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Diver Performance—Nitrogen Narcosis and Anxiety
Diver Performance—Nitrogen Narcosis and Anxiety J. P. O S B O R NE and F. M . D A V I S* United London Hospitals Diving Group and Royal Naval Physiological Laboratory, Alverstoke, Hants. 1. Introduction . . . . . . . · 2. Methods A. Experimental design . . . . . . B. Experimental tasks . . . . . · C. Physiological measurements . . . . . 3. Results A. Performance tests . . . . . · B. Plasma Cortisol . . . . . . · C. Electrocardiographic (EGG) and heart rate monitoring 4. Discussion . . . . . . . . . Acknowledgements . . . . . . . . References . . . . . . . . · .
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.217 218 .218 .219 220 221 .221 .221 .223 223 224 225
1. Introduction I n the simulate d condition s of a dry pressur e chamber , diver perfor mance is impaire d by the effects of nitroge n narcosi s (Keisling and Maag, 1962). Two experiment s conducte d in open water (Baddeley , 1965, 1966) showe d that there was a much greate r reductio n in diver efficienc y at depth than would be anticipate d from the pressur e chambe r studies , althoug h a third experimen t (Baddele y et al., 1968) did not show this difference . In his examinatio n of thes e results , Baddele y (1967) suggeste d that anxiety may be the caus e of the extra impairmen t of performance . Those experiment s were carried out in the Mediterranean . The presen t experiment , carried out under the more strenuou s condition s of British coasta l waters by the United London Hospital s Diving Group, was designe d to see whethe r diver performanc e at depth was impaire d to an extent similar to that in the Mediterranean , and if anxiety at depth could be demonstrate d by physiologica l measurements . The physiologica l respons e to anxiety is mediate d throug h the * Present address : 3500 90th Ave. S.E., Apt. 257, Mercer Island, Washington, 98040, U.S.A. 217
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J . P . O S B O R N E A N D F . M. DAVIS
sympatheti c nervou s syste m and the endocrin e organs , particularl y the pituitary and adrena l glands (Selye, 1957). It result s in change s in heart rate, blood pressure , respiration , metabolism , etc., which can be easily measure d on dry land but presen t greate r problem s during diving. However , the activity of the endocrin e glands themselves can be assesse d with moder n technique s by measurin g the levels in body fluidsof the hormone s they secrete . In this experiment , plasma levels of Cortisol, secrete d by the adrena l cortex , and its urinary excretion product s were measured , and electrocardiograph y (ECG) was performe d during the dives. 2. Methods A Experimental Design Each subjec t performe d 4 psychometri c tasks once at 3 m depth and once at 30 m in open water, all on the same day. Some delay betwee n dives was cause d by the subjec t having to remove all his diving equipment excep t dry suit for the collectio n of physiologica l data. The depth at which the subjec t would be teste d first was selecte d randoml y and subject s informe d the evenin g before . The subject s practise d each task 3 times on dry land and once in the sea at 3 m depth in order to minimize learnin g effects during the experiment . Procedure. The tests were carried out from the island of Kerrera , off Oban on the west coas t of Scotland , over a two week period in the summe r of 1969. The 3 and 30 m sites were both within 80 m of the shore . Polythen e sheet s four metres squar e were sprea d over the bottom at each site to preven t divers disturbin g the sand (at 3 m) or mud (at 30 m) and reducin g visibility. Temperature , depth and visibility were recorde d before each "run". Average water temperatur e throughou t the experimen t was 11°G with the shallo w site usuall y 1°C warmer than the deep one; tidal range was 3-4 m with a mean depth of 30 m at the deep site; visibility varied betwee n 3 and 10 m (mean 5 m) at the deep site. During the "runs " the subjec t sat on a rigid metal frame with a flat surfac e in front of him on which the tasks were performed , and with a 30 lb weight belt over his lap for stability . Althoug h artificial lighting was not though t necessar y at the shallo w site, the test bench at 30 m was always illuminate d (seale d beam lamp connecte d by cable to 2 X 12 V accumulator s on shore) . I n order to reach the sites , divers descende d directly down "into the blue", a procedur e generall y considere d more alarmin g than following the seabe d down. Subject s were then teste d by an experience d buddy diver who was in contac t with the surfac e via a D U GS set. Tasks were
219
NITROGEN NARCOSIS AND ANXIETY
