Nitrogen NarcosisNCT07446348
The Effect of Nitrogen Narcosis on Motor Performance in Divers Who Have Sustained an Inner Ear Decompression Illness
An observational study of Nitrogen Narcosis and Inner Ear Decompression Illness, run by University of Plymouth.
Trial summary
Nitrogen starts to have narcotic properties depths below 30m and can cause symptoms such as euphoria, impaired judgement and impaired neuromuscular coordination. This is an important safety and performance consideration for divers working at depth. Read more about this study
- Who is it for?
- Ages 18 to 60 yearsHealthy volunteers can take part
- Conditions the study is for
- Nitrogen Narcosis, Inner Ear Decompression Illness
- What is being tested?
- Nitrogen-oxygen breathing mixture
- How many people
- 40 participants
- Where
- No sites listed yet
- Study dates
- 1 Sep 2026to 1 Sep 2029
- Phase
- Observational
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 60 years
- All sexes
- Healthy volunteers accepted
- Adult
Study population: Open to all interested participants
Who may be able to join
- 'Healthy/normative' participants with no history of orthopaedic/ neurological disorders that could affect balance or cognition.
- Diver participants with a history of inner ear decompression illness, have returned to diving and have had a confirmed negative patent foramen ovale (PFO) screen or closure procedure.
Who cannot join
- History of substance abuse
- Excessive caffeine intake within 24 hours (1 cup coffee max.)
- Alcohol intake within 24 hours
- Known PFO
- IEDCS diver with residual severe vestibular/ balance symptoms (unable to stand with feet together and eyes closed for 30 seconds)
About this study
Nitrogen starts to have narcotic properties depths below 30m and can cause symptoms such as euphoria, impaired judgement and impaired neuromuscular coordination. This is an important safety and performance consideration for divers working at depth. 'Dry dive' experiences (also known as 'pot dives') are frequently run by DDRC Healthcare for dive clubs or students who wish to experience nitrogen narcosis and the effects of pressure in a more controlled environment than underwater. The purpose of this study is to investigate the effect of this narcotic effect on oculomotor, vestibular and motor performance by asking participants to perform tasks whilst in the chamber at depth. There will be two groups of participants - those who have had no previous decompression illness or issues with their balance/ inner ear, and divers who have previously sustained an inner ear decompression sickness (IEDCS). It is theorised that divers who have previously sustained an IEDCS injury will struggle more with tasks involving balance and co-ordination under the effect of narcosis. This is because around 60% of divers with IEDCS will have some long-lasting damage to their inner ear and nitrogen narcosis impairs areas of the brain that are being used to compensate for the injury. Therefore, it is possible that inner ear symptoms such as dizziness or disorientation may recur temporarily whilst at depth. Understanding if these divers are at risk will help guide safety advice for returning to diving in the water after an IEDCS injury. If participants decide to take part, they will be asked to complete a medical screening form to ensure that they are safe to undertake a dive in the chamber. They will also be sent some information by DDRC Healthcare including a disclaimer/ consent form which will outline any potential risks or considerations regarding the dive. When participants attend DDRC Healthcare for the planned 'dry' dive they will be shown around the chamber room, and the procedure will be explained. They may ask questions at any point if they have any queries or concerns. The whole session including the dive will take up to 2 hours in total. Prior to entering the chamber, participants will have electrodes attached to areas on their face, head and neck. These will track hand and eye movement and postural stability. Once comfortable, participants will enter the chamber, inside they will be accompanied by a researcher/dive doctor and a chamber attendant. Before the chamber is compressed participants will be asked to perform a series of tasks that the researcher will assist with. The chamber will then be compressed to the equivalent of 40m for a maximum time of 10 minutes, at 40m the series of tasks will be repeated. The chamber will then be slowly decompressed to 6m and then to 3m giving a total time of 36 minutes for the whole dive. For the last 18 minutes participants will breathe oxygen from a mask. Once at surface the series of tasks will be repeat for a third time. Tasks: 1) Recording of eye movements: a. Looking forward with eyes closed b. Following a moving target on a screen c. Looking forward whilst head is moved from left to right by researcher 2) 9-hole peg test (placing pegs into a board and then removing them again) 3) Finger to nose test (pointing to and from a target on a screen and nose) 4) Trial making test (paper and pencil test identifying a sequenced pattern) 5) Postural sway (standing with feet together with eyes open and then closed).
