Platelet aggregability in chronic arterial occlusive diseases

It is generally accepted that platelets play an important and primary role in arterial thrombosis. Present study was carried out to clarify the platelet aggregability in patients with Buerger's disease (TAO) and Arteriosclerosis obliterans (ASO).Sixty male cases with TAO aged 25-65 (average and SD: 43.2±9.7), 60 male cases with ASO aged 46-75 (62.5±8.1), and 50 healthy males aged 28-70 (48.5±12.0) were studied with optical density method.According to the clinical course of the disease, the patients of each group were further classified into 4 stages: stationary, improving, chronically aggravating, and acute occlusive stages in ASO or acute stage of thrombophlebitis migrans (TPm) in TAO.Four concentrations of ADP and three concentrations of collagen suspension were used to induce aggregation. The maximal aggregation rate (MAR, described as percentage of maximal transmittance change of PRP in 5 minutes after adding the aggregating agents to that of PPP) and the appearance rate of the second aggregation at each ADP concentration were employed as the parameters of aggregability.In patients with TAO in the aggravating and stationary stages, reduced aggregability was found at the lower concentrations of aggregating agents. In the improving stage the aggregability was almost normal and significantly enhanced in the TPm stage.In patients with ASO in the stationary and improving stages, enhanced aggregability was found, and it was the most marked in the acute occlusive stage. In the aggravating stage, the aggregability was normal.In the chronically aggravating stage, chronic narrowing of arterial lumen is suspeited to derelope probably due to repeated thrombus formation and its partial dissolution and partial organization. In the improving stage such a process does not take place and the development of the collateral circulations or recanalization of the thrombosed arteries lead to the improv ement of the peripheral circulation. This difference between the two stages may account for the difference of the platelet aggregability, reduced in the aggravating stage and maintained normal in the improving stage. This relative difference of the platelet aggregability between the two stages were found not only in patients with TAO but also with ASO.It was of interest that in patients with TAO the platelet aggregability in the stationary stage was the same as in the aggravating stage. This result lead to the speculation that in patients with TAO there exists even in the stationary stage a certain change similar to that in the aggravating stage.In patients with ASO enhanced platelet aggregability was noticed in the stationary stage. This result cannot be explained only by the effect of aging and the contribution of some plasma factors is probable.In the acute occlusive stage in ASO and the TPm stage in TAO, markedly enhanced platelet aggregability was observed. This may be explained partially by the relatively increased number of young platelets in the circulating blood secondary to the rapid platelet consumption by the acute thrombus formation. Considering that the patients in such an acute stage are in a stressed condition, many other unknown factors might contribute to the enhanced platelet aggregability.