United States Patent [19]
`Goodman et al.
`
`[11] Patent Number:
`
`[45] Date of Patent:
`
`4,938,218
`
`Jul. 3, 1990
`
`[54] PERINATAL PULSE OXIMETRY SENSOR
`Inventors: David E. Goodman, San Francisco;
`[75]
`Jessica A. Warring, Millbrae; Paul D.
`Mannheimer, San Mateo, all of Calif.
`
`[73] Assignee: Nellcor Incorporated, Hayward,
`Calif.
`
`4,281,659 8/1981 Farrar et al. ........................ 128/635
`4,299,232 11/1981 Zilianti ................................ 128/642
`4,321,930 3/1982 Jobsis et al. ......................... 128/633
`4,324,256 4/1982 Vesterager .
`4,350,165 9/1982 Striese .
`4,370,984 2/1983 Cartmell .
`(List continued on next page.)
`
`[21] Appl. No.: 264,196
`
`[22] Filed:
`
`Oct. 28, 1988
`
`Related U.S. Application Data
`[60] Continuation-in-part of Ser. No. 217,080, Jul. 7, 1988,
`abandoned, and Ser. No. 206,918, Jun. 13, 1988, aban­
`doned, which is a continuation of Ser. No. 105,509,
`Oct. 5, 1987, abandoned, which is a continuation of
`Ser. No. 941,540, Dec. 11, 1986, abandoned, which is a
`continuation of Ser. No. 789,580, Oct. 21, 1985, aban­
`doned, which is a division of Ser. No. 644,05 I, Aug. 24,
`1984, abandoned, said Ser. No. 217,080, is a continua­
`tion of Ser. No. 935,060, Nov. 21, 1986, abandoned,
`which is a continuation of Ser. No. 644,051, which is
`a continuation-in-part of Ser. No. 527,726, Aug. 30,
`1983, abandoned.
`Int. Cl,5 ................................................ A61B 5/00
`[51]
`[52] U.S. CI ..................................... 128/633; 128/664;
`128/666; 128/643
`[58] Field of Search ................ 128/633, 634, 664-677,
`128/643
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`Richter .
`3,167,658 1/1965
`Gordy.
`3,599,629 8/1971
`3,602,213 8/1971
`Howell .
`Lavallee ................................ 356/41
`3,647,299 3/1972
`3,659,586 5/1972
`Johns et al . .
`Herczfeld et al.
`3,704,706 12/1972
`Smart et al . .
`3,769,974 11/1973
`Page ................................ 128/205 P
`3,841,314 10/1974
`Page ................................ 128/205 T
`3,858,574 1/1975
`Ulrich et al. .................... 128/205 P
`3,983,866 10/1976
`4,013,067 3/1977
`4,041,932 8/1977
`4,091,803 5/1978
`4,197,853 4/1980
`4,244,375 1/1981
`
`122
`
`FOREIGN PATENT DOCUMENTS
`671279 10/1963 Canada .
`72185 2/1983 European Pat. Off . .
`104619 4/1984 European Pat. Off . .
`0135840 4/1985 European Pat. Off . .
`94749 11/1988 European Pat. Off . .
`1909882 9/1970 Fed. Rep. of Germany .
`2517129 4/1975 Fed. Rep. of Germany .
`2830412 1/1980 Fed. Rep. of Germany .
`9053585 5/1985 Japan .
`
`OTHER PUBLICATIONS
`Holscher, Uvo, "A Novel Approach for an ECG Elec­
`trode Integrated Into a Transcutaneous Sensor", Con-
`(List continued on next page.)
