Clinical Hemorheology and Microcirculation

Fetal blood can now be routinely studied by intrauterine sampling. Low erythrocyte aggregability is one of its most prominent hemorheological characteristics before 32 wk gestation. We investigated whether increased RBC aggregability is a marker of fetal pathologies. After we established in 119 fetuses a control group for fetal blood rheology, we measured erythrocyte aggregation with the Myrenne apparatus (i.e. a micromethod using 1 droplet of blood) in 111 fetuses explored for various diseases. RBC aggregation was increased (>2 Sd for gestational age) in 24 fetal blood samples, with the following diseases: 12.5% toxoplasmosis; 12.5% rhesus immunization; 8.33% autoimmune thrombocytopenia; 8.33% kidney polycystosis; 8.33% old maternal age; 8.33% heart malformation; 8.33% fetal hypotrophia. In autoimmune diseases (rhesus; thrombocytopenia) RBC aggregation was increased in 5/10 cases (50%); in heart or kidney malformations 5/10 (50%); in toxoplasmosis seroconversion 3/23 i.e. 13% of the fetuses had increased aggregation. These data suggest that RBC aggregation is increased in several fetal diseases and may be a nonspecific marker of them.

Pregnancy is associated with erythrocyte hyperaggregation which acutely returns to baseline during delivery, while a transient hyperviscosity syndrome induced by uterine contractions can be observed. We aimed at analyzing more precisely the modifications of erythrocyte aggregation during labor. 71 uterine contractions in 30 pregnant women (19–45 yr, mean 27.2 ± 9) were studied, with RBC aggregation (SEFAM erythroaggregometer) measured before, during and after the contraction. Aggregation indices at 10 and 60 sec progressively increased throghout labor (p<0.01). Partial and total dissociation thresholds progressively decrease during labor with a nadir (−10%) at delivery (p<0.01). The aggregation time is transiently shortened (p<0.01) during labor. Although previous measurements with the Myrenne aggregometer showed only during labor a return to nonpregnant values, this analysis by laser backscattering indicates that the stressful events which occur during uterine contractions increase the tendency of RBCs to form aggregates, although they disaggregate more easily.

An association has been shown to exist between hypertension in adult life and fetal intrauterine growth retardation. In this study clear similarities have been found between the haemorheological profiles of adults with essential hypertension and infants who are significantly growth retarded at birth. In both groups, When compared with normal controls whole blood viscosity, haematocrit and plasma viscosity were elevated and erythrocyte deformability reduced. In hypertensive males there was also a significant elevation of plasma fibrinogen concentration, this difference was not demonstrated in growth retarded fetuses.

Further investigation of the regulatory mechanisms that determine whole blood viscosity and its major components in fetal intrauterine development may reveal a mechanism to explain the association between intrauterine growth retardation and adult hypertension.

This paper presents a new micropipette technique to study tether formation (i.e. membrane fragility) of individual red blood cells (RBC). Point attached adult and full-term neonatal RBC were aspirated at different negative pressures into a large micropipette with an internal diameter of 7.8 μm. We measured the onset of tether formation at aspiration pressures of −3 and −5 mm H₂O and the length of the membrane tethers after 2, 5, 10, 15, 20, 25, and 30 s. The minimum aspiration pressure for tether formation was −3 mm H₂O for neonatal and −5 mm H₂O for adult RBC. At a pressure of −5 mm H₂O tether formation began after 10.3 ± 5.4 s in adults and 4.1 ± 2.8 s in full-term neonates. 25 s after the beginning of tether formation, the tether lengths were 14.0 ± 3.9 μm for adult RBC and 21.1 ± 4.7 μm for neonatal RBC. We conclude that plastic deformation of neonatal RBC begins at lower pressure and is faster compared with adult RBC.

The decrease in erythrocyte deformability was observed in renal failure and also in renal transplanted patients. In this work, we studied the effects of a daily dietary supplement of fish oil concentrate (maxEPA) against olive oil on the erythrocyte deformability in 23 renal transplanted patients. This study included 13 men and 10 women with the mean age of 32.8 +/− 12.3 who had been transplanted within 36 +/− 20 months and their renal functions had been stable for at least 3 months. The immunosuppressive treatment was stabilized and associated with cyclosporine A, azathioprine and corticosteroids. The capsules of maxEPA or olive oil (n=6/day) were given following randomised and controlled trials. After six months treatment, the index of erythrocyte deformability in two groups was evaluated according to the Dormandy and Reid modified technique. Significant improvements were found in treated patients with maxEPA. The composition of erythrocyte phospholipids membranes was determined by gas chromatography. An increase of omega 3 fatty acids was observed in the treated patients. These results showed that a supplementation with unsaturated fatty acids, was able to improve the mechanical aspects of red blood cells in renal transplanted patients treated with immunosuppressive drugs.

