Susan Niermeyer

HUMAN ADAPTATION TO HIGH ALTITUDE : REGIONAL AND LIFE-CYCLE PERSPECTIVES

Studies of the ways in which persons respond to the adaptive challenges of life at high altitude have occupied an important place in anthropology. There are three major regions of the world where high-altitude studies have recently been performed: the Himalayas of Asia, the Andes of South America, and the Rocky Mountains of North America. Of these, the Himalayan region is larger, more geographically remote, and likely to have been occupied by humans for a longer period of time and to have been subject to less admixture or constriction of its gene pool. Recent studies of the physiological responses to hypoxia across the life cycle in these groups reveal several differences in adaptive success. Compared with acclimatized newcomers, lifelong residents of the Andes and/or Himalayas have less intrauterine growth retardation, better neonatal oxygenation, and more complete neonatal cardiopulmonary transition, enlarged lung volumes, decreased alveolar-arterial oxygen diffusion gradients, and higher maximal exercise capacity. In addition, Tibetans demonstrate a more sustained increase in cerebral blood flow during exercise, lower hemoglobin concentration, and less susceptibility to chronic mountain sickness (CMS) than acclimatized newcomers. Compared to Andean or Rocky Mountain high-altitude residents, Tibetans demonstrate less intrauterine growth retardation, greater reliance on redistribution of blood flow than elevated arterial oxygen content to increase uteroplacental oxygen delivery during pregnancy, higher levels of resting ventilation and hypoxic ventilatory responsiveness, less hypoxic pulmonary vasoconstriction, lower hemoglobin concentration, and less susceptibility to CMS. Several of the distinctions demonstrated by Tibetans parallel the differences between natives and newcomers, suggesting that the degree of protection or adaptive benefit relative to newcomers is enhanced for the Tibetans. We thus conclude that Tibetans have several physiological distinctions that confer adaptive benefit consistent with their probable greater generational length of high-altitude residence. Future progress is anticipated in achieving a more integrated view of high-altitude adaptation, incorporating a sophisticated understanding of the ways in which levels of biological organization are articulated and a recognition of the specific genetic variants contributing to differences among high-altitude groups.

Evaluation of diagnostic criteria and incidence of acute mountain sickness in preverbal children.

OBJECTIVEnThe Childrens Lake Louise Score (CLLS) established the diagnostic criteria for acute mountain sickness (AMS) in preverbal children. Prospective application of the CLLS and interobserver agreement for the score had not been evaluated in a controlled trial. A study of children and their parents was used to evaluate the CLLS and determine the incidence of AMS in preverbal children.nnnMETHODSnA prospective, controlled trial. Children > or =3 months and < or =36 months old and their parents living below 1645 m were studied over 7 separate days. The CLLS, measured daily by the mother as well as by the father on days 5 and 6, is the sum of scores for fussiness (FS), eating (E), playfulness (P), and sleep (S). Children were studied on days 1 and 2 at home, on day 3 after travel without altitude gain to a hotel, on day 4 at home, on days 5 and 6 at a hotel at 3109 m, and on day 7 at home. Using our previous criteria, AMS was diagnosed if the CLLS was > or =7 with both the FS > or =4 and the E + P + S > or =3. Agreement between mothers and fathers CLLS values was measured with the kappa statistic (K). Adults were also evaluated for AMS by the CLLS on days 5 and 6.nnnRESULTSnThirty-seven children (mean age +/- SD = 16.5+/-10.5 months; 21 girls) participated, and AMS occurred in 7 of them (19%; 95% CI, 8.35%). Among 33 adults, 8 (24%; 95% CI, 9.39%) had AMS. Although the agreement of the parents on the CLLS components was poor, the agreement on the classification of AMS between mother and father was excellent (K = .67; P < .001), with both parents scores exceeding the CLLS threshold for AMS.nnnCONCLUSIONSnIn this prospective trial, parents demonstrated excellent interobserver agreement for independent use of the CLLS to detect AMS. Consistent with our previous retrospective study, the incidence of AMS at moderate altitude in preverbal children (19%) was similar to that in adults (24%).

