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Biomedical subjects

G A Machin

Publications and source records attributed to G A Machin.

At least 19 recordsLinked to original sources
PubMed2000

Balloon tracheal occlusion for congenital diaphragmatic hernia: experimental studies.

PURPOSE: Temporary tracheal occlusion is an effective strategy to enlarge fetal lungs, but the optimal technique to accomplish occlusion is unknown. External clips are effective when applied fetoscopically (Fetendo clip), but require a difficult fetal neck dissection. This study was undertaken to assess the feasibility of intratracheal balloon occlusion, revisiting the internal occlusion strategy. METHODS: (1) The internal diameter (ID) of human fetal trachea (53 fetuses; 14 to 41 weeks' gestation) was compared using a computer-assisted image analyzer and sonography, ex vivo. (2) Volume to diameter relationship of the balloon (balloon configuration curve) was defined using an image analyzing computer. (3) Using the trachea of fetal sheep, pressures that break balloon tracheal seal (seal pressure) were investigated. RESULTS: (1) Between 16 and 41 weeks' gestation, tracheal ID (range, 0.7 to 5.4 mm) correlates significantly with gestational age. (2) Balloon volume required to achieve tracheal seal could be determined based on the tracheal growth curve and the balloon configuration curve. (3) Tracheal seal breaking points varied depending on the tracheal specimen tested. CONCLUSION: Internal tracheal occlusion using a balloon is feasible with minimal tracheal damage if the balloon volume is adjusted to fetal tracheal growth.

Balloon Occlusion↗
PubMed2000

Zygosity of twins: is it time for a new terminology?

The term zygosity reflects the origin of twins--when twins are monozygotic, they are derived from a single fertilized ovum; when twins are dizygotic--the come from two fertilized ova. Zygosity assessment seemed straightforward 50 years ago. Currently, as more information and more technology becomes available, zygosity testing becomes a real problem. It is important to realize the importance of correct zygosity testing not only in the antepartum care of the pregnant mother, but more importantly--during the whole lifetime of twin individuals. This paper discusses revolving around zygosity, methods of assessment, their limitations and proposes new terminology which incorporates the recent knowledge about early human development.

Algorithms↗
PubMed2000

[Peculiarities of multiple pregnancy: embryology].

Multiple pregnancies are not physiologic in humans and the understanding of the pathogenesis of this phenomenon is not fully established. Embriology of multiple pregnancy has been extensively investigated and this paper presents the phases of embrional development of monozygotic and dizygotic twins.

Embryonic and Fetal Development↗
PubMed2000

[Peculiarities of multiple pregnancy: diagnosis].

Before ultrasound was aggressively introduced into everyday obstetrical practice, diagnosis, prophylaxis and active pre- and perinatal management were at best inadequate, but more often nonexistent. Twin pregnancies were complicated by high perinatal morbidity and mortality. The use of classical radiography was limited due to proven teratogenic and carcinogenic properties. Introduction of ultrasound dramatically changed the obstetrician's approach to twin pregnancy management. This paper discusses in detail the recent advances in ultrasound diagnosis of twin pregnancy.

Female↗
PubMed2000

[Peculiarities of multiple pregnancy: complications].

Multiple pregnancies are considered high risk. This qualification is associated with the multitude of conditions which are known to complicated these pregnancies. Early diagnosis of these complications is the fundamental element of clinical managements. In numerous cases therapeutic protocols are widely known and in many others intensive monitoring and appropriate management may save the fetus from early and late complications. This paper will discuss the most common prenatal and perinatal complications associated with multiple pregnancies as well as the most widely accepted therapeutic protocols.

Abnormalities, Multiple↗
PubMed1998

Twin zygosity testing for medical purposes.

After being poisoned by eating the mushroom species Cortinarius speciosissimus, a twin developed interstitial nephritis with acute renal failure. He received a renal transplant from his living twin brother, who was presumed dizygotic on phenotypic grounds. Fifteen years later, the twins were zygosity tested by DNA "fingerprint analysis" and found to be monozygotic, despite important phenotypic discordances. The recipient has discontinued immunosuppression therapy and remains well after 9 months. We suggest that, for medical and other reasons, zygosity should be determined at birth on all like-sexed twins.

Acute Kidney Injury↗
PubMed1998

Cranio-facial skeletal development in three human synophthalmic holoprosencephalic fetuses.

