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PubMed1984

Measurement of inhibitors of calcium phosphate precipitation in plasma ultrafiltrate.

Two methods are described to measure quantitatively the inhibitory activity of calcium phosphate precipitation in undiluted plasma ultrafiltrates. The first, called the "seed test," is based on the determination of the amount of apatite needed to induce the precipitation of calcium phosphate from the ultrafiltrate that previously had been brought to a constant [Ca X Pi] supersaturation. The second, called the "supersaturation test," is based on the determination of the minimum [Ca X Pi] product necessary to induce the precipitation of calcium phosphate, care being taken to eliminate the influence of chelators. With both techniques pyrophosphate was found to be the most effective inhibitor, magnesium and citrate being less active. At the physiological concentrations present in plasma ultrafiltrate, magnesium represented the greatest part of the activity in the seed test, while pyrophosphate was the most important in the supersaturation test. However, the three known inhibitors represented only part of the total inhibitory activity. In a pilot study, patients with renal failure showed an increase in inhibitory activity both in the known and unknown fractions.

Adult↗
PubMed2006

Treatment time and ultrafiltration rate are more important in dialysis prescription than small molecule clearance.

Chronic hemodialysis sessions, as developed in Seattle in the 1960s, were long procedures with minimal intra- and interdialytic symptoms. Over the next three decades, dialysis duration was shorten to 4, 3, even 2 h in thrice weekly schedules. This method spread rapidly, particularly in the United States, after the National Cooperative Dialysis Study suggested that the time of dialysis is of minor importance as long as urea clearance multiplied by dialysis time and scaled to total body water (Kt/V(urea)) equals 0.95-1.0. This number was later increased to 1.3, but the assumption that hemodialysis time is of minimal importance remained unchanged. However, Kt/V(urea) measures only the removal of low molecular weight substances and does not consider the removal of larger molecules. Nor does it correlate with the other important function of hemodialysis, namely ultrafiltration. Rapid ultrafiltration is associated with cramps, nausea, vomiting, headache, fatigue, hypotensive episodes during dialysis, and hangover after dialysis; patients remain fluid overloaded with subsequent poor blood pressure control leading to left ventricular hypertrophy, diastolic dysfunction, and high cardiovascular mortality. Kt/V(urea) should be abandoned as a measure of dialysis quality. The formula suggests that it is possible to decrease t as long as K is proportionately increased, but this is not true. Time of dialysis should be adjusted in such a way that patients would not suffer from symptoms related to rapid ultrafiltration, would not have other uremic symptoms and most patients would have blood pressure controlled without antihypertensive drugs.

Body Composition↗
PubMed1990

Ultrafiltration of dialysis fluid to obtain a sterile solution during hemodialysis.

As the quality of water in the dialysis fluid varies considerably, and in view of the fact that endotoxin or active derivates can cause acute and chronic side effects in patients under chronic hemodialysis treatment, the dialysis fluid must be sterile and endotoxin free. The predialyzer fluid in 20 hemodialysis patients was investigated. The bacterial load was between 5/ml and 12,000/ml, the endotoxin concentration was high and extremely variable. Therefore, we introduced the ultrafiltration of the dialysis fluid by a polyamide hollow fiber membrane before entering the dialyzer. All samples were free of bacteria, and the concentration of endotoxin was lower than the detectable limit. With this procedure, we can obtain sterile dialysis fluid, which is endotoxin free. Our preliminary results showed that interleukin-1 in the patients was significantly (p less than 0.005) lower under ultrafiltration of the dialysis fluid than without ultrafiltration.

Bacteria↗
PubMed1992

Net ultrafiltration in peritoneal dialysis: role of direct fluid absorption into peritoneal tissue.

