Biomedical subjects

J Waniewski

Publications and source records attributed to J Waniewski.

63 records · Page 4Linked to original sources

PubMedDate not supplied

Diffusive mass transport coefficients are not constant during a single exchange in continuous ambulatory peritoneal dialysis.

Mass transport coefficients usually are assumed to be constant during single 6 hr exchanges of dialysis fluid in continuous ambulatory peritoneal dialysis (CAPD). To check this assumption, the authors estimated diffusive mass transport coefficients, KBD, for five low molecular weight solutes in 34 dwell studies with glucose 3.86% (20 studies), glucose 2.27% (nine studies), and glucose 1.36% (nine studies) dialysis fluids for time periods 3-30, 30-60, 60-90, 90-120, 120-180, 180-240, and 240-360 min. Dialysate volume and the rate of fluid reabsorption were measured using radiolabeled serum albumin (RISA) as a marker. Convective transport was described using a sieving coefficient of 0.55 for all solutes. The KBD values were constant for sodium, but higher at the beginning (3-30 min) than at the end (180-360 min) of the exchanges by an average of approximately 50% for urea, creatinine, and glucose, and by approximately 120% for potassium with all three dialysis fluids. This initial increment did not depend upon the concentration of glucose in dialysis fluid, except for urea. The steady state value of KBD was reached at 120 min for all solutes. The time patterns of KBD values for urea, creatinine, glucose, and potassium were well described by an exponential decay function, with the decay constant approximately 0.02 min-1. The patterns were similar for electrically neutral solutes, but different for electrolytes. The initial increments in KBD values mean that clearances during short dwell time (30-60 min) may be higher by 5-15% than clearances calculated from the steady state KBD values.

Biological Transport, Active↗

PubMedDate not supplied

Sieving coefficients for small solutes during experimental peritoneal dialysis in rats.

A single 4-hour experimental peritoneal dialysis was performed in 6 normal Sprague-Dawley rats to investigate sieving coefficients (S) for small solutes during peritoneal dialysis. A modified 3.86% Dianeal solution with approximately the same concentrations of urea, sodium, and potassium as in the rat plasma (isochratic solution) was used to avoid diffusion of investigated solutes and to achieve sufficient ultrafiltration. As a control, a 4-hour peritoneal dialysis in 7 normal Sprague-Dawley rats was performed using the conventional 3.86% Dianeal solution. The infusion volume was 30 ml. A dilution of radioiodinated serum albumin was used to determine the intraperitoneal dialysate volume. S was calculated (1) from the mass and volume balances for the initial 30 min of the exchange with the isochratic solution (SI, isochratic method) and (2) by using a membrane model based on the thermodynamic theory of mass transport (SM). The diffusive mass transport coefficient KBD for the solutes investigated was estimated using the membrane model. The SI values for urea, sodium, and potassium were similar with the isochratic solution. For urea and sodium, the S values were within the physiological range 0-1, whereas the S values for glucose were close to 0 and for potassium were negative. SM for glucose, urea, and sodium using the conventional solution did not differ from the values obtained with the isochratic solution; however, SM for potassium was significantly lower than with the isochratic solution. SI and SM for potassium and sodium were correlated. The KBD values for glucose, urea, and sodium using the isochratic solution did not differ from the values obtained with the conventional solution, whereas the KBD values for potassium were significantly higher with the isochratic solution as compared with the conventional solution. We conclude that the net sieving coefficients SI and SM for urea and sodium were lower than unity in the rats dialyzed with the two solutions and did not differ from the previously reported S values measured in continuous ambulatory peritoneal dialysis patients with the isochratic solution. However, the transport of potassium was abnormal with the isochratic solution, suggesting mechanisms other than passive diffusive and convective potassium transport.

Animals↗

PubMedDate not supplied

Lyphatic absorption in CAPD patients with loss of ultrafiltration capacity.

