HBOT Radar: They Scanned ME/CFS Brains Before and After 40 Sessions. The Thalamus Changed (October 2025)

This article is part of the HBOT Radar series, where we summarize the latest published hyperbaric oxygen therapy research.

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Disclaimer: This article is intended for educational and informational purposes only. It summarizes published medical research conducted in clinical settings and does not evaluate Brain Spa Hyperbaric products. The hyperbaric chambers offered on this website are non-medical wellness devices and are not intended to diagnose, treat, cure, or prevent any disease. Do not make medical decisions based on this article — consult a qualified healthcare professional.

📌 They Scanned ME/CFS Brains Before and After 40 Sessions. The Thalamus Changed.

🔍 What this study explored

There's a disease that affects roughly 0.1 to 0.7% of the world's population, has no approved treatment, no reliable diagnostic test, and until recently was dismissed by much of the medical establishment as psychological. It's called ME/CFS — myalgic encephalomyelitis/chronic fatigue syndrome.

ME/CFS isn't "being tired." Profound fatigue that doesn't improve with rest. Cognitive impairment patients call brain fog. Autonomic dysfunction. Pain. And the hallmark: post-exertional malaise, where minor physical or mental effort triggers a crash that can last days.

That last symptom is why studying anything in this population is genuinely difficult. A treatment requiring forty hospital visits asks a lot of someone who can crash from a shower.

Since COVID-19, ME/CFS has become far more visible — SARS-CoV-2 is now among the most common triggers, and 90% of the patients in this study developed the illness after a COVID infection.

A team at Charité — Universitätsmedizin Berlin, Germany's largest university hospital, set out to test whether hyperbaric oxygen therapy could help. And they didn't just measure symptoms. They put patients in an MRI scanner before and after, and compared their brains against healthy controls.

🌬️ The protocol — and one design decision that mattered

• Patients: 30 completed treatment (mean age 42, 23 women, 7 men). Diagnosed by Canadian Consensus Criteria with PEM lasting at least 14 hours. Mean illness duration 27 months. All moderately to severely disabled.
• Chamber: Multiplace Starmed-Quadro (HAUX), at the hyperbaric medicine centre of Vivantes Klinikum im Friedrichshain, Berlin
• Pressure and gas: 100% oxygen via mask at 2 ATA
• Session: 90 minutes, with five-minute air breaks every 20 minutes
• Course: 40 sessions over 8 to 16 weeks, up to five per week, outpatient. Average time to complete: 13 weeks.
• Comparison group: 30 age- and sex-matched healthy controls — for brain imaging only, not for treatment

That "8 to 16 weeks" detail is the interesting part, and it wasn't accidental.

The post-COVID trial this study builds on used the same 40 sessions at the same pressure — but packed into a fixed 8 weeks at five sessions per week. The Charité team knew that ME/CFS patients are considerably sicker than post-COVID patients generally, and that travelling to a treatment centre and sitting upright for 90 minutes carries a real risk of triggering PEM.

So they built in flexibility: same total dose, spread across up to twice as long, with patients taking breaks between sessions whenever they needed to prevent symptom flares.

That decision appears to have worked, which we'll come back to.

Important: This is a preprint. It has been posted on medRxiv but has not yet been peer-reviewed.

This study was conducted in a clinical hospital setting under medical supervision. Results from clinical research cannot be directly applied to other settings or devices — always consult a healthcare professional.

📊 Key findings

Physical function improved — for about a third of patients, substantially

The primary outcome was the SF-36 Physical Functioning score, a self-reported measure where higher is better.

It improved significantly during treatment: a mean increase of 6.3 points on the final day of HBOT (p = 0.006), with an effect size of Hedges' g = 0.71 — moderate to large. Four weeks after finishing, the improvement was still significant at 4.5 points (p = 0.047, g = 0.51).