'Net ultrafiltration' in peritoneal dialysis refers to the difference between the osmotically induced ultrafiltration into the peritoneal cavity and the fluid loss from the cavity during dialysis. Recent research has demonstrated that, during a 3- to 4-hour experimental dialysis, 5-25% of the total fluid loss is via lymphatics and the remaining fluid is absorbed directly into the tissue surrounding the peritoneal cavity. The driving force for this convection into tissue is the hydrostatic pressure gradient between the peritoneal cavity and the tissue, which ranges from 2 to 8 mm Hg during the typical 2-liter dialysis in humans. Because the convection from the cavity occurs during periods of a positive net ultrafiltration, the peritoneum and its underlying tissue cannot be represented as a single membrane but function as a composite of 'tight' and 'loose' membranes. More data on the mechanical properties of the peritoneal tissue space and its response to hydrostatic pressure in the cavity are required before we fully understand fluid transport at the tissue level.

Absorption↗
PubMed1994

Ultrafiltration and clearance studies in human isolated peritoneal vascular loops.

Eight samples of human peritoneal tissue were obtained from patients undergoing hemicholectomy for cancer. An artery and a vein were cannulated and perfused with blood in vitro with a special circuit able to provide different perfusion pressures. Ultrafiltration and clearance studies were performed in these samples. Both ultrafiltration and small-solute clearances linearly correlated with the blood flow, demonstrating a strong dependence on this parameter. The peritoneal capillary showed a typical filtration pressure equilibrium with a constant filtration fraction at different blood flows. The results suggest that the blood flow may be a factor limiting the efficiency of peritoneal dialysis both in terms of mass transfer coefficients and maximal ultrafiltration rates.

Blood↗
PubMed1985

Fate of parathyroid hormone during hemodialysis and ultrafiltration.

In order to shed light on the discrepant changes in plasma immunoreactive parathyroid hormone (iPTH) during hemodialysis (HD) and ultrafiltration (UF) in end-stage renal failure, the influence of filtration of PTH fragments on the iPTH level in plasma was examined in 2 sets of experiments: in vitro dialysis of 125I-bPTH 1-84, 125I-hPTH 1-34 and 125I-hPTH 53-84 added to plasma was successively performed through a cuprophane membrane. Gel filtration on a Biogel P-100 column and subsequent counting of the eluate were performed with the plasma before and after dialysis, and with the dialysate fluid after dialysate fluid after dialysis. An ultrafiltrate obtained from a patient with renal failure was also analyzed for iPTH with a 'C-' and with an 'N-terminal' antiserum (GP 500 MA and AS 211/32), and so was his plasma before and after UF, and after a subsequent dialysis session. Fluid obtained by lavage of the filter with acetic acid after dialysis was also analyzed. Chromatography with measurements of iPTH in the eluate was performed in each case, and the procedure was repeated applying a different transmembrane pressure. Immunoreactive material found in the concentrated ultrafiltrate, but not in plasma, was characterized by means of dilution curves in different RIA performed with the C-terminal antiserum preincubated with various synthetic PTH fragments. Results showed that intact PTH does not cross the cuprophane membrane during both in vitro dialysis and in vivo UF. The 1-34 fragments are poorly dialyzed in vitro; either they stick to the membrane or they are disintegrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Gel↗
PubMed1978

Effects of ultrafiltration of diffusion and convection in two newer coils.

Clearances of sodium and B12 were measured with increasing ultrafiltration in two newer coils with new types of membrane support. In all other coil studies previously reported, clearance increases with ultrafiltration did not equal predictions from contributions of convection implying simultaneous decreases in diffusive solute transport with increasing transmembrane pressure. Such deterioration was attributed to masking of membrane surface area by the membrane support, widening of blood channels, and/or channeling of dialysate flow. In these newer coils, clearance increases were very near to predicted enhancement by convection while diffusion was stable in one type and decreased only modestly in the other. Coil volumes assessed with the kerosene technique increased with higher transmembrane pressure similar to findings in previous coils studies. Thus, although coil blood path dimensions are altered with increasing pressure as in older coils, diffusive clearances remain stable and increases in total clearances equal that predicted from convective solute transport. These results suggest that membrane masking is probably the major mechanism for decreases in diffusion with ultrafiltration in other coils and that the problem has been minimized with improved membrane supports.

Chemical Phenomena↗
PubMed1980

Response of plasma aldosterone to sequential ultrafiltration, dialysis and conventional hemodialysis.

