TUBE COLLAPSE AND VALVE CLOSURE IN AMBULATORY VENOUS-PRESSURE REGULATION - STUDIES WITH A MECHANICAL MODEL

Purpose: To determine the role of valve closure and column segmentatio n in ambulatory venous pressure regulation. Methods: Using a mechanica l model consisting of a graduated adjustable valve and a collapsible t ube, we studied the differential effects of valve closure and tube col lapse on venous pressure regulation. By utilizing materials with diffe ring wall properties for the infravalvular tube, the influence of wall property changes on tube function and pressure regulation was explore d. Results: Valve closure, per se, does not cause venous pressure redu ction. Collapse of the tube below the valve is the primary pressure re gulatory mechanism. The nonlinear volume-pressure relationship that ex ists in infravalvular tubes confers significant buffeting properties t o the collapsible tube, which tends to retain a near-constant pressure for a wide range of ejection fractions, residual tube volumes, and va lve leaks. Changes in tube wall property affect this buffering action, at both the low and high ends of the physiological venous pressure ra nge. Conclusions: The valve and the infravalvular venous segment shoul d be considered together in venous pressure regulation. Tube collapse of the segment below the valve is the primary pressure regulatory mech anism. An understanding of the hydrodynamic principles involved in pre ssure regulation derived from this model will provide the basis for co nstruction of more complex models to explore clinical physiology and d ysfunction.