`
`Primary Examiner-Francis Jaworski
`Assistant Examiner-John C. Hanley
`Attorney, Agent, or Firm-Mark D. Rowland
`[57]
`ABSTRACT
`An apparatus for use in measuring fetal blood flow
`characteristics. The apparatus includes a non-invasive
`pulse oximetry probe that is inserted into the uterus
`between the fetus and the uterine wall. The probe is
`deformable and is positively attached to the fetal tissue
`surface using a vacuum pump which causes the probe to
`deform from a pre-set curvature to the curvature of the
`fetal tissue surface and to form a gasket-type seal with
`the fetal tissue surface. The probe is manually inserted
`into the uterus using a curved insertion tool, and is
`shaped to fit through a slightly dilated cervix. In a pre­
`ferred embodiment, the probe includes fetal and mater­
`nal ECG sensors and additional sensing devices, and is
`provided with apparatus for improving the efficiency of
`the pulse oximetry optics.
`
`12 Claims, 8 Drawing Sheets
`/------
`
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`
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`
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`
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`
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`/56 // gl' .::,
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`144
`
`/02
`
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`
`�/42
`
`I /
`
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`
`MASIMO 2010
`Apple v. Masimo
`IPR2020-01526
`
`

`

`4,938,218
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`Jobsis et a1.
`4,380,240 4/ 1988
`4,396,017
`8/1983 Delpy et a1.
`4,510,938
`4/1985 Jobsis et a1.
`4,537,197
`8/1985 Hulka.
`
`......................... 128/633
`.
`......................... 128/633
`
`OTHER PUBLICATIONS
`
`tinuous Transcutaneous Monitoring, Plenum Press, 1987;
`pp. 291—293.
`Rudelstorfer, Rudolf, et a1., “Scalp Heat Flux and its
`Relationship to Scalp Blood pH of the Fetus”, Am. J.
`Obstset, Gynecol, Aug. 1977; 157:372—377.
`Geddes, et a1., Med. & Bio. Eng. & Comput., May 1977;
`15:228—231.
`
`Takatani, et a1., ACEMB, LA, Ca1if., Nov. 1977; 30:171.
`Viniker, D. A., The Fetal EEG (Detection of Oxygen
`Deprivation), British Journal of Hospital Medicien,
`Nov. 1979; 504-510.
`Weller, C., et a1., Fetal Electroencephalography Using
`a New, Flexible Electrode, British Journal of Obstetrics
`and Gynecology, Oct. 1981; 88:983—986.
`Silicon Detector Corporation (“SDC”), Data Sheet,
`General Purpose Detectors, undated.
`
`EG&G Electro Optics, Data Sheet, “Silicon Diffused
`Pin Photodiodes, SGD Series”.
`United Detector Technology (“UDT”), Data Sheet,
`Planar Diffused Silicon Pin Photodiodes, undated.
`Goodlin, R. C., Intrapartum Fetal Heart Rate Re-
`sponses and Plethysomographic Pulse, Amer. J. Obstet.
`Gynec, 1971; 1102210.
`Goodlin, R. C., Fabricant, S. J., A New Fetal Scalp
`Electrode, Obstet. GynecaL, 1970; 35:646.
`Goodlin, R. C., Girard J., Hollmen A., Systolic Time
`Intervals in the Neonate, Obstet. Gynecol., 1972;
`39:295.
`
`Seeds, J. W., Cefalo, R. 0., Near Infrared Spectropho-
`tometry: A New Technique for Assessing Fetal Hyp-
`oxia, Surg. Forum, 1982; 33:481.
`Jobsis, F. F., Noninvasive, Infrared Monitoring of Ce-
`rebral and Hyocardial Oxygen Sufficiency and Circula-
`tory Parameters, Science, 1977; 198:1264.
`Goodlin, R. C., Fetal Heart Rate Monitoring, In: Goo-
`dlin, R. C., Care of the Fetus, New York:Masson Pub-
`lishing, 1979:101—110.
`Seeds, .1. W., Cefalo, R. C., et a1., The Relationship of
`Intracranial Light Absorbance to Fetal Oxygenation,
`Am. J. Obstet. Gynec, 1984; 149:679.
`
`

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`1
`
`4,938,218
`
`PERINATAL PULSE OXIMETRY SENSOR
`
`REFERENCE TO PRIOR APPLICATIONS
`
`This application is a continuation-in-part of co-pend-
`ing and commonly assigned United States application
`Ser. No. 217,080, filed July 7, 1988, now abandoned,
`and application Ser. No. 206,918, filed June 13, 1988.
