Indication; Technical Description - MIETHKE DUALSWITCH VALVE Mode D'emploi

| INSTRUCTIONS FOR USE
GB

INDICATION

The DUALSWITCH VALVE is used for fluid drai-
nage from the ventricles into the peritoneum in
cases of hydrocephalus.

TECHNICAL DESCRIPTION

The DUALSWITCH VALVE was developed with
the aim to avoid known problems (blocked
drainage system, overdrainage, influence of
the subcutaneous pressure) in the treatment of
hydrocephalus. The DUALSWITCH VALVE fea-
tures two parallel chambers, one for the patient
vertical and one for the horizontal position. Fig.
1 shows a schematic cross section of the DU-
ALSWITCH VALVE. The robust titanium casing
(1) contains two titanium discs (3) connected
to the casing by two silicone membranes (2).
Two yoke springs (5), (6) of different strength
act on these discs and determine the opening
pressure with their respective preload force.
The springs press the pressure discs against a
ball (4) integrated into the casing. In this way,
the drill holes in the discs are closed and the
valve is closed. The stronger one of the two
1 2 5 3
10 6
Fig. 1: Schematic cross section of the DUALSWITCH VALVE
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springs (5) controls the opening and closing for
the high-pressure side (7); the weaker spring (6)
determines the opening and closing of the low-
pressure side (8). A secondary tantalum ball
(9) on the lowpressure side acts as the switch
between the two pressure levels. Inlet port (10)
and outlet port (11) are also made of titanium.
FUNCTION OF THE DUALSWITCH VALVE
The DUALSWITCH VALVE regulates the intra-
ventricular pressure in different ways
depending on the position of the patient (vertica
or horizontal).
The operating principle of the DUALSWITCH
VALVE is illustrated in figures 2 and 3. Fig. 2a
shows the closed valve in the lying-down po-
sition. Both membranes are pressed onto the
casing ball; the valve blocks any fluid drainage.
Fig. 2b shows the valve open (lying-down posi-
tion). The IVP of the patient has risen, the spring
pressure on the low-pressure side is overcome,
and the membrane is pressed up from the ball,
thereby opening a gap for fluid drainage. The
pressure cannot rise any further.
7
4 8 9
a)
b)
Fig. 2: Valve states in the lying-down position:
a) closed, b) open
As soon as the patient rises, the tantalum ball
closes the drainage channel on the low-pres-
sure side. As long as the sum of the IVP and
the hydrostatic pressure does not exceed the
closing force of the stronger spring, the valve
remains closed, see fig. 3a. Only if the pressure
rises further, the high-pressure side of the valve
opens and thereby prevents any further pressu-
re rise, see fig. 3b.
a)
Fig. 3: Valve states in the vertical
position: a) closed, b) open
The DUALSWITCH VALVE has large active swit-
11
ching surfaces, which ensures precise operati-
on. The valve opening force, F, which is brought
about by ventricular pressure, is governed by
the level of ventricular pressure, p, and the sur-
face, A, on which the ventricular pressure acts.
In conventional valves this active surface is very
small. Consequently, the valve opening forces
are small as well.
Thus, countervailing forces (sticking caused by
fluid residues, e.g. blood cells) can severely im-
pair the valve's functionality.
F
interference
F
F
p= =
A
A
Conventional
Valve
To minimize the effects of such interfering
forces, but still be able to use the same valve
pressure rating, the opening force needs to be
increased. In this way, the sticking forces will
be very small compared to the opening force
so that their influence on valve performance is
reduced considerably. Assuming the ventricular
pressure is unchanged, the opening force can
be increased by providing for a larger active sur-
face in the valve design. In the DUALSWITCH
VALVE, the fluid is distributed over a surface
significantly larger than in conventional valves.
Therefore the valve is much less susceptible to
conglutinations of the membrane through pro-
teins (fibrin)-rich cerebrospinal fluid.
To realize the advantage of strong opening
forces, the valve is about 28 x 5mm in size. The
DUALSWITCH VALVE is placed in the thoracic
region, like cardiac pacemakers, which have
been implanted there successfully for many
years.
b)
Fig. 4: Fluid and pressure distribution in the closed
valve
INSTRUCTIONS FOR USE |
GB
F
interference
F
F
= =
A
A
DUALSWITCH-
Valve
17