The proGAV is a posture-dependent valve. This means that the opening pressure varies depending on the body position of the patient. It consists of a ball-cone valve with an adjustable opening pressure, and a fixed pressure gravitational unit. In order to configure the proGAV according to the patient´s individual needs, the surgeon determines the opening pressure required for both the horizontal and vertical positions.
When the patient moves to the horizontal position, the gravitational unit opens completely. Thus, there is no longer any resistance to the flow of the CSF and the gravitational unit has no effect at all while the patient is lying down. The opening pressure of the proGAV is defined solely by the adjustable unit.
The setting of the opening pressure is determined by the clinical needs of the patient. The range of the adjustable unit is defined from 0 to 20 cmH₂O
As long as the IVP (intraventricular pressure) is under the defined opening pressure the adjustable unit is closed and the CSF-drainage is prevented. If the patient's IVP increases and continues to rise, the spring pressure of the ball-cone unit will eventually be overcome and the sealing ball will move away from the cone. Now the proGAV is open and CSF can flow.
As soon as the patient moves into an upright position the gravitational unit closes and therefore the total opening pressure of the proGAV is significantly increased. The flow of CSF is blocked until the sum of the intraventricular and hydrostatic pressures exeeds the total opening pressure of the proGAV. In this case the gravitational unit opens and the drainage of CSF is possible. The opening pressure of the gravitational unit increases steadily as the patient moves to the upright position. This provides effective protection against overdrainage.