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Biomedical subjects

S Stiller

Publications and source records attributed to S Stiller.

At least 37 records · Page 2Linked to original sources
PubMed1985

Ionometry versus flame photometry in dialysis therapy.

In order to decide whether the ionometer can be accepted as an alternative to the flame photometer in the measurement of sodium and potassium, extensive measurements with ionometry in parallel with flame photometry were performed in serum and dialysis fluid during dialysis. The influence of parameters which influence both ionometry and flame photometry in a different way (protein concentration, pH, acetate, and bicarbonate concentration) was investigated. The correlation between the two methods for potassium in serum and dialysis fluid was excellent (r greater than 0.95), but unsatisfactory for sodium in serum (r = 0.77) and in dialysis fluid (r less than 0.85). This low correlation is attributed in a greater extent to the random errors caused by flame photometry than by ionometry. Ionometry can be accepted as an alternative to flame photometry in dialysis therapy.

Evaluation Studies as Topic↗
PubMed1983

Electrodialysis and reverse osmosis as a regeneration system for hemofiltrate.

The separation of urea from the hemofiltrate (or from spent dialysis fluid) must be considered the critical step in all regeneration systems. A promising solution for this problem is the combination of electrodialysis and reverse osmosis. A mathematical stimulation of the process and in vitro experiments have been carried out in order to determine operating conditions and design specifications. The experiments confirmed the predicted performance of the regeneration system with respect to the separation of urea and the recovery of electrolytes. As expected, some ionic toxins, such as uric acid, and some middle molecules are recovered also. These substances, however, can be easily removed by a small adsorption cartridge.

Adsorption↗
PubMed1978

Theoretical aspects of various ultrafiltration methods in artificial kidney therapy.

A mathematical model including urea, creatinine and other osmotically important solutes (such as sodium, potassium and chloride) is applied to calculate volume shifts, caused by ultrafiltration, between the fluid compartments of the body. The volume shifts between the intracellular (ICV) and the extracellular (ECV) compartments are mainly caused by alteration of extracellular sodium concentration. Various methods of achieving ultrafiltration, including conventional dialysis, initial ultrafiltration using Cuprophan (without dialysis) or hemofiltration, produce different responses. In choosing a method, one must consider that both a rapid decrease of ECV and a fast shift of water from ICV to ECV should be avoided. In pure hemofiltration, ultrafiltrate is isotonic and water is removed from ECV only. Hemofiltration with dilution produces a very slow shift of water between ICV and ECV dependent on sodium concentration of plasma and diluting fluid. In initial ultrafiltration through Cuprophan, water is shifted from ICV to ECV. With ultrafiltration throughout the entire dialysis, there are pronounced shifts between ICV and ECV dependent on the difference of the sodium concentration between plasma and dialysate.

Biological Transport, Active↗
PubMed1976

Biological balance of sodium and potassium: a control system with oscillating correcting variable.

The rhythm of renal sodium and potassium excretion was measured in 4-h-intervals in 12 subjects. Each person exhibited clear circadian variations of each variable with a maximum between 8 a.m. and 4 p.m. In each subject and for both circadian rhythms the oscillation mean was correlated to the range of oscillation (amplitude). Increase in sodium or potassium excretion during 1 day resulted in an increase of oscillation range. The oscillation means of sodium and potassium periodicity did not correlate. The properties of biological control systems with oscillating correcting variables are comparable to those of technical control systems. The significance of circadian rhythm for the control of electrolyte balance is indicated.

Circadian Rhythm↗
PubMedDate not supplied

A critical review of sodium profiling for hemodialysis.

In sodium profiling, the sodium concentration in the dialysis fluid, instead of being constant, follows a time-dependent profile over the course of a hemodialysis session. The main aim of this manipulation is to avoid osmotic disequilibrium by keeping plasma osmolality in the physiological range. Further advantages of sodium profiling are a reduction in the incidence of muscle cramps, improved sodium removal, and improved vascular stability. Many different profiles have been used by various investigators. However, if sodium profiling is not appropriately conducted, sodium accumulation with resulting augmented thirst, increase of interdialytic weight gain, and hypertension may result. Sodium accumulation may, in fact, explain the reduced intradialytic morbidity reported in some short-term sodium profiling studies. Randomized, double-blind studies meeting strict statistical criteria and providing a careful control to maintain equivalent sodium balances between the compared treatments are difficult to perform and have not yet been published. However, because sodium profiling has potential benefits, provided that sodium balance is carefully controlled, it should nevertheless be regarded as a tool that experienced nephrologists can use for the treatment of patients who experience intolerable side effects during standard dialysis.

Blood Volume↗
PubMedDate not supplied

Changes in blood volume during dialysis are dependent upon the rate and amount of ultrafiltrate.

Actual circulating blood volume during dialysis therapy can be monitored by continuous hemoglobinometry. Using this method in 15 stable, clinically nonoverhydrated dialysis patients, blood volume was recorded applying different modes of ultrafiltration: constant ultrafiltration (less than 500 ml/hr); high initial (greater than 1,500-2,000 ml/hr), subsequently decreasing ultrafiltration; and intermittently high (greater than 1,500 ml/hr) ultrafiltration. Mean amount of ultrafiltrate in all patients was 3,400 ml. Mean decrease in blood volume by 20% was generally tolerated without a decrease in blood pressure. Irrespective of the different modes of ultrafiltration, a decrease in blood volume was dependent only on the amount of ultrafiltered fluid. A constant, low ultrafiltration rate was not superior to a high ultrafiltration rate. In stable dialysis patients, decrease in blood volume is dependent only on the amount of ultrafiltrate. Up to a 20% decrease in blood volume, fluid can be removed from the patient even at a rate of 2,000 ml/hr.

