Symptoms of infection and acute mountain sickness; associated metabolic sequelae and problems in differential diagnosis

Gastrointestinal syndrome encountered during a train voyage to high altitudes: A 14-day survey of 69 passengers in China

BACKGROUND

The diagnosis and evaluation of the severity of acute mountain sickness (AMS) continue to be problematic due to a lack of consensus on the inclusion of symptoms in a scoring system. Recent investigations highlight the significance of gastrointestinal symptoms in identifying this condition. However, the specific gastrointestinal symptoms associated with AMS have not been thoroughly elucidated in previous studies, and the underlying risk factors remain inadequately comprehended.

METHODS

This study aimed to investigate the characteristics, trends, and risk factors related to gastrointestinal symptoms encountered during train travel to high altitude. A total of 69 passengers, specifically all with medical backgrounds, were surveyed 6 times over a period of 14 days.

RESULTS

The daily incidence of abdominal discomfort was higher than non-gastrointestinal symptoms within 14 days. Gastrointestinal symptoms demonstrated a greater prevalence, longer duration, and increased risk compared to non-gastrointestinal symptoms, such as headaches. The symptoms of abdominal distension and bowel sound hyperaction were found to be prevalent and persistent among patients diagnosed with AMS, exhibiting a high incidence rate. Gender, age, body mass index (BMI), smoking habits, and alcohol consumption were identified as risk factors associated with the occurrence and duration of gastrointestinal symptoms.

CONCLUSION

This study suggests that gastrointestinal symptoms are more common and persistent when traveling to the plateau by train. These symptoms should be taken into consideration in the further diagnosis and prevention of AMS. Therefore, this study provides a significant theoretical foundation for the prevention and treatment of AMS.

Nox2 Upregulation and p38α MAPK Activation in Right Ventricular Hypertrophy of Rats Exposed to Long-Term Chronic Intermittent Hypobaric Hypoxia

One of the consequences of high altitude (hypobaric hypoxia) exposure is the development of right ventricular hypertrophy (RVH). One particular type of exposure is long-term chronic intermittent hypobaric hypoxia (CIH); the molecular alterations in RVH in this particular condition are less known. Studies show an important role of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex-induced oxidative stress and protein kinase activation in different models of cardiac hypertrophy. The aim was to determine the oxidative level, NADPH oxidase expression and MAPK activation in rats with RVH induced by CIH. Male Wistar rats were randomly subjected to CIH (2 days hypoxia/2 days normoxia; n = 10) and normoxia (NX; n = 10) for 30 days. Hypoxia was simulated with a hypobaric chamber. Measurements in the RV included the following: hypertrophy, Nox2, Nox4, p22phox, LOX-1 and HIF-1α expression, lipid peroxidation and H₂O₂ concentration, and p38α and Akt activation. All CIH rats developed RVH and showed an upregulation of LOX-1, Nox2 and p22phox and an increase in lipid peroxidation, HIF-1α stabilization and p38α activation. Rats with long-term CIH-induced RVH clearly showed Nox2, p22phox and LOX-1 upregulation and increased lipid peroxidation, HIF-1α stabilization and p38α activation. Therefore, these molecules may be considered new targets in CIH-induced RVH.

The Lake Louise Score: A Critical Assessment of Its Specificity

Moore, James, Martin J. MacInnis, Jon Dallimore, and Matt Wilkes. The Lake Louise Score: A Critical Assessment of Its Specificity. High Alt Med Biol. 21:237-242, 2020. Introduction: The Lake Louise Score (LLS) has low specificity for diagnosing acute mountain sickness (AMS). As this tool is used for research and clinical decision making, it is important to understand the origins of this poor specificity. We reviewed AMS diagnoses in a population trekking at low altitude ("false positives") to critically assess LLS specificity. Method: We retrospectively analyzed data from a sample of 123 adolescents trekking at low altitude to establish the predominant causes of false-positive AMS diagnoses (1993 LLS criteria), separately removing each LLS component to assess its contribution to the final score. Exploratory factor analysis (EFA) was applied to the data to establish component patterns. Results: Removal of LLS components individually showed fatigue contributed slightly more to false-positive AMS diagnoses than sleep quality in this group. An EFA from morning data highlighted sleep quality as a stand-alone factor in the measurement of AMS. Although of smaller significance, an EFA of the evening data highlighted fatigue and headache as the stand-alone factor. Conclusion: Our findings not only supported the recent removal of sleep quality from the LLS, but also demonstrated that fatigue had an equal part to play in the misdiagnosis of AMS in this population. These data highlighted the poor specificity of the LLS and suggest that the measurement of illness at altitude undergo further review.

Effects of Repetitive Altitude Training on Salivary Immunoglobulin A Secretion in Collegiate Swimmers

Background

Altitude training has often been conducted just before main competition games in many sports. An increase in the frequency of upper respiratory tract infections and gastrointestinal infections due to an altitude-induced suppression of the immune system has been reported after altitude training. Salivary secretory immunoglobulin A (SIgA) is the major immunoglobulin of the mucosal immune system. A suppressive effect of heavy training on SIgA has been reported. However, little is known regarding the effects of repetitive altitude training and hypoxic exposure on SIgA. The objective of this study was to evaluate the changes in SIgA in swimmers undergoing repetitive altitude training at 1,900 m.

