mTBI Mechanisms of Action of HBO2 for Persistent Post-Concussive Symptoms

Inclusion Criteria * On active duty (TRICARE beneficiary) at the time of consent and through the 6-month visit or a Veteran, as well as Active Duty military who become Veterans after enrollment. * Men and women 18-65 years of age at the time of study enrollment. * Able to equalize middle ear pressure in a test of chamber pressure and tolerate the chamber environment. * Able to speak and read English, as primary language. * Agrees to and appears able to participate in all outcome assessments. * Agrees to provide blood samples for clinical lab tests. * Demonstrates the ability to offer informed consent and signs the study informed consent document. * Participants stationed or living outside the Colorado Springs/Denver, Colorado area must be willing and able to travel. A reliable companion may accompany the participant if travel supervision is required. * Active duty participants must obtain a letter of support from a supervisor or commanding officer prior to the outcome assessments (and travel, if necessary) to the OAC. Participants must have a history of at least one (minimum requirement) mild traumatic brain injury (mTBI) with persistent symptoms that meets all the following criteria: * Brain injury that occurred more than 3 months prior to baseline screening at the local site, with the most recent injury occurring no more than 5 years prior to randomization. * Most recent traumatic brain injury (TBI) occurred on active duty. * TBI was caused by non-penetrating trauma or b…