Altitude and Cold Weather Effects on the Contemporary Battlefi eld

Preparing soldiers for today’s battlefield seems primarily directed toward heat adaption and the extremely warm temperatures associated with the desert climate of the Middle East. However, military operations have been conducted at altitude and in cold weather throughout history. For example, during the Second Punic War (218 BC–201 BC), Hannibal crossed both the Pyrenees and the Alps to attack the Romans.1 Napoleon’s Grande Armée was devastated by the winter of 1812 during its invasion of Russia.2 The Battle of San Matteo in 1918, during World War I, was fought between the Italians and the Austro-Hungarians on the Punta San Matteo (at more than 11,500 feet).3 Cold weather had a significant impact on soldiers fighting during World War II (1939 - 1945; Battle of the Bulge and Operation Barabossa are especially well known), the Korean War (1950 - 1953, Chosin Reservoir), British forces in the Falkland Islands (1982), and Russian forces in Afghanistan (1980 - 1988).4 The Kargil Conflict (1999) was fought in terrain with peaks ranging from 13,000 feet to 18,000 feet, and valley floors upward of 7,000 feet between India and Pakistan.5 A more recent example of challenging environmental conditions faced by soldiers is Operation Enduring Freedom in Afghanistan against the Taliban regime and al-Qaeda terrorist network. During Operation Anaconda in 2002, fighting took place against al-Qaeda forces on the 10,000 foot mountain of Takur Ghar.6 In these conflicts, a large proportion of non-battle injuries directly resulted from cold weather.7 This trend of conflicts at altitude and in the extreme cold is likely to continue in the future with “hot spots” around the globe in places such as Iran, China, Russia (including former republics), and North Korea. The possibility of future conflicts in these geographical regions makes it imperative to understand these types of environment and their effects. Environmental Conditions Before discussing how the body adapts physiologically to altitude, or how it responds to cold weather, we must understand exactly what occurs to characterize these conditions. Since there are few negative physiological effects below 1,500m (4,921 feet), we will consider the term at altitude any elevation above this height.8 High altitude settings are referred to as hypobaric environments due to decreased barometric pressure (Pb) or the weight exerted by the atmosphere at a given altitude.9 No matter where someone is on earth, the air around them is always made up of approximately 79.04 percent nitrogen, 20.93 percent oxygen, and 0.03 percent carbon dioxide.10With increased altitude, the weight of the atmosphere decreases, which results in a proportional decrease in the partial pressure of oxygen (PO2) or the amount of the air that is oxygen.11 Another condition to consider at altitude is the air temperature, which decreases at an approximate rate of 1°C (1.8°F) for every 150m (or 490 feet).12 Cold air cannot hold very much water, so in addition to being just plain cold at high altitudes, the partial pressure of water or water vapor pressure (PH2O) is also low.13 This low PH2O creates a situation where a very large PH2O gradient exists between the outside air and the skin, and the outside air and the air within the body. This sizable gradient increases the risk for dehydration at altitude; therefore, it is very important to continue proper fluid intake and normal hydration strategies to prevent dehydration. An increase in solar radiation is related to the decreased Pb and PH2O at high altitudes. Light from the sun travels through less of the atmosphere before reaching earth, and there is less water vapor to absorb its radiation, which increases radiant exposure.14 The reflective properties of snow, usually found at high elevations, also intensify solar radiation exposure.15 Skin protection with clothing, sun block, lip balm, and sunglasses are essential. In fact, there have been reports of people being sunburned on the roof of the mouth by breathing with their mouths open. Characterizing cold weather is a bit difficult; what seems cold to one person is not necessarily considered cold to another. A good definition of cold