Methods

Nine collegiate swimmers who experienced their first altitude training experience (FT group) were compared to nine swimmers who experienced repetitive training (RT group) and non-training subjects (Con group). Saliva was collected before ascent and eight times every 2 days during altitude training. SIgA levels were measured by enzyme-linked immunosorbent assays.

Results

Compared to the Con group, SIgA levels and the secretion velocity were decreased after ascent and were slowly restored in both the FT and RT groups. The chronological trends in SIgA levels were similar, even though the decline in SIgA levels in the FT group was larger than that in the RT group.

Conclusion

Altitude training and experience with altitude training may be one of the factors influencing SIgA.

A journey between high altitude hypoxia and critical patient hypoxia: What can it teach us about compression and the management of critical disease?

High altitude sickness (hypobaric hypoxia) is a form of cellular hypoxia similar to that suffered by critically ill patients. The study of mountaineers exposed to extreme hypoxia offers the advantage of involving a relatively homogeneous and healthy population compared to those typically found in Intensive Care Units (ICUs), which are heterogeneous and generally less healthy. Knowledge of altitude physiology and pathology allows us to understanding how hypoxia affects critical patients. Comparable changes in mitochondrial biogenesis between both groups may reflect similar adaptive responses and suggest therapeutic interventions based on the protection or stimulation of such mitochondrial biogenesis. Predominance of the homozygous insertion (II) allele of the angiotensin-converting enzyme gene is present in both individuals who perform successful ascensions without oxygen above 8000 m and in critical patients who overcome certain disease conditions.

Acute mountain sickness, arterial oxygen saturation and heart rate among Tibetan students who reascend to Lhasa after 7 years at low altitude: a prospective cohort study

Objectives

The aim of the present study was to estimate the incidence of acute mountain sickness (AMS) and address the changes in arterial oxygen saturation (SaO₂) and heart rate (HR) in native Tibetans who reascend to the high-altitude city of Lhasa (3658 m) after a 7-year stay at low altitude.

Methods

We followed two cohorts of students aged 17–21 years (859 Native Tibetan and 801 Han Chinese), travelling from lowland China until 3 days after their arrival in highland city of Lhasa. Questionnaire information of the symptoms of AMS using the Lake Louise Scoring System, resting SaO₂ and HR were assessed both before leaving the lowland and after arriving in Lhasa. Linear regression was performed to compare changes in SaO₂ and HR levels from low to high altitude in Tibetan and Han Chinese.

Results

New cases of AMS occurred in only 1.2% (95% CI 0.4% to 2.0%) of the Tibetan students who came to Lhasa by train compared with 32.7% (95% CI 28.0% to 37.3%) and 42.9% (95% CI 38.0% to 47.7%) of the Han Chinese students who came to Lhasa by train and by air, respectively. Tibetan students had less changes in SaO₂ (−2.95 percentage points, 95% CI −3.24% to −2.65%) and HR (10.89 beats per minute (bpm), 95% CI 9.62 to 12.16 bpm) from low to high altitude compared with Han Chinese students, although measurements did not differ between the two groups when measured at low altitude.

Conclusions

Healthy Tibetans are mostly protected against AMS and primarily maintain their good adaptation to high altitude, even after a long period of stay at low altitude.

Altitude training for elite endurance athletes: A review for the travel medicine practitioner

High altitude training is regarded as an integral component of modern athletic preparation, especially for endurance sports such as middle and long distance running. It has rapidly achieved popularity among elite endurance athletes and their coaches. Increased hypoxic stress at altitude facilitates key physiological adaptations within the athlete, which in turn may lead to improvements in sea-level athletic performance. Despite much research in this area to date, the exact mechanisms which underlie such improvements remain to be fully elucidated. This review describes the current understanding of physiological adaptation to high altitude training and its implications for athletic performance. It also discusses the rationale and main effects of different training models currently employed to maximise performance. Athletes who travel to altitude for training purposes are at risk of suffering the detrimental effects of altitude. Altitude illness, weight loss, immune suppression and sleep disturbance may serve to limit athletic performance. This review provides an overview of potential problems which an athlete may experience at altitude, and offers specific training recommendations so that these detrimental effects are minimised.

Prediction of the susceptibility to AMS in simulated altitude

Acute mountain sickness (AMS) develops when rapidly ascending to high altitudes. However, some mountaineers will suffer from AMS even at 2,000 m and others not until 5,000 m. The awareness of the individual susceptibility for AMS would be helpful for preventive strategies. Thus, the main purpose of this paper is the comparison of existing studies dealing with the prediction of AMS susceptibility and to draw conclusions on presently most valuable tests.