Altitude-related illness in children

[] ~ ntil relatively recently, clinical illness related to exposure to high altitude was a concern mainly of mountaineers and physiologists. As our understanding of these conditions has grown, however, it has become clear that children are among those at highest risk of having altitude-related illnesses. In addition, with the growth of the populations of the mountainous regions of North America, as well as the advent of jet travel to those areas, greater numbers of children are either living at or vlsiting areas of sufficientaltitude to cause clinical illness. The rapidity of the ascent to altitude allowed by modem jet travel also allows less time for acclimatization and may increase the risk of these conditions developing. Finally, a number of pediatric illnesses are associated with either acute or chronic hypoxemia, and there may be lessons of relevance to the care of these children to be learned from the effects of altitude exposure. All of these factors combine to make altitude-related illness in children a topic of clinical relevance to pediatric practitioners. Despite intense research over the last half century, however, much of the basic pathophysiologic mechanism of illness related to altitude remains obscure. Although recent progress has been made toward identifying at least some therapeutic interventions for these conditions, approximately 20 deaths per year worldwide are ascribed to high-altitude pulmonary edema alone, and the number of hospital visits and mined vacations attributable to altitude-related illness as a whole is undoubtedly much higher. Unfortunately, little of the research on the physiologic and pathophysiologic

Clinical Description of Heat Illness in Children, Melbourne, Australia—A Commentary

Concerns about the health effects of global warming and the adequacy of the public health response to environmental crises heightened recently when record-high temperatures across France in the summer of 2003 resulted in the death of nearly 15 000 persons, many of them elderly. The accompanying article by Danks and associates highlights another group vulnerable to heat illness, that of young children. The authors describe their experience treating heat illness in young children during a 3- to 7-day heat wave in the region around Melbourne, Australia, in 1959. This heat wave was distinguished as the most intense on record for the previous 50 years. The temperatures were sustained at 35 Ct o 48C (95F– 109F) during the day and 24 to 32C (75F–90F) at night. Of 47 ill children, 6 were pronounced dead on arrival, and 6 more died from heat-related causes after admission. This report presents one of the first and most detailed clinical descriptions of heat illness in children. As is true of many conditions encountered in wilderness and environmental medicine, the early scientific interest in heat illness centered primarily on adults in the military. [A review of the paper by Buskirk, ‘‘Work performance after dehydration: effects of physical conditioning and heat acclimatization,’’ previously appeared in Lessons from History (Wilderness Environ Med. 2000;11:202–203)]. Initial epidemiological study of deaths among civilian populations during environmental heat waves identified the elderly, the poor, and those with pre-existing disease as being at special risk. The authors of the current paper turned a potentially overwhelming influx of critically ill children into a careful analysis that demonstrated the vulnerability to heat illness in the other extreme of the age spectrum. It deserves note that 2 physicians in training (a registrar and a house physician) and a social worker at the children’s hospital in Melbourne formed an unusual and effective team of investigators to perform this study. They present a vivid and useful clinical description based on the classical elements of the medical history (past medical history, history of present illness, review of systems, family and social history) and physical examination, despite their limited access to laboratory and diagnostic resources. All children in the series reported were 6 years of age or younger and only 2 children were older than 4 years. The most striking feature of the case series is the importance of specific medical and social risk factors among the children. The authors report an analysis of preexisting medical conditions, developmental state, acute illnesses, conditions of the home environment, and skills of the mother. The most important predisposing factor for illness or fatal outcome, in 31 of 47 children, was severe chronic disease, most often developmental delay, associated with the history of feeding difficulty. ‘‘Maternal ability’’ and housing conditions were assessed by the social worker, who conducted home visits in 38 cases. Among those patients who were dead on arrival, poor maternal ability (failure to recognize the need for additional fluid or fluids other than cow’s milk) and poor housing (excessive internal temperatures) were notable. The authors did cite delayed or misleading advice from physicians and distance from home to hospital as playing a role in several fatal cases because of the rapidity of the final deterioration. The descriptions of the sequence of clinical signs and the sudden changes that occur with heat illness in young children remain accurate and useful today. ‘‘On arrival at hospital. . . the outstanding features were dehydration, poor peripheral circulation, and impairment of consciousness. . . Rapid deep respiration, without acidotic breath or ketonuria, was frequent, and irregular respirations occurred in the most ill.’’ The authors make the important point that dehydration, rather than hyperpyrexia, was more closely related to severe disturbance of consciousness and to subsequent seizures. They also emphasize the prodromal phases as variable in duration but leading inevitably to decompensation, at which point intervention may be too late. ‘‘The symptoms preceding