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Biomedical subjects

M R Hardeman

Publications and source records attributed to M R Hardeman.

At least 19 recordsLinked to original sources
PubMed2006

Association between arterial stiffness and the deformability of red blood cells (RBCs).

The relationship between the flexibility of atherosclerotic vessels and RBC deformability has been investigated. A significant difference of RBC deformability was found among the arterial stiffness groups classified by oscillometric measurement of blood pressure. The deformability was determined by direct microscopic observation of RBCs subjected to shear stress of 0.3 to 40.0 Pa with a rotating rheoscope. The deformability of stiffen group - abnormal pulse wave pattern group or moderate cardiovascular risk group - was found to be much higher than that of normal groups in wide shear stress region (3.0, 10.0, 30.0, and 40.0 Pa). We postulate that the body adapts high shear stress in vivo by making RBCs more distensible, and therefore less likely to rupture under strain or microcirculatory alterations.

Adult↗
PubMed2004

Decreased deformability of donor red blood cells after intrauterine transfusion in the human fetus: possible reason for their reduced life span?

BACKGROUND: The life span of donor red blood cells (RBCs) is reduced in the fetus with Rh hemolytic disease. This may have resulted from donor or recipient factors. STUDY DESIGN AND METHODS: Studied in vitro was the effect of gamma irradiation on hemolysis, methemo-globin (metHb), and lipid peroxidation of donor RBCs and the ability of fetal and adult plasma to protect irradiated RBCs from induced lipid peroxidation. Also studied in vivo were the effects after the time that donor RBCs reside in the fetus by measuring its lipid peroxidation, cholesterol-to-phospholipid ratios, and deformability of RBCs. RESULTS: Irradiation barely increased hemolysis and metHb formation and did not increase lipid peroxidation. Plasma samples of D+ fetuses inhibited induced oxidative stress less than plasma samples of adults. Nevertheless, in vivo lipid peroxidation of the donor RBC membrane had not increased, whereas the molar cholesterol-to-phospholipid ratio increased from 1.08 +/- 0.11 to 1.38 +/- 0.12. It became identical to that of the fetal RBCs (1.44 +/- 0.12). Before transfusion, the deformability of the adult RBCs (elongation index, 0.578 +/- 0.013) was better than that of the fetal cells (elongation index, 0.494 +/- 0.027), but decreased to fetal levels after transfusion (elongation index, 0.518 +/- 0.039). CONCLUSION: Irradiation of the RBCs and a reduced fetal antioxidant capacity do not lead to in vivo lipid peroxidation. The shorter life span of donor cells in the fetus probably results from a decreased deformability of the RBCs after transfusion, most likely owing to an increased cholesterol-to-phospholipid ratio.

Blood Donors↗
PubMed2004

Validation and application of an automated rheoscope for measuring red blood cell deformability distributions in different species.

BACKGROUND: The deformability of red blood cells (RBCs) is of great importance for the conservation of oxygen delivery in the microcirculation. Even a small fraction of rigid cells is considered to harm the exchange of respiratory gases. Techniques that measure RBC deformability often provide an indication of the mean deformability. It may not be possible, however, to assess whether this mean value is reduced by the presence of a small rigid cell fraction or by a slight overall reduction in RBC deformability. A technique that provides a deformability distribution would be of great value to study diseases that are marked by subpopulations with a reduced deformability. METHODS: This paper describes a rheoscope system that uses advanced image analysis techniques to quickly quantify the deformability of many individual cells in shear flow, in order to find the RBC-deformability distribution. Since variations in the shear stress are responsible for variations in cell elongation, and hence introduce an additional spread in the cell deformability distribution, we first determined the spread caused by instrumental error. We then utilized the technique to investigate the relation between cell deformability and cell size of single blood samples of different species (human, pig, rat and rabbit). RESULTS: The spread caused by instrumental error was small compared to the actual RBC-deformability spread in blood samples. The deformability distribution of human and pig cells are alike although their cell sizes are different. Rat and rabbit cells show comparable deformability and size distributions. With this technique no correlation was found between cell deformability and cell size in animal RBCs. In the human sample a minor correlation was found between cell deformability and cell size. CONCLUSIONS: The automated rheoscope enables us to study the mechanical properties of RBCs more thoroughly by their deformability distribution. These deformability distributions are hardly influenced by the technique or by cell size.