DATA SOURCE

A PubMed search has been performed, and preliminary observations from our laboratory have been included. The cautious conclusion derived from the reviewed 16 studies is that values of arterial oxygen saturation (SaO(2)), determined 20-30 min after exposure to simulated hypoxia equivalent to 2,300-4,200 m, seem to be the most useful predictors of AMS susceptibility (>80% correct prediction). Because the sympathetic activation during acute exposure to hypoxia may well contribute to the AMS development, parameters like heart rate variability or blood lactate could even enhance this predictability. The ventilatory response to hypoxia is easily trainable by pre-exposures to hypoxia but considers only part of the complex acclimatization process.

Transient myoclonic jerks and restless legs during periodic tachypnea in acute mountain sickness

A 46-year-old man with lower airway infection developed acute mountain sickness (AMS) at a 5,100 m high base camp. AMS was associated with myoclonic jerks (7-8/h) and restless legs. AMS with neurological manifestations could be relieved only upon descent to 3,500 m. To avoid pulmonary or neurological problems at high altitude, adequate acclimatization is a prerequisite.

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.

Exercising in Environmental Extremes

Athletes, military personnel, fire fighters, mountaineers and astronauts may be required to perform in environmental extremes (e.g. heat, cold, high altitude and microgravity). Exercising in hot versus thermoneutral conditions (where core temperature is > or = 1 degrees C higher in hot conditions) augments circulating stress hormones, catecholamines and cytokines with associated increases in circulating leukocytes. Studies that have clamped the rise in core temperature during exercise (by exercising in cool water) demonstrate a large contribution of the rise in core temperature in the leukocytosis and cytokinaemia of exercise. However, with the exception of lowered stimulated lymphocyte responses after exercise in the heat, and in exertional heat illness patients (core temperature > 40 degrees C), recent laboratory studies show a limited effect of exercise in the heat on neutrophil function, monocyte function, natural killer cell activity and mucosal immunity. Therefore, most of the available evidence does not support the contention that exercising in the heat poses a greater threat to immune function (vs thermoneutral conditions). From a critical standpoint, due to ethical committee restrictions, most laboratory studies have evoked modest core temperature responses (< 39 degrees C). Given that core temperature during exercise in the field often exceeds levels associated with fever and hyperthermia (approximately 39.5 degrees C) field studies may provide an opportunity to determine the effects of severe heat stress on immunity. Field studies may also provide insight into the possible involvement of immune modulation in the aetiology of exertional heat stroke (core temperature > 40.6 degrees C) and identify the effects of acclimatisation on neuroendocrine and immune responses to exercise-heat stress. Laboratory studies can provide useful information by, for example, applying the thermal clamp model to examine the involvement of the rise in core temperature in the functional immune modifications associated with prolonged exercise. Studies investigating the effects of cold, high altitude and microgravity on immunity and infection incidence are often hindered by extraneous stressors (e.g. isolation). Nevertheless, the available evidence does not support the popular belief that short- or long-term cold exposure, with or without exercise, suppresses immunity and increases infection incidence. In fact, controlled laboratory studies indicate immuno-stimulatory effects of cold exposure. Although some evidence shows that ascent to high altitude increases infection incidence, clear conclusions are difficult to make because of some overlap with the symptoms of acute mountain sickness. Studies have reported suppressed cell-mediated immunity in mountaineers at high altitude and in astronauts after re-entering the normal gravity environment; however, the impact of this finding on resistance to infection remains unclear.

Prediction of susceptibility to acute mountain sickness by SaO2 values during short-term exposure to hypoxia

Prediction of the development of acute mountain sickness (AMS) in individuals going to high altitudes is still a matter of debate. Whereas some studies found that subjects with a blunted hypoxic ventilatory response (HVR) are predisposed to AMS, others did not. However, the HVR has often been determined under very acute (5 to 10 min) isocapnic hypoxia without consideration of the subsequent hypoxic ventilatory decline (HVD), and the assessment of AMS susceptibility was based on a single altitude exposure. Therefore, the aim of the present study was to evaluate the relationship between the individual arterial oxygen saturation (Sa(O2)) after a 20- to 30-min exposure to poikilocapnic hypoxia and the AMS susceptibility based on repeated observations. A total of 150 healthy male and female mountaineers (ages: 42 +/- 13 yr), 63 of whom had known susceptibility to AMS and 87 of whom never suffered from AMS, were exposed to various degrees of normobaric and hypobaric hypoxia. Sa(O2) values were taken by finger pulseoximetry after 20 to 30 min of hypoxic exposure. Sa(O2) values after 20 to 30 min of hypoxia were on average 4.9% lower in subjects susceptible to AMS than in those who were not. Logistic regression analysis revealed altitude-dependent Sa(O2) values to be predictive for AMS susceptibility. Based on the derived model, AMS susceptibility was correctly predicted in 86% of the selected individuals exposed to short-term hypoxia. In conclusion, Sa(O2) values after 20 to 30 min of exposure to normobaric or hypobaric hypoxia represent a useful tool to detect subjects highly susceptible to AMS.