Cerebral blood flow regulation during general anesthesia

In this thesis, we studied cerebral hemodynamics in man during general anesthesia, specifically by quantifying interactions between cerebral autoregulation (CA) and other known or potential of cerebral blood flow (CBF) modulators. CA is generally defined as the ability of the brain to guarantee a stable CBF despite blood pressure fluctuations and is regarded as a fundamental physiological principle of intracranial circulation. However, studying the mechanisms of CBF has historically been, and remains, a significant challenge. Central to this difficulty is the brain’s location within a closed space, which limits accurate in vivo observation. Technological advancements have made observations of cerebral hemodynamics increasingly accessible using non-invasive methods in awake subjects. However, anesthesia exacerbates the observational difficulties of studying CA. Our group published and validated a method for inducing consistent and large enough oscillations of blood pressure using positive pressure ventilation, which allows for studying CA during general anesthesia. The aim of this thesis was to investigate CA under various conditions during general anesthesia.
Our findings align with existing literature, though we challenge several persistent assumptions regarding CA that hamper data interpretation. These outdated concepts continue to appear despite consistent evidence rejecting them. We argue that CA is, at best, inadequately defined and resists the accumulating body of evidence that calls for a rigorous revision and mechanistic explanation. We conclude by proposing a new framework for interpreting observations at the correct level of abstraction.