But means hide the more interesting picture. The researchers defined a clinically meaningful individual response as at least a 10-point gain. Four weeks after treatment, 11 of 30 patients (37%) hit that threshold. The largest individual improvement was 35 points.

So this wasn't a treatment that nudged everyone slightly. It appears to have worked well for roughly a third of patients and less for the rest — which is a genuinely different clinical picture, and one worth stating plainly.

Fatigue and pain dropped, with large effect sizes

Fatigue, measured by the Chalder Fatigue Scale, fell by 2.93 points at four weeks post-treatment (p < 0.001), with an effect size of g = −0.89 — a strong effect. Both mental and physical fatigue components improved.

Pain improved by 10.25 points on the SF-36 pain domain (p = 0.002, g = 0.79).

The objective tests improved too — and this matters

Self-reported questionnaires in an unblinded study invite an obvious objection: patients knew they were being treated. So the researchers ran physician-assessed physical tests at baseline and four weeks after.

Sit-to-stand test (how many times you can stand up from a chair in one minute): median rose from 14 to 17.5 repetitions (p = 0.001, g = 0.66).

Handgrip strength: median increase of 1.14 kg (p = 0.048, g = 0.40).

Processing speed (Symbol Digit Modalities Test): improved from −1.07 to −0.7 standard deviations below normative values (p = 0.011, g = 0.52).

These are measured, not reported. They don't eliminate expectation effects — effort on a physical test can be influenced by belief — but they're harder to dismiss than a questionnaire alone.

An unexpected autonomic finding

During a passive standing test, resting heart rate didn't change. But maximum standing heart rate increased after treatment (p < 0.001, g = 0.65), and the difference between lying and standing heart rate rose from 16 to 24 bpm.

The researchers suggest this may reflect improved baroreflex sensitivity — the body responding more robustly to the challenge of standing up, rather than failing to respond. In a population where 13 of 30 patients had comorbid POTS, that's an interesting signal.

The brain scans: thalamic hyperconnectivity normalized

This is the part that makes the study novel.

Before treatment, ME/CFS patients' brains differed from healthy controls in a specific way. The thalamus — the brain's central relay station, routing sensory and motor information to the cortex — showed abnormally increased connectivity with sensorimotor regions (precentral and postcentral gyri, superior parietal lobule) and visual regions (lateral occipital cortex, lingual gyrus, cuneus).

The researchers interpret this as possible impaired filtering: heightened sensory gain, or thalamocortical circuits working too hard. It's consistent with the sensory overload, motor slowing, and cognitive fog patients describe.

After 40 sessions, that hyperconnectivity was no longer detectable. Comparing patients post-treatment against healthy controls showed no significant differences.

And the connection to symptoms held: patients who met the responder threshold showed substantially larger reductions in thalamic hyperconnectivity than non-responders (p < 0.001). Responders showed widespread connectivity reductions; non-responders showed only small clusters.

Brain volume, by contrast, didn't change at all — no differences between patients and controls, or before and after treatment. That supports the idea that ME/CFS involves functional network dysregulation rather than structural brain damage.

Cognition and pain improved regardless of responder status

A nuance easy to miss: improvements in processing speed and pain were comparable in responders and non-responders.

In other words, patients whose physical function didn't improve still got better on cognition and pain. Whatever HBOT is doing, it doesn't appear to be a single effect that either works or doesn't — it may act on several systems somewhat independently.

🩺 Who dropped out, and why

Thirty-seven patients started. Seven didn't finish:

• 4 discontinued due to pressure-related pain in the sinuses and ears
• 2 due to a feeling of tightness and anxiety in the chamber
• 1 due to recurrent upper respiratory tract infections

The study states explicitly that none discontinued due to PEM or worsening of ME/CFS symptoms.

For anyone familiar with the history of exertion-based interventions in ME/CFS, that sentence carries weight. It also appears to be a direct result of the flexible scheduling — the authors credit the extended timeline and permitted breaks for the high adherence and absence of PEM-related dropouts.

