Why Is Carbon Dioxide Present in a Pressurised Oxygen Chamber? CO₂, the Bohr Effect & Safety Explained
CO₂ is not simply a “waste gas”. It is a powerful regulator of breathing, blood pH and haemoglobin’s affinity for oxygen.
But that physiology does not mean that adding more CO₂ is automatically beneficial. Concentration, partial pressure, duration, monitoring and the person exposed all matter.
Carbon dioxide affects breathing drive, blood acidity and oxygen release from haemoglobin. The Ekonstal chamber specification and the corrected published chamber study describe CO₂ as a partial pressure of approximately 0.7–2 kPa at 1500 hPa total pressure. This is technically different from saying “0.7–2% CO₂”. At 150 kPa total pressure, 0.7–2 kPa corresponds to roughly 0.47–1.33% of the gas mixture, assuming a uniform mixture.
Partial pressure is not the same thing as percentage concentration
The chamber manufacturer Ekonstal specifies an absolute chamber pressure of about 1500 hPa, or 150 kPa. Its published carbon-dioxide parameter is approximately 0.7–2 kPa partial pressure.
This distinction matters for both physiology and safety. A chamber can have a CO₂ partial pressure higher than normal ambient air because the total pressure is also higher, while the percentage concentration is a separate quantity.
Why does CO₂ change how we breathe?
Carbon dioxide is one of the main signals controlling ventilation. When arterial CO₂ rises, chemoreceptors increase breathing so that more CO₂ can be exhaled.
Controlled human experiments show that breathing 1–2% inspired CO₂ can increase ventilation and can also raise arterial CO₂ and lower blood pH, depending on the individual and the exposure conditions.
How does carbon dioxide affect haemoglobin and oxygen release?
The Bohr effect is established human physiology: higher CO₂ and lower pH reduce haemoglobin’s affinity for oxygen, which can favour oxygen unloading in tissues.
This is part of the body’s normal oxygen-transport system. Active tissues produce CO₂ and acids, helping haemoglobin release oxygen where metabolism is high.
It does not prove that deliberately raising inspired CO₂ to any chosen concentration improves whole-body oxygen delivery, recovery or health. The normal tissue-level mechanism and an externally enriched breathing environment are not the same experiment.
What do controlled CO₂ studies tell us?
| Study | Exposure | Main finding | Limit |
|---|---|---|---|
| Ellingsen et al., 1987 | 1% and 2% inspired CO₂ in healthy adults, short exposures | Arterial PCO₂ rose and pH fell; ventilation increased but did not completely compensate. | Very small study; mostly minutes, not two hours. |
| Anthonisen & Dhingra, 1978 | 1–2% CO₂ during hyperoxia and hypoxia | Low inspired CO₂ altered ventilation, with individual variability. | Only six participants and short steady-state exposures. |
| Kujawski et al., 2020; corrected 2024 | 10 × two-hour chamber sessions at 1500 hPa with O₂, CO₂ and H₂ partial pressures controlled | Changes in some cognitive, fatigue and biochemical outcomes were reported. | No control group; pressure and three gases changed together, so CO₂ cannot be isolated. |
| Hypobaric-flight feasibility study, 2026 | 0.1% vs 1.0% CO₂ for 6 hours in hypobaric hypoxia, 17 healthy adults | 1% CO₂ increased ventilation and improved several oxygenation measures in that hypoxic setting. | Different pressure, lower oxygen environment and different purpose from Oxygen Clinic. |
Why older percentages should not be copied into new articles
The 2020 chamber paper was formally corrected in 2024 because the gas-pressure information had been incorrectly reported. The corrected publication now describes the atmosphere using partial pressures: oxygen 32–40 kPa, carbon dioxide 0.7–2 kPa and hydrogen 0.4–0.5 kPa at a total pressure of 1500 hPa.
For new Oxygen Clinic content, those corrected units are the safer technical reference. Older versions quoting values such as 37% O₂, 1.079% CO₂ and 0.44% H₂ should not be treated as the current definitive specification without reconciling them against the corrected paper and manufacturer documentation.
How do UK occupational CO₂ limits compare?
The UK Health and Safety Executive lists workplace exposure limits for CO₂ of 5,000 ppm (0.5%) averaged over eight hours and 15,000 ppm (1.5%) averaged over 15 minutes.
These are occupational limits for workers, not a specific public-session standard for customers in a wellness chamber. They also use time-weighted averages, so they should not be compared mechanically with a chamber set-point.
A published range is not enough — actual chamber values matter
For a controlled atmosphere, the meaningful safety questions include the actual CO₂ partial pressure during the session, how uniformly the gas is distributed, how sensors are calibrated, what alarm thresholds are used and how the chamber responds if a parameter leaves its operating range.
That is especially important in a room occupied by several people, because occupants also produce CO₂ through normal respiration. Manufacturer controls, active gas management and monitoring are therefore more informative than a single marketing percentage.
A balanced reading of the evidence
CO₂ influences breathing drive, arterial CO₂, pH and haemoglobin oxygen affinity.
Controlled studies have exposed healthy adults to low-percentage CO₂ and measured respiratory and circulatory responses.
That the chamber’s CO₂ component independently causes the outcomes reported in the small 2020 multi-gas study.
That deliberately raising CO₂ within this range treats disease or guarantees better recovery or oxygen delivery.
CO₂ in oxygen chambers: quick answers
Why is carbon dioxide used in a pressurised oxygen chamber?
CO₂ changes ventilation, blood pH and haemoglobin oxygen affinity. Those physiological mechanisms help explain why CO₂ is a meaningful chamber parameter, but they do not by themselves establish a health benefit from a particular added concentration.
What is the Bohr effect?
The Bohr effect describes reduced haemoglobin affinity for oxygen when CO₂ rises and/or pH falls, favouring oxygen unloading in tissues.
Does Oxygen Clinic use 0.7–2% CO₂?
The current Oxygen Clinic About page says 0.7–2%, but Ekonstal and the corrected chamber study specify 0.7–2 kPa partial pressure at 1500 hPa total pressure. That corresponds approximately to 0.47–1.33% of the gas mixture and the website unit should be corrected.
Is 1% CO₂ enough to affect breathing?
Yes, controlled human experiments have found ventilatory and blood-gas responses around 1–2% inspired CO₂, although the size of the response varies between individuals and exposure conditions.
What are the UK workplace limits for CO₂?
HSE lists 5,000 ppm over an eight-hour reference period and 15,000 ppm over a 15-minute reference period. These are occupational limits and are not a direct customer-session standard.
Does CO₂ improve oxygen delivery?
CO₂ and pH influence haemoglobin oxygen unloading through the Bohr effect. Whether deliberately enriched inspired CO₂ improves clinically meaningful oxygen delivery in a particular chamber protocol is a separate question and is not established by the Bohr effect alone.
Sources used for this guide
See how all four chamber parameters fit together
Pressure, oxygen, CO₂ and hydrogen need to be interpreted together. Read the chamber-mechanics guide for the full picture.