US2790438A - Earpieces for oximeters - Google Patents

Description

April 30, 1957 R. H. TAPLIN ETAL EARPIEcEs FOR oxIMETERs 2 Sheets-Sheet l Filed Jan. l5, 1956 April 30, 1957 R. H. TAPLIN ETAL 2,790,438

EARPIECES FOR OXIMETERS Filed Jan. 13, 1956 2 Sheets-Sheet 2 which, unlike the rubber capsules previously used does not change its colour with age.

The invention will now be described with the assistance of the accompanying drawings, wherein a preferred embodiment is shown. It will be realized that various changes could be made in the embodiment shown and described and other apparently different embodiments of the invention could be constructed without departing from the scope thereof. Accordingly it is intended that :all matter shown in the accompanying drawings or described herein shall be interpreted as illustrative and not in a limiting sense.

In the drawings wherein like parts are denoted by identical reference numerals,

, Figure l shows an oblique threeuarters view of a preferred embodiment of the invention;

Figure 2 shows a side elevation View of the device illustrated in Figure l;

Figure 3 shows a cross-sectional view of the device illustrated in Figures l and 2 as it would be used in association with the pinna of the ear;

' Figure 4 shows a fragmentary cross-sectional view indicating the structure 4of the inilatable capsule;

IFigure shows a cross-sectional view `taken as at 5 5 in Figure 2;

Figure 6 shows an oblique three-quarters partly eX- ploded view of the device; and

Figure 7 shows a circuit diagram illustrating the function of the device described herein.

' Referring to the accompanying drawings wherein the same reference numerals denote like parts in all figures, the earpiece device will be seen to have a bifurcated or clamp-shaped structure adapted to surround the pinna of the ear. For convenient reference the earpiece may be described -as consisting of a light-emitting portion, which is cylindrical in shape and a light-receiving portion of box-like appearance connected by a bracket denoted by 2. The pinna of the ear is denoted by 1.

The light adapted to be transmitted through the pinna 1 'is supplied by any convenient source, such as a small incandescent lamp shown at 3. Lamp 3 preferably consumes approximately one watt, which, in addition to supplying the necessary light, will provide suilicient heat to dilate the blood vessels of the pinna 1. It` is contemplated that alternating current of a frequency of, for example 30 cycles per second will be supplied to lamp 3, the reason for which will be apparent below. Lamp 3 is mounted in a conventional socket, shown at 4, and socket 4- is suitably held in a tubular lamp holder denoted by 5.

Lamp holder 5 is preferably provided with a pair of flanges denoted by 6 and 7, flange 7 being at the end of ltubular member 5 and of slightly larger diameter than flange 6. The purpose of iianges 6 and 7 is to effect suitable mounting on bracket 2 and to this end bracket 2 is provided with a ring denoted by 8 of such internal diameter that ange 6 slides easily wihtin ring 8 but flange 7 is unable to enter the said ring. A set-screw denoted by 9 is threadably mounted in a suitable opening in the part of bracket 2 where the latter is formed into ring S. The power supply wires for lamp 3, denoted by 10 and 11, pass out of lamp holder 5 -through one or more suitable openings.

Extending from lamp holder 5 is a telescopic tubular member denoted by 12 having an internal diameter such that it is able to receive lamp holder 5 therewithin, and is able to slide freely over the said lamp holder. It is contemplated that the ends of tubular member 12 opposite lamp holder 5 will be pressed toward the pinna 1 in a manner to be described below.

A helical spring denoted by 13 is provided inside tubular member 12, and it is preferable if spring 13 is of such size that it touches the internal walls of tubular member 12 without sticking or binding. At the end of tubular member 12 opposite lamp holder 5 is a transparent window denoted by 14.V A slidable collar shown` at 15 is also provided of such size that it moves easily along the inner wall of tubular member 12, and it is contemplated that spring 13 will urge Window 14- and collar 15 apart thereby tending to telescopically extend tubular member 12 away from lamp holder 5.

Attached to collar 1S is a threaded shaft denoted by 16 and shaft 16 passes loosely through an unthreaded opening in bracket 2, denoted by 17. A clamping nut denoted by 18, suitably threaded to engage shaft 15 is provided, and it will be apparent that when clamping nut 1S is tightened, tubular member 12 is locked between collar 15 and bracket 2. A slot, denoted by 19 is provided in tubular member 12 so that when clamping nut 18 is loose, tubular member 12 may be telescopically slid on lamp holder 5, and will be urged away from the said lamp holder; and alternatively, the tightening of clamping nut 18 will lock tubular member 12 in whatever position it then happens to be in relation to lamp holder 5.