During continuous ambulatory peritoneal dialysis (CAPD) treatment, loss of ultrafiltration capacity (UFC) is a common complication that can be associated with increased peritoneal fluid absorption rate. The aim of the present study was to investigate the relative importance of lymphatic absorption for total peritoneal fluid absorption in patients with permanent loss of UFC associated with a high peritoneal absorption rate (KE, ml/min; high-KE group, n = 4). Clinically stable CAPD patients (n = 23) as well as patients with loss of UFC associated with increased diffusive mass transport coefficients (KBD, ml/min; high-KBD group, n = 8) served as control groups. The patients were investigated with a 6-hour dwell study with 3.86% glucose solution. The total fluid absorption rate was estimated by the disappearance rate (KE) of 131I-radioiodinated human serum albumin (RISA) from the peritoneal cavity, and the lymphatic absorption rate was estimated by the rate of RISA appearance in plasma (KPP, ml/min). The values of KE and KPP in the high-KE group (4.65 +/- 0.93 and 0.42 +/- 0.31 ml/min, respectively) were markedly higher than in the clinically stable CAPD patients (1.77 +/- 0.60 and 0.15 +/- 0.06 ml/min, respectively; both p < 0.001 vs. the high-KE group). In the high-KBD group, KE was lower (2.19 +/- 0.38 ml/min, p < 0.001) compared to the high-KE group, whereas KPP was similar (0.26 +/- 0.09 ml/min, NS). The fraction of KE which could be accounted for by KPP was on average only 9 +/- 5% in the high-KE group and did not differ from the fractions in the clinically stable patients or in the high-KBD group (9 +/- 5 and 12 +/- 4%, respectively). In 5 patients in whom plasma RISA activity was measured for 24 h from the beginning of the 6-hour dwell study, a continuous increase of the RISA level in plasma was observed during this time period. We conclude that although KPP was increased in patients with UFC loss associated with high KE, it accounted for only a minor part of KE. Furthermore, the relatively slow but prolonged appearance of RISA in plasma indicates that the interstitial compartment may serve as a reservoir of macromolecules which are slowly absorbed by local lymphatics. The present study supports previous findings that direct lymphatic absorption is only of relatively minor importance for the fluid absorption in peritoneal dialysis.

Absorption↗

PubMedDate not supplied

The effects of ouabain and potassium on peritoneal fluid and solute transport characteristics.

BACKGROUND: We reported anomalous transport characteristics of potassium during experimental peritoneal dialysis in rats and suggested that mechanisms of peritoneal potassium transport could be other than simple passive transport. Intracellular transport of potassium in cultured human mesothelial cells was reported to be regulated by three different pathways, such as channels blocked by ouabain, channels blocked by furosemide, and other. OBJECTIVE: To investigate the effect of ouabain on peritoneal potassium and water transport characteristics. METHODS: A single 4-hour peritoneal dwell was performed in 28 Sprague-Dawley rats. To minimize the diffusive transport of potassium, 4.5 mmol/L of KCl was added into conventional dialysis solution with 3.86% glucose [acidic peritoneal dialysis solution (APD)]. To evaluate the effect of the pH of dialysis solution on the transport of potassium and water, 4 mmol/L of NaOH was added into the potassium-containing study solutions [neutral peritoneal dialysis solution (NPD)]. To evaluate the effect of a potassium channel blocker on peritoneal potassium transport ATPase sensitive Na+-K+-transport inhibitor, ouabain (10(-5) mmol/L) was added to dialysis solutions immediately before the dwell study in eight rats with APD (APD-O) and six rats with NPD (NPD-O). Ouabain was not added in eight and six rats with APD and NPD (APD-C and NPD-C, respectively). They were used as control. Infusion volume was 30 mL. The intraperitoneal volume (V(D)) was estimated by using a volume marker dilution method with corrections for the elimination of volume marker, radioiodinated human serum albumin (RISA), from the peritoneal cavity (K(E)). The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S) were estimated using the modified Babb-Randerson-Farrell model. RESULTS: V(D) was significantly higher (p < 0.05 from 90 min to 240 min) and K(E) (0.027+/-0.018 mL/min for APD-O, 0.026+/-0.017 mL/min for NPD-O, and 0.030+/-0.022 mL/min for NPD-C, vs 0.058+/-0.030 mL/min for APD-C, p < 0.05 for each) significantly lower during dialysis with APD-O, NPD-O, and NPD-C than with APD-C. The intraperitoneal glucose expressed as a percentage of the initial amount was significantly higher with APD-O, NPD-C, and NPD-O than with APD-C (p < 0.05 from 90 min to 240 min). K(BD) for sodium was higher during dialysis with ouabain than without ouabain, while K(BD) for urea, glucose, and potassium, and S for urea, glucose, sodium, and potassium did not differ between the four groups. CONCLUSIONS: The physiologic potassium concentration in neutral dialysis solutions and the use of ouabain decreased the intraperitoneal fluid absorption. The diffusive transport coefficient and sieving coefficient for potassium did not differ, while the diffusive transport coefficient for sodium increased during use of ouabain.

