The flow of blood cell suspensions through 3 microns and 5 microns Nuclepore membranes: a comparison of kinetic analysis with scanning electron microscopic examinations

Maternal and umbilical cord erythrocyte omega-3 and omega-6 fatty acids and haemorheology in singleton and twin pregnancies

BACKGROUND

Being devoid of both nuclei and mitochondria, mature human erythrocytes provide an opportunity to study membrane structure and function outwith the restrictions of genetic control. With its unique rapid increase in vascularisation, pregnancy is considered the most opportune period in which to investigate blood rheology.

METHODS

Maternal and fetal (cord) bloods were retained at delivery from 32 (25 singleton and seven twin) normal pregnancies at two maternity hospitals in the Glasgow area over a nine month period. Erythrocyte fatty acid compositions were assessed by mass spectroscopy, and corresponding membrane deformabilities measured by ultrafiltration through a membrane of 5 micro m diameter pore size, to mimic placental microcirculation.

RESULTS

Significant direct correlations (Spearman rank) were found between erythrocyte membrane omega-3 docosahexaenoic acid concentrations and corresponding deformabilities in maternal and cord blood from both singleton and twin pregnancies, whereas greater omega-6 arachidonic acid content was associated with increased maternal membrane rigidity. Membrane concentrations of omega-3 fatty acids only correlated strongly both within and between maternal and cord bloods. Mean cord erythrocyte docosahexaenoic acid concentration was higher than maternal in singletons but lower in twins. When maternal erythrocyte concentrations exceeded about 7% (of total fatty acids), resistance to erythrocyte flow was virtually eliminated.

CONCLUSIONS

It may be that a greater maternal intake of docosahexaenoic acid should be encouraged in some pregnancies for optimal tissue perfusion. Fetal demand for docosahexaenoic acid may not be entirely satisfied in multiple pregnancies.

Rheological properties and function of blood cells in stored bank blood and salvaged blood

The technique involving filtration of diluted blood enables the separate analysis of the flow properties of different cell subpopulations. This study was designed to assess the changes occurring in the flow properties and function of blood cells in stored bank blood and salvaged blood compared to patient blood in a given clinical situation. We measured hydrogen peroxide production by neutrophils and the filterability, through 5 microm Nucleopore filters, of isolated red blood cells and of diluted blood. Samples were obtained from patients undergoing aortic surgery and blood intended for transfusion: either salvaged during surgery or stored bank blood. Both salvaged and bank blood were much less filterable than patient blood, with reduced deformability of both red and white blood cells. However, salvaged blood contained highly activated neutrophils with a prolonged transit time of the 'fast-flowing' cells in the analysis compared to bank blood. Bank blood contained significantly more particles which acted as pore-blockers. Cells in bank and salvaged blood therefore have markedly abnormal flow and biochemical properties compared to patient blood.

Rheological studies during treatment of renal anaemia with recombinant human erythropoietin

Whole blood, plasma, and serum viscosity together with red cell deformability were measured before and during treatment of renal anaemia with recombinant human erythropoietin (EPO). Whole blood viscosity (WBV) progressively increased during the first 4 months of treatment in association with the rise in haemoglobin concentration. When the WBV was corrected to a standard haemoglobin concentration no change in blood viscosity was observed, neither was there any alteration in a derived index of red cell deformability, or in the plasma and serum viscosities. In addition, a direct measurement of red cell deformability using a filtration technique before EPO therapy was similar to that obtained in 30 healthy volunteers. There was no significant change in this parameter over the first 9 months of treatment. The rheological changes which occur with correction of anaemia with EPO can be explained solely by the increase in circulating haemoglobin mass rather than to any change in the properties of the plasma or red cells themselves.

Effects of a fish oil supplement on serum lipids, blood pressure, bleeding time, haemostatic and rheological variables. A double blind randomised controlled trial in healthy volunteers

Sixty male volunteers were randomised to take 10-16 ml of a fish oil supplement (MaxEPA) or 10-16 ml of olive oil for a period of 3-6 weeks. A fall in serum triglyceride of 54% (P less than 0.01) and a fall in diastolic blood pressure of 7% (P less than 0.05) was attributable to taking fish oil supplements. The bleeding time was prolonged by 12%, but this did not reach conventional levels of statistical significance. A global test of heparin-neutralising activity, the heparin thrombin clotting time, increased by 14% (P = 0.05) but there was no demonstrable effect on thrombin time, fibrinogen or (intraplatelet) platelet factor 4. A fall in red cell pore transit time of 23% was attributable to fish oil, but was not statistically significant. There was no convincing evidence of an effect of fish oil supplementation on total serum cholesterol, HDL-cholesterol, blood counts or platelet aggregation. A beneficial effect of fish oil on the cardiovascular risk profile was confirmed in this study. However, with this regime changes in total cholesterol, HDL-cholesterol and platelet aggregation are of unlikely clinical importance.

Erythrocyte rheology

Erythrocyte deformability was formerly measured by its contribution to whole blood viscosity. It is now more commonly measured by filtration of erythrocytes through, or aspiration into, pores of 3-5 microns diameter and by the measurement of shear induced erythrocyte elongation using laser diffractometry. Recent improvements in the technology for erythrocyte filtration have included the removal of acute phase reactants from test erythrocyte suspensions, ultrasonic cleaning and reuse of filter membranes, awareness of the importance of mean cell volume as a determinant of flow through 3 microns diameter pores, and the ability to detect subpopulations of less deformable erythrocytes. Measurements of erythrocyte elongation by laser diffractometry, using the Ektacytometer, are also influenced by cell size and need to be corrected for mean cell volume. These advances have greatly improved the sensitivity and specificity of rheological methods for measuring the deformability of erythrocytes and for investigating the mode of action of rheologically active drugs.