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PubMed2002

Effect of high altitude on protein metabolism in Bolivian children.

In Bolivia, malnutrition in children is a major health problem that may be caused by inadequate protein, energy, and micronutrient intake; exposure to bacterial and parasitic infections; and life in a multistress environment (high altitude, cold, cosmic radiation, low ambient humidity). However, no data on protein absorption and utilization at high altitude were available. Therefore, we evaluated the effect of altitude on protein metabolism in Bolivian children. We measured protein utilization using leucine labeled with a stable isotope ((13)C) in two groups of healthy prepubertal children matched for age. Group 1 (n = 10) was examined at high altitude (HA) in La Paz (3600 m), and group 2 (n = 10) at low altitude (LA) in Santa Cruz (420 m). The nutritional status did not differ between groups but, as was to be expected, the HA group had higher hemoglobin concentration than the LA group. The children consumed casein that was intrinsically labeled with L-(1-(13)C) leucine and expired (13)CO(2) was analyzed. Samples of expired air were measured by isotope ratio mass spectrometer in Clermont-Ferrand. It was found that cumulative leucine oxidation ((13)CO(2)) at 300 min after ingestion was 19.7 +/- 4.9% at HA and 25.2 +/- 3.2% at LA. These results showed that protein absorption and/or utilization is significantly affected by altitude.

Altitude↗
PubMed2003

Cardiopulmonary transition in the high altitude infant.

The perinatal cardiopulmonary transition at high altitude differs from that at sea level because oxygen plays a fundamental role in the developmental changes from fetus to newborn infant. Under conditions of high altitude hypoxia, arterial oxygen saturations are lower, breathing patterns and maturation of respiratory control reflexes differ, and regression of fetal characteristics of the pulmonary vasculature proceeds more slowly. Several aspects of transition vary not only with postnatal age and altitude, but also with population group, suggesting an effect of genetic adaptation on perinatal physiology. Exposure to chronic high altitude hypoxia during the perinatal transition also results in apparent lifelong alterations in respiratory reflex responses and pulmonary vasoreactivity. Disruption of the normal process of cardiopulmonary transition can result in symptomatic high altitude pulmonary hypertension. The exaggerated hypoxemia associated with acute respiratory infections in young infants still undergoing transition contributes to infant mortality at high altitude.

Adaptation, Physiological↗
PubMed2004

Sleep disturbance after rapid ascent to moderate altitude among infants and preverbal young children.

Rapid ascent to high altitude is known to result in sleep disturbances among adults. No data exist regarding the effects of altitude exposure on sleep in children. The objective of this study was to determine the effect of rapid ascent to moderate altitude on sleep in infants and young children. In this prospective study, each child served as his or her own control. Each subject was studied over 7 days and nights. On days 1 and 2, children were studied at home (1601 m), day 3 at a hotel without ascent (travel control), day 4 at home, days 5 and 6 at a hotel after ascent (3109 m), and day 7 at home. Since increased motion is a characteristic of sleep disturbance among infants and young children, continuous measurements of motion were made using an ankle-mounted Actigraph. Thirty children, 17 girls and 13 boys, with a median age of 16.5 months (range = 4 to 33 months) participated in the study. Significant changes in the activity counts, reflecting a sleep disturbance during nocturnal sleep, were noted between the travel control night (20.9 +/- 1.9) and the first night at altitude (29.4 +/- 2.5): p < 0.01. This sleep disturbance is most significant during the first night at altitude and may be similar to sleep disturbance with altitude exposure seen in adults.

Altitude↗
PubMed2006

Acetazolamide improves cerebral oxygenation during exercise at high altitude.

