HBOT Glossary: 50 Hyperbaric Terms Defined

This HBOT glossary defines 50 hyperbaric and oxygen-therapy terms in plain, clinical language, from ATA and oxygen toxicity to the Wagner grade and US Navy Treatment Table 6. Each entry gives a short, precise definition you can rely on, with links to the BaricBoost guides that cover the topic in depth. Terms are listed alphabetically.

A

Air break

An air break is a scheduled interval during a hyperbaric session when the patient breathes ordinary chamber air instead of 100 percent oxygen. It lowers the cumulative oxygen dose to the lungs and central nervous system, which reduces the risk of oxygen toxicity and seizure.

Angiogenesis

Angiogenesis is the growth of new blood vessels from existing ones. Hyperbaric oxygen therapy promotes angiogenesis in poorly perfused tissue, which is one of the mechanisms behind its use in wound healing and radiation injury.

Arterial gas embolism (AGE)

Arterial gas embolism is a condition in which gas bubbles enter the arterial circulation and block blood flow to organs such as the brain. It is a diving and medical emergency treated with immediate recompression, typically on US Navy Treatment Table 6 or 6A.

ASME PVHO-1

ASME PVHO-1 is the American Society of Mechanical Engineers Safety Standard for Pressure Vessels for Human Occupancy. It governs the design and fabrication of hyperbaric chambers and applies to any vessel enclosing a person at a differential pressure above 2 psi.

ATA (atmosphere absolute)

ATA, or atmosphere absolute, is the unit that expresses total pressure inside a hyperbaric chamber, where 1 ATA equals normal pressure at sea level. Clinical HBOT typically runs at 2.0 to 2.8 ATA, while mild chambers reach about 1.3 ATA. See our guide to the 1.5 ATA hyperbaric chamber and what a hyperbaric chamber is.

B

Barotrauma

Barotrauma is tissue injury caused by a pressure difference between a gas-filled body space and the surrounding environment. In hyperbaric medicine it most often affects the ears, sinuses, and lungs during compression or decompression.

BIBS hood

A BIBS hood is a Built-In Breathing System device, usually a clear head hood or mask, that delivers a controlled breathing gas inside a multiplace chamber. It lets a patient breathe 100 percent oxygen while the surrounding chamber stays filled with air.

C

Carbon monoxide (CO) poisoning

Carbon monoxide poisoning is a toxic exposure in which CO binds hemoglobin and blocks oxygen delivery to tissue. Hyperbaric oxygen is an FDA-recognized treatment because it speeds CO removal and reduces the risk of delayed neurological injury. See our list of FDA-cleared HBOT indications.

CHT (Certified Hyperbaric Technologist)

A CHT, or Certified Hyperbaric Technologist, is a healthcare worker trained and credentialed to operate hyperbaric chambers and monitor patients during treatment. The certification is granted through recognized bodies such as the National Board of Diving and Hyperbaric Medical Technology.

Cluster headache oxygen therapy

Cluster headache oxygen therapy is the use of high-flow 100 percent oxygen through a mask to abort an acute cluster headache attack. It is delivered at normal pressure, not inside a pressurized chamber, and is a recognized first-line acute treatment.

CNS oxygen toxicity

CNS oxygen toxicity is a form of oxygen toxicity affecting the central nervous system, whose most serious sign is a generalized seizure. Risk rises with oxygen partial pressure, which is why recreational diving caps exposure near 1.4 ATA and clinical protocols use air breaks. See hyperbaric chamber side effects.

Compression (descent)

Compression, also called descent, is the phase of a hyperbaric session in which chamber pressure is gradually raised to the treatment level. Patients equalize their ears during this phase to prevent middle ear barotrauma.

D

Decompression (ascent)

Decompression, also called ascent, is the phase of a hyperbaric session in which chamber pressure is gradually returned to normal. A controlled rate allows dissolved gas to leave the body safely and prevents decompression sickness.

Decompression sickness (DCS)

Decompression sickness is a condition caused by nitrogen bubbles forming in blood and tissue when pressure drops too quickly, commonly after diving. It is treated with recompression and hyperbaric oxygen, most often on a US Navy treatment table.

Dive medicine

Dive medicine is the branch of medicine concerned with the health effects of underwater and high-pressure environments. It covers decompression sickness, arterial gas embolism, and the recompression protocols that hyperbaric therapy originally grew from.

E

Efrati protocol

The Efrati protocol is a hyperbaric treatment approach developed by Dr. Shai Efrati that uses repeated sessions, typically around 60, to drive neuroplasticity in post-stroke and brain-injury patients. It is associated with fluctuating oxygen levels intended to trigger tissue regeneration.

EWOT (exercise with oxygen therapy)

EWOT, or exercise with oxygen therapy, is a practice of breathing high-concentration oxygen while exercising at normal atmospheric pressure. It is not hyperbaric therapy because it involves no chamber pressurization.