timed by the buddy diver with a stop-watc h in a pressure-proo f perspe x case, and the surfac e was informe d simultaneously . The teste r signalle d the beginnin g and end of tasks to the subjec t by visual signals or by remova l of the task. The total time require d to complet e all four tasks was a maximum of 25 min from leaving the surface , thus necessitatin g a 5 min decompressio n stop at 3 m after the 30 m dives. Subjects. The subject s were 10 young male divers from the United London Hospital s Diving Group ; all excep t one were medica l students . Three had their first open water diving experienc e during the experiment, two had severa l years diving experience , and the rest were in their first or secon d year of diving. B. Experimental Tasks All subject s performe d the following four tasks : Sentence comprehension g test comprisin g a series of senThis was measure d with a reasonin tence s claiming to describ e the order of the two letters A and Β which followed the sentenc e as a pair—eithe r AB or BA. The subjec t had to decide whethe r the sentenc e describe d the letter pair correctly , i.e. :
True
1. A follows B — A B 2. Β is preceded by A — A B 3. A does not follow Β—ΒΑ
False
ν
The subjec t complete d as many items as possibl e in three minutes ; at each testin g he was given a differen t test form on which the same items occurre d in a differen t random order. Manual dexterity A modificatio n of the Hand Tool Dexterity Test (Bennett , 1965) was used in which nuts and bolts were transferre d from one end of a brass plate to the other in a specifie d manne r using a set of spanners . One of the three rows of nuts and bolts was omitted so that the task was complete d within the time allocate d during the dive. Time taken for complet e transfe r was recorded .
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Simple arithmetic The subjec t was given two period s of 30 second s in which to do as many simple additio n sums as possible . Each sum consiste d of 5 randoml y selecte d digits and the score was taken as the numbe r of sums correctl y complete d in the time allowed . Memory Each subjec t was require d to memoriz e a list of 10 words selecte d randoml y from the Teacher' s Word Book of 40,000 Words (Thorndik e and Large, 1944). This was done on four occasion s using a differen t list each time, and on each occasio n 30 s were allowed in which to memoriz e the list and 45 s in which to recall and write them down (this was ample time to write all 10 words down if the subjec t could remembe r them). However , on the secon d and third occasion s the period s of memorizin g and recall were separate d by the 30 second s arithmeti c describe d above . Thus, the first and last occasion s teste d the combine d effect of long- and short-ter m memor y whilst the secon d and third teste d only long-ter m memory . C. Physiological Measurements Attempts were made to monito r a numbe r of physiologica l paras and E GG monitorin g will meters , but only plasma Cortisol estimation be considere d here. P l a s m a Cortisol The maximum levels of Cortisol occur 30 min after the causativ e stress , so venou s blood sample s were taken in heparinize d syringe s immediatel y upon the subject' s return to the shore after each dive. A contro l sampl e was also taken prior to diving and a furthe r contro l was taken at a later date, after 30 min rest at the same time of day as the dive had been conducted . The sample s were store d frozen and subsequentl y measure d using the fluorimetric analysi s of Mattingle y (1962). ECG monitoring A very simple E CG techniqu e was used in which two stick-o n electrode s were placed at either end of the subject' s sternum . These were connecte d to a short cable passin g out of the dry suit (which ensured that the electrode s remaine d dry) throug h a seal at the right hand shoulder . This cable terminate d in one half of a McMurdo Water Mate underwate r connector . On reachin g the site the subjec t was
N I T R O G E N NARCOSIS A N D A N X I E T Y
221
connecte d via this plug to a cable runnin g to the shore where the signal s were collecte d by a Honeywel l Cardiovie w batter y operate d E CG machin e with a hot-wire pen recorder . Even with over 100 m of cable, some of it ordinar y lighting flex, the signal at the surfac e was perfectl y adequat e and require d no furthe r amplification . Meticulou s attentio n to electrod e applicatio n with thoroug h cleansin g of the skin was important . An earth electrod e was placed outsid e the suit on the divers cheek ; a poor earth connectio n resulte d in useles s recordings . 3. Results A. Performance Tests Each task was examine d for deterioratio n of performanc e at depth by a direct compariso n betwee n the score s of each individua l diver at the two depths ; these were then averaged . Three out of the four tests showe d significan t deterioratio n of performanc e at depth—sentenc e comprehension , manua l dexterit y and arithmetic ; these change s are TABLE
1. Average deterioration in performance of 3 tasks between 3 m and 3 0 m
depth. Test
Deterioration
1. Sentence Comprehension Arithmetic
16% 16% errors 6% to 14%
2.
