Consensus statement on chronic and subacute high altitude diseases

Lessons in hypoxic adaptation from high-altitude populations

An increase in hemoglobin level is seen in virtually all lowlanders who move to or train at altitude; however, studies of high-altitude native populations illustrate that this response is not necessary for successful long-term residence. Indigenous populations living at the same altitude have differences not only in hemoglobin level but also in other traits like oxygen saturation. Support for a genetic causation for differences in features of oxygen transport, namely hemoglobin levels and oxygen saturation, is derived from kindred studies among the highlander populations. Indeed, evidence from Tibet suggests that inferred genes for high oxygen saturation are associated with higher offspring survival. It may be that signaling molecules like nitric oxide and transcription factors such as hypoxia-inducible factor could act as an upstream regulator for highlander traits. However, the preponderance of data suggests that it is unlikely that one process or even a common set of processes is responsible for successful biologic adaptation shown in all three resident high-altitude populations. Future studies will require the ability to identify combinations of genetic variants with outcomes including expression levels, appropriate phenotypes, and functional responses.

Hematological and lipid profile changes in sea-level natives after exposure to 3550-m altitude for 8 months

The aim of this epidemiological study was to determinate the effects on hematological and lipid profile in a young group of newcomers to altitude after being exposed chronically for 8 months to 3550 m (n = 50), age 17.8 +/- 0.7; and not overweight, BMI 22.9 +/- 0.5). Readings taken at altitude on day 1 and on month 8 were hematocrit (Hct, %), hemoglobin (Hb, g/dL), Sa(O(2)), total leukocyte and subset count (mm(3), %), and lipid profile (mg/dL). The same measurements were taken in a comparative group (CG) at sea level (SL). At altitude, elevations of Hct (44.6 +/- 0.4; 51.2 +/- 0.4) and Hb (15.5 +/- 0.1; 17.3 +/- 0.1) were seen (p < 0.001) and none with Hb >/= 21 g/dL. No correlation was observed between Hb and Sa(O(2)), r = 0.11, p > 0.05. Total leukocyte count showed no changes (6037 +/- 74; 6002 +/- 43), but a relative neutropenia (55.2 + -1.5; 50.6 + -1.3) and lymphocytosis (34.2 + 1; 42.4 + 1, p < 0.001) between periods were found and also when compared to SL. Also, an inverse relationship between Sa(O(2)) and total leukocytes on month 8 (r = 0.46; r(2) = 0.204), suggesting a probable representation of a hypoxia effect. Total cholesterol (153.8 +/- 4.5; 157.3 +/- 5.1; p, ns) showed no changes, but a mild decrease of LDL-cholesterol (88.4 +/- 3.3; 81.0 +/- 3.9; p < 0.05), and a rise in triglycerides (121.6 +/- 10.9; 178.8 +/- 11.7; p < 0.001) was found. Changes observed in leukocytes subset count and triglycerides could suggest a contributory role of hypoxic conditions, raising some future epidemiological concerns regarding immune system and fatty acid behaviour at altitude.

Chronic intermittent hypoxia at high altitude exposure for over 12 years: assessment of hematological, cardiovascular, and renal effects

The aim of this cross-sectional study was to assess the health status of subjects weekly commuting between sea level and 3550-m altitude for at least 12 yr (average 22.1 +/- 5.8). We studied 50 healthy army men (aged 48.7 +/- 2.0) working 4 days in Putre at 3550-m altitude, with 3 days rest at sea level (SL) at Arica, Chile. Blood pressure, heart rate, Sa(O(2) ), and altitude symptoms (AMS score and sleep status) were measured at altitude (days 1, 2, and 4) and at SL (days 1, 2, and 3). Hematological parameters, lipid profile, renal function, and echocardiography were performed at SL on day 1. The results showed signs of acute exposure to hypoxia (tachycardia, high blood pressure, low Sa(O(2) )), AMS symptoms, and sleep disturbances on day 1, which rapidly decreased on day 2. In addition, echocardiographic findings showed pulmonary hypertension (PAPm > 25 mmHg, RV and RA enlargement) in 2 subjects (4%), a PAPm > 20 mmHg in 14%, and a right ventricle thickness >40 mm in 12%. Hematocrit (45 +/- 2.7) and hemoglobin (15 +/- 1.0) were elevated, but lower than in permanent residents. There was a remarkably high triglyceride level (238 +/- 162) and a mild decrease of glomerular filtration rate (34% under 90 mL/min and 8% under 80 mL/min of creatinine clearance). In conclusion, in these preliminary results, in chronic intermittent hypoxia exposure even over longer periods, most subjects still show symptoms of acute altitude illnesses, but a faster recovery. Findings in triglycerides, in the pulmonary circulation and in renal function, are also a matter of concern.

