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Biomedical subjects

S Weiner

Publications and source records attributed to S Weiner.

At least 55 records · Page 3Linked to original sources
PubMed1999

[Surgical management of liver rupture].

The management of 178 patients with liver trauma (132 male, 46 female; mean age 34 years (range 3-88) presenting from January 1979 to August 1996 is reviewed. There were 165 cases of blunt trauma and 13 cases of penetrating injury. 110 cases were classified as simple injuries (grade I or II) and 68 cases as complex injuries (grade III to V). The overall mortality was 32% (57 patients). The mortality for true hepatic injury was 15.7%. None of the patients with penetrating injuries died. Mortality was influenced by the type of liver injury and the number of associated injuries. The postoperative complication rate was 55%. The most-frequent postoperative complications related to the hepatic injury were intrahepatic or subcapsular hematoma (12.9%) and postoperative bleeding (9.6%). Intraabdominal abscess formation was seen in 2.8%. Operative therapy for liver injuries depends on the grade of the injury. The majority of liver injuries can be managed by simple techniques, including electrocautery and application of hemostatic agents. In complex injuries hepatotomy, direct vessel ligation, and debridement of necrotic tissue is the method of choice (Pachter's procedure). In non-controlled bleeding, perihepatic picking is a standard method.

Adolescent↗
PubMed1999

Anisotropic mechanical properties of lamellar bone using miniature cantilever bending specimens.

The flexural modulus and work-to-fracture properties of circumferential lamellar bone from baboon tibia are presented, based on experiments with miniature cantilever bending specimens. Data is provided for specimens in three orthogonal directions that show marked anisotropy. The advantages of such miniature specimens (about 150 microm in diameter and 2 mm long) include the possibility of sampling very small volumes within a heterogeneous structure such as osteonal bone, or studying biological materials that are not available in large enough volumes for conventional mechanical analysis.

Animals↗
PubMed1999

Effects of occlusal loading and thermocycling on the marginal gaps of light-polymerized and autopolymerized resin provisional crowns.

STATEMENT OF PROBLEM: Resin crowns appear to be increasingly at risk for increases in marginal gap size as a result of thermocycling and occlusal loading. PURPOSE: This in vitro study compared the effects of occlusal loading and thermocycling on the margins of provisional crowns made from a conventional autopolymerized provisional acrylic resin (Jet) to those made from a light-polymerized resin (Unifast LC). METHODS AND MATERIAL: Crowns made from the 2 materials were thermocycled and loaded on custom dies to simulate 6 to 8 weeks of oral function. Gap sizes were measured before and after thermocycling and occlusal loading. RESULTS: Provisional crowns made from light-polymerized resin exhibited smaller changes in marginal gap size than did those made from conventional autopolymerized resin. CONCLUSIONS: The improved characteristics of the light-polymerized material may prove useful for provisional crowns that must remain for long periods in the oral environment.

Acrylic Resins↗
PubMed1999

Comparison of the accuracy of working casts made by the direct and transfer coping procedures.

STATEMENT OF PROBLEM: A working cast with dies that accurately record the prepared abutments, surrounding soft tissues, and adjacent and opposing teeth is necessary. PURPOSE: This study compared the accuracy of the direct and transfer coping methods in recording the vertical and horizontal dimensional relationship of a pair of removable dies in a working cast before and after separation from the stone base. Among the procedures used for making impressions of abutments for fixed partial dentures, the transfer coping procedure has specific advantages. In particular, where there are multiple abutments, this procedure, in which individual impressions are made of the abutments, transfer copings are made, and a transfer impression of the copings is used for seating the dies and fabrication of a dental stone base, is useful. METHODS: Two groups of working casts were fabricated from a stone master cast containing 2 ivorine teeth to simulate abutments. The first group of working casts was fabricated directly from the elastomeric impression of the abutments using a 2-pour procedure. The second group of working casts was made using the transfer coping procedure. RESULTS: When the interdie dimensions in each group were compared with that of the master cast, after separation and replacement of the dies in the stone base, the differences were less than 100 microm and similar for both the direct and transfer coping techniques. CONCLUSIONS: These findings show that either procedure is equally effective in positioning the dies in the working casts.

Analysis of Variance↗
PubMed1999

The ex utero intrapartum treatment procedure for a large fetal neck mass in a twin gestation.

