Where the Evidence Is Advancing, Which Questions Remain Unanswered, and How Modern Studies Are Refining HBOT
Hyperbaric oxygen therapy, commonly abbreviated as HBOT, has established roles in conditions such as decompression sickness, arterial gas embolism, carbon monoxide poisoning, delayed radiation injury, selected advanced diabetic foot ulcers, refractory osteomyelitis, and compromised grafts or flaps.
Current research is moving beyond the broad question of whether oxygen under pressure produces biologic effects. Those effects are already well documented. Investigators are increasingly asking more clinically useful questions:
- Which patients are most likely to benefit?
- How early should treatment begin?
- What pressure and oxygen duration provide the best balance of benefit and risk?
- Which outcomes should determine whether treatment continues?
- Can biomarkers or imaging predict response?
- Are improvements durable after the treatment course ends?
The answers are indication specific. Research supporting HBOT for radiation cystitis cannot automatically be applied to traumatic brain injury, diabetic wounds, long COVID, or routine postoperative recovery. Each condition requires its own treatment rationale, comparison group, dosing strategy, and patient-centered outcomes.
Late Radiation Injury Is Producing Some of the Strongest New Evidence
Delayed radiation injury remains one of the most active areas of hyperbaric research. Radiation can progressively damage small blood vessels, reduce capillary density, increase fibrosis, and leave previously treated tissues chronically hypoxic.
The RICH-ART randomized trial previously demonstrated that HBOT improved patient-reported urinary symptoms in patients with chronic radiation cystitis. Five-year follow-up published in 2025 found that symptom improvements remained clinically meaningful among many initial responders. Of the 70 patients included in the long-term analysis, 48 met the study’s responder criteria after treatment. Some patients received an additional course when symptoms recurred. (PubMed)
These long-term findings are important because HBOT is intended to stimulate tissue and vascular remodeling, not simply produce temporary symptom relief during chamber exposure. The study also identified several priorities for future research, including optimal treatment protocols, predictive biomarkers, and health-economic evaluation. (PubMed)
Research involving late radiation effects after breast cancer treatment has produced more nuanced results. In a 2024 randomized clinical trial, offering HBOT did not significantly reduce pain in the intention-to-treat analysis, but it did reduce fibrosis. Among the smaller group of participants who completed treatment, both pain and fibrosis improved. Low treatment uptake demonstrated that a therapy can appear biologically effective while remaining difficult for patients to complete because of time, travel, or treatment burden. (PubMed)
A 2025 systematic review of comparative studies involving late bowel and bladder radiation injury continued to find evidence of benefit in selected patients while emphasizing heterogeneity in patient selection, protocols, and outcome measurement. (PubMed)
The research direction is therefore shifting from treating all delayed radiation complications as one category toward identifying which organs, symptoms, injury patterns, and stages respond most reliably.
Researchers Are Examining the Optimal Hyperbaric Oxygen Dose
A hyperbaric treatment is defined by more than the presence of oxygen. Pressure, oxygen-breathing time, air breaks, session frequency, and total treatment number all contribute to the dose.
Many established protocols were developed through clinical experience, physiologic reasoning, and institutional practice rather than direct randomized comparisons of different pressure levels. Current research is beginning to evaluate whether lower or higher pressures produce meaningful differences in outcomes and adverse effects.
A 2026 retrospective comparison of HBOT at 2.0 and 2.5 atmospheres absolute for hemorrhagic radiation cystitis found that fewer patients treated at 2.5 ATA experienced gross hematuria within one year. However, the time to recurrence and other urinary symptoms were similar, while adverse events were more frequent at the higher pressure. Because the study was retrospective and involved treatment at two different sites, randomized research is still needed before concluding that one pressure is superior. (Wiley Online Library)
This type of research reflects a central principle of modern hyperbaric medicine: more pressure is not automatically more therapeutic.
A higher oxygen partial pressure may increase tissue oxygenation and selected cellular responses, but it may also increase barotrauma, oxygen-toxicity risk, visual effects, and treatment intolerance. A lower-pressure protocol may be easier to tolerate but could require longer oxygen periods or more sessions to achieve a comparable biologic exposure.
Future comparative trials will need to evaluate several outcomes simultaneously:
- Symptom response
- Durability of benefit
- Adverse effects
- Treatment completion
- Number of sessions required
- Cost and resource utilization
- Patient quality of life
The most effective protocol may differ by diagnosis. The oxygen dose needed for an acute gas embolism is not necessarily the appropriate dose for a chronic radiation injury or diabetic foot ulcer.
Patient Selection Remains Central to Diabetic Wound Research
Research involving diabetic foot ulcers continues to produce mixed results because the term diabetic foot ulcer includes wounds with very different causes and healing potential.
Some ulcers are primarily neuropathic and exposed to ongoing pressure. Others are ischemic, infected, deeply invasive, or complicated by osteomyelitis. Studies also differ in vascular assessment, offloading quality, wound severity, surgical care, and definitions of healing or amputation.
