Grant: Travel Awards - Institute Community Support

The blood vessels in the brain are very sensitive to carbon dioxide (CO2). To measure how sensitive the blood vessels are, researchers often use a technique where they alter the amount of CO2 that individuals breathe while they are measuring the blood flow in the brain. However, a review of the current literature reveals that the methods that researchers use to modify CO2, and how they analyse their data, varies a lot between research groups. The objective of this study is to analyse a set of data in different ways to see if the results change depending on how the analysis is performed. 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 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.