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What is
Hydrocephalus

VALVES


The Phoenix CRx Valve Mechanism Application : The CRx Valve mechanism is designed to provide progressive resistance in shunting of cerebrospinal fluid (CSF) from the ventricles of the brain. Description : The valve mechanism consists of medical grade silastic dome with two crossed slits. The differential pressure mechanism found in the CRx valve was designed by John Holter D.Sc. to reduce overdrainage when shunting cerebrospinal fluid (CSF) from ventricles of the brain to the peritoneal cavity. The valve mechanism is housed in a type stainless steel or a polysulfone protective assembly. Two valve mechanisms are incorporated into a medical grade silastic body which forms the pumping chamber of the Cruciform, the CRx and the Diamond Valves. In each of these valves, sleeves extend over the connectors protecting the proximal and distal catheter connections from ligature stress and disconnection. The Single valve consists of a single valve mechanism placed in the stainless steel housing. The valve mechanism consists of a sillicone elastomer dome with two crossed slits. This design incorporated an inherent resistance to the tendancy of most shunts to overdrain due to the hydrostatic column which is created when a shunted patient stands.
The outer circumference where the valve is inelastic (arrow A of figure 1), comprises 56% of the surface area referencing positive proximal or negative distal pressure. The area between the outer circumference and the center (arrow B of figure 1), where the valve leaflets are somewhat elastic and more resistant to the effects of pressure, comprises 33% of the surface area. The center of the mechanism (arrow C of figure 1), where the valve leaflets are most elastic, comprises less than 11% of the surface area.

When viewed from the side, it can be seen that the base of the dome mechanism of the valve (arrow A of figure 2) is inelastic due to the continuity of material around the circumference. Halfway up the dome (arrow B of figure 2), where the slits start, the valve leaflets are moderately elastic, and more resistant to the effects of pressure. At the "top" of the dome (arrow C of figure 2), at the center of the mechanism, the valve leaflets are most elastic.

The four compound curved leaflets of the dome provides a more positive closing force than conventional differential pressure valves (Figure 2). Together, these two features result in a progressive resistance valve which increases resistance to overdrainage. Performance of the CRx valve mechanism is such that flow rate increases with increasing ICP and conversely, decreases with decreasing ICP.


catalog revision date 7/03

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