Vuyk, Jaap, Jan Van Den Bos, Kees Terhell, Rene De Bos, Ad Vletter, Pierre Valk, Martie Van Beuzekom, Jack Van Kleef, and Albert Dahan. Acetazolamide improves cerebral oxygenation during exercise at high altitude. High Alt. Med. Biol. 7:290-301, 2006.--Acute mountain sickness is thought to be triggered by cerebral hypoxemia and be prevented by acetazolamide (Actz). The effect of Actz on cerebral oxygenation at altitude remains unknown. In 16 members of the 2005 Dutch Cho Oyu (8201 m, Tibet) expedition, the influence of Actz and exercise (750 mg PO daily) on heart rate, peripheral and regional cerebral oxygen saturation (Sa(O(2) ) and rS(O(2) )), the Lake Louise score (LLS), and psychomotor function were studied at 0 m 14 days prior to the expedition, after arrival at 3700 m on day 3, after arrival at 5700 m on day 29, and again at 5700 m before the end of the expedition on day 51. After arrival at 3700 m, the LLS of the climbers taking Actz (n = 8) was significantly lower compared to those who did not take Actz (n = 8): 0.75 +/- 1.0 versus 2.9 +/- 2.0, p < 0.05 (ANOVA). High LLSs were associated with low rS(O(2) ) values in rest and exercise (p < 0.01 and p < 0.001). With altitude, resting Sa(O(2) ) and resting rS(O(2) ) decreased significantly (p < 0.001), irrespective of Actz use. Exercise at 3700 m and 5700 m reduced Sa(O(2) ) and rS(O(2) ) even further compared to rest (p < 0.001), although at 3700 m the rS(O(2) ) was preserved better in those who took Actz (55.3 +/- 4.3% versus 47.9 +/- 5.7%, p < 0.05). Irrespective of Actz use, with altitude, the percentage of omissions in the vigilance and tracking test increased while the climbers' scores on vigor decreased (p < 0.05). In conclusion, at altitude, exercise-induced reduction in cerebral oxygenation is less in climbers on Actz compared to climbers not taking Actz. This effect is nullified after several weeks at altitude due to acclimatization in climbers not taking Actz.

Acetazolamide↗
PubMed2026

Comparative analysis of olfactory receptor repertoires reveals evolutionary dynamics and high-altitude adaptation in Schizopygopsis younghusbandi based on the chromosome-level genomes.

The olfactory receptor (OR) gene represent a significant multigene family in vertebrates, forming the core molecular basis of olfactory perception and playing a crucial role in the environmental adaptation of species. High-altitude ecosystems represent extreme habitats characterized by specific abiotic stresses, including low oxygen levels, low temperatures, and intense ultraviolet radiation. These environments also exhibit low aquatic biodiversity and a limited variety of odor molecules, factors that have influenced the adaptive evolution of the sensory systems in endemic species. However, the genetic mechanisms underlying olfactory adaptation in high-altitude freshwater fish remained inadequately understood. In this study, we performed comparative genomics analyses to reveal the evolutionary processes underlying the adaptive and functional evolution of OR genes in S. younghusbandi, a cyprinid fish endemic to the Qinghai-Xizang Plateau. The results indicated that, compared to their low-altitude relatives, S. younghusbandi possessed a significantly smaller number of OR genes, with only 98 genes, which revealed the contraction of the gene family. Phylogenetic analysis revealed that the OR genes of cyprinid fish could be categorized into two major lineages: type I and type II. The &#x3b7; and &#x3b4; families, which perceive water-soluble odors, in S. younghusbandi underwent significant and specific expansion, while the &#x3b5; family was completely absent. This pattern reflected adaptive changes in olfactory recognition to accommodate the simplified odor spectrum of high-altitude water bodies. Chromosomal localization analysis demonstrated that OR genes were clustered, and collinearity analysis confirmed the presence of conserved genomic fragments among species. Selection pressure analysis revealed that the Ka/Ks values of all homologous gene pairs were less than 1, indicating that the OR genes of S. younghusbandi underwent strong purifying selection as a group to preserve core olfactory function. A few genes exhibited relaxed selection characteristics, which may have facilitated the fine-tuning of adaptability to high-altitude environments. In conclusion, this study elucidated the evolutionary dynamics and adaptive characteristics of the OR gene in S. younghusbandi, offering a new perspective on the molecular mechanisms underlying olfactory adaptation at high altitudes and enriching the research on sensory evolution in vertebrates.