`Application Ser. No. 217,080 is a continuation of appli-
`cation Ser. No. 935,060, filed Nov. 21, 1986 and now
`abandoned, which is a continuation of application Ser.
`No. 644,051, filed Aug. 24, 1984 and now abandoned,
`which is a continuation-in—part of application Ser. No.
`527,726, filed Aug. 30, 1983 and now abandoned. Appli-
`cation Ser. No. 206,918 is a continuation of application
`Ser. No. 105,509, filed Oct. 5, 1987, which is a continua-
`tion of application Ser. No. 941,540, filed Dec. 11, 1986
`and now abandoned, which is a continuation of applica-
`tion Ser. No. 789,580, filed Oct. 21, 1985 and now aban-
`doned, which is a divisional of the above-referenced
`application Ser. No. 644,051 now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a non-invasive pulse
`oximetry intrauterine sensor.
`Pulse oximetry is typically used to measure various
`blood flow characteristics including, but not limited to,
`the blood-oxygen saturation of hemoglobin in arterial
`blood, the volume of individual blood pulsations sup-
`plying the tissue, and the rate of blood pulsations corre-
`sponding to each heartbeat of a patient. Measurement of
`these characteristics has been accomplished by use of a
`non-invasive sensor which passes light through a por-
`tion of the patient’s tissue where blood perfuses the
`tissue, and photoelectrically senses the absorption of
`light in such tissue. The amount of light absorbed is then
`used to calculate the amount of blood constituent being
`measured.
`
`The light passed through the tissue is selected to be of
`one or more wavelengths that are absorbed by the
`blood in an amount representative of the amount of the
`blood constituent present in the blood'. The amount of
`transmitted light passed through the tissue will vary in
`accordance with the changing amount of blood constit-
`uent in the tissue and the related light absorption. For
`measuring blood oxygen level, such sensors have been
`provided with two sets of light sources and photodetec-
`tors that are adapted to operate at different wave-
`lengths, in accordance with known techniques for mea-
`suring blood oxygen saturation.
`Known non-invasive sensors include devices that are
`secured to a portion of the body, such as a finger, ear or
`the scalp. In animals and humans, the tissue of these
`body portions is perfused with blood and the tissue
`surface is readily accessible to the sensor.
`It is desirable that photoelectric pulse oximetry also
`be useful for monitoring the blood flow characteristics
`and constituents of a fetus. For example, monitoring
`fetal oxygen levels provides an effective way to detect
`and provide indications for treating hypoxia in the fetus
`during labor. However, known sensors adapted for use
`on infants or adults are not suited for intrauterine place-
`ment.
`The environment in which the non-invasive intrau-
`terine sensor must operate is fluid-filled (e. g., by amni-
`otic fluid) and is only accessible through the restricted
`opening of the cervix. Visual inspection of the fetus and
`the sensor is likewise restricted. Moreover, the operat-
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`ing environment presents certain variants that interfere
`with detection of the fetal blood flow characteristics
`using known pulse oximetry techniques. For example,
`the presence of the waxy vemix caseosa, hair, mucus,
`blood and dead tissue cells on top of the fetal tissue
`surface against which the sensor is to be positioned
`create a problem in establishing contact between the
`optical components of the sensor and the surface of
`blood-perfused tissue. Detection of fetal blood flow
`characteristics by pulse oximetry is particularly compli-
`cated by the relatively low perfusion and low oxygen
`saturation of blood in fetal tissue. These environmental
`factors prevent known sensors from providing reliable
`information needed to calculate fetal blood characteris-
`tics.
`
`It is known that positive attachment of a sensor to the
`tissue surface improves the quality of the photoelectric
`signal provided by the sensor. Positive attachment to a
`human’s tissue may be obtained by vacuum, adhesives,
`tapes or devices such as Clothespin-type clips. How-
`ever, fetal tissue is relatively moist and there is limited
`access to the tissue surface. Consequently, conventional
`adhesives or tapes or clips are not adapted for intrauter- _
`ine use.