Absorption↗

PubMedDate not supplied

Discriminative impact of ultrafiltration on peritoneal protein transport.

OBJECTIVE: The dialysate concentration of large proteins increases, on average, linearly during the whole peritoneal dialysis dwell, and this linear pattern seems to be independent of the rate of ultrafiltration induced by dialysis fluid. However, we observed a high variability of protein kinetics in individual dwell studies. Therefore, we studied the details of the kinetic pattern of peritoneal transport. DESIGN AND METHODS: Kinetics of beta2-microglobulin, albumin, and total protein was examined in 23 clinically stable continuous ambulatory peritoneal dialysis patients using Dianeal 3.86% (15 dwell studies) or Dianeal 1.36% (9 dwell studies) dialysis fluid. Dialysate volume was measured using radioisotopically labeled albumin as a volume marker, with corrections for sample volume and absorption of fluid and marker from the peritoneal cavity. The generalized version of the Babb-Randerson-Farrell model was applied to estimate diffusive mass transport coefficient (K(BD)) and sieving coefficient (S) for proteins and small solutes (urea, creatinine, glucose, sodium, potassium). To quantify deviations from the linear pattern of protein dialysate concentration increase, the ratio (SR) of the slope of the linear regression line for the initial 3-30 minutes, divided by the slope for the next 60 - 360 minutes, was evaluated for albumin. RESULTS: In 5 dwell studies with Dianeal 3.86% fluid, SR was lower than 1 [low albumin transport (LAT) group, median SR = 0.49, range -4.39 - 0.71], while in the other 10 dwell studies with this solution, SR was higher than 1 [high albumin transport (HAT) group, median SR = 2.77, range 1.32 - 7.56]. Clearances of albumin up to 120 minutes were higher in the HAT group than in the LAT group. The transport of fluid, beta2-microglobulin, and small solutes did not differ between the LAT and the HAT groups. K(BD) values for proteins did not differ between the groups, but S values for albumin and total protein were lower for the LAT group than for the HAT group. A similar diversity was found in the dwell studies with Dianeal 1.36%: In three dwell studies, SR for albumin was lower than 1 (median SR = 0.95, range 0.70 - 0.97), and in six dwells it was higher than 1 (median SR = 1.55, range 1.23 - 1.98). In general, the SR values observed with Dianeal 1.36% were closer to 1 than those for Dianeal 3.86%. CONCLUSIONS: Ultrafiltration may affect the initial kinetic patterns of large protein (such as albumin) transport in two opposing ways: (1) by slowing the increase of protein concentration in dialysate (due to a low sieving coefficient, LAT group), and (2) by speeding up the increase of protein concentration in dialysate (due to a high sieving coefficient, HAT group). The average pattern in a non-selected group of studies is, however, close to a steady (linear) increase.

