Pocket-size medical spirometer comprising a housing and a measurement unit, for measuring rate of total flow when a user exhales through the spirometer. Specifically, a medicament comprising the said derivative or a salt thereof as an active ingredient is used for preventive andor therapeutic treatment of a neurodegenerative diseases caused by abnormal activity of GSK3\u03b2 such as Alzheimer’s disease. A device is used to divide the gas stream, the device having a plurality of conduits in fluid communication with a plenum.