I-VED (In-Vivo Embolic Detector) refers to a patented electrical impedance spectroscopy device of exceptional high spatial and temporal resolution (European Patent Office, Application Number: EP14188200.1), aiming to sense bubbles presence in the human body during Decompression Sickness (e.g. in astronauts, scuba divers, metro workers, etc). I-VED technique measures for varying excitation frequency values the electrical impedance of a medium composed of dispersed phases having different electrical properties, such as gas bubbles in blood or other tissues. The innovative hardware and signal analysis/processing have improved sensitivity and accuracy about two and one orders of magnitude, respectively, comparing to any other conventional method allowing for capturing considerably slight impedance changes as those expected due to bubbles presence in the human body.
I-VED technique was first calibrated and validated in-vitro and then was tested in-vivo on anesthetized swines having similar cardio-vascular system with that of humans. It was demonstrated that the novel impedance spectroscopy technique is sufficiently sensitive to sense the presence of bubbles ~20 μm in swines’ blood flow by placing electrodes over partially conductive tissues & skin. Next, a series of impedance measurements was performed for bubbles detection applying self-adhesive ECG pads at the sites of chest and forearm of twenty divers, according to relevant European safety regulations. Bubbles were either injected in the blood circulation through the cephalic vein, or generated due to decompression as a result of divers’ treatment (“dry dive”) in the Decompression Chamber of Hyperbaric Medicine Lab, in St. Paul General Hospital of Thessaloniki, Greece. It is mentioned that in all cases the presence of bubbles was validated by means of ultrasound measurements. The obtained results show that the presence of a few bubbles injected through the cephalic vein are successfully detected when ECG pads are placed either at the forearm or at the chest. In both cases, the use of Continuous Wavelet Transform in the frequency component 0.5-10 Hz of the acquired signals enhances considerably bubble sensing. Concerning bubbles due to decompression, ultrasound measurements showed that very few tiny bubbles (not constituting a real DCS incident) are generated only in the body of a few divers. However, several signal processing tools are still tested (such as FFT and STFT, wavelets, spectrograms, Hilbert Huang Transform, etc) in an effort to correlate any features to bubbles presence.