Ivan Ivanov

Erythrocyte aggregation at non-steady flow conditions: A comparison of characteristics measured with electrorheology and image analysis

In the present study electro-rheology (Contraves LS30 viscometer-based system) and optical shearing microscopy (Lincam CSS450 system and image analysis) techniques have been utilized in order to provide quantitative data on the behaviour of the microstructural properties of whole normal human blood at non-steady flow conditions. The objective of this work is to contribute towards a better understanding of red blood cell aggregation at flow conditions similar to that occurring in a circulatory system and to aid the interpretation and validation of electro-rheological data through a quantitative comparison with data acquired with optical shearing microscopy. Electro-rheology is a promising technique that has been used to provide bulk fluid properties, showing potential for basic research and diagnostic purposes, whereas optical shearing techniques offer a direct assessment of blood microstructure at a cellular level. However, little information exists in the literature regarding the relationships between electro-rheological measurements and blood microstructural characteristics. The results showed that the different non-steady flow conditions affect differently the dynamics of aggregation varying from a parabolic-decrease to an inverted S-shape curve with time. For a wide range of the non-steady flows results obtained with the two different techniques agree to a difference between 1.2 and 12%.

Platelet morphological, functional and rheological properties attributable to addictions.

Hemorheological abnormalities such as elevated whole blood viscosity, plasma viscosity, erythrocyte deformability and platelet aggregation, hematocrit and fibrinogen levels, are frequently examined as diagnostic tool and prognostic relevance in socially important hemorheological disorders. Distinct biological - morphological and functional platelet alterations, have been described in different addictions (heroin-, cocaine-, nicotine-, alcohol-, etc.). Chronic addictions could cause biochemical and conformational changes in platelets and their membranes, thus modulating platelet receptor expression, morphology (anisocytosis, giant platelets) and activation (alpha-granule release), platelet aggregation and hemorheological properties. Some of these alterations in chronic addicts - documented at cellular- and molecular level, could be easily used as a precise diagnostic tool with regard to thromboembolic complications and microcirulation injuries attributable to addictions. The present review focuses on some changes in platelet morphological, functional and rheological properties induced by chronic opiate/opioid abuse. Hypothesis is accumulated that free fatty acids (FFAs) and especially oleic acid (OA) could cause positive molecular and conformational changes in platelets of addicts with hemorheological disorders.

Experimental evaluation of mechanical and electrical properties of RBC suspensions under flow. Role of RBC aggregating agent

Mechanical and electrical properties of red blood cells (RBC) suspensions in dextran 70 (Dx70), dextran 150 (Dx150), dextran 500 (Dx500) and polyethileneglycol (PEG) 35,000 with different concentrations were evaluated through apparent viscosity and conductivity measurements under steady and unsteady flow conditions. RBCs suspensions of the washed RBS in PBS (control) and Dx70, Dx150, Dx500 and PEG in PBS with different concentrations, adjusted to the same hematocrit of 40% were used for the experiments. Conductivity time and shear rate dependences in parallel with the rheological properties of the samples were studied under transient flow regimes at different local structure of the uniform Couette flow. Their relationships on dextrans and PEG concentrations were evaluated too. Low shear viscosity increased and conductivity decreased of RBC suspensions, compared to non-aggregating suspensions, depending on dextrans and PEG concentrations. A time course of blood conductivity recorded under different flow conditions provides experimental description of RBC aggregation-disaggregation processes and other cell-cell interactions. The results show that the blood conductivity is strongly dependent on the considered blood factors and is influenced by flow, shear rates and concentration of dextran and PEG solutions.

