Tiina Pääkkönen

Effect of repeated exposures to cold on cognitive performance in humans.

The effects of repeated exposure to cold temperature on cognitive performance were examined in 10 male subjects who were exposed to control (25 degrees C) and cold (10 degrees C) conditions on 10 successive days. A cognitive test battery (ANAM-ICE) was administered each day to assess complex and simple cognitive functioning accuracy, efficiency and response time. Rectal (T(rect)) and skin temperatures, thermal sensations, metabolic rate (M) and cardiovascular reactivity were also recorded. With the used cold exposure, inducing cold sensations and discomfort, superficial skin cooling (6-7 degrees C) and a slightly lowered T(rect) (0.4 degrees C) we observed three distinct patterns of cognitive performance: 1) negative, reflected in increased response times and decreased accuracy and efficiency; 2) positive, reflected in decreased response time and increased efficiency; and 3) mixed, reflected in a pattern of increases in both accuracy and response time and decreases in efficiency, and a pattern of decreases in both accuracy and response time. T(rect), thermal sensations, diastolic blood pressure (DBP) and heart rate (HR) were independent predictors of decreased accuracy, but also decreased response time. Cognitive performance efficiency was significantly improved and response times shorter over the 10-d period both under control and cold exposures suggesting a learning effect. However, the changes in cognitive performance over the 10-d period did not differ markedly between control and cold, indicating that the changes in the thermal responses did not improve performance. The results suggest that cold affects cognitive performance negatively through the mechanisms of distraction and both positively and negatively through the mechanism of arousal.

Autonomic nervous function during whole-body cold exposure before and after cold acclimation.

INTRODUCTION Cold habituation could affect sympatho-vagal balance, which modulates cold stress responses. The study examined cardiovascular autonomic function at the sinus node level during controlled breathing and while undertaking isometric exercise during whole-body cold exposure before and after cold acclimation. METHODS There were 10 male subjects who were exposed to control (25 degrees C) and cold (10 degrees C) environments for 2 h on 10 successive days in a laboratory. Time and frequency domain heart rate variability (HRV) in terms of root mean square of successive differences in RR intervals, total, high, and low frequency power were determined from controlled breathing at the beginning and end of cold acclimation. Heart rate and blood pressure during an isometric handgrip test (30% MVC for 3 min) were recorded at the beginning and end of cold acclimation. Catecholamines (NE and E), mean skin (Tsk), and rectal temperatures (Trect) were measured. RESULTS Acute cold exposure increased total (36%), low (16%), and high frequency power (25%) and RMSSD (34%). Cold acclimation resulted in higher Tsk (0.6 degrees C) and lower NE (24%) response in cold. The cold-induced elevation in high frequency power became significant after cold acclimation, while other HRV parameters remained unchanged. A smaller increase in heart rate and blood pressure occurred at 10 degrees C during the handgrip test after cold acclimation. DISCUSSION Cold exposure increased sympathetic activity, which was blunted after cold acclimation. Parasympathetic activity showed a minor increase in cold, which was enhanced after cold acclimation. In conclusion, cold habituation lowers sympathetic activation and causes a shift toward increased parasympathetic activity.

Urinary melatonin: a noninvasive method to follow human pineal function as studied in three experimental conditions

Abstract:  The aim of this study was to examine whether urinary melatonin, rather than urinary 6‐sulfatoxymelatonin (aMT6s), can be used as an indicator of diurnally and seasonally changing melatonin secretion. The subjects (n = 15) spent three separate 24‐hr periods in a climatic chamber during winter (n = 7) and summer (n = 8). Blood and urine samples were obtained during each period at 2‐ to 5‐hr intervals. Serum melatonin and urinary melatonin and aMT6s were assayed by radioimmunoassay. The serum melatonin levels increased nearly 10‐fold from low daytime to high nocturnal values. The mean nocturnal increase of urinary melatonin was 1.7‐fold and that of urinary aMT6s was 4.6‐fold. Both urinary melatonin and aMT6s correlated significantly with area under the curve melatonin in serum during the night, during the day and throughout the entire 24‐hr observation period in all cases. The ratio between urinary melatonin and aMT6s excretion showed significant diurnal variation, being ninefold higher at 16:00 hr than at 07:00 or at 09:00 hr. The ninefold decrease in the urinary melatonin/aMT6s excretion ratio between the evening and the morning may reflect increased liver metabolism of melatonin during the night. Both urinary melatonin and aMT6s are good indicators of melatonin secretion, but the variation is significantly smaller for the former molecule.

