Pulsatile microvascular cerebral blood flow waveforms change with intracranial compliance and age.

Significance: Diffuse correlation spectroscopy (DCS) is an optical method to measure relative changes in cerebral blood flow (rCBF) in the microvasculature. Each heartbeat generates a pulsatile signal with distinct morphological features that we hypothesized to be related to intracranial compliance (ICC).

Aim: We aim to study how three features of the pulsatile rCBF waveforms: the augmentation index (AIx), the pulsatility index, and the area under the curve, change with respect to ICC. We describe ICC as a combination of vascular compliance and extravascular compliance.

Approach: Since patients with Chiari malformations (CM) ($n=30$) have been shown to have altered extravascular compliance, we compare the morphology of rCBF waveforms in CM patients with age-matched healthy control ($n=30$).

Results: AIx measured in the supine position was significantly less in patients with CM compared to healthy controls ($p<0.05$). Since physiologic aging also leads to changes in vessel stiffness and intravascular compliance, we evaluate how the rCBF waveform changes with respect to age and find that the AIx feature was strongly correlated with age ($R_{\text{healthy subjects}}=-0.63$, $R_{\text{preoperative}\mathrm{CM}\text{patient}}=-0.70$, and $R_{\text{postoperative}\mathrm{CM}\text{patients}}=-0.62$, $p<0.01$).

Conclusions: These results suggest that the AIx measured in the cerebral microvasculature using DCS may be correlated to changes in ICC.