Preliminary study of pulsed-electromagnetic fields effects on endothelial (HUVEC) cell secretions--modulation of the thrombo-hemorrhagic balance.

We investigated the role of low-amplitude magnetic pulse with low repetition frequency superimposed on the environmental electromagnetic field (EMF) on the secretion of anti-aggregant (Prostacyclin or PGI(2)) and pro-aggregant (Thromboxane A(2)) agents in endothelial cells of the human umbilical cord vein (HUVEC). We established that magnetic pulse exposure modulates both PGI(2) and TXA(2). These modulations depend on the frequency, width of the pulse, and intensity of the magnetic field. Moreover, we corroborated previous results obtained with an endothelial cell line (EaHy-926), concerning the increased thrombo-embolic risk for the 1 Hz frequency.

Application of validated ultrasound indices to investigate erythrocyte aggregation in pigs. Preliminary in vivo results.

Although some studies concerning the ultrasound (US) characterization of erythrocyte aggregation reported in the literature have been conducted in vivo, none of them has led to quantitative indices. To achieve this objective, we first finalized a method on a hydrodynamic bench. Particularly, we define a kinetic protocol consisting of applying a 200 s(-1) shear rate followed up by a rapid decrease to reach a residual shear rate between 0 to 32 s(-1). From the backscattered intensity curve recorded all along the kinetic procedure, US dynamic parameters were defined and validated by correlation with reference laser indices obtained with the same model suspensions of erythrocytes (different concentrations of dextran 70 kD). A particular interesting behavior has been demonstrated when studying aggregation vs. the residual shear rate applied. The aim of the present study was to test the applicability of this aggregation kinetics protocol during in vivo investigations in pigs and possibly to recover the same aggregating behavior. The backscattered intensity was recorded all along the kinetic procedure as defined in vitro. Taking the derivative of the velocity profile recorded on 56 electronic windows, the shear rate was finely computed in the same measurement window where the backscattered intensity was calculated. Each US parameter could, therefore, be correlated with the residual shear rate corresponding to the same depth of measurement. We found that the blood aggregation behavior was identical to that observed in vitro. Apparently, a specific range of residual shear rates accelerates the activation of the aggregation process and the final aggregation level attained.

Comparison of new ultrasound index with laser reference and viscosity indexes for erythrocyte aggregation quantification.

We have previously established new ultrasonic indexes for erythrocyte aggregation using a Couette device, and validated them toward the Rayleigh's theory and reproducibility. Two hydrodynamic protocols were applied on various suspensions and their aggregation degrees were characterized by: 1. for the decreasing shear rates protocol: the power P(US) at the nominal frequency of the transducer used; 2. for the kinetic protocol: aggregation times (latency and half-rise times), variation between initial disaggregated state (Vo) and final aggregated state (V(inf)) and AI(US), which is the integral of the kinetic curve over time. The objective of the present study was to demonstrate the ability of these indexes to characterize the aggregation dynamics of suspensions with various levels of aggregation induced by concentrations of dextran 70 kD (Dx) of 10, 20 and 40 g/L added to washed red cells resuspended in saline solution. The results showed a maximum of backscattered power (P(US)) for Dx = 40 g/L with the decreasing shear rates protocol. We measured a final aggregation level (V(inf)), a minimal aggregation time (T(m)) and a maximal value of AI(US) for Dx = 40 g/L with the aggregation kinetics protocol. On the other hand, viscosity is increased with dextran concentration. These evolutions of the ultrasound (US) indexes and viscosity with dextran concentrations are consistent with literature reports. In addition, a particularly interesting phenomenon of US backscattering enhancement was observed for kinetics with no null final shear rate, which has never before been reported in such a precise manner. By another way, each of the dextran suspensions was tested on the laser erythroaggregometer that is presently considered as the "gold standard" method for erythrocyte characterization. The laser indexes (aggregation time T(a), aggregation indexes AI(10s) and AI(60s)), deduced from a kinetic protocol, have similar significance to the US ones. Statistical comparisons have been done between laser and ultrasonic indexes and significant correlations (0.001 < p < 0.01) were obtained. The set of results allowed us to conclude that ultrasonic indexes are suitable markers for the erythrocyte aggregation.