Patients who will be referred to Military University Hospital Prague with suspicion of normal pressure hydrocephalus will be tested by conventional methods to consider implantation of a ventriculo-peritoneal shunt. This testing is performed during hospitalization and includes clinical examination of the patient by a neurosurgeon, neurologist and neuropsychologist including neuropsychological questionnaires or tests - MoCA, AVLT, ROCFT, TMT A + B, Phonemic Verbal Fluency Test (N, K, P), Semantic Fluence Test (animals, vegetables), subtest of battery WAIS III and GDS. Clinical examinations are followed by magnetic resonance imaging. Functional testing of cerebrospinal fluid circulation is initiated on the second day unless another cause of the patient's symptoms (AD, Parkinson's disease, vascular dementia, tumor, obstructive type of hydrocephalus - eg aqueductal stenosis, Blake's pouch cyst etc.) is present. The functional testing will involve lumbar infusion test and subsequent external lumbar drainage (ELD) for 120h, including biochemical analysis of CSF during the ELD. After this time, the objective improvement of the patient's gait with the aid of the Dutch Gait Scale will be evaluated with respect to the subjective evaluation by the patient or family (changes in urinary incontinence / urgency, headaches, etc.). If the diagnosis of normotensive hydrocephalus is confirmed, the patient will be indicated for a VP shunt implantation, which is used for permanent derivation of cerebrospinal fluid into the peritoneal cavity. As a result of cerebrospinal fluid derivation, the clinical condition of most of the patients improves. The operation process described by Michael J. Fritsch (Fritsch et al. 2014) will be modified for various valve types in accordance with the manufacturer's recommendations and assumed conditions for proper valve adjustment. Patients will be randomly implanted with a M.blue® or proGAV 2.0® (with SA 2.0®) valve (Christoph Miethke GmbH \& Co. KG) in a randomized manner to form two study groups. The efficacy and safety of the proGAV 2.0® (with SA 2.0®) valve has already been confirmed in a randomized prospective study in patients with idiopathic normotensive hydrocephalus (Lemcke et al. 2013). The theoretical benefit of the M.blue® valve lies in the targeted modification of the cerebrospinal fluid diversion during the active time of a day, when the opening pressure of the valve's gravitational unit is controlled according to the angle between the valve and the horizontal line. The basal opening pressure of the valve that has to be overcome in the supine position is controlled with a fixed differential pressure unit. ProGAV 2.0® is an adjustable differential pressure valve implanted with a shunt-assistant SA 2.0®. The shunt-assistant represents a fixed gravity unit that increases the pressure in the standing position, which must be overcome for the cerebrospinal fluid flow through th shunt. The opening pressure of the valve could be selected according to the patient's height and sex. The basal opening pressure of the valve that must be overcome in the supine position is controlled with an adjustable differential pressure unit that can be adjusted before and after the shunt implantation. In both valves, the opening pressure is the sum of the opening pressures of the gravitational and differential pressure units. The theoretical benefit of the M.blue® valve is the possibility of changing the opening pressure of the gravitational unit regulated according to the position of the head in the space and thus aiming more at the pressure conditions when the valve is not parallel to the horizontal line.

Patients will not be familiar with the type of valve implanted with respect to subjective evaluation of patients during the follow-up. Initial valve settings will be in accordance with the manufacturer's recommendations. Follow-up of the patients will be guided in the usual regime according to the natural history of the disease: at one month of follow-up an outpatient clinical examination by a neurosurgeon, including brain CT scan; at three-months of follow-up an evaluation during a two-day hospitalization including collection of the following questionnaires, brain MRI, clinical examination by a neurosurgeon, neurologist and neuropsychologist and collection of cerebrospinal fluid from the pre-chamber for the biochemical analysis; at six-months an outpatient examination by a neurosurgeon; at one year of follow-up an evaluation during a two-day hospitalization including collection of the following questionnaires, brain MRI, clinical examination by a neurosurgeon, neurologist and neuropsychologist and collection of cerebrospinal fluid from the pre-chamber valve for biochemical analysis; at two-years of follow-up an outpatient clinical examination by neurosurgeon and neuropsychologist including brain CT scan including collection of the following questionnaires and collection of the cerebrospinal fluid from the pre-chamber of the valve for biochemical analysis.

For the purpose of the study, the Dutch Gait scale (gait), UI-SF (incontinence) and MoCA (dementia) will be used to assess the outcome of the shunt operation to monitor the severity and nature of the main symptoms during the follow-up in pre-implant, three months, one year and after two years. The SF-12V2 will be used in a similar mode to monitor the quality of life of the patients. Severity of the symptoms will also be assessed by the Kiefer Scale, which was developed directly to monitor patients with idiopathic normotensive hydrocephalus. Charlson comorbidity index will be used to monitor covariates. All clinical examinations by a neurosurgeon will monitor early and late complications of the short-circuit operation (infection, hemorrhage, overdrainage, underdrainage, shunt malfunction), the number of valve setting changes and their range, unscheduled checks and shunt revisions and other unexpected events.

The expected number of patients who will undergo all examinations after an annual check is 40 (20 and 20).

The expected benefit of the study is in particular to confirm the theoretical assumptions of an adjustable gravitational valve in patients with idiopathic normal pressure hydrocephalus and thus in improvement of the quality and life expectancy of these patients.