Abstract
Mean cerebral blood flow velocity (mean-CBFV) obtained from Transcranial Doppler (TCD) poorly predicts cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH). Variability descriptors of mean-CBFV obtained during extended TCD recordings may improve this prediction. We assessed the feasibility of generating reliable linear and non-linear descriptors of mean-CBFV variability using extended recordings in aSAH patients and in healthy controls. We also explored which of those metrics might have the ability to discriminate between aSAH patients and healthy controls, and among patients who would go on to develop vasospasm and those who would not. Bilateral mean-CBFV, blood pressure, and heart rate were continuously recorded for 40 minutes in aSAH patients (n = 8) within the first 5 days after ictus, in age-matched healthy controls (n = 8) and in additional young controls (n = 8). We obtained linear [standard deviation, coefficient of variations, and the very-low (0.003-0.040 Hz), low (0.040-0.150 Hz), and high-frequency (0.15-0.4 Hz) power spectra] and non-linear (Fractality, deterministic Chaos analyses) variability metrics. We successfully obtained TCD recordings from patients and healthy controls and calculated the desired metrics of mean-CBFV variability. Differences were appreciable between aSAH patients and healthy controls, as well as between aSAH patients who later developed vasospasm and those who did not. A 40-minute TCD recording provides reliable variability metrics in aSAH patients and healthy controls. Future studies are required to determine if mean-CBFV variability metrics remain stable over time, and whether they may serve to identify patients who are at greatest risk of developing cerebral vasospasm after aSAH.
Highlights
Mean cerebral blood flow velocity obtained from Transcranial Doppler (TCD) poorly predicts cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage
We explored which metrics might have the ability to assess differences in variability between aSAH patients and healthy controls, and among patients who would go on to develop vasospasm and those who would not
Of the patients with aSAH, three developed cerebral vasospasm according to our criteria
Summary
Mean cerebral blood flow velocity (mean-CBFV) obtained from Transcranial Doppler (TCD) poorly predicts cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage (aSAH). Increasing attention has been directed toward investigating the role of variability in cerebral blood flow velocity as a predictor of vasospasm in aSAH.[5] Both linear and non-linear descriptors of variability have been investigated in this context.[5] Linear metrics, such as standard deviations, averages, and total power spectra values, have shown limited predictive accuracy, likely as a consequence of the multiple factors that influence cerebral perfusion over time, including systemic blood pressure, respiratory rate, arterial content of carbon dioxide (PCO2), cardiac output, hematocrit, and cerebral metabolism.[6,7,8] Non-linear descriptors such as the use of fractal and chaotic characteristics of cerebral blood flow velocity may better predict vasospasm[7] though it is not clear which metrics might have the best predictive capabilities.[5,9,10,11] it remains unclear if it is feasible to perform TCD recordings that would reliably generate linear and non-linear estimates of variability under routine clinical conditions In this feasibility study, we sought to determine whether we could perform adequate TCD recordings to assess a series of linear and non-linear metrics of cerebral blood flow variability in patients with aSAH as well as in healthy controls. We selected a comprehensive set of variability descriptors (see Supplementary Table S-1) in the time and frequency domains as well as non-linear indices of fractality and deterministic chaos that have been investigated previously.[5,7,12,13,14,15]
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