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  • Intratubular Pressure  (2)
  • Polymer and Materials Science  (2)
  • Risk factors  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Predicting vertebral fracture incidence from prevalent fractures and bone density among non-black, osteoporotic women (1993)
    Springer
    Osteoporosis international 3 (1993), S. 120-126 
    Details
    ISSN: 1433-2965
    Schlagwort(e): Bone density ; Prospective studies ; Risk factors ; Vertebral fracture incidence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We evaluated the ability of bone density and vertebral fractures at baseline to predict vertebral fracture incidence in a cohort of postmenopausal women with osteoporosis. The study population was 380 postmenopausal women (mean age 65 years) treated for osteoporosis in a randomized, placebo-controlled, clinical trial of the bisphosphonate etidronate at seven geographic centers in the United States. Baseline measurements of bone mineral density were obtained in 1986 by quantitative computed tomography at the spine and dual-photon absorptiometry at the lumbar spine and hip. Vertebral fractures were documented on serial spine radiographs. Proportional hazards models were used to evaluate the ability to predict the risk of subsequent fractures during an average of 2.9 years of follow-up. Presence of one or two fractures increased the rate of new vertebral fractures 7.4-fold (95% confidence interval = 1.0 to 55.9). Additional fractures at baseline further increased the fracture rate. A decrease of 2 standard deviations in spinal bone density by absorptiometry was associated with a 5.8-fold increase in fracture rate (95% confidence interval = 2.9 to 11.6). The lowest and highest quintiles of bone density had absolute fracture rates of 120 and 6 cases per 1000 patient-years, respectively. In general, the simultaneous use of two predictors (bone density and prevalent fractures or two bone density measurements) improved fracture prediction, compared with the use of a single predictor. We conclude that both bone density and prevalent vertebral fractures are strong, complementary predictors of vertebral fracture risk. The results suggest that physicians can use bone density and prevalent vertebral fractures, individually or in combination, as risk factors to identify patients at greatest risk of new fractures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01623272
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  • 2
    Digitale Medien
    Digitale Medien
    Spine fracture risk is predicted by non-spine fractures (1994)
    Springer
    Osteoporosis international 4 (1994), S. 1-5 
    Details
    ISSN: 1433-2965
    Schlagwort(e): Bone mass ; Bone density ; Fracture incidence ; Fracture prevalence ; Longitudinal studies ; Risk factors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A prospective cohort study of 1098 postmenopausal Japanese-American women evaluated the relationship between baseline non-spine fractures and new (incident) spine fractures. At the baseline examination in 1981, prevalent non-spine fractures were ascertained by interview, and prevalent spine fractures by radiograph. Bone mass measurements of the distal radius, proximal radius, calcaneus (1981), the lumbar spine (1984) were obtained and repeated at 1- to 2-year intervals. Women with existing non-spine fractures have a threefold greater risk of subsequent spine fractures, independent of bone mass, and independent of the known association between prevalent spine fractures and subsequent spine fractures. Women with both a prevalent non-spine fracture and low bone mass (50th percentile or lower) have an eightfold greater risk of new spine fractures compared with women above the 50th percentile of bone mass and no prevalent fractures. In addition to low bone mass, both prevalent spine fractures and prevalent non-spine fractures are strong risk factors for subsequent spine fracture. These data suggest that not all osteoporotic risk factors are expressed via bone mass, and that other, unmeasured risk factors, such as bone quality defects, may explain these results. In clinical terms, women with both prevalent fractures and low bone mass should be recognized as being at extremely high risk, and treatment potency should be commensurate with this level of risk.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02352253
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  • 3
    Digitale Medien
    Digitale Medien
    Micropuncture method for the determination of nephron filtration rate (1972)
    Springer
    Pflügers Archiv 333 (1972), S. 271-280 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Nephron Filtration Rate ; Tubulo-Glomerular Feedback ; Intratubular Pressure ; Polyfructosan
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Two possible artifacts may explain the phenomenon that nephron GFR (N-GFR) measured by distal tubular puncture is smaller than that measured by proximal tubular puncture: a loss of the inulin-like substance used in this laboratory (polyfructosan) from the tubular lumen or unreliable distal punctures. To test these possibilities (a) known amounts of polyfructosan were injected into the proximal tubule and the percentage recovery from the distal tubule measured, (b) N-GFR was measured by distal puncture, subsequently by recollection from the same site and finally by a proximal puncture. On the average, 98.5±7.5% of the proximally injected polyfructosan was recovered from the distal tubule. This is not significantly different from 100% (p〉0.1) and demonstrates that proximal tubule and loop of Henle are impermeable to polyfructosan. The ratio between the N-GFR measured by a distal puncture and that measured by subsequent