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  • Ferrocyanide Method  (3)
  • Intratubular Pressure  (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
    The effect of antidiuretic hormone on the distribution of nephron filtration rates in rats with hereditary diabetes insipidus (1971)
    Springer
    Pflügers Archiv 330 (1971), S. 323-334 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Nephron Filtration Rate ; Antidiuretic Hormone ; Diabetes Insipidus Rats ; Ferrocyanide Method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effect of antidiuretic hormone on the distribution of nephron filtration rates was studied in rats with hereditary diabetes insipidus using the Hanssen method for determination of nephron filtration rates as modified by de Rouffignacet al. [18]. Conversion of water diuresis to antidiuresis by infusion of ADH resulted in a moderate, but highly significant increase in the filtration rate of the juxtamedullary nephrons, while the nephrons of all other cortex regions filtered at an unaltered rate. A mechanism based on the action of ADH on distal nephron water permeability is proposed as an explanation: water inflow into the medulla very likely decreases when water diuresis is converted to antidiuresis. This occasions a rise in medullary osmolality which then causes an increase in the apparent viscosity of the blood flowing through the vasa recta. This is responsible for a rise in juxtamedullary postglomerular resistance which results in an increase in the effective filtration pressure and thus in the juxtamedullary nephron filtration rate. The results suggest that an increased juxtamedullary filtration rate participates in the establishment and maintenance of the inner medullary solute gradients, possibly as a consequence of an increased solute delivery to the ascending limbs of the long loops of Henle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00588584
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  • 4
    Digitale Medien
    Digitale Medien
    Relationship between salt loading and distribution of nephron filtration rates in the dog (1974)
    Springer
    Pflügers Archiv 350 (1974), S. 259-272 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Dog Kidney ; Saline Infusion ; Nephron Filtration Rate ; Filtrate Distribution ; Ferrocyanide Method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The intrarenal distribution of nephron filtration rate (N-GFR) was assessed using the Hanssen ferrocyanide technique in dogs which were chronically salt loaded with or without an additional acute sodium load and in sodium depleted dogs. In 4 dogs fed 7–10 days on a high sodium diet, superficial nephron filtration rate (SN-GFR) was 56.7±13.1 nl/min, middle nephron filtration rate (MN-GFR) was 65.2±14.3 nl/min, and the juxtamedullary nephron filtration rate (JN-GFR) was 82.4±17.1 nl/min, a value 52.3% higher than the SN-GFR. Creatinine clearance in these animals averaged 22.0±3.9 ml/min. In 4 animals which received an additional infusion of 0.9% NaCl at 4.0–4.5 ml/min for 2.5 h, the mean creatinine clearance rose from 16.6±2.0 ml/min to 20.3±0.7 ml/min and the distribution of N-GFR was: SN-GFR 70.5±21.2 nl/min, MN-GFR 83.6±23.8 nl/min and JN-GFR 91.2±24.3 nl/min. In this case, the JN-GFR was 29.3% higher than the SN-GFR. In one sodium depleted dog, (creatinine clearance 15.7 ml/min) the distribution of N-GFR was: SN-GFR 41.1±10.5 nl/min, MN-GFR 48.0±16.5 nl/min, and JN-GFR 58.0±19.0 nl/min, a value exceeding SN-GFR by 41.1%. These results imply that acute saline infusion in dogs induces a proportionately greater change in GFR of superficial than of juxtamedullary nephrons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00587805
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  • 5
    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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  • 6
    Digitale Medien
    Digitale Medien
    The effect of experimental alterations in urine concentration on nephron filtration rate (1973)
    Springer
    Pflügers Archiv 344 (1973), S. 69-74 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Nephron Filtration Rate ; Ferrocyanide Method ; Redistribution of GFR ; Urine Osmolarity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Experiments were performed to clarify the cause of the dependency of juxtamedullary nephron filtration rate (JN-GFR) on the diuretic state of the animal. Using the ferrocyanide technique of de Rouffignacet. al. [5] the distribution of nephron filtration rates was determined during selective modification of final urine osmolarity by papillary superfusion with concentrated or isotonic solutions. Papillary superfusion with a 2000 mosmolar solution led to a mean urine osmolarity of 1848±78 mOsm/l. JN-GFR displayed a mean increase of 66.6% over the superficial nephron filtration rate (SN-GFR). When the superfusion fluid was isotonic urine osmolarity averaged 754±53 mOsm/l and JN-GFR increased by a mean of only 26.3% over the SN-GFR. Using the micropuncture technique it was shown that SN-GFR in a given animal was not altered when the superfusion fluid was interchanged. We conclude therefore that the change in the percentage increase in GFR from superficial to juxtamedullary nephrons is caused by a change of juxtamedullary nephron filtration rate. Since plasma ADH concentration was not altered this effect appears to be elicited by the changed medullary solute concentration rather than by a vasomotor action of the antidiuretic hormone.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00587442
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  • 7
    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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