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).