3.
Manual Dexterity
22%
set out in Table 1. The memor y test showe d no significan t deterioratio n at depth either for short-ter m or long-ter m memory . Short-ter m memory was obtaine d from the differenc e betwee n immediat e recall (short + long) and delaye d recall (long only). B. Plasma Cortisol These estimation s show a numbe r of interestin g changes , and the values obtaine d are shown in Table 2. Pre-dive levels in all subject s were raised compare d with contro l levels, whethe r the divers were about to dive to 3 m or to 30 m first. Post-3 0 m dive levels were raised well above both contro l levels and the levels obtaine d after diving to
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3 m. Only subject s who had yet to dive to 30 m were levels after the 3 m dives significantl y above pre-dive values (Table 3).
TABLE
2. (a) Plasma Cortisol levels ( m i c r o g r a m m e s p e r 100 m l p l a s m a ) i n d i v e r s
d i v i n g to 30 m a n d t h e n 3 m . (b)
Plasma Cortisol levels ( m g per
100 m ; p l a s m a )
i n d i v e r s d i v i n g to 3 m a n d t h e n 30 m . Method error =
(a) Subject
±2
Pre-dive
Post 30 m
Post 3 m
Control (av. of 2)
14.5 9.0 22.0 17.0 21.0
22.5 14.5 20.0 27.0 20.5
21.0 7.0 10.0 16.0 15.0
12.5 13.75 19.5 9.5 10.0
Pre-dive
Post 3 m
Post 30 m
Control (av. of 2)
19.5 7.5 22.5 12.5 15.5
19.5 17.5 14.0 20.25 15.0
20.0 21.5 14.0 20.75 23.5
14.0 9.5 10.25 11.0 10.0
A.H. R.B. J.W. I.G. T.M.
(b) Subject
J.G. P.C. J.A. R.S. R.C.
TABLE
mg/100 m l p l a s m a .
3. Comparison of plasma Cortisol levels between different diving situations. Comparison
1. 2. 3. 4. 5. 6.
Pre-dive v. control Pre 3 m v. pre 30 m Post 30 m v. control Post 30 m v. post 3 m Post diving v. control Post 3 m/pre 30 m v. control
% Difference
+48% insignificant +87% +31% insignificant + 71%
Statistical analysis η = 10
t = 3.10, (ρ 0.05) t = 5.39, t = 3.59, (ρ 0.05) t = 6.98,
ρ 0.01 ρ 0.01 ρ 0.01 ρ 0.01
NITROGEN NARCOSIS AND ANXIETY
223
C. Electrocardiographic (ECG) and Heart Rate Monitoring Where E CG monitorin g was not possible , heart rate was measure d at the right wrist by palpatio n of the radial artery. No particula r pattern of chang e was noted in these divers , and heart rates were not raised significantl y during dives to either depth even in novice divers . Only intermitten t E CG monitorin g was achieved . During these periods no abnormalitie s of cardia c rhythm were demonstrate d at any time. Althoug h some excellen t E CG tracing s were obtained , the data are insufficien t for detaile d analysis . What has been shown is that with simple equipmen t adequat e tracing s from working divers at depth can be obtained .