recollection was 1.016±0.096 and not significantly different from 1.000 (p〈0.20), demonstrating the reliability of distal tubular puncture. The mean distal N-GFR of 27.9±5.3 nl/min was significantly smaller (p〈0.001) than the proximal N-GFR of 35.1±8.0 nl/min. The existence of the proximal-distal N-GFR difference thus is confirmed and two possible artifacts eliminated. The best explanation remains the operation of a tubulo-glomerular feedback mechanism. A current point of dispute is the effect of alterations in intratubular pressure (ITP) on N-GFR. Collection of tubular fluid at ITPs below the previously measured free flow pressure (FFP) resulted in a change of N-GFR of 0.45 nl/min· cm H2O. In contrast, fluid collection at ITPs greater than the FFP resulted in a change of N-GFR of 1.48 nl/min· cm H2O. We conclude that although N-GFR is sensitive to ITP changes in both directions, pressure decreases are of little practical importance for the determination of N-GFR whereas intratubular pressure increases are to be avoided.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00592688
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  • 4
    Digitale Medien
    Digitale Medien
    Technical problems in the micropuncture determination of nephron filtration rate and their functional implications (1971)
    Springer
    Pflügers Archiv 329 (1971), S. 307-320 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Nephron Filtration Rate ; Saline Diuresis ; Intratubular Pressure ; Retrograde Contamination ; Sampling Pipettes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The theory of a functional coupling between distal tubular fluid composition and glomerular filtration rate implies that the blockade of flow at a proximal site should lead to a marked increase of GFR. This potential alteration of steady state GFR was studied by comparing the influence of sampling from distal or proximal sites on the filtration rate of identical nephrons. During antidiuresis an average GFR of 25.2 nl/min±7.5 S.D. was found in distal collections, while proximally collected samples gave an average GFR of 34.5 nl/min±8.4 S.D. This difference of 9.3 nl/min is highly significant (p〈0.001). During saline diuresis a mean nephron GFR of 41.6 nl/min±5.0 was found by distal sampling and of 45.3 nl/min±5.4 by proximal sampling (p〉0.05). The proximal-distal difference in nephron GFR is interpreted to indicate the operation of a tubulo-glomerular feedback control system. Thus, a true steady-state GFR probably cannot be obtained by proximal fluid collection. Even in the presence of high intratubular pressures and unusually short oil blocks no evidence of sample contamination by retrograde fluid flow past an injected oil block was obtained. The application of a counter-pressure to the sampling pipette which has been recommended by Gertzet al. [5] as a means to standardize fluid collections, was found to lead to abnormally high intratubular pressures. The reason for this finding appears to be an unexpectedly high and inconstant tip resistance to flow during fluid flow into the pipette.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00588002
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  • 5
    Digitale Medien
    Digitale Medien
    The search for correlation between electrokinetic phenomena and blood thrombus formation on implant materials (1968)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 2 (1968), S. 51-79 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Bioelectric charge transfer at the blood-wall interface may be a crucial factor affecting thrombosis on implant materials. A program of studies was conducted to determine the electrokinetic and other physical properties of a wide spectrum of materials including organic polymers, metals, inorganics, heterogeneous compounds, and animal tissue. From these tests, materials were selected for in-vivo cannulation experiments. In this manner, a search was made to find a correlation between surface charge characteristics and thrombosis on cardiovascular implant materials. It was found that materials exhibiting a substantial positive charge were prone to rapid thrombosis. No clear correlation can be stated, as yet, regarding the thrombogenecity of highly charged negative surfaces or slightly charged surfaces. However, many heterogeneous materials have exhibited prolonged in-vivo patency. It appears necessary to isolate surface effects from volumetric effects to seek the role of bioelectric charge transfer in blood thrombus formation.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820020105
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  • 6
    Digitale Medien
    Digitale Medien
    On wave propagation in viscoelastic media (1961)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 50 (1961), S. 475-488 
    Details
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A mathematical analysis is made of the problem of wave propagation in a one-dimensional bounded viscoelastic medium under prescribed boundary conditions. Closed form expressions are obtained for viscoelastic waves for the case of a relaxation function involving a single relaxation time. An expression for the phase velocity as a function of ratio of relaxation frequency to frequency of applied periodic displacement is obtained for the steady state part of the solution. The generalization to a relaxation function involving a finite number of relaxation times is discussed, and a method is sketched out for solving the more general integropartial differential equation of motion. Comments are made on the molecular interpretation of viscoelastic models.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1961.1205015416
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