Original Article: Changes in Platelet Function, von Willebrand Factor and Factor VIII in Patients Undergoing Aorto-bifemoral By-pass with Dacron Grafts.

Platelets play a major role in the development of patency complications in vascular grafts. The aim of this study was to evaluate changes in platelet count and function, and also in factor VIII:C (FVIII:C) and von Willebrand factor (vWF) plasma levels, induced by aorto-bifemoral by-pass with Dacron grafts in seven patients. Platelet count, platelet aggregate ratio (PAR), and platelet aggregability induced by several stimuli, as well as FVIII:C and vWF plasma levels were evaluated before and on days 1,4,9 and 11 after surgery. We observed a mild thrombocytopenia on day 1, followed by a progressive increase in platelet count, which attained a relative thrombocytosis on the 11th day. PAR did not vary significantly during the whole observation period. Platelet aggregation, assayed by the optical method using ADP, epinephrine, arachidonic acid, collagen and ristocetin, (decreased on days 1 and 4). Thereafter, an increase in aggregation was observed until day 11 when hyperaggregability was verified. FVIII:C and vWF peaked on the 4th day, decreasing progressively to pre-surgery values on day 11.

Effect of propranolol, barbiturate anesthesia and splenectomy on factor VIII:C and plasminogen activator release induced by DDAVP. An experimental study on the dog.

After the injection of DDAVP in 39 non-anaesthetized dogs (0.4 micrograms/kg) factor VIII:C activity rose to 145% of baseline values (p less than 0.0001) and the fibrinolytic potential of euglobulin precipitate rose to 196% (p less than 0.0001). The injection of DDAVP was repeated three times in each dog of a group of good responder animals at weekly intervals, but after: A) Pentobarbital anesthesia (30 mg/kg)--the increase of factor VIII:C was reduced from 164% to 116% (n = 11; p less than 0.0005) and the increase in fibrinolytic activity was reduced from 270% to 192% (n = 11; p less than 0.05). B) Injection of propranolol (1 mg/kg)--the increase of factor VIII:C was reduced from 167% to 110% (n = 13; p less than 0.0005) and there was no significant decrease of fibrinolytic activity (n = 13; n.s.) C) Splenectomy--the increase of factor VIII:C was reduced from 166% to 122% (n = 10; p less than 0.0005) and fibrinolytic activity was not significantly changed from 196% to 256% (n = 9; n.s.). There were no statistically significant differences in the increases of factor VIII:C and fibrinolytic potential of euglobulin precipitate after repeating only the injection of DDAVP three times in the same animal at weekly intervals (n = 5; n.s.). We conclude that the increases in factor VIII:C and fibrinolytic activities observed after DDAVP infusion in the dog are due to different mechanisms of action.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet sequestration during hypothermia in dogs treated with sulphinpyrazone and ticlopidine--reversibility accelerated after intra-abdominal rewarming.

During body cooling, a progressive thrombocytopenia is observed, with platelet sequestration mainly in the liver. Platelets return progressively to the circulation during rewarming. In this work the presence of platelet clumps is demonstrated by electron microscopy inside the hepatic sinusoids of dogs cooled to 20 degrees C by immersion in iced water. Such clumps were not found either before cooling or after body rewarming. Similar platelet clumps in the hepatic microcirculation were found in two other groups of dogs cooled and rewarmed as before, but previously treated with the antiaggregants sulphinpyrazone or ticlopidine. Another group of dogs was cooled and rewarmed by intra-abdominal circulation of physiological saline respectively at 4 degrees C and 40 degrees C. In these animals a similar decrease of circulating platelets was observed. However, just after rewarming was started, with the body temperature still at 22 degrees C, sequestered platelets came back abruptly to circulation. We conclude that hepatic platelet sequestration induced by hypothermia appears mainly due to local haemodynamic conditions.