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PubMed1985

Blood respiratory properties in pigeons at high altitudes: effects of acclimation.

Many birds thrive at high altitudes where environmental temperatures are low. Previous studies have shown that tolerance of and acclimation to hypoxia involve cardiopulmonary and hematological adaptations. We investigated blood respiratory properties during exposure to simulated high altitude (hypobaric hypoxia) and low temperature in unanesthetized resting pigeons (Columbia livia, mean mass 0.38 kg). A control group (C) and a group acclimated to 7 km above sea level (ASL) in a hypobaric chamber at 25 degrees C (HA group) were used. All were acutely exposed to altitudes through 9 km ASL at 5 or 25 degrees C. Arterial and mixed venous blood gas tensions and O2 and CO2 content during steady state decreased with increased altitude, whereas blood lactate increased in both groups at both temperatures. Acute high-altitude exposure did not affect hematocrit, hemoglobin concentrations, or O2 carrying capacity, but at any altitude these were all greater in HA than in C birds. At 5 degrees C blood pH increased with altitude in controls but remained unchanged in HA birds. At 25 degrees C in both groups mean intracellular pH did not change, averaging 6.97, whereas extracellular (venous) pH increased with altitude. At the highest altitudes tissue O2 extraction was virtually complete in both groups. Acclimation changed blood O2 and CO2 combining properties in ways likely to improve gas transport at high altitudes. The previously unreported shifts in blood respiratory and acid-base properties with acclimation indicate that innate extrapulmonary adaptations contribute to avian hypoxia tolerance.

Acid-Base Equilibrium↗
PubMed1984

Adrenocortical responses to maximal exercise in moderate-altitude natives at 447 Torr.

Serum hydrocortisone and aldosterone (Aldo) responses to maximal exercise were examined in six low-altitude natives (LAN) (373 m or less, aged 19-25 yr) and eight moderate-altitude natives (MAN) (1,830-2,200 m, aged 19-23 yr) at their residence (home) altitudes (740 and 587 Torr, respectively) and later in a hypobaric chamber at a simulated altitude of 4,270 m (447 Torr). After 2 days at their respective residence altitude and in the chamber, each subject exercised to voluntary exhaustion on the bicycle ergometer. Fluid intake was similar in both groups at all testing locations. Preexercise 24-h urinary Aldo was lower in both groups at 447 Torr but only significantly reduced in the LAN group. In general, the changes in maximum exercise cardiorespiratory variables were twice as large in LAN as in MAN subjects going from residence altitude to 447 Torr. Both serum hydrocortisone and Aldo concentrations were increased (P less than 0.01) after exercise in both groups at residence altitude and 447 Torr. Aldo was lower (P less than 0.05) postexercise at 447 Torr than at residence altitude in both groups, but this decrease was more pronounced (P less than 0.01) in the LAN group. Thus it appears that high-altitude Aldo concentrations are more like resident altitude values in MAN than in LAN subjects.

Acclimatization↗
PubMed1996

Acclimatization to 4,300-m altitude decreases reliance on fat as a substrate.

We tested the hypothesis that exposure to altitude decreases reliance on free fatty acids (FFA) as substrates and increases dependency on blood glucose. Therefore, the effects of exercise, hypobaric hypoxia, and altitude acclimatization on FFA, glycerol and net glucose uptake and release [= 2(leg blood flow)(arteriovenous concentration)] and on fatty acid (FA) consumption by the legs (= 3 x glycerol release + FFA uptake) were measured. Because sympathetic responses have been implicated, we utilized nonspecific beta-blockade and observed responses to exercise, altitude, and altitude acclimatization. We studied six healthy beta-blocked men (beta) and five matched controls (C) during rest and cycle ergometry exercise (88 W) at 49% of sea-level (SL) peak O2 uptake at the same absolute power output on acute altitude exposure (A1; barometric pressure = 430 Torr) and after 3 wk of chronic altitude exposure to 4,300 m (A2). During exercise at SL, FA consumption rates increased (P < 0.05). On arrival at 4,300 m, resting leg FFA uptake and FA consumption rates were not significantly different from those at SL. However, after acclimatization to altitude, at rest leg FA consumption decreased to essentially zero in both C and beta groups. During exercise to altitude after acclimatization, leg FA consumption increased significantly, but values were less than at SL or A1 (P < 0.05), whereas glucose uptake increased relative to SL values. Furthermore, beta-blockade significantly increased glucose uptake relative to control. We conclude that 1) chronic altitude exposure decreases leg FA consumption during rest and exercise; 2) relative to SL FFA uptake decreases while glucose uptake increases during exercise at altitude; and 3) beta-blockade potentiates these effects.

