Effects of Various Gases used for Diving on Hearing Acuity V. K. SING H

60 divers of d i f fe ren t cate- gories reported for this study. Another 60 sailors w e r e kept as a control group. On pro- dive screening 5 divers f rom each category w e r e selected for a practical dive w i th a part icular gas/gas mixture. They were exposed to these gases for 30-45 minutes at d i f fe ren t depths.

A def in i te t e m p o r a r y thre- shold shi f t was not iced in the hearing acui ty among oxygen- ni trogen, He l ium-Ai r , and He- l ium-Oxygen mixture group. A comple te recovery was ob- served w i th in 7 days.

It was found tha t a short exposure had a t e m p o r a r y e f f - ect over hearing acuity. Re- peated exposures may pro- duce permanent changes, but these are d i f f icu l t to ascer- tain as o ther factors are also present, like decompression and noise induced changes due to equipment .

Diving is considered to be an art. It is descending under water and remaining there for a short period. There have been divers

in all ages. Man must have learned to dive almost as soon he learnt to swim, but he must also have learned that his physiological struc- ture, as an air breathing land creature, imposed very definite and narrow limits upon his acti- vity under water. Limits which remained unaltered for many cen- turies. The biggest physical bar- rier in the changed medium are the absence of respirable air and the great pressure of water at the depths of ocean.

The first known dive was made in 460 B.C., the famous Greek diver Scyllis dived for treasure from a wrecked Persian ship. Modern diving is only just over a century old. In 1837 Augustus Siebe's closed dress became a land-mark in the history of diving. It enclosed the diver in a con- tinuous air-tight dress. There has been considerable progress in this field, modifications in the d ivers" suit, and the use of various gases and their mixtures. The following gases are being used by divers for different depths : (1) Oxygen (2) Air (3) Oxygen Et Nitrogen (4) Oxygen 8" Helium (5) Helium 8 air (6) Helium, Oxygen Et Nitrogen.

V. K. Singh, Officer-in-charge, Neuro- Otology Research 8 Dept. of E.N.T., I.N.H.S. Kalyani, Naval Base, Visakha- patnam-530 014

Paper read at 23rd annual conference of the Association of Otolaryngologists of India 1980, at Jaipur,

I am thankful to Brig. G. V. Ramani, Consultant in Otolaryngology, Surgeon Commander N. B. Idnani, Chief Medical Officer Coast Guard and Surgeon Commander A. Jagdish Chan- dran, Commanding Officer, INHS Kalyani, Visakhapatnern, for their encouragement.

Each gas or gas mixture has its limitations and it is strange that a vital gas like oxygen could prove fatal after a certain depth. These gases can produce adverse effects systemically or locally on certain parts, like oxygen toxicity beyond one atmosphere pressure, Nitrogen narcosis on bubble formation in certain tissues like brain or around joints.

On the surface of the earth various chemicals and drugs are known to produce adverse effects on hearing acuity if used syste- mically or locally. Though these

gases are in use for a considerable time, nothing is definitely known about their effect on hearing acuity. Due to certain known adverse effects on other parts of body like Central Nervous system, Car- diovascular system and joints, restrictions have been imposed on the use of each gas for a cer- tain depth, which narrows the field of study, i.e., it is not advis- able to give oxygen beyond 10 meters depth, so no study can be made on divers for its effects beyond 10 meters, similarly it is not permitted to put new recruits or the control group in any other gas or gas mixture except air. The second factor involved is varying the percentage of each at different depths and measuring its effect on hearing acuity at that depth, can only be studied on a particular group who can achieve that depth. While studying the toxic effects of these gases, the second barrier of depth has its effect on the hearing acuity at the same time and it becomes difficult to distinguish the effect of each factor. Considering the above problems, the field of study becomes limited, only selected per- sonnel can be subjected to a parti- cular gas or gas mixture at a particular depth.

