[A new parameter for evaluating platelet aggregation in patients with chronic cerebral infarction].

We present a new sensitive parameter for evaluating ADP- and collagen-induced platelet aggregations. This parameter was used to re-evaluate platelet functions in chronic cerebral infarction. This parameter, the platelet aggregatory threshold index (PATI), was determined by the platelet aggregation curves obtained with four concentrations of two inducers (ADP; 0.5, 1.0, 2.0, 4.0 mumol/l and collagen; 0.125, 0.25, 0.5, 1.0 microgram/ml), and it indicated the concentration of the inducer that produced 50% of the aggregation rate at 5 min of ADP (4.0 mumol/l) or collagen (1.0 microgram/ml) induced aggregation curve. PATI was significantly correlated with the minimum concentration in ADP and collagen-induced aggregation, at which irreversible aggregation was induced. A negative correlation was shown between PATI and the rate of ADP (4.0 mumol/l)-induced maximum aggregation determined by the ordinary method, while no correlation was found between PATI and the rate of collagen (1.0 microgram/ml)-induced maximum aggregation. In normal elderly individuals, PATI obtained with ADP decreased significantly with age and showed no sex difference. Patients who had chronic cerebral infarction showed a significantly lower PATI with both inducers when compared to healthy elderly individuals, but the maximum aggregation rates obtained from the same platelet aggregation curves induced by ADP (4.0 mumol/l) or collagen (1.0 microgram/ml) showed no difference between the two groups. PATI reflects to be a more quantitative sensitivity of platelet than ordinary parameters such as the maximum aggregation rate. Determination of PATI may allow the detection of activated platelets in patients with chronic cerebral infarction.