Transcranial Doppler velocities in a large, healthy population

Transcranial Doppler (TCD) ultrasonography has been extensively used in the evaluation and management of patients with cerebrovascular disease since the clinical application was first described in 1982 by Aaslid and colleagues TCD is a painless, safe, and noninvasive diagnostic technique that measures blood flow velocity in various cerebral arteries. Numerous commercially available TCD devices are currently approved for use worldwide, and TCD is recognized to have an established clinical value for a variety of clinical indications and settings. Although many studies have reported normal values, there have been few recently, and none to include a large cohort of healthy subjects across age, race, and gender. As more objective, automated processes are being developed to assist with the performance and interpretation of TCD studies, and with the potential to easily compare results against a reference population, it is important to define stable normal values and variances across age, race, and gender, with clear understanding of variability of the measurements, as well as the yield from various anatomic segments.

To define normal TCD values in a healthy population, we enrolled 364 healthy subjects, ages 18-80 years, to have a complete, nonimaging TCD examination. Subjects with known or suspected cerebrovascular disorders, systemic disorders with cerebrovascular effects, as well as those with known hypertension, diabetes, stroke, coronary artery disease, or myocardial infarction, were excluded. Self-reported ethnicity, handedness, BP, and BMI were recorded. A complete TCD examination was performed by a single experienced sonographer, using a single gate nonimaging TCD device, and a standardized protocol to interrogate up to 23 arterial segments. Individual Doppler spectra were saved for each segment, with velocity and pulsatility index (PI) values calculated using the instrument's automated waveform tracking function. Descriptive analysis was done to determine the mean velocities and PI, and all data were analyzed for changes by decade of age, sex race, handedness, BMI, and BP.

Among the key intracranial segments, mean blood flow velocities (MBFV) were highest in the MCA and lowest in the PCA across all ages, sexes, and ethnic groups. There was no difference in the MBFVs between left and right side segments of the Circle of Willis, with the exception of the distal M1 (P = .022) and the C1 (P < .0001), both slightly higher on the left. MBFV were higher among women than men in all segments except for the OA. MBFV decreased with advancing age in both men and women, but this was specific to Caucasian subjects. There were lower velocities in the OA for non-Caucasians. The PI was lower in the left VA (P < .0001), and for most segments was lower in women than men. The PI increased with age in all segments for women, but only in some segments for men, and this finding was also specific to Caucasian subjects. The yield of usable data ranged from 99.7% for the VA and BA, to 88.2% for C2.

Our study provides normal, reference TCD values for a large cohort of healthy subjects across a wide range of age, sex, and race groups. We observed decreased MBFV and increased PI with aging, and higher MBFV in women. There were few differences in MBFV related to side or ethnicity, but the MFBV and PI changes with age were specific to Caucasians. We provide means and standard deviations of MBFVs across various demographic groups in key intracranial arteries. Such normal TCD values across age, gender, and ethnic groups in healthy subjects represent a useful reference tool for detecting individuals with TCD values outside normal limits and at increased vascular risk. TCD studies in large multiethnic populations are still required to determine differences in brain hemodynamics across various ethnic groups.