COLD EXPOSURE AND HORMONAL SECRETION: A REVIEW

Low ambient temperature during winter seasons is typical for all circumpolar areas. This sets definite demands for every day life and work. Naked, man is quite helpless in polar winter, but he has been able to inhabit all corners of the ear th using technical developments in clothing and housing. Yet there are situations, especially in circumpolar areas, when bodily exposure to cold environment cannot be avoided. Homeothermic animals protect themselves from the cold by increasing heat production and decreasing heat losses. For practical reasons man has very few means of reducing heat loss by natural ways. Heat is produced by muscular work and by chemical reactions. Oxidative phosphorylation of dietary fuels such as carbohydrates and fats brings forward energy-rich phosphate compounds, at the same time liberating heat for bodily uses. Thyroid and adrenal hormones and the sympathetic nerve system maintain and regulate the oxidative phosphorylation that occurs mainly in the mitochondria of brown and white fat and skeletal muscle tissues. It is notewor thy that animals from which thyroid or adrenal glands are removed do not tolerate cold.

Seasonal levels of melatonin, thyroid hormones, mood, and cognition near the Arctic Circle.

INTRODUCTION The associations between melatonin and thyroid hormones and changes in mood and cognitive performance caused by exposure to cold and darkness were examined in 12 circumpolar residents during winter and summer. METHODS Each participant was exposed to three different experimental conditions in random order: 1) 22 degrees C and bright light; 2) 10 degrees C and bright light; and 3) 10 degrees C and dim light. The duration of each exposure was 24 h. RESULTS Increased serum melatonin and thyrotropin were associated with decreased rectal temperature (r = -0.446 - -0.580) and increased mean skin temperature (r = 0.204-0.519). Higher serum melatonin was associated with increased vigor (r = 0.330) and decreased accuracy on simple cognitive tasks (r = -0.332 - -0.430). Increased serum free triiodothyronine (fT3) was associated with decreased negative mood scores (r = -0.365 - -0.483), decreased response time (RT) on the simple reaction time (SRT) task (r = -0.606), and decreased accuracy on the addition/subtraction task (r = -0.372). Higher serum free thyroxine was associated with decreased fatigue and anger (r = -0.409 - -0.522). Increased serum thyrotropin was associated with decreased accuracy and RT on the SRT task and decreased RT on the grammatical reasoning task (r = -0.315 - -0.415). CONCLUSIONS Associations between serum melatonin and thyroid hormones with mood were consistent with the psychological changes associated with the polar triiodothyronine syndrome. Also, serum melatonin and thyrotropin were associated with impaired and fT3 with improved cognitive performance, supporting the decrements in cognitive performance associated with the polar triiodothyronine syndrome.

Melatonin and thyroid hormones in the cold and in darkness. Association with mood and cognition

The purpose of the study was to examine the cold-induced effects on pineal and thyroid hormones as well as the associations of these hormones with psychological performance and to determine how psychological performance could be affected by demographic, anthropometric, physiological or biochemical measures during cold acclimatisation. The feasibility of urinary melatonin (MT), rather than 6-sulphatoxymelatonin (aMT6s), as an indicator of MT secretion was also examined. In the laboratory study, seasonal cold acclimatisation, its effects on hormones and their associations with mood and cognition were assessed in 15 young urban subjects exposed to cold in winter or summer in bright or dim light. In the field study, the associations of mood and cognition with demographic, anthropometric, physiological and biochemical measures were determined in healthy, euthyroid subjects (n = 133) in Antarctica in the beginning and at the end of summer and winter seasons. In both seasons, simple task performance was consistently impaired in the cold in experimental and field conditions. In complex tasks, negative, positive and mixed effects were observed. In the experimental study, serum MT and thyroid hormone levels were positively associated with mood. MT was negatively associated with simple task performance. Free triiodothyronine (T3) and thyrotropin (TSH) had mixed effects on simple task performance. TSH was positively associated with complex task performance. In the field study, higher age was associated with impaired cognition, especially in complex task performance. Total T3 was positively associated with mood and total thyroxine (T4) with complex task accuracy. Both urinary MT and aMT6s were good indicators of MT secretion, but the variation was smaller for MT. In conclusion, the associations of serum MT, TSH and thyroid hormone levels with mood and cognition found in experimental and field conditions are consistent with the psychological changes associated with the onset and consequent stages of the previously established polar T3 syndrome. In the field study, cognition and mood were associated with subject’s age and gender, which seemed to affect the physiological changes during acclimatisation to cold and darkness in Antarctica.

