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J C Challier

Publications and source records attributed to J C Challier.

5 recordsLinked to original sources
PubMed1992

Mathematical modeling of the human fetal arterial blood circulation.

A mathematical model of the human fetal arterial circulation based on mass and momentum conservation for one-dimensional flow is presented. We simplified the fetal arterial vascular system from the heart to the placenta, defined 16 anatomical segments and studied the characteristics of the vascular system in relation to changes in morphology and hemodynamics. The two-step Lax-Wendroff finite difference scheme was used to solve the system of equations, after introducing the rheological constants, the diameter and length of the segments measured by two-dimensional imaging and the mean arterial velocity at the inlet segments obtained by pulsed Doppler. The model was validated by comparing the numerical results to our non-invasive ultrasound direct measurements and to previous published data.

Arteries↗
PubMed1992

Passage of S(+) and R(-) gamma-vinyl-GABA across the human isolated perfused placenta.

1. The maternal to foetal transfers of S(+)- and R(-)-gamma-vinyl-GABA (VGB) across the human isolated perfused placenta were low and comparable with those of acidic alpha-amino acids. 2. The placental uptake of the active S(+)-isomer from the maternal circulation exceeded that of the R(-)-isomer and this was reflected by a corresponding difference in placental tissue concentrations. 3. During perfusion with recirculation of the foetal medium, the two enantiomers were present at a similar concentration and did not concentrate in foetal perfusate, indicating that the excess amount of S(+)-VGB cleared from the maternal circulation was not accessible to the foetal perfusate. Furthermore, stable concentrations of both isomers in the foetal perfusate suggested a lack of placental metabolism. 4. Possible explanations of these findings include the operation of a stereoselective sodium-dependent-GABA placental uptake system on the maternal side, similar to that observed in neuronal tissue, or stereoselective binding to a placental GABA transaminase.

Aminocaproates↗
PubMed1979

Transfer in vitro of three benzodiazepines across the human placenta.

A comparative study of the placental transfer to the foetus of three benzodiazepines was performed using a dual perfusion system of the human placental lobule. A transport fraction was calculated for each benzodiazepine and was compared with reference substances. Relative to antipyrine, the transport fraction of diazepam was 85%, and that of nordiazepam was 84%. The transport fraction of clorazepate represented only 20% of that of tritiated water. The relatively high transfer of diazepam and nordiazepam can be attributed to their high lipid solubility, and the lower transfer of clorazepate is due to its polar nature. It is suggested that in certain instances this benzodiazepine may be of especial value to obstetricians.

Anti-Anxiety Agents↗
PubMed1976

In vitro perfusion of human placenta. V. Oxygen consumption.

02 consumption by human term placenta has been measured during perfusion in vitro, with a technique that permits perfusion of the intervillous space as well as the umbilical circulation. The rate at which 02 was consumed was directly related to the rate at which it was supplied, within the limits studied. Previous estimates of 02 consumption yielded figures approximating 3 ml. per minute per kilogram of placenta, but these estimates were attained under conditions of limited oxygen supply. When oxygen was delivered to the placenta at rates believed to be those achieved in vivo, oxygen consumption approximated 10 ml. per minute per kilogram. This rate of 02 consumption is similar to those obtained from studies of animal placentas in vivo and is more consistent with that of an active metabolic organ. If one were to accept estimates of 02 consumption by the human fetus in utero, the present studies indicate that approximately one fifth of maternal oxygen supplied to the conceptus is diverted to support placental metabolism.

Female↗