The response of plasma aldosterone to sequential ultrafiltration dialysis has been studied during 16 sessions and compared with the response to 12 conventional sessions of hemodialysis. During the isolated ultrafiltration phase an important and significant increase in plasma aldosterone and plasma renin activity was observed. There was a substantial removal of extracellular fluid, but no change in plasma biochemistry. During conventional hemodialysis over the same time scale the concentration of plasma aldosterone decreased significantly, plasma renin underwent a small increase and plasma osmolality and plasma potassium decreased. Several possible pathophysiological mechanisms are discussed. We conclude that rapid isosmotic ultrafiltration without change in plasma potassium or sodium, the maintenance of plasma potassium at normal elevated values, and the increase of angiotensin II are factors favoring aldosterone biosynthesis.

Adult↗
PubMed1996

Morphological changes in the peritoneal vasculature of patients on CAPD with ultrafiltration failure.

Vascular changes in the peritoneum were histochemically assessed in patients on continuous ambulatory peritoneal dialysis (CAPD) with ultrafiltration failure. Light microscopy showed extensive interstitial fibrosis, mesothelial denudation and vascular changes. Morphological changes in the vasculature were observed at different levels. The specific changes in the vasculature in these patients were characterized by severe fibrosis and hyalinization of the media of venules. Immunofluorescence microscopy revealed extensive deposition of such extracellular matrices as type IV collagen and laminin in the vascular wall. Electron microscopy revealed a significant increase in collagenous fibers and degeneration of smooth muscle cells in the media. However, the endothelial cells at the levels of vasculature affected were relatively well preserved. These pathological alterations in the vasculature in CAPD patients with ultrafiltration failure suggest that certain toxic factors, such as a high osmolar dialysate or low pH of dialysate, had affected the peritoneal vasculature from the adventitial side rather than the endothelial side. These vascular changes in the peritoneum are thought to be irreversible, associated with deterioration of peritoneal function, and to cause ultrafiltration failure in the patients on long-term CAPD therapy.

Adult↗
PubMed1983

Regulation of lymphocyte transformation by components identified in ultrafiltrates prepared from leukocyte extracts.

Leukocyte components which can inhibit or enhance the uptake of 3H-thymidine by peripheral lymphocytes can be prepared by ultrafiltration of leukocyte extracts followed by gel filtration on Sephadex G-10. A potent inhibitor of lymphocyte transformation is present in an ultrafiltrate fraction having a nominal molecular weight of 5,000-10,000. Three other components having inhibitory, and one component having enhancing, activity on lymphocyte transformation were found in an ultrafiltrate fraction having a molecular weight less than 5,000. The inhibitory components in the latter were principally derived from polymorphs and inhibited both T and B lymphocyte proliferation. Enhancing components were mainly derived from mononuclear cells and augmented the proliferation of T cells only.

Cell Extracts↗
PubMed1998

Modified ultrafiltration in paediatric cardiac surgery.

The effect of modified ultrafiltration (MUF) after cardiopulmonary bypass for paediatric cardiac surgery was evaluated in 138 children with moderate to severe congenital heart disease. The median age was 0.4 years (0 days to 6.5 years), and the weight 5.3 kg (2.2-20 kg). The operation was discontinued in six cases, three because of technical problems and three because of unstable circulation. One-hundred-and-thirty-four patients were ultrafiltrated for a median of 12 min (2-27 min) with an ultrafiltrate of median 44 ml/kg (6-118 ml/kg). Haematocrit was significantly increased from 28% (20-39%) to 36% (26-51%) and systolic arterial pressure from 56 mmHg (30-85 mmHg) to 74.0 mmHg (32-118 mmHg). Furthermore arterial oxygenation was significantly increased from 30.8 kPa (4.8-70.4 kPa) to 34.1 kPa (4.9-80.6 kPa), and arterial carbon dioxide tension from 4.8 kPa (3.1-7.3 kPa) to 5.1 kPa (3.1-7.6 kPa). Heart rate was significantly reduced from 145 beats/min (92-201 beats/min) to 136 beats/min (88-200 beats/min). There were no significant differences in central venous pressure, left atrial pressure and base excess before and after MUF. MUF increases systolic blood pressure, haematocrit, arterial oxygen and carbon dioxide tension coming off bypass in paediatric cardiac surgery and reduces heart rate and postoperative fluid overload.