`
`Known techniques involving invasive attachment to
`fetal tissue, such as by a screw attachment penetrating
`the tissue, creates a risk that the fetus will suffer an
`infection or disfigurement. Non-invasive attachment,
`such as by vacuum, may also result in disfigurement if
`the sensor includes sharp surfaces that press into the
`fetal tissue surface, or if the sensor is attached to the
`fetal tissue surface with excessive force (e.g., heavy
`vacuum suction).
`Moreover,
`the intrauterine probe sensor must be
`safely and reliably deliverable to the point of contact
`with the fetus. It is desirable that intrauterine fetal moni-
`toring be available early in labor, for example, to detect
`and treat hypoxia in the fetus during labor. Contact
`with the fetus can be made after natural rupture of the
`amniotic membrane by manually inserting a probe sen-
`sor into the uterus from the vagina, but access to the
`fetus through the vaginal canal is restricted by the cer-
`vix, which may be only slightly dilated to one or two
`centimeters when the membrane ruptures. Thus there is
`need for a fetal probe sensor that can be delivered to the
`fetus through a slightly dilated cervix, and a delivery
`system for doing so safely and reliably.
`The present invention is directed to measurement of
`the fetal blood flow characteristics using a probe sensor
`adapted for intrauterine placement. The sensor can be
`adapted to operate in accordance with the photoelectric
`pulse oximetry measuring techniques described above
`as well as to accomplish other measurement techniques
`for monitoring the well-being of the fetus. For example,
`it is well known that electrical heart activity corre-
`sponding to the heartbeat can be monitored externally
`and characterized by the electrocardiogram (“ECG”)
`waveform. The present invention contemplates that the
`ECG waveform of the fetus can be measured by provid-
`ing the probe sensor with an ECG electrode which is in
`electrical contact with the fetus when the probe sensor
`is in place in the uterus. Further, the present invention
`contemplates that maternal blood flow characteristics
`and the maternal ECG waveform also can be measured
`by providing the probe sensor with one or more light
`sources, one or more photoelectric detectors and an
`ECG electrode directed toward the uterine wall.
`
`

`

`4,938,218
`
`3
`the
`invention also contemplates that
`The present
`intrauterine probe sensor may include a thermistor to
`measure the temperature of the fetus, and a heat flux
`sensor to provide an indication of the adequacy of fetal
`tissue perfusion.
`The present invention contemplates further that non-
`invasive positive attachment can be accomplished with-
`out disfigurement of the fetus by using a deformable
`probe sensor which is positively attached by creating a
`partial vacuum in a cavity formed in the probe to cause
`the probe to conform to the tissue surface of the fetus
`and to form a gasket-type seal with the fetal tissue sur-
`face.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides an intrauterine probe
`sensor that can be inserted in the uterus shortly after
`rupture of the amniotic membrane and selectively posi-
`tioned between a fetus and the uterine wall, the probe
`including connections for a vacuum source for creating
`a partial vacuum in the probe to positively attach the
`probe to the fetus, and electrical connections for con-
`necting the probe sensor to equipment for powering the
`, sensor and for evaluating the signal outputs of the sen—
`sor. In the preferred embodiment, the probe sensor is a
`pulse oximetry sensor and the cabling is electrical ca‘
`bling for connecting the probe sensor to an external
`pulse oximeter.
`The probe has a narrow, oblong body that permits
`the probe to be inserted through a slightly dilated cer-
`vix. The body of the probe includes one or more hollow
`cavities and is made of a flexible, inert biomaterial such
`as silicone rubber. The probe has a concave peripheral
`surface for attaching the probe to the fetus.
