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BackgroundElectroencephalography (EEG) is increasingly used for monitoring the depth of general anaesthesia, but EEG data from general anaesthesia monitoring are rarely reused for research. Here, we explored repurposing EEG monitoring from general anaesthesia for brain-age modelling using machine learning. We hypothesised that brain age estimated from EEG during general anaesthesia is associated with perioperative risk.MethodsWe reanalysed four-electrode EEGs of 323 patients under stable propofol or sevoflurane anaesthesia to study four EEG signatures (95% of EEG power ResultsClinical exploration in ASA 1 or 2 patients revealed that brain age was positively correlated with intraoperative burst suppression, a risk factor for general anaesthesia complications. Surprisingly, brain age was negatively correlated with burst suppression in patients with higher ASA scores, suggesting hidden confounders. Secondary analyses revealed that age-related EEG signatures were specific to propofol anaesthesia, reflected by limited model generalisation to anaesthesia maintained with sevoflurane.ConclusionsAlthough EEG from general anaesthesia may enable state-of-the-art age prediction, differences between anaesthetic drugs can impact the effectiveness and validity of brain-age models. To unleash the dormant potential of EEG monitoring for clinical research, larger datasets from heterogeneous populations with precisely documented drug dosage will be essential.

— The photoacoustic effect in liquids, generated by nanotransducers excited withshort laser pulses, offers high contrast imaging and promising medical treatment techniques.Understanding the role of the thermal boundary resistance (TBR) and the laser pulse durationin the generation mechanism of acoustic waves is essential to implement efficient photoacousticnanotransducers [1–3]. This work theoretically investigates, for the paradigmatic case ofwater-immersed gold nanoplates, gold-nanocylinders [2] and carbon nanotubes [3], the role of theTBR [4] and laser pulse duration in the competition between the launching mechanisms: thethermophone and the mechanophone. In the thermophone, the nanoparticle acts as a nanoheaterand the wave is launched by water thermal expansion. In the mechanophone, the nanoparticledirectly acts as a nanopiston. Specifically, for a laser pulse duration far exceeding the heat transfertime from the nanostructure to the surronunding water, the thermophone prevails. For theopposite case the mechanophone dominates. Activation of the mechanophone effect is sought totrigger few nanometers wavelength sound waves in water, matching the nanotransducer acousticfrequencies. This is at variance with respect to the commonly addressed case of water-immersednanotransducer excited with ns laser pulses, where only the thermophone effect significantly contributes.The present findings might be of impact in fields ranging from nanoscale non-destructivetesting to water dynamics at the meso to nanoscale. Furthermore, the results point to high-TBR,liquid-immersed nanoparticles as potentially efficient photoacoustic nanogenerators [5], with theadvantage of keeping the liquid environment temperature unaltered.REFERENCES1. Prost, A., F. Poisson, and E. Bossy, “Photoacoustic generation by a gold nano-sphere: Fromlinear to nonlinear thermoelastics in the long-pulse illumination regime,” Phys. Rev. B, Vol. 92,115450, 2015.2. Diego, M., M. Gandolfi, S. Giordano, F. Vialla, A. Crut, F. Vall´ee, P. Maioli, N. Del Fatti,and F. Banfi, “Tuning photoacoustics with nanotransducers via thermal boundary resistanceand laser pulse duration,” Appl. Phys. Lett., Vol. 121, 252201, 2022.3. Diego, M., M. Gandolfi, A. Casto, F. M. Bellussi, F. Vialla, A. Crut, S. Roddaro, M. Fasano,F. Vall´ee, N. Del Fatti, P. Maioli, and F. Banfi, “Ultrafast nano generation of acoustic wavesin water via a single carbon nanotube,” Photoacoustics, Vol. 28, 100407, 2022.4. Casto, A., F. M. Bellussi, M. Diego, N. Del Fatti, F. Banfi, P. Maioli, and M. Fasano, “Waterfilling in carbon nanotubes with different wettability and implications on nanotube/water heattransfer via atomistic simulations,” Int. J. Heat Mass Transf., Vol. 205, 123868, 2023.5. Yu, K., Y. Yang, J. Wang, G. V. Hartland, and G. P. Wang, “Nanoparticle-fluid interactionsat ultrahigh acoustic vibration frequencies studied by femtosecond time-resolved microscopy,”ACS Nano, Vol. 15, 1833–1840, 2021.