Acclimatization↗
PubMed1998

Catecholamine response during 12 days of high-altitude exposure (4, 300 m) in women.

We have previously demonstrated that acclimatization to high altitude elicits increased sympathetic nerve activity in men. The purpose of this investigation was to determine 1) whether women respond in a similar manner as found previously in men and 2) the extent to which menstrual cycle phase influences this response. Sixteen eumenorrheic women (age, 23.6 +/- 1.2 yr; weight, 56.2 +/- 4. 3 kg) were studied at sea level and during 12 days of high-altitude exposure (4,300 m) in either their follicular (F; n = 11) or luteal (L; n = 5) phase. Twenty-four-hour urine samples were collected at sea level and during each day at altitude. Catecholamines were determined by high-performance liquid chromatography with electrochemical detection. Compared with sea-level values, urinary norepinephrine excretion increased significantly during altitude exposure, peaking on days 4-6. Thereafter, levels remained constant throughout the duration of altitude exposure. The magnitude of this increase was similar between the F (138%) and L (93%) phase. Urinary epinephrine levels were elevated on day 2 of altitude exposure compared with sea-level values for both F and L subjects (93%). Thereafter, urinary epinephrine excretion returned to sea-level values, and no differences were found between F and L subjects. Plasma catecholamine content was consistent with urinary values and supports the concept of an elevation in sympathetic activity over time at altitude. Mean and diastolic blood pressure as well as heart rate adjustments to high altitude correlated significantly with urinary norepinephrine excretion rates. It was concluded that 1) urinary and plasma catecholamine responses to 12 days of high-altitude exposure in women are similar to those previously documented to occur for men; 2) whereas no differences in catecholamine levels were observed between F- and L-phase assignments, for a given urinary norepinephrine excretion rate, blood pressure and heart rates were lower for F vs. L subjects; and 3) several cardiovascular adaptations associated with high-altitude exposure correlated with 24-h urinary norepinephrine excretion rates and thus sympathetic nerve activity.

Adrenal Glands↗
PubMed2003

Intermittent altitude exposures improve muscular performance at 4,300 m.

Chronic altitude residence improves muscular performance at altitude, but the effect of intermittent altitude exposures (IAE) on muscular performance at altitude has not been defined. The purpose of this study was to determine the effects of 3 wk of IAE, in combination with rest and cycle training, on muscular performance at altitude. Six lowlanders (23 +/- 2 yr, 77 +/- 6 kg; means +/- SE) completed a cycle time trial and adductor pollicis endurance test at sea level and during a 30-h acute exposure to 4,300 m altitude equivalent (barometric pressure = 446 mmHg) once before (pre-IAE) and once after (post-IAE) a 3-wk period of IAE (4 h/day, 5 days/wk, 4,300 m). During each IAE, three subjects cycled for 45-60 min/day at 60%-70% of maximal O2 uptake and three subjects rested. Cycle training during each IAE did not appear to affect muscular performance at altitude. Thus data from all six subjects were combined. Three weeks of IAE resulted in 1) a 21 +/- 6% improvement (P < 0.05) in cycle time-trial performance (min) from pre-IAE (32.8 +/- 3.7) to post-IAE (24.8 +/- 1.2), 2) a 63 +/- 26% improvement (P < 0.05) in adductor pollicis endurance (min) from pre-IAE (9.2 +/- 2.8) to post-IAE (14.8 +/- 4.2), and 3) a 10 +/- 4% increase (P < 0.05) in resting arterial O2 saturation (%) from pre-IAE (82 +/- 2) to post-IAE (90 +/- 1). These improvements in muscular performance after IAE correlated strongly with increases in resting arterial O2 saturation and were comparable to those reported previously after chronic altitude residence. IAE may therefore be used as an alternative to chronic altitude residence to facilitate improvements in muscular performance in athletes, soldiers, mountaineers, shift workers, and others that are deployed to altitude.

Adaptation, Physiological↗
PubMed2006

Cerebral vasodilatation to exogenous NO is a measure of fitness for life at altitude.