Schizopygopsis younghusbandi↗
PubMed2001

FiO2 and positive end-expiratory pressure as compensation for altitude-induced hypoxemia in an acute respiratory distress syndrome model: implications for air transportation of critically ill patients.

OBJECTIVES: To determine whether increases in FiO2 or positive end-expiratory pressure will compensate for hypoxemia resulting from exposure to 8000 feet (2440 m) of altitude in a model of acute respiratory distress syndrome. DESIGN: Intervention and crossover design. SETTING: Military research altitude chamber. SUBJECTS: Sixteen Yucatan miniature swine (Sus scrofa). INTERVENTIONS: Swine initially were placed on mechanical ventilation (zero positive end-expiratory pressure, 21% FiO2). Twelve animals had moderate to severe acute respiratory distress syndrome (50% to 70% FiO2 at sea level to maintain PaO2 of 50-70 torr [6.65-9.31kPa]) induced by intravenous oleic acid. Four animals were controls (no lung injury). The animals were taken to 8000 feet (2440 m) in an altitude chamber, and then stepwise increases of either 5% FiO2 (six animals) or 2.5 cm H2O positive end-expiratory pressure (six animals) were made until PaO2 values exceeded 75 torr (10.0 kPa). If PaO2 did not reach 75 torr (10.0 kPa), and time permitted, the animal was crossed over to the other group. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases were drawn at baseline (sea level and at altitude) and after every change in ventilator settings. Positive end-expiratory pressure increases from 5 to 12.5 cm H2O were required to bring the PaO2 in the injured pigs to 75 torr (10.0 kPa). FiO2 increases did not achieve a PaO2 of 75 torr (10.0 kPa) for three of six animals despite reaching 100% FiO2. One animal crossed over from Fio2 to positive end-expiratory pressure and achieved a PaO2 of 75 torr (10.0 kPa) with 5 cm H2O of positive end-expiratory pressure. CONCLUSIONS: Fifty percent of the animals with lung injury had altitude-induced hypoxia that was resistant to increases in FiO2. Increases in positive end-expiratory pressure are more reliable than increases in FiO2 for correcting altitude-induced hypoxia in this model of acute respiratory distress syndrome.

Air Ambulances↗
PubMedDate not supplied

Bronchoarterial ratio on thin section CT: comparison between high altitude and sea level.

PURPOSE: Our goal was to measure normal bronchial to accompanying pulmonary arterial diameter ratios and normal bronchial wall thickness on thin section CT at high altitude and at sea level. METHOD: Seventeen normal, healthy, nonsmoking subjects living at 1,600 m altitude and 16 living at sea level underwent thin section CT (1.5 to 2.0 mm collimation). All images were photographed at window levels of -450 and -700 HU and window width of 1,500-1,600 HU. Internal diameters of the segmental and subsegmental bronchi were measured and compared with the diameter of the adjacent pulmonary artery. Bronchial wall thickness of each bronchus was measured. Only bronchi and arteries seen in cross section and within 1 mm from each other were included in the analysis. RESULTS: Four hundred sixty-seven bronchi (215 at high altitude, 252 at sea level) were assessed. At window level of -450 HU, the bronchoarterial ratio was 0.76 +/- 0.14 (mean +/- SD) at altitude and 0.62 +/- 0.13 at sea level (p < 0.001). Bronchial wall thickness measured 0.92 +/- 0.09 mm (mean +/- SD) at altitude and 1.12 +/- 0.19 mm at sea level (p < 0.001). At window level of -700 HU, there was an artifactual decrease in the bronchoarterial diameter ratios and an increase in bronchial wall thickness. CONCLUSION: Bronchoarterial ratio increases and bronchial wall thickness decreases with altitude. These findings are presumably related to hypoxic bronchodilatation and vasoconstriction.