Hemorheological changes and hematometric erythrocyte characteristics in rats after sodium nitrite intoxication

Sodium nitrite (NaNO2) is a precursor to a variety of organic compounds (pharmaceuticals, dyes and pesticides), but it is best known as a food additive. The aim of the study is to investigate the influence of acute (i.p.) treatment of Wistar rats with NaNO2 (at the dose of 50 mg/kg b.w.) on the blood rheological properties and erythrocyte hematometric indices (Hb, HCT, RBC, MCV, RDW, MCH, MCHC). The significant differences were not found in the whole blood viscosity (WBV) values of the control and NaNO2-treated groups. The changes in the erythrocyte hematometric indices were statistically significant for RDW, MCHC and MCH at the 1st hour, five- and ten days after NaNO2 administration. Interestingly, at the day 5th of the NaNO2 treatment we obtained statistically significant lower values for the RBC count, Hb, HCT, RDW, as well as elevated indices MCV (no statistically significant), MCH, MCHC. The results obtained indicate that hemorheological and hematometric parameters examined should be monitored in cases of acute exposure to nitrites — for the purposes of clinical toxicology. The quantitative values of hematometric indices reported in our experimental model could be suitable for predicting NaNO2 intoxication and methemoglobinemia in animals and humans.

Rheological and Electrical Properties of RBC Suspensions in Dextran 70. Changes in RBC Morphology

Apparent viscosity and conductivity of red blood cells (RBC) suspensions in dextran 70 (Dx 70) with various concentrations were evaluated in vitro under steady and unsteady flow conditions. Conductivity time and shear rate dependences in parallel with the rheological properties of the samples were studied under transient flow regimes at different local structure of the uniform Couette flow. Their relationships on Dx 70 concentrations were evaluated too. A concurrent measurement system, using a Contraves Low Shear 30 rotational rheometer was used in the study [1-3]. Low shear viscosity increased and conductivity decreased of RBC suspensions in dextran 70, depending on dextran concentration, compared to non-aggregating control RBC suspension in PBS. A time course of conductivity of RBC suspensions in Dx 70 was recorded under different flow conditions and provides experimental description of RBC aggregation-disaggregation processes and other cell-cell interactions. Dx 70 induces morphological alterations in RBC shape and arrangement in the suspensions. Echinocytes are observed at low Dx 70 concentrations while spherocytes are found mainly in smears at higher Dx 70 concentrations. Their morphological characteristics affect blood electrical and mechanical properties.

Simple procedure for quantification of the gravitational stress field in fractured hard rock massifs

Abstract In this paper, a quantitative procedure for evaluating the gravitational stress field in a hard rock massif is presented, using only a geological hammer and compass. Using the orientation of the fracture planes and their statistical distribution, a method for calculating of the tendency of the fractures to reactivate under gravitational load is proposed, based on Coulomb failure criterion. The method is applicable for assessing the most stable layout of the underground excavations and for evaluating the geometry of the stress field at a point during the initial stage of rock failure.

Study of Rheological and Electrical Behaviour of RBC Suspensions in Dextran and PEG under Non-steady Flow. Role of RBC Deformability and Morphology

A concurrent measuring system, using a Contraves Low Shear 30 rotational rheometer, previously described [1-2], was used in the study. It includes a resin replica of the Couette type measuring system MS 1/1 of the rheometer with a pair of platinum electrodes embedded into the wall; a device, constructed by the conductometric method and software (Data acquisition system) [1]. A method, based on dielectric properties of dispersed systems in Couette viscometric blood flow was applied to investigate the kinetics of RBC aggregation and the formation and break-up of the aggregates. Apparent viscosity and conductivity of normal human red blood cell (RBC) suspensions in dextran 70 (Dx 70) and polyethilenglycol (PEG) with various concentrations were evaluated in vitro under steady and unsteady flow conditions. Conductivity time and shear rate dependences in parallel with the rheological properties of the samples were studied under transient flow regimes at different local structure of the uniform Couette flow. Their dependence on dextrans concentrations were evaluated as well. Low shear viscosity and conductivity of RBC suspensions in dextrans were determined and compared to non-aggregating control RBC suspension in PBS. RBCs were treated with glutaraldehyde (GA) with different concentrations (from 0,01% to 1%). A time course of conductivity of normal RBCs and treated with GA suspended in dextran 70 was recorded under trapezoid change of shear rates. It provides experimental description of RBC aggregation-disaggregation processes and other cell-cell interactions. Dextrans induce morphological alterations in RBC shape and arrangement in the suspensions. Echinocytes are observed at low Dx 70 concentrations while spherocytes are found mainly in smears at higher Dx 70 concentrations. Their morphological characteristics affect blood electrical and mechanical properties.