Methodological considerations for cerebrovascular reactivity testing and analysis (1184.3)

Abstract

The cerebral microvasculature is exquisitely sensitive to carbon dioxide (CO2) and this cerebrovascular reactivity (CVR) is often used as a measure of cerebrovascular function. However, a review of the current literature reveals that the details of CVR protocols and analyses vary considerably between research groups. The objective of this study is to determine the sensitivity of CVR to these methodologies.We used dynamic end‐tidal forcing to measure CVR to CO2 under conditions of controlled normoxia, hypoxia and hyperoxia. Low levels of end‐tidal CO2 were obtained by hyperventilation; high levels by hypoventilation with added inspired CO2. Supine blood pressure and middle cerebral artery blood flow velocity (MCAv) were continuously recorded, as were inspired and expired oxygen (O2) and CO2.Here we discuss the physiological implications of different analysis techniques and also consider the effects on quantitative outcomes. We include the rationale and results of: different types of curve fitting; methods of normalizing MCAv; accounting for blood pressure changes; controlling O2; and introducing a phase lag between end‐tidal CO2 and MCAv.It is difficult to know whether CVR results are widely generalizable, or reflect unique protocols or analyses. This work is intended to stimulate discussion and encourage the publication of transparent methods in an effort to improve research reproducibility.Grant Funding Source: Supported by the Heart and Stroke Foundation of B.C. and Yukon (V.E.C.)