4.1 Part 1: POSTAL QUESTIONNAIRE SURVEY
4.1.5 Forgetfulness or loss of concentration
Duration of years worked in respective industries: The duration of a diver’s career (p<0.001), but not offshore workers (p=0.5), was related to reported forgetfulness or loss of concentration (Figure 3).
total years worked offshore
>15 11-15 5-10
<5
% report forgetful or loss of concentration
40
30
20
10
0
5% (6)
8% (13) 7% (17)
5% (24)
total years worked as a profedssional diver
> 15 11-15 5-10
< 5
% report forgetful or loss of concentration
40
30
20
10
0
7% (9)
13% (39) 19% (70)
24% (145)
Figure 3 Relationship between reported ‘forgetfulness or loss of concentration’ and duration of offshore and diving careers (raw data)
Diving experience
There was no difference in the prevalence of reported forgetfulness or loss of concentration between the divers who were currently diving professionally (20%) and those who were not (18%).
Decompression illness: 52% of the forgetful divers compared with 32% of non forgetful divers reported having suffered DCI (p<0.001). The proportion of forgetful divers who reported having suffered pain only DCI but not neurological DCI (25%) and those who had suffered neurological and pain only (31%) did not differ significantly (p=0.11). Furthermore, the difference in the proportion of forgetful divers who reported suffering from DCI only once (22%) or more than once (30%) failed to reach a level of statistical significance at the 5% level (p=0.07). These comparisons suggest that having had DCI is an important factor with relation to reported forgetfulness, but the type of DCI and the number of events is less significant. There was no indication, therefore of a dose related effect. Forgetfulness or loss of concentration was not fully explained by DCI, since the difference between divers and offshore workers remained
highly significant after including DCI in the logistic regression model (odds ratio (95% CI): 2.3 (1.6-3.3), p<0.001).
Diving techniques: As illustrated in Figure 4, reported forgetfulness was associated with increased experience of the diving technique for surface oxygen decompression dives, mixed gas bounce dives and days spent in saturation, but not SCUBA or other air/nitox (surface supply / demand with air or nitrox) diving.
Surface Decompression dives (no. of dive)
>1000 501-1000 101-500 1-100 none OSW
% report forgetful or loss of concentration
40
30
20
10
0 6% (60)
10% (34) 13% (59)
23% (87) 30% (68)
23% (24)
SCUBA (no. of dives)
>1000 501-1000 101-500 1-100 none OSW
% report forgetful or loss of concentration
40
30
20
10
0 6% (60)
21% (18) 17% (47)
19% (86) 16% (46)
19% (74)
Saturation dives (no. of days in saturation)
>1000 301-1000 1-300 none OSW
% forgetful or loss of concentration
40
30
20
10
0 6% (60)
13% (110) 20% (53)
32% (73)
24% (36)
Other air /nitrox Dives (no. of dives)
>500 101-500 1-100 none OSW
%forgetful or loss of concentration
40
30
20
10
0 6% (60)
14% (76) 21% (78)
19% (50) 22% (68)
Mixed gas bounce dives (no. of dives)
>500 101-500 1-100 none OSW
% report forgetful or loss of concentration
40
30
20
10
0 6% (60)
13% (115) 23% (121)
36% (9)
31% (27)
Figure 4 Percent (number) of divers reporting ‘forgetfulness or loss of concentration’
using different diving techniques (raw data)
A logistic regression model including each diving technique as a continuous variable was adjusted for lifestyle factors, head injury, welding and lost time accidents. The model showed a significant positive relationship between surface oxygen decompression diving, mixed gas bounce diving and saturation diving and reported ‘forgetfulness or loss of concentration’
(Table 9). The odds ratios are based per 100 dives or days in saturation. Since DCI was associated with forgetfulness, this was added to the logistic regression model. Adjustment for DCI resulted in the loss of the effect of surface oxygen decompression diving, but saturation diving and mixed gas bounce diving remained highly related to reports of forgetfulness or loss of concentration.
Divers who had only used SCUBA (n=183) did not differ significantly from offshore workers when reporting forgetfulness (9% vs. 6%, p=0.1). This difference remained the same when divers having only used SCUBA or surface demand (n=263) were compared with offshore workers. For those divers who had used all the techniques described, 20% reported forgetfulness or loss of concentration. The techniques associated with forgetfulness are those used predominantly in the offshore diving industry.