4. Discussion The deterioratio n of 2 2% in manua l dexterit y is similar to that found in Mediterranea n boat diving (20% at 30 m) and far greate r than that found under simulate d condition s in a pressur e chambe r (Baddeley , 1965). The deterioratio n of 16% in sentenc e comprehensio n is comparable to the 15% found by Baddele y et aL (1968) in the same experiment in which deterioratio n of manua l dexterit y was only 3.5%. Arithmetic errors follow the same trend as seen by Baddele y (1966) in boat dives to 60 m—6% at 3 m to 2 1% at 60 m. Thus performanc e in British waters seem s to be impaire d to an extent similar to boat diving in Mediterranea n conditions . One possibl e interpretatio n of the discrepanc y betwee n manua l dexterit y and sentenc e comprehensio n result s is that the manua l dexterit y task was clearly made more difficult by being performe d in the water (Baddeley , 1965) wherea s this is not the case for sentenc e comprehensio n (Baddele y et aL, 1968). This implies that the manua l dexterit y task was more sensitiv e underwate r becaus e of the increase d difficulty which therefor e allows it to exhibit a larger eifect of anxiety / narcosis . There is no correlatio n betwee n the increas e in plasma C o r t i s o l and the decreas e in performance ; this would be expecte d since it is known that a rise in C o r t i s o l level is a non-specifi c respons e to a psychologica l stres s and is not correlate d with the degre e of anxiety of the individua l (Bridges et aL, 1968). However , the increas e in Cortisol associate d with the 30 m dives is most likely to be due to an anxiety respons e to the deep diving. Unfortunately , the influenc e of cold stres s on the Cortisol levels canno t be ruled out in this experimen t as it is known that exposure to a cold environmen t also result s in raised plasma C o r t i s o l levels
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(Keatinge , 1969). Only oral temperature s were taken with any regularity, and this is undoubtedl y inadequat e for a reasonabl e assessmen t of the cold stres s experience d in this series of dives. Accurat e body temperatur e measurements , thoug h difficult to obtain in divers , are a necessit y for furthe r studies . The result s presente d here fulfil the aims of this initial field study in showin g a deterioratio n in some aspect s of diver performanc e over and above that demonstrate d in dry pressur e chambe r work or in nonstressfu l open water diving. In addition , change s in at least one physio logical parameter—plasm a Cortisol—known to be influence d by anxiety , were demonstrated . Of interes t is the differenc e in the result s of the manua l dexterit y test and the reasonin g test performe d in stressfu l and non-stressfu l diving conditions . This suggest s that differen t factors are influencin g differen t aspect s of diver performanc e at depth . Interpretatio n of these result s can only be tentativ e as a numbe r of variable s have been inadequatel y assessed , most particularl y body temperatur e and the tightnes s of diving procedur e control . Acknowledgements We are indebted to Dr. A. Baddeley, Dr. P. Cole, Dr. H . V. Hempleman, and Dr. G. Wilton-Davis for their invaluable advice and assistance. We would also like to thank our sponsors: T h e British Sub-Aqua Club, British Petroleum, T h e British Oxygen Company, T h e Gilchrist Educational Trust, and the Deans of King's College, St. Bartholemew's and St. Thomas's Hospital Medical Schools.
References Baddeley, A. D. (1965). T h e influence of depth on manual dexterity of free divers: a comparison between open sea and pressure chamber testing. J. Appl. Psychol. 50, 81-85. Baddeley, A. D. (1965). T h e relative efficiency at depth of divers breathing air and
oxyhelium, Underwater Assoc. Symp. Malta, 1965, 13.
Baddeley, A. D . (1967). T h e interaction of stresses and diver performance. Under-
water Assoc. Rep. 1966-1967, 35.
