Tiina M. Mäkinen

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.

Physical Activity and Body Composition Changes during Military Service

PURPOSE To examine how body composition changes in different body mass index (BMI) categories among young Finnish men during military service, which is associated with marked changes in diet and physical activity. In addition, this study examined how reported previous physical activity affected the body composition changes. METHODS Altogether 1003 men (19 yr) were followed throughout their military service (6-12 months). Height, weight, BMI, waist circumference, and waist-to-hip ratio (WHR) were recorded. Previous physical activity was assessed at the beginning of the service by a questionnaire. Body composition was measured by bioelectrical impedance assessments (BIA) at the beginning and at the end of the service. The measured parameters were fat mass (FM), fat percentage (fat %), fat-free mass (FFM), visceral fat area (VFA), lean body mass (LBM), and skeletal muscle mass (SMM). RESULTS On average, military training decreased weight by 0.7%, FM by 9.7%, fat % by 6.6%, and VFA by 43.4%. FFM increased by 1.3%, LBM by 1.2%, and SMM by 1.7%. The group of underweight and normal-weight men gained weight, FM, and FFM, whereas overweight and obese men lost weight and FM and gained FFM. FM was most reduced in the groups of overweight (20.8%) and obese (24.9%) men. The amount of VFA was reduced in all BMI groups (38%-44%). Among overweight men who reported being inactive previous to the military service, more beneficial changes in body composition were observed compared with those who reported being physically active. CONCLUSIONS The lifestyle changes associated with military service markedly reduce fat tissue and increase the amount of lean tissue. These beneficial changes are prominent among previously inactive subjects with high BMI.

Cold-related respiratory symptoms in the general population

Introduction:  Cold‐related respiratory symptoms are common among northern populations, especially among people suffering from respiratory diseases. However, the prevalence of such symptoms in the general population and the threshold temperatures at which the symptoms start to emerge are poorly known.

The health of Arctic populations: Does cold matter?

The objective of the study was to examine whether cold climate is associated with poorer health in diverse Arctic populations. With climate change increasingly affecting the Arctic, the association between climate and population health status is of public health significance. The mean January and July temperatures were determined for 27 Arctic regions based on weather station data for the period 1961–1990 and their association with a variety of health outcomes assessed by correlation and multiple linear regression analyses. Mean January temperature was inversely associated with infant and perinatal mortality rate, age‐standardized mortality rate from respiratory diseases, and age‐specific fertility rate for teens and directly associated with life expectancy at birth in both males and females, independent of a variety of socioeconomic, demographic, and health care factors. Mean July temperature was also associated with infant mortality and mortality from respiratory diseases, and with total fertility rate. For every 10°C increase in mean January temperature, the life expectancy at birth among males increased by about 6 years and infant mortality rate decreased by about 4 deaths/1,000 livebirths. Cold climate is significantly associated with higher mortality and fertility in Arctic populations and should be recognized in public health planning. Am. J. Hum. Biol., 2010.

ENERGY COST AND THERMOREGULATION OF UNRESTRAINED RATS DURING EXERCISE IN THE COLD

The effect of cold ambient temperature on the energy cost and thermoregulation during exercise was studied in 18 male Sprague-Dawley rats accustomed to running for 2 weeks. For measuring T(b) and ensuring an unrestrained exercise performance, the rats were implanted with intraperitoneal telemetric radio transmitters. The rats ran at three submaximal exercise intensities (10, 15 and 20 m.min-1) at different T(a) values (22 degrees, 0 degree, -10 degrees and -20 degrees C) for 30 min. VO2 and Tb were continuously measured. During exercise at 0 degree C a 100% substitution of thermoregulatory heat production by exercise thermogenesis was observed. At T(a) values below 0 degree C the physical strain of exercise increased considerably: Vo2 increased 34-61% at -10 degrees C and 51% at -20 degrees C compared to the corresponding exercise intensity at T(a) 22 degrees C. A partial substitution of thermoregulatory heat production by exercise thermogenesis was observed in the cold. At -10 degrees C the cost for thermoregulation during exercise was 28% and at -20 degrees C 31% lower than at rest at the corresponding T(a) values. The rat could not maintain normal Tb during exercise below 0 degrees C. The T(b) dropped 1.5-1.8 degrees C at -10 degrees C and 2.5 degrees C at -20 degrees C. It is concluded that exercising below 0 degree C at submaximal levels (below 50% of VO2max) partially substitutes for thermoregulatory costs but is thermally unfavorable for the small-sized rat.

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.

A MODEL FOR MANAGING COLD-RELATED HEALTH AND SAFETY RISKS AT WORKPLACES

Cold conditions increase health and safety risks at work in several ways. The effects of cold have not been sufficiently taken into consideration in occupational safety and health practices. A systematic model and methods were developed for managing cold-related health and safety risks at workplaces. The development work was performed, in a context-bound manner, in pilot industries and workplaces. The model can be integrated into the company’s occupational health and safety management system, such as OHSAS 18001. The cold risks are identified and assessed by using a checklist. The preventive measures are systematically planned in a written form specifically produced for cold workplaces. It includes the organisational and technical preventive measures, protective clothing and personal protective equipment, as well as training and information of the personnel. According to the model, all the workers, foremen, occupational safety personnel and occupational health care personnel are trained to recognise the cold risks and to conduct preventive actions. The developed model was evaluated in the context of cold outdoor (construction) and indoor work (fish processing), and by occupational health and safety professionals. According to the feedback, the model and methods were easy to use after a one-day introduction session. The continuum between the cold risk assessment and management worked well, although there was some overlap in the documentation. The cold risk management model and its methods form an essential part of ISO CD 15743 Strategy for risk assessment, management and work practice in cold environments.

Usability of isothermal standards for cold risk assessment in the workplace.

In this study the usability of ISO thermal standards suitable for cold risk assessment in the workplace was evaluated. Persons who were not earlier familiar with the methods were trained to be able to perform the assessments.The assessments were conducted at two different stages according to method complexity, duration and need for expertise.The methods tested at stage 1 included observation and simple measurements (ISO CD 15265, ISO 8996, ISOTR 11079) and were assumed to be relatively simple to use. The methods tested at stage 2 included measurements and quantitative analyses (ISO 7726, ISO 8996, ISO 10551, ISO 9920, ISO 9886, ISO TR 11079). Training to use the methods was provided to the observers and measur ers. The assessments at stage 1 were performed by 5 observers repeated on three different occasions with 5 different workers. The measurements (stage 2) were conducted by four persons and repeated four times. A questionnaire concerning the usability of the method tested was filled in after each assessment. The results show that the methods of stage 1 were considered easy to adopt, the duration of the assessment was short (average 30 min), the results were easy to analyse and the amount of training was considered to be adequate. The methods of stage 2 were considered more laborious to perform and the total duration of the assessment was on average 4 h 40 min. Furthermore, the training provided was not considered to be entirely sufficient and additional instructions were frequently asked for, especially when analysing the results. Usable elements were recognised from the ISO thermal standards, which could be used at the more advanced stages of cold risk assessment.