Time-domain diffuse correlation spectroscopy at large source detector separation for cerebral blood flow recovery

In this research we evaluate the performance of the time-domain diffuse correlation spectroscopy (td-DCS) technique at three source-detector separation (SDS) of 1.5, 2 and 2.5 cm to recover cerebral blood flow (CBF). In order to evaluate the performance of each SDS to recover the blood flow, we carry out series of stimulations including the post-occlusive reactive hyperaemia (PORH) test on healthy subject’s arm and brain cortex perfusion on the forehead of healthy adult volunteers during breath hold (BH) and hyperventilation (HV) tasks. The research protocol was approved by the bioethics committee at the military medical chamber in Warsaw, Poland (Approval No. 17/23).The PORH test was carried out at each SDS separately on both left and right arms of four healthy volunteers (three females, one male, average age of 32). Data in each trial acquired using the following time scheme: 60 s of baseline followed by 40 s of arm occlusion (cuff pressure of 180 mmHg) and 60 s of release which was repeated twice per trial at each SDS separately. Thus, 16 data set for each SDS were collected.During the BH and HV, healthy volunteers (four females and two males with the average age of 36) were sitting on an armchair in a comfortable position (with body angle of 45°). The BH task consisted of a 60 s baseline, 30 s holding the breath without an initial inhale or exhale and 60 s recovery. The HV task, started with 60 s baseline, followed by 40 s attempt to fully exhale and inhale to maximize the respiratory exchange ratio and 60s recovery. Each task was repeated twice for every SDSs.