Adult↗
PubMed1999

High altitude pulmonary edema.

High altitude pulmonary edema. Med. Sci. Sports Exerc., Vol. 31, No. 1 (Suppl.), pp. S23-S27, 1999. Altitude, speed and mode of ascent, and, above all, individual susceptibility are the most important determinants for the occurrence of high altitude pulmonary edema (HAPE). This illness usually occurs only 2-5 d after acute exposure to altitudes above 2500-3000 m. Chest radiographs and CT scans show a patchy predominantly peripheral distribution of edema. Wedge pressure is normal at rest, and there is an excessive rise of pulmonary artery pressure (PAP) that precedes edema formation and appears to be a crucial pathophysiologic factor for HAPE. Additional factors such as an inflammatory response and/or a decreased fluid clearance from the lung may, however, be necessary for the development of this noncardiogenic pulmonary edema. Bronchoalveolar lavage in patients with mostly advanced HAPE shows evidence of inflammatory response with increased permeability. There are, however, no prospective data to decide whether the inflammatory response is a primary cause of HAPE or a consequence of edema formation. Supplemental oxygen is the primary treatment in areas with medical facilities whereas the treatment of choice in remote mountain areas is immediate descent. When this is impossible and supplemental oxygen is not available, treatment with nifedipine is recommended until descent is possible. Even susceptible individuals can avoid HAPE when they ascend slowly with an average gain of altitude not exceeding 300-350 m.d-1 above an altitude of 2500 m.

Altitude Sickness↗
PubMed2006

Effects of altitude on effort tolerance in non-acclimatized patients with ischemic left ventricular dysfunction.

BACKGROUND: Few studies exist on the effects, in terms of work capacity and safety, of exposure to moderately high altitudes in patients with stable ischemic left ventricular dysfunction. Moreover no data are currently available on the cardiorespiratory response to walks in the mountains. AIM: The objective of this study is to evaluate the effects of altitude on effort tolerance during walks in the mountains and to determine whether exposure to altitude may be harmful to patients with ischemic left ventricular dysfunction. METHODS: Forty-five patients with stable chronic ischemic left ventricular dysfunction (ejection fraction=35+/-4%, and peak VO2>/=18/ml/kg per min in a preliminary effort test) were compared to 24 normal subjects. All subjects underwent a series of 6-min walking tests at three different altitudes: 500, 2000 and 2970 m above sea level. Cardiorespiratory response was assessed by a validated portable instrument. The resting arterial PO2 was measured at the three altitudes. RESULTS: No complications were observed during any tests in either the patients or the healthy controls. Overall, healthy subjects had higher values of 6-min walking test VO2 and walked longer distances in the test than did the patients with left ventricular dysfunction. The mean distances walked in the 6-min walking test were similar at 500 and at 2000 m in both the healthy controls and the patients; at 2970 m, however, the distances decreased in both groups, and more so in the patients (-11+/-3%) than in the controls (-5+/-2%) (P<0.01). VO2 during the 6-min walking test remained stable when the test was carried out at 500 and 2000 m (20.4+/-3.6 versus 19.9+/-4.1 ml/kg per min in patients, and 30.2+/-3.4 versus 29.8+/-4.2 ml/kg per min in the controls; P, NS), but decreased at 2970 m by 13.9+/-3% in patients (P<0.01) and by 6.6+/-2.1% in controls (P<0.01) (patients versus controls, P<0.01). Finally, a similar, significant decrease in arterial PO2 was observed in both groups only at 2970 m (-29%, P<0.01). CONCLUSION: Patients with stable ischemic left ventricular dysfunction had good tolerance while walking at high altitudes, but showed a moderate decrease in work capacity at 2970 m, which was greater than in normal subjects.

