RHYTHMIC OSCILLATIONS WITH A WAVELENGTH OF 0.5-2-MIN IN TRANSCRANIAL DOPPLER RECORDINGS

We have studied intracranial pressure (ICP) B-waves and their associat ion with rhythmic changes in blood flow velocity (B-wave equivalents) by transcranial Doppler sonography (TCD) monitoring. In overnight TCD recordings in 10 normal young adults, these rhythmic changes in blood flow velocity were higher and more frequent during REM sleep and sleep stage 1 than during other sleep stages. B-wave equivalents also had a longer wavelength during REM sleep. Their relative frequency in these normal subjects over one night ranged from 35 to 73%. Peripheral resi stance (assessed by the Pourcelot index) was lower and heart rate was higher at the peak of these oscillations. These results support the hy pothesis that ICP B-waves are caused by vasodilation. A non-linear rel ationship between ICP and blood flow velocity was found during B-waves in 9 of 11 patients with suspected NPH. Our results throw doubt on th e suggestion that a relative frequency of less than 80% B-wave activit y can be a valid indicator for shunt responsiveness in patients with s uspected normal pressure hydrocephalus (NPH). ICP recordings in suspec ted NPH should be accompanied by polysomnography to avoid misleading r esults due to variability of B-wave appearance dependant on sleep patt ern.