Mater ia l and M e t h o d

This work was conducted at the ENT Department of the Naval hospital and Diving unit at Visa- khapatnam. Divers of all categories were asked to report to these centres. A total of 120 personnel were selected for this study at the first screening.

Ship divers (Shallow water divers) 30

Clearance divers 15 Deep divers 15 Control 60

Indian Journal of Otolaryngology, Volume 33, No. 2, June, 1981 59

Scheme of examinat ion :

1. Age of diver 2. Length of service 3. Type of div ing 4. Duration E~ depth of div ing 5. Type of div ing set used 6. Any history of acc ident - -

Giddiness, Deafness (Tem- porary/permanent) Uncon- sciousness.

7. Examination of the ear before and after d iv ing- -Nys tagmus, External audi tory canal, Tympanic membrane and middle ear and Audiometry.

Gas/Gas mix ture used for the study

i. Oxygen ii. Air

iii. Oxygen ~ Nitrogen iv. Hel ium E~ Ai r v. Hel ium Et Oxygen

On the basis of the pre-dive screening, personnel having di- minished hearing (Pure tone au- diometry) were excluded from the practical dive. Volunteers were selected as seen in Table I.

Results

I. Screen ing- - Deep divers were an elderly group,

their d iv ing experience was higher and they stayed longer under water. (Table I I) .

2 Personnel rejected during screening

A t o t a l of 30 personnel were re- jected during screening due to various cl inical f indings, i.e., Gid- diness, hearing loss, Negative val- salva or general systemic il lness (Table I I I ) .

3. Post dive giddiness and pain ear - is shown in Table IV.

. Audiometry -Sensor ineura l hearing l o ss - - i s shown in Table V.

No hearing loss was seen among divers using the oxygen set, divers wi th the air set showed one case of monoaural sensorineural hearing loss which recovered wi th in 48 hours. One binaural hearing loss noticed among the Oxygen Er Nitro-

HEARING ACUITY IN DIV ING--S INGH

gen group, also recovered wi th in 48 hours. In the Helium Et Air mixture group there was one mono and

one binaural hearing loss, the binaural hearing loss persisted be- yond 48 hours and recovered

TABLE I

Volunteers Selected

Gas used Number of Type of Subjected Duration Volunteers divers depth

Oxygen 5 SD 30 ft 30 mts.

Air 5 CD 60 ft 30 mts.

Oxygen-Nitrogen 5 CD 90 ft 30 mts.

Helium-Air 5 DD 200 ft 30-45 mts.

Helium-Oxygen 5 DD 200 ft 30-45 mts.

Control (air) 30 1st Dive 30 ft 30 mrs.

SD--Sh ips diver CD--Clearance diver DD--Deep diver

TABLE II

Screening

Mean S.D. C.D. D.D. Control

Total No. 30 15 15 60

Age 25.33 yrs 28.6 yrs 30.55 yrs 21.66 yrs

Diving experience 1.85 yrs. 6.2 yrs. 8.02 yrs. Nil

Diving time 1 hr36 mts 2hrs6 mts 2hrs30 mts 18.2mts

S.D.--Ships diver C.D.--Clearance diver D.D.--Deep diver.

TABLE III

Personnel rejected during screening

Type of D ivers

Total Negative History of Hearing General Total Number Valsalva giddiness loss Exam

Ships diver 30 3 1 6 3 13

Clearance diver 15 -- 1 2 - - 3

Deep diver 15 - - - - 1 1 2

Control 60 5 u 2 5 12

60 Indian Journal of Otolaryngology, Volume 33, No. 2, June, 1981

HEARING A C U I T Y IN D I V I N G - - S I N G H

w i t h i n 7 days (Fig. 1, 2, 3). T w o cases of b inaural hearing loss were seen among the Hel ium- Oxygen group, one recovered w i t h - in 48 hours wh i l e the other recovered w i t h i n 7 days. One case of binaural hearing loss persisted beyond 7 days among the control g roup out of the 3 mono-aura l and 5 binaural hearing loss cases in th is group.

