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  • Electronic Resource  (14)
  • Chemical Engineering  (6)
  • Nephron Filtration Rate  (5)
  • Osteoporosis  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Evaluation of adverse health outcomes associated with vertebral fractures (1991)
    Springer
    Osteoporosis international 1 (1991), S. 134-140 
    Details
    ISSN: 1433-2965
    Keywords: Osteoporosis ; Pain and disability ; Psychosocial problems ; Risk analysis ; Statistical methods ; Vertebral fractures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Little is known about the frequency or degree to which vertebral fractures cause pain and physical disability. The purpose of this investigation was to examine the advantages of risk analysis over other statistical techniques (e.g., correlation analysis) for quantifying relationships between vertebral fractures and outcomes such as pain and disability. Subjects who volunteered to participate in studies of osteoporosis were asked about pain and disability. The number and degree of vertebral deformities were assessed from radiographs. Strong associations were observed between the most severe vertebral deformities and the risk of high pain or disability scores, while weaker associations were observed for moderate deformities. There did not appear to be any association between vertebral deformity and risk of moderate levels of pain or disability. Because of the potential for bias in cross-sectional studies such as this, the magnitude of these findings must be considered tentative. We conclude that risk analysis is an appropriate method for quantifying the relationship of vertebral fractures with pain and disability, but that prospective studies are now needed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01625442
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  • 2
    Electronic Resource
    Electronic Resource
    Relation of height and weight to the regional variations in bone mass among Japanese-American men and women (1995)
    Springer
    Osteoporosis international 5 (1995), S. 234-238 
    Details
    ISSN: 1433-2965
    Keywords: Anthropometry ; Bone mass ; Height ; Osteoporosis ; Weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01774012
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  • 3
    Electronic Resource
    Electronic Resource
    When should bone density measurements be repeated? (1994)
    Springer
    Calcified tissue international 55 (1994), S. 243-248 
    Details
    ISSN: 1432-0827
    Keywords: Osteoporosis ; Bone density ; Longitudinal studies ; Statistical models ; Decision models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract We calculated how long to wait before repeating bone mineral density (BMD) measurements to reassess fracture risk. Correlation results from serial measurements of 495 postmenopausal Japanese-American women were used to estimate 95% confidence intervals (CI) for future BMD. After 7 years of follow-up, BMD correlations with the initial measurement ranged between 0.81 and 0.94, depending on age group and measurement site. In this analysis, the period between measurements was defined as the time required for the lower 95% CI to fall below the BMD value corresponding to doubling of fracture risk. Progressive bone loss causes fracture risk to double after 10 years, on average. However, the 95% CIs indicate that a second BMD measurement will detect risk doubling after only 2 or 3 years for some women. For untreated, early postmenopausal women, the period between measurements was approximately 2–5 years for the radius and 4–6 years for the calcaneus, depending on the initial BMD level. The period was approximately 1 year longer for women age 60 and older. Treatments that halve the bone loss rate would increase the period by 1–3 years. In the absence of a second measurement of BMD, the CI will continue to expand with time, corresponding to a wider range in risk between individuals, and a greater proportion of women will be at increased fracture risk. Obtaining a second BMD measurement pinpoints the patient's status within the precision of the measurement. We conclude that repeated BMD measurements will provide a more accurate estimate of fracture risk than a single, baseline measurement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310399
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Nephron Filtration Rate ; Antidiuretic Hormone ; Diabetes Insipidus Rats ; Ferrocyanide Method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588584
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: Dog Kidney ; Saline Infusion ; Nephron Filtration Rate ; Filtrate Distribution ; Ferrocyanide Method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587805
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  • 6
    Electronic Resource
    Electronic Resource
    Micropuncture method for the determination of nephron filtration rate (1972)
    Springer
    Pflügers Archiv 333 (1972), S. 271-280 
    Details
    ISSN: 1432-2013
    Keywords: Nephron Filtration Rate ; Tubulo-Glomerular Feedback ; Intratubular Pressure ; Polyfructosan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00592688
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Keywords: Nephron Filtration Rate ; Ferrocyanide Method ; Redistribution of GFR ; Urine Osmolarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587442
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  • 8
    Electronic Resource
    Electronic Resource
    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
    Keywords: Nephron Filtration Rate ; Saline Diuresis ; Intratubular Pressure ; Retrograde Contamination ; Sampling Pipettes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00588002
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  • 9
    Electronic Resource
    Electronic Resource
    Gross error detection when variance-covariance matrices are unknown (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1335-1341 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Equations introduced here identify measurement biases and process leaks, when gross errors exist in measured process variables and the variance-covariance matrix of the measurements, Σ, is unknown. Σ is estimated by the sample variance, S, using process data.For an unknown Σ, the global test statistic is the well-known Hotelling T2 statistic. Its power function has a noncentral F-distribution. For component tests used for specific identification of measurement biases and nodal leaks, two tests are presented with Σ unknown. The first test is independent of the number of component tests, k, and is given by a statistic with an F-distribution. The second test depends on k and has a student t-distribution. The power functions for both component tests are provided. Process examples and a Monte Carlo simulation study presented demonstrate the use and performance of these statistical equations in identifying biases and process leaks.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690390810
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  • 10
    Electronic Resource
    Electronic Resource
    Unbiased estimation of gross errors in process measurements (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 563-572 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new approach to gross error detection provides unbiased estimates and 100(1-α)% simultaneous confidence intervals of process variables when biased process measurements and process leaks exist. Presented in this article are estimation equations for process variables, as well as equations that help identify biased measurements and process leaks. These equations include the power function for a global test, and two types of α-level component tests and their power functions. Important strengths and weaknesses of this approach are compared to those of the serial compensation strategy, in particular, by varying the significance level (α), the variance-covariance matrix (Σ), the size of measurement bias (δ), the number of biased variables, and the sample size (N). Accuracy of δ estimation and performance in detecting the presence of process leaks (γ) are also evaluated and compared. The proposed approach has unique features that can provide a basis for improving the reconciliation of variables in process operations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690380410
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