Animals↗
PubMed2002

Measurement of the distribution of red blood cell deformability using an automated rheoscope.

BACKGROUND: Red blood cells (RBCs) have to deform markedly to pass through the smallest capillaries of the microcirculation. Techniques for measuring RBC deformability often result in an indication of the mean value. A deformability distribution would be more useful for studying diseases that are marked by subpopulations of less deformable cells because even small fractions of rigid cells can cause circulatory problems. METHODS: We present an automated rheoscope that uses advanced image analysis techniques to determine a RBC deformability distribution (RBC-DD) by analyzing a large number of individual cells in shear flow. The sensitivity was measured from density-separated fractions of one blood sample and from cells rendered less deformable by heat treatment. A preliminary experiment included the RBC-DDs of a patient with sickle cell anemia, one on dialysis and being treated with erythropoietin, and one with elliptocytosis. RESULTS: Measurement of the RBC-DD was highly reproducible. The sensitivity test showed markedly different deformability distributions of density-separated cells and yielded distinct RBC-DDs after each additional minute of heat treatment. CONCLUSION: The automated rheoscope enabled the determination of RBC-DDs from which less deformable subpopulations can be established. The shape of an RBC-DD may be valuable in assessing cell fractions with normal and anomalous deformability within pathologic blood samples.

Erythrocyte Deformability↗
PubMed2001

Erythrocyte deformability and erythrocyte aggregation in preeclampsia.

One of the features of preeclampsia is impaired blood rheology due to altered erythrocyte aggregation and erythrocyte deformability. We investigated these two parameters which affect the viscosity of blood, along with serum and intraerythrocytic magnesium concentrations, immunoglobulin titres and fibrinogen concentration in 12 preeclamptic women. Eighteen (18) other non-preeclamptic, gestation-matched women acted as controls. Erythrocyte deformability, expressed as elongation index (EI), and erythrocyte aggregation expressed as aggregation half-time (t 1/2) were measured with the Laser-assisted Optical Rotational Cell Analyser (LORCA). Serum and intraerythrocytic magnesium concentrations were analysed by atomic absorption spectrometry, immunoglobulin titres by radial immunodiffusion and fibrinogen concentration by a clot weight technique. There was no statistically significant difference in these parameters between preeclamptics and controls suggesting that erythrocyte deformability and aggregation as well as serum and intraerythrocytic concentrations, fibrinogen levels and immunoglobulin titres are not altered in preeclampsia. Further investigations are required in severe preeclampsia and in preeclamptic women taking magnesium sulphate supplement.

Adolescent↗
PubMed2001

The Laser-assisted Optical Rotational Cell Analyzer (LORCA) as red blood cell aggregometer.

The Laser-assisted Optical Rotational Cell Analyzer (LORCA) is unique in its capacity to measure at least two important hemorheological parameters, i.e., deformability of red blood cells (RBC) as well as their aggregation behaviour. In this communication the main principles and characteristics of the aggregometer mode of this instrument are described. Via syllectometry (i.e., laser backscatter versus time), the method allows the measure of both static and kinetic parameters of the aggregation process, e.g., total extent of aggregation, aggregation half time and a combination of these, defined as aggregation index. When the syllectogram deviates from that representing normal rouleaux formation, e.g., in the case of RBC clump formation, this is signalled by a fit error. Maximal flexibility is obtained by various options like an automated re-iteration procedure (which enables to measure the aggregation tendency and/or the aggregate stability) and aggregation at low shear rate. Experiments dealing with reproducibility, stability and sensitivity of the instrument are described. The latter include a few "classic" methods for inducing subtle changes in RBC aggregation behaviour both regarding cellular factors (heat treatment) and changes in medium constituents (fibrinogen, dextrans).It can be concluded that the aggregometer mode of the LORCA considerably increases the feasibility of this instrument for hemorheological investigations.