`A gasket made of a material having greater compli-
`ancy than the fetal tissue surface is bonded to the con-
`cave peripheral surface of the probe. When the probe is
`positioned such that the gasket is adjacent the fetal
`tissue surface, a partial vacuum is created in one or
`more interior cavities of the probe, whereby the suction
`causes the probe body to deform and conform to the
`curvature of the fetal tissue surface. The gasket flattens
`outwardly to form a soft, substantially continuous area
`of contact with the fetus. A cream or gel sealant may be
`applied to the gasket to improve the seal between the
`gasket and the fetal tissue surface.
`The partial vacuum is created in the interior cavity of
`the probe by connecting the probe cavity to a pump in
`a sump configuration. A vent tube connects the interior
`cavity of the probe to the open atmosphere, creating a
`constant flow of air through the probe to prevent clog-
`ging of the vacuum line and to control the vacuum
`pressure in the probe. Humid air or a saline solution also
`may be pumped through the probe to prevent the fetal
`tissue surface from becoming dry. A porous material
`such as open cell silicone foam is used in the interior
`cavity of the probe to prevent fetal tissue from being
`drawn into the vacuum port, and to diffuse the flow of
`air through the cavity.
`The pump can be protected against contamination by
`a suction trap which contains filtering stages compris-
`ing hydrophobic filter elements to prevent passage to
`the pump of any fluid or airborne contaminants that
`have been evacuated from the probe, and which oper-
`ates independently of the orientation of the suction trap.
`Alternatively, the suction trap may be replaced by filter
`elements in the vacuum line including an absorbent
`medium for absorbing fluid and a bacterial filter for
`
`4
`removing contaminants from the air. In another alterna-
`tive embodiment, the suction trap or serial in-line ele-
`ments may be housed in a disposable cassette.
`The probe includes a structure located in one or more
`interior cavities for supporting the sensor, preferably
`pulse oximetry optics. In a preferred embodiment, the
`optics, which include two or more light emitting diodes
`(“LEDs”) for generating light at a plurality of selected
`wavelengths, and a photoelectric detector responsive to
`the wavelengths of light generated by the LEDs, are
`mounted on a flat substrate having electrical leads for
`connection to electrical cables extending outside of the
`uterus. The substrate can be lengthened, if desired, to
`permit the electrical leads to extend out of the uterus
`when the probe is in place, such that the connection
`between the leads and the electrical cable can be accom-
`plished outside of the uterus.
`-
`The probe is configured to assure that an adequate
`amount of light passes from the light sources through
`the blood-perfused fetal tissue to the photodetector to
`provide a signal for measuring the fetal blood flow
`characteristics. An optical barrier is provided between
`the LEDs and the photoelectric detector to prevent
`light from passing from the LEDs directly to the photo-
`electric detector without traveling through the fetal
`tissue In the preferred embodiment, a reflective material
`surrounding the LEDs and shaped for example as a
`cylindrical or parabolic reflector is provided to direct
`the light generated by the LEDs into the fetal tissue
`beneath the probe. A second reflector surrounding the
`photoelectric detector also is provided to direct light
`from the fetal tissue to the photoelectric detector and to
`prevent the detector from sensing shunted light. The
`optical barrier or either reflector may be formed of a
`conductive material and may operate as an ECG elec-
`trode. Alternately, a separate ECG electrode, which is ‘
`spring-loaded to provide good electrical contact with
`the fetal tissue, may be provided.
`The devices housed in the probe are mounted in a
`manner which protects the probe from the intrauterine
`environment, protects the fetal tissue surface from the
`probe, and imposes a contour on the fetal tissue surface
`in the vicinity of the optical devices to improve the
`consistency of measurements made by the sensor. For
`example, the probe can be provided with clear windows
`to cover and protect the optical devices. In a preferred
`embodiment, one or both of the windows have curved
`surface portions which, when brought into a contact
`with the fetal tissue surface, cause the tissue surface to
`dimple around the window. The dimpling effect thus
`created helps to prevent light from being shunted be-
`tween the light source and photodetector devices and
`improves the coupling between the optical devices and
`blood-perfused fetal tissue. The perfusion of blood in
`the fetal tissue between the light source and the photo-
`detector can be increased by creating a concave area in
`the surface of the probe between the optical devices.
