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

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: Not yet recruiting
• Conditions: Nitrogen Narcosis; Inner Ear Decompression Illness
• Intervention / Treatment: Drug: Nitrogen-oxygen breathing mixture

• Study Type: Observational
• Enrollment (Estimated): 40

Participation Criteria

Eligibility Criteria

• 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

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
'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

Outcome Measure	Measure Description	Time Frame
Presence of Nystagmus	Present or absent on EOG recording	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	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	During hyperbaric dive (30 seconds)
Assessment of visual smooth pursuit tracking a sinusoidal target	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 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	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	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	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 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	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	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	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	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

• Sponsor: University of Plymouth

Study record dates

Study Major Dates

• Study Start (Estimated): September 1, 2026
• Primary Completion (Estimated): September 1, 2028
• Study Completion (Estimated): September 1, 2029

Study Registration Dates

• First Submitted: February 12, 2026
• First Submitted That Met QC Criteria: February 25, 2026
• First Posted (Actual): March 3, 2026

Study Record Updates

• Last Update Posted (Actual): March 3, 2026
• Last Update Submitted That Met QC Criteria: February 25, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Chemically-Induced Disorders; Poisoning; Occupational Diseases; Gas Poisoning; Inert Gas Narcosis
• Other Study ID 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