Acclimatization↗
PubMed2006

The effect of altitude on parasite density case definitions for malaria in northeastern Tanzania.

OBJECTIVES: Malaria clinical trials need precise endpoints to measure efficacy. In endemic areas where asymptomatic parasitaemia is common, 'fever plus parasitaemia' may not differentiate between malaria cases and non-cases. Case definitions based on parasite cut-off densities may be more appropriate but may vary with age and transmission intensity. This study examines appropriate case definitions from parasitological surveys conducted over a broad range of transmission intensities, using altitude as a proxy for transmission intensity. METHODS: Cross-sectional data collected from 24 villages at different altitudes in an endemic area of northeastern Tanzania were used to calculate malaria-attributable fractions using a modified Poisson regression method. We modelled fever as a function of parasite density and determined the optimum cut-off densities of parasites to cause fever using sensitivity and specificity analyses. RESULTS: The optimum cut-off density varied by altitude in children aged under 5 years: a case definition of 4,000 parasites per mul at altitudes <600 m (high transmission intensity) was most appropriate, compared with 1,000 parasites per mul at altitudes >600 m (low transmission intensity). In children aged over 5 years and adults, there was little variation by altitude and a case definition of any parasites plus fever was the most appropriate. CONCLUSIONS: Locally appropriate case definitions of malaria should be used for research purposes. In our setting, these varied independently with age and transmission intensity.

Adolescent↗
PubMed2006

Human behaviour and development under high-altitude conditions.

Although we are far from a universally accepted pattern of impaired function at altitude, there is evidence indicating motor, perceptual, memory and behavioural deficits in adults. Even relatively low altitudes (2500 m) may delay reaction time, and impair motor function. Extreme altitude exposure (>5000 m) may result in more pronounced impairment that can persist after returning to the lowlands. Research into the effects of altitude exposure earlier in development is lacking by comparison. Un-acclimatized children can suffer from acute mountain sickness, and, in native populations born at altitude, subtle cognitive and behavioural deficits suggest incomplete adaptation to hypoxia. The study of neurobehavioural functioning at altitude may provide important information about the effects of clinical hypoxia on the human brain and behavioural development.

Altitude↗
PubMed2004

Respiratory function in pregnancy at sea level and at high altitude.

OBJECTIVE: To determine the effect of pregnancy on respiratory function in a non-Caucasian group and determine whether there was an interaction between pregnancy and altitude of residence. DESIGN: Prospective cross sectional study. SETTING: Antenatal clinics in Peru, at sea level in Lima and at high altitude in Cerro de Pasco. SAMPLE: Peruvian women with singleton pregnancies; 122 living at sea level and 192 living at 4300 m altitude in the Peruvian Andes. At each location, 19 non-pregnant women were also studied. METHODS: Respiratory function was measured in pregnant and non-pregnant women living at sea level and at 4300 m. MAIN OUTCOME MEASURES: Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), peak expiratory flow rate (PEFR), total lung capacity (TLC), inspiratory capacity (IC), residual volume (RV), expiratory residual volume (ERV) and functional residual capacity (FRC). RESULTS: At sea level, RV and TLC were higher in the third compared with the first trimester (P < 0.05). At high altitude, FEV1 (P < 0.01), ERV (P < 0.01) and FRC (P < 0.01) were lower in the third compared with the first trimester. Pregnant and non-pregnant women at high altitude were 4 cm shorter (P < 0.0001) and had larger lung volumes (P < 0.01); their total lung capacities were approximately 1 L greater than women living at sea level (P < 0.0001). CONCLUSION: These results suggest that the effect of pregnancy on the respiratory function of healthy women is influenced by altitude of residence.

Altitude↗
PubMed1999

High-altitude effects on respiratory gases, acid-base balance and pulmonary artery pressures in equids.