`The probe may further be provided with optics and
`an ECG electrode for measuring maternal blood flow
`characteristics. The maternal ECG electrode may for
`example comprise a metallic button mounted on the
`surface of the probe body. In accordance with fetal
`ECG measurement techniques, the differential voltage
`between the fetal ECG electrode and the maternal
`ECG electrode can be used to determine the fetal ECG.
`In addition, other sensors such as a thermistor or a heat
`flux sensor or both may be provided, for example, to
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`4,938,218
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`5
`measure the temperature of the fetus and the perfusion
`of blood in the fetal tissue.
`The probe body preferably also includes one or more
`receptacles for receiving an end portion of the insertion
`tool. The insertion tool can be a narrow, shaped mem-
`ber preferably comprising a flexible material formed
`into a single or double curve. The insertion tool prefera-
`bly has a shaped end portion for insertion into one or
`more corresponding receptacles in the body of the
`probe to safely and reliably deliver the probe.
`It is therefore an object of the present invention to
`provide an improved intrauterine probe sensor which
`can be positively attached to fetal tissue without risk of
`disfigurement of the fetus.
`It is another object of the present invention to pro-
`vide an improved fetal pulse oximetry sensor that effi-
`ciently couples light signals between the sensor and
`blood-perfused fetal tissue.
`It is an additional object of the present invention to
`provide an improved fetal pulse oximetry sensor in
`which the sensor geometry imposes a contour on the
`fetal tissue surface in the vicinity of the optical devices
`of the sensor to improve the consistency of the oximetry
`measurements.
`
`It is also an object of the present invention to provide
`an improved fetal pulse oximetry sensor having a non-
`invasive fetal ECG electrode which also serves as an
`optical barrier and/or a reflector for improving the
`signal to noise ratio of the light detected by the sensor.
`It is yet a further object of the present invention to
`provide an improved intrauterine probe sensor having
`one or more spring-loaded ECG electrodes.
`It is yet an even further object of the present inven-
`tion to provide an intrauterine probe sensor that can be
`inserted in the uterus early in labor, and a delivery
`system for safely and reliably delivering the sensor to a
`desired location on the fetus.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The above and other objects and advantages of the
`present invention will be apparent upon consideration
`of the following detailed description, taken in conjunc-
`tion with the accompanying drawings, in which like
`reference characters refer to like parts throughout, and
`in which:
`
`FIG. 1 is a partially-exploded elevated perspective
`view of a first embodiment of the probe sensor of the
`present invention.
`FIGS. 2(a)—2(c) are perspective views of the optics,
`electrical cable, substrate and inner boot of the probe of
`FIG. 1.
`
`FIG. 3 is an exploded perspective view of an embodi-
`ment of a suction trap for use with the probe sensor of
`FIG. 1.
`
`FIGS. 4(a)—(b) are perspective views of an embodi-
`ment of an insertion tool of the present invention.
`FIG. 5 is a cross-sectional side view of a second em-
`bodiment of the probe sensor of the present invention
`having a segmented outer body.
`FIG. 6 is an elevated perspective view of a third
`embodiment of the probe sensor of the present inven-
`tion having an outer body shaped as a thin diaphragm.
`FIGS. 7(a)-(b) are top plan and bottom perspective
`views of a fourth embodiment of the probe sensor of the
`present
`invention including a fetal ECG electrode
`which also serves as an optical barrier.
`FIGS. 8(a)—(b) are top plan and bottom perspective
`views of a fifth embodiment of the probe sensor of the
`
`6
`invention including a fetal ECG electrode
`present
`which also serves as an optical barrier and a reflector.
`FIGS. 9(a)—(b) are top plan and bottom perspective
`views of a sixth embodiment of the probe of the present
`invention including two reflectors for increasing the
`efficiency of light
`transmission, and a spring-loaded
`fetal ECG electrode.