weather is any environmental condition that causes a loss of body heat that threatens homeostasis mainly through air and water.16The cooling effect of wind (wind chill) also drastically increases the effects of cold weather by increasing convective heat loss and the rate of bodily cooling.17 High, strong winds are very common at altitude. The presence of water greatly confounds the effects of cold weather, which can happen by being, or getting, wet on dry land, or being immersed in cold water. Water conducts heat much faster than air, making it a very good conductor of heat.18 Altitude and Cold Weather Effects and Adaptations At Altitude One of the first and most noticeable responses to being at altitude is a respiratory response. Pulmonary ventilation increases within seconds of exposure at altitude.19 The low PO2 is detected by che-moreceptors in the body that signal the brain to increase ventilation or breathing.20 This increased rate of ventilation remains elevated for several hours, or days, at a level proportional to the altitude.21 Increased ventilation causes the body to expire lots of carbon dioxide (CO2), lowering the partial pressure of carbon dioxide (PCO2) in the blood, which raises blood pH.22 This condition is referred to as “respiratory alkalosis,” which helps offset hypobaric hypoxia by increasing the binding of oxygen to hemoglobin (the oxygen carrying component of the red blood cell) from around 80 percent to 89 percent.23 Hypobaric hypoxia is the state of inspiring decreased levels of PO2, creating an oxygen deficiency to bodily tissues.24Respiratory alkalosis allows more oxygen to be carried to working tissue, such as muscle, to fuel work; however, the flip side of the coin is that respiratory alkalosis makes unloading oxygen to working muscle in the peripheral capillaries more difficult. Eventually, the hypoxic drive (the need for oxygen) begins to override respiratory alkalosis by the kidneys, excreting additional bicarbonate buffering carbonic acid formed from CO2.25 This process allows increased ventilation to continue. More importantly than the decreased saturation of oxygen in the lungs at altitude is the 75 percent decrease in the diffusion gradient between arterial and tissue PO2.26 This gradient is responsible for driving oxygen from hemoglobin in the blood into muscle tissue for use. The greater the gradient, the quicker gases, such as oxygen, can pass from one area to another. Gases continuously move back and forth in the body according to these partial pressure gradients. Decreased gradients slow diffusion of oxygen to the muscle inhibiting work capacity. Another way the body adapts to the conditions at altitude is by increasing levels of erythropoietin (EPO), which stimulates the production of erythrocyte (red blood cell [RBC]) production.27 EPO levels will drop back to normal in about a month, but increased RBCs will be present up to 3 months or longer.28 “The presence of water greatly confounds the effects of cold weather, which can happen by being, or getting, wet on dry land, or being immersed in cold water. Water conducts heat much faster than air, making it a very good conductor of heat.” — 33

More RBCs means an increased capacity for oxygen transport within the body. These physiological responses are the underlying causes of decreased physical capacity, motor ability, and possible alterations in mood and personality at altitude and must be considered in mission planning with as much time allowed for acclimatization as possible.29 A general rule is to allow approximately 3 weeks for acclimatization at moderate altitudes and an additional week for every 1,970 feet (600 m) after that.30To avoid health risks, such as acute altitude (mountain) sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE), ascent should be slow and gradual, refraining from climbing more than 984 feet (300m) per day at elevations above 9,840 feet (3,000m).31 If proper time for acclimatization is not available (common with military operations), leaders must pay extra attention to warning signs of high altitude physical and mental issues. Cardiovascular and metabolic responses also occur once exposed at altitude. Cardiac output initially increases due to an increased heart rate, pumping