Rheological properties of fetal red cells with special reference to aggregability and disaggregability analyzed by light transmission and laser backscattering techniques.

Blood viscosity factors and fetal erythrocyte aggregability were investigated with light transmission (Myrenne device) during a cross-sectional study of blood drawn in utero by cord venepunctures in 119 normal fetuses between 18 and 39 weeks gestation. There was a progressive increased blood viscosity at native hematocrit (p < 0.01) explained by a gradual increase in both hematocrit (from 33% to 40%, p < 0.05) and Dintenfass' 'Tk' RBC rigidity index (p < 0.05), while plasma viscosity remained constant at 1.18 +/- 0.01 mPa x s as well as the h/eta ratio (188.4 +/- 2.7 mPa(-1) x s(-1)). The RBC aggregation index 'M' remained almost equal to zero (mean value: 0.04 +/- 0.01) before 32 wk gestation and then increased (p < 0.05) until delivery. The upper physiological limit for this parameter before 32 wk (mean +/- 2 SD) is 0.18. The RBC aggregation index 'M1' remained constant during pregnancy at 2.98 +/- 0.26, i.e., the upper physiological limit for this parameter during the intrauterine life (mean +/- 2 SD) is 7.85. Both fibrinogen (r = 0.479, p < 0.05) and albumin (r = 0.494, p < 0.01) correlated with time so that the albumin/fibrinogen ratio remained stable. We then studied with the laser retrodiffusion technique the venous blood of 20 women (18-43 yr, 37-40 wk gestation) and the cord blood of their newborns at birth, comparing RBC aggregation of: mothers (M), maternal RBCs resuspended on newborn plasma (MF), newborn RBCs resuspended on maternal plasma (FM), and newborns (F). Aggregability is higher in M (RBC aggregation time M < MF < FM < F; p < 0.01); RBC aggregation index at 10 s M > MF > FM > F; p < 0.01), with in turn the symmetric inverse picture for the partial disaggregation threshold (M > MF = FM > F). Thus RBC disaggregability is higher in newborns, and suspensions on maternal and newborn plasma suggest that half of this difference in aggregability (and disaggregability) between fetal and adult blood results from plasma factors and another half from erythrocytes.

Aggregability and disaggregability of erythrocytes in women suffering from ovarian cancer: evidence for an increased disaggregation threshold.

In order to further characterize the alterations of erythrocyte aggregation described in ovarian cancer, we measured it with laser backscattering in eleven women suffering from ovarian cancer (mean age: 44.7 +/- 3.6, extreme values: 28-61 yr) compared with thirteen matched control women. Blood rheology exhibited a wide variability in cancer patients, with some unusually high values of plasma viscosity and/or RBC aggregation in individual cases. The only significant differences were found for the RBC disaggregation threshold which was higher in patients than in controls (78.06 +/- 10.14 vs 52.6 +/- 3.15 s(-1), p < 0.05), while hematocrit was lower (34.45 +/- 1.42 vs 38.23 +/- 0.75, p < 0.05). A negative correlation between hematocrit and corrected blood viscosity on the whole sample of subjects (r = 0.454, p < 0.05) indicates that hematocrit is decreased in subjects prone to high viscosity, resulting in similar values of apparent blood viscosity in controls and patients. Thus, a lower disaggregability of RBCs is evidenced in women with ovarian cancer, as well as a tendency to blood hyperviscosity compensated by a reduction of hematocrit which suggests that there may be some degree of 'viscoregulation'.

100 mg acetylsalicylic acid acutely decreases red cell aggregation in women taking oral contraceptives.

Since oral contraceptives (OC) are known to impair blood fluidity and to increase the risk of venous and arterial thrombosis, while acetylsalicylic acid (ASA) decreases the thrombotic risk and modifies some rheologic parameters, we compared the hemorheologic effects of ASA on blood rheology between women treated by OC and women who never received this medication. 25 women under OC were compared to 25 matched women who had never used OC. Blood viscosity (MT90 viscometer) and RBC aggregation (Myrenne aggregometer and AFFIBIO erythroaggregometer) were measured before and 1 hr after women received per os 100 mg ASA, after an overnight fast. The only significant difference between women under OC and controls was an increased RBC aggregation ('M' index +28%, p < 0.04; Affibio aggregation time -21%, p < 0.03). On the whole sample of 50 women as well as in the subgroup of women under OC, ASA decreased RBC partial disaggregation threshold (-1.7%, p < 0.01). These results confirm that RBC aggregation is increased under OC and suggest that 100 mg ASA acutely induces a partial reversal of this RBC hyperaggregation.

[Hemorrheological characteristics of fetal blood drawn in utero from the cord]. / Caractéristiques hémorhéologiques du sang foetal prélevé in utero par cordocentèse.

Extensive studies of hemorheology of cord blood (drawn just after delivery) have evidentiated a peculiar rheological pattern: less filterable red cells, reduced erythrocyte aggregation, lowered plasma viscosity. This pattern has been suggested to be important for maintaining a sufficient O2 supply to fetal tissues, by avoiding hyperviscosity despite increased RBC rigidity. However, cord blood at birth is not exactly fetal blood and we are not yet aware of studies of fetal blood drawn in utero several weeks before delivery. For this reason, we investigated the rheological properties of fetal blood during intrauterine cord venepunctures in 27 pregnant women (25-30 week's gestation) who were explored for detection of fetal genetic or infectious diseases. Fetuses have lower plasma viscosity (p less than 0.001), lower RBC flexibility (measured by filterability on the Hémorhéomètre) (p less than 0.01) and higher hematocrit/viscosity ratio (p less than 0.01) than their mothers. While no temporal modification during the studied period (20-40 wk) was detected for hematocrit and plasma viscosity, RBC filterability (rigidity) seems to exhibit a 'U shaped curve' with a nadir between 25 and 30 weeks. This pilot study supports the hypothesis that the previously reported rheological properties of cord blood at birth reflect to some extent those of intra-uterine fetal blood.