In three human fetuses with synophthalmic holoprosencephaly (8, 14, 23 wks. p.c.) and two normal human fetuses (9 and 13 wks. p.c.) the anatomy of the cranial base, facial cranium and their relation to the notochord was studied using serial histological sections and computer aided three-dimensional reconstruction methods. Mesethmoidal cartilage differentiation was variably deficient in all three holoprosencephalic cases. The premaxillary bones were rudimentary with missing tooth buds. The development of the sphenoid bone was defective in two of the holoprosencephalic cases (8, 14 wks. p.c.). The notochord terminated normally within the sphenoid body in all investigated cases. Our results indicate that in holoprosencephaly there is a general defect in the midline cranial cartilage differentiation rostral to the notochord.

Abortion, Spontaneous↗
PubMed1997

Velamentous cord insertion in monochorionic twin gestation. An added risk factor.

OBJECTIVE: To study the effects of umbilical cord insertion combinations on outcomes in monochorionic (MC) twin placentas. STUDY DESIGN: Sixty consecutive MC placentas were analyzed by cord insertion patterns with regard to growth discordance, placental parenchymal sharing, types and patterns of intertwin vascular anastomoses, perinatal mortality and frequency of fetofetal transfusion. Cord insertions were classified as central/eccentric (CEN) or velamentous/marginal (VEL). RESULTS: Forty-five percent of the twins had VEL insertions. The CEN/VEL combination was found in 53% of pairs. The CEN/VEL group had the highest rates of growth discordance > 20%, unequal placental parenchymal sharing, uncompensated anastomoses and perinatal demise. CONCLUSION: VEL cord insertion and the CEN/VEL combination are indicators of high-risk subgroups within MC twins. VEL cord insertions can be diagnosed by ultrasound, identifying these high-risk groups.

Diseases in Twins↗
PubMed1996

Some causes of genotypic and phenotypic discordance in monozygotic twin pairs.

The use of the adjective "identical" rather than monozygotic leads to misunderstandings about the biology of monozygotic twinning. Most monozygotic twin pairs are not identical; there may be major discordance for birth weight, genetic disease, and congenital anomalies. These indicate that postzygotic events may lead to the formation of two or more cell clones in the inner cell mass and early embryo that actually stimulate the monozygotic twinning event. There is also evidence that there may be unequal allocation of numbers of cells to the monozygotic twins; this may have widespread implications for the cascade of developmental events during embryogenesis, formation, and vascularization of the placenta. Large-scale zygosity testing at birth could be the template for analysis of twin outcomes and their biologic causes.

Chorion↗
PubMed1996

Zygosity and placental anatomy in 15 consecutive sets of spontaneously conceived triplets.

Most triplets are trizygotic because they result from assisted reproduction. Prognosis is generally good. We analyzed 15 sets of triplets who were conceived spontaneously. Six sets were monozygotic, 7 were dizygotic, and only 2 sets were trizygotic. Considered as 45 twin pairs, 25 pairs (56%) were monozygotic. Twenty percent of these twins died as a result of twin-twin transfusion. Spontaneously conceived triplets have high risks compared with those resulting from assisted reproduction. These risks result from a high proportion of monozygotic embryos, many of whom have monochorionic placentas with vascular anastomoses, causing twin-to-twin transfusion.

Birth Weight↗
PubMed1996

Two pairs of male monozygotic twins discordant for Wiedemann-Beckwith syndrome.

Wiedemann-Beckwith syndrome (WBS) is a congenital anomaly syndrome which classically consists of exomphalos, macroglossia, and gigantism. The syndrome is also associated with a variety of minor anomalies and affected individuals have an increased risk of developing rare embryonal cell tumors. To date, 15 monozygotic (MZ) twin pairs have been reported of which 13 are discordant for WBS. All except one pair of the discordant WBS twin pairs have been female. We report two pairs of male MZ twins, each discordant for WBS.

Adult↗
PubMed1996

Computer graphic three-dimensional reconstruction of normal human embryo morphogenesis.

Three-dimensional computer graphic reconstructions of four human embryos at Carnegie stages 11 to 23 portray the relationships and dimensions of individual organ systems. This paper illustrates the cranial, neural, pharyngeal, gut, vascular and nephric architecture in these developing embryos. This technology can be applied to in situ hybridization and immunohistochemistry to map zones and times of developmental gene activity.

Embryo, Mammalian↗