Table 9 Logistic regression models assessing the relationship between the amount of diving using different techniques and symptoms
Model 1*
OR (95% CI) p
Model 2**
OR (95% CI) p Forgetful or loss of concentration
Main group (diver)
Diving techniques (per 100 dives):
Other air/nitrox dives (surface demand) SCUBA
Surface decompression Saturation days Mixed gas bounce
2.23 (1.52-3.28) <0.001
0.99 (0.96-1.01) 0.25 1.00 (0.98-1.02) 0.98 1.04 (1.01-1.08) 0.02 1.04 (1.01-1.07) 0.01 1.27 (1.07-1.50) 0.006
1.98 (1.32-2.97) 0.001
0.99 (0.94-1.02) 0.41 1.00 (0.98-1.03) 0.95 1.03 (0.99-1.07) 0.10 1.04 (1.00-1.07) 0.02 1.22 (1.03-1.44) 0.02 Joint pain or muscle stiffness
Main group (diver)
Diving techniques (per 100 dives):
Other air/nitrox dives (surface demand) SCUBA
Surface decompression Saturation days Mixed gas bounce
0.98 (0.74-1.30) 0.89
1.04 (1.00-1.07) 0.04 0.99 (0.97-1.01) 0.17 1.01 (0.98-1.04) 0.58 1.01 (0.98-1.04) 0.61 1.24 (1.06-1.45) 0.007
0.89 (0.66-1.19) 0.43
1.04 (1.00-1.07) 0.05 0.99 (0.97-1.01) 0.21 1.00 (0.97-1.04) 0.84 1.00 (0.98-1.03) 0.78 1.22 (1.04-1.42) 0.02 Impaired hearing
Main group (diver)
Diving techniques (per 100 dives):
Other air/nitrox dives (surface demand) SCUBA
Surface decompression Saturation days Mixed gas bounce
0.93 (0.65-1.33) 0.69
1.00 (0.96-1.05) 0.89 1.00 (0.98-1.03) 0.78 1.01 (0.97-1.05) 0.68 1.05 (1.02-1.09) 0.002 1.03 (0.85-1.24) 0.78
0.91 (0.62-1.32) 0.61
1.00 (0.96-1.05) 0.89 1.00 (0.98-1.03) 0.76 1.01 (0.97-1.04) 0.73 1.05 (1.02-1.09) 0.003 1.02 (0.85-1.24) 0.81
* analysis adjusted for age, smoking, binge drinking, head injury, welding and lost time accidents.
** adjusted as for model 1 plus DCI
Other symptoms
Although the other 2 main symptoms, joint pain or muscle stiffness and impaired hearing, did not show a difference between divers and offshore workers after adjustments were made for work related factors (welding and accidents), their relationship with the use of different diving techniques was investigated (Table 9).
Joint pain or muscle stiffness
Adjustment for lifestyle and work related factors did not show a difference between divers and offshore workers, but there was a significant dose response with mixed gas bounce diving and
‘other’ air/nitrox (surface supply / demand with air or nitrox) dives for joint pain or muscle stiffness. The additional adjustment for DCI (see Table 9 model 2) did not alter the dose response relationships seen in model 1.
Decompression illness: Divers reporting joint pain or muscle stiffness were more likely to have suffered DCI (49%) than those not reporting these symptoms (31%) (p<0.001). Of the divers having suffered DCI, the same proportion reporting and not reporting joint pain or muscle stiffness had suffered pain only DCI but not neurological DCI (72% vs. 70%) and neurological DCI (with or without pain only DCI) (28% vs. 30%) (p=0.7). Divers with joint pain or muscle stiffness were more likely to have suffered more than one episode of DCI (pain only or neurological) (26%) than those without joint pain (14%) (p<0.001). This suggests, from this limited data, that there might be a dose response with DCI and reported joint pain or muscle stiffness.
Impaired hearing
As seen with joint pain and muscle stiffness, there was no difference between divers and offshore workers for impaired hearing after adjustments for lifestyle and work related factors, but there was a significant dose relationship with saturation diving. Adjustment for DCI did not alter the dose response with saturation diving.
Decompression illness: Divers reporting impaired hearing (48%) were more likely to have suffered DCI than divers not reporting impaired hearing (34%) (p<0.001). These two groups did not differ significantly in the type of DCI suffered (p=0.1). Of those reporting DCI, 36% of divers with impaired hearing had suffered neurological DCI compared with 28% not reporting hearing impairment. Impaired hearing, however, did not appear to be associated with increased incidence of DCI (p=0.2).