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Biomedical subjects

S Weiner

Publications and source records attributed to S Weiner.

At least 127 records · Page 7Linked to original sources
PubMed1991

Topographic imaging of mineral and collagen in the calcifying turkey tendon.

Topographic imaging, a method of providing a direct view of ultrastructure in three dimensions, has been newly applied to a study of mineral crystals and collagen from calcifying turkey leg tendon. Individual crystals obtained from intact tendon were observed as thin platelets of irregular shape having a relatively smooth surface. Mineralized collagen fibrils isolated singly or examined in thin tissue sections were found to exhibit the characteristic 64-70 nm period and were associated with platelets and needle-like mineral. The crystals were disposed in numerous fashions, notably as small groups of platelets within individual collagen hole zones, as a number of needle-like densities arranged parallel to one another, or as a combination of platelets and needles over entire stretches of single collagen fibrils. The topographic observations of crystals and crystal-collagen interaction clearly demonstrate the plate-like habit of the mineral in calcifying turkey tendon and suggest that these crystals are located both within and on the surface of collagen fibrils. In certain sites such as the collagen hole zones, the crystals appear organized in a specific manner, possibly with a preferred c-axial orientation. Crystals of hydroxyapatite prepared in vitro and examined topographically are similar in habit and texture to the crystals from tendon. When interpretation of this method is corroborated by other independent microscopic techniques, topographic imaging has widespread potential application in many fields of study in which structural surface features of biological tissues or non-biological materials are of interest at the electron microscope level.

Animals↗
PubMed1991

Electron imaging and diffraction study of individual crystals of bone, mineralized tendon and synthetic carbonate apatite.

A transmission electron microscope study of carbonate apatite crystals isolated from bone and mineralizing tendon, as well as those produced synthetically under approximated-physiological conditions, shows that they are thin irregular shaped plates. Electron diffraction patterns of individual crystals confirm that the large developed crystal face is (100), and that the longest dimensions of the biogenic crystals are aligned with the crystallographic c axes. As the latter are also aligned with collagen fibril axes, the observations provide additional information on the tissue organization itself. The marked similarity between the biologic and synthetic crystals suggests that the biological environment in which the crystals form may not be primarily responsible for controlling their shape.

Animals↗
PubMed1991

Idiopathic aldosteronism in pregnancy.

This is the first reported case of the idiopathic type of primary aldosteronism in pregnancy. The severely hypertensive patient was unresponsive to treatment with high doses of four antihypertensive agents administered concurrently. A drastic improvement in blood pressure was noted within 24 hours of beginning enalapril maleate, although subsequent deterioration in fetal status led to delivery at 26 weeks' gestation. Alternatives to standard medical therapy may be necessary for this rare but potentially life-threatening disease during pregnancy.

Adult↗
PubMed1990

[Coincidence of hypertensive changes of the eye fundus and regulation disorders of peripheral microcirculation: I--Skin].

In cases of arterial hypertension, funduscopy is an established method of estimating systemic vascular lesions. In this study the relation between the extent of retinal vascular changes and dynamic processes in the microcirculation of the skin was investigated by nailfold capillaroscopy in 88 patients. With increasing vascular changes a progressive loss of vasodilator reserve and transcutaneous partial pressure was observed (no morphologic changes--fundus hypertonicus II--fundus hypertonicus III). It thus appears possible to evaluate the functional state of the macro- and microcirculation by funduscopy.

Adult↗
PubMed1990

[Coincidence of hypertensive fundus changes and regulatory disorders of peripheral microcirculation. II--Skeletal muscles].

In patients with hypertensive fundus changes considerable morphologic changes of the entire vascular system may be assumed. In the present study, the effects of these processes on the partial oxygen pressure of the skeletal musculature were investigated in 62 patients via a macro puncture electrode placed in the tibial muscle. The extent of fundus changes and the reduction in muscular partial oxygen pressure were found to be correlated. With advancing stages of fundus changes, blood flow measured in the common carotid artery decreased. Vascular changes which are clearly recognizable in the hypertensive fundus thus appear to be accompanied by a deterioration in partial oxygen pressure in muscular tissue and restriction of flow in the macrocirculation.

Aged↗
PubMed1990

Maternal and fetal plasma vitamin E to total lipid ratio and fetal RBC antioxidant function during gestational development.

