We developed and tested, via functional near-infrared spectroscopy (fNIRS), a method for recordings suitable to be applied to TBI patients, from their hospital admission, on healthy volunteers. The capacity to separate the optical signal between the intracranial (ICT) and extracranial tissues (ECT), and to monitor changes of hemoglobin in the ICT, were then tested in 18 healthy volunteers. Participants were scanned with a frequency-domain near-infrared spectroscopy device, during 5 Valsalva maneuvers (VM), in a simulated ICU environment.