more blood to active muscles to compensate for decreased oxygen per liter of blood.32 This peaks after about 6 to10 days, after which cardiac output and heart rate begin to decrease.33 Basal metabolic rates also increase at altitude with a growing reliance on carbohydrates for bodily fuel, but decreased appetite as being at altitude makes maintaining body weight and muscle mass very difficult.34 The eyes, along with internal body parts, have also been shown to be affected at altitude, primarily a decrease in color discrimination of the tritan (blue) color vision axis.35This effect has proven to be transient and is highly correlated to increased heart rate and decreased oxygen saturation, which have been mentioned previously.36 Not only is the body affected at altitude, but the mind is as well. Decrements in individual performance in problem solving (IPPS) have also been demonstrated at altitude; however, these results seems to be more of a combination of altitude effects and anxiety generated through problems faced at altitude.37 These occurrences warrant attention at the leader level to ensure soldiers eat, regardless of a lack of appetite; are aware of possible changes in their vision, so they can still operate at 100 percent without increased anxiety or fear; and leaders should consider relying more heavily on added input before making decisions to avoid dangerous errors in judgment, which have been shown to occur in high altitude problemsolving. Finally, one of the factors most easily influenced by leaders is aerobic fitness. Aerobic adaptations are closely related to the physiological responses at altitude. Thus, emphasis should be placed on aerobic fitness when preparing for altitude. Soldiers, who are more aerobically fit before being placed in a high-altitude environment, will have a higher level of performance and a greater chance of adapting. In Cold Weather The foremost goal of the body in cold weather is to maintain a core body temperature of around 37°C (98.6°F).38When the weather is cold, the body has three main responses. The first response is peripheral vasoconstriction, which decreases blood flow to the periphery of the body, reducing convective heat transfer between the body and the outside environment, thereby increasing insulation and heat conservation.39Next, is an increase in basal metabolic rate, which increases internal heat production (non-shivering thermogenesis).40When both these responses are not enough to maintain core body temperature, the body responds with shivering, an involuntary and rapid contraction “To avoid health risks, such as acute altitude (mountain) sickness (AMS), high-altitude pulmonary edema (HAPE), and high-altitude cerebral edema (HACE), ascent should be slow and gradual, refraining from climbing more than 984 feet (300m) per day at elevations above 9,840 feet (3,000m). If proper time for acclimatization is not available (common with military operations), leaders must pay extra attention to warning signs of high altitude physical and mental issues.” 34 — and relaxation of the skeletal muscles, which can increase heat production 4 to 5 times normal values.41These responses make the extremities (hands and feet) of the body particularly susceptible to the effects of cold weather. Cold weather can severely retard muscle function. The cooling of the periphery affects the neural recruitment of muscle fibers, force production, and the viscosity of the fluid and tissues that are crucial to appendage movement and sensory perception.42 This translates into decreased manual dexterity and causes fine motor movements to be much more difficult such as knot tying.43 If performance of military skills and tasks is to be maintained in cold weather, it is imperative that those skills and tasks be practiced in warm weather beforehand.44 There is some evidence that over time some acclimatization or habituation can occur in the hands through repeated exposure and a more effective cold-induced vasodilatation response (CIVD).45 However, heavy loads, such as rucksacks, can impair blood flow to the hands and inhibit the CIVD response.46 Cognitive performance can also be adversely affected by cold weather with performance deficits being shown at core body temperatures