TABLE IV

Post dive giddiness and pain ear

Gas Used No. of Depth in Duration No. of Pain ear Volunteers Fee t Exposure Giddiness

Oxygen 5 Ships diver 30 30 mts 1 2

Air 5 Clearance diver 60 30 mts - - 1

Oxygen 8- Nitrogen 5 Clearance diver 90 30 mts - - - -

Helium 8- Air 5 Deep diver 200 30-45 mts

Helium 8- Oxygen 5 Deep diver 200 30-45 mtso

Control (air) 30 Recruits 30 30 mts 5 9

Fig. I Audiogram of a Diver who used Helium-air set. (Before dive)

TABLE V

A u d i o m e t r y - - S e n s o r i n e u r a l Hear ing Loss a f te r diving

Gases used No. of After 1 hr After 48 hrs After 7 days

Volunt- Mono- Bin- Mono- Bin- Mono- Bin- eers aural aural aural aural aural aural

Fig. 2 Audiogram afteronehour (having binaural hearing loss)

Oxygen 5 - -

Air 5 1

Oxygen El- Nitrogen 5 - -

Helium 8- air 5 1

Helium 8- Oxygen 5 - -

Control (Air) 30 3

6 1

1 2 - - 1

D i s c u s s i o n

Fig. 3 Audiogram after 7 days.

In this series all the groups of divers showed a certain percen- tage of sensorineural hearing loss, after one hour of the d ive on audiometry examinat ion except the divers using the oxygen set. On the second aud iomet ry done after 48 hours improvement in

hearing acu i ty was observed among the var ious groups, wh i l e the th i rd aud iometry done after 7 days showed complete recovery in all cases except in one binaural hear- ing loss case from the contro l group. The exper iment conducted on surface pressure on 3 divers breathing He l i um-Oxygen (80%- 20%) for 30 minutes, (Waterman

Indian Journal of Otolaryngology, Volume 33, No. 2, June, 1981 61

HEARING ACUITY INDIV ING- -S INGH

Smith, 1970) no significant effect was seen on the hearing acuity.

In this series there is definite evidence of temporary threshold shift (TTS) among the various gas mixture groups, there is a slightly higher incidence in the helium-air and helium-oxygen group, complete recovery indicates that a short exposure does not have a permanent effect. It is very diff icult to say whether one particular gas or gas mixture can produce a temporary threshold shift on hearing acuity, The factors which may be responsible could be as fol lows : (1) Toxic effects of gas or gas mixtures at various depths. (2) Bubble formation in the labyrinth at the time of de- compression--apparently maximum wi th Nitrogen and least with Helium. (3) Direct effect of pres-

sure produces TTS. (4) Noise induced deafness due to the equipment used and (5) Laby- rinthine ischaemia.

It is very difficult to pinpoint the causative factors separately. On the screening examination, 9 divers of the various groups were found to have hearing loss, this could be due to the repeated effect of the above mentioned factors in combination or separately. As mentioned earlier, experiments done at surface pressure will have no bearing over the effects of gases under increased pressure. The changed response of the body tissue under pressure gave birth to under-water physiology, which is a subject by itself now. It is not feasible in practice to study solitary effects of gases on hearing acuity due to the combined effect of pressure.

C o n c l u s i o n

Divers using Oxygen-Nitrogen, Hel ium-Air and Hel ium-Oxygen mixture showed TTS in hearing acuity after using these gases for 30-45 minutes and complete re- covery accrued within one week. This indicates a temporary effect of these gases during a short exposure on hearing acuity which is fully recoverable, repeated such exposures for a longer time may produce a higher frequency loss which could be of a permanent type.

References

Waterman, D. and Smith, P.F. (19~0) An investigation of the effects of Helium Oxygen breathing mixture on hearing in Naval personnel US, NS, Medical Centre Report No. 70--7.

62 Indian Journal of Otolaryngology, Volume 33, No. 2, June, 1981