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  • Bone mass  (3)
  • Intratubular Pressure  (2)
  • Risk factors  (2)
  • 1
    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
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Calcified tissue international 55 (1994), S. 249-252 
    ISSN: 1432-0827
    Schlagwort(e): Bone mass ; Ethnicities ; Hawaiian ; Filipino ; Japanese ; White
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract Our study compares the bone mass of Hawaiian, Filipino, Japanese, and white women living in Oahu, Hawaii. Eligible women ranged in age from 25 to 34; all had bone mass measurements at the spine, calcaneus, and proximal and distal radius. Their average bone mineral density (BMD) remained stable with age at all four bone sites, indicating that the age range 25–34 may represent the peak bone mass. Bone mass varied, however, between ethnicities; differences in BMD up to 11% were observed. The Hawaiian women had the greatest BMD, and whites had the second greatest BMD at the spine and calcaneus. The Japanese most frequently had the lowest BMD. Differences in body size partly explained the differences; most ethnic differences were reduced or eliminated after adjusting for height and weight. At the spine, the ethnic differences for BMD were also apparent with BMC and with vertebral area. Hawaiian and white women had greater values than Japanese or Filipino women. Differences at the proximal radius resembled the spine, except that whites had the widest proximal widths. The results were more complex for the distal radius. At the distal radius whites had the lowest BMD of the four ethic groups. The difference between whites and Hawaiians derived from the greater bone mineral content (BMC) of the Hawaiian women. By contrast, the difference between whites and the Japanese and Filipinos derived from the wider distal widths of the white women. Compared with the Japanese and Filipino women, the white women appeared to disperse their BMC at the distal radius across a wider bone width. Such differences in bone distributions might lead to an altered risk of distal radius (wrist) fractures. Within ethnicities there was marked variation among individuals in bone mass. At the extremes, women differed by 50–100% or more within all four ethnic groups.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    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
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Pflügers Archiv 333 (1972), S. 271-280 
    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
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Osteoporosis international 4 (1994), S. 1-5 
    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
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Osteoporosis international 5 (1995), S. 234-238 
    ISSN: 1433-2965
    Schlagwort(e): Anthropometry ; Bone mass ; Height ; Osteoporosis ; Weight
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract We examined the magnitude of regional variations in bone mass among elderly, Japanese-American men and women. All subjects had bone measurements at the calcaneus, and at the distal and proximal radius sites. A subset of the women had, in addition, spine bone mass measurements. To provide a common measurement scale, the bone measurements were converted to age- and sex-specificZ-scores. TheZ-scores between pairs of bone sites were then subtracted to yield the differences in bone mass between bone sites (expressed inZ-score units). For most individuals the differences were less than 1.0Z-score; however, 12%–20% of the differences were at least 1Z-score apart. The most similar sites were the distal and proximal radius: different regions within the same bone. Among the other bone pairs, the calcaneus and spine were the most similar to one another. The magnitudes of the differences in bone mass were associated with height and weight. Heavier subjects, for instance, had greater calcaneus than radius bone mass measurements, and greater spine than radius measurements. The spine and calcaneus are more weight-bearing than the radius sites. Associations were observed up to 0.25Z-score per 10 kg difference in weight. Height was associated with bone mass differences in an opposite direction to weight. Taller subjects had greater bone mass at the radius sites than expected from their calcaneus or spine bone measurements (0.1 to 0.2Z-score difference per 5 cm difference in height). Bone width partly explained the associations with height; that is, adjusting the radius widths reduced the associations with height. Overall, our results indicate that small to moderate differences between bone sites were common among our study population, and that the magnitudes of the differences were associated with height and weight.
    Materialart: Digitale Medien
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