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Biomedical subjects

L Djordjevich

Publications and source records attributed to L Djordjevich.

10 recordsLinked to original sources
PubMed1989

Synthetic erythrocytes.

Synthetic erythrocytes (SEs) are made by incorporation of stroma-free hemoglobin (SFH) or lipid-heme into liposomes. They form spontaneously at the interface between the phospholipid material and aqueous solution. SEs are spheroid vesicles with diameters between 0.01 and 4 microns, capable of carrying and delivering oxygen in a manner similar to red blood cells (RBCs). Oxygen-dissociation curve is virtually identical to that of RBCs, with P50 = 28 torr, and adjustable by the addition of 2,3-DPG or inositol hexaphosphate. Liposome/heme containing lipid-heme, a synthetic O2-carrying substance, is capable of carrying as much O2 as RBCs. Liposome-encapsulated SFHs have smaller O2-carrying capacity, but can be made to equal that of RBCs. Viscosity of SE suspensions is somewhat higher than blood's viscosity, but has otherwise similar rheologic properties. A large number of in vivo experiments with laboratory animals prove the ability of SEs to maintain life after virtually complete removal of blood. Cardiorespiratory functions remain near-normal, blood chemistry exhibits reversible mild changes, and vital organs do not show significant abnormalities. Blood coagulation is not affected. Hemoglobin does not appear in urine and plasma, indicating mechanical stability in circulation and absence of diffusion through the membrane. SEs do not cause significant acute toxicity. The absence of blood groups makes them a universal blood donor. However, massive doses suppress the reticuloendothelial system (RES). The animals undergoing total exchange transfusions may die of septic shock, apparently caused by nonsterile infusate in combination with strong suppression of the RES. Longevity of SEs in circulation is proportional to the dose. At doses corresponding to more than 90% exchange transfusions, half-life is longer than 24 h. Since all materials used in preparation of SEs are naturally occurring in blood, SEs are easily metabolized and eliminated without allergic reactions. The absence of membrane proteins and chemical stability of SFH and phospholipids promises long shelf-life. SE suspensions are difficult to sterilize, particularly against the viruses that may be present in SFH. However, the use of sterile procedures during manufacturing, and extraction of hemoglobin from animals bred under strict infection control may eliminate that problem.

Animals↗
PubMed1988

Hemodynamic effects of exchange transfusions with liposome-encapsulated hemoglobin.

The ability of liposome-encapsulated hemoglobin (LEH) to sustain life in rats at hematocrits 45% below lethal levels was demonstrated by virtually total exchange transfusions. All control animals (transfused with 7% albumin in Erilyte) died at a mean hematocrit of 5.35%, with corresponding oxygen-carrying capacity of 2.65 ml/100 ml. All LEH animals survived with a final RBC hematocrit of 2.96% and an oxygen-carrying capacity of 7.05 ml/100 ml. LEH animals maintained normal blood pressures and essentially normal cardiac output, while control animals failed to do so. Systemic vascular resistance of control animals at 78% exchange was reduced to 33% of baseline, while of LEH animals at 92% exchange, to 80% of baseline. In-vitro measurements were made of LEH and RBC suspension viscosity as a function of shear rate, suspension concentration, and lipid membrane composition. The viscous behavior of the LEH suspensions was non-Newtonian and nearly the same as suspensions of natural RBC prepared similarly, though LEH suspensions had slightly higher viscosity.

Animals↗
PubMed1987

Cardiorespiratory effects of exchange transfusions with synthetic erythrocytes in rats.

Synthetic erythrocytes (SE) can maintain life with near-normal hemodynamics in rats with hematocrits (Hct) 45% below the lethal levels, as shown when we exchanged virtually all their blood. We compared cardiorespiratory variables between the SE and control animals, which were hemodiluted with 7% albumin, at the 78% exchange level. In addition, SE animals at 92% exchange were compared with the 78% exchange and baseline levels. All our control rats died at Hct above 5% with corresponding oxygen-carrying capacity of 2.65 ml/dl. All SE rats survived, having a final Hct of 2.96% with an oxygen-carrying capacity of 7.05 ml/dl. SE animals maintained normal BP and marginally increased cardiac output, while control animals did not. Vascular resistance of control animals at 78% exchange was reduced to 30%, while in SE animals at 92% exchange, vascular resistance was lowered to 80% of baseline values.

