Indication; Technical Description; Physical Background - MIETHKE miniNAV Mode D'emploi

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INDICATION

The miniNAV is used for draining cere-
brospinal fluid from the ventricles into the peri-
toneum in hydrocephalus patients.

TECHNICAL DESCRIPTION

The miniNAV was developed to offer a small-
sized valve without the obstruction-related
problems that are known to arise in the treat-
ment of hydrocephalus. The miniNAV is com-
posed of a robust titanium casing (1) whose
proximal end contains a ballcone valve. A spi-
ral spring (2) maintains the opening pressure
of the ball-cone valve and the sapphire ball (3)
ensures the precise closure of the valve. The
inlet connector (4) and the outlet connector (5)
are also made of titanium.
Fig. 1: Schematic cross-section of the miniNAV
1. titanium housing
2. spiral spring
3. sapphire ball
4. inlet connector
5. outlet connector
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PHYSICAL BACKGROUND

Horizontal position
When the body is in a lying position, the pres-
sure at the valve is calculated by determin-
ing the difference between the intraventricu-
lar pressure and the pressure in the abdomen
(see fig. 2). In a healthy person, the intra-
ventricular pressure is positive when the body
is in a lying position. To adjust this pressure
by means of valve drainage, the appropriate
pressure level must be chosen, taking the
abdominal cavity pressure into account. The
IVP is then calculated by determining the sum
of the valve opening pressure and the abdom-
inal cavity pressure (see fig. 2).
Vertical position
In a healthy person, the ventricular pressure is
slightly negative when the body is in a stand-
ing position. To adjust this pressure by means
of valve drainage, the valve opening pres-
sure must be set much higher than would be
required if the person was lying down. It is
only in this way that the valve can compensate
for the level of hydrostatic pressure minus the
abdominal cavity pressure and the desirable,
slightly negative, intraventricular pressure.
miniNAV