Assessment of Alertness and Cognitive Performance of Closed Circuit Rebreather Divers With the Critical Flicker Fusion Frequency Test in Arctic Diving Conditions

Abstract

Introduction: Cold water imposes many risks to the diver. These risks include decompression illness, physical and cognitive impairment, and hypothermia. Cognitive impairment can be estimated using a critical flicker fusion frequency (CFFF) test, but this method has only been used in a few studies conducted in an open water environment. We studied the effect of the cold and a helium-containing mixed breathing gas on the cognition of closed circuit rebreather (CCR) divers. Materials and Methods: Twenty-three divers performed an identical dive with controlled trimix gas with a CCR device in an ice-covered quarry. They assessed their thermal comfort at four time points during the dive. In addition, their skin temperature was measured at 5-min intervals throughout the dive. The divers performed the CFFF test before the dive, at target depth, and after the dive. Results: A statistically significant increase of 111.7% in CFFF values was recorded during the dive compared to the pre-dive values (p < 0.0001). The values returned to the baseline after surfacing. There was a significant drop in the divers' skin temperature of 0.48°C every 10 min during the dive (p < 0.001). The divers' subjectively assessed thermal comfort also decreased during the dive (p = 0.01). Conclusion: Our findings showed that neither extreme cold water nor helium-containing mixed breathing gas had any influence on the general CFFF profile described in the previous studies from warmer water and where divers used other breathing gases. We hypothesize that cold-water diving and helium-containing breathing gases do not in these diving conditions cause clinically relevant cerebral impairment. Therefore, we conclude that CCR diving in these conditions is safe from the perspective of alertness and cognitive performance.

Keywords: arctic diving; inert gas narcosis; mixed gas diving; technical diving; thermal control.

Figure 1

The critical flicker fusion frequency device that was used in the study to evaluate the divers’ level of alertness.

Figure 2

Percentage variation of CFFF during and after the dive to 45 meters with CCR (low set point 0.7 and high set point 1.2, the diluent being trimix 19/40) in relation to pre-dive measurements. The pre-dive measurements are marked as the 100% reference line. Each subject is compared to his or her own measurements. The box plot represents quantiles, and the diamond represents the 95% confidence interval (^***p = < 0.0001, ns = not significant). Sample size is 20 in the pre-dive analysis and 17 in the pre-post analysis.

Figure 3

The subjective warmth assessment for four time points at 30, 40, 50, and 60 min after the beginning of the dive. The scale is from 5 to 1, where 5 stands for neutral warmth and 1 for freezing cold. The boxes represent the percentage of answers in each category. There is a statistically significant drop in the “5” category and a statistically significant increase in the “3” category. The sample size is 22 in the ST body 30 min, ST body 40 min and ST body 50 min categories, and 20 in the ST body 60 min category.

Figure 4

The linear regression model of temperature measurements from immersion, when the divers put their faces into the water, when the divers submersed and from that point onward in 5-min intervals. There was a statistically significant (p < 0.001) drop in temperature in all locations of measurement.