Placental transfer of vitamin E was investigated from 19 to 35 weeks of gestation by analysis of fetal and maternal blood samples for total tocopherol, total lipids, and fetal red blood cell antioxidant reserves. Fifty-two fetal blood samples were obtained under ultrasonographic guide by percutaneous umbilical blood sampling. Thirteen were from fetuses with gestational age less than or equal to 22 weeks (x serum vitamin E = 0.4 +/- 0.14 mg/dl), 12 were from fetuses at 23-27 weeks gestation (x serum vitamin E = 0.4 +/- 0.21 mg/dl), and 27 were from fetuses with gestational age 28-38 weeks (x serum level = 0.37 +/- 0.18). Total lipid levels ranged from 140 to 216 mg/dl. Maternal plasma vitamin E concentrations correlated significantly with concurrent values in the fetus. There were no significant differences in serum vitamin E levels or vitamin E to total lipid ratio in samples from early, mid, or late gestation in either the mother or fetus. Red blood cell antioxidant reserve on samples from 18 fetuses were grossly abnormal by three different functional assays. On the basis of these data, placental transfer of vitamin E appears to be relatively constant through advancing gestation. Red blood cell antioxidant reserve is uniformly low.

Erythrocytes↗
PubMed1990

Natural history of androgenetic alopecia.

Twenty-two men with patterns III-Va androgenetic alopecia were entered into a 10-month study aimed at establishing information on the natural progression of hair loss over a period of time typical of studies of hair growth promoters. The methodology employed was the same as that in published clinical trials of topical minoxidil, but the men refrained from application of either active drug or vehicle to their scalps. As one of the potential explanations for the observed 'placebo-effect' seen in non-vellus hair counts in the topical minoxidil trials was a learning curve of novice hair counters, we were particularly interested in evaluating this in our 'no-treatment' trial. To that end, both a novice (Observer I) and an experienced (Observer II) hair counter independently performed the hair counts. There was a mean decline in the number of vertex target area non-vellus hairs (-17.2 +/- 80.3 for Observer I and -26.6 +/- 63.5 for Observer II) at the end of 10 months; this was not significant. The novice's hair counts were lower than the experienced observer's counts at baseline, and the difference remained relatively constant during the study. Without the application of a placebo, there was no increase in hair growth, making it unlikely that the methods of hair counting led to the 'placebo-effect' seen in prior topical minoxidil studies.

Adult↗
PubMed1990

Ultrastructure, morphology and crystal growth of biogenic and synthetic apatites.

The morphology, structure and crystal growth of apatite crystals isolated from calcified turkey tendon and synthetic carbonated apatites have been examined using high resolution transmission electron microscopy. The biogenic apatite consisted of small (35 x 20 x 5 nm) platelike crystals. Despite their irregular shape and ill-defined edges, individual particles were single domain crystals. Lattice images recorded from isolated turkey tendon crystals indicated that the crystallographic c-axis (0001) of apatite lies in the plane of the plate and parallel to the length of the crystallites. Lattice images suggested that the top face corresponds to the (1100) face of carbonated apatite. Lattice fringes observed in platelike crystallites viewed from the side corresponded to the projection of the apatite structure viewed along the [1120] direction. Thus, it can be argued that crystal growth is constrained along the [1100] direction, extends laterally along the [1120] direction, and is maximal along the [0001] direction. This latter direction is aligned with the collagen fiber axis. A mean length to width ratio (1.7) was determined by systemically measuring the maximum distances parallel and perpendicular to the c-axis identified from lattice images of the crystals. Similar information was obtained from lattice images of crystals located in collagen fibres. This confirmed that the morphological and structural features of isolated turkey tendon apatite crystals correlate directly with the in vivo crystallochemical characteristics of apatite. Crystals of synthetic carbonated apatite prepared at 37 degrees C were also platelike and, although generally much larger, had length to width ratios comparable with the turkey tendon apatite. The synthetic carbonated apatites were noticeably more sensitive to radiolytic damage than the turkey tendon crystals. The crystallographic c-axis of the inorganic particles was aligned parallel with the long, physical axis of the plate and the top face was identified as (1100). Similar data were also obtained from noncarbonated synthetic apatite samples. The results of the present study offer critical information about the crystal growth of individual carbonated apatite crystals in calcified turkey tendon and its relationship to the morphology of the crystallites. As similar growth characteristics are expressed in synthetic analogues, the data bring into question the putative regulatory role of the collagen-based matrix upon the nucleation and growth of biogenic apatite.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Use of a prefabricated splint for segmental augmentation of the mandibular alveolar ridge with hydroxyapatite.

