`oxygen content on the scale previously indicated.
`2. In a colorimeter. the combination of a light
`filter and alight sensitive cell responsive to green
`light which is equally absorbed by oxyhemo-
`globin and red