- Conditions
- Nitrogen Narcosis, Inner Ear Decompression Illness
- Being tested
- Nitrogen-oxygen breathing mixture
- Medical subject headings
- Inert Gas Narcosis
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Nitrogen-oxygen breathing mixtureDrug
Hyperbaric chamber dive exposing participants to hyperbaric nitrogen inducing a transitory nitrogen narcosis
| Study group | Role | What they receive |
|---|---|---|
| 'Healthy' participants with no prior decompression illness or inner ear/balance conditions | Not described Receives: Drug: Nitrogen-oxygen breathing mixture | |
| Divers with prior inner ear decompression illness | Not described Receives: Drug: Nitrogen-oxygen breathing mixture |
What is being measured
The primary outcome is the main question the study is designed to answer.
Presence of Nystagmus
Present or absent on EOG recording
Measured: During hyperbaric dive (30 seconds)
Direction of Nystagmus
If nystagmus is present the direction of the slow phase (up/down/left/right) will be recorded as seen on EOG recording
Measured: During hyperbaric dive (30 seconds)
Speed of Nystagmus
If nystagmus is present the average speed of the nystagmus (in degrees per second) will be recorded as seen on EOG recording
Measured: During hyperbaric dive (30 seconds)
Assessment of visual smooth pursuit tracking a sinusoidal target
Measure of gain (%) of eye movement on EOG recording
Measured: During hyperbaric dive (60 seconds)
Hand co-ordination - time to complete 9 hole peg test
Time to place all 9 pins and remove all 9 pins measured in seconds
Measured: During hyperbaric dive (60 seconds maximum)
Hand co-ordination - mean jerk of wrist during 9 hole peg test
Mean jerk of wrist during 9 hole peg test, measured by inertial sensors on wrist. Jerk = sqrt(acceleration x2+ acceleration y2+ acceleration z2)
Measured: During hyperbaric dive (60 seconds maximum)
Finger to nose co-ordination - error to target
Absolute error to target (cm) measured using co-ordinates on touch screen
Measured: During hyperbaric dive (45 seconds)
Finger to nose co-ordination - mean jerk of wrist
Mean jerk of wrist during test measured using inertial sensor on wrist. Where jerk = sqrt(acceleration x2+ acceleration y2+ acceleration z2)
Measured: During hyperbaric dive (45 seconds)
Trail making test - total time for completion
Time Trail Test A and Trail Test B take to complete in seconds (A+B)
Measured: During hyperbaric dive (90 seconds maximum)
Postural sway - feet together eyes open - sagittal velocity
Mean angular velocity in sagittal direction over 30 seconds with feet together eyes open. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Measured: During hyperbaric dive (30 seconds)
Postural sway - feet together eyes open - coronal velocity
Mean angular velocity in coronal direction over 30 seconds with feet together eyes open. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Measured: During hyperbaric dive (30 seconds)
Postural sway - feet together eyes closed - sagittal velocity
Mean angular velocity in sagittal direction over 30 seconds with feet together eyes closed. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Measured: During hyperbaric dive (30 seconds)
Postural sway - feet together eyes closed - coronal velocity
Mean angular velocity in coronal direction over 30 seconds with feet together eyes closed. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Measured: During hyperbaric dive (30 seconds)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted3 Mar 2026
- Study start1 Sep 2026 (estimated)
- Primary completion1 Sep 2028 (estimated)
- Study completion1 Sep 2029 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Nitrogen NarcosisStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Case-control
- Time perspective
- Prospective
- Enrolment
- 40 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Plymouth
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Rosanna J Stokes, University of Plymouth
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07446348
- Sponsor's protocol ID
- 7032
- Status last verified
- Feb 2026
- First submitted
- 12 Feb 2026
- Last updated
- 3 Mar 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
Study at a glance
From the registry record, last updated by the sponsor on 3 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of Nitrogen Narcosis on Motor Performance in Divers Who Have Sustained an Inner Ear Decompression Illness
- ClinicalTrials.gov ID
- NCT07446348
- Acronym / sponsor ID
- 7032
- Conditions
- Nitrogen Narcosis, Inner Ear Decompression Illness