BACKGROUND: Large fetal neck masses can make it difficult or impossible to secure airways at birth, with associated risks of hypoxia, brain injury, and death. Based on a MEDLINE search from 1966 to June 1998, using the keywords EXIT procedure, placental support, twins, and neck mass, we report the first ex utero intrapartum treatment procedure performed in a twin gestation complicated by a large fetal neck mass. CASE: A giant fetal cervical mass was diagnosed in one fetus of a 20-week twin gestation by sonography and magnetic resonance imaging. At 35 weeks' gestation, the ex utero intrapartum treatment procedure was performed successfully for delivery of the normal twin, followed by intrapartum airway access of the twin with the neck mass. CONCLUSION: Even in twin gestations, the ex utero intrapartum treatment procedure is the delivery method of choice for fetuses with giant neck masses.

Adult↗
PubMed1999

The effects of maternal indomethacin therapy on human fetal branch pulmonary arterial vascular impedance.

OBJECTIVE: To examine whether maternal indomethacin therapy affects human fetal pulmonary arterial vascular impedance without constriction of the ductus arteriosus and to determine the changes in the pulmonary arterial vascular impedance in the presence of ductal constriction. STUDY DESIGN: In this cross-sectional study, 52 normal fetuses without maternal medication (control group), 33 fetuses without ductal constriction (Study group I) and 11 fetuses with ductal constriction (Study group II) during maternal indomethacin therapy between 24 and 34 weeks of gestation were examined by Doppler echo-cardiography. Blood velocity waveforms across the proximal right or left pulmonary artery were obtained and the pulsatility index (PI) of the proximal pulmonary arteries was calculated. RESULTS: In the control group, the proximal pulmonary artery PI was higher (p < 0.0001) at 24-25 weeks (n = 7) (3.73 +/- 0.33; mean +/- SD) than at 33-34 week of gestation (n = 11) (2.98 +/- 0.27). The PI was constantly greater (p < 0.005) in Study group I than in the control group. However, in this group the mean average weekly decrease in the PI of the proximal pulmonary arteries was similar to that in the control group. After 26 weeks of gestation, the PI values in Study group II were significantly higher than in the control group (27 weeks: 4.12 vs. 3.34 (p < 0.005); 30 weeks: 4.48 vs. 3.14 (p < 0.0001); 34 weeks: 4.96 vs. 3.00 (p < 0.0001), respectively). CONCLUSIONS: Human fetal pulmonary arterial vascular impedance is increased by maternal indomethacin therapy even without ductal constriction. In the presence of ductal constriction, the magnitude of the increase in the vascular impedance is related to the gestational age.

Blood Flow Velocity↗
PubMed1999

Fetal cardiac development and hemodynamics in the first trimester.

OBJECTIVE: To describe fetal cardiac and hemodynamic development in the first trimester of pregnancy. SUBJECTS AND METHODS: Forty-eight pregnancies were prospectively studied with transvaginal ultrasound and color Doppler. Fetal heart rate and size were documented together with the presence of inflow and outflow wave-forms and valve signals. RESULTS: Heart rate and size showed a positive correlation with gestational age. At 6 weeks of gestation, 20% of the cardiac cycle was occupied by the isovolumic contraction time (ICT); the isovolumic relaxation time (IRT) occupied 16% and remained unchanged, while the ICT progressively shortened and was not measurable after 12 weeks. The peak inflow velocities had changed from monophasic to biphasic by 10 weeks of gestation. At 7 weeks of gestation, semilunar valves were detected in 10% of examinations and the atrioventricular valves in 3%. The detection rate for both valves at 12 weeks was > or = 90%. In pregnancies that miscarried, the detection rate for both was < 25%. CONCLUSIONS: The Doppler signals that characterize the heart during the first trimester suggest effective heart compliance by 12 weeks. Normal valve development can be inferred from non-invasive Doppler recordings.

Female↗
PubMed1998

Evidence for the use of fire at zhoukoudian, china

Zhoukoudian is widely regarded as having the oldest reliable evidence for the controlled use of fire by humans. A reexamination of the evidence in Layer 10, the earliest archaeological horizon in the site, shows that burned and unburned bones are present in the same layer with stone tools. However, no ash or charcoal remnants could be detected. Hence, although indirect evidence for burning is present, there is no direct evidence for in situ burning.

Journal Article↗
PubMed1998

Reactivity of the human fetal pulmonary circulation to maternal hyperoxygenation increases during the second half of pregnancy: a randomized study.

