Post-traumatic stress disorder (PTSD), affecting approximately 6% of the general population and up to one-third of individuals exposed to combat zones and disasters, is a significant contributor to morbidity and mortality among IDF personnel. Hyperbaric oxygen therapy (HBOT), in which patients breathe oxygen at a partial pressure higher than 1 atmosphere in a hyperbaric chamber, has been investigated in the context of treating a wide range of neuropsychiatric disorders, including PTSD and mild traumatic brain injury (mTBI).

Four controlled studies conducted in patients with mTBI, about half of whom also suffered from PTSD, have yielded conflicting conclusions regarding the potential efficacy of hyperbaric therapy. A single study involving approximately 30 patients with PTSD without mTBI demonstrated significant clinical improvement; however, it was characterized by several methodological limitations-chief among them the absence of blinding or a placebo control. None of the studies conducted to date have reported long-term findings (beyond one year), included patients with a short duration of symptoms ("early PTSD"), or included female participants.

The aim of the proposed study is to conduct a prospective, double-blind, controlled investigation of the biological effect of hyperbaric therapy in PTSD, continuously throughout the hyperbaric treatment course, at the end of treatment, and during a substantial follow-up period of two years after treatment completion.

We intend to include adult participants who are capable of providing informed consent and who meet DSM-5 diagnostic criteria for PTSD. In order to maintain a pragmatic study with high external validity, exclusion criteria will be limited to those indicating risk (concrete suicidality, or a history of manic or psychotic disorder) or factors likely to impair treatment efficacy (incompatibility with hyperbaric chamber treatment, inability to complete the full treatment protocol, or pregnancy). Participants who miss a substantial number of treatments (five consecutively or one-third of the total treatments) will be withdrawn from the study.

The primary outcome measure will be the CAPS-5 questionnaire. In addition, PTSD symptom questionnaires, surveys assessing cognitive, executive, affective functioning, and health-related quality of life will be administered. An exploratory outcome will focus on sleep quantity and quality and physiological monitoring using wearable devices, currently considered the most promising biomarker in the context of PTSD.

Following enrollment and the provision of informed consent, balanced randomization will be performed with respect to covariates previously described as potential confounders (such as age, duration, and severity of symptoms, …). Participants will receive 60 hyperbaric treatments, five days per week, at either 2.0 atmospheres or 2.5 atmospheres. Both the participants and the evaluating clinical staff will be blinded to treatment allocation.

Inclusion Criteria:

• Age over 18 years and up to 80 years
• Ability to understand the researcher's explanation and give informed consent.
• Any sex or gender (unlike previous studies, a significant effort will be made to include women in this study)
• A diagnosis of PTSD according to DSM-5 criteria with a severity that warrants discharge from military service.

Exclusion Criteria:

• The lack of ability to attend 120 daily (5 times/week) treatments at the INMI
• Current or past psychotic disorder
• Evidence of active suicidal ideation
• Evidence of past or present manic disorder
• Difficulty equalizing pressures, including pulmonary emphysema, significant sinusoidal obstruction, eustachian tube dysfunction, or an pneumothorax that is not drained.
• Known or suspected pregnancy.

All data collection will be carried out solely by the investigators outlined below. A designated clinical research form (CRF) using microsoft excel will be created to handle all data collected. All identified data will be saved on a designated unclassified (בלמ"ס) password protected computed. Access will be restricted to the abovementioned investigators. The CRF will be encrypted by a 128 bit RAS protocol. Removing all identifiers (including dates - to be replaced by time intervals, names, addresses, ID, military ID and phone numbers) and coding the information will be performed by Mj. Dror Ofir, PhD, who'll be keeping the coding key. Handling coded information will be performed on a separate, unclassified, password protected and designated computer, access to which will be restricted to investigators handling data analysis as detailed below.