Baddeley, A. D., De Figueredo, J . W., Hawkswell Curtis, J . W. and Williams, A. N. (1968). Nitrogen narcosis and underwater performance. Ergonomics 11(2), 157-164. Bennett, G. K . (1965). "Manual of Directions, H a n d Tool Dexterity Test". T h e Psychology Corporation, New York. Bridges, P. K . , Jones, M . T . and Leak, D. (1968). A comparative study of four
psychological concomitants of anxiety. Archiv. Gen. Psychiat. 19, 141-145. Keatinge, W. R . (1969), "Survival in Cold Water". Blackwell Scientific Publications, Oxford. Keisling, R . J . and M a a g , C. H . (1962). Performance impairment as a function of
nitrogen narcosis. J. AppL Physiol. 46, 91-95. Mattingley, D. (1962). J. Clin. Path. 15, 374. Selye, H . (1957). "The Stress of Life". Longmans Green, London.
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.217 218 .218 .219 220 221 .221 .221 .223 223 224 225
1. Introduction I n the simulate d condition s of a dry pressur e chamber , diver perfor mance is impaire d by the effects of nitroge n narcosi s (Keisling and Maag, 1962). Two experiment s conducte d in open water (Baddeley , 1965, 1966) showe d that there was a much greate r reductio n in diver efficienc y at depth than would be anticipate d from the pressur e chambe r studies , althoug h a third experimen t (Baddele y et al., 1968) did not show this difference . In his examinatio n of thes e results , Baddele y (1967) suggeste d that anxiety may be the caus e of the extra impairmen t of performance . Those experiment s were carried out in the Mediterranean . The presen t experiment , carried out under the more strenuou s condition s of British coasta l waters by the United London Hospital s Diving Group, was designe d to see whethe r diver performanc e at depth was impaire d to an extent similar to that in the Mediterranean , and if anxiety at depth could be demonstrate d by physiologica l measurements . The physiologica l respons e to anxiety is mediate d throug h the * Present address : 3500 90th Ave. S.E., Apt. 257, Mercer Island, Washington, 98040, U.S.A. 217
218
J . P . O S B O R N E A N D F . M. DAVIS
sympatheti c nervou s syste m and the endocrin e organs , particularl y the pituitary and adrena l glands (Selye, 1957). It result s in change s in heart rate, blood pressure , respiration , metabolism , etc., which can be easily measure d on dry land but presen t greate r problem s during diving. However , the activity of the endocrin e glands themselves can be assesse d with moder n technique s by measurin g the levels in body fluidsof the hormone s they secrete . In this experiment , plasma levels of Cortisol, secrete d by the adrena l cortex , and its urinary excretion product s were measured , and electrocardiograph y (ECG) was performe d during the dives. 2. Methods A Experimental Design Each subjec t performe d 4 psychometri c tasks once at 3 m depth and once at 30 m in open water, all on the same day. Some delay betwee n dives was cause d by the subjec t having to remove all his diving equipment excep t dry suit for the collectio n of physiologica l data. The depth at which the subjec t would be teste d first was selecte d randoml y and subject s informe d the evenin g before . The subject s practise d each task 3 times on dry land and once in the sea at 3 m depth in order to minimize learnin g effects during the experiment . Procedure. The tests were carried out from the island of Kerrera , off Oban on the west coas t of Scotland , over a two week period in the summe r of 1969. The 3 and 30 m sites were both within 80 m of the shore . Polythen e sheet s four metres squar e were sprea d over the bottom at each site to preven t divers disturbin g the sand (at 3 m) or mud (at 30 m) and reducin g visibility. Temperature , depth and visibility were recorde d before each "run". Average water temperatur e throughou t the experimen t was 11°G with the shallo w site usuall y 1°C warmer than the deep one; tidal range was 3-4 m with a mean depth of 30 m at the deep site; visibility varied betwee n 3 and 10 m (mean 5 m) at the deep site. During the "runs " the subjec t sat on a rigid metal frame with a flat surfac e in front of him on which the tasks were performed , and with a 30 lb weight belt over his lap for stability . Althoug h artificial lighting was not though t necessar y at the shallo w site, the test bench at 30 m was always illuminate d (seale d beam lamp connecte d by cable to 2 X 12 V accumulator s on shore) . I n order to reach the sites , divers descende d directly down "into the blue", a procedur e generall y considere d more alarmin g than following the seabe d down. Subject s were then teste d by an experience d buddy diver who was in contac t with the surfac e via a D U GS set. Tasks were