Albumins↗

PubMedDate not supplied

Peritoneal transport of glucose in rat.

OBJECTIVE: To evaluate the convective transport characteristics of glucose and the effect of high glucose and insulin during experimental peritoneal dialysis in rat. METHODS: Male Sprague-Dawley rats weighing 300-400 g were used in this study. Mannitol (5%) was used as osmotic agent. Glucose was added to dialysis solution to yield a concentration of 100 mg/dL (group 1) or 300 mg/dL (group 2). Mannitol solution (5%) containing the same concentration of electrolytes and lactate but without glucose was used as control (group 3). In group 2, blood sugar was maintained at approximately 300 mg/dL by continuous intravenous infusion of 25% glucose solution and 0.9% NaCl solution. A 2-hour dwell study was performed with 30 mL of test solutions. Intraperitoneal volume was calculated by volume marker (18.5 kBq of 131I-human radioiodinated serum albumin, RISA) dilution with corrections made for the elimination of RISA from the peritoneal cavity (K(E)) and sample volume. The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S(BRF)) were calculated by using the Babb-Randerson-Farrell model. S was also calculated directly by using isocratic methods (S(I)). The peritoneal fluid absorption rate (K(E)) was taken into account for the calculation of S(I). RESULTS: Intraperitoneal volume was significantly higher in group 2 compared with groups 1 and 3. Peritoneal fluid absorption rate, K(E), was similar in all three groups. S(BRF) and S(I) for glucose were significantly lower in group 2 compared with groups 1 and 3. S(BRF) for glucose in group 2 was below zero and S(I) near zero. K(BD) for glucose was significantly higher in group 2 than in groups 1 and 3. Plasma and dialysate concentrations of insulin increased during the initial hour and then decreased to the baseline value in groups 1 and 3, while in group 2 it continuously increased. CONCLUSION: Significantly lower sieving coefficients for glucose in the high glucose and high insulin group suggest that transport mechanisms other than simple passive transport are involved in peritoneal glucose transport, and that high glucose per se and/or high insulin may be important factors that determine glucose transport characteristics.

Animals↗

PubMedDate not supplied

A comparative analysis of mass transport models in peritoneal dialysis.

To better understand the differences in published estimates of peritoneal mass transport coefficients, a comparative analysis of seven mathematical models of peritoneal transport was performed. Uniform investigation involving measurements of solute concentrations and accurate determination of peritoneal dialysate volume was undertaken in twenty-eight 6 hour dwell studies using 3.86% glucose dialysate in non-diabetic patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The investigated models were all based on the theory of transport across a homogeneous membrane. Diffusive mass transport coefficients (KBD) calculated during a period of dialysate isovolemia served as reference values in the comparative analysis. The evaluation of models involved calculations of transport coefficients and comparison of calculated dialysate-to-plasma concentration ratios (D/P) with experimental D/P. The best fit of theoretically predicted D/P to experimental D/P was obtained with Pyle-Popovich's model, which accounts for both the diffusive (KBD) and convective (sieving coefficient [S]) characteristics of the peritoneal membrane. Garred's model, assuming S = 1, yielded acceptable results for small solutes (except sodium), whereas Henderson's model, in which convective transport is neglected, proved to be surprisingly accurate for KBD for both small solutes (except sodium) and protein. S values (mean +/- SD) calculated using Pyle-Popovich's model were found to be out of the physically interpretable range for glucose (S = -0.38 +/- 0.48) and potassium (S = 1.57 +/- 0.19), and therefore these S values should be treated as phenomenologic rather than physical quantities.

Biological Transport↗

PubMedDate not supplied

The effect of dialysate acidity on peritoneal solute transport in the rat.