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`10
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`FIGS. 10(a)-(b) are top plan and bottom perspective
`Views of a seventh embodiment of the probe of the
`present invention.
`FIGS. 11(a)—(b) are top plan and cross-sectional side
`views of a preferred eighth embodiment of the probe of
`the present invention having protrusions over the light
`source and photodetector regions.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Various embodiments of the probe of the present
`invention are described herein and are shown in the
`figures. The preferred embodiment, which incorporates
`many features described in connection with other em-
`bodiments, is shown in FIGS. 11(a)—(b) and is described
`last.
`
`Referring to FIG. 1, probe 100 comprises outer body
`102 and inner boot 104 which house the photoelectric
`pulse oximetry measuring devices of the sensor. Inner
`boot 104 is shown apart from outer body 102 in FIG.
`2(c). Outer body 102 is molded in a substantially rectan-
`gular, oblong shape, and has a hollow interior cavity
`106 in which inner boot 104 is positioned.
`Outer body 102 and inner boot 104 are molded or cast
`from a flexible, inert biocompatible material such as
`silicone rubber. The outer body is preferably made
`opaque, such as by addition of a coloring agent (e.g.,
`white titanium dioxide). Inner boot 104, which encases
`the pulse oximetry optics, is preferably colored black to
`provide optical isolation between the probe’s pulse ox-
`imetry light sources and photoelectric detector, which
`are described in greater detail below.
`The height (or thickness) and width of outer body
`102 are preferably sized to fit probe 100 through a cer-
`vix which is approximately 1—2 centimeters dilated,
`although a probe having larger dimensions can of
`course be used after the cervix has become further di-
`lated. Accordingly, the probe of the present invention
`has a slender appearance. A typical length of probe 100
`is approximately 1.5 inches, although its length can be
`extended as necessary to encapsulate the electrical com-
`ponents of the probe (including electrical leads con-
`nected to those components) to isolate them from bio-
`logical fluids. A typical height of probe 100 is 0.45
`inches, and a typical width is 0.5 inches.
`Outer body 102 has a pair of narrow channels 108 and
`110 for receiving respectively legs 112 and 114 of U-
`shaped wire 116. Wire 116 forces outer body 102 to
`bend along its length in a concave curve defined by the
`strength of the wire, the curvature of legs 112 and 114
`and the stiffness of probe 100. When legs 112 and 114 of
`wire 116 are inserted fully in channels 108 and 110,
`curved neck 118 of wire 116 abuts the underside of lip
`120 of outer body 102, and is fixed in place by a flexible
`biocompatible adhesive. Wire 116 is formed from stain-
`less steel, and is heat treated to harden the steel and to
`help maintain its form. With wire 116 in place, probe
`100 has a concave curvature that preferably conforms
`approximately to the typical curvature of a fetal head.
`A typical value for the diameter of the fetal head is 4
`inches.
`
`

`

`7
`The approximate conformance of the pre-set concave
`curvature of probe 100 to the fetal tissue surface allows
`a partial vacuum to be created in cavity 106 when gas-
`' ket 122 of probe 100 is positioned against the fetal tissue
`surface and a negative pressure (vacuum) “is applied to
`cavity 106. As described further below, the negative
`pressure causes gasket 122 bonded to lip 120 of outer
`body 102 to create a soft-contact seal with the fetal
`tissue surface. By providing the probe with a pre-set
`curvature that closely approximates the curvature of 10
`the fetal tissue surface, the amount of negative pressure
`required to deform probe 100 sufficiently to create the
`seal between gasket 122 and the fetal tissue surface is
`minimized. In this manner the contact between the
`probe and the fetal tissue surface is softened, and the
`risk of potential disfigurement caused by the positive
`attachment of the probe to the fetal tissue surface is
`minimized.
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`5
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`15
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`In an alternative embodiment of probe 100, outer
`body 102 may be molded with the desired concave
`curvature to eliminate the need for wire 116 and to
`increase the flexibility of outer body 102.
