Abstract
Cerebrovascular autoregulation (CA) is often impaired following traumatic brain injury. Established technologies and metrics used to assess CA are invasive and conducive for measurement, but not for continuous monitoring. We developed a trans-ocular brain impedance (TOBI) method that may provide non-invasive and continuous indices to assess CA. In this study, we monitored impedance metrics such as respiratory-induced impedance amplitude changes (dz) as well as a novel impedance index (DZx), which is a moving Pearson correlation between mean arterial pressure (MAP) and dz. Yorkshire swine were instrumented to continuously record ICP, MAP, and cerebral blood flow (CBF). TOBI was recorded by placement of standard ECG electrodes on closed eyelids and connected to a data acquisition system. MAP, ICP and CBF were manipulated utilizing an intravenous vasopressor challenge. TOBI indices (dz and DZx) were compared to the hemodynamic indicators as well as pressure reactivity index (PRx). During the vasopressor challenge, dz was highly correlated with ICP, CPP, and CBF (r = < − 0.49, p < 0.0001). ICP, CPP, and CBF had a mean percent increase (standard deviation) from baseline of 29(23.2)%, 70(25)%, and 37(72.6)% respectively while dz decreased by 31(15.6)%. Receiver operator curve test showed high predictive performance of DZx when compared to PRx with area under the curve above 0.86, with high sensitivity and specificity. Impedance indices appear to track changes in PRx and hemodynamics that affect cerebral autoregulation. TOBI may be a suitable less invasive surrogate to PRx and capable of tracking cerebral autoregulation.
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Acknowledgements
The authors would like to thank the Michigan Center for Integrative Research in Critical Care for their technical support.
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This study was supported by a grant from the Department of Defense (#W81XWH-18-1-0005).
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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Mohamad Tiba, Brendan McCracken, Danielle Leander, Carmen Colmenero, Brandon Cummings, and Nicholas Greer. The first draft of the manuscript was written by Mohamad Tiba, Brendan McCracken and Kevin Ward. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Dr. Tiba and Dr. Ward have intellectual property on the technology and methodology described through the University of Michigan. The technology has been licensed by New Vital Signs, Inc. in which Dr. Ward is a founder.
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All procedures outlined in this study adhere to the principles stated in the eighth edition of the Guide for the Care and Use of Laboratory Animals and were approved by the University of Michigan’s Institutional Animal Care and Use Committee.
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Tiba, M.H., McCracken, B.M., Leander, D.C. et al. Trans-ocular brain impedance index for assessment of cerebral autoregulation in a porcine model of cerebral hemodynamic perturbation. J Clin Monit Comput 35, 1007–1014 (2021). https://doi.org/10.1007/s10877-020-00556-1
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DOI: https://doi.org/10.1007/s10877-020-00556-1