**7. Conclusions**

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an ironic association, since a key aspect of Virchow's work on venous thrombi was his threepart distinction between thrombus and clot and his demonstration that a DVT is formed when leukocytes as well as platelets swarm to the site of injury, the venous valve cusp. As a result, mainstream research in the DVT field since 1962 has taken on an increasingly haematological character, which has entailed a tacit dismissal of the important discoveries made prior to the mid-20th century, not least those of Virchow. The valve cusp hypoxia (VCH) thesis is founded on the recognition of these discoveries and on our knowledge of vascular physiology, particularly the dynamics of blood flow in venous valve pockets. It was advanced as a hypothesis in 1977 and was corroborated and validated by critical experiments during the 1980s.

In clinical terms, the VCH thesis adds nothing to accepted standards of treatment for actual, manifest thromboembolism other than to augment the rational basis for mechanical prophylaxis and to suggest reconsideration of prolonged muscle relaxant use during surgery, a potential 'silent killer'. Mechanical prophylaxis should be based not on altering the venous blood flow velocity, which is almost certainly irrelevant to thrombogenesis, but to ensuring that flow is always pulsatile. The pulses need not be frequent: once per hour will suffice to ensure that valve pocket hypoxaemia does not become seriously injurious to the endothelia, and should therefore preclude the formation of thrombi, though optimal timing can only be established on the basis of experience. The key point is to ensure that the valve pockets are emptied and refilled regularly with fresh venous blood. On the other hand, the VCH thesis indicates that anticoagulants do not prevent the initiation of deep venous thrombosis, though they restrict or retard the growth of thrombi that have already formed.

The approaches to mechanical prophylaxis inferred from VCH are testable on experimental animals. Such tests should certainly be conducted before a randomised controlled clinical trial is initiated. We encourage colleagues throughout the world to undertake these experiments – and, subject to the results, clinical trials – since only by consistent findings from different laboratories and clinical establishments can a consensus be obtained that would make rational mechanical prophylaxis the standard of care for patients at risk for DVT/ VTE.