F

FDA 510(k) clearance

FDA 510(k) clearance is a regulatory pathway in which a device maker shows a product is substantially equivalent to one already on the market. Hyperbaric chambers cleared this way are authorized only for specific listed indications, not for every advertised use. See FDA-cleared HBOT indications.

Fire suppression system

A fire suppression system is the safety equipment that detects and extinguishes fire inside or around a hyperbaric chamber. It is critical because the oxygen-enriched environment makes combustion faster and more intense, a requirement addressed under NFPA 99.

H

Hard-shell chamber

A hard-shell chamber is a rigid hyperbaric chamber, typically made of steel or acrylic, built to hold higher pressures and deliver 100 percent oxygen. These chambers support clinical HBOT at pressures of 2.0 ATA and above.

Harch protocol

The Harch protocol is a low-pressure hyperbaric approach developed by Dr. Paul Harch that treats traumatic brain injury and post-concussion syndrome, commonly with 40 sessions at 1.5 ATA. It targets brain recovery rather than acute wound or diving conditions.

Henry’s law

Henry’s law is the physical principle that the amount of a gas dissolved in a liquid is proportional to the partial pressure of that gas above the liquid. It explains why raising chamber pressure forces far more oxygen into the blood plasma during HBOT.

HIF-1a (hypoxia-inducible factor 1-alpha)

HIF-1a is a protein that regulates how cells respond to changing oxygen levels by switching on genes for blood vessel growth and tissue repair. Hyperbaric oxygen cycling is thought to influence HIF-1a signaling, which supports angiogenesis and stem cell activity.

Hyperbaric oxygen therapy (HBOT)

Hyperbaric oxygen therapy is a treatment in which a patient breathes 100 percent oxygen inside a chamber pressurized above normal atmospheric pressure. The combination dissolves far more oxygen into the blood than breathing air at sea level. Learn more in our guide to what a hyperbaric chamber is.

Hyperoxia

Hyperoxia is a state in which body tissue is exposed to oxygen levels far above normal. It is the intended effect of hyperbaric oxygen therapy and also the source of oxygen toxicity when the dose is too high.

I

Inside attendant

An inside attendant is a trained staff member who is pressurized alongside patients inside a multiplace chamber to monitor and assist them. Because they share the pressure exposure, attendants follow their own decompression limits to avoid decompression sickness.

M

mHBOT (mild hyperbaric oxygen therapy)

mHBOT, or mild hyperbaric oxygen therapy, is hyperbaric treatment delivered at low pressure, generally around 1.3 ATA, usually in a soft-shell chamber with ambient or lightly enriched air. It is FDA-cleared only for acute mountain sickness, so other uses are off-label.

Middle ear barotrauma

Middle ear barotrauma is injury to the eardrum and middle ear caused by failure to equalize pressure during compression. It is the most common side effect of hyperbaric therapy and is prevented by slow descent and ear-clearing techniques. See hyperbaric chamber side effects.

Mild hyperbaric chamber

A mild hyperbaric chamber is a low-pressure chamber, usually soft-sided, that operates near 1.3 ATA. It delivers a smaller oxygen dose than clinical hard-shell systems and is marketed for wellness and recovery rather than the full range of medical indications.

Monoplace chamber

A monoplace chamber is a single-occupancy hyperbaric chamber in which one patient lies inside a tube usually filled entirely with 100 percent oxygen. It is the most common design in outpatient wound care. Compare designs in our multiplace hyperbaric chamber guide.

Multiplace chamber

A multiplace chamber is a larger hyperbaric chamber that holds several patients plus an inside attendant, pressurized with air while patients breathe oxygen through masks or hoods. It allows hands-on care and treatment of critically ill patients. See our multiplace hyperbaric chamber guide.

N

NFPA 99

NFPA 99 is the National Fire Protection Association Health Care Facilities Code that sets safety requirements for hyperbaric facilities. It requires chambers to meet ASME PVHO-1 and governs fire protection, ventilation, and grounding in oxygen-enriched spaces.

Normobaric oxygen

Normobaric oxygen is supplemental oxygen delivered at normal atmospheric pressure, such as through a nasal cannula or mask. It raises inspired oxygen but not the dissolved plasma oxygen achieved by pressurized hyperbaric therapy.

O

Off-label use

Off-label use is the application of an approved device or drug for a condition outside its cleared indications. Many advertised hyperbaric uses, such as autism or anti-aging, are off-label because they are not among the FDA-recognized indications.

Osteoradionecrosis

Osteoradionecrosis is the death of bone tissue, most often in the jaw, following radiation therapy. It is an established hyperbaric oxygen indication because HBOT improves blood supply and oxygenation in the damaged, poorly healing bone.