Stable isotope and DNA evidence for ritual sequences in Inca child sacrifice

Four recently discovered frozen child mummies from two of the highest peaks in the south central Andes now yield tantalizing evidence of the preparatory stages leading to Inca ritual killing as represented by the unique capacocha rite. Our interdisciplinary study examined hair from the mummies to obtain detailed genetic and diachronic isotopic information. This approach has allowed us to reconstruct aspects of individual identity and diet, make inferences concerning social background, and gain insight on the hitherto unknown processes by which victims were selected, elevated in social status, prepared for a high-altitude pilgrimage, and killed. Such direct information amplifies, yet also partly contrasts with, Spanish historical accounts.

Who should not go high: chronic disease and work at altitude during construction of the Qinghai-Tibet railroad

From 2001 to 2005, a new railroad linking Beijing with Lhasa was built by more than 100,000 workers, of whom 80% traveled from their lowland habitat to altitudes up to 5000 m to work on the railroad. We report on the medical conditions of 14,050 of these altitude workers, specifically with regard to preexisting illness. All subjects were seen at low and high altitude. Average age was 29.5 +/- 7.4 (SD) yr, range 20 to 62 yr; 98.8% of the subjects were men and 1.2% were women. Overall incidence of AMS upon first-time exposure was 51%, that of HACE 0.28%, and that of HAPE 0.49%. About 1% of the subjects were hypertensive before altitude exposure. Those with blood pressure >or=160/95 were excluded from employment at altitude. Altitude exposure led to a greater increase of blood pressure in hypertensives compared to normotensives. On prealtitude screening prevalence of cardiac arrhythmias was 0.33%. Since the majority of these were rather benign and occurring in young and otherwise healthy subjects, we allowed altitude employment. Follow-up at altitude was uneventful. Subjects with coronary heart disease and diabetes were excluded from altitude employment. Obesity was a risk factor for acute mountain sickness and for reduced work performance at altitude. Overweight subjects lost more weight during their altitude stay than subjects with normal weight. Altitude exposure was a risk factor for upper gastrointestinal tract bleeding, especially in combination with alcohol, aspirin, and dexamethasone intake. Asthmatic subjects generally did better at altitude compared to low altitude, with the exception of one subject who experienced an asthma episode from pollen exposure. In conclusion, careful evaluation of preexisting chronic illness and risk factors allowed prevention of altitude deterioration of a preexisting health condition, all the while allowing subjects with some specific conditions to work and live at altitude without problems.

Does chronic mountain sickness (CMS) have perinatal origins?

Chronic mountain sickness (CMS) occurs in approximately 10% of male high-altitude residents. It is characterized by hypoventilation and hypoxemia but its underlying cause remains unknown. We hypothesized that CMS' origins reside in exaggerated perinatal hypoxia that serves, in turn, to impair the development of pulmonary structure and/or respiratory control. As a preliminary test, we asked if birth weights were low and other signs of perinatal hypoxia were present in 12 young men with excessive erythrocytosis (EE, Hb>or=18.3g/dL), a condition thought to be a preclinical phase of CMS. Their birth weights were uniformly low (2571+/-243g) and all but one demonstrated perinatal hypoxia as manifested either by being small for their gestational age (SGA, 8%), preterm (67%), born to a preeclamptic (PE) mother (50%), or diagnosed with neonatal hypoxia (83%). Impaired growth in utero has been shown to raise susceptibility to adult disease; these are the first data to demonstrate a possible influence of reduced fetal growth and/or exaggerated perinatal hypoxia on increasing the susceptibility to CMS. Future studies, with more detailed testing in larger samples of control as well as EE subjects, with longitudinal follow-up, are required to determine the role of perinatal hypoxia in the development of CMS.

