Cerebrovascular impedance estimation with near-infrared and diffuse correlation spectroscopy

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Physics

Background:

• Cerebrovascular impedance (CVI) is intrinsically linked to cerebral autoregulation (CA), the brain's mechanism for maintaining stable cerebral blood flow (CBF) despite fluctuating cerebral perfusion pressure (CPP).
• Blood vessel impedance dynamics are crucial for stabilizing cerebral blood flow.
• Assessing CVI holds potential for quantifying CA and serving as a biomarker for neurological health.

Purpose of the Study:

• To develop and validate a noninvasive method for quantifying cerebrovascular impedance (CVI).
• To assess the relationship between CVI and cerebral autoregulation (CA).
• To explore CVI as a potential biomarker for cerebral health.

Main Methods:

• A novel, high-speed diffuse correlation spectroscopy (DCS) and continuous wave near-infrared spectroscopy (CW-NIRS) system was developed for simultaneous, noninvasive measurement of cerebral blood flow (CBF) and blood volume.
• Cerebrovascular impedance (CVI) was calculated as the spectral ratio of blood volume to blood flow changes, using blood volume as a surrogate for blood pressure.
• The technique was validated on six healthy human volunteers undergoing postural changes (head of bed tilting) to induce changes in CVI.

Main Results:

• The combined DCS-NIRS system successfully measured simultaneous CBF and blood volume changes.
• Averaged across subjects, a decrease in CVI was observed during head of bed tilting.
• These CVI changes were reversible upon returning to the baseline position.

Conclusions:

• A noninvasive DCS-NIRS system was successfully developed to measure CVI.
• CVI measurement using this technique can quantify CA.
• CVI shows promise as a valuable metric for assessing cerebral health, especially in clinical scenarios involving altered CPP.