of around 34-35°C.47 It appears that race may also be a factor in the occurrence of cold weather injuries (CWI). African Americans, in past studies conducted between 1980 and 1999, experienced CWI at a disproportionately higher rate than Caucasians.48 However, another study conducted in 1993 showed that African Americans did not show any difference in incidences of nonfreezing cold injuries (NFCI) compared to Cauca-sians, but possibly the factor of smoking history may play a bigger role.49Regardless, if smoking is or is not a factor for increased risk of CWI (both freezing and nonfreezing), it is not an advantageous habit to have in this environment, especially at altitude for reasons already discussed. Alcohol also warrants discussion; alcohol restrictions, despite personal opinions, are scientifically warranted in a cold weather environment. Alcohol has been shown to impair shivering thermogenesis, helping lower core body temperatures, as well as blunting cold perception.50 Unlike gradual cooling of the body on dry land, immersion in extremely cold water can cause death before the body even experiences a drop in core temperature.51 It is known that some people are allergic to cold, and sudden exposure can cause anaphylactic shock.52 Sudden entry into cold water can also cause severe cardiovascular responses, leading to death from stroke and myocardial infarction (heart attack).53 Uncontrollable hyperventilation is also a response to sudden contact of cold to the skin, which may lead to impaired consciousness (marked respiratory alkalosis), tetany (cramps), and a decrease in voluntary breath-hold, often leading to a person drowning before they experience other effects such as hypothermia.54 If a person survives the initial response to cold water, it is very unlikely that the person could swim more than 50 to 100m to dry land due the decreased muscle function previously mentioned.55 Body composition, the amount of body fat and muscle, can greatly affect the strategy chosen for survival in cold weather. Leaner people should stay put and move as little as possible to make the most of limited natural insulation (fat and muscle).56 If they attempt to use physical exertion to keep warm, they lose heat quicker because their limited natural insulation does not retain heat as well due to increased convective heat loss. Larger people would have a better chance of employing beneficial physical exertion; however, they are still subject to diminished muscle function mentioned above. Both types of people are ultimately subject to certain time constraints; they must either be removed from the cold water or heat the entire body of water to an acceptable temperature to prevent hypothermia and death.57 This article briefly discusses some of the fundamental physiological occurrences at altitude and in cold weather situations. Although mitigation strategies and “Aerobic adaptations are closely related to the physiological responses at altitude. Thus, emphasis should be placed on aerobic fitness when preparing for altitude. Soldiers, who are more aerobically fit before being placed in a high-altitude environment, will have a higher level of performance and a greater chance of adapting.” — 35 techniques to combat these environments is not a topic of this article, it is written to provide a knowledge base for leaders to assess their actions in these environments and ensure everything possible is done to preserve combat power and take care of soldiers. We can always improve how we do business through education, and learning how to manage altitude and cold weather is no exception. Notes 1Captain M. Rav-Acha, Major Y. Heled, and Lieutenant Colonel D. S. Moran, “Cold Injuries among Israeli Soldiers Operating and Training in a Semiarid Zone: A 10-Year Review,” Military Medicine, 169, 2004, pp. 702-706. 2Ibid. 3K. Beighton, BBC News, “WWI Bodies are Found on Glacier,” 23 August 2004, Retrieved 24 January 2009, online at http://news.bbc.co.uk/2/hi/europe/3592268.stm. 4D. W. DeGroot, J. W. Castellani, J. O. Williams, and P. J. Amoroso, “Epidemiology of U. S. Army Cold Weather Injuries, 1980-1999,” Aviation, Space, and Environmental Medicine, 74 (5), 2003, pp. 564-570; and Lieutenant Colonel R. Craig, “Military Cold Injury During the War in The Falkland Islands 1982: An Evaluation of Possible Risk Factors,” Journal of the Royal Army Medical Corps, 153 (Suppl 1), 2007, pp. 63-68. 