[Nycthemeral change in the anticoagulant effect of heparin given at a constant rate by the intravenous route].

Six subjects with venous thromboembolism volunteered for this prospective study. Heparin was administrated intravenously at a constant rate with an infusion pump. The activated partial thromboplastin time (A.P.T.T.) and thrombin time (T.T.) were measured every 4 hrs. for 48 hrs. These coagulation tests exhibited a nycthemeral variation with a large amplitude which was reproducible from one day to the next and statistically validated by the cosinor method (p less than 0.001). All patients had a nocturnal peak of A.P.T.T. and T.T. on both days. In four patients this peak for A.P.T.T. exceeded the upper desired limit.