Cardiac Surgical Procedures↗
PubMed1988

Vancomycin serum protein binding determination by ultrafiltration.

Sixty-two serum concentrations were obtained from 12 infected patients enrolled in a vancomycin pharmacokinetic study. Both unbound and total serum vancomycin concentrations were measured using ultrafiltration and a commercial fluorescent polarization immunoassay. Ultrafiltrates were obtained by centrifugation at 1000 X g for ten minutes at room temperature and their assay indicated a range in protein binding from 7.9 to 71 percent. The mean protein binding (mean +/- SD) was 41.95 +/- 14.15 percent. No measurable adsorption of vancomycin onto the ultrafiltration membrane was noted. Orthogonal regression of unbound versus total vancomycin concentrations was described by the equation y = 0.597x-0.362 with a correlation coefficient of 0.948.

Adult↗
PubMed1992

Validation of the ultrafiltration technique for creatinine analysis by HPLC: a comparison with direct serum injection.

The determination of creatinine by HPLC was performed by direct injection of serum onto the column, and after ultrafiltration of the sample, and the results were compared. A modified weak cation exchange column was used for HPLC. This eliminates the protein displacement effect and the Gibbs-Donnan effect, thus permitting a rapid direct analysis. Three of the four ultrafiltration methods gave almost identical analytical results. Regression analyses of the results from direct serum injection versus ultrafiltration showed a bias of 5% on the slope y = 1.050 . xpure serum + 1.856, which was in our view solely due to the volume displacement effect of the proteins; correction of each data point by a protein-dependent correction factor resulted in an almost perfect regression line.

Blood Proteins↗
PubMed1984

Serum free T4, T3, rT3, 3,3'-diiodothyronine and 3',5'-diiodothyronine measured by ultrafiltration.

A simple and accurate method for estimation of the free fractions (FFT) of T4, T3, rT3, 3,3'-diiodothyronine (3,3'-T2) and 3',5'-diiodothyronine (3',5'-T2) in serum is presented. The method is based on ultrafiltration of serum pre-incubated with tracers of high specific activity, followed by purification of the ultrafiltrate on small Sephadex columns. The addition of tracer only dilutes serum negligible (about 5%) and the ultrafiltration procedure only removes about 7% of the volume of serum, thus probably not disturbing the equilibrium between the free and protein bound fraction of iodothyronine. Progressive reduction of tracer to less than 10% of the amount usually used did not reduce the FFT of any of the iodothyronines. In contrast, addition of T4 to serum led to an increase of all FFTs except that of 3',5'-T2. These data suggest that FFT of T4, T3, rT3 and 3,3'-T2 primarily is determined by the amount of T4 present in serum and that significant amounts of these iodothyronines are bound to TBG, whereas 3',5'-T2 possibly primarily is bound to albumin. The median FFT of T4, T3, rT3, 3,3'-T2 and 3',5'-T2 in serum from euthyroid subjects (n = 38) was: 0.030, 0.29, 0.14, 1.10 and 1.07%, respectively. The corresponding median free concentrations in pmol/l were: 30, 4.79, 0.59, 0.44 and 0.77, respectively. Pregnant women in 3rd trimester had normal levels of free T4, free T3 and free rT3, whereas the median free 3,3'-T2 was reduced in contrast to elevated median free 3',5'-T2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

Evaluation of a micro volume pulsed ultrafiltration cell for screening ligands in non-covalent complexes.

A pulsed ultrafiltration cell with a 35 microL binding chamber was evaluated for its ability to screen ligands that formed non-covalent complexes with protein targets. The cell was tested with ligands to the targets of carbonic anhydrase and serum albumin. Non-covalent ligand binding to both of these targets was observed and bound ligands were eluted from the cell in less than five min. The cell was also demonstrated to effectively screen a methanolic fermentation broth extract spiked with a known inhibitor to carbonic anhydrase. In addition to detecting specific binding events, the pulsed ultrafiltration method was investigated for its ability to distinguish non-specific binding events. Using carbonic anhydrase with the zinc-binding site removed, it was found that non-specific complexes observed when using electrospray ionization alone were not detected when using the pulsed ultrafiltration mass spectrometry method.

