From Light to Insight: Hemodynamic Models for Optical Monitoring of the Brain in Cardiac Arrest

Optical neuromonitoring has matured from descriptive oxygenation trends to model-informed quantification of cerebral physiology. This review synthesizes evidence on near-infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS), and laser Doppler flowmetry (LDF) for monitoring cerebral blood flow (CBF), blood volume (CBV), and cerebral metabolic rate of oxygen (CMRO2) during cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). We focus on using hemo-metabolic models, especially Coherent Hemodynamic Spectroscopy (CHS) and the BrainSignals models, as a framework to explain what optical signals do (and do not) tell us about microvascular oxygen transport and mitochondrial metabolism. We compare linear vs. non-linear CHS formulations for large perturbations (e.g., CA/CPR), summarize emerging depth-sensitivity and extracerebral-signal suppression strategies, and outline how DCS pairs with NIRS to link oxygen delivery with use. Across animal and human studies, we highlight convergent patterns (rapid oxygenation collapse, partial reperfusion during CPR, lagging metabolic recovery), recurring limitations (extracerebral contamination, calibration to absolutes, motion), and standardization efforts required for translation. We conclude with a pragmatic roadmap for bedside implementation: harmonized physiological endpoints (CBF, CMRO2, rCCO), reporting standards, and model-informed thresholds to guide resuscitation. This review aims to bridge instrumentation, physiology, and modeling to enhance neuroprotective care in CA/CPR.