Methods for the advanced analysis of bio-signals acquired in a non-hospital environment for the support of fragile subjects

This PhD dissertation focuses on the design and validation of advanced methods for analyzing cerebral hemodynamic biosignals acquired through functional transcranial Doppler (fTCD), with the aim of supporting the rehabilitation and care of vulnerable individuals. The goal is to provide objective, non-invasive and accessible tools for functional brain monitoring following properly designed stimuli, particularly in patients recovering from stroke or affected by progressive neurodegenerative diseases. Due to its high vascularization, the brain relies on sophisticated autoregulatory mechanisms, supported by peculiar arterial architectures like the Circle of Willis, to maintain perfusion and compensate for local hemodynamic imbalances. Among these mechanisms, functional hyperemia refers to the localized increase in cerebral blood flow that accompanies neuronal activation, ensuring adequate energy supply to activated regions. This response engages the entire cerebrovascular network, from the large cerebral arteries to the microcirculation, where neurovascular coupling takes place through dynamic adjustment in vascular tone. The resulting hemodynamics changes can be precisely measured using the fTCD, which monitors in real-time any changes in blood flow velocity in large cerebral arteries. In this thesis work, the possibility of quantitatively assessing the effectiveness of the rehabilitation process in terms of cerebral hemodynamics was first explored in the context of stroke, a condition that typically involves lateralized deficits. Furthermore, the use of the hemodynamic lateralization index, derived from the difference in flow in the two-correspondent hemispheric cerebral arteries during unilateral tasks, was investigated as a potential biomarker of functional recovery and rehabilitation assessment. Experiments were conducted on healthy participants using highly lateralized motor and visual tasks, to characterize interhemispheric flow dynamics and establish a normative reference dataset. This reference is necessary to understand how hemispheric activation differs in individuals with unilateral brain damage, contributing to characterize the interhemispheric differences in pathological versus healthy populations