Diver performance in cold water

Cognitive Performance During Night Work in the Cold

Objective: The objective of this study was to investigate how night work at low ambient temperatures affects cognitive performance (short-term memory and reaction time), skin- and core temperature, thermal comfort, sleepiness, and cortisol. We hypothesized that cognitive performance is reduced at night compared with daytime and worsened when exposed to low ambient temperatures.

Method: Eleven male subjects were recruited to perform three tests in a climatic chamber at night and daytime: Night –2°C, Night 23°C and Day 23°C. Each test lasted 6 h. Cognitive performance (short-term memory and reaction time), skin- and core temperature, thermal sensation and comfort, cortisol levels and sleepiness were measured during the tests.

Results: A lower mean skin temperature and corresponding lower thermal sensation were observed at Night –2°C compared to Day 23°C and Night 23°C. Night work caused increased sleepiness and lower cortisol levels, but was not affected by changes in ambient temperatures, thermal comfort, or skin temperatures. There was no effect of either day/night work nor ambient temperature on the short-term memory or reaction time test.

Conclusion: Lower skin- and core temperature were observed at night when exposed to low ambient temperature (–2°C), but there was no effect on short-term memory or reaction time. Increased sleepiness and lower cortisol levels were observed at night compared to daytime and was not influenced by low ambient temperature at night. The result from this study suggests that cognitive performance (short-term memory and reaction time) is not adversely affected by night work when exposed to low ambient temperatures if adequate protective clothing is worn.

Evaluation of cognitive performance and neurophysiological function during repeated immersion in cold water

Exposure to cold causes disturbances in cognitive performance that can have a profound impact on the safety, performance, and success of populations that frequent cold environments. It has recently been suggested that repeated cold stress, resulting in cold acclimation, may be a potential strategy to mitigate the cognitive impairments frequently seen upon exposure to cold temperatures. The purpose of this study, therefore, was to examine cognitive and neurophysiological function during repeated cold water immersion. Twelve healthy participants consisting of 8 males and 4 females (mean ± SD age: 26 ± 5 years, height: 174.0 ± 8.9 cm, weight: 75.6 ± 13.1 kg) completed seven 90-minute immersions in 10 °C water, each separated by 24 h. During immersions 1, 4, and 7, a double-digit addition task and a computer-based psychomotor vigilance task (PVT) were administered to assess cognitive performance, while neurophysiological function was assessed using electroencephalography (EEG) measurements collected during the PVT. Findings suggest that participants experienced an insulative type of cold acclimation, evidenced by greater heat retention and less shivering, with possible improvements in cognitive performance. Participants had more correct responses on the double-digit addition task on Immersion 7 (39 ± 5) compared with Immersion 1 (33 ± 6); p < 0.001, yet no differences were observed for reaction time between Immersion 7 (286 ± 31 ms) and Immersion 1 (281 ± 19 ms); p = 0.59. Additionally, EEG analyses indicate no beneficial changes in neurophysiological function. Results demonstrate that individuals who are frequently exposed to cold water may be more suited to handle certain cognitive challenges after several exposures, although additional investigations are needed to provide neurophysiological support for this.

Cold acclimation and cognitive performance: A review

Athletes, occupational workers, and military personnel experience cold temperatures through cold air exposure or cold water immersion, both of which impair cognitive performance. Prior work has shown that neurophysiological pathways may be sensitive to the effects of temperature acclimation and, therefore, cold acclimation may be a potential strategy to attenuate cold-induced cognitive impairments for populations that are frequently exposed to cold environments. This review provides an overview of studies that examine repeated cold stress, cold acclimation, and measurements of cognitive performance to determine whether or not cold acclimation provides beneficial protection against cold-induced cognitive performance decrements. Studies included in this review assessed cognitive measures of reaction time, attention, logical reasoning, information processing, and memory. Repeated cold stress, with or without evidence of cold acclimation, appears to offer no added benefit of improving cognitive performance. However, research in this area is greatly lacking and, therefore, it is difficult to draw any definitive conclusions regarding the use of cold acclimation to improve cognitive performance during subsequent cold exposures. Given the current state of minimal knowledge on this topic, athletes, occupational workers, and military commands looking to specifically enhance cognitive performance in cold environments would likely not be advised to spend the time and effort required to become acclimated to cold. However, as more knowledge becomes available in this area, recommendations may change.

Critical care at extremes of temperature: effects on patients, staff and equipment

Modern travel and military operations have led to a significant increase in the need to provide medical care in extreme climates. Presently, there are few data on what happens to the doctor, their drugs and equipment when exposed to these extremes. A review was undertaken to find out the effects of 'extreme heat or cold' on anaesthesia and critical care; in addition, subject matter experts were contacted directly. Both extreme heat and extreme cold can cause a marked physiological response in a critically ill patient and the doctor treating these patients may also suffer a decrement in both physical and mental functioning. Equipment can malfunction when exposed to extremes of temperature and should ideally be stored and operated in a climatically controlled environment. Many drugs have a narrow range of temperatures in which they remain useable though some have been shown to remain effective if exposed to extremes of temperature for a short period of time. All personnel embarking on an expedition to an extreme temperature zone should be of sufficient physical robustness and ideally should have a period of acclimatisation which may help mitigate against some of the physiological effects of exposure to extreme heat or extreme cold. Expedition planners should aim to provide climatic control for drugs and equipment and should have logistical plans for replenishment of drugs and medical evacuation of casualties.

Environmental effects on brain function

Environmental extremes can result in local and systemic illness, or even death. A majority of cases involving environmental mishap are related to excessive heat, cold, or high altitude exposure. Heat- or cold-related illness occurs when the body's homeostatic mechanisms are overwhelmed, resulting in an accumulation or loss of heat, respectively. Altitude illness results from a combination of low temperature and hypoxia. All three environmental injuries have significant effects upon brain function. This article discusses the pathophysiology of heat, cold, and altitude illness and their effects upon brain function.

