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Digitale Medien

Acute increase in femoral artery resistance in response to direct physical stimuli in the human fetus (2003)

Smith, Richard P. ; Glover, Vivette ; Fisk, Nicholas M.

Oxford, UK : Blackwell Science Ltd

BJOG 110 (2003), S. 0

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ISSN: 1471-0528

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Objective To determine whether fetal response to needling resembles the fetal ‘brain sparing’ response seen with hypoxaemia.Design Prospective observational study.Setting Centre for Fetal Care, Queen Charlotte's and Chelsea Hospital, London.Population Eighty-five pregnant women undergoing invasive procedures associated with fetal prenatal diagnosis and/or management.Methods The femoral artery and the middle cerebral artery pulsatility index were measured by Doppler ultrasonography before and after 89 invasive procedures (fetal blood sampling, transfusion, bladder or cyst aspiration, shunt insertion and amniocentesis, between 17 and 36 weeks). Cases in which the fetal body was transgressed were compared with ‘control’ fetuses undergoing invasive procedures which did not directly involve needling the fetus (amniocentesis and placental cord insertion procedures).Main outcome measures Femoral artery and middle cerebral artery pulsatility index.Results The femoral artery pulsatility index rose after transgression [median change (Δ) 0.73; 95% confidence interval (CI) 0.51 to 0.98]. In contrast, there was no significant change in femoral artery pulsatility index after non-transgression procedures (mean Δ 0.28; 95% CI −0.20 to 0.76). Analysis confirmed the fall in middle cerebral artery pulsatility index after transgression procedures (median Δ−0.19; 95% CI −0.07 to −0.35), but there was also a significant fall in middle cerebral artery pulsatility index after non-transgression procedures (mean Δ−0.47; 95% CI −0.23 to −0.71).Conclusions The human fetus mounts a peripheral haemodynamic response to invasive procedures involving transgression of the fetal body, which is consistent with the brain sparing effect. However, the change in middle cerebral artery pulsatility index in both transgression and control procedures suggests that the changes and mechanisms may be more complex than previously thought.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1471-0528.2003.02373.x

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Digitale Medien

Configurational entropy of polyethylene and other linear polymers (1966)

Smith, Richard P.

New York : Wiley-Blackwell

Journal of Polymer Science Part A-2: Polymer Physics 4 (1966), S. 869-880

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ISSN: 0449-2978

Schlagwort(e): Physics ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: The configurational entropy of the polyethylene chain at the melting points calculated in two ways. In both calculations, tetrahedral angles and discrete trans and gauche arrangements of all bonds are assumed, and trans bonds are assumed more stable than gauche by energy U1. First, calculations are made on chains of up to N = 18 bonds, disallowing all configurations having overlapping atoms, and the result is extrapolated to large N. Second, a calculation is made directly for long chains, with overlaps excluded only over every short chain segment. The results are in almost exact agreement, suggesting that the second method can be safely used with other molecules. The calculated configurational entropy is in line with that suggested by the entropy of fusion, assuming the chains to acquire a configurational freedom in the melt which approaches that of independent chains.

Zusätzliches Material: 3 Ill.