Noninvasive Monitoring of Intracranial Pulse Waves

Andreas Spiegelberg, Andrea Boraschi, Fariba Karimi, Myles Capstick, Arya Fallahi, Esra Neufeld, Niels Kuster, and Vartan Kurtcuoglu, IEEE Transactions on Biomedical Engineering, Volume 70, Issue 1, January 2023, online 28 June 2022; doi: 10.1109/TBME.2022.3186748

The clinical management of several neurological disorders relies on diagnostic information obtained by measuring intracranial pressure to determine craniospinal compliance. However, the procedures involved are invasive in nature. Here, we aimed to determine whether noninvasive measurement of naturally occurring periodic changes in the dielectric properties of the head could serve as a biomarker and surrogate for craniospinal compliance. To achieve this goal, we developed a highly sensitive device with head-mounted electrodes, and we characterized the properties of the device-electrode-head system through measurements involving healthy volunteers as well as computational and electromechanical modeling. The signals obtained from the volunteers revealed the characteristic cardiac and respiratory modulations of interest that can be attributed primarily to changes in the electrical resistance properties of the head. Hyperventilation tests subsequently confirmed that the measured signal contained information of intracranial origin: hyperventilation-induced end-tidal CO₂ reduction, which primarily affects intracranial vasculature, resulted in a signal amplitude decrease associated with a cardiovascular action. If confirmed in larger cohorts, including patients with various disorders, these results suggest that noninvasive measurement of changes in the dielectric properties of the head is a promising approach for obtaining a biomarker that could serve as a surrogate for craniospinal compliance.

The scientific and technical impact of the study can be summarized as:

• A novel capacitive device that noninvasively and sensitively measures changes in dielectric properties of the head through electrically isolated electrodes was developed
• Computational and electromechanical models of the static and dynamic components of the electrode-head-system impedance were established and found to be in agreement
• These models indicate that, while the measurement method is capacitive in nature, the periodic signal is generated primarily by changes in head-resistance associated with ohmic losses, with only minor contributions from capacitance changes
• Hyperventilation testing confirmed that the noninvasively acquired signal contains information of intracranial origin
• Further studies are needed to investigate whether this approach can be used to obtain a reliable surrogate of craniospinal compliance that is sufficiently reliable to replace invasive methods and thus serve as valuable diagnostic tool for space-occupying neurologic pathologies