BACKGROUND: The aims of the present study were to determine whether maternal hyperoxygenation affects human fetal pulmonary circulation and whether there is a gestational age-related response in the fetal pulmonary circulation to maternal hyperoxygenation during the second half of gestation. METHODS AND RESULTS: Twenty women between 20 and 26 weeks of gestation and 20 women between 31 and 36 weeks of gestation with normal singleton pregnancies were randomized to receive either 60% humidified oxygen or medical compressed air (room air) by a face mask. Fetal aortic and pulmonary valve; ductus arteriosus (DA); and right (RPA), left (LPA), and distal (DPA) pulmonary artery blood velocity waveforms were obtained by Doppler ultrasound before, during, and after maternal administration of either 60% oxygen or room air. Left and right ventricular cardiac outputs, DA volume blood flow, and RPA and LPA volume blood flows (Qp) were calculated. Foramen ovale volume blood flow (left ventricular cardiac output-Qp) was estimated. Pulsatility index (PI) values of DA, RPA, LPA, and DPA were calculated. Maternal hyperoxygenation did not change any of the measured fetal parameters between 20 and 26 weeks, whereas between 31 and 36 weeks, the PI values of RPA, LPA, and DPA decreased (P<.0001) and the PI of DA increased (P<.0001). In addition, Qp increased (P<.001), and DA volume blood flow (P<.01) and foramen ovale volume blood flow (P<.03) decreased. Left and right ventricular cardiac outputs were unchanged. All changes returned to baseline after maternal hyperoxygenation was discontinued. CONCLUSIONS: Reactivity of the human fetal pulmonary circulation to maternal hyperoxygenation increases with advancing gestation; this suggests that fetal pulmonary circulation is under acquired vasoconstriction at least after 31 to 36 weeks of gestation.

Blood Flow Velocity↗
PubMed1998

The addiction of overeating: self-help groups as treatment models.

This article defines eating disorders and compares it to other addictions, gives a brief etiology, and presents two treatment models: Overeaters Anonymous and Weight Watchers International. The same personality factors that place individuals at risk for substance abuse are often found in individuals with eating disorders. These predispositions are explored from both a developmental and sociological perspective. Resources within our own communities can provide valuable interventions. Overeaters Anonymous emphasizes the psychological and spiritual components, with its main focus being the commitment to the group. Weight Watchers is also rooted in the fellowship of community but adopts a more behavioristic model. Although Weight Watchers supplies more practical strategies for managing overeating, both groups provide a framework for developing positive, adaptive, and self-nurturing modalities.

Behavior, Addictive↗
PubMed1998

Strain-structure relations in human teeth using Moiré fringes.

Teeth are subjected to stress during normal function. The manner in which the resulting strain is distributed within the tooth is related to its structure. The Moiré fringe technique was used to map the in-plane strain distribution in slices from human tooth crowns under compression. The strain inside enamel is much less than in dentin, and there is a roughly 200 microm thick zone in dentin beneath the dentin enamel junction which undergoes larger strain than the central coronal dentin. This zone is softer and less mineralized than the bulk of the dentin. The strain distribution in this zone along the dentin-enamel junction shows localized maxima on both the lingual and the labial sides. This study is consistent with the hypothesis that within the dentin there are structural adaptations for transferring and minimizing stress.

Bicuspid↗
PubMed1998

Rostrum of a toothed whale: ultrastructural study of a very dense bone.

The rostral bones of the toothed whale, Mesoplodon densirostris, consist mainly of hypermineralized secondary osteons and have yielded among the highest values for density (2.6 g/cm3) and mineral content (86.7%) yet reported for any bone. Scanning and transmission electron microscopy show parallel rods of mineral oriented along the length of the rostrum. These consist of platey crystals of carbonated hydroxyapatite, which, judging from electron diffraction, are extremely well and coherently aligned. The collagen component of the rostral bone consists largely of very thin fibrils aligned in longitudinal register to form tubular networks. The collagen fibrils are also aligned with the lengths of the mineral rods, which are apparently accommodated in the tubular spaces of the collagenous network. This peculiar ultrastructure clearly differs from the densely packed mineralized fibrils commonly observed in vertebrate lamellar osseous tissues, although histological examination has indicated some vestiges of "normal" primary bone surrounding the secondary osteons. Thus, the bone tissue in the rostrum is characterized by a remarkably sparse collagenous component. This ultrastructure can explain the high density, stiffness, and brittleness of the rostrum that have been observed. It also raises interesting questions about possible modes of crystal growth during ongoing mineralization in normal bone, and may have some relevance in the mechanical behavior of dense bones in pathological conditions.

Animals↗
PubMed1998

Human root dentin: structural anisotropy and Vickers microhardness isotropy.

The demanding mechanical functions and the variable structure of dentin make it an invaluable material for studying the structure-mechanical function relations of a mineralized collagen-containing tissue. The mineralized collagen fibril axes in human root dentin are mainly located on the incremental plane. Within this plane there is a preferred orientation in the general root-crown direction. The apatite crystals are aligned in three dimensions within an individual collagen fibril, but this orientation does not necessarily extend to the neighboring fibrils. Crystals are also present as aggregates without any preferred orientation. The structure is therefore clearly anisotropic with respect to the collagen fibril orientation, but less so with respect to overall crystal orientation. Vickers microhardness measurements of the root dentin are essentially the same on the three orthogonal planes with respect to the incremental plane. Knoop microhardness measurements are also the same on all three orthogonal planes when the major diagonal is aligned perpendicular to the collagen fibril axis preferred orientation direction. In-plane variations of up to 20% are observed in the orthogonal direction. The material is thus isotropic in the three main directions with respect to Vickers microhardness, but anisotropic in structure. This paradoxical situation is attributed mainly to the variable modes of crystal organization.