219
NITROGEN NARCOSIS AND ANXIETY
timed by the buddy diver with a stop-watc h in a pressure-proo f perspe x case, and the surfac e was informe d simultaneously . The teste r signalle d the beginnin g and end of tasks to the subjec t by visual signals or by remova l of the task. The total time require d to complet e all four tasks was a maximum of 25 min from leaving the surface , thus necessitatin g a 5 min decompressio n stop at 3 m after the 30 m dives. Subjects. The subject s were 10 young male divers from the United London Hospital s Diving Group ; all excep t one were medica l students . Three had their first open water diving experienc e during the experiment, two had severa l years diving experience , and the rest were in their first or secon d year of diving. B. Experimental Tasks All subject s performe d the following four tasks : Sentence comprehension g test comprisin g a series of senThis was measure d with a reasonin tence s claiming to describ e the order of the two letters A and Β which followed the sentenc e as a pair—eithe r AB or BA. The subjec t had to decide whethe r the sentenc e describe d the letter pair correctly , i.e. :
True
1. A follows B — A B 2. Β is preceded by A — A B 3. A does not follow Β—ΒΑ
False
ν
The subjec t complete d as many items as possibl e in three minutes ; at each testin g he was given a differen t test form on which the same items occurre d in a differen t random order. Manual dexterity A modificatio n of the Hand Tool Dexterity Test (Bennett , 1965) was used in which nuts and bolts were transferre d from one end of a brass plate to the other in a specifie d manne r using a set of spanners . One of the three rows of nuts and bolts was omitted so that the task was complete d within the time allocate d during the dive. Time taken for complet e transfe r was recorded .
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J . P. OSBORNE AND F. M. DAVIS
Simple arithmetic The subjec t was given two period s of 30 second s in which to do as many simple additio n sums as possible . Each sum consiste d of 5 randoml y selecte d digits and the score was taken as the numbe r of sums correctl y complete d in the time allowed . Memory Each subjec t was require d to memoriz e a list of 10 words selecte d randoml y from the Teacher' s Word Book of 40,000 Words (Thorndik e and Large, 1944). This was done on four occasion s using a differen t list each time, and on each occasio n 30 s were allowed in which to memoriz e the list and 45 s in which to recall and write them down (this was ample time to write all 10 words down if the subjec t could remembe r them). However , on the secon d and third occasion s the period s of memorizin g and recall were separate d by the 30 second s arithmeti c describe d above . Thus, the first and last occasion s teste d the combine d effect of long- and short-ter m memor y whilst the secon d and third teste d only long-ter m memory . C. Physiological Measurements Attempts were made to monito r a numbe r of physiologica l paras and E GG monitorin g will meters , but only plasma Cortisol estimation be considere d here. P l a s m a Cortisol The maximum levels of Cortisol occur 30 min after the causativ e stress , so venou s blood sample s were taken in heparinize d syringe s immediatel y upon the subject' s return to the shore after each dive. A contro l sampl e was also taken prior to diving and a furthe r contro l was taken at a later date, after 30 min rest at the same time of day as the dive had been conducted . The sample s were store d frozen and subsequentl y measure d using the fluorimetric analysi s of Mattingle y (1962). ECG monitoring A very simple E CG techniqu e was used in which two stick-o n electrode s were placed at either end of the subject' s sternum . These were connecte d to a short cable passin g out of the dry suit (which ensured that the electrode s remaine d dry) throug h a seal at the right hand shoulder . This cable terminate d in one half of a McMurdo Water Mate underwate r connector . On reachin g the site the subjec t was