High-altitude physiology and pathophysiology: implications and relevance for intensive care medicine

Cellular hypoxia is a fundamental mechanism of injury in the critically ill. The study of human responses to hypoxia occurring as a consequence of hypobaria defines the fields of high-altitude medicine and physiology. A new paradigm suggests that the physiological and pathophysiological responses to extreme environmental challenges (for example, hypobaric hypoxia, hyper-baria, microgravity, cold, heat) may be similar to responses seen in critical illness. The present review explores the idea that human responses to the hypoxia of high altitude may be used as a means of exploring elements of the pathophysiology of critical illness.

Treatment of chronic mountain sickness: critical reappraisal of an old problem

A review is made on the different treatment strategies essayed to date in the management of chronic mountain sickness (CMS). After a brief presentation of the epidemiology and of the pathophysiological mechanisms proposed for explaining the disease, the advantages and drawbacks of the different treatment approaches are discussed, along with their pathopysiological rationale. A particular emphasis is dedicated to the scientific foundations underlying the development of acetazolamide and angiotensin-converting enzyme inhibitors as promising therapeutic agents for CMS, as well as the clinical evidence existing so far on their usefulness in the treatment of CMS. Various methodological issues that need to be addressed in future clinical studies on efficacy of therapies for CMS are discussed. There is also a brief discussion on potential treatment options for chronic high altitude pulmonary hypertension. Closing remarks on the need of taking increasingly into account the development and implementation of preventive measures are made.

Postnatal cardiopulmonary adaptations to high altitude

Postnatal cardiopulmonary adaptations to high altitude constitute a key component of any set of responses developed to face high altitude hypoxia. Such responses are required ultimately to meet the energy demands necessary for adequate functioning at cell and organism level. After a brief insight on general and cardiopulmonary comparative studies in growing and adult organisms, differences and possible explanations for varying cardiopulmonary pathology, pulmonary artery hypertension, persistent right ventricular predominance and subacute high altitude pulmonary hypertension in different populations of children living at high altitude are discussed. Potential long-term implications of early chronic hypoxic exposure on later diseases are also presented. It is hoped that this review will help the practicing physician working at high altitude to make informed decisions concerning individual pediatric patients, specifically with regard to diagnosis and management of altitude-related cardiopulmonary pathology. Finally, plausibility and the knowledge-base of public health interventions to reduce the risks posed by suboptimal or inadequate postnatal cardiopulmonary responses to high altitude are discussed.

The Heart and Pulmonary Circulation at High Altitudes

More than 140 million people worldwide live >2500 m above sea level. Of them, 80 million live in Asia, and 35 million live in the Andean mountains. This latter region has its major population density living above 3500 m. The primary objective of the present study is to review the physiology, pathology, pathogenesis, and clinical features of the heart and pulmonary circulation in healthy highlanders and patients with chronic mountain sickness. A systematic review of worldwide literature was undertaken, beginning with the pioneering work done in the Andes several decades ago. Original articles were analyzed in most cases and English abstracts or translations of articles written in Chinese were reviewed. Pulmonary hypertension in healthy highlanders is related to a delayed postnatal remodeling of the distal pulmonary arterial branches. The magnitude of pulmonary hypertension increases with the altitude level and the degree of exercise. There is reversal of pulmonary hypertension after prolonged residence at sea level. Chronic mountain sickness develops when the capacity for altitude adaptation is lost. These patients have moderate to severe pulmonary hypertension with accentuated hypoxemia and exaggerated polycythemia. The clinical picture of chronic mountain sickness differs from subacute mountain sickness and resembles other chronic altitude diseases described in China and Kyrgyzstan. The heart and pulmonary circulation in healthy highlanders have distinct features in comparison with residents at sea level. Chronic mountain sickness is a public health problem in the Andean mountains and other mountainous regions around the world. Therefore, dissemination of preventive and therapeutic measures is essential.