Tyrosine supplementation mitigates working memory decrements during cold exposure

In rats, dietary supplementation with the amino acid tyrosine (TYR) prevents depletion of central catecholamines observed during acute environmental stress. Concomitant changes in the animals' behavioral responses to stress suggest that TYR might have similar effects on central catecholamines and cognition in humans exposed to environmental stress. This study aimed to determine if severe cold exposure impairs human cognition and if dietary supplementation with TYR would ameliorate such deficits. Volunteers (N=19) completed three test sessions on different days (35 degrees C control/placebo, approximately 10 degrees C/placebo, approximately 10 degrees C/TYR) using a double-blind, within subjects design. During each session, volunteers completed two 90-minute water immersions and consumed a food bar (150 mg/kg TYR or placebo) before each immersion (total TYR 300 mg/kg). Cognitive performance, mood, and salivary cortisol were assessed. Cortisol was elevated in the cold (p<.01). Volunteers made fewer correct responses on a Match-to-Sample memory measure (p<.05) and reaction time (RT) and errors increased on a choice RT test (p<.01) in the cold. Self-reported tension (p<.01), depression (p<.05) and confusion (p<.01) also increased in the cold. When volunteers consumed TYR, correct responses increased on a Match-to-Sample memory measure (p<.05) and study time for the sample was shorter (p<.05), indicative of more rapid and accurate information processing. Finally, RT on the memory measure revealed a similar pattern across immersions for TYR and thermoneutral conditions, but not cold/placebo (p<.05). This study demonstrates cold exposure degrades cognitive performance and supplementation with TYR alleviates working memory decrements.

Influence of seasonally adjusted exposure to cold and darkness on cognitive performance in circumpolar residents

The effects of seasonally adjusted 24-h exposure to cold and darkness on cognitive performance in urban circumpolar residents was assessed in 15 male subjects who spent three 24-h periods in a climatic chamber at 65 degrees latitude during the winter (January-March) and/or summer (August-September). Each subject was exposed to three different environmental conditions in random order: (1) 22 degrees C temperature and 500 lx lighting; (2) 10 degrees C temperature and 500 lx lighting; and (3) 10 degrees C temperature and 0.5-l lx lighting. Accuracy on an addition-subtraction task was significantly greater in the summer than in the winter (p= 0.038), while accuracy on a repeated acquisition task was significantly greater in the winter than in the summer (p < 0.001). Independent of season, exposure to cold and darkness was significantly associated with a decline in response time on five cognitive tests, an improvement in accuracy on three tests measuring complex cognitive tasks, and a decline in accuracy on two tests measuring simple tasks. Increased performance on complex tasks may result from increased arousal in response to the combination of cold temperatures and dim light characteristic of the winter in urban circumpolar settings.

Relationship between body heat content and finger temperature during cold exposure

The purpose of the present experiment was to examine the relationship between rate of body heat storage (S˙), change in body heat content (ΔHb), extremity temperatures, and finger dexterity. S˙, ΔHb , finger skin temperature (Tfing), toe skin temperature, finger dexterity, and rectal temperature were measured during active torso heating while the subjects sat in a chair and were exposed to −25°C air. S˙ and ΔHb were measured using partitional calorimetry, rather than thermometry, which was used in the majority of previous studies. Eight men were exposed to four conditions in which the clothing covering the body or the level of torso heating was modified. After 3 h, Tfing was 34.9 ± 0.4, 31.2 ± 1.2, 18.3 ± 3.1, and 12.1 ± 0.5°C for the four conditions, whereas finger dexterity decreased by 0, 0, 26, and 39%, respectively. In contrast to some past studies, extremity comfort can be maintained, despite S˙ that is slightly negative. This study also found a direct linear relationship between ΔHb and Tfing and toe skin temperature at a negative ΔHb. In addition, ΔHb was a better indicator of the relative changes in extremity temperatures and finger dexterity over time than S˙.

A field study of the ventilatory response to ambient temperature and pressure in sport diving

This study reports on the relationship between minute ventilation (VE) and environmental variables of temperature (T) and pressure (P) during open water diving. The author conducted a total of 38 dives involving either a light (20 dives) or a moderate (18 dives) level of physical activity. Within each of these groups, P and T taken together accounted for about two thirds of the variance in the VE data. A very significant increase in VE was observed as T decreased (1 < T(degrees C) < 22), and the magnitude of this increase at a given pressure level was similar in the 'light' and the 'moderate' data sets. A second order observation, particularly notable at lower temperature, was the decrease in VE with increasing pressure under conditions of light work. Empirical functions of the from VE = A+B/P n[1 + exp(T - 8)/10], where A, B, and n are adjustable variables, could accommodate both data sets over the whole range of T and P. These results are the first obtained under actual diving conditions to provide evidence for interactions between P, T, and VE. Understanding the physiological mechanisms by which these interactions occur would assist in appreciation of the limitations imposed on scuba divers by the environmental conditions as they affect their ventilatory responses.

The effects of cold on the performance of serial choice reaction time and various discrete tasks

Two experiments are reported in which subjects performed a number of tasks before, during, and following exposure to cold. The main performance task, involving serial choice reaction times, yielded consistently large increases in error that were attendant upon reductions in mean skin temperature, and appeared largely independent of any fall in rectal temperature. Other more discrete tasks investigated over the two experiments included a simple reaction time test and the Stroop Word Color Test. The results of these tests indicated no significant performance changes in the cold. Performance on a verbal reasoning test, however, was slightly improved in the cold. The results are discussed in terms of an arousal versus distraction hypothesis of cold effects.