N I T R O G E N NARCOSIS A N D A N X I E T Y
221
connecte d via this plug to a cable runnin g to the shore where the signal s were collecte d by a Honeywel l Cardiovie w batter y operate d E CG machin e with a hot-wire pen recorder . Even with over 100 m of cable, some of it ordinar y lighting flex, the signal at the surfac e was perfectl y adequat e and require d no furthe r amplification . Meticulou s attentio n to electrod e applicatio n with thoroug h cleansin g of the skin was important . An earth electrod e was placed outsid e the suit on the divers cheek ; a poor earth connectio n resulte d in useles s recordings . 3. Results A. Performance Tests Each task was examine d for deterioratio n of performanc e at depth by a direct compariso n betwee n the score s of each individua l diver at the two depths ; these were then averaged . Three out of the four tests showe d significan t deterioratio n of performanc e at depth—sentenc e comprehension , manua l dexterit y and arithmetic ; these change s are TABLE
1. Average deterioration in performance of 3 tasks between 3 m and 3 0 m
depth. Test
Deterioration
1. Sentence Comprehension Arithmetic
16% 16% errors 6% to 14%
2.
3.
Manual Dexterity
22%
set out in Table 1. The memor y test showe d no significan t deterioratio n at depth either for short-ter m or long-ter m memory . Short-ter m memory was obtaine d from the differenc e betwee n immediat e recall (short + long) and delaye d recall (long only). B. Plasma Cortisol These estimation s show a numbe r of interestin g changes , and the values obtaine d are shown in Table 2. Pre-dive levels in all subject s were raised compare d with contro l levels, whethe r the divers were about to dive to 3 m or to 30 m first. Post-3 0 m dive levels were raised well above both contro l levels and the levels obtaine d after diving to
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J . P . O S B O R N E A N D F . M. D A V I S
3 m. Only subject s who had yet to dive to 30 m were levels after the 3 m dives significantl y above pre-dive values (Table 3).
TABLE
2. (a) Plasma Cortisol levels ( m i c r o g r a m m e s p e r 100 m l p l a s m a ) i n d i v e r s
d i v i n g to 30 m a n d t h e n 3 m . (b)
Plasma Cortisol levels ( m g per
100 m ; p l a s m a )
i n d i v e r s d i v i n g to 3 m a n d t h e n 30 m . Method error =
(a) Subject
±2
Pre-dive
Post 30 m
Post 3 m
Control (av. of 2)
14.5 9.0 22.0 17.0 21.0
22.5 14.5 20.0 27.0 20.5
21.0 7.0 10.0 16.0 15.0
12.5 13.75 19.5 9.5 10.0
Pre-dive
Post 3 m
Post 30 m
Control (av. of 2)
19.5 7.5 22.5 12.5 15.5
19.5 17.5 14.0 20.25 15.0
20.0 21.5 14.0 20.75 23.5
14.0 9.5 10.25 11.0 10.0
A.H. R.B. J.W. I.G. T.M.
(b) Subject
J.G. P.C. J.A. R.S. R.C.
TABLE
mg/100 m l p l a s m a .
3. Comparison of plasma Cortisol levels between different diving situations. Comparison
1. 2. 3. 4. 5. 6.
Pre-dive v. control Pre 3 m v. pre 30 m Post 30 m v. control Post 30 m v. post 3 m Post diving v. control Post 3 m/pre 30 m v. control
% Difference
+48% insignificant +87% +31% insignificant + 71%
Statistical analysis η = 10
t = 3.10, (ρ 0.05) t = 5.39, t = 3.59, (ρ 0.05) t = 6.98,
ρ 0.01 ρ 0.01 ρ 0.01 ρ 0.01
NITROGEN NARCOSIS AND ANXIETY
223
C. Electrocardiographic (ECG) and Heart Rate Monitoring Where E CG monitorin g was not possible , heart rate was measure d at the right wrist by palpatio n of the radial artery. No particula r pattern of chang e was noted in these divers , and heart rates were not raised significantl y during dives to either depth even in novice divers . Only intermitten t E CG monitorin g was achieved . During these periods no abnormalitie s of cardia c rhythm were demonstrate d at any time. Althoug h some excellen t E CG tracing s were obtained , the data are insufficien t for detaile d analysis . What has been shown is that with simple equipmen t adequat e tracing s from working divers at depth can be obtained .
