Analysis of platelet aggregation using particle collision theory.

The aggregometer monitors changes in light transmission through stirred suspensions of aggregation platelets. Arbitrary measurements from aggregometer recorder tracings have been used to investigate platelet aggregation without regard to mechanisms involved. To determine the applicability of particle collision theory to assessment of in vitro platelet sensitivity to proaggregating agents, platelet-rich plasma (PRP) from five volunteers was used to obtain recorder tracings after addition of ADP in five doses (0.4-4.0 mumol/l PRP) to aliquots of PRP stirred and incubated in an aggregometer. Using the equation describing light transmission through particulate suspensions, particle collision theory, and s (the probability of particle union after collision), a subject- and dose-independent relationship between aggregation rate (dn/dt) and particle number (n) at the recorder tracing inflection point was found (dn/dt = -k X s X n1.56, where k is a constant dependent on particle size and speed and on the proportion of unreactive particles). Determinations of mean particle size at the tracing inflection point indicated that k was also dose independent. Dose-response curves of ADP added vs. s could therefore be constructed. This methodology provides conveniently obtainable quantitative information concerning in vitro platelet "stickiness."