The window 14 at the end of tubular member 12 has already been referred to. For reasons which will be apparent below, window 14 should be so mounted in tubular member 12 that an air-tight seal is produced. In order to provide appropriate pressure on pinna 1, it is contemplated that an inatable capsule will be provided by stretching a resilient membrane over window 14 and incorporating means for supplying air under pressure to the space between the window 14 and such membrane. The membrane, denoted by 20 is preferably made of polyvinyl acetate plastic film which does not change its colour with age. Membrane 2i) is stretched over the end of tubular member 15 and secured by a fastening ring denoted by 21, which may be, for example, several strands of thread wound therearound. An air tube denoted by 22 communicates with the space between window 14 and membrane 20, and a iiexible tube, denoted by 23 is used to apply air under pressure to tube 22.

It will be apparent that the device disclosed above is convenient for applying the proper pressure to the pinna 1. The telescopic relationship of tubular member 12 and lamp holder S, and the action of spring 13 provides a simple manner of engaging vpinnae of a wide range of sizes. When such engagement is made, clamping nut 18 may be tightened to hold tubular member 12 in place, and appropriate air pressure can then be applied to tube 23 to compress the pinna to the required degree and to release such pressure when desired.

Referring now to the light-receiving portion of the device, in contact with which ination of membrane 20 compresses pinna 1, the said light-receiving portion consists of two housing members denoted by 24 and 25 and various components contained therein, kto be described below. Housing member 24 is integraly with bracket 2 and housing member 25 is attached to housing member '24 by means of capscrews denoted by 26.

Held within housing members 24 and 25 is a block of transparent material denoted by 27, preferably of the particular shape shown. Block 27 is preferably of an acrylic resin with suitable optical properties such as Lucite which provides a significantlight-pipe effect common to such materials. The light-pipe elect is produced by the combination of transparency and a highly reective surface and accordingly various other materials having similar characteristics could of course be used.

It is intended that the light transmitted through the pinna' will be gathered by block 27 and transmitted through a length at least three times that of the aperture diameter where the light enters block 27, with little light loss and absence of image formation.

Block 27 has a forward polished face denoted by 27a forming the light-receiving aperture adapted to touch the pinna 1. Housing member 24 is so constructed that forward portion 27a lies flush with the surface of housing member 24facing tubular member 12. Block 27 also has adiagonal face denoted by 27b,the surface of n which is also polished. The remainder of block 27 deiined` by surfacesdenoted by 27d and 27e'is a simple rectangular prism highly polished so Vas to reflect any light falling upon its inner `surface. The end of block 27 opposite face 27a is denoted by 27c, and attached'to face 27e is a filter block, denoted by 28 to be described below. Obviously, all the surfaces of block 27 have ito be fiat as opposed to rounded, otherwise thereY would be a tendency to focussing, with bright andY dull gradations of light intensity.

The manner in which the light is transmitted from lamp 3 will be apparent from the foregoing description, but for greater certainty will now be `reiterated. Light from lamp 3 passes through4 window 14, membrane 20 and thence through pinna 1 where it falls upon the surface 27a of block 27. 'It will be apparent that the pinna 1 being translucent but not transparent will transmit light therethrough in such a manner that the light passes out of the pinna 1 through a solid angle of 180. Accordingly the light reaching surface 27a is passing in every direction and is necessarily scattered. A large portion of the light so transmitted falls upon surface 27b, and as a result of the characteristics of the surface 27b previously referred to, such light is further scattered. The light not falling on surface 27b strikes the surface 27d over that portion of its surface which is adjacent surface 27a and by virtue of the light scattering characeristics of the block 27 is reflected downward to surface 27e and thence to filter block 28. In the result, the light reaching filter block 28 is almost completely scattered and entirely homogeneous and forms no image.

The filter block 28 attached to block 27 will now be described. As seen in Figure 7 the filter block consists of four filter components denoted by reference numerals 28a, 28b, 28C and 28d. Integral with the said filter components are photoelectric cells denoted by 29a, 29b, 29e and 29d, respectively.

The filter components 28a and 28d are so arranged as to provide maximum sensitivity of photoelectric cells 29a and 29d at 650 mp and filter components 28b and 28e will provide maximum sensitivity of photoelectric cells 29h and 29e at 800 mp.. It will be appreciated that it is not necessary that the sensitivity characteristics be in the exact arrangement described, and there are several obvious juxtapositions. Photoelectric cells 29a and 29d are connected to outlet lead 30 and photoelectric cells 29b and 29e are connected to outlet lead 31. Leads 30 and 31 are connected to amplifier means to be described below where the light transmission characteristics are interpreted in terms of degree of blood oxygenation.

Leads 30 and 31 pass through a cable denoted by 33 which connects the earpiece to the amplifiers. Since the leads 30 and 31 carry very weak currents, it is preferable that they be shielded. Lines and 11 already referred to also pass through cable 33. Line 10 passes through an opening in housing 24, denoted by 32 and thence to lamp 3. Line 11 also passes through opening 32 and to the other side of lamp 3, and line 11 is connected to the body of housing 24 near where it enters cable 33. A-t the end of cable 33 opposite the earpiece, line 11 is suitably grounded. The current supply for lamp 3 is shown at 34 and furnishes an oscillating current of the order of cycles per second.

