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Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding

What is the central question of this study? We developed and validated a ‘stimulus index’ (SI; ratio of end‐tidal partial pressures of CO2 and O2) method to quantify cerebrovascular reactivity (CVR) in anterior and posterior cerebral circulations during breath holding. We aimed to determine whether the magnitude of CVR is correlated with breath‐hold duration. What is the main finding and its importance? Using the SI method and transcranial Doppler ultrasound, we found that the magnitude of CVR of the anterior and posterior cerebral circulations is not positively correlated with physiological or psychological break‐point during end‐inspiratory breath holding. Our study expands the ability to quantify CVR during breath holding and elucidates factors that affect break‐point.