`Outer body 102 further includes a pair of lengthwise
`receptacles 124 and 126 (not shown) for receiving the
`end portion of an insertion tool during insertion and
`placement of the probe in the uterus. Outer body also
`includes at one end conduits 128, 130 and 132 which
`receive respectively vacuum tube 134, vent tube 136
`and electrical cable 138. Vacuum tube 134 and vent tube
`136 are connected respectively via conduits 128 and 130
`to cavity 106 to provide a partial vacuum in and a flow
`of air through cavity 106, and may comprise conven-
`tional double-lumen tubing. Hereafter, the partial vac-
`uum created in the probe also is referred to simply as a
`“vacuum”. The end 139 of vacuum tube 134 is con-
`nected via a suction trap to a vacuum pump (trap and
`pump not shown in FIG. 1). The end 140 of vent tube
`136 is open to the atmosphere, such that when the pump
`is operated it draws air into vent tube 136 from the
`atmosphere and causes the air to pass through cavity
`106 and into the suction trap via vacuum tube 134. A
`conventional quick-disconnect (or “Luer”) connector
`142 is provided for releasably connecting vacuum tube
`134 to the suction trap, and a conventional clamp 144 is
`provided to clamp vacuum tube 134 when desired, such
`as during insertion, positioning and removal of probe
`100.
`
`Although vent tube 136 is not necessary to create a
`vacuum in cavity 106, it prevents vacuum tube 134 from
`becoming clogged by fluids and solid matter drawn into
`vacuum tube 134 from cavity 106.
`The level of vacuum in cavity 106 is a function of the
`length and diameter of vacuum and vent tubes 134 and
`136, and the flow rate of the vacuum pump. The vac-
`uum in cavity 106 is maintained at a level which is suffi-
`cient to achieve positive attachment to the fetal surface.
`Because of the pre-set curvature and flexibility of outer
`body 102 and the compliancy of gasket 122 (discussed
`below), positive attachment can be achieved at a vac-
`uum level which is not so high as to cause disfigurement
`of the fetal surface from the contact force of the probe.
`For example, positive attachment has been achieved
`using a diaphragm pump, set to a pressure within the
`range of 75-150 mmHg, with a 0.78 inch inner diameter
`vacuum tube 134 and a 0.020 inch inner diameter vent
`tube 136, both tubes being made of medical implant
`grade clear silicone and having equal lengths of approx-
`imately 3 feet.
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`4,938,218
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`8
`In an alternative embodiment, humid air or a saline
`solution may be suctioned from a source connected to
`vent tube 136, through cavity 106 and into vacuum tube
`134, to maintain a flow of liquid through cavity 106 for
`moistening the fetal tissue surface under probe 100.
`Inner boot 104 supports a substrate 155 on which two
`light sources are mounted in light source region 156,
`and on which a photodetector is mounted in photode-
`tector region 158. Regions 156 and 158 of the substrate
`are each coated by a thin layer of clear epoxy to protect
`the optical devices. Electrical connections to the light
`sources and photodetector from electrical cable 138 are
`provided by leads 146 which are electrically attached to
`the substrate. The exposed wire portions of leads 146
`and the solder joints by which they are attached to the
`substrate are insulated by encapsulating the ends of
`inner boot 104 with silicone adhesive 148. Adhesive is
`also used to hold inner boot 104 in place in outer body
`102.
`
`The inner walls of outer body 102 that surround pho-
`todetector region 158 are coated with a layer of black
`silicone rubber to prevent shunting. Shunting occurs
`when light emitted by the light sources reaches the
`photodetector without first passing through fetal tissue.
`A flexible, black silicone rubber optical barrier 152
`having a height when mounted approximately equal to
`the inner rim 154 of outer body 102 is provided between
`light source region 156 and photodetector region 158 to
`further optically isolate the photodetector from light
`generated by the light sources which does not pass
`through the fetal tissue. The optical barrier 152 prefera-
`bly is formed from the same material as outer body 102
`and inner boot 104, although other inert biomaterials
`may be used.
`Light source region 156 and photodete