Blood Flow Velocity↗
PubMedDate not supplied

Characteristic profiles of circulating blood volume during dialysis therapy.

From continuous measurements of the hemoglobin concentration in the arterial blood line during 50 hemodialysis sessions in 20 stable dialysis patients, the influence of the amount of ultrafiltered fluid, the ultrafiltration rate, and overhydration of the patient upon the circulating blood volume was derived. If ultrafiltration is stopped, blood volume increases until equilibrium is obtained. The amount of refilling is proportional to the ultrafiltration rate [2.5%/(L/hr)]. The decrease of blood volume after re-equilibration depends upon the ultrafiltered amount and the degree of overhydration. The mean decrease of blood volume per liter of ultrafiltrate was found to be 5.5% for an average overhydration of 3 L.

Blood Flow Velocity↗
PubMedDate not supplied

Less symptomatic hypotension using blood volume controlled ultrafiltration.

Symptomatic hypotension due to ultrafiltration (UF) is one of the most frequent unwanted side effects of dialysis therapy. Using hemoglobinometry for continuous monitoring of blood volume (BV), ultrafiltration rate (UFR) can be adapted to actual changes in BV. A control system is shown in which UFR is set according to a predefined profile of BV. The conditions of control are: relative BV shall decrease steadily; BV shall decrease rapidly during the first 60 min of dialysis, thereafter decrease in BV should be less; UFR shall be as high as possible; and dry weight should be obtained within a given time. Application of this controlled UF method in 10 dialysis patients shows significantly fewer hypotensive periods and muscle cramps compared to conventionally constant UFR. It is concluded that BV controlled UF is an important step toward optimizing dialysis therapy.

Blood Flow Velocity↗
PubMedDate not supplied

Vasoactive hormones during hemodialysis with intermittent ultrafiltration.

The correlations between actual blood volume (BV), blood pressure (BP), heart rate, and plasma levels of renin activity (PRA), serum aldosterone (ALD), antidiuretic hormone (ADH), epinephrine (E), norepinephrine (NE), atrial natriuretic factor (ANF), cGMP, and cAMP were investigated in 10 stable patients during HD. HD consisted of four periods of about 60 min each. One half with an UF rate greater than 1,000 ml/h, followed by a time interval of 30 min without UF resulting in a "saw tooth" profile of BV. Decrease in BV was measured by continuous hemoglobinometry. Average total decrease in BV was 25%, while BP and HR did not change significantly. E, NE, ANF and ADH levels were directly related to actual changes in BV, suggesting that BP regulation in this special mode of HD is mainly supported by endogenous catecholamine and ADH secretion. The second messenger cGMP did not follow actual BV changes, but showed a significant decrease correlated with diminished BV. A significant change in PRA and ALD was missing. It is concluded that vascular stability in these patients is maintained by the response of catecholamins and ADH to decrease in blood volume, and not by the renin-aldosterone system.

Aldosterone↗
PubMedDate not supplied

A new method of continuous haemoglobinometric measurement of blood volume during haemodialysis.

Since the total amount of haemoglobin in blood is constant during haemodialysis, haemoglobin concentration reflects changes of blood volume caused by ultrafiltration and solute transport. Haemoglobin concentration therefore could serve as a control parameter for ultrafiltration. Blood is taken continuously from the arterial blood line at the very small rate of 0.1 ml/h and diluted at a constant ratio of 1/200 by a sterile solution 0.05 per cent NH3. By the diluting medium the erythrocytes are haemolysed and the haemoglobin is transformed into oxyhaemoglobin. The haemoglobin concentration is determined measuring the absorbance at 415 nm. The error in the measurement of the haemoglobin concentration is less than 3 per cent. The method was tested in vivo during 10 haemodialysis treatments of five patients. Haemoglobin concentration appeared to reflect the well-known effects of ultrafiltration, of food intake and changes of position (sitting, lying). If the body weight approached the suspected dry weight, haemoglobin concentration increased more rapidly. During high ultrafiltration rates (1.0 litre/h) and sudden changes of ultrafiltration rate haemoglobin concentration seemed to be unevenly distributed in the vascular space. If haemoglobin concentration indeed reflects changes in blood volume the method can be used to study the relationship between blood volume and blood pressure in haemodialysis therapy and to control ultrafiltration.

Blood Volume↗
PubMedDate not supplied

The Donnan effect in artificial kidney therapy.

The calculation of the effective sodium gradient in dialysis has to consider a membrane potential difference which is generally derived from the Donnan effect. Strictly this is allowed only under equilibrium conditions. This paper considered the effect of the deviation from equilibrium in haemodialysis and haemofiltration. The mathematical analysis is based on the integration of the local transport rate over the membrane area. The local transport rate is calculated from the Nernst-Planck equation using the constant field assumption. Deviation from equilibrium results in a diffusion potential across the membrane. Experimental evidence was presented for part of the theoretical results. The diffusion potential, both in haemodialysis and in haemofiltration, is too small to have any clinical significance. From the theory it follows that better tolerance of haemofiltration in comparison with haemodialysis cannot be explained by a difference in sodium transport. Calculation of the sodium transport in dialysis therapy based on the equilibrium Donnan effect is sufficiently accurate for kinetic considerations in the dialysis routine.

Acetates↗