Hydroxyapatite is a biocompatible material for augmentation of edentulous ridges to improve patient comfort and denture stability. The problems associated with hydroxyapatite are generally related to the amount of material introduced and the site of implantation. This article describes the use of a prefabricated splint that permits localization of the implant material to selected sites of the mandible and restricts the amount of material used. Fabrication of this splint under the guidance of the prosthodontist and oral surgeon permits the most effective use of this technique.

Acrylic Resins↗
PubMed1990

Management of midtrimester oligohydramnios: a case for amnioinfusion.

Ultrasonic evaluation and diagnosis in cases of severe oligohydramnios is extremely difficult, and management problems exist. With appropriate diagnostic procedures, management becomes less of a dilemma. Amnioinfusion, which is the instillation of fluid into the amniotic cavity, enhances ultrasonic resolution necessary for observation of fetal anatomy and behavior. The cases of severe oligohydramnios reviewed typify those in which amnioinfusion was used to diagnose and manage mid-trimester pregnancies. This technique enabled the practitioner to define the specific cause of the oligohydramnios. Interventions, risks, and outcomes of the cases are discussed.

Adult↗
PubMed1989

Fetal exsanguination following intrauterine angiographic assessment and selective termination of a hydrocephalic, monozygotic co-twin.

Selective termination by intracardiac potassium chloride injection was performed in twins discordant for hydrocephaly at 20 weeks' gestation. Because of the potential for vascular anastomoses to exist between the twins, fetal angiography was performed prior to the selective termination procedure. Determination of vascular connections between the fetuses was hindered by fetal bradycardia following intracardiac administration of contrast material. Selective termination was performed without difficulty using intracardiac potassium chloride (KCl) to produce asystole in the twin with hydrocephaly. The unaffected fetus appeared active and had a normal heart rate during and immediately after the procedure. However, both twins were found to have died the following day. Pathologic examination documented several vascular anastomoses between the monochorionic, diamniotic fetuses. A likely cause of death was exsanguination of the normal twin into the abnormal one. This case illustrates the difficulties encountered in selective termination of monozygotic twins and, to our knowledge, represents the first reported use of intrauterine fetal angiography.

Adult↗
PubMed1989

Restoration of fixed partial dentures with fractured porcelain veneers using an overcasting.

Fracture and loss of the porcelain veneer of a fixed partial denture is troublesome. Dentists have frequently used overcastings to avoid removal of the restoration. However, development of proximal resistance and retention form for the preparation creates a problem because reduction of the connector causes fracture. Nevertheless, a box-type occlusal cavity form in the central portion of the preparation will enhance the stability of the restoration without encroachment on the connectors. This design is more applicable to endodontically treated teeth.

Cementation↗
PubMed1989

Three-dimensional ordered distribution of crystals in turkey tendon collagen fibers.

The organization of apatite crystals and collagen fibrils in mineralized turkey tendon has been studied by electron microscopy and electron diffraction. To minimize artifactual distortions the tissue was examined, for the first time, as isolated fibrils in an aqueous environment of vitreous ice, as well as in conventionally prepared sections. The electron micrographs show that the plate-shaped apatite crystals are arranged in parallel arrays across the collagen fibrils. This provides direct evidence for highly asymmetric assembly in collagen fibrils, and, indeed, the fibrils were observed to be elongated rather than round in cross-section. There is, furthermore, a pronounced tendency for the layers of crystals to be coherently aligned in adjacent fibrils. These observations may also be important for understanding the mechanical behavior of bone at the molecular level, as such extended, aligned aggregates of flat crystals could develop into natural fracture planes in mature bone.

Animals↗
PubMed1989

Structural and stereochemical relations between acidic macromolecules of organic matrices and crystals.

Detailed studies of the molecular organization of various mineralized tissues highlight the role played by acidic glycoproteins in controlling crystal formation. In vitro experiments show that these macromolecules are able to interact with specific faces of different crystals, influencing both nucleation and crystal growth. Significantly a common stereochemical motif can be recognized in all the interacting faces studies to date.

Animals↗
PubMed1989

Crystal size and organization in bone.

Size measurements of dispersed rat bone crystals show that with age a greater proportion exceeds 400 A in length. The surface fractures of more heavily mineralized bones tend to be smooth and stepped, whereas those of less mineralized bones are fibrous. These observations combined with information reported elsewhere on the crystal-collagen relations in adjacent fibrils in turkey tendon, suggest that some crystals grow out of the confines of the collagen gap regions to form extended aggregates of large flat crystals with well developed fracture planes.

Animals↗