After an acute brain injury, the brain’s ability to keep blood flow stable is often disrupted. This protective process is difficult to monitor in clinical practice, yet it plays a key role in recovery. A new study by Giulio Bicciato and colleagues from University Hospital Zurich and the University of Zurich explores whether subtle, non-invasive measurements of brain oxygenation could help assess this function and predict patient outcomes.
Assessing brain function in the acute phase after injury remains challenging. Many physiological processes that influence recovery cannot be directly observed with standard imaging or routine monitoring. To address this gap, researchers investigated whether slow changes in brain oxygenation could provide additional information about how the injured brain responds and adapts. The study focused on near-infrared spectroscopy (NIRS), a bedside technique that uses light to measure changes in brain oxygen levels through the skull. Rather than analyzing average oxygenation, the researchers examined very slow oscillations in the NIRS signal – gentle, rhythmic fluctuations that are thought to reflect how blood vessels gradually adjust blood flow. This ability to adapt blood flow is a key component of the brain’s protective response after injury.
Twenty mechanically ventilated patients with acute brain injury underwent short, carefully controlled increases in oxygen delivery. During these periods, NIRS signals were recorded from the forehead. The researchers then measured how strongly the slow oxygen oscillations responded and compared these responses with clinical severity scores and long-term neurological outcomes.
Patients who later showed more favorable recovery displayed a clear increase in slow oxygen oscillations during the oxygen challenge, whereas patients with poorer outcomes showed little or no response. In patients with subarachnoid hemorrhage, the largest subgroup in the study, the strength of this response was associated with disease severity. Importantly, it also independently predicted how well patients functioned in daily life months later.
These findings suggest that slow fluctuations in brain oxygenation may offer a new, non-invasive way to assess blood-flow regulation after acute brain injury. Although the study is exploratory, it supports the idea that future neuromonitoring approaches could become more individualized, helping clinicians better understand and anticipate recovery trajectories.
Reference: Bicciato G, de Trizio I, Brandi G, Willms JF, Keller E. NIRS frequency analysis to evaluate cerebrovascular reactivity after acute brain injury. Neurophotonics. 2025; 12(4). https://doi.org/10.1117/1.NPh.12.4.045011
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