Density Functional Theory Studies on the Formation of CaCO3 Depositions on Cristobalite, Diamond, and Titanium Carbide Surfaces

Fouling caused by inversely soluble salts, like CaCO3, is a general problem on heat transfer surfaces. Carbonate depositions are typically cleanable with acids, but costs of energy losses, operation, and maintenance are significant. In this study, formation of CaCO3 depositions was investigated on cristobalite, diamond, and titanium carbide surfaces. The aim of the study was to clarify the detailed mechanisms of crystallization fouling during the initiation on crystalline phases existing in materials used as coatings (SiOx, TiCN, diamond-like carbon [DLC]), and to compare the results to the fouling mechanism of stainless steel (Cr2O3). In experimental studies of fouling, detailed mechanisms and description of sterical and electrostatic factors of surfaces are often very much simplified. In this work, molecular modeling was used to describe surface structures and to investigate the effect of process fluid (water) on the structures. The adsorption of water can be molecular or dissociative. During the dissociative adsorption, hydroxylated surface structures are formed. The existence of hydroxyl groups on the surfaces has an effect on the fouling mechanism. First, the dissociation probability of water on different surfaces was determined according to the adsorption mechanism and energies, and then the attachment of CaCO3 onto optimized and hydroxylated surfaces was investigated. As a result, the formation mechanism with detailed intermediate steps of CaCO3 deposition was obtained. The fouling takes place via hydrogen carbonate intermediates, but the final deposition structure was found to vary between surfaces.

Urinary thrombomodulin and catecholamine levels are interrelated in healthy volunteers immersed in cold and warm water.

ABSTRACT Severe hypothermia has been shown to influence the levels of catecholamines and thrombomodulin, an endothelial protein essentially involved in the regulation of haemostasis and inflammation. A link between thrombomodulin and catecholamines during cold exposure has also been previously suggested. The aim of this study was to assess the influence of short-term cold exposure without hypothermia on catecholamines and the circulating and urinary thrombomodulin levels. Seven healthy male subjects were immersed in cold water (+10°C) for 10 minutes followed by a 20-minute immersion in +28°C water. Warm water immersion was performed separately for each subject (+30°C for 30 minutes). Thrombomodulin and catecholamine concentrations were measured from pre- and post-immersion (up to 23 hours) samples. In urine, the thrombomodulin level correlated strongly with adrenaline (ρ = 0.806) and noradrenaline (ρ = 0.760) levels. There were no significant differences in thrombomodulin levels between immersion temperatures. Post-immersion urinary thrombomodulin levels were significantly lower than the pre-immersion level at both immersion temperatures. Median concentrations of plasma noradrenaline and urinary adrenaline were higher after exposure to +10°C than to +30°C. Thus, further evidence of the association between thrombomodulin and catecholamines was gained in a physiologically relevant setting in humans. Additionally, it is evident that a short-term cold exposure was not able to elicit changes in the thrombomodulin levels in a follow-up period of up to 23 hours. These findings provide further understanding of the physiological responses to cold during immersion, and of the potential influence of stress on haemostatic and inflammatory responses.

Surface Patterning of Stainless Steel in Prevention of Fouling in Heat Transfer Equipment

Fouling of surfaces is a major challenge in design and operation of many industrial heat transfer equipment. Fouling causes significant energy, material and production losses, which increase the environmental impact and decrease economic profitability of processes. Even small improvements in prevention of fouling would lead to significant savings in a wide range of heat transfer applications. In this study, crystallization fouling of aqueous calcium carbonate solutions on a heated stainless steel surface is used to investigate the prevention of fouling in heat transfer equipment by physical surface modifications. Fouling behaviour of different surface patterns are studied experimentally in a laboratory scale fouling test apparatus. CFD modelling is used to study hydrodynamic and thermal conditions near surfaces with different patterns. In addition, the effect of surface pattern on the removal of particles is studied numerically. Surface patterning is found to affect the hydrodynamic and thermal conditions near the wall, and therefore to change the conditions for fouling layer build-up and removal, when compared to a flat heat transfer surface. The most promising surface pattern includes curved shapes, and it seems to create flow conditions in which improved convective heat transfer decreases the driving force for crystallization fouling. In addition, curved surfaces increase the shear forces at the wall, which prevents adhesion of the foulants to the surface and increases resuspension.