- Study type
- Observational
- Recruitment status
- Not yet recruiting
- Enrolment
- 40 participants (estimated)
- Lead sponsor
- University of PlymouthUniversity, hospital or other
- Study start
- 1 Sep 2026 (estimated)
- Primary completion
- 1 Sep 2028 (estimated)
- Study completion
- 1 Sep 2029 (estimated)
- First posted
- 3 Mar 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
Nitrogen starts to have narcotic properties depths below 30m and can cause symptoms such as euphoria, impaired judgement and impaired neuromuscular coordination. This is an important safety and performance consideration for divers working at depth. 'Dry dive' experiences (also known as 'pot dives') are frequently run by DDRC Healthcare for dive clubs or students who wish to experience nitrogen narcosis and the effects of pressure in a more controlled environment than underwater. The purpose of this study is to investigate the effect of this narcotic effect on oculomotor, vestibular and motor performance by asking participants to perform tasks whilst in the chamber at depth. There will be two groups of participants - those who have had no previous decompression illness or issues with their balance/ inner ear, and divers who have previously sustained an inner ear decompression sickness (IEDCS). It is theorised that divers who have previously sustained an IEDCS injury will struggle more with tasks involving balance and co-ordination under the effect of narcosis. This is because around 60% of divers with IEDCS will have some long-lasting damage to their inner ear and nitrogen narcosis impairs areas of the brain that are being used to compensate for the injury. Therefore, it is possible that inner ear symptoms such as dizziness or disorientation may recur temporarily whilst at depth. Understanding if these divers are at risk will help guide safety advice for returning to diving in the water after an IEDCS injury. If participants decide to take part, they will be asked to complete a medical screening form to ensure that they are safe to undertake a dive in the chamber. They will also be sent some information by DDRC Healthcare including a disclaimer/ consent form which will outline any potential risks or considerations regarding the dive. When participants attend DDRC Healthcare for the planned 'dry' dive they will be shown around the chamber room, and the procedure will be explained. They may ask questions at any point if they have any queries or concerns. The whole session including the dive will take up to 2 hours in total. Prior to entering the chamber, participants will have electrodes attached to areas on their face, head and neck. These will track hand and eye movement and postural stability. Once comfortable, participants will enter the chamber, inside they will be accompanied by a researcher/dive doctor and a chamber attendant. Before the chamber is compressed participants will be asked to perform a series of tasks that the researcher will assist with. The chamber will then be compressed to the equivalent of 40m for a maximum time of 10 minutes, at 40m the series of tasks will be repeated. The chamber will then be slowly decompressed to 6m and then to 3m giving a total time of 36 minutes for the whole dive. For the last 18 minutes participants will breathe oxygen from a mask. Once at surface the series of tasks will be repeat for a third time. Tasks: 1) Recording of eye movements: a. Looking forward with eyes closed b. Following a moving target on a screen c. Looking forward whilst head is moved from left to right by researcher 2) 9-hole peg test (placing pegs into a board and then removing them again) 3) Finger to nose test (pointing to and from a target on a screen and nose) 4) Trial making test (paper and pencil test identifying a sequenced pattern) 5) Postural sway (standing with feet together with eyes open and then closed).
Study design
- Observational model
- Case-control
- Time perspective
- Prospective
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| 'Healthy' participants with no prior decompression illness or inner ear/balance conditions | – | Drug: Nitrogen-oxygen breathing mixture |
| Divers with prior inner ear decompression illness | – | Drug: Nitrogen-oxygen breathing mixture |
Who may qualify
- Ages
- 18 to 60 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
- Study population
- Open to all interested participants
Key inclusion criteria (2 listed)
- 'Healthy/normative' participants with no history of orthopaedic/ neurological disorders that could affect balance or cognition.
