Thudium, Marcus, Kornilov, Evgeniya, Moestl, Stefan, Hoffmann, Fabian, Hoff, Alex, Kulapatana, Surat, Urechie, Vasile, Oremek, Maximilian, Rigo, Stefano, Heusser, Karsten, Biaggioni, Italo, Tank, Jens, & Diedrich, André. (2025). Continuous wavelet based transfer function analysis of cerebral autoregulation dynamics for neuromonitoring using near-infrared spectroscopy. *Frontiers in Physiology, 16*, Article 1616125. https://doi.org/10.3389/fphys.2025.1616125
Near-infrared spectroscopy (NIRS) is a popular tool for monitoring brain activity by measuring how oxygen flows through the brain. Some advanced techniques, like the cerebral oxygenation index and Fast Fourier Transform (FFT)-based methods, are used to understand how the brain adjusts to changes in blood pressure (a process called cerebral autoregulation). However, these methods work best when the data being measured is stable over time and don’t respond quickly to sudden changes.
In this study, researchers explored a different method called wavelet transfer function analysis. Unlike the older methods, wavelet analysis can handle quickly changing data and still provide reliable results. The researchers improved an existing wavelet software tool to better measure brain responses, specifically focusing on how well the brain maintains steady blood flow under changing conditions.
They tested this improved tool using both simulated data and real data from five healthy men who experienced large changes in blood pressure and oxygen levels through a procedure that altered pressure in their lower bodies. The team compared results from their wavelet method to those from the traditional FFT method.
They found strong agreement between the two methods, especially for detecting changes in lower frequency brain activity, which is important for understanding how the brain regulates its blood flow. In some frequency ranges, the wavelet method even performed better than FFT, especially when the brain’s response changed quickly.
In conclusion, the wavelet method the researchers developed showed good accuracy and could be a powerful way to study how the brain regulates blood flow, especially in real-world situations where brain activity and blood pressure change over time.
Figure 1. Experimental setup to study response of cerebral blood flow, brain tissue oxygenation, cardiovascular parameters to lower body positive pressure (Protocol A) or negative pressure and hypoxia (Protocol B). ECG electrocardiogram, SpO2 peripheral oxygen saturation, TCD transcranial Doppler, MCAV middle cerebral artery velocity, NIRS near infrared spectroscopy, cTOI tissue oxygenation index by NIRS, BP blood pressure, SV stroke volume, CO cardiac output, LBP lower body pressure, LBNP lower body negative pressure, LBPP lower body positive pressure.
