Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1997-04-02
2001-02-27
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S323000
Reexamination Certificate
active
06195575
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a non-invasive fetal intrauterine sensor, in particular a pulse oximeter 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 supplying the tissue, and the rate of blood pulsations corresponding 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 portion 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 constituent in the tissue and the related light absorption. For measuring blood oxygen level, such sensors have been provided with light sources and photodetectors that are adapted to operate at two different wavelengths, in accordance with known techniques for measuring 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 placement.
The environment in which the non-invasive intrauterine sensor must operate is fluid-filled (e.g., by amniotic 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 operating 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 vernix 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 complicated 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 characteristics.
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. However, 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 intrauterine use.
U.S. Pat. No. 5,247,932 shows a bladder between the fetus and the uterine wall which presses the active face of the sensor against the fetus' skin. U.S. Pat. No. 5,377,675 discloses a sensor using a fulcrum to bias the sensor against the fetus.
SUMMARY OF THE INVENTION
The present invention provides a fetal sensor with a means for biasing the sensor against the fetus, with the biasing means being automatically self-inflating and insertable in compressed form. The biasing means in a preferred embodiment is a compressed foam or sponge which expands upon being exposed to fluid, such as amniotic fluid within the uterus. Thus, the biasing means can be compressed to allow easy insertion, and then can automatically expand once in place to provide the pressure needed to hold the sensor against the fetus.
Preferably, the biasing means is made of an open-cell foam or sponge, with the foam or sponge cells being connected by capillaries to provide a capillary force for maximum expansion upon exposure to fluid. The foam is preferably covered with a smooth material, such as silicone, for minimizing friction during insertion and facilitating cleaning of the sensor. The cover has an opening for allowing the fluid to enter the internal foam.
REFERENCES:
patent: 3306966 (1967-02-01), Matejcek et al.
patent: 3903232 (1975-09-01), Wood et al.
patent: 4768522 (1988-09-01), Shapiro
patent: 5247932 (1993-09-01), Chung et al.
Nellcor Puritan Bennett Incorporated
Townsend and Townsend / and Crew LLP
Winakur Eric F.
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