Arterial and venous blood were analysed at rest and post exercise for pH, PCO2, and PO2, and bicarbonate ([HCO3-]), base excess (BE), and strong ion difference (SID) were calculated in response to a 10 day sojourn to 3800 m. Pulmonary artery pressures (PAP) were measured at rest. Post exercise samples were restricted to venous blood. The equids (n = 6) experienced a profound hypoxia-hypocapnia and a respiratory alkalosis. PaO2 decreased 42% and PaCO2 41%. PaCO2 increased to 80% of initial values after 8 days at altitude. Arterial [HCO3-] decreased by 34%; however, it returned to normal by Day 4. Base excess decreased initially, but increased at altitude with time. Strong ion difference was decreased during the altitude exposure and continued to be depressed even after return to low altitude. Pulmonary artery pressure increased 63% on Day 1 of exposure (from 27.9 +/- 2 to 45.4 +/- 3 mmHg); Days 2 and 6 averaged 36.3 +/- 3 and 37.5 +/- 3 mmHg. Thirty-six hours after return to 225 m, most variables (except [SID] and post exercise BE) returned to normal. The most profound changes in the indicators of gas exchange, at altitude, occurred during the first 3 days and only [HCO3-] returned to normal during the subsequent acclimatization to altitude.

Acid-Base Equilibrium↗
PubMed1967

Athletes at altitude.

1. Six international middle-distance runners were investigated during 4 weeks in England and during a similar period in Mexico City (2270 m (7450 ft.))2. In 3-mile (4828 m) time trials at 2270 m the increase in time taken by four subjects compared with sea level was 8.5% on the 4th day and 5.7% on the 29th day. There was thus a gain of 2.8% or 20 sec in time associated with acclimatization.3. In 1-mile (1609 m) time trials the times were increased by 3.6% in the first week at altitude and by 1.5% in the 4th week. The improvement amounted to 2.1%, or 4.9 sec.4. In 5 min maximum exercise on the ergometer maximum O(2) intake for six subjects at altitude was reduced by 14.6% on the 2nd day and 9.5% on the 27th. Only one subject showed no change in maximum oxygen intake (V(O2, max)) with time spent at altitude.5. Although V(O2, max) was persistently reduced at altitude work rates finally exceeded sea-level values, owing to increased over-all efficiency.6. Forty-minute recovery O(2) intakes after 5 min maximum exercise averaged 17.35 l. at sea level and 17.53 l. at altitude. Mean values from 40th to 50th min were within +/- 7% of pre-exercise values.7. Serial tests at increasing loads yielded a straight-line relation between O(2) intake and work rate over a wide range of work rates at sea level and at altitude. Heart rate and ventilation for given work intensity were maximal in the first 2-10 days at altitude and thereafter declined.8. Capillary HbO(2) saturation fell from 93% at rest to 87% in maximum exercise. The corresponding alveolar gas tensions were P(A, O2) 89 mm Hg, P(A, CO2) 24 mm Hg. About half the total unsaturation in maximum exercise was explained by the Bohr effect.9. In six of eight pairs of determinations V(O2, max) measured on the ergometer was within +/- 0.15 l./min of V(O2, max) measured on the running track. Nevertheless, it was not possible to predict running performance from ergometer measurements.

Acclimatization↗
PubMed1966

Microorganisms of the upper atmosphere. 3. Relationship between altitude and micropopulation.

Simultaneous sampling for microorganisms was accomplished at altitudes of 690, 1,600, and 3,127 meters. The location of temperature inversions in relation to the collection altitude determined, to a great extent, the micropopulation. High micropopulations were found when an inversion was above the sampling altitude, and low populations when the inversion was below the sampling altitude. Diurnal periodicity which could be generally correlated with periods of minimal and maximal convective activity was observed. Evidence is presented showing that the micropopulation is more stable at higher altitudes than at lower altitudes.