Cryoglobulinemia↗
PubMed1999

Red blood cell deformability as a predictor of anemia in severe falciparum malaria.

Decreased erythropoiesis and increased clearance of both parasitized and noninfected erythrocytes both contribute to the pathogenesis of anemia in falciparum malaria. Erythrocytes with reduced deformability are more likely to be cleared from the circulation by the spleen, a process that is augmented in acute malaria. Using a laser diffraction technique, we measured red blood cell (RBC) deformability over a range of shear stresses and related this to the severity of anemia in 36 adults with severe falciparum malaria. The RBC deformability at a high shear stress of 30 Pa, similar to that encountered in the splenic sinusoids, showed a significant positive correlation with the nadir in hemoglobin concentration during hospitalization (r = 0.49, P < 0.002). Exclusion of five patients with microcytic anemia strengthened this relationship (r = 0.64, P < 0.001). Reduction in RBC deformability resulted mainly from changes in unparasitized erythrocytes. Reduced deformability of uninfected erythrocytes at high shear stresses and subsequent splenic removal of these cells may be an important contributor to the anemia of severe malaria.

Adult↗
PubMed1999

Clinical potential of in vitro measured red cell deformability, a myth?

For many years the study of Red Blood Cell (RBC) deformability has been limited to specialised hematological research institutes and this has hampered a widespread clinical testing of this dynamic RBC property. Consequently, the clinical relevance of such in vitro measurements has remained questionable now for a considerable time. The recent availability of the LORCA, a routinely applicable and computer assisted instrument for this purpose, opens now the possibility to evaluate RBC deformability on a large scale in various pathological situations associated with impaired microcirculatory flow. In this communication we present our clinical experience obtained thusfar with this instrument. Besides the effect of physiological aging of normal RBC, the results of a clinical study on malaria tropica, case studies of hereditary elliptocytosis, Smith-Lemli-Opitz syndrome (a cholesterol biosynthesis defect), the treatment of sickle cell crisis with hydroxy-urea as well as the clinical intervention with Cyclosporin, are collected. In conclusion, it can be stated that the limited clinical experience with the LORCA as is reported here, yields sufficient evidence about the clinical potential of this technique.

Adult↗
PubMed1998

Red blood cell rigidification during cyclosporin therapy: a possible early warning signal for adverse reactions.

In a previous retrospective study with kidney-transplant patients, immunosuppressive treatment with Cyclosporin A (CsA) was found to be associated with impaired red blood cell (RBC) deformability. The aim of the present study was to evaluate and substantiate a possible causal relationship between the use of CsA and its effect on RBC deformability in a prospective study on non-transplant patients. Blood samples of 12 patients with psoriasis were taken before and after 2, 4, 8, 12 and 16 weeks of treatment with CsA (3-5 mg/day). Red cell deformability, expressed as Elongation Index (EI), was measured with the Laser-assisted Optical Rotational Cell Analyzer (LORCA), a new ektacytometric instrument. Mean values +/- SD for EI found after 16 weeks of treatment with cyclosporin (0.570 +/- 0.008) were significantly (p < 0.001) lower than the value before treatment (0.589 +/- 0.011). A dose-response relation could not be established within the small range of CsA doses used in this study. Irrespective of the dose, however, a significant correlation (r = -0.55; p = 0.0001) between duration of treatment and decrease in EI was demonstrated. In vitro incubation of blood with cyclosporin was not able to reproduce this effect, suggesting that a direct effect of the drug on RBCs is unlikely. Despite its use in relatively low doses, CsA causes a reduction in RBC deformability, an effect that increases during the course of treatment. It is suggested that this slow, but continuously increasing, RBC rigidification plays a role in the early pathogenesis of the adverse nephrotoxic complications frequently associated with this immunosuppressive regimen.