OBJECTIVE: To investigate the possible effect of unphysiologically low pH in dialysis fluid on peritoneal transport. DESIGN: A 4-hour single-cycle experimental session of peritoneal dialysis was performed in six Sprague-Dawley rats using Dianeal 3.86% solution modified by adding 5 mmol/L of sodium hydroxide, neutral pH solution (NpHS) (pH 7.4). The intraperitoneal volume (VD) and peritoneal bulk fluid reabsorption (Qa) were calculated using a marker, 131I-labeled human serum albumin (RISA). The diffusive mass transport coefficient (KBD) as well as sieving coefficient (S) for glucose, urea, sodium, and potassium were calculated using the Babb-Randerson-Farrell model. The same study was performed in seven rats using Dianeal 3.86% solution, acidic pH solution (ApHS) (pH 5.7) to provide control values. RESULTS: The dialysate pH was stable with NpHS; 45 min after the infusion of ApHS it increased rapidly and reached the physiological value 7.4. Dialysate volume and KBD values for sodium and potassium with NpHS were significantly higher than with ApHS, while the KBD values for glucose and urea did not differ between the two solutions. S values for sodium and urea did not differ between the two solutions, while the values for glucose and potassium with NpHS were significantly higher and lower, respectively, than the values with ApHS (0.92 +/- 1.04 vs 0.04 +/- 0.63 and 0.56 +/- 060 vs 1.15 +/- 0.39, p < 0.05). The absorption of glucose from the dialysis solution expressed as a percentage of the initial amount of dialysate glucose was significantly lower with NpHS than with ApHS at 30 min (17.3 +/- 1.7% vs 29.7 +/- 2.0%, p < 0.05). CONCLUSION: We conclude that the peritoneal transport of fluid and small solutes might to some extent be influenced by the acidity of the dialysis solution. The vasodilatory effect of acidic dialysis solution might be the most important mechanism for these differences. However, a larger KBD value and a lower S value for potassium and higher S values for glucose during dialysis with the neutral dialysis solution may indicate that transport mechanisms other than simple passive transport are involved in peritoneal transport for glucose and electrolytes.

Absorption↗

PubMedDate not supplied

Daily exposure to dialysis fluid results in changes in peritoneal transport.

OBJECTIVE: To study the effects of daily infusion of peritoneal dialysis fluids on peritoneal transport characteristics. DESIGN: Twenty-four rats were randomly divided into three groups: group A, daily infusions of 20 mL 3.86% glucose dialysis function for 10 days (8 rats); group B, daily infusions of 1.36% glucose dialysis solution for 10 days (8 rats); group C, no daily infusion, the control group (8 rats). Twenty-four hours after the last infusion, a 4-hour dwell study using 25 mL 3.86% glucose dialysis solution with frequency dialysate and blood samples was performed in each rat. Radio-labeled human albumin (RISA) was added to the solution as an intraperitoneal volume marker. EXPERIMENTAL ANIMALS: Twenty-four male Sprague-Dawley rats (300 g) were used. MAIN OUTCOME: Fluid and small solute (glucose, urea, sodium, potassium, phosphate, and urate) transport characteristics were evaluated. RESULTS: After 10 days of exposure to dialysis fluid, the fluid absorption rate increased in the 3.86% dialysate group compared to the other groups (p < 0.05). The clearance of RISA to plasma (an estimation of lymphatic absorption), and the absorption of glucose were significantly increased in the two experimental groups compared to the control group but there was no difference between the two experimental groups. The dialysate/plasma ratio for urea, potassium and urate, and the sieving coefficient for phosphate and urate were significantly higher in the 3.86% dialysate group compared to the other two groups, but there was no significant difference between the 1.36% dialysate group and the control group. The clearances of sodium and potassium were significantly lower in the 3.86% dialysate group compared to the control group. CONCLUSION: Our results suggest that (1) daily infusion of dialysis fluid into the peritoneal cavity may increase peritoneal lymphatic absorption: (2) daily infusion of 3.86% glucose dialysate may increase peritoneal transport for small solutes.

Absorption↗