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Pain & inflammation

Fibromyalgia and chronic pain

Controlled studies have measured pain scores, tender points, sleep and brain activity in people with fibromyalgia before and after a course of hyperbaric oxygen. The main trial reported reduced pain and changes in brain activity in the treated group.

Evidence so far
Early
Reading timeAbout 12 minutes

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Why this is being studied

Fibromyalgia is a long-term condition of widespread pain, fatigue, poor sleep and cognitive fog in which the brain and spinal cord appear to amplify ordinary sensations into pain. Imaging studies suggest altered blood flow and activity in pain-processing regions, and some researchers think low-grade inflammation and poor cellular energy supply play a part. Hyperbaric oxygen is being studied because it delivers very high levels of dissolved oxygen to tissue, which may influence inflammation, mitochondrial function and how the brain processes pain.

Where the evidence stands

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The mechanism

What is going on, and why this might help

What is going on in the body

Fibromyalgia and related chronic pain conditions are increasingly understood as disorders of pain processing rather than of the tissues where pain is felt. The central nervous system becomes sensitised: pain signals are amplified in the spinal cord and brain, descending inhibitory pathways that normally dampen pain are weaker, and functional imaging shows altered activity in regions such as the insula, anterior cingulate and prefrontal cortex. Microglia and astrocytes, the brain's immune cells, appear activated, producing cytokines including TNF-α and IL-1β that further sensitise neurones. Peripheral small-fibre nerve changes, poor sleep and mitochondrial dysfunction in muscle add to the picture.

Where oxygen comes in

The proposed mechanism targets central sensitisation. In animal models of neuropathic and inflammatory pain, hyperbaric oxygen reduces glial activation and spinal cytokine levels, and produces measurable analgesia that persists after treatment. In humans with fibromyalgia, SPECT imaging before and after a course of sessions has shown normalisation of activity in pain-processing regions, with hyperactive areas quietening and under-active areas increasing, alongside changes in pain thresholds. Improved mitochondrial function and reduced oxidative stress are proposed peripheral contributions. The hyperoxic-hypoxic paradox (Hadanny and Efrati 2020) provides the general framework for why intermittent exposure may induce lasting neuroplastic change rather than a transient effect.

How solid is this

Analgesic and anti-neuroinflammatory effects are well demonstrated in animal models. Human evidence in fibromyalgia comes from a crossover trial with brain imaging (Efrati et al. 2015) and a small earlier controlled study (Yildiz et al. 2004), so mechanisms are supported by trials but the trials are few, unblinded and from limited groups. Key references: Efrati et al. 2015; Hadanny and Efrati 2020.

Explainer illustration

The studies

Every study is laid out the same way: what the researchers wanted to find out, who took part, what they actually did, what they found, why it might work and where the limits are. No jargon, and a link to the original if you want to read it yourself.

Each study is laid out the same way: what the researchers asked, who took part, what they did, what they found, why it might work, and where the limits are. The clinician layer at the end of each one carries the numbers.

Paper 1

Hyperbaric oxygen therapy can diminish fibromyalgia syndrome: prospective clinical trial

Efrati et al. · PLOS ONE · 2015 · prospective, randomised, crossover-controlled trial, n=60

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What they asked

Fibromyalgia is a chronic pain condition in which the nervous system appears to amplify pain signals, and brain imaging often shows unusual patterns of activity in pain-processing regions. Efrati and colleagues at Assaf Harofeh Medical Centre in Israel asked whether a course of hyperbaric oxygen could change symptoms, pain thresholds and brain activity in women with long-standing fibromyalgia.

Who took part

Sixty women aged 21 to 67 were enrolled, all diagnosed at least two years earlier (average 6.5 years). Twelve left the study, mostly before treatment started, because of claustrophobia, ear discomfort or a decision not to enter the chamber. Forty-eight completed the trial: 24 treated immediately and 24 in a crossover group.

