Respiration Can Trigger Cerebrovascular Reactivity: A Novel Method to Quantify Cerebrovascular Resistance Dynamics...

Area of Science:

• Cardiovascular Imaging
• Neurovascular Research
• Respiratory Physiology

Background:

• Cerebrovascular resistance dynamics (CRD) are crucial for brain health.
• Current methods for assessing CRD are often invasive or lack specificity.
• Quantifying respiration's impact on CRD is essential for understanding cerebrovascular control.

Purpose of the Study:

• To develop and validate a gas-free MRI technique for directly quantifying respiration-driven CRD.
• To utilize the internal carotid artery (ICA) to external carotid artery (ECA) flow ratio (ratio_Q) to isolate CRD from cardiac influences.
• To assess the repeatability and responsiveness of this novel MRI framework.

Main Methods:

• Real-time phase-contrast MRI (RT-PC) was employed at the C2-C3 cervical level.
• Dedicated software extracted respiratory-frequency components of ICA and ECA flow (Q_ICA, Q_ECA).
• The ratio_Q (Q_ICA/Q_ECA) was calculated; its mean (aver_ratio_Q) indicated baseline cerebrovascular resistance, and its pulsatility index (PI_ratio_Q) quantified CRD.

Main Results:

• The ratio_Q method demonstrated excellent repeatability for mean values (ICC=0.96) and good repeatability for pulsatility index (ICC=0.79).
• Sustained deep breathing significantly increased cerebrovascular resistance, shown by a decrease in aver_ratio_Q (2.5 to 1.7).
• Respiration-driven CRD (PI_ratio_Q) significantly increased by ~69% during deep breathing compared to free breathing.

Conclusions:

• The gas-free RT-PC approach using the ICA-to-ECA flow ratio offers a stable and reproducible measure of respiration-driven CRD.
• This method effectively separates cerebrovascular resistance modulation from cardiac effects.
• The technique holds potential for developing faster and more accessible cerebrovascular resistance assessment strategies.