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Biomedical subjects

R Allen

Publications and source records attributed to R Allen.

At least 163 records · Page 9Linked to original sources
PubMed1989

Objective evaluation of the shoulder dystocia phenomenon: effect of maternal pelvic orientation on force reduction.

This report describes the use of maternal pelvic and fetal models, a tactile sensing glove, and a microcomputer data acquisition system to measure fetal shoulder extraction forces. Sixty-nine experiments were carried out in the laboratory setting to simulate vaginal delivery of the aftercoming fetal shoulders. The tests were conducted using a variety of fetal biclavicular diameters (10-13 cm) and maternal pelvic angle positions (McRoberts, 10 degrees; lithotomy, 25 degrees). When comparing lithotomy versus McRoberts positioning, there was a consistent reduction in force needed to extract the fetal shoulders with the latter maneuver. No simulated clavicles were fractured during shoulder delivery until a biclavicular diameter of 12.0 cm was reached. At this point, five of eight clavicles (63%) were fractured at 25 degrees and zero of seven (0%) were fractured at 10 degrees (P less than .025). For all 69 experiments, fetal neck extension readings were consistently lower than the total traction forces recorded by the tactile sensing glove. This suggests that, in addition to the axially oriented fetal neck forces, a component of flexion (lateral force) was also present. As the difficulty of shoulder delivery increased, the impact of these inadvertent flexion forces became most pronounced at the level of the brachial plexus. This is the first study to measure shoulder extraction forces reproducibly using a laboratory model for shoulder dystocia and to describe the pathophysiology of specific neonatal injuries from a force perspective. The results document objectively that McRoberts positioning reduces shoulder extraction forces, brachial plexus stretching, and the incidence of clavicular fracture.

Delivery, Obstetric↗
PubMed1988

Isolation of genes encoding the Neurospora vacuolar ATPase. Analysis of vma-2 encoding the 57-kDa polypeptide and comparison to vma-1.

In partially purified preparations of the vacuolar ATPase from Neurospora crassa, the two most prominent components are polypeptides of Mr = 70,000 and 60,000. We previously reported the isolation of the gene vma-1, which encodes the Mr = 70,000 polypeptide, and presented evidence that the polypeptide contains the site of ATP hydrolysis (Bowman, E. J., Tenney, K., and Bowman, B. J. (1988) J. Biol. Chem. 263, 13994-14001). We now report the isolation of a gene (designated vma-2), that encodes the Mr = 60,000 polypeptide. Analysis of the DNA sequence shows that the polypeptide has 513 amino acids and a molecular mass of 56,808 daltons (and will thus be referred to as the 57-kDa polypeptide). It is fairly rich in polar amino acids and has no apparent membrane-spanning domains. The vma-2 gene contains five short introns (55-71 bases), all clustered in the 5' end of the coding region. The gene maps to the right arm of linkage group II, near 5 S RNA gene 3. Thus, it is unlinked to vma-1 and to other known ATPase genes in N. crassa. The 57-kDa polypeptide shows 25% amino acid sequence identity with the vma-1 gene product. It shows essentially the same degree of similarity (25-28%) to both the alpha and beta subunits of F0F1 ATPases. Analysis of specific regions of the 57-kDa polypeptide, however, suggests it may have a function like that of the alpha subunit in F0F1 ATPases. The data indicate that all four types of ATPase polypeptides have evolved from a common ancestor and that the vacuolar-type ATPases have a structure surprisingly similar to that of the F0F1 ATPases.

Adenosine Triphosphatases↗
PubMed1988

Maternal interaction and language development in children with and without speech-related anomalies.

