Transcranial Doppler: The influence of age and hematocrit in normal children

A total of 64 healthy children were studied with transcranial Doppler ultrasound (TCD). The purpose was to determine the relative influence of age and hematocrit (HCT) on intracranial arterial velocities and to establish approximate normal ranges for TCD findings based on age. Blood velocities decreased with advancing age and increasing HCT; velocities were highest in young children (aged 4-8) and declined toward adult levels by age 16. Unexpected findings included a significantly higher velocity in girls compared with boys, which was associated with a higher pulse rate but no difference in HCT. Modest left-to-right asymmetries (12 ± 10%) were observed in middle cerebral artery (MCA) velocities. Knowledge of the hematocrit did not add to the prediction of MCA velocities after age and sex were considered. We conclude that intracranial arterial velocities decline with increasing age and HCT in early childhood but that knowledge of the HCT is not necessary to interpret TCD findings in children without severe anemia. Side-to-side asymmetries of up to 30% do not necessarily represent abnormal conditions. Such information will be useful in the application of TCD to the detection of intracranial vessel stenosis in such diseases as moyamoya, sickle cell anemia, and arteritis.