4. Discussion The deterioratio n of 2 2% in manua l dexterit y is similar to that found in Mediterranea n boat diving (20% at 30 m) and far greate r than that found under simulate d condition s in a pressur e chambe r (Baddeley , 1965). The deterioratio n of 16% in sentenc e comprehensio n is comparable to the 15% found by Baddele y et aL (1968) in the same experiment in which deterioratio n of manua l dexterit y was only 3.5%. Arithmetic errors follow the same trend as seen by Baddele y (1966) in boat dives to 60 m—6% at 3 m to 2 1% at 60 m. Thus performanc e in British waters seem s to be impaire d to an extent similar to boat diving in Mediterranea n conditions . One possibl e interpretatio n of the discrepanc y betwee n manua l dexterit y and sentenc e comprehensio n result s is that the manua l dexterit y task was clearly made more difficult by being performe d in the water (Baddeley , 1965) wherea s this is not the case for sentenc e comprehensio n (Baddele y et aL, 1968). This implies that the manua l dexterit y task was more sensitiv e underwate r becaus e of the increase d difficulty which therefor e allows it to exhibit a larger eifect of anxiety / narcosis . There is no correlatio n betwee n the increas e in plasma C o r t i s o l and the decreas e in performance ; this would be expecte d since it is known that a rise in C o r t i s o l level is a non-specifi c respons e to a psychologica l stres s and is not correlate d with the degre e of anxiety of the individua l (Bridges et aL, 1968). However , the increas e in Cortisol associate d with the 30 m dives is most likely to be due to an anxiety respons e to the deep diving. Unfortunately , the influenc e of cold stres s on the Cortisol levels canno t be ruled out in this experimen t as it is known that exposure to a cold environmen t also result s in raised plasma C o r t i s o l levels
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J . P . O S B O R N E A N D F . M. D A V I S
(Keatinge , 1969). Only oral temperature s were taken with any regularity, and this is undoubtedl y inadequat e for a reasonabl e assessmen t of the cold stres s experience d in this series of dives. Accurat e body temperatur e measurements , thoug h difficult to obtain in divers , are a necessit y for furthe r studies . The result s presente d here fulfil the aims of this initial field study in showin g a deterioratio n in some aspect s of diver performanc e over and above that demonstrate d in dry pressur e chambe r work or in nonstressfu l open water diving. In addition , change s in at least one physio logical parameter—plasm a Cortisol—known to be influence d by anxiety , were demonstrated . Of interes t is the differenc e in the result s of the manua l dexterit y test and the reasonin g test performe d in stressfu l and non-stressfu l diving conditions . This suggest s that differen t factors are influencin g differen t aspect s of diver performanc e at depth . Interpretatio n of these result s can only be tentativ e as a numbe r of variable s have been inadequatel y assessed , most particularl y body temperatur e and the tightnes s of diving procedur e control . Acknowledgements We are indebted to Dr. A. Baddeley, Dr. P. Cole, Dr. H . V. Hempleman, and Dr. G. Wilton-Davis for their invaluable advice and assistance. We would also like to thank our sponsors: T h e British Sub-Aqua Club, British Petroleum, T h e British Oxygen Company, T h e Gilchrist Educational Trust, and the Deans of King's College, St. Bartholemew's and St. Thomas's Hospital Medical Schools.
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Baddeley, A. D . (1967). T h e interaction of stresses and diver performance. Under-
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