This study explores relationships among maternal behavior, child language, and location of congenital structural anomaly in three groups of 24-month-old children: 21 with speech-related anomalies (SRA), 13 with non-speech-related anomalies (NSRA), and 45 normal controls. In addition to standardized assessment of intelligence and language, children and mothers were observed in a half-hour videotaped play session, later coded for maternal and child interactive behavior. SRA children showed significantly poorer performance than controls on standardized tests. Mothers of SRA children showed significantly more Physical Teaching and Initiating relative to controls. Mothers of both SRA and NSRA children used significantly more Attention Management than did controls. The pattern of poorer child performance and maternal interactive compensations is largely confined to children whose structural disabilities are speech-related. Maternal interactive behavior is not global in its response to child disability; rather, it varies with the particular pattern of child disabilities found.

Child, Preschool↗
PubMed1988

Reversion toward an earlier stage of differentiation and loss of polarity during progression of N-methyl-N-nitrosourea-induced rat mammary tumours.

To work toward an understanding of the mechanisms of cancer progression, we have followed the changes in expression of several genes in rat mammary carcinomas during the development of invasion. Tumors were induced by N-methyl-N-nitrosourea and serially transplanted to isogeneic rats. Gene expression in individual cells was followed by immunofluorescence microscopy. We show that invading cells do not express the same genes as the primary tumor or normal adult mammary gland but are similar to the primitive mammary duct cells present in late embryos. In the most advanced tumors, the most fundamental epithelial characteristic, polarity, is lost. Relative to the mechanism of invasion, we observe that the basal lamina, often thinner than normal, always coats the strands of invading cells and may be entirely absent from single invasive cells only. These observations suggest that the basal lamina ultimately disappears because of reduced expression of the genes or the failure to assemble the components. In these tumors it is the progressive alteration in gene expression rather than the enzymatic breakdown of the basal lamina that leads to invasion. These results show that the most important aspect of cancer progression is the progressive alteration of gene expression. They also raise questions about the mechanism that causes tumor cells to retrace the steps in their differentiation.

Animals↗
PubMed1987

Evaluation and improvements of a rapid microassay for measuring superoxide anion production by phagocytes. 2. Biochemical aspects.

Superoxide anion synthesis by stimulated human polymorphonuclear leukocytes (PMNL) may be measured as superoxide dismutase-inhibitable cytochrome C (Cytc) reduction in a rapid microplate assay. However, when determinations are made over a fixed time interval (15 min) a lack of proportionality is observed between the amount of Cytc reduced and the number of cells stimulated. Examination of the reduction kinetics indicated that depressed superoxide detection at higher cell densities might be a consequence of Cytc re-oxidation by later metabolites in the oxidative burst. This was confirmed using dithionite-reduced Cytc as substrate in the assay. A method of analysis which avoids this source of error in determining superoxide anion synthesis is proposed.

Cytochrome c Group↗
PubMed1987

Bombesin alters the sympathetic nervous system response to cold exposure.

The accumulation of dopamine in interscapular brown fat, heart, kidney and mesenteric white fat has been used as an index of sympathetic nervous activity in rats in which dopamine beta-hydroxylase has been blocked. Intracerebroventricular administration of bombesin impaired the cold-induced increase of dopamine accumulation in interscapular brown fat but not in other tissues. These studies provide evidence that bombesin acts within the central nervous system to modify efferent sympathetic nervous system responses to cold exposure in a viscerotopically specific manner. This action of bombesin is consistent with the other central nervous system actions of this peptide, i.e. inhibition of heat production and disruption of thermoregulation.

Adipose Tissue, Brown↗
PubMed1987

Optic nerve dysfunction during gravity inversion. Visual field abnormalities.

Inversion in a head-down position (gravity inversion) results in an intraocular pressure of 35 to 40 mm Hg in normal subjects. We used computerized static perimetry to measure the visual fields of normal subjects during gravity inversion. There were no visual field changes in the central 6 degrees of the visual field compared with the baseline (preinversion) values. However, when the central 30 degrees of the visual field was tested, reversible visual field defects were found in 11 of 19 eyes. We believe that the substantial elevation of intraocular pressure during gravity inversion may pose potential risks to the eyes, and we recommend that inversion for extended periods of time be avoided.

Adult↗