What they did

This was a prospective crossover trial rather than a blinded sham trial. One group had 40 sessions of 100 per cent oxygen at 2.0 ATA for 90 minutes, five days a week, over about two months. The other group first spent two months with no treatment (serving as their own control period), was reassessed, and then had the same 40-session course. Everyone was assessed before and after with a pressure dolorimeter (an instrument that measures how much pressure it takes to cause pain), tender-point counts, the Fibromyalgia Impact Questionnaire, the SF-36 quality-of-life survey, a psychological distress checklist and SPECT brain-perfusion scans.

What they found

During the two months of no treatment nothing changed. After the oxygen course, in both groups, pain thresholds rose, the number of tender points fell by roughly eight to twelve out of eighteen, and questionnaire scores for function, quality of life and distress improved, with large effect sizes. Several participants reduced or stopped analgesic medication. SPECT scans showed brain activity shifting towards a more typical pattern, with less over-activity at the back of the brain and more activity in frontal regions involved in dampening pain.

Why it might work

Breathing oxygen at twice normal pressure dissolves far more oxygen in blood plasma than usual, which the authors propose may improve energy supply to poorly perfused brain tissue, calm inflammatory signalling from glial cells, and support neuroplasticity, meaning the brain partially rewires its pain-processing circuits. This is a hypothesis supported by the imaging, not a proven mechanism.

Limits

This is a single-centre study of 48 women with no sham chamber, so participants knew they were being treated and expectation may account for part of the improvement in self-reported measures. Objective tests and scan analysis were blinded, which helps. There was no follow-up beyond a few weeks after the course, so durability is unknown. Funding came from the hospital research fund and academic donors with no commercial involvement.

Paper 2

Effectiveness of hyperbaric oxygen for fibromyalgia: a meta-analysis of randomized controlled trials

Wang et al. · Clinics and Practice · 2023 · meta-analysis of 4 RCTs, n=163

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What they asked

By 2022 several small randomised trials of hyperbaric oxygen for fibromyalgia had been published, with differing pressures and course lengths. Wang and colleagues in China set out to pool them and ask, across all the available controlled evidence, whether HBOT improves pain, overall fibromyalgia impact and tender points, and how often it causes side effects.

Who took part

Four randomised controlled trials met the criteria, two from Israel, one from Turkey and one from Spain, with 163 participants in total (82 receiving HBOT, 81 controls). Participants were mostly women, with an average age in the mid-40s. Follow-up averaged about eight weeks, ranging from three weeks to three months. One uncontrolled study was excluded.

What they did

The authors searched six databases up to May 2022, assessed each trial with the Cochrane risk-of-bias tool, and combined results using standardised mean differences. The trials themselves used 90-minute sessions five days a week, but with different pressures (roughly 1.45 to 2.4 ATA) and different course lengths, from 15 to 60 sessions. Control conditions also varied, including no treatment, usual medication and waiting-list comparisons; none used a convincing sham chamber.

What they found

Pooled together, HBOT was associated with a large improvement in the Fibromyalgia Impact Questionnaire and a large reduction in tender-point count. Pain scores on a visual analogue scale also moved in a favourable direction, but the result was not statistically significant because the trials disagreed with one another so strongly. Side effects were much more common with HBOT, about 25 times the rate in controls, though these were mainly middle-ear pressure problems that settled on their own without lasting harm.

Why it might work

The review discusses the same ideas raised by the individual trials: that very high oxygen delivery may reduce inflammatory signalling in the nervous system, improve mitochondrial energy production in muscle and brain, and encourage changes in brain regions that process pain. These remain proposed explanations rather than established facts.

Limits

Four trials and 163 people is a very small evidence base. None of the trials was judged low risk of bias; two were high risk, largely because participants could not be blinded and control groups were not sham-treated. Heterogeneity was very high (I-squared 77 to 96 per cent), meaning the pooled numbers should be treated as rough indications. Follow-up was short, so nobody knows how long any benefit lasts. The review was funded by Chinese national and regional science foundations.