tangential force Dotaz Zobrazit nápovědu
Journal of parenteral science and technology, ISSN 0279-7976 vol. 46, no. S1, suppl., 1992
S13 s. : grafy ; 30 cm
OBJECTIVE: Translation of the contact zone in articulating joints is an important component of joint kinematics, yet rarely investigated in a biological context. This study was designed to investigate how sliding contact areas affect cartilage mechanobiology. We hypothesized that higher sliding speeds would lead to increased extracellular matrix mechanical stress and the expression of catabolic genes. DESIGN: A cylindrical Teflon indenter was used to apply 50 or 100 N normal forces at 10, 40, or 70 mm/s sliding speed. Mechanical parameters were correlated with gene expressions using a multiple linear regression model. RESULTS: In both loading groups there was no significant effect of sliding speed on any of the mechanical parameters (strain, stress, modulus, tangential force). However, an increase in vertical force (from 50 to 100 N) led to a significant increase in extracellular matrix strain and stress. For 100 N, significant correlations between gene expression and mechanical parameters were found for TIMP-3 (r(2) = 0.89), ADAMTS-5 (r(2) = 0.73), and lubricin (r(2) = 0.73). CONCLUSIONS: The sliding speeds applied do not have an effect on the mechanical response of the cartilage, this could be explained by a partial attainment of the "elastic limit" at and above a sliding speed of 10 mm/s. Nevertheless, we still found a relationship between sliding speed and gene expression when the tissue was loaded with 100 N normal force. Thus despite the absence of speed-dependent mechanical changes (strain, stress, modulus, tangential force), the sliding speed had an influence on gene expression.
- Publikační typ
- časopisecké články MeSH
Za příčinu vzniku décollement se obvykle považuje tangenciální hrubé tupé násilí účinkující na povrch těla zejména při přejetí nebo najetí vozidla na tělo chodce. Mluví se též o valivém účinku, resp. mechanismu. Dochází tak k disociaci tkáňových vrstev s dalšími průvodními jevy. Předložený soubor 152 décollement zjištěných u 103 zemřelých pitvaných v průběhu 4 let zahrnuje pozorování décollement různé úrazové etiologie (dopravní nehody, pády z výše, smáčknutí trupu); u dopravních nehod pak výskyt u různých účastníků dopravního provozu, a to nejen při kolizi chodců s různými dopravními prostředky, ale i u řidičů různých dopravních prostředků i spolucestujících. Sledována byla dále topika, lokalizace, obsah, rozsah, vitální reakce décollement a sdružená poranění. Z rozmanitosti úrazové etiologie, neomezené jen na tradiční pojetí mechanismu décollement, je zřejmé, že tradovaná poučka zdaleka nevyčerpává skutečný obsah tohoto pojmu. Alternativní výklad dosud udávaného mechanismu jsme v literatuře nenašli. Lékařská literatura se zaměřuje spíše na klinický význam tohoto zranění. V tomto sdělení se diskutuje biomechanika vzniku décollement též při stlačení tkáně tlakem působícím kolmo k povrchu těla, závislosti na fyzikálních vlastnostech aktivně či pasivně účinkujícího předmětu, význam poměru mezi stlačením tkáňových struktur v jednom směru a příčnou dilatací v jiných dvou směrech v závislosti na velikosti Poissonovy konstanty, otázka tečné složky násilí i při svislém pádu těla na vodorovnou plochu a biomechanické poměry při dopadu těla na šikmou plochu. Mechanismus décollement je tak komplikovanější, než jak se dosud prezentuje. Tomu by měla odpovídat i forenzní interpretace nálezů.
The cause of décollement is usually considered to be tangential brute blunt force impacting the body surface especially in case of hitting or running-over injury of the pedestrian's body by a car. The term rolling effect or rolling mechanism is used as well. The dissociation of tissue layers with other epiphenomenon occurs. The presented group of 152 décollement determined in 103 autopsy cases during the 4 years period comprises the observation of décollement of different etiology of the injuries (traffic accidents, falls from the high, compression of the torso); in the traffic accidents the occurrence in various participants of the traffic, not only in the case of the collision of the pedestrians with various traffic vehicles, but also in drivers of various traffic vehicles, and fellow-travelers as well. The topic, the localization, the content, the extent, and vital reaction and combination injuries were followed-up. According to the variability of the injury etiology, not restricted to the traditional conception of the décollement mechanism, it is obvious that the passed on rule by far is not covering the whole content of this concept. We didn't find any alternative interpretation of until now presented mechanism in the literature. The medical literature focuses mostly on the clinical aspect of this injury. In this paper, the biomechanics of the décollement origin also in case of the tissue compression by the pressure applied perpendicularly to the body surface, the dependences on physical properties of the actively or passively affecting object, the relevance of the ratio of the tissue structures compression in one direction and transversal dilation in other two directions according to the Poisson's constant, the question of tangential factor of the force in case of vertical falling on the horizontal plane, and biomechanical relations in case of body landing on an oblique surface are discussed. The mechanism of décollement is more complex as presented until now. The forensic interpretation of findings should reflex the above-mentioned facts.
BACKGROUND: We evaluated visual outcomes after vitrectomy for diabetic cystoid macular edema and factors possibly influencing final visual acuity. MATERIALS AND METHODS: Studied prospectively, pars plana vitrectomy was performed on 72 consecutive eyes of 61 patients with diabetic cystoid macular edema not responsive to laser photocoagulation therapy. Vitreomacular traction was observed on biomicroscopy, B-scan ultrasonography, and optical coherence tomography in 21 eyes, 15 eyes had a complete posterior vitreous detachment (PVD) and 36 eyes had partial peripheral PVD. Vitrectomy with releasing vitreomacular tangential and axial tractional forces was performed. All patients were followed up for at least 6 months. RESULTS: The anatomical results were satisfactory in 69 of 72 eyes (96 %), the final visual acuity improved by 2 or more lines in 45 of 72 eyes (63 %), remained unchanged in 22 of 72 eyes (31 %), and deteriorated after surgery in 5 of 72 eyes (7 %), due to residual cystoid macular edema and massive macular hard exudates. The best results were obtained in edema with tractional predominance and in eyes with a duration of cystoid macular edema shorter than 6 months. CONCLUSIONS: Vitrectomy for diabetic cystoid macular edema is an effective procedure for reducing the edema and improving visual acuity. Surgery was beneficial not only in eyes with vitreomacular traction but also in eyes with complete PVD. Visual improvement after vitrectomy is related to duration of edema, therefore the timing of the surgery is an important prognostic factor.
- MeSH
- diabetická retinopatie diagnóza chirurgie MeSH
- financování organizované MeSH
- lidé MeSH
- makulární edém diagnóza chirurgie MeSH
- následné studie MeSH
- odchlípení sítnice diagnóza chirurgie MeSH
- perforace sítnice diagnóza chirurgie MeSH
- pooperační komplikace etiologie MeSH
- vitrektomie MeSH
- zraková ostrost MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
