Surgery – Diagnostic testing
Reexamination Certificate
1999-11-26
2002-01-22
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
C128S898000, C600S301000
Reexamination Certificate
active
06340346
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a method and system for simplification of the relation between two physiological systems and, more particularly, to simplification of the relation between two physiological systems using system identification techniques.
Physiological Background
It has become a common practice in obstetrics to evaluate the well being of the fetus in utero. This practice, which is known as antepartum testing, has been extensively practiced since the early 1970 on certain high risk obstetrical patients. One of the uses of antepartum testing is to determine how well the placenta is supplying the oxygen and nutrient needs of the growing fetus, and removing fetal wastes therefrom.
Almost 70% of fetal deaths occur before the onset of labor. Antepartum fetal death accounts for nearly 40% of all prenatal mortality in the United States. The majority of fetal deaths occur before 32 week's gestation.
Antepartum fetal deaths may be categorized into four broad categories: (i) chronic asphyxia of diverse origin; (ii) congenital malformations; (iii) superimposed complications of pregnancy, such as Rhesus isoimmunization, placental abruption, hypertension, diabetes and fetal infection; and (iv) deaths of unexplained cause.
Based on available data, approximately 30% of antepartum fetal deaths may be attributed to asphyxia, 30% to maternal complications, especially placenta abruption, hypertension, and preeclapmsia, 15% to congenital malformations and chromosomal abnormalities, and 5% to infection.
The clinical experience has demonstrated that antepartum fetal assessment can have a significant impact on the frequency and cause of fetal deaths.
Indications for antepartum fetal monitoring in patients known to be at risk of utero-placental insufficiency include maternal, fetal, placental and background indications. Maternal indications include prolonged pregnancy; diabetes mellitus; hypertension and advanced maternal age. Fetal indications include: suspected intrauterine growth restriction (IUGR) and decreased fetal movements. Placental indications include: abruption of the placenta and abnormal amniotic fluid. Background indications include: previous stillbirth.
The fetus and the placenta well being depend upon unique physiological systems responsible at providing an environment capable of supporting fetal growth and development.
To appreciate the complexity of the placenta as a bidirectional transfer organ, it is necessary to point out that the placenta provides the fetus with products which are essential for its well being including essential nutrients, fluids and oxygen, and it serves as a route for clearance of fetal excretory products [Williams Obstetrics, Pritchard and Mc Donald eds., Appleton-Century-Crofts, New York, 1980].
The transport characteristics of the placenta allow respiratory gases and many solutes to reach equal concentration between the maternal intervillous space blood and fetal capillary blood. Thus, the rate of blood flow in these two circulations is important in the determination of fetal oxygen and nutrient supply. Over the course of a normal singleton gestation, uterine blood flow increases more than 50-fold above non-pregnant values. Two factors contribute to this dramatic increase in blood flow: placental growth and maternal arterial vasodilatation.
The uterine artery behaves as a nearly maximally dilated system. Fetal blood flow to the umbilical circulation represents approximately 40% of the fetal cardiac output. During the first trimester, increase in umbilical blood flow is directly proportional to fetal growth.
Many maternal organs undergo physiological changes during the course of pregnancy. Maternal cardiac output, i.e., the product of heart rate and stroke volume, increases by about 30-50% during pregnancy. The distribution of maternal cardiac output changes as pregnancy progresses. In the first trimester the uterus receives about 3% of the cardiac output, however it receives about 17% of the cardiac output near term.
The percentage of cardiac output devoted to kidney, brain and skin is not dramatically altered by pregnancy. Peripheral vascular resistance falls during pregnancy. The cause for this is the smooth muscle relaxing effect of high progesterone levels associated with the pregnancy. There is a progressive rise in venous pressure in the lower extremities.
The placenta, the mother and the fetus make important contribution to the immunological maintenance of pregnancy.
Advances in prenatal and neonatal health care have resulted in a substantial reduction in prenatal and neonatal mortality. These improvements primarily relate to better capabilities in treating maternal diseases during pregnancy, advance in neonatal care and may also be due to improvements in antepartum fetal surveillance techniques.
There are some medical conditions in pregnancy that may lead to poor placental functioning such as diabetes, hypertension, anemia and prolonged pregnancy. In these conditions it is of great importance to evaluate placental functioning. For these or other indications obstetrician will determine whether one is in need to have antepartum testing during the pregnancy.
Antepartum fetal testing is a term that embraces data from fetal movement counts to biophysical monitoring methods, such as contraction stress test, nonstress test, fetal biophysical monitoring profile, amniotic fluid assessment, Doppler velocimetry, vibro-acoustic fetal stimulation and computerized fetal heart rate.
The following lists few of the tests used for fetal monitoring.
Antepartum Fetal Heart Rate Testing (non stress test, NST)
In NST, fetal heart rate acceleration in response to fetal movement are recorded via electronic equipment on a strip of paper.
Cardiotocography (CTG)
CTG utilizes electronic equipment to record the fetus' heart rate pattern. Uterine contractions, if present, are also registered. This information is recorded on a strip of paper, producing a tracing that is read by the obstetrician. Certain changes in the fetal heart rate pattern can signal a problem.
Amniotic Fluid Index (AFI)
The amount of amniotic fluid surrounding the fetus may be decreased in some high-risk pregnancies. The amount of amniotic fluid present is measured by ultrasound scanning and is known as AFI.
Fetal Biophysical Profile (FBP)
The CTG trace is obtained and then four parameters are observed by ultrasound. The four parameters are fetal tone, fetal movements, fetal breathing, and the amniotic fluid index. Not all of these tests need to be performed at the same time.
Since there are many different pathophysiological processes leading to fetal asphyxia, indication-specific testing is reasonable and it may allow early identification of at-risk fetuses. The FBP is useful in the detection of developing fetal asphyxia even before it irreversible affects the fetus.
No program of antepartum fetal testing can completely remove the risk of fetal death. The most appropriate antepartum tests appear to be amniotic fluid volume assessment, fetal tone and fetal heart monitoring.
The use of Doppler ultrasound is not beneficial in most clinical cases. The single most effective test that distinguishes normal-small from compromised small fetuses is the determination of the umbilical artery Doppler waveform.
Doppler velocimetry seems to be reliable in diagnosing conditions predisposing to IUGR such as chronic hypertension, collagen vascular disorders, and other diseases in which vasospasm plays a major role.
Hence, it remains uncertain which is the optimal Doppler ultrasound measurement of the uteroplacental circulation to obtain the best sensitivity and predictive values for evaluation of fetal and placental pathologies such as preeclampsia and IUGR [Northe R. A., Ferrier C, Long D, Townend K and Pinkus-Smith P. Uterine artery and flow velocity waveforms in the second trimester for the prediction of preeclampcia and fetal growth retardation. Obstetrics and Gynecology Vol 83 pp. 378-386, 1994].
The usual decrease in utheroplacental blood
Almog Yael
Toledo Eran
T.A.O. Medical Technologies Ltd.
Winakur Eric F.
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