The specific aim of this trial is to make OxiplexTS a clinically usable instrument, especially for research and clinical diagnosis and monitoring of sleep disorders. An additional goal is to determine the usefulness of this instrument for providing measurements in various clinical situations including intensive care management or prolonged surgical procedures, such as cardiothoracic surgery that require critical information of brain oxygenation and hemodynamics. This trial emerges from previous phase I and phase II studies which determined the feasibility of using OxiplexTS to assess brain vascular autoregulatory responses to hypoxic stimuli.