Lead 30 is connected to an amplifier denoted by 35 and lead 31 is connected to a second amplifier denoted by 36. These two amplifiers are quite conventional and are similar except for one feature to be described below.

The output of amplifier 35 is applied to a rectifier shown at 37 which is in turn connected to a vacuum-tube voltmeter the principal components of which are triode 38 and meter 39. A bias control shown at 40, and an associated rectifier shown at 41 are also provided.

Amplifier 36 is similarly connected to a rectifier shown at 42, which is in turn connected to vacum-tube voltmeter elements consisting of triode 43 and meter 44. A

YIt will be apparent that there are two principal variables here involved, namely the thickness of the -pinna through which light is transmitted, and the attenuation of the light because of the degree of oxygen saturation. It is contemplated that the amplifier 36 will provide the means of measurement ofthe degree of oxygen saturation, and

amplifier 35 will provide a correction for the vthicknessl of the pinna observed. Accordingly, amplifier 36'- will sense the amplitude of waves resulting from 'lighttransmitted of the order of 60 mp. (red) and ampliiierfSS will sense the amplitude of waves resulting from light transmitted of the order of 800 my. (infra red). Since the latter are not significantly affected by the degree of oxygen saturation, it is convenient -to use amplifier 35 to provide the correction for the pinna thickness.

A description of the operation of the device will illustrate the method of calibration as well as the other operational features. The pinna is first placed in the proper position as shown in Figure 3 and the membrane 20 is inflated so as to press most of the blood out of the pinna. Lamp 3 will then be emitting light as well as heat, and this heat will assist in dilating the blood vessels of the pinna, so as to assist in providing light transmission therethrough. The light passes through the pinna 1 rela-tively easily. Since the light is produced by an oscillating current of the order of 30 cycles per second, there will be produced at the photoelectric cells modulated waves of the same frequency, and these waves will be passed to amplifiers 35 and 36. Both meters 39 and 44 will normally show initial readings and bias controls 40 and 45 are then adjusted so that both meters 39 and 44 read zero.

The pressure on membrane 20 is then released and a definite reading will then be shown on meters 39 and 44. There is a-relationship between the readings of meters 39 and 44, such that a plot of V(where R47 is the resistance of shunt 47, R44 is the resistance of meter 44 and Ias is the current read at meter 39) is a straight line. That is to say, the amplifier 36 may be corrected by adjustment of shunt 47 in accordance with the reading of meter 39 to allow meter 44 `to give an indication which is independent of the thickness of pinna 1. Meter 44, by suitable calibration with the assistance of .known samples of arterial blood, the `oxygen saturation of which is determined gasometrically, can indicate percentage saturation directly.

After shunt 47 has been adjusted as above, meter 44 will show a changed reading, and this new reading by virtue of the calibration referred to will indicate percent oxygen saturation. It may be mentioned that the device may be continued in use for a considerable period after it has once been put in operation as described, and it is only necessary to change the setting of shunt 47 in accordance with the reading of meter 39," if necessary, to restore correct conditions, and the condition of the blood of the subject wearing the device described will be continuously indicated on meter 44.

It will be seen that the device described herein has numerous advantages; it is simple and rugged in construction, simple to apply and can be used Without extensive training on the part of the operator.

What is claimed is:

1. An oximeter earpiece capable of being used in as sociation with the human ear, comprising a source of light adapted to be placed on one side of a portion of the ear,

averties a -light scattering means adapted to be placed on the opposite side ofthe said portion of the ear, said light scattering means consisting of a polished transparent block having a at surface facing said source of light, an angular face making an acute angle with said Hat surface and a rectangular prismatic section oneend of which is formed by said angular face, a bifurcated frame member attached to said source of light and to said light scattering means and photoelectric light-receiving means attached to said frame member on the same side thereof as said light scat tering means.

2. A device according to claim l, wherein said photoelectric light receiving means consists of a plurality of photoelectric cells adjacent the end of said light-scattering means opposite said angular face, and having lter means interposed between said photoelectric cells and said light scattering means.

Y 3. A device according to claim 1, Ywherein said photoelectric light receiving means consists of a plurality of photoelectric cells one half of which have maximum sen sitivity at the region of 650 ma and the other half of which have maximum sensitivity at the region of 850 mu, said cells which have maximum sensitivity at the region of 650 my. being intel-spaced with said cells having maximum sensitivity at the region of 850 mp, and having in addition, lter means interposed between said photoelectric cells and said light scattering means.

References Cited in the le of this patent UNITED STATES PATENTS 2,754,819 Kirschbaum July 17, 1956

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