Platelet aggregation in Poiseuille flow: I. A double infusion technique

This paper describes the design of a double infusion microtube and its use to directly observe the aggregation of platelets undergoing Poiseuille flow immediately after the introduction of 1 μM ADP. Citrated human platelet-rich plasma flowed between two reservoirs through a 100-μm-diameter flow tube at the entrance of which ADP was simultaneously infused through the tip of a concentrically located micropipet. With the aid of microcinematography, the time course of platelet aggregation was followed by measuring the number distribution of single cells and aggregates across the median plane of the tube at various distances downstream of the micropipet. Preliminary studies covering a range of mean tube shear rates from 2 to 30 sec^?1 showed that, for a given donor, the fraction of platelets in aggregates, both in control runs (infusion of Tyrodes) and in experimental runs (infusion of ADP) was reproducible to within ± 1%. Except at the lowest shear rate, the extent of aggregation increased with increasing distance down the tube.