Current research increasingly recognizes that HBOT should not be studied as a replacement for comprehensive diabetic foot care. It must be evaluated alongside:
- Effective pressure offloading
- Vascular assessment and revascularization
- Debridement
- Infection treatment
- Glucose management
- Nutritional support
- Appropriate wound dressings
The most clinically relevant question is not whether HBOT helps an average diabetic wound. It is whether it improves healing or limb preservation in a defined subgroup whose tissue remains hypoxic despite appropriately delivered standard care.
Modern studies are also exploring methods of identifying that subgroup. Transcutaneous oxygen measurement, toe pressure, Doppler waveforms, wound classification, perfusion imaging, and the wound’s early response to standard treatment may all contribute to more precise patient selection.
This precision is essential because a treatment can appear ineffective when applied to patients whose primary barrier is not oxygen responsive. HBOT cannot compensate for untreated arterial obstruction, continued pressure, retained necrotic tissue, or an undrained infection.
Infection Research Is Focused on Timing and Treatment Integration
Necrotizing soft tissue infections remain an important but difficult area of HBOT research.
The physiologic rationale includes increased oxygen tension in hypoxic tissue, support of leukocyte microbial killing, inhibition of selected anaerobic organisms, reduction of edema, and modulation of inflammatory injury. However, these infections require immediate surgery, antimicrobial treatment, and critical care. Randomized trials are difficult because the condition is uncommon, rapidly progressive, and clinically heterogeneous.
A 2025 prospective Scandinavian observational study found an association between HBOT and lower 30-day mortality. However, patients who received HBOT were less acutely ill at baseline, creating a substantial risk of selection bias. The investigators concluded that randomized research is still needed to determine whether HBOT itself caused the observed outcome difference. (PubMed)
Another 2025 study reported a stronger apparent mortality association among patients with larger wounds and higher APACHE II severity scores. These findings may help generate hypotheses about which patients should be prioritized in future trials, but they do not establish definitive treatment criteria. (PubMed)
Current infection research is therefore addressing several operational questions:
- How soon after the first debridement should HBOT begin?
- Which microbial or clinical patterns are most oxygen responsive?
- Should treatment be delivered once or more than once daily during the acute phase?
- Can HBOT reduce the amount of tissue removed during later operations?
- Does treatment improve survival independently of specialized-center care?
Until these questions are resolved, HBOT remains an adjunct. It must never delay surgical source control, antibiotic administration, resuscitation, or a necessary return to the operating room.
Trauma Research Is Moving Toward Function, Not Only Limb Survival
Earlier trauma research often focused on amputation, infection, or visible tissue necrosis. Newer studies increasingly recognize that long-term function may be equally important.
Severe crush injuries and open fractures can leave a limb technically intact but affected by chronic pain, stiffness, weakness, nerve injury, infection, repeated surgery, or poor quality of life. Research must therefore measure more than whether amputation occurred.
Important outcomes include:
- Amount of tissue necrosis
- Number of repeat operations
- Infection and osteomyelitis
- Fracture healing
- Need for reconstruction
- Pain and mobility
- Return to work
- Long-term limb function
This broader approach may identify meaningful benefits that a single short-term composite endpoint does not capture. It also prevents researchers from overstating success when a limb is preserved but remains severely impaired.
Future trials in acute traumatic ischemia will need to coordinate HBOT tightly with vascular repair, fasciotomy, fixation, debridement, and reconstructive surgery. Timing is likely to matter because HBOT is most biologically plausible while threatened tissue remains viable.
Neurologic Research Remains Promising but Investigational
The brain is a major focus of emerging hyperbaric research. Proposed mechanisms include improved oxygen availability, altered cerebral blood flow, angiogenic signaling, neuroplasticity, mitochondrial effects, and modulation of neuroinflammation.
These mechanisms have led investigators to study HBOT in persistent traumatic brain injury symptoms, post-concussion syndromes, stroke recovery, cognitive decline, and other neurologic conditions.
The evidence remains unsettled. Neurologic trials are especially difficult to interpret because pressurized air may not function as a completely inactive placebo. Even modest increases in pressure can alter gas partial pressures and produce physiologic effects. Symptoms such as fatigue, concentration difficulty, headache, sleep disturbance, and mood change are also influenced by rehabilitation, expectation, time, and concurrent treatment.
A registered blinded, adaptive, randomized, placebo-controlled trial is currently evaluating HBOT for mild to moderate traumatic brain injury in veterans and active-duty military personnel. The study is designed to address persistent uncertainty using stronger masking and adaptive trial methods. (ClinicalTrials.gov)
Until sufficiently rigorous trials demonstrate reproducible clinical benefit, neurologic uses outside recognized indications should be described as investigational. Mechanistic plausibility and changes on functional imaging do not automatically establish improved daily function.
