The management of traumatic brain injury (TBI), in the critical care setting, centers around the reduction of ongoing secondary injury. Disruption in the brain’s ability to control its own blood flow, known as cerebrovascular reactivity (CVR), has been identified as a key contributor to ongoing secondary injury following TBI. Contemporary methods of monitoring CVR continuously rely on invasive intracranial pressure (ICP) monitoring. This limits the use of these ICP-based indices of CVR to the acute phase of TBI where ICP monitoring is already indicated. As a result, continuous examination of CVR has not previously been performed in the chronic phase of TBI or in healthy subjects.

Near infrared spectroscopy (NIRS)-based indices of CVR provide a less invasive alternative. They have been found to perform similarly to ICP-based indices, however, their examination in the clinical setting has been limited. In this thesis, the utility of NIRS-based indices of CVR following moderate-to-severe TBI was extensively examined.

The relationship between ICP- and NIRS-based indices of CVR was examined through machine learning and time series analysis techniques. Further, a novel, entirely non-invasive technique of measuring NIRS-based CVR was developed. This technique was employed to examine CVR in both healthy subjects and through the chronic phase of recovery from TBI. This allowed for insights to be gleaned into how CVR differs in these settings. Finally, the outcome association of NIRS-based CVR in the acute and chronic phase of TBI was studied.

This thesis provides a solid foundation for the further exploration of NIRS-based indices of CVR in TBI. Further, it opens the door to the continuous examination of CVR in pathophysiologic states outside of TBI.