Cyclosporine↗
PubMed1997

Exercise performance, red blood cell deformability, and lipid peroxidation: effects of fish oil and vitamin E.

Previous studies have indicated that fish oil supplementation increases red blood cell (RBC) deformability, which may improve exercise performance. Exercise alone, or in combination with an increase in fatty acid unsaturation, however, may enhance lipid peroxidation. Effects of a bicycle time trial of approximately 1 h on RBC characteristics and lipid peroxidation were, therefore, studied in 24 trained cyclists. After 3 wk of fish oil supplementation (6 g/day), without or with vitamin E (300 IU/day), trial performance, RBC characteristics, and lipid peroxidation were measured again. RBC deformability appeared to decrease during endurance exercise. After correction for hemoconcentration, plasma total tocopherol concentrations decreased by 0.77 micromol/l (P = 0. 012) or 2.9% and carotenoid concentrations by 0.08 micromol/l (P = 0. 0008) or 4.5%. Endurance exercise did not affect the lag time and rate of in vitro oxidation of low-density lipoproteins (LDLs), but the maximum amount of conjugated dienes formed decreased by 2.1 +/- 1.0 micromol/mmol LDL cholesterol (P = 0.042) or 1.2%. Fish oil supplementation with and without vitamin E did not affect RBC characteristics or exercise performance. Both supplements decreased the rate of LDL oxidation, and fish oil supplementation with vitamin E delayed oxidation. The amount of dienes, however, was not affected. The supplements also did not change effects of exercise. We conclude that the changes observed during endurance exercise may indicate increased oxidative stress, but further research is necessary to confirm this. Fish oil supplementation does not improve endurance performance, but it also does not cause or augment changes in antioxidant levels or LDL oxidation during exercise.

Adult↗
PubMed1997

Prognostic significance of reduced red blood cell deformability in severe falciparum malaria.

Severe falciparum malaria is associated with microvascular obstruction resulting from sequestration of erythrocytes containing mature stages of the parasite. Since reduced red blood cell deformability (RBC-D) can contribute to impaired microcirculatory flow, RBC-D was measured in 23 patients with severe falciparum malaria (seven of whom subsequently died), 30 patients with uncomplicated malaria, and 17 healthy controls. The RBC-D, measured by ektacytometry, was significantly reduced in severe malaria and was particularly low in all fatal cases. At a low shear stress of 1.7 Pascal (Pa), a red blood cell elongation index less than 0.21 on admission to the hospital predicted fatal outcome with a sensitivity of 100% (confidence interval [CI] = 59-100%) and a specificity of 88% (CI = 61-98%). The reduction in the RBC-D appeared to result mainly from changes in unparasitized erythrocytes. Reduced deformability of unparasitized red blood cells in severe malaria may contribute to impaired microcirculatory flow and a fatal outcome in severe falciparum malaria.

Adult↗
PubMed1995

Hemorheological response to prolonged exercise--no effects of different kinds of feedings.

Thirty-one male triathletes performed three experimental trials at one week intervals, with either a semi-solid or liquid carbohydrate feeding, or a liquid placebo. Exercise consisted of three hours of alternately cycling, running, cycling, and running at 75% VO2 max. Venous blood samples were taken before and immediately after the exercise. Viscometry was performed with a Contraves LS-30 viscometer and erythrocyte deformability was measured with the LORCA, a laser diffractometric system. Exercise caused a significant increase in whole blood and plasma viscosity, hematocrit, and osmolality, and a very small, but significant decrease in erythrocyte deformability, irrespective of the feedings consumed. Changes were not related to exercise performance, as defined by the maximal test time, probably due to a large fluid intake. The intake of different amounts of carbohydrate had no influence on the hemorheological parameters, probably since water content was equal among feedings. Erythrocyte deformability changes were small in comparison with the other hemorheological changes and a correlation between erythrocyte deformability and other parameters was absent. This may be due to erythrocyte properties to counterbalance volume shifts to ensure an optimal oxygen delivery in the microcirculation.