Adolescent↗
PubMed1997

Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function.

The teeth of sea urchins comprise a variety of different structural entities, all of which are composed of magnesium-bearing calcite together with a small amount of organic material. The teeth are worn down continuously, but in such a way that they remain sharp and functional. Here we describe aspects of the structural, compositional and micromechanical properties of the teeth of Paracentrotus lividus using scanning electron microscopy, infrared spectrometry, atomic absorption. X-ray diffraction and microindentation. The S-shaped single crystalline calcitic fibres are one of the main structural elements of the tooth. They extend from the stone part to the keel. The diameter of the fibres increases gradually from less than 1 micron at the stone tip to about 20 microns at the keel end, while their MgCO3 contents decrease from about 13 mol% to about 4.5 mol%. Each fibre is coated by a thin organic sheath and surrounded by polycrystalline calcitic discs containing as much as 35 mol% MgCO3. This structure constitutes a unique kind of gradient fibre-reinforced ceramic matrix composite, whose microhardness and toughness decrease gradually from the stone part to the keel. Primary plates are also important structural elements of the tooth. Each primary plate has a very unusual sandwich-like structure with a calcitic envelope surrounding a thin apparently amorphous CaCO3 layer. This central layer, together with the primary plate/disc interface, improves the toughness of this zone by stopping and blunting cracks. The self-sharpening function of the teeth is believed to result from the combination of the geometrical shape of the main structural elements and their spatial arrangement, the interfacial strength between structural elements, and the hardness gradient extending from the working stone part to the surrounding zones. The sea urchin tooth structure possesses an array of interesting functional design features, some of which may possibly be applicable to materials science.

Animals↗
PubMed1997

Long-term stroke risk in children with sickle cell disease screened with transcranial Doppler.

Stroke is an important complication of sickle cell disease. Stroke prediction is clinically important because it offers the possibility of primary prevention. In 1992, transcranial Doppler (TCD) evidence of elevated intracranial internal carotid or middle cerebral artery velocity was demonstrated to be associated strongly with an increased risk of ischemic stroke. This study extends the original study and includes 125 more children, longer follow-up, and intracranial hemorrhage in the stroke-risk model. Elevated time averaged mean maximum blood flow velocity, especially when velocity is 200 cm/sec or greater by TCD, was associated strongly with stroke risk. The cases not predicted by TCD point to the need for more information on the optimal timing of TCD surveillance for stroke risk.

Adolescent↗
PubMed1997

Cervical ultrasonography compared with manual examination as a predictor of preterm delivery.

OBJECTIVE: Our purpose was to compare the accuracy of ultrasonographic and manual cervical examinations for the prediction of preterm delivery. STUDY DESIGN: One hundred two singleton pregnancies at high risk for preterm delivery were followed up prospectively from 14 to 30 weeks with both serial cervical ultrasonography measurements and manual examinations of the length of the cervix. The primary outcome studied was preterm (< 35 weeks) delivery. RESULTS: Excluding six induced preterm deliveries, 96 pregnancies were analyzed. The mean cervical length measured by ultrasonography was 20.6 mm in pregnancies delivered preterm (n = 17) and 31.3 mm in pregnancies delivered at term (n = 79) (p = 0.003); the mean cervical lengths measured by manual examination were 16.1 mm and 18.6 mm in the same preterm and term pregnancies, respectively (not significant). The sixteenth- and twentieth-week ultrasonographic cervical lengths predicted preterm delivery most accurately (p < 0.0005). The 25th percentiles of ultrasonographic (25 mm) and manual (16 mm) cervical lengths showed relative risks for preterm delivery of 4.8 (95% confidence interval 2.1 to 11.1, p = 0.0004) and 2.0 (95% confidence interval 0.5 to 4.7, p = 0.1), respectively; sensitivity, specificity, and positive and negative predictive values were 59%, 85%, 45%, 91%, and 41%, 77%, 28%, and 86%, respectively. CONCLUSION: Cervical length measured by ultrasonography is a better predictor of preterm delivery than is cervical length measured by manual examination. Cervical ultrasonography in patients at high risk for preterm birth seems to be most predictive of preterm delivery when it is performed between 14 and 22 weeks' gestation.

Cervix Uteri↗