5S. Qadir, “An Analysis of the Kargil Conflict 1999,” Royal United Services Institute for Defence and Security Studies, April 2002, Retrieved 24 January 2009 at http://www.ccc.nps. navy.mil/research/kargil/JA00199.pdf. 6Jim Garamone, “The Battle of Takur Ghar,” American Forces Press Service News Articles, 24 May 2002, Retrieved 24 January 2009 at http://www.defenselink.mil/news/newsarticle. aspx?id=44020. 7DeGroot, et al., “Epidemiology of U. S. Army Cold Weather Injuries, 1980-1999;” Craig, “Military Cold Injury During the War in The Falkland Islands 1982: An Evaluation of Possible Risk Factors.” 8J. H. Wilmore, D. L. Costill, and W. L. Kenney, Physiology of Sport and Exercise (4th ed.). Human Kinetics Publishers, Champaign, Illinois, 2008. 9Wilmore, et al., Physiology of Sport and Exercise; and MAJ A. G. Truesdell and Captain R. L. Wilson, “Training for Medical Support of Mountain Operations,” Military Medicine, 171 (6), 2006, pp. 463-467. 10Wilmore, et al., Physiology of Sport and Exercise. 11Wilmore, et al., Physiology of Sport and Exercise; and Truesdell and Wilson, “Training for Medical Support of Mountain Operations.” 12Wilmore, et al., Physiology of Sport and Exercise; and E. Lloyd, “Temperature and Performance I: Cold,” British Medical Journal (BMJ), 309 (6953), 1994, pp. 531-534. 13Wilmore, et al. Physiology of Sport and Exercise. 14Ibid. 15W. Ambach, M. Blumthaler, and E. Schöpf, “Increase of Biologically Effective Ultraviolet Radiation with Altitude,” Journal of Wilderness Medicine, 4, 1993, pp. 189-197. 16Wilmore, et al., Physiology of Sport and Exercise. 17Lloyd, “Temperature and Performance I: Cold;” and T. Noakes, “Exercise and the Cold,” Ergonomics, 43, 2000, pp. 1461- 1479. 18Noakes, “Exercise and the Cold;” and J. W. Castellani, A. J. Young, M. B. Ducharme, G. G. Giesbrecht, E. Glickman, and R. E. Sallis, “Prevention of Cold Injuries during Exercise,” Medicine & Science in Sports & Exercise, 2006, pp. 2012-2029. 19Wilmore, et al., Physiology of Sport and Exercise; Truesdell and Wilson, “Training for Medical Support of Mountain Operations;” and J. West, “Acclimatization and Tolerance to Extreme Altitude, Journal of Wilderness Medicine, 4, 1993, pp. 17-26. 20Wilmore, et al., Physiology of Sport and Exercise. 21Ibid. 22Wilmore, et al., Physiology of Sport and Exercise; Truesdell and Wilson, “Training for Medical Support of Mountain Operations;” and West, “Acclimatization and Tolerance to Extreme Altitude.” 23Ibid. 24Ibid. 25Ibid. 26Wilmore, et al., Physiology of Sport and Exercise. 27Ibid. 28Ibid. 29Wilmore, et al., Physiology of Sport and Exercise; Truesdell and Wilson, “Training for Medical Support of Mountain Operations;” West, “Acclimatization and Tolerance to Extreme Altitude;” and J. Tougne, B. Paty, D. Meynard, J. Martin, T. Letellier, and E. Rosnet, “Group Problem Solving and Anxiety During Simulated Mountaineering Ascent,” Environment and Behavior, 40, pp. 3-23. 30Wilmore, et al., Physiology of Sport and Exercise. 31Ibid. 32Ibid. 33Ibid. 34Wilmore, et al., Physiology of Sport and Exercise; and B. Bales, A. C. Hackney, J. T. Coyne, E. Shaw, G. McAninch, A. Kramer, and R. Brownsberger, “Mountaineering Sojourn: Effects on Body Composition of Prolonged Exposure to High Altitude in a Cold Environment,” Journal of Wilderness Medicine, 4, 1993, pp. 32-39. 35M. Tekavi-Pompe, and I. Tekavi, “Color Vision in the Tritan Axis Is Predominately Affected at High Altitude,” High Altitude Medicine & Biology, 9, 2008, pp. 38-42. 36Ibid. 37Tougne, et al., “Group Problem Solving and Anxiety During Simulated Mountaineering Ascent.” 38Lloyd, “Temperature and Performance I: Cold.” 39Lloyd, “Temperature and Performance I: Cold;” Noakes, “Exercise and the Cold;” Castellani, et al., “Prevention of Cold Injuries during Exercise;” and A. J. Young, and J. W. Castellani, “Exertional Fatigue and Cold Exposure: Mechanisms of Hiker’s Hypothermia,” Applied Physiology, Nutrition & Metabolism, 32, 2007, pp. 793-798. 40Wilmore, et al., Physiology of Sport and Exercise; Castellani, et al., “Prevention of Cold Injuries during Exercise;” and Young and Castellani, “Exertional Fatigue and Cold Exposure: Mechanisms of Hiker’s Hypothermia.” 