A comparison study of cerebral autoregulation assessed with transcranial Doppler and cortical laser Doppler flowmetry

Objectives: We compared autoregulation monitored with cortical laser Doppler flowmetry (LDF) and autoregulation monitored with transcranial Doppler (TCD) in the middle cerebral artery (MCA) to verify the hypothesis that, following brain trauma, cortical vessel autoregulation to intracranial hypertension is different than assessed in the MCA. Methods: Data collected from 29 head injured patients were analysed retrospectively. Arterial blood pressure (ABP), intracranial pressure (ICP), flow velocity (FV) of the MCA and cortical flux (LDF) were monitored. Indices of cortical autoregulation (Lx) and autoregulation of cerebral blood flow in the MCA (Mx) were calculated as a moving correlation coefficient between slow waves of LDF and cerebral perfusion pressure (CPP) (Lx) or FV and CPP (Mx), respectively. Intact autoregulation was indicated by negative values for Lx and Mx; disturbed autoregulation was reflected by positive values. Results: FV and LDF showed a high coherence in the slow wave spectrum of 1-4 cycles/min (mean: 0.79 +/- 0.12), indicating that similar information regarding autoregulation is carried by both signals. Mx and Lx correlated in all patients (R=0.43, p=0.02). On average, Lx was significantly higher than Mx; the mean difference was 0.13 +/- 0.38 (p=0.032), potentially due to severe intracranial hypertension above 40 mmHg, driving CPP values below 60 mmHg. Conclusion: After traumatic brain injury, cortical autoregulation appears to be worse than autoregulation assessed in the MCA during rising ICP and falling CPP. When CPP is above 60 mmHg, cortical assessed autoregulation is similar to autoregulation assessed in the MCA.