Oxidative stress

Oxidative stress is an imbalance between reactive oxygen species and the body’s antioxidant defenses that can damage cells. Hyperbaric oxygen deliberately induces a controlled, brief burst of oxidative stress that triggers protective and healing responses.

Oxygen concentrator

An oxygen concentrator is a device that pulls in room air and filters out nitrogen to deliver oxygen-enriched gas. It supplies breathing oxygen for mild chambers and clinical setups but does not itself pressurize the chamber.

Oxygen toxicity

Oxygen toxicity is tissue injury caused by breathing oxygen at high partial pressure for too long. Its two main forms affect the central nervous system, causing seizures, and the lungs, causing inflammation, and both are limited by dose and air breaks.

P

Partial pressure

Partial pressure is the share of total gas pressure contributed by a single gas in a mixture. In hyperbaric medicine, raising the partial pressure of oxygen is what forces extra oxygen to dissolve into the blood.

Prolozone

Prolozone is an injection therapy that combines ozone gas with nutrients and local anesthetic into joints or soft tissue. It is a separate alternative treatment and is not a form of hyperbaric oxygen therapy.

Pulmonary oxygen toxicity

Pulmonary oxygen toxicity is a form of oxygen toxicity that inflames and irritates the lungs after prolonged high-pressure oxygen exposure. Early signs include chest tightness and cough, and it is managed by limiting cumulative oxygen dose.

R

Radiation necrosis

Radiation necrosis is tissue death in an area previously treated with radiation, caused by damaged blood vessels and poor oxygen supply. Hyperbaric oxygen is used to stimulate new vessel growth and improve healing in these injuries.

Reactive oxygen species (ROS)

Reactive oxygen species are highly reactive oxygen-containing molecules produced during normal metabolism and amplified by high oxygen exposure. In hyperbaric therapy, a controlled rise in ROS acts as a signal that drives repair and adaptation.

S

Soft-shell chamber

A soft-shell chamber is a flexible, zippered hyperbaric chamber that inflates with air to about 1.3 ATA. It is FDA-cleared only for acute mountain sickness and is not designed for high-pressure oxygen delivery. Compare it with rigid systems in our chamber types guide.

Stem cell mobilization

Stem cell mobilization is the release of stem and progenitor cells from bone marrow into the bloodstream. Research shows repeated hyperbaric oxygen sessions can increase circulating stem cells, which supports tissue repair.

T

TCOM / TcPO2

TCOM, or transcutaneous oximetry, is a noninvasive test that measures the oxygen tension in tissue through the skin, reported as TcPO2. Clinicians use it to judge whether a wound has enough blood supply to benefit from hyperbaric oxygen.

Treatment table (US Navy Table 6)

A treatment table is a standardized hyperbaric protocol specifying pressure, gas, and timing, and US Navy Treatment Table 6 is the most widely used. It compresses the patient to 60 feet of seawater, about 2.82 ATA, with oxygen periods split by air breaks to treat decompression sickness and arterial gas embolism.

U

UHMS (Undersea and Hyperbaric Medical Society)

UHMS is the professional body that sets clinical standards and publishes the list of approved indications for hyperbaric oxygen therapy. Its accreditation and guidelines are the main reference for evidence-based hyperbaric practice.

W

Wagner grade

The Wagner grade is a classification system that ranks diabetic foot ulcers from grade 0 to grade 5 by depth and infection. A Wagner grade 3 or higher ulcer that has failed standard care is the usual threshold for hyperbaric oxygen coverage.

Wound debridement

Wound debridement is the removal of dead, damaged, or infected tissue from a wound to support healing. It is standard care that works alongside hyperbaric oxygen therapy rather than being a hyperbaric technique itself.

Sources

• Undersea and Hyperbaric Medical Society, approved indications and safety guidance: https://www.uhms.org/
• Cooper JS, et al. Oxygen Toxicity. StatPearls, NCBI Bookshelf: https://www.ncbi.nlm.nih.gov/books/NBK430743/
• US Navy Diving Manual, recompression treatment tables (UHMS reproduction): https://uhms.org/images/DCS-and-AGE-Journal-Watch/US_DIVING_MANUAL_REV7_1_v7-chapter_17.pdf
• National Board of Boiler and Pressure Vessel Inspectors, Pressure Vessels for Human Occupancy in Clinical Hyperbaric Medicine (ASME PVHO-1, NFPA 99): https://www.nationalboard.org/index.aspx?pageID=164&ID=202
• Hyperbaric Oxygen Therapy for Diabetic Foot Ulcers Based on Wagner Grading, PRS Global Open: https://journals.lww.com/prsgo/fulltext/10.1097/gox.0000000000005692
• Tal S, Hadanny A, Efrati S, et al. HBOT-induced angiogenesis and nerve fiber regeneration in TBI, Frontiers in Human Neuroscience: https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2017.00508/full
• US FDA, hyperbaric oxygen therapy device clearances and consumer guidance: https://www.fda.gov/