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The CO2 stimulus for cerebrovascular reactivity: Fixing inspired concentrations vs. targeting end-tidal partial pressures. | LitMetric

The CO2 stimulus for cerebrovascular reactivity: Fixing inspired concentrations vs. targeting end-tidal partial pressures.

J Cereb Blood Flow Metab

Department of Anesthesiology University Health Network, and Department of Physiology, University of Toronto, Toronto, Canada

Published: June 2016

AI Article Synopsis

  • Cerebrovascular reactivity (CVR) studies focus on how cerebral blood flow is regulated and measured using carbon dioxide (CO2) as a stimulus with advanced magnetic resonance techniques.
  • The assessment of CVR typically evaluates how changes in blood flow respond to changes in CO2 levels, with precision being a key concern in the methodology used.
  • This text examines the trade-offs between costly computerized methods and simpler, improvised methods for measuring CVR, highlighting issues like misleading precision claims and lack of standardization in the latter.

Article Abstract

Cerebrovascular reactivity (CVR) studies have elucidated the physiology and pathophysiology of cerebral blood flow regulation. A non-invasive, high spatial resolution approach uses carbon dioxide (CO2) as the vasoactive stimulus and magnetic resonance techniques to estimate the cerebral blood flow response. CVR is assessed as the ratio response change to stimulus change. Precise control of the stimulus is sought to minimize CVR variability between tests, and show functional differences. Computerized methods targeting end-tidal CO2 partial pressures are precise, but expensive. Simpler, improvised methods that fix the inspired CO2 concentrations have been recommended as less expensive, and so more widely accessible. However, these methods have drawbacks that have not been previously presented by those that advocate their use, or those that employ them in their studies. As one of the developers of a computerized method, I provide my perspective on the trade-offs between these two methods. The main concern is that declaring the precision of fixed inspired concentration of CO2 is misleading: it does not, as implied, translate to precise control of the actual vasoactive stimulus - the arterial partial pressure of CO2 The inherent test-to-test, and therefore subject-to-subject variability, precludes clinical application of findings. Moreover, improvised methods imply widespread duplication of development, assembly time and costs, yet lack uniformity and quality control. A tabular comparison between approaches is provided.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4908627PMC
http://dx.doi.org/10.1177/0271678X16639326DOI Listing

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