Eighty-four hours of sustained operations alter thermoregulation during cold exposure

PURPOSE; This study examined the effects of short-term (3.5 d) sustained military operations (SUSOPS) on thermoregulatory responses to cold stress. METHODS: Ten men (22.8 +/- 1.4 yr) were assessed during a cold-air test (CAT) after a control week (control) and again after an 84-h SUSOPS (sleep = 2 h.d (-1), energy intake = approximately 1650 kcal.d(-1), and energy expenditure = approximately 4500 kcal.d(-1). CAT consisted of a resting subject (seminude) being exposed to an ambient temperature ramp from 25 degrees C to 10 degrees C during the initial 30 min of CAT, with the ambient temperature then remaining at 10 degrees C for an additional 150 min. RESULTS: SUSOPS decreased (P< 0.05) body weight, % body fat, and fat-free mass by 3.9 kg, 1.6%, and 1.8 kg, respectively. During CAT, rectal temperature decreased to a greater extent (P< 0.05) after SUSOPS (0.52 +/- 0.09 degrees C) versus control (0.45 +/- 0.12 degrees C). Metabolic heat production was lower (P< 0.05) after SUSOPS at min 30 (55.4 +/- 3.3 W.m (-2)) versus control (66.9 +/- 4.4 W.m(-2)). Examination of the mean body temperature-metabolic heat production relationship indicated that the threshold for shivering was lower (P< 0.05) after SUSOPS (34.8 +/- 0.2 degrees C) versus control (35.8 +/- 0.2 degrees C). Mean weighted skin temperatures ( degrees C) were lower during the initial 1.5 h of CAT in SUSOPS versus control. Heat debt was similar between trials. CONCLUSION: These results indicate that sustained (84-h) military operations leads to greater declines in core temperature, due to either a lag in the initial shivering response or heat redistribution secondary to an insulative acclimation.     

Human performance research for military operations in extreme cold environments

ObjectivesSoldier performance in the Arctic depends on planning and training, protective equipment, and human physiological limits. The purpose of this review was to highlight the span of current research on enhancing soldier effectiveness in extreme cold and austere environments.MethodsThe practices of seasoned soldiers who train in the Arctic and cold-dwelling natives inform performance strategies. We provide examples of research and technology that build on these concepts.ResultsExamples of current performance research include evaluation of equipment and tactics such as the bioenergetics of load carriage over snow in Norwegian exercises; Canadian field monitoring of hand temperatures and freezing cold injuries for better protection of manual dexterity; and Dutch predictive modeling of cold-wet work tolerances. Healthy young men can respond to cold with a substantial thermogenic response based on US and Canadian studies on brown adipose tissue and other mechanisms of non-shivering thermogenesis; the potential advantage of greater fat insulation is offset in obese unfit subjects by a smaller thermogenic response. Current physiological studies are addressing previously unanswered problems of cold acclimation procedures, thermogenic enhancement and regulation, and modulation of sympathetic activation, all of which may further enhance cold survival and expand the performance envelope.ConclusionThere is an inseparable behavioral component to soldier performance in the Arctic, and even the best equipment does not benefit soldiers who have not trained in the actual environment. Training inexperienced soldiers to performance limits may be helped with personal monitoring technologies and predictive models.     

Malaria prophylaxis during military operations in Thailand

Thai soldiers deployed along the Thai-Kampuchean border experience high attack rates of drug-resistant falciparum malaria. Adequate drug prophylaxis has proven difficult with the failure of chloroquine, pyrimethamine/sulfadoxine, and pyrimethamine/dapsone. Under some circumstances, mefloquine, doxycycline, and proguanil/sulfamethoxazole can successfully prevent falciparum malaria in Thailand. Decisions regarding chemoprophylaxis drugs in Thailand depend on a complex interaction of effectiveness, compliance, side effects, and long-term usefulness.     

The medical challenge of military operations in the Mississippi Valley during the American Civil War.

