Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-03-10
2004-06-15
Bockelman, Mark (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
Reexamination Certificate
active
06751498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates generally to biomedical devices and, in particular, comprises a non-invasive and passive apparatus and method that uses sensors and signal processing techniques to monitor fetal electrocardiographic waveform (EKG
f
), heart rate, heart rate variability and heart vector orientation and maternal heart rate and uterine contraction noise artifacts.
2. Description of the Related Art
Though the perinatal mortality rate in the United States has decreased significantly in the past three decades, the vast majority of the current perinatal deaths are thought to be attributable to potentially preventable etiologies. Prematurity, intrauterine hypoxia, perinatal infections, and maternal complications account for 60 to 80% of perinatal losses.
Maximizing the health and well-being of the mother and fetus by appropriate medical intervention is the general goal of obstetrical care. Effective monitoring of a fetus may require continuous assessment, and is commonly performed using electronic technology. However, recent escalation of the frequency of normal births by cesarean section has called into question the validity of present monitoring techniques with respect to specificity of identifying the fetus at risk. Reducing the number of unnescessary cesarean sections and, in general, reducing the number of babies that are seriously ill at birth has been raised as a national health care priority in an effort to reduce the cost of both short- and long-term health care.
Fetal assessment in this context is intended to detect conditions that, if continued; would likely result in fetal and newborn damage or death. The condition of the fetus is reflected by the cardiovascular responses in utero and may be recognized by monitoring the fetal heart rate.
The difficulties in monitoring fetal well-being have long been recognized by the medical profession. The variable position of the fetus within the womb, surrounded by the amnion and amniotic fluids makes direct examination of the fetus impossible or very difficult using most examination techniques.
Present electronic fetal heart rate monitoring shows great sensitivity, but inadequate specificity, and poor positive predictive value in correlating fetal heart rate changes with subsequent adverse neonatal outcome. Such electronic fetal heart rate monitoring, despite these limitations, remains an integral part and standard of care in the assessment of fetal status.
Presently, the primary non-invasive fetal monitoring technique is the Doppler/tocometer. The technique is cumbersome and subject to data loss as a result of fetal and maternal movement. Typically, a Doppler transducer is placed on the mother's abdomen in a position that focuses the ultrasound signal at the fetal heart. Should the fetus move relative to the transducer, it is highly likely that the transducer will no longer be in proper position and, thus, not record an accurate heart signal. In fact, the use of a Doppler monitor is not precise enough for reliable analysis of subtle heart rate changes.
U.S. Pat. No. 5,257,627 to Rapoport relates to a portable apparatus for the non-invasive, simultaneous, self-testing of fetal and maternal signals. The device has a signal processing means for simultaneously processing fetal heart rate and maternal input signals, and also has a communication linking means for the simultaneous transmission of the fetal heart rate and maternal input data to a remote output device. Rapoport's device uses ultrasonic means to detect the fetal heart rate.
Other non-invasive techniques are also in use. These include the processing of electrocardiograph and electromyogram signals for determination of the fetus's well-being.
U.S. Pat. No. 4,299,234 to Epstein et al. relates to a fetal heart rate monitor which combines electrocardiograph and electromyogram type signals to increase reliability and accuracy of the resulting heart rate information.
U.S. Pat. No. 4,781,200 to Baker relates to a self-contained, lightweight ambulatory fetal monitoring system for substantially continuous analysis of fetal well-being. The monitor includes a sensor garment which is worn by the mother and has a plurality of sensors. The sensors detect fetal heartbeats and movements of the fetus within the mother. Signals developed by the sensors are processed by signal processing equipment and analyzed by a programmable data processing unit which can be provided with a variety of analytical programs which are proposed to automatically and continuously analyze fetal well-being. The sensor belt goes around the waist of the mother, and thus obstructs the surgical field.
U.S. Pat. No. 5,042,499 to Frank et al. relates to a fetal heart rate monitor that monitors weak fetal electrocardiogram signals in the presence of strong interfering noise. Frank et al's invention non-invasively obtains from the abdomen of a pregnant subject the fetal EKG
f
signal, fetal heart rate, and accurate beat-to-beat heart rate variability. An operator views the EKG
f
signal and optimally places the set of thoracic electrodes in an attempt to adaptively cancel the maternal EKG
f
signal from the signal separately derived from a variably located abdominal electrocardiograph lead. There is no uniform placement of the abdominal electrodes for all patients. Placement of such leads is dependent on prior examination by a trained medical professional to identify optimal lead orientation.
The above patents, and all patents and publications mentioned in this application, are all incorporated herein in their entireties by reference.
Evaluation of the fetal electrocardiographic waveform itself might provide increased insight into the status of the fetus. Unfortunately, direct accessibility of the fetus has limited the electrocardiogram as an indicator of well-being. During labor, after the rupture of the amniotic sac, a fetal scalp electrode may be attached to the fetus's skin. This requires twisting a wire corkscrew electrode into the presenting part of the fetus, e.g., scalp or buttocks, via the vaginal opening.
In the absence of direct electrode contact with the fetus, a large maternal signal and the presence of electrical noise (e.g. muscle artifact) has substantially precluded recognition of the fetal electrocardiogram. The placement of a fetal scalp electrode is clearly invasive, generally less comfortable for the mother, and has associated increased risks, such as infection, to the fetus, mother, and caretakers. The issue of infection has received more attention recently with increased risks of serious bloodbome infections such as AIDS.
Regardless of the monitoring technique, critical difficulties frequently arise when there is an emergent need to transfer the monitored patient from the labor area to the operating room. The monitors are usually detached during this critical interval with the mother and her fetus unmonitored during the transfer. Reattachment to monitors in the operating room (if at all) requires additional, possibly precious time and attention. Doppler transducers, if used, are inevitably in the operative field for an emergency cesarean section. Likewise, scalp electrodes must be removed or cut and withdrawn with the baby through the abdominal incision, again increasing the risk of infection.
This established need, therefore, creates a requirement for a reliable, accurate, and noninvasive technique to monitor the electrocardiogram of the fetus. Furthermore, the technique must maintain a clear operative field, accommodate movement of the mother and fetus, and be usable for a relevant portion of gestation. Moreover, it will be very desirable for the monitor output to include the fetal electrocardiogram waveform in addition to the fetal heart rate and description of heart rate variability. Monitoring of maternal heart rate and the state of uterine contractions and noise artifacts attributable to the uterus would also be desirable.
SUMMARY OF THE INVENTION
The present invention provides a method of monitoring a fetal biopotentia
Christion John A.
Greenberg Robert S.
Moses Edward J.
Sternberger Wayne I.
Bockelman Mark
Cooch Francis A.
The Johns Hopkins University
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