Hyperbaric Oxygen Therapy: Mechanisms, Evidence, and Chamber Types

## What Is Hyperbaric Oxygen Therapy? Hyperbaric oxygen therapy (HBOT) involves breathing 100% pure oxygen while inside a pressurised chamber at greater than normal atmospheric pressure — typically 1.5 to 3.0 atmospheres absolute (ATA). At sea level, air contains 21% oxygen and the atmosphere exerts 1 ATA of pressure. HBOT elevates both variables simultaneously. The physics are straightforward. At 2.0 ATA breathing 100% O₂, the partial pressure of oxygen in the lungs increases approximately 10-fold compared to breathing room air at 1 ATA. By Henry's Law, this drives dissolved oxygen directly into blood plasma (not just haemoglobin), enabling oxygen delivery to areas with compromised circulation where red blood cells cannot reach. ## Established Clinical Applications HBOT has a well-established evidence base in specific clinical contexts. The Undersea and Hyperbaric Medical Society (UHMS) recognises 14 approved indications, including: **Wound healing** — The best-supported non-emergency use. A 2010 Cochrane review (Kranke et al.) found HBOT significantly improved the chance of wound healing in diabetic foot ulcers versus standard care. The mechanism involves neovascularisation: elevated oxygen stimulates VEGF (vascular endothelial growth factor) and collagen synthesis in hypoxic wound tissue. **Decompression sickness** — The original indication. Dissolved nitrogen bubbles in tissue are reabsorbed faster under pressure. HBOT remains the standard of care for divers who surface too quickly. **Carbon monoxide poisoning** — High-pressure oxygen displaces CO from haemoglobin and cytochrome c oxidase with far greater speed than breathing room air. Treatment within 6 hours reduces the risk of delayed neurological sequelae. **Radiation tissue injury** — Post-radiation soft tissue necrosis and osteoradionecrosis (bone death from radiation) respond to HBOT. A 2012 Cochrane review found benefit for mandibular osteoradionecrosis in particular. **Necrotising soft tissue infections** — Used as an adjunct to surgery and antibiotics, where elevated oxygen is directly bacteriostatic against anaerobic organisms. ## Emerging and Off-Label Applications Research into HBOT's potential extends well beyond its approved indications. Results are promising but require more replication before clinical adoption. **Traumatic brain injury and concussion** — Multiple small trials suggest HBOT (1.5–2.0 ATA, 40 sessions) improves cognitive function and post-concussion symptoms. A 2013 randomised trial by Wolf et al. in *Journal of Neurotrauma* showed significant cognitive improvements in veterans with mild-to-moderate TBI. The 2022 Tel Aviv University studies by Shai Efrati's group showed HBOT reversed measurable white matter microstructure damage in chronic TBI at 1-year follow-up. **Longevity and cellular senescence** — A 2020 study by Hachmo et al. in *Aging* (Tel Aviv University) found that 60 HBOT sessions at 2.0 ATA produced a significant reduction in senescent T-cells (by 37% for CD28−CD57+ T cells) and increased telomere length in peripheral blood mononuclear cells — an unusual finding given that most interventions shorten or have no effect on telomeres. This single study requires replication, but represents a compelling signal. **Post-COVID neurological symptoms** — A 2022 randomised controlled trial by Zilberman-Itskovich et al. in *Scientific Reports* demonstrated that HBOT significantly improved cognitive function, energy, sleep quality, and pain in long COVID patients versus a sham control group. **Stroke recovery** — Several trials show improved neurological outcomes when HBOT is used in the sub-acute phase following ischaemic stroke, particularly in patients with penumbral tissue (viable but non-functioning brain tissue surrounding the infarct core). ## Hard Chambers vs Soft Chambers This distinction is clinically significant and frequently misrepresented in the wellness market. **Hard chambers (monoplace or multiplace)** - Reach 1.5–3.0 ATA - Deliver 100% medical-grade oxygen - Required for all UHMS-approved clinical indications - Typically found in hospitals, wound care centres, and licensed hyperbaric clinics - Sessions are supervised by trained hyperbaric technicians and physicians **Soft chambers (mHBOT)** - Reach 1.1–1.5 ATA maximum - Use ambient air (21% oxygen) unless supplemental oxygen is added via mask - Cannot deliver equivalent dissolved oxygen to hard chambers at therapeutic doses - Widely used in wellness centres, sports recovery, and athlete training - Evidence supporting soft chamber use at 1.3 ATA is limited to a handful of small studies The physiological effects differ significantly. At 1.3 ATA breathing air, the dissolved oxygen increase is modest — roughly 30% above normal versus the 10-fold increase at 2.0 ATA breathing 100% O₂. Soft chambers are not equivalent to clinical HBOT for wound healing, TBI, or other medical applications. For general recovery, inflammation reduction, and subjective wellbeing, they may offer benefit, but this should not be conflated with clinical evidence from hard chamber studies. ## What a Typical Protocol Looks Like For clinical indications, standard protocols involve **40 sessions** (sometimes called "dives") at 1.5–2.5 ATA, each lasting 60–90 minutes, usually delivered daily Monday–Friday over 8 weeks. Emergency indications (CO poisoning, decompression sickness) use different acute protocols. Wellness soft chamber sessions are typically 60 minutes at 1.3 ATA, used 3–5 times per week for 4–8 weeks. ## Contraindications HBOT has a small but important list of contraindications: - **Untreated pneumothorax** (collapsed lung) — absolute contraindication - **Certain chemotherapy drugs** (bleomycin, doxorubicin, cisplatin) — relative contraindication - **Claustrophobia** — a practical concern manageable in multiplace chambers - **Ear and sinus barotrauma** — requires the ability to equalise pressure; active upper respiratory infections are a temporary contraindication - **Optic neuritis** — relative contraindication All reputable HBOT facilities conduct a medical intake screening before the first session.