Blood viscosity was measured at different shear rates using a rotational viscometer, and the correlation between blood viscosity and blood haemoglobin concentration was studied. In 10 healthy controls correlation coefficients were: 0,966 at shear rate 40,0 s⁻¹, 0,931 at 19,6 s⁻¹, 0,817 at 2,3 s⁻¹ and 0,816 at 0,8 s⁻¹, p<0,01 to p<0,001. The regression lines for these relationships were then applied to the patient groups to calculate what blood viscosity should be predicted solely from the individual haemoglobin concentration, “predicted blood viscosity”. In 34 patients with cardiovascular diseases (20 patients with coronary artery disease (CAD), 8 patients with idiopathic dilated cardiomyopathy and 6 patients with primary pulmonary hypertension) the correlation between blood viscosity and haemoglobin concentration was less good, for the total patient material 0,748 to 0,613, p<0,001 at all shear rates, and for the CAD patients 0,664 to 0,428, p<0,05 at 3 out of 4 shear rates. Apparently the poorer correlation in the patients was due to a larger influence from factors unrelated to haemoglobin concentration/ haematocrit, as the quotients between individually measured and predicted blood viscosity correlated with measured blood viscosity when the haematocrit factor had been eliminated by in vitro standardisation of sample haematocrits to 45%.

Present work concerns quantitative analysis of parameters that affect apparent blood viscosity at different low shear rates in acute cerebrovascular accidents. Viscosity profile of a large number of blood samples from thromboembolic stroke cases and age and sex matched healthy and hypertensive as well as diabetic controls were studied which confirmed non-Newtonian power law behaviour of blood. The importance of power law parameters namely non-Newtonian behaviour index “n” and flow consistency index “k” is discussed. Other apparent blood viscosity parameters such as, red cell filterability, red cell rigidity, hematocrit, plasma viscosity and biochemical parameters are evaluated and discussed. The cumulative effect of these parameters did not appear in terms of elevated whole blood viscosity in acute cases as compared to healthy controls since hematocrit value was on the lower side of the normal range. The whole blood viscosity in acute cases at any of the seven shear rates selected, was not significantly different from healthy controls. However power law parameters are shown to reveal the difference of apparent blood viscosity between acute stroke and controls. Hence the power law parameters may be considered a better tool to understand the significance of apparent blood viscosity in health and disease.

It is now recognised that variations in plasma protein composition exist in different ethnic groups. This can be expected to lead to differences in blood rheology. Accordingly, a pilot study was made of a variety of hemorheological factors in five ethnic groups (Afro-Caribbeans, Arabs, Caucasians, Chinese and Indo-subcontinentals). The major rheological difference was in the plasma viscosity, which was significantly increased in all the other groups compared to the Caucasians. The differences in blood viscosity were much less marked and were generally masked by large intersubject variation. Nevertheless, the Chinese males exhibited a raised native whole blood viscosity at low shear rate (0.277s⁻¹) over their Caucasian male counterparts. The Arab, Afro-Caribbean and Chinese subjects displayed a higher erythrocyte aggregation index (Myrenne M1 mode) than the Caucasian group. These differences largely reflect significant variations with regard to total plasma protein and immunoglobulin (IgG, IgA) concentrations between the groups. Interestingly, the content of other proteins studied (IgM, fibrinogen and alpha-2-macroglobulin) was similar between groups.

The effect of i.v. infusion of adenosine (20/μg/kg/min over 10 min + 40/μg/kg/min over 10 min) on peripheral haemodynamics, blood rheology and platelet aggregation has been studied in 8 volunteers. Blood pressure, heart rate, rest flow at the lower limbs, blood viscosity, whole blood filterability, haemoglobin affinity for O₂ (P₅₀), 2,3-diphosphoglycerate (2,3-DPG), platelet aggregation were measured. Free cytosolic calcium levels were evaluated in platelets in resting conditions and after in vitro stimulation. Plasma adenosine levels were detected by HPLC. Adenosine infusion did not induce significant changes in rest flow, blood pressure and heart rate. At the end of infusion a significant reduction in blood viscosity (p<0.01) with a concomitant significant increase of blood filterability (p<0.05) was observed. P₅₀ and 2,3-DPG tended to increase at the end of infusion as an expression of reduced haemoglobin affinity for O₂ potentially associated to an increased delivery of O₂ to peripheral tissues. Adenosine induced a significant reduction of platelet aggregability (p<0.01) with a decrease of free cytosolic calcium levels.

In conclusion adenosine induces a series of biological changes possibly useful at the microcirculatory level at infusion rates that are well tolerated and devoid of significant haemodynamic effect.

Hyperviscosity may be termed the physicochemical risk factor of stroke. The case-control study is designed to clarify whether elevated blood viscosity is causally related to the ischemic event or is associated with the epidemiological risk factors of stroke. A total of 127 patients with acute ischemic stroke were recruited in the study. There were 25 females and 102 males with a mean age 65 ± 10 years (range 46 to 78 years). An equal number of control cases matched with age and sex were selected from healthy volunteers. The fasting blood was taken for the measurement of blood viscosity parameters. The results showed statistically significant differences in plasma viscosity (P<0.01), whole blood viscosity (P < 0.001), erythrocyte aggregability (P<0.001) and fibrinogen level (p < 0.001) between the patients and controls, but no significant difference in RBC deformability and hematocrit. Follow-up studies conducted three weeks (96 cases) and three months (64 cases) later showed that the hyperviscosity phenomenon persisted. We concluded that impairment of blood viscosities are present not only in patients with acute cerebral infarction, but also in those with chronic stage of stroke which may be associated with the risk factors of stroke such as hypertension, diabetes or ischemic heart diseases.