Cerebral Hemodynamic Effects of Oxygen and Antioxidants (CHEOXANT)

This study is called CHE-OX-ANT (Cerebral Hemodynamic Effects of Oxygen and Antioxidants). It is a single-center, academic research project led by the Department of Intensive Care at Erasme Hospital (Université Libre de Bruxelles). The study focuses on understanding how the brain and blood vessels react when a person breathes pure oxygen and how these effects may be influenced by giving vitamin C, an antioxidant. Oxygen is one of the most common treatments in hospitals. While it can be life-saving, too much oxygen may sometimes cause harmful effects, such as oxidative stress (an imbalance between damaging molecules called free radicals and the body's defenses). Antioxidants like vitamin C may help counteract these effects. The goal of the study is to examine how a short period of high oxygen (30 minutes of 100% oxygen through a mask) affects cerebral hemodynamics, microcirculation, microperfusion, blood markers (levels of oxidative stress, antioxidant activity, and microparticles). The study will also test whether giving vitamin C beforehand changes these responses compared to a placebo (saline solution). Each volunteer will participate in two sessions, one week apart. Before each session, participants will receive either vitamin C (given intravenously) or a placebo (saline). They will not know which one they receive. Then, they will breathe 100% oxygen for 30 minutes through a facial mask. Measurements will be taken at three times: before oxygen (t0), just after oxygen (t1), and 1 hour later (t2). These include: ultrasound of the brain's blood flow (transcranial Doppler), measurements of skin perfusion and blood samplings.