The carotid artery as an alternative site to the middle cerebral artery for reproducible estimates of autoregulation index.

Temporal insonation is not always possible for the middle cerebral artery (MCA) for blood flow velocity (BFV) measurements, to estimate cerebral autoregulation. We compared BFV and cerebral autoregulation estimates from the common-carotid (CCA) and internal-carotid arteries (ICA) with the MCA. BFV was measured at the CCA, ICA and MCA, synchronously with blood pressure, heart rate and end-tidal CO2 and was recorded onto a data acquisition system. The autoregulation index (ARI) estimated using the Tiecks model. Eleven healthy volunteers (7 women, 33 ± 9 years old) were recruited. BFVs in the MCA, CCA and ICA were 60.3 ± 8.9, 64.4 ± 6.5 and 69.2 ± 4.8 cm/s, respectively. ARI estimates were not significantly different (5.6 ± 0.8, 6.0 ± 1.1 and 5.9 ± 0.5, respectively). Good reproducibility over repeated measurements was evidenced by low coefficient of variation of standard error of measurement for BFV and ARI. The CCA and ICA are alternatives to the MCA, where insonation is impossible, because of an absent trans-temporal window or where it cannot be tolerated, such as in patients with head injury.