The prevention and treatment of disease was as important as combat operations in the campaigns along the Mississippi River during the American Civil War. Throughout the Vicksburg campaign, many more soldiers were disabled by sickness than by combat injury. While this held true for both sides, a greater proportion of the Union army was healthy than of the opposing Confederate force. In the last 2 years of the war, the North tried to occupy the Confederate states in the Mississippi Valley. The failure to accomplish this goal was partly due to the deteriorating health of the Union army. Medical knowledge and action taken to prevent disease were of major importance in the success and the failure of military campaigns in the Mississippi Valley during the American Civil War.     

Nicotine effects on thermoregulatory responses of men and women during acute cold exposure

INTRODUCTION: Due to the impact of nicotine (NIC) on the physiological processes involved in temperature regulation during cold exposure, it is conceivable that NIC may affect the body's thermoregulatory abilities during a cold stress. Thus, the purpose of this study was to examine the effects of NIC on thermoregulatory responses during acute cold exposure. METHODS: There were six men and six women between the ages of 18 and 25 yr who participated in this study. All subjects were active, apparently healthy smokers. Each subject performed two cold air trials consisting of a 30-min baseline period (BASE) and a 120-min exposure to 10 degrees C air. One cold air trial was performed following a NIC dosing using a 21-mg transdermal patch while the other trial was performed after a placebo (PL) treatment. RESULTS: During the cold air trials, there were no differences in rectal temperature (Tre) or mean skin temperature (Tsk) between the PL and NIC treatments in either sex (p > 0.05). However, in men, heat production (M) was 12% lower (p < or = 0.05) and tissue insulation was 17% higher (p < or = 0.05) during the NIC treatment compared with the PL treatment, while these responses in women were unaffected. In both men and women, finger skin vascular conductance (SVCfin), expressed as a percentage of the BASE value, was higher during the NIC treatment compared with the PL treatment during the cold air trials (p < or = 0.05). Lastly, throughout the cold air trials, there was no difference in thermal sensation between the PL and NIC treatments (p > 0.05). DISCUSSION: In conclusion, although NIC administration resulted in sex-specific alterations in M and tissue insulation during cold exposure, the response in Tre was unaffected.     

Winter sports athletes: long-term effects of cold air exposure

Athletes such as skaters and skiers inhale large volumes of cold air during exercise and shift from nasal to mouth breathing. Endurance athletes, like cross-country skiers, perform at 80% or more of their maximal oxygen consumption and have minute ventilations in excess of 100 l/min. Cold air is always dry, and endurance exercise results in loss of water and heat from the lower respiratory tract. In addition, athletes can be exposed to indoor and outdoor pollutants during the competitive season and during all-year training. Hyperpnoea with cold dry air represents a significant environmental stress to the airways. Winter athletes have a high prevalence of respiratory symptoms and airway hyper-responsiveness to methacholine and hyperpnoea. The acute effects of exercise in cold air are neutrophil influx as demonstrated in lavage fluid and airway epithelial damage as demonstrated by bronchoscopy. Upregulation of pro-inflammatory cytokines has been observed in horses. Chronic endurance training damages the epithelium of the small airways in mice. Airway inflammation has been observed on bronchoscopy of cross-country skiers and in dogs after a 1100-mile endurance race in Alaska. Neutrophilic and lymphocytic inflammation with remodelling is present in bronchial biopsies from skiers. Repeated peripheral airway hyperpnoea with dry air causes inflammation and remodelling in dogs. As it is currently unknown if these airway changes are reversible upon cessation of exposure, preventive measures to diminish exposure of the lower airways to cold air should be instituted by all winter sports athletes.     

Thermogenesis induced by inhibition of shivering during cold exposure in exercise-trained rats.

The present investigation was conducted to examine the role of nonshivering and shivering thermogenesis caused by cold exposure in exercise-trained rats. Wistar rats were divided into warm-acclimated (WA), exercise-trained (ET) and cold-acclimated (CA) groups. The trachea was cannulated and a ventilator was connected under light anesthesia and in the supine position. Shivering, oxygen consumption, colonic temperature, blood glucose, and free-fatty acids were measured at 25 degrees C and then at 0 degrees C room temperatures. D-tubocurarine chloride (curare, 0.04 mg/100 g body weight, ip) was given to inhibit muscular activity. Cold-induced oxygen consumption in the ET and WA groups did not decrease when shivering was inhibited, whereas it increased in the CA. The magnitude just after shivering onset for the ET and CA groups as significantly greater than for the WA group. Colonic temperature at the onset of shivering was significantly higher in the WA group than in the ET and the CA groups. The blood glucose concentration during cold exposure and curarization was elevated in the ET group, and did not change in the CA or WA groups. The present results suggest that endurance training at a thermoneutral environment increases cold-induced thermogenic capacity in rats, which may be attributed to preferential carbohydrate utilization.     