Actinomycetales↗
PubMed1998

Living at high altitude and risk of sudden infant death syndrome.

OBJECTIVE: To investigate the association between altitude of residence and risk of sudden infant death syndrome (SIDS). METHODS: A retrospective, case control study in the Tyrol, Austria enrolled 99 infants with SIDS occurring between 1984 and 1994, and 136 randomly selected control cases. Data on pregnancy, delivery, child care practice, and socio-demographic characteristics including altitude of residence were collected with a standardised questionnaire. RESULTS: The risk of SIDS increased gradually with increasing altitude of residence. This relation remained independently significant when the analysis was adjusted for gestational age, birth weight, prenatal care, mother's age at delivery, educational level of parents, and cigarette smoking during pregnancy. The prone sleeping position emerged as an obligatory cofactor in this association. In the whole of Austria, a similar trend of association emerged between the average altitudes in the 99 political counties and the rates of SIDS. CONCLUSIONS: This study identified altitude of residence as a significant risk predictor of SIDS, primarily in combination with the prone sleeping position. Respiratory disturbances, reduced oxygen saturation, and lower temperatures at high altitude might explain this association.

Altitude↗
PubMed1994

Prediction of hypoxaemia at high altitude in children with cystic fibrosis.

OBJECTIVE: To assess the usefulness of a hypoxic challenge in a laboratory at sea level in predicting acute desaturation at altitude in children with lung disease. DESIGN: Comparison of responses to hypoxic challenge in different settings. SUBJECTS: 22 children (12 boys) aged 11 to 16 years with cystic fibrosis in whom the mean forced expiratory volume in one second was 64% (range 24-100%). SETTING: Lung function laboratory, the Alps, and aboard commercial jet aircraft. MAIN OUTCOME MEASURES: Spirometric lung function at sea level and finger probe oximetry with air and 15% oxygen. Oximetry during high altitude flight and on a mountain at altitude of 1800 m. RESULTS: Significant desaturation (range 0 to 12%) occurred with all hypoxic challenges (P < 0.002). The best predictor of hypoxic response from a single reading was the laboratory test (r2 = 76% for flight and r2 = 47% for mountain altitude), but the mean errors of prediction were not clinically significantly different. In six children who showed the greatest desaturation the laboratory test overestimated desaturation, but other predictors underestimated desaturation in three by up to 5%. CONCLUSIONS: The laboratory hypoxic challenge directly predicted the worst case of desaturation during flight and at equivalent high altitude. Spirometry and baseline oxygen saturations may underestimate individual hypoxic response. The test may have wider applications to other patients with stable chronic lung diseases, particularly in determining who needs supplementary oxygen during air travel and who should be advised against holidays at high altitude.

Acute Disease↗
PubMed1977

Changes in transthoracic electrical impedance at high altitude.

Mean transthoracic electrical impedance (impedance) which is inversely related to intrathoracic extravascular fluid volume was measured in 121 normal healthy volunteers at sea-level and at 3658 metres altitude. Fifty (group A) reached the high altitude location after an hour's journey in a pressurised aircraft. Twenty-five (group D) underwent slow road ascent including acclimatisation en route. Thirty permanent residents (group B) and 16 temporary residents at high altitude (group C) were also studied. Serial studies in the 30 subjects of group A who developed symptoms of high altidue sickness showed a significant decrease of impedance up to the fourth day of exposure to high altitude which later returned to normal. The 4 volunteers who developed severe symptoms showed the largest drop in impedance. A case of acute pulmonary oedema developing at 4300 metres showed an impedance value of 24-1 ohms on admission. After effective treatment the impedance increased by 11-9 to 36-0 ohms. Twenty asymptomatic subjects of group A and 25 of group D showed a small average increase in impedance values at high altitude. These obstructions suggest that measurement of transthoracic electrical impedance may be a valuable means of detecting incipient high altitude pulmonary oedema.

Acclimatization↗