Microrheology and light transmission of blood. III. The velocity of red cell aggregate formation.

The formation of primary (rouleaux) and secondary (rouleaux networks) RCA was studied by microcinematography (12 frames/sec) and photometry in a counterrotating "rheoscope" chamber. The blood was first subjected to rapid viscometric flow (460 sec-1, all RBC dispersed and aligned in flow) and then brought abruptly to full stop. In normal human blood, primary and secondary RCA occurred simultaneously, and were completed within 8 to 10 sec after stop. Blood from pregnant women at term, known for its pronounced red cell aggregation, shows a dissociation between the formation of short primary rouleaux (initiated even before full stop and completed 1-2 see thereafter) and secondary RCA completed 3-5 see after stop. RCA increases the light transmission of blood (measured by an increase in photovoltage V), the process and its first derivative (dV/dt equals I) can be recorded. After flow stop, there is an exponential decay of I(I equals t-I-o with e-lambda-t). The half time of this decay is recorded and correlated to the kinetics of red cell aggregate formation In human blood the half time of this process varies between 1.0 and 6.0 sec. In suspensions of human RBC in artificial plasmas, t-1/2 decreases with increasing concentration of fibrinogen and/or Dextran 250000, the second component appearing at concentrations above 500 mg-%. The method lend sitself for the quantification of RCA in small blood samples (20 mul).