Military Preventive Medicine: Mobilization and Deployment, Vol 1 Chapter 19 Environmental Medicine: Heat, Cold, and Altitude

Environmental Medicine: Heat, Cold, and Altitude Chapter 19 ENVIRONMENTAL MEDICINE: HEAT, COLD, AND ALTITUDE ROBERT E. BURR, MD INTRODUCTION GENERAL PRINCIPLES A MODEL FOR ENVIRONMENTAL STRAIN AND DISEASE HOT ENVIRONMENTS PREVENTION OF HEAT ILLNESS HEAT ILLNESSES COLD ENVIRONMENTS PREVENTION OF ILLNESS AND INJURY IN THE COLD ILLNESS AND INJURY DUE TO COLD MOUNTAIN ENVIRONMENTS PREVENTION OF HIGH ALTITUDE ILLNESSES HIGH ALTITUDE ILLNESSES SUMMARY 363 Military Preventive Medicine: Mobilization and Deployment, Volume 1 R. E. Burr; Director of Endocrine Education, Division of Endocrinology; Bayside Medical Center, 3300 Main Street, Suite 3A, Spring- field, MA 01199; formerly, Lieutenant Colonel, Medical Corps, US Army; Medical Advisor, Office of the Commander, US Army Research Institute of Environmental Medicine, Natick, MA 01760 364 Environmental Medicine: Heat, Cold, and Altitude INTRODUCTION Since the beginning of recorded history, there are clear descriptions of the effect of the environment on EXHIBIT 19-1 military campaigns. The armies of Alexander in Cen- tral Asia, Hannibal in the Alps, and Napoleon in Rus- MILITARY OCCUPATIONAL STRESSORS sia all suffered the consequences of harsh climate. American military personnel, too, have had ample ex- Environmental Toxic Hazards perience with cold and heat from Valley Forge to the Persian Gulf. And there does not seem to be a reduc- Dehydration tion in the requirement for military forces to deploy Weight Loss and operate in these places. Just in the 1990s, military Physical Stress conflict has appeared in the altitude of the Himalayan and Andean mountains, in the heat of African and Physical Fatigue Asian deserts, and in the cold of Central Europe and Emotional Fatigue Central Asia. This chapter is concerned with three terrestrial en- Cognitive Fatigue vironments: hot, cold, and high altitude. Each is char- Climatic Extremes acterized by a dominant physical stressor: heat, cold, Protective Uniforms or hypobaric hypoxia. These three are military occupational stressors that produce measurable physiological or psychological strain, which is a necessary first step on the path to illness (Exhibit 19-1). Although the incidence of illness and injury is a stochastic pro- assume that their management is within everyone’s cess and predictable only in population terms, strain experience and competence. That is not necessarily is universally present in deployed populations. These the case, to the detriment of service members deployed stressors are not novel or exotic but everyday, so we or training in these environments around the world. GENERAL PRINCIPLES There are several important principles concerning cannot be mitigated, efforts to guarantee adequate hy- the relationship of these environmental stressors and dration and to control work rates in the heat become illness. The first of these is that all these stressors are even more important preventive medicine tools. interactive and synergistic. The strain each produces It is important to remember, though, that a particu- cumulates with the strains produced by all the others lar exposure does not result exclusively in any par- to cause a general reduction in physical and psycho- ticular clinical illness. For example, trauma from a logical performance and to increase the likelihood of vehicular accident can be as much a consequence of illness and injury. Typically, military deployments altitude exposure as acute mountain sickness. expose service members to several of these stressors Frequently, one characteristic of an area of opera- simultaneously. These exposures are an inescapable tions will be so extreme as to seem to require exclu- effect of the psychological, physiological, and social sive attention and intervention. However, the amount dislocations of military operations. that this attention to a single stressor distracts atten- The clinical illnesses consequent on these exposures tion from other stressors will prevent the implemen- usually reflect the net effect of several stressors. For tation of a successful program of surveillance and example, dehydration, exercise-related heat exposure, prevention. Important and effective strategies to sus- and sleep loss all independently contribute to heat ill- tain health and performance may be overlooked if ness. Moderating any one of these three factors will medical personnel become too focused on any one reduce the risk. So, in circumstances where sleep loss stressor. A MODEL FOR ENVIRONMENTAL STRAIN AND DISEASE The conceptual model used throughout this chap- and by protective technology. Disease only occurs in ter expresses the idea that strain is a result of expo- the presence of strain. It is important to remember that sure to an environmental stressor moderated both by there are many potential clinical expressions of strain, the capability of the individual to tolerate the stress including psychological stress reactions, accidents 365 Military Preventive Medicine: Mobilization and Deployment, Volume 1 Cycle of Operational Stress Stressors Stressors • Physical fatigue • Sleep Loss • Emotional fatigue • Weight Loss • Reduced host defense • Dehydration • Cognitive impairment • Anxiety • Reduced physical capacity • Frustration • Jet Lag • Load carriage Military • Reduced Combat Consequence • MOPP • Effectiveness • Environmental Stress • Etc ........ • Casualties Fig. 19-1. Operational stressors reduce combat effectiveness and increase casualty rates through a variety of mechanisms. Loss of combat forces through stressor-related attrition increases the operational load on those not yet affected which contributes to an acceleration of the loss of combat effectiveness. and trauma, and environmental illnesses. The indi- alty rates (Figure 19-1). The loss of personnel will vidual feels the effect of all the stressors to which take a toll in morale and increase the demands on he or she is exposed. The cumulated strain will de- those who remain, a process that will accelerate the grade physical and psychological performance, accumulation of strain and further degrade unit ef- reducing military effectiveness and increasing casu- fectiveness. HOT ENVIRONMENTS Heat and the other threats associated with hot The Environment environments are a constant of military training and operations. Acute and chronic heat illnesses have Hot environments are characterized by a combi- affected the outcomes of military campaigns since nation of temperature, humidity, and radiant heat; there have been military campaigns.1,2 Heat illnesses by affecting the rate at which heat energy can be continue to be a threat to US forces today.3,4 Four of dissipated from the body, these factors are associ- the major deployments in the 1990s were to hot en- ated with intense heat strain and dehydration dur- vironments: Panama, the Persian Gulf, Somalia, and ing work. These conditions are usually thought of Haiti. Heat stress affected operations in each of as confined to tropical or desert regions, but hot en- these deployments, both as a cause of casualties and vironments are encountered in every operational as a threat complicating logistics and maneuver. setting. In ground operations, the microenviron- As the US experience in the Persian Gulf dem- ment of protective uniforms, even when outside onstrated, when military forces understand the temperatures are low, can be tropical and produce threat of heat stress, provide appropriate logistic considerable heat stress. Military vehicles,6 aircraft support, and incorporate prevention into the plan- cockpits,7,8 and mechanical spaces aboard ship9 expose ning and execution of operations, heat illness is al- service members to high radiant and ambient heat most entirely preventable.5 Heat illness rates have loads. The outcomes of exposure to all hot environ- also fallen in the ordinary day-to-day activities of ments are the same: reduced performance and illness. training and operations, but exertional heat illness, Hot regions of the world, where heat is a climatic hyponatremia, and rhabdomyolysis continue to be norm, present other threats beside heat stress and common diagnoses among military populations and heat illness. They include limitations of water sup- remain a cause of death and disability. ply from either low rainfall or poor water quality, 366 Environmental Medicine: Heat, Cold, and Altitude skin disease from sunburn or miliaria, and bron- to maintain a narrow range of body temperature chospasm from dry air and dust. for optimal function. In response to a rise in body temperature from an internal or external heat Physiological Adaptation to Heat Exposure source, we increase both cutaneous blood flow and sweating.11 Heat energy is then dissipated to the Humans have well-defined physiological mecha- environment either directly from the warmed skin nisms to counteract rises in body temperature from surface by conduction-convection and radiation12 either internal heat production or environmental or by evaporation of sweat (Exhibit 19-2). heat stress.10 These mechanisms support our need The rate of direct transfer of heat energy by con- EXHIBIT 19-2 CORE TEMPERATURE AND THE HEAT BALANCE EQUATION Core temperature is determined by the balance between heat loss and heat gain from the environment and metabolism. If, on average, the two are equal, core temperature will remain constant, permitting optimum function. If heat gain exceeds heat loss, core temperature rises; conversely, if heat loss exceeds heat gain, core temperature will fall. Heat balance can be expressed algebraically

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