The Effect of Nitrogen Narcosis on Motor Performance in Divers Who Have Sustained an Inner Ear Decompression Illness

February 25, 2026 updated by: Rosanna J Stokes, University of Plymouth
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 Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Observational

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
40

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

Open to all interested participants

Description

Inclusion Criteria:

  • '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.

Exclusion Criteria:

  • 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)

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort

Group / Cohort

A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
'Healthy' participants with no prior decompression illness or inner ear/balance conditions
Drug: Nitrogen-oxygen breathing mixture
Hyperbaric chamber dive exposing participants to hyperbaric nitrogen inducing a transitory nitrogen narcosis
Divers with prior inner ear decompression illness
Drug: Nitrogen-oxygen breathing mixture
Hyperbaric chamber dive exposing participants to hyperbaric nitrogen inducing a transitory nitrogen narcosis

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Presence of Nystagmus
Time Frame: During hyperbaric dive (30 seconds)
Present or absent on EOG recording
During hyperbaric dive (30 seconds)
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
During hyperbaric dive (30 seconds)
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
During hyperbaric dive (30 seconds)
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
During hyperbaric dive (60 seconds)
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
During hyperbaric dive (60 seconds maximum)
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)
During hyperbaric dive (60 seconds maximum)
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
During hyperbaric dive (45 seconds)
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)
During hyperbaric dive (45 seconds)
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)
During hyperbaric dive (90 seconds maximum)
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)
During hyperbaric dive (30 seconds)
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)
During hyperbaric dive (30 seconds)
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)
During hyperbaric dive (30 seconds)
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)
During hyperbaric dive (30 seconds)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
University of Plymouth

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
September 1, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
September 1, 2028

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
September 1, 2029

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
February 12, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 25, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
March 3, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
March 3, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 25, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
February 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 7032 (CTEP)

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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