2007, Piran, Slovenia

Diving Physiology
same sequence. The dose of 30% nitrous oxide was selected as previous studies have
suggested that doses of between 20% and 30% produce marked and consistent effects
on performance (Fagan et al., 1994). During the first trial subjects inspired air, whilst
during the subsequent 10 minute periods they inspired a normoxic mixture containing
30% N2O. Assessment during the second condition did not begin until ten minutes of
continuous inhalation had passed, in order to achieve a stable plateau of
approximately 95% concentration in the brain (Eger, 1985). In each condition subjects
started with VSRT and continue with TMT-A, than with TMT-B. Before each test the
procedure was explained and after that performed for familiarization. The order was
the same for all subjects. The breathing mixtures were humidified by passing them
through a water bath maintained at room temperature (23-25 o C). The difference in
susceptibility was evaluated using Students test-t and Chi-square test (p≤0.05).
RESULTS
There was no statistical difference between groups in age and body mass index.
During both the Air and N2O trials, the average (SD) VSRT were significantly shorter
in male than in females (Table 1). Similar results were noticed in TMT-A, but the
differences were not significant. In contrast, there was a tendency, albeit not
significant, of the females requiring less time for execution of the more demanding
TMT-B in both conditions.
Table 1. Difference in response between females and males in Visual Simple Reaction Time (VSRT)
and Trial Making Test (TMT) during Air and N2O trials.
AIR 30% N2O
Women Men Significance Women Men Significance
VSRT (ms) 244 (36) 214 (14) p=0.018 272 (44) 223 (38) p=0.009
TMT-A (s) 17.4 (5.3) 15.7 (3.8) NS 18.4 (6.0) 17.1 (3.6) NS
TMT-B (s) 34.7(10.6) 39.7 (14.5) NS 37.4 (22.5) 47.5 (23.7) NS
The changes in VSRT were significant only for the females (Table 2). There were no
statistically significant differences in the times for completing TMT-A or TMT-B in
either of the two groups. Time for TMT-A execution was prolonged in both groups
similar and statistically not significant.
Table 2. Difference inside women’s and men’s group in Visual Simple Reaction Time (VSRT) and
Trial Making Test (TMT) during breathing air and normoxic mixture of 30% N2O.
Females Males
AIR 30% N2O Significance AIR 30% N2O Significance
VSRT (ms) 244 (36) 272 (44) p=0.007 214 (14) 223 (38) NS
TMT-A (s) 17.4 (5.3) 18.4 (6.0) NS 15.7 (3.8) 17.1 (3.6) NS
TMT-B (s) 34.7 (10.6) 37.4 (22.5) NS 39.7 (14.5) 47.5 (23.7) NS
Eight subjects (3 females and 5 males) performed VSRT equally or better during the
N2O as in the Air trial. Likewise eight subjects (5 females and 3 males) performed
TMT-A equally or better. Eleven subjects (seven women and four men) needed equal
or shorter time to perform TMT-B. There were no statistical differences between
genders in the number of subjects who develop acute tolerance in all three tests.
DISCUSSION
Our results are in agreement with those of Dane and Erzurumluoglu (2003) and Der
and Deary (2006), who reported that in almost every age group, males have faster
67