Evidence for a genetic basis for altitude-related illness

Altitude-related illnesses are a family of interrelated pulmonary, cerebral, hematological, and cardiovascular medical conditions associated with the diminished oxygen availability at moderate to high altitudes. The acute forms of these debilitating and potentially fatal conditions, which include acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE), often develop in incompletely acclimatized lowlanders shortly after ascent, whereas, the chronic conditions, such as chronic mountain sickness (CMS) and high altitude pulmonary hypertension (HAPH), usually afflict native or long-term highlanders and may reflect a loss of adaptation. Anecdotal reports of particularly susceptible people or families are frequently cited as evidence that certain individuals have an innate susceptibility (or resistance) to developing these conditions and, in recent decades, there have been a number of studies designed to characterize the physiology of individuals predisposed to these conditions, as well as to identify the specific genetic variants that contribute to this predisposition. This paper reviews the epidemiological evidence for a genetic component to the various forms of altitude-related illness, such as innate susceptibility, familial clustering, and patterns of population susceptibility, as well as the molecular evidence for specific genetic risk factors. While the evidence supports some role for genetic background in the etiology of altitude-related illness, limitations in individual studies and a general lack of corroborating research limit the conclusions that can be drawn about the extent of this contribution and the specific genes or pathways involved. The paper closes with suggestions for future work that could support and expand on previous studies, as well as provide new insights.

Respiratory control in residents at high altitude: physiology and pathophysiology

Highland population (HA) from the Andes, living above 3000 m, have a blunted ventilatory response to increasing hypoxia, breathe less compared to acclimatized newcomers, but more, compared to sea-level natives at sea level. Subjects with chronic mountain sickness (CMS) breathe like sea-level natives and have excessive erythrocytosis (EE). The respiratory stimulation that arises through the peripheral chemoreflex is modestly less in the CMS group when compared with the HA group at the same P(ET(O2)). With regard to CO(2) sensitivity, CMS subjects seem to have reset their central CO(2) chemoreceptors to operate around the sea-level resting P(ET(CO2)). Acetazolamide, an acidifying drug that increases the chemosensitivity of regions in the brain stem that contain CO(2)/H(+) sensitive neurons, partially reverses this phenomenon, thus, providing CMS subjects with the possibility to have high CO(2) changes, despite small changes in ventilation. However, the same type of adjustments of the breathing pattern established for Andeans has not been found necessarily in Asian humans and/or domestic animals nor in the various high altitude species studied. The differing time frames of exposure to hypoxia among the populations, as well as the reversibility of the different components of the respiratory process at sea level, provide key concepts concerning the importance of time at high altitude in the evolution of an appropriate breathing pattern.

Biochemistry, physiology, and complications of blood doping: facts and speculation

Competition is a natural part of human nature. Techniques and substances employed to enhance athletic performance and to achieve unfair success in sport have a long history, and there has been little knowledge or acceptance of potential harmful effects. Among doping practices, blood doping has become an integral part of endurance sport disciplines over the past decade. The definition of blood doping includes methods or substances administered for non-medical reasons to healthy athletes for improving aerobic performance. It includes all means aimed at producing an increased or more efficient mechanism of oxygen transport and delivery to peripheral tissues and muscles. The aim of this review is to discuss the biochemistry, physiology, and complications of blood doping and to provide an update on current antidoping policies.