Animals↗
PubMed1985

Immunoreactive parathyroid hormone and calcitonin in plasma and ultrafiltrate before and after haemodialysis.

The effects of haemodialysis on circulating immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were determined in relation to alterations in total (Ca) and ionized (Ca2+) plasma calcium. The hormones were measured in plasma, in dialysate and in ultrafiltrate in eight patients with elevated iPTH concentrations. There was a small, but significant reduction in plasma iPTH during haemodialysis concomitant with an increase in Ca and Ca2+. Only small changes were found in plasma iCT during dialysis. Ultrafiltrate iPTH concentrations were reduced from 46% of plasma values at the beginning of dialysis to 27% of plasma values at the end of 4 h dialysis. Gel chromatography of plasma and ultrafiltrate showed corresponding molecular profiles of intact iPTH and hormone fragments suggesting that none of the PTH peptides were restricted by the dialysis membrane. Clearance of intact iPTH (dialysance) was as expected according to molecular weight. From the PTH clearance we calculated that only 5 to 10 micrograms of intact hormone were removed during dialysis. We therefore conclude that the reduction in plasma iPTH during dialysis is probably related to a relative suppression of PTH secretion rather than due to loss of hormone during dialysis.

Adult↗
PubMed1986

Ultrafiltration method for direct radioimmunoassay measurement of free thyroxine and free tri-iodothyronine in serum.

Ultrafiltration at physiological pH and temperature of undiluted serum followed by direct radioimmunological determination of T3 and T4 in the protein-free ultrafiltrate offers the best possible approach towards estimation of in vitro plasma levels of free T3 and free T4. The major technical difficulties in meeting this apparently simple proposition are: establishing adequately sensitive radioimmunoassays; avoidance of adhesion to ultrafilters and glassware; removal from the ultrafilters of compounds which would cross-react or interfere in the radioimmunoassays; and avoidance of co-filtration of thyroid hormone binding proteins in serum, which would obviously imply spurious data. This methodological study describes the magnitude and significance of each of these obstacles and how to circumvent them. Practically all other available methods, including equilibrium dialysis, imply dilution of serum samples with buffer often leading to alterations in ionic composition to which thyroid hormone binding to proteins is peculiarly sensitive. Dilution itself alters the fraction of free thyroid hormones in serum especially when pharmaca or compounds are present which compete for the binding sites. These pitfalls are avoided in ultrafiltration of undiluted serum. This is illustrated through measurements on serum containing therapeutic concentrations of Fenclofenac which was found to displace 120% more T4 in undiluted than in diluted (1:28) serum. Using the described technique FT3 was 8.8 +/- 1.7 pmol/l and FT4 30.8 +/- 8.2 (SD) pmol/l in serum from 29 normal subjects. Pregnant women in their third trimester had lower levels: FT3 7.1 +/- 2.1 and FT4 17.6 +/- 5.8 pmol/l (SD, n = 24).

Female↗
PubMed1977

Clinical evaluation of the clearance profiles of a portable, compact, dialysate-free system incorporating microencapsulated charcoal hemoperfusion for blood purification with ultrafiltration for fluid removal.

A total of 30 procedures have been carried out in two patients using a new portable, compact, dialysate-free system formed by combining 300 gms of albumin--cellulose nitrate microencapsulated activated charcoal (ACAC) in series with a small Amicon ultrafiltrator. Blood passing through the ACAC hemoperfusion system is purified of waste metabolites and toxins. Fluid removal is carried out with the hydrostatic pressure of the blood passing through the dialysate-free ultrafiltrator. Since ACAC hemoperfusion is much more efficient than hemodialysers for blood purification, the combined system with the ultrafiltrator results in a very efficient system for blood purification and fluid removal. Typical clearance data for the combined systems include: 75 ml/min for 2000--5000 MW; 112.7 ml/min for 300--1500 MW; 235 ml/min for creatinine; 240 ml/min for uric acid; 2500--2700 ml/2 hours for water removal; and 17--18 gm/2 hours for NaCl removal. Guanidines, mercaptans, and PTH are also cleared very efficiently.

Charcoal↗