某部在高寒山地军事演习中防疫工作的主要做法

2004年我部接受了某高寒山地军事演习中的防御任务,为确保参加演习部队官兵的身体健康,降低非战斗减员,有效提高部队战斗力。在演习前经周密计划,严密组织,进驻演习地域后,应加强检查指导和督促,根据高寒山地的疫情特点,加强心理卫生教育和针对性教育,对参演部队进行全方位的防     

美军既往军事行动致伤因素分析研究

主要介绍美军利用伤情编码PC－code和巴雷尔伤情转换矩阵组成的标准化的伤员分类和编码体系,采集分析越南战争、索马里作战、伊拉克战争等伤员数据,得出武器致伤因素和战场环境因素对伤员伤类、损伤部位造成的影响,可以有效提高各类卫勤资源利用效率和卫勤保障针对性,对我军战时卫勤保障有一定启示借鉴作用。     

Factors enhancing cardiac output in resting subjects during cold exposure in air environment.

Six young males, in semi-nude conditions, resting in dorsal reclining position, were exposed successively to a thermoneutral environment (30 min), a cold environment (1 degree C) (Cold) or thermoneutrality (Control) (120 min), and during 60 min recovery in thermoneutral conditions. Cardiac output has been measured using a Dual Beam Doppler. During cold stress a significant increase of heart rate (66.4 +/- 6.4 to 91.0 +/- 14.9 beats.min-1), systolic blood pressure (119.5 +/- 7.8 to 218.7 +/- 18.7 mmHg), diastolic blood pressure (68.1 +/- 11.7 to 114.3 +/- 28.3 mmHg) and cardiac output (5.42 +/- 0.96 to 8.08 +/- 1.28 l.min-1) were observed. On the contrary initial systolic aorta flow acceleration is significantly lowered (1130 +/- 120 to 840 +/- 170 cm.s-2). Systolic ejection volume remained unchanged throughout the whole experiment. Increase in cardiac output during cold air (1 degree C) exposure is thus only imputed to the higher heart rate partly due to hypersecretion of catecholamines. The diminution of the blood flow acceleration could be related to a lesser arterial compliance and/or to the cold induced hemoconcentration. Enhanced heart's mechanical work due to sympathetic stimulation, seems thus to be absorbed by the increase in the peripheral resistance.     

Cognition during sustained operations: comparison of a laboratory simulation to field studies

INTRODUCTION: Military operations, especially combat, expose individuals to multiple stressors, including sleep loss, food deprivation, and sustained physical activity. Civilians, such as woodland firefighters, disaster victims, and relief workers, are also exposed to such environments. Our laboratory developed a brief, intense, laboratory-based simulation of a multistressor environment which included sleep loss, continuous physical activity, and food deprivation. METHODS: During this sustained operations (SUSOPS) scenario, and a control period, cognitive performance and mood were measured in 13 volunteers. The scenario included road marches, battle drills, and land navigation. Physical activity and sleep were assessed with actigraphs. RESULTS: Significant decrements in visual vigilance, choice reaction time, and matching-to-sample, a test of short-term memory, were observed. Marksmanship was stable and physical activity significantly increased. Mood states assessed by the Profile of Mood States (POMS: Tension, Depression, Anger, Vigor, Fatigue and Confusion) also significantly deteriorated. DISCUSSION: Cognitive function declined more extensively and rapidly than physical performance. Decrements in cognitive performance were comparable to those in a field study conducted for an equivalent period of time in uncontrolled conditions. This demonstrates that decrements in cognitive function and increased physical activity, similar to those in highly stressful field environments, can be duplicated under controlled conditions. The simulated SUSOPS scenario is an appropriate paradigm for assessment of adverse effects of military and civilian multistressor environments on human performance, physiology, and interventions designed to mitigate them.