Cardiovascular disease is a prominent cause of death. Among the markers of cardiovascular morbidity, the Augmentation Index (AIx) is the ratio between augmentation pressure and pulse pressure. AIx’s increase is associated to vascular stiffness and cardiovascular risk. Currently, AIx is measured employing pressure cuffs reaching the supra-systolic pressure. In order to avoid the use of pressure cuffs and to foster wearable technology capable of assessing vascular diseases, in this study a novel method to predict AIx from multisite photoplethysmography (PPG) through a Deep Convolutional Neural Network (DCNN) model is presented. Seventy-six volunteers (age: 20-80 years) were enrolled in the study. AIx was measured using a commercial instrument (Enverdis Vascular Explorer, VE), whereas PPG was recorded from right tibial, radial and brachial arteries, using a custom-made ECG-PPG system. A leave-one-out cross-validation procedure was performed to test DCNN generalization performances. The DCNN estimated AIx reaching a correlation coefficient between real and predicted AIx of r = 0.74 (p<0.001). Based on the cardiovascular risk provided by VE, a two-class classification (i.e. high- and low-risk) from the cross-validated output of the DCNN was performed. Since the two classes were not balanced, a bootstrap (10000 iterations) was implemented, obtaining an area under the Receiver Operating Curve of 0.93±0.04. Although further studies are necessary to provide a finer classification of the risk (i.e. high-, medium-, low-, very-low-risk) and to exploit the multisite PPG potentialities to early detect cardiovascular pathologies, these results could foster the employment of PPG and DCNN approaches for wearable device-based screenings of cardiovascular risk.
This paper summarizes the results of an EU project called ACTION: ACTive Implant for Optoacoustic Natural sound
enhancement. The project is based on a recent discovery that relatively low levels of pulsed infrared laser light are capable
of triggering activity in hair cells of the partially hearing (hearing impaired) cochlea and vestibule. The aim here is the
development of a self-contained, smart, highly miniaturized system to provide optoacoustic stimuli directly from an array
of miniature light sources in the cochlea. Optoacoustic compound action potentials (oaCAP) are generated by the light
source fully inserted into the unmodified cochlea. Previously, the same could only be achieved with external light sources
connected to a fiber optic light guide. This feat is achieved by integrating custom made VCSEL arrays at a wavelength of
about 1550 nm onto small flexible substrates. The laser light is collimated by a specially designed silicon-based ultra-thin
lens (165 um thick) to get the energy density required for the generation of oaCAP signals. A dramatic miniaturization of
the packaging technology is also required. A long term biocompatible and hermetic sapphire housing with a size of less
than a 1 cubic millimeter and miniature Pt/PtIr feedthroughs is developed, using a low temperature laser assisted process
for sealing. A biofouling thin film protection layer is developed to avoid fibrinogen and cell growth on the system.
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