Adult↗
PubMed1994

Activation of platelets by low-osmolar contrast media: differential effects of ionic and nonionic agents.

PURPOSE: To determine the effects of an ionic low-osmolar contrast medium (ioxaglate) and two nonionic low-osmolar contrast media (iohexol and iopamidol) on human platelet activation in vitro. MATERIALS AND METHODS: Flow cytometry analysis subsequent to reaction with fluorescence-labeled monoclonal antibodies was used to detect antigens that appear on the platelet surface on activation. RESULTS: Ioxaglate did not activate platelets, but evidence of platelet activation by iohexol and iopamidol was found in blood from two and three healthy volunteers, respectively, of the six volunteers studied. In addition, ioxaglate inhibited the thrombin-induced in vitro activation of platelets, whereas iohexol and iopamidol did not. CONCLUSION: These findings support a tendency toward a higher frequency of thromboembolic complications with nonionic low-osmolar contrast media, although clinical trials will be needed to confirm this possible trend.

Female↗
PubMed1993

No decreased erythrocyte deformability in type 1 (insulin-dependent) diabetes, either by filtration or by ektacytometry.

A lower erythrocyte deformability, which causes impairment of the microcirculation, is postulated to contribute to diabetic organ complications. Erythrocyte deformability was measured in four groups of type 1 (insulin-dependent) diabetic subjects and 30 controls by filtration and ektacytometry. Twenty-five patients without organ complications, 21 with microalbuminuria, 13 with overt nephropathy and 12 with leg ulceration were studied. No decreased erythrocyte deformability was found in any of the diabetic groups with either technique, and neither did the total group of 71 diabetic subjects have a lower erythrocyte deformability when compared with the controls. In order to imitate local conditions in the kidney, erythrocyte deformability was also measured in hyperosmolar solutions. Again no differences were found between the diabetic groups separately or as a whole and the controls. Furthermore no correlation was found between erythrocyte deformability and the plasma glucose or glycosylated haemoglobin level.

Adult↗
PubMed1993

The effects of propofol compared to high-dose fentanyl anesthesia on rheologic parameters in coronary artery surgery.

Propofol has previously been found to decrease hematocrit values. Because hematocrit is an important determinant of blood viscosity, lower hematocrits may cause a decrease in blood viscosity, improving blood flow and oxygen delivery. This phenomenon may be beneficial in certain intraoperative situations. To study the influence of two anesthetic techniques on a variety of rheologic parameters, 32 patients scheduled for coronary artery bypass grafting (CABG) were divided into two groups. Group I (n = 18) was induced with high-dose fentanyl anesthesia (100 micrograms/kg), and group II (n = 16) with a combination of propofol and fentanyl anesthesia (1 to 1.5 mg/kg and 35 to 50 micrograms/kg, respectively). Maintenance anesthesia continued with infusions of the same drugs. Blood and plasma viscosity, hematocrit, erythrocyte aggregation factor, and erythrocyte deformability were measured preoperatively, intraoperatively, and up to 48 hours postoperatively. Whole blood viscosity was corrected to a standard hematocrit of 0.45. The two groups were comparable with respect to age, bypass duration, blood loss, urine output, transfusions, and fluid management. Erythrocyte deformability did not decrease during or after cardiopulmonary bypass (CPB). In both groups, hematocrit and blood and plasma were decreased significantly during and after CPB (P < 0.01) and returned to baseline levels 48 hours after surgery. After induction and before CPB, blood viscosity was only decreased in group II. However, the corrected blood viscosity was significantly elevated at all shear rates in group II compared to group I at 24 and 48 hours postoperatively (P < 0.01). In group II at these sampling times, this parameter was also significantly elevated compared to preoperative values.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