title: Tube collapse and valve closure in ambulatory venous pressure regulation: studies with a mechanical model.
abstract: OBJECTIVE
  To determine the role of valve closure and column segmentation in ambulatory venous pressure regulation.
  
  
  METHODS
  Using a mechanical model consisting of a graduated adjustable valve and a collapsible tube, we studied the differential effects of valve closure and tube collapse on venous pressure regulation. By utilizing materials with differing wall properties for the infravalvular tube, the influence of wall property changes on tube function and pressure regulation was explored.
  
  
  RESULTS
  Valve closure, per se, does not cause venous pressure reduction. Collapse of the tube below the valve is the primary pressure regulatory mechanism. The nonlinear volume-pressure relationship that exists in infravalvular tubes confers significant buffering properties to the collapsible tube, which tends to retain a near-constant pressure for a wide range of ejection fractions, residual tube volumes, and valve leaks. Changes in tube wall property affect this buffering action, at both the low and high ends of the physiological venous pressure range.
  
  
  CONCLUSIONS
  The valve and the infravalvular venous segment should be considered together in venous pressure regulation. Tube collapse of the segment below the valve is the primary pressure regulatory mechanism. An understanding of the hydrodynamic principles involved in pressure regulation derived from this model will provide the basis for construction of more complex models to explore clinical physiology and dysfunction.
authors.affiliation: Department of Surgery, the University of Mississippi Medical Center, Jackson, USA.
authors.forename: S
authors.initials: S
authors.lastname: Raju
authors.forename: A B
authors.initials: AB
authors.lastname: Green
authors.forename: R K
authors.initials: RK
authors.lastname: Fredericks
authors.forename: P N
authors.initials: PN
authors.lastname: Neglen
authors.forename: C A
authors.initials: CA
authors.lastname: Hudson
authors.forename: K
authors.initials: K
authors.lastname: Koenig
mesh_terms: D001696:Biomechanical Phenomena; D001794:Blood Pressure / Q000502:physiology*; D001808:Blood Vessels / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D011138:Polytetrafluoroethylene
chemical_list: D011138:Polytetrafluoroethylene