Slow oscillations in middle cerebral artery cerebral blood flow velocity and aging

A recent study using near infrared spectroscopy (NIRS) showed that low frequency oscillations of regional cerebral blood flow (CBF) decline with age. Using transcranial Doppler ultrasound (TCD), it is possible to monitor similar fluctuations in cerebral blood velocity (CBV) in basal cerebral vessels. Such oscillations have been used widely in the assessment of cerebral autoregulation. We postulated that it should be possible to observe similar age related reductions in the amplitude of slow waves recorded using TCD.

We studied 187 patients with head injury, who were admitted to Addenbrooke's Neuro Critical Care unit between 1992 and 1998. Intermittent recordings of CBV were undertaken using TCD, which were subsequently analysed using software developed in-house. Power spectra were computed in the very low frequency (VLF: 0.01-0.05 Hz) and low frequency (LF: 0.07-0.11 Hz) ranges for all signals and a regression analysis was performed to assess the correlation between power in each frequency band and age.

No significant correlation was found between VLF or LF power and age (VLF: r=0.037; p=0.63; LF: r=-0.05, p=0.517).

While remaining cogniscent of the complex nature of our patient group, we find that age dependent reductions in CBF oscillations seen using NIRS do not translate to recordings of CBV in the middle cerebral artery in patients with head injury.