41Wilmore, et al., Physiology of Sport and Exercise; Lloyd, “Temperature and Performance I: Cold;” Castellani, et al., “Prevention of Cold Injuries during Exercise;” and Young and Castellani, “Exertional Fatigue and Cold Exposure: Mechanisms of Hiker’s Hypothermia.” 42Wilmore, et al., Physiology of Sport and Exercise; Lloyd, “Temperature and Performance I: Cold;” Noakes, “Exercise and the Cold;” and C. Marrao, P. Tikuisis, A. A. Keefe, V. Gil, and G. C. Giesbrecht, “Physical and Cognitive Performance During Long-Term Cold Weather Operations,” Aviation, Space, and Environmental Medicine, 76, 2005, pp. 744-752. 43Lloyd, “Temperature and Performance I: Cold;” and Marrao, et al., “Physical and Cognitive Performance During Long-Term Cold Weather Operations.” 44J. Oksa, H. Rintamäki, and T. Mäkinen, “The Effect of Training of Military Skills on Performance in Cold Environment,” Military Medicine, 171, 2006, pp. 757-761. 45R. G. Hoffman and L. E. Wittmers, Jr., “Cold Vasodilatation, Pain, and Acclimatization in Arctic Explorers,” Journal of Wilderness Medicine, 1, 1990, pp. 225-234; and C. O’Brien and P. N. Frykman, “Peripheral Responses to Cold: Case Studies From an Arctic Expedition,” Wilderness and Environmental Medicine, 14, 2003, pp. 112-119. 46O’Brien and Frykman, “Peripheral Responses to Cold: Case Studies From an Arctic Expedition.” 47Lloyd, “Temperature and Performance I: Cold;” Marrao, et al., “Physical and Cognitive Performance During Long-Term Cold Weather Operations.” 48DeGroot, et al., “Epidemiology of U. S. Army Cold Weather Injuries, 1980-1999.” 49D. Tek and S. Mackey, “Nonfreezing Cold Injury in a Marine Infantry Battalion,” Journal of Wilderness Medicine, 4, 1993, pp. 353-357. 50B. J. Freund, C. O’Brien, and A. J. Young, “Alcohol Ingestion and Temperature Regulation During Cold Exposure,” Journal of Wilderness Medicine, 5, 1994, pp. 88-98. 51Lloyd, “Temperature and Performance I: Cold;” and Noakes, “Exercise and the Cold.” 52Lloyd, “Temperature and Performance I: Cold.” 53 Lloyd, “Temperature and Performance I: Cold; and Noakes, “Exercise and the Cold.” 54Ibid. 55Noakes, “Exercise and the Cold.” 56Ibid. 57Ibid. Captain Russ Nowels is currently a military movement instructor, Department of Physical Education, U. S. Military Academy, West Point, NY. He received a B. S. from the U. S. Military Academy and an M. S. in Kinesiology from Indiana University. His military education includes Armor Officer Basic Course, Armor Captain Career Course, Airborne School, Scout Leader Course, and Master Fitness Trainer Course. He has served in various command and staff positions, to include commander, A Troop, 1st Squadron, 10th Cavalry, Fort Carson, CO; assistant operations officer, 3d Squadron, 3d Armored Cavalry Regiment, South Baghdad, Iraq; and adjutant, Regimental Headquarters and Headquarters Troop, 3d Armored Cavalry Regiment, Tall Afar, Iraq. Captain Coley Tyler is currently working on his M. S. in Kinesiology at Indiana University. He received a B. S. from the U. S. Military Academy. His military education includes Field Artillery Officer Basic Course, Field Artillery Captain Career Course, Ranger School, Airborne School, and Master Fitness Trainer Course. He has served in various command and staff positions, to include commander, Headquarters and Headquarters Company, 3d Brigade Special Troops Battalion, 3d Brigade, 1st Cavalry, Fort Hood, TX; battalion intelligence officer and assistant operations officer, 2d Battalion, 82d Field Artillery, Baghdad and Balad, Iraq, and Fort Hood; and battalion fire support officer, 2d Battalion, 7th Cavalry, 1st Cavalry, Taji and Fallujah, Iraq. Dr. Phil Henson is an assistant professor, Department of Kinesiology, Indiana University. He received a Ph. D. in Human Performance from Indiana University. His activities and research center on understanding and improving human athletic performance, especially in the sport of track and field. Most notably, he served as the competition director for the 1996 Olympic Games in Atlanta, GA. In this position, he dealt with potential heat issues involving track and field events, to include marathons and the 50K walk. 36 —