Chronic Mountain Sickness, Optimal Hemoglobin, and Heart Disease

For the male inhabitants of La Paz, Bolivia (3200-4100 m), and other high altitude regions in America and Asia, chronic mountain sickness (CMS) is a major health problem. Since CMS was first described by Carlos Monge in the Peruvian Andes in 1925, numerous research papers have been devoted to this topic, but many unanswered questions still exist with respect to the beginning of the disease and its cause(s). The experience with CMS has shown that an excessively high hemoglobin concentration is not favorable for high altitude acclimatization, and the hypothesis of theoretically "optimal" hematocrit and "optimal" hemoglobin has been made. The calculated optimal hemoglobin concentration of 14.7 g/dL for resting men in the Andes is discussed as theoretical and not applicable in real life. The most frequent congenital and acquired heart diseases are discussed, such as patent ductus, atrial septum defect, ventricle septum defect among congenital heart diseases and the still very frequent rheumatic valve cardiopathies and Chagas disease as acquired cardiopathies. Among the typical acquired heart diseases of the high altitude dweller, special attention is given to chronic cor pulmonale as a consequence of severe CMS with pulmonary hypertension.

Cardiopulmonary Pathology Among Children Resident at High Altitude in Tintaya, Peru: A Cross-Sectional Study

Symptomatic high-altitude pulmonary hypertension and structural cardiac abnormalities related to high altitude have been reported previously. However, their true prevalence has not been systematically determined. We assessed clinical indicators of cardiovascular health or disease and correlated them with anatomic and physiologic cardiovascular features in preschool and schoolchildren living at 4000 m. We also estimated the prevalence of cardiovascular problems in the population, with emphasis on symptomatic high altitude pulmonary hypertension and structural cardiopathies. Three hundred and twenty-six children residents of Tintaya, Peru, were cross-sectionally studied. Methods included structured interviews, anthropometry and physical examination, arterial oxygen saturation, hemoglobin determination, electrocardiography, and echocardiography. The prevalence of structural cardiac problems was 1.5%, with less than 1% possibly attributable to high altitude. All children with structural cardiac abnormalities were identified by a focused physical exam prior to echocardiography. None were identified by the health interview. No symptomatic high altitude pulmonary hypertension was identified in the absence of underlying structural anomalies. The prevalence of structural cardiac problems was consistent with data from sea level. Active monitoring of the health status of a pediatric population at high altitude is valuable in the timely detection of cardiac abnormalities. Although our study children enjoyed generally excellent health, comparative, longitudinal studies are warranted to determine the incidence of high altitude cardiopulmonary problems and to identify risk factors and early markers for later disorders associated to life at high altitude. Our findings are applicable to children with some degree of high altitude genetic background and high mobility patterns to lower altitudes and living in comparatively good nutritional and socioeconomic conditions.

Jack Reeves and his science

John T. (Jack) Reeves' science is reviewed across the 37 years of his research career at the University of Colorado Health Sciences Center, a period which occupied approximately half his remarkable life. His contributions centered on understanding the inter-relatedness as well as the underlying mechanisms controlling the various components of the O(2) transport system. We review here his studies on exercise performance; these encompassed about half his scientific output with the other half being devoted to the study of hypoxic pulmonary hypertension. Early studies concerned cardiac output, showing how it was a balance between O(2) uptake and O(2) extraction, and that cardiac output during exercise at high altitude was reduced, most likely because of decreased plasma volume and left ventricular filling. Jack's many studies addressed virtually every aspect of the O(2) transport system -- adding significantly to our understanding of the syndromes of altitude illness, the mechanisms by which ventilatory sensitivity to hypoxia and hypercapnia influenced ventilatory acclimatization, and the contributions of the various limbs of the autonomic nervous system on systemic blood pressure, vascular resistance and substrate utilization. His scientific career ended abruptly in 2004 when struck by a car while biking to work, but his legacy remains in his more than 385+ research articles or chapters, the 40+ fellows he trained, and the countless number of younger (and older) scientists for whom he served as a role model for learning how to scrutinize their data and present their findings in clear and sometimes bold prose. An integral man, he is sorely missed.