Long COVID Research Illustrates Why Controlled Trials Matter
Early studies of HBOT for post-COVID conditions reported improvements in fatigue, cognition, sleep, pain, and quality of life. These findings generated interest because long COVID may involve endothelial dysfunction, inflammation, altered oxygen utilization, autonomic disturbance, and neurologic symptoms. (PubMed)
A 2025 randomized, double-blind, placebo-controlled phase 2 trial produced a more cautious result. Eighty participants received either 10 HBOT sessions or placebo treatment. Both groups improved, but there was no significant difference between HBOT and placebo in the primary short-term physical-function outcomes. (PubMed)
This trial does not prove that every possible hyperbaric protocol is ineffective for long COVID. It evaluated a defined course of 10 treatments in a particular population. However, it shows why uncontrolled improvement cannot automatically be attributed to HBOT.
Researchers still need to determine whether:
- A specific long COVID phenotype is more responsive
- More than 10 sessions are required
- Benefits are cognitive, autonomic, respiratory, or systemic
- Improvements persist after treatment
- The treatment is cost effective
- A truly credible sham protocol can be designed
Feasibility studies and additional registered trials are continuing to examine whether larger, well-controlled research is practical. (ClinicalTrials.gov)
For now, HBOT for long COVID should remain within appropriately reviewed research or carefully defined investigational settings rather than being represented as established therapy.
Biomarkers May Help Predict Who Will Respond
One of the most important research directions is the development of predictive biomarkers.
Current hyperbaric practice often relies on diagnosis, wound classification, clinical examination, imaging, tissue oxygen testing, and response over time. These methods are useful but do not always predict which individual patient will complete treatment successfully.
Potential research targets include:
- Transcutaneous oxygen response
- Endothelial and angiogenic markers
- Inflammatory cytokines
- Circulating progenitor cells
- Tissue perfusion imaging
- Microvascular density
- Metabolic or mitochondrial markers
- Baseline symptom severity
- Time from injury to treatment
A useful biomarker must do more than change after HBOT. It should predict a clinically meaningful outcome, such as wound closure, cessation of bleeding, tissue salvage, improved function, or reduced need for surgery.
Researchers must also distinguish between markers of oxygen exposure and markers of therapeutic response. An increase in arterial or tissue oxygen confirms that the dose reached the patient. It does not prove that the underlying disease process improved.
Patient-Reported Outcomes Are Becoming More Important
Traditional hyperbaric research frequently measured wound size, amputation, survival, or visible bleeding. These outcomes remain important, but they do not fully describe how treatment affects a patient’s life.
A patient with radiation cystitis may value uninterrupted sleep, freedom from clot retention, or the ability to travel without fear of bleeding. A person with late breast radiation injury may value reduced tissue tightness and improved shoulder movement. A trauma survivor may prioritize walking ability and return to work over the appearance of the wound.
Current and future studies increasingly need to include:
- Pain
- Mobility
- Urinary or bowel function
- Fatigue
- Sleep
- Cognitive function
- Independence
- Return to work
- Treatment burden
- Quality of life
Patient-reported outcomes were central to the RICH-ART research and helped demonstrate that HBOT’s effects on chronic radiation cystitis extended beyond a simple yes-or-no assessment of hematuria. (PubMed)
Research Must Account for Treatment Burden and Access
HBOT often requires attendance five days per week for several weeks. A scientifically effective treatment may still have limited real-world value when patients cannot access or complete it.
Research should therefore evaluate:
- Travel distance
- Missed work
- Caregiver requirements
- Transportation
- Insurance authorization
- Treatment discontinuation
- Chamber availability
- Cost per meaningful clinical outcome
The 2024 breast radiation trial demonstrated this challenge clearly. Only a minority of patients offered HBOT completed treatment, complicating interpretation of both effectiveness and real-world feasibility. (PubMed)
Health-economic research is particularly important for long treatment courses. Investigators must determine whether the cost of HBOT is offset by reductions in hospitalization, transfusion, surgery, amputation, long-term wound care, or loss of function.
The Next Phase of Hyperbaric Research
The field does not need more studies that group unrelated diagnoses together or measure only whether a biologic marker changed after oxygen exposure.
The highest-priority research questions are increasingly clear:
- Which patient phenotypes respond to HBOT?
- What is the minimum effective oxygen dose?
- When should treatment begin?
- Which standard therapies must be completed first?
- What outcomes justify continuing treatment?
- How durable are the benefits?
- Which adverse effects are pressure dependent?
- Can biomarkers guide treatment selection?
- Is HBOT cost effective compared with available alternatives?
Current research supports a disciplined view of hyperbaric medicine. Evidence continues to strengthen for selected delayed radiation injuries, while dose optimization and long-term outcomes remain active areas of study. Observational findings in severe infection are encouraging but require randomized confirmation. Neurologic conditions and long COVID remain investigational, with controlled trials producing mixed or negative results.
This is how a medical specialty matures. The objective is not to prove that HBOT works for everything or to dismiss it because evidence varies among indications. The objective is to identify where oxygen under pressure produces measurable, durable, and patient-important benefits, then deliver it at the safest and most effective dose.
