Quantitative analysis of platelet function using stagnation point flow aggregometry. First clinical results

The clinical consequences of atherosclerosis result from vascular occlusion. The central role of platelet-vessel wall interaction in the initiation and perpetuation of this process is well established. Individual analysis and quantification of two major platelet functions underlying atherosclerosis and thrombosis, i.e. adhesion (platelet-wall interaction) and aggregation (platelet-platelet interaction), would contribute significantly towards elucidation of the mechanisms involved and therefore towards optimization of prophylaxis and therapy. The Stagnation-Point-Flow-Adhesio-Aggregometer (SPAA), in which such an evaluation of platelet function is possible, was thus standardized and its clinical reproducibility and predictive power assessed.

Using the SPAA, a morphometric separation of adhesion and aggregation is obtained via dark field micrographs of platelet microthrombi formed during stagnation point flow of platelet rich plasma (PRP). Quantification is achieved via biomathematical evaluation of simultaneously obtained growth curves, whereby the degree of adhesivity and aggregability is reflected in the respective growth rate constants Kpw (%) and Kpp (%). Experiments with the PRP of 36 healthy volunteers were performed and the results compared to those obtained for 32 patients exhibiting angiographically verified peripheral arterial disease (PAD).

The control group exhibited values (Kpw) ranging from 0.40% to 1.10% (average Kpw: 0.71 +/- 0.21%). Differences in average Kpw value between the control subgroup over and that under 45 years of age were absent. A spontaneous platelet aggregation was not observed in the controls (Kpp = 0%). The overall intraindividual Kpw variation in 18 volunteers examined 3 times or more ranged from a minimum of 3% to a maximum of 20% of respective Kpw value. The patients were divided into two subgroups: diabetics and nondiabetics. The nondiabetic group demonstrated an average Kpw of 1.56%. In addition, a spontaneous aggregation was observed in 50% of all experiments (average Kpp = 1.42%). The diabetic group exhibited the highest average adhesion value (Kpw = 1.94%) occurrence of spontaneous aggregation in all experiments (Kpp = 2.10%).

The consistency in adhesion values obtained among the controls as well as the minimal intraindividual variance observed, demonstrates the reproducibility of the method. The statistically significant increase (p < 0.001) in adhesivity of patients as compared to controls, as well as the common occurrence of spontaneous aggregation can therefore be considered a pathologic platelet response reflecting the severity of the disease. Results obtained verify the presence of circulating hyperreactive platelets in PAD patient and indicate the predictive power of the method. Thus the SPAA may be of considerable aid in improving thrombosis prophylaxis and therapy.