- Diver participants with a history of inner ear decompression illness, have returned to diving and have had a confirmed negative patent foramen ovale (PFO) screen or closure procedure.
Key exclusion criteria (5 listed)
- History of substance abuse
- Excessive caffeine intake within 24 hours (1 cup coffee max.)
- Alcohol intake within 24 hours
- Known PFO
- IEDCS diver with residual severe vestibular/ balance symptoms (unable to stand with feet together and eyes closed for 30 seconds)
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Nitrogen-oxygen breathing mixtureHyperbaric chamber dive exposing participants to hyperbaric nitrogen inducing a transitory nitrogen narcosis | Drug | 'Healthy' participants with no prior decompression illness or inner ear/balance conditions, Divers with prior inner ear decompression illness |
Primary outcome
Presence of Nystagmus
Time frame: During hyperbaric dive (30 seconds)
Present or absent on EOG recording
Direction of Nystagmus
Time frame: During hyperbaric dive (30 seconds)
If nystagmus is present the direction of the slow phase (up/down/left/right) will be recorded as seen on EOG recording
Speed of Nystagmus
Time frame: During hyperbaric dive (30 seconds)
If nystagmus is present the average speed of the nystagmus (in degrees per second) will be recorded as seen on EOG recording
Assessment of visual smooth pursuit tracking a sinusoidal target
Time frame: During hyperbaric dive (60 seconds)
Measure of gain (%) of eye movement on EOG recording
Hand co-ordination - time to complete 9 hole peg test
Time frame: During hyperbaric dive (60 seconds maximum)
Time to place all 9 pins and remove all 9 pins measured in seconds
Hand co-ordination - mean jerk of wrist during 9 hole peg test
Time frame: During hyperbaric dive (60 seconds maximum)
Mean jerk of wrist during 9 hole peg test, measured by inertial sensors on wrist. Jerk = sqrt(acceleration x2+ acceleration y2+ acceleration z2)
Finger to nose co-ordination - error to target
Time frame: During hyperbaric dive (45 seconds)
Absolute error to target (cm) measured using co-ordinates on touch screen
Finger to nose co-ordination - mean jerk of wrist
Time frame: During hyperbaric dive (45 seconds)
Mean jerk of wrist during test measured using inertial sensor on wrist. Where jerk = sqrt(acceleration x2+ acceleration y2+ acceleration z2)
Trail making test - total time for completion
Time frame: During hyperbaric dive (90 seconds maximum)
Time Trail Test A and Trail Test B take to complete in seconds (A+B)
Postural sway - feet together eyes open - sagittal velocity
Time frame: During hyperbaric dive (30 seconds)
Mean angular velocity in sagittal direction over 30 seconds with feet together eyes open. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Postural sway - feet together eyes open - coronal velocity
Time frame: During hyperbaric dive (30 seconds)
Mean angular velocity in coronal direction over 30 seconds with feet together eyes open. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Postural sway - feet together eyes closed - sagittal velocity
Time frame: During hyperbaric dive (30 seconds)
Mean angular velocity in sagittal direction over 30 seconds with feet together eyes closed. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Postural sway - feet together eyes closed - coronal velocity
Time frame: During hyperbaric dive (30 seconds)
Mean angular velocity in coronal direction over 30 seconds with feet together eyes closed. Measured using inertial sensors placed on C7 spinous process. (degrees/second)
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 3 Mar 2026.
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
The record lists no contact. Use the official record to reach the sponsor.
Questions about this trial
What is this clinical trial studying?
An observational study of Nitrogen Narcosis and Inner Ear Decompression Illness, run by University of Plymouth.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 2 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: opening soon, as of the sponsor's last update on 3 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Presence of Nystagmus (time frame: During hyperbaric dive (30 seconds)). The study lists 13 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 3 Mar 2026.