Side effects among those who completed: ear pressure or mild ear pain (43%) and reversible myopia (57%) — both typical for hyperbaric oxygen at this pressure and duration. None were severe or permanent.

Patient experience: 77% reported subjective improvement, and 87% said they would want HBOT again.

⚖️ What this study can't tell us

No control group. This is the central limitation and the authors say so directly. Every patient received HBOT. Without a sham arm, the improvements can't be definitively attributed to the treatment rather than to time, attention, or expectation. The brain imaging findings carry the same caveat.

It's a preprint. Not yet peer-reviewed. Methods, statistics, and conclusions haven't been independently vetted.

Thirty patients. Enough to detect effects of this size, not enough to be definitive.

The sickest patients were excluded. Anyone unable to leave their home due to illness severity was not eligible. Of 95 interested patients, 28 were excluded for contraindications or because they judged themselves too ill to attend regular appointments. Another 39 were excluded for living more than 100 km away. Whatever this study shows, it doesn't extend to severe, housebound ME/CFS.

Dose questions remain open. The authors list them: optimal number of sessions, optimal frequency, durability of effects, and which patients benefit most. A second cohort is currently running a shortened 20-session protocol to start answering the first of those.

Predicting who responds is currently unreliable. Better baseline general health, lower baseline physical fatigue, and better baseline processing speed all correlated with greater improvement — but a logistic regression model combining them had only modest discriminative ability (AUC = 0.66). Not good enough to guide treatment decisions.

Declared interests: most authors report none. The senior author has consulting and speaking arrangements with several pharmaceutical companies and holds a leadership position in the German ME/CFS Society. One co-author sits unpaid on the board of the German Diving and Hyperbaric Medicine Society. The funders had no role in the study's design, analysis, or reporting.

📌 Takeaway for the community

• Thirty ME/CFS patients (90% post-COVID triggered) completed 40 HBOT sessions at 2 ATA. Physical functioning improved significantly, and 37% achieved a clinically meaningful individual gain — with the largest single improvement being 35 points
• Fatigue and pain both improved with large effect sizes, and objectively measured tests — sit-to-stand, handgrip strength, processing speed — improved as well
• Brain imaging showed ME/CFS patients had abnormally hyperconnected thalamic circuits compared with healthy controls. After treatment, that pattern normalized, and the largest reductions occurred in patients who improved most clinically
• No patient discontinued due to PEM or symptom worsening. The seven early discontinuations were for ear and sinus pressure pain, chamber-related anxiety, and infection
• The researchers deliberately spread 40 sessions across 8 to 16 weeks rather than a fixed 8-week schedule, specifically to reduce PEM risk — and credit that decision for the high adherence
• No control group, small sample, preprint status, and exclusion of housebound patients all limit what can be concluded. A controlled trial is the necessary next step
• This study was conducted in a clinical hospital setting under medical supervision — results cannot be directly applied to other settings or devices

Source: https://www.medrxiv.org/content/10.1101/2025.10.29.25339096v1

Kim L, Cammà G, Kedor Peters C, Mantwill M, Müller O, Leprêtre N, Heindrich C, Rust R, Krill M, Hartung TJ, Reeß LG, Krohn S, von Heymann C, Wittke K, Finke C, Scheibenbogen C. Hyperbaric oxygen therapy improves clinical symptoms and functional capacity and restores thalamic connectivity in ME/CFS. medRxiv preprint. 2025 Oct 31. doi: 10.1101/2025.10.29.25339096.

Educational disclaimer

This content summarizes findings from published medical research for educational purposes only.

The hyperbaric chambers sold on this website are non-medical wellness devices and are not intended to diagnose, treat, cure, or prevent any disease.

The studies discussed here were conducted in clinical medical settings using medical-grade interventions. The inclusion of research summaries does not imply that similar outcomes can be achieved using non-medical wellness devices.