Prevention and treatment of thromboembolism has to be directed toward two main goals: (1) prevention of formation of primary and secondary thrombi and (2) prevention of mobilization of a locally formed thrombus causing embolism. Prevention of thrombus formation can be achieved by modern anticoagulants such as heparin or Dicumarol (3,3′-methylene-bis-[4-hydroxycoumarin]). However, once the thrombus has formed, attention has to concentrate toward preventing the formed thrombus from being broken off and carried into the circulation. This obviously is a mechanical problem and can be solved either by interruption of the continuity of the vein above the thrombus or by prevention of mobilization of the thrombus from its venous bed.
Linton and Chapman have recently discussed the importance of intravenous pressure (Valsalva's experiment) in the production of pulmonary embolism. In the Valsalva experiment, in sudden straining and in the act of defecation there occurs an impediment of venous return with rise in