Measuring Cerebrovascular Reactivity: Sixteen Avoidable Pitfalls.

Area of Science:

• Neuroscience
• Cardiovascular Science
• Medical Imaging

Background:

• Assessing cerebral vascular reactivity (CVR) commonly uses increased arterial partial pressure of carbon dioxide (PCO2) as a stressor.
• Despite CO2's ease of administration and safety, extracting clinically relevant flow data presents challenges.
• Over 2,000 individuals, many with cerebrovascular pathology, have been studied using CO2 and blood oxygen-level-dependent (BOLD) MRI.

Purpose of the Study:

• To systematically explore blood flow signal changes in response to precise hypercapnic stimuli.
• To understand the influence of stimulus characteristics (e.g., PCO2 magnitude, rate, pattern) on CVR.
• To interpret flow response characteristics (e.g., magnitude, speed, direction) and establish normal ranges.

Main Methods:

• Utilizing CO2 as a vasoactive agent to induce controlled hypercapnia.
• Employing blood oxygen-level-dependent (BOLD) MRI signal as a surrogate for cerebral blood flow.
• Analyzing data from over 2,000 individuals, including those with cerebrovascular disease.

Main Results:

• Detailed understanding of how stimulus aspects like baseline PCO2, oxygen levels, and CO2 change dynamics affect CVR.
• Improved interpretation of flow response features, including magnitude, speed, and direction.
• Development of methods to assess if CVR responses fall within normal ranges.

Conclusions:

• Accumulated insights from extensive research provide 16 "lessons learned" regarding CO2-based CVR assessment.
• These findings offer generalizable principles applicable to various CO2 stimuli and perfusion metrics.
• The research aims to enhance the scientific and clinical utility of CVR measurements.