Animals↗
PubMed1987

Measurements of viscosity of synthetic erythrocyte suspensions.

Measurements were made of the viscosity of suspensions of synthetic erythrocytes composed of hemoglobin solutions encapsulated in liposomes, as a function of shear rate, temperature, suspension concentration, lipid membrane composition, and the viscosity of the suspending medium. It was found that the viscous behavior of the synthetic erythrocyte suspensions was non-Newtonian and nearly the same as that of suspensions of natural erythrocytes prepared similarly, with the major difference being that synthetic erythrocyte suspensions are somewhat more viscous. Suspensions of Fluosol FC-43 prepared similarly were found to be essentially Newtonian fluids, and substantially different and more viscous than either erythrocyte suspension. The higher viscosity of synthetic erythrocyte suspensions probably accounts for the ability of these suspensions to maintain normal systemic vascular resistance in transfusion experiments, in spite of the fact that synthetic erythrocytes are smaller than natural erythrocytes.

Blood Proteins↗
PubMed1981

Basic principles of electrohaemodynamics.

Electrohaemodynamics (EHD) is a method of measuring cardiac output continuously, also cardiac index, stroke volume, blood flow through limbs, vascular resistance, useful work output from the heart, elastic properties of arterial walls, and contractile and rate of energy generation properties of heart muscle. The method is based on simultaneous measurements of the time variations of arterial blood pressure and electrical conductance in a portion of human body. The measurements, in the form of analogue signals, are processed by means of a microprocessor or a mini-computer. The processing is based on equations which combine haemodynamics with measurements of electrical conductance and arterial pressure variation. Direct comparison of simultaneous cardiac output measurements using EHD and thermal dilution, as well as indirect comparisons with the Fick and dye dilution methods, show that EHD is at least as accurate as these methods. The reproducibility of EHD is within one percent when the subjects are in the steady state, which appears to be better than any other known technique.

Cardiac Output↗
PubMed1980

Effective sampling time for saccadic eye movement from experiments using a vergence input.

The results of analyzing the amplitude and latency of the saccadic component of the compound response are consistent with the notion that the saccadic system operates with a dead zone and an effective sampling time. The size of the dead zone was found to be 0.2 degrees. The latency between the onset of target motion and the onset of the saccade can be divided into three distinct time segments. The first is time for the target image to cross the dead zone boundary. This time segment is inversely proportional to target velocity. The second is the time between the dead zone crossing and the sample. This time segment has a constant duration of 191 msec. The remaining segment is the time between the sample and the saccade. If the target velocity is finite at the time of the sample, the duration of this segment decreases as target velocity increases. If the target velocity is zero at the time of the sample, this segment has a constant duration of about 70 msec.

Eye Movements↗
PubMed1980

Synthetic erythrocytes from lipid encapsulated hemoglobin.

Synthetic erythrocytes have been formed by encapsulating concentrated hemoglobin solutions in microcapsules consisting of phospholipid-cholesterol mixtures. The microcapsules (hemosomes) are of the order of one micron in diameter or smaller, are osmometers, are somewhat sturdier than erythrocytes (RBC), and are stable upon freezing. They have essentially the same oxygen and carbon dioxide carrying capacity as RBC, and can be tailored to have the same electrokinetic properties. They appear to evoke no immune response in the rat. In experiments involving complete replacement of natural blood hemosomes appear to sustain life. Rats can live and breathe normally without signs of hypoxia or acidosis for extended periods of time after the hematocrit of natural RBC drops well below the critical level. Synthetic erythrocytes do not appear to cause disseminated coagulation, microembolism, or any observable changes in internal organs.

Animals↗
PubMedDate not supplied

Experimental study of the relationship between the base impedance and its time derivative in impedance plethysmography.

Transthoracic electrical impedance Z consists of a constant baseline component Z0 and the time variable component delta Z such that Z = Z0 + delta Z. The first time derivative of Z has a negative peak, the magnitude of which is (dZ/dt)min. Measurements of 170 volunteers show that (dZ/dt)min is a function of the constant baseline component Z0. This implies that at least a part of the difference of the magnitudes of (dZ/dt)min on Z0 must be taken into account in order to avoid erroneous conclusions or inaccurate calculations.

Adolescent↗