BACKGROUND AND PURPOSE: Andean highlanders, unlike Ethiopians, develop chronic mountain sickness (CMS), a maladaptation to their native land. Ambient hypoxia induces NO-mediated vasodilatation. Fitness for life at altitude might be revealed by cerebrovascular responses to NO. METHODS: Nine altitude-native men were examined at 3622 and 794 m in Ethiopia and compared with 9 altitude-native Andean men tested at 4338 and 150 m in Peru. We assessed CMS scores, hematocrits, end-tidal pressure of carbon dioxide (P(ET)co2), oxygen saturations, and cerebral blood flow velocity (CBV). We evaluated fitness for life at altitude from the cerebrovascular response to an exogenous NO donor. RESULTS: At high altitude, CMS scores and hematocrits were higher in Andeans, and they had lower oxygen saturations. Ethiopians had higher P(ET)co2 at all study sites. At low altitude, saturations were similar in both groups. Responsiveness of the cerebral circulation to NO was minimal in Ethiopians at low altitude, whereas Andeans had a large response. In contrast, at high altitude, Ethiopians showed large responses, and Peruvians had minimal responses. CONCLUSIONS: By our measure, high altitude-native Peruvians were well-adapted lowlanders, whereas Ethiopian highlanders were well adapted to altitude life. Environmental pressures were sufficient for human adaptation to chronic hypoxia in Africa but not South America. The mechanisms underlying these differences are unknown, although studies of neurovascular diseases suggest that this may be related to a NO receptor polymorphism.

Acclimatization↗
PubMed1996

Elevation of serum cholesterol at high altitude and its relationship to hematocrit.

The positive relationship between hematocrit and serum cholesterol may be due to dilution. Accordingly, high hematocrits would yield reduced serum pools for dilution of cholesterol, thus producing higher levels. To test this effect, the relationships between hematocrit and cholesterol were evaluated at low-altitude and high-altitude clinics. Retrospective chart reviews were conducted at Madison, WI (264 m) and Leadville, CO (3105 m) to identify family practice patients who underwent hematocrit and serum cholesterol determinations on the same day. We excluded patients with medical conditions or on medications that affect cholesterol, patients with high glucose and triglyceride levels, and patients with extreme cholesterol levels. Remaining patients (153 in each altitude group) were matched by age and sex. The mean hematocrits and cholesterol levels were compared using analysis of variance. The linear relationships between hematocrit and cholesterol were compared using analysis of covariance. The mean hematocrit was significantly higher at high altitude (47.5% versus 41.3%; p < 0.0005) as were the mean serum cholesterol (190 mg/dL versus 177 mg/dL; p < 0.002) and the low-density lipoprotein:high-density lipoprotein ratio (2.80 versus 2.27; p < 0.05). Whereas a significant, positive relationship existed between hematocrit and cholesterol at low altitude (2.15 mg/dL per %; p < 0.002), no such relationship was found at high altitude. Hematocrit and serum cholesterol were elevated for family practice patients living at high altitudes. Differences exist between altitudes in the relationship between hematocrit and cholesterol. Acclimatization to high altitude and its resultant erythropoiesis may increase serum cholesterol levels. Consequently, relocation to a high altitude may increase the risk of arteriosclerotic cardiovascular disease.

Acclimatization↗
PubMed1998

Altitude-related illness in two California national parks.

High-altitude illness encompasses a spectrum of disorders related to the hypoxia experienced by individuals at elevation. Altitude-related illness has been well described in the United States, but there are no studies published in the medical literature looking at the occurrence of high-altitude illness within the US National Parks system. The purpose of this study is to describe the incidence, treatment, and outcomes of visitors to Sequoia and Kings Canyon National Parks who presented to emergency medical services (EMS) personnel with signs and symptoms consistent with high-altitude illness. We conducted a retrospective review of all EMS patient care records (PCRs) from Sequoia and Kings Canyon National Parks during the study period of June 1992 to August 1995. There were 23 cases of altitude-related illness identified by EMS personnel in the parks during the 38-month study period, including five cases of high-altitude pulmonary edema and 19 cases of acute mountain sickness. One patient died, nine patients were transported to local hospitals, nine patients were assisted in their descent and then released from medical care, and four patients were treated and then allowed to continue their travels. There was an average of 5.9 cases per year of high-altitude illness and an incidence of one case per 27 EMS contacts. We conclude that altitude-related illness does occur in Sequoia and Kings Canyon National Parks and, although high-altitude illness accounts for only 4% of EMS contacts, caring for these patients uses a significant amount of national park resources. We suggest continued training of emergency medical technicians and park medics in the recognition and treatment of these disorders. We also support education of hikers to reduce or prevent the morbidity associated with altitude-related illness.

Adolescent↗
PubMed1996

Hematologic and body fluid changes during simulated high altitude exposure in naproxen-treated rats.

Arterial blood oxygen saturation, body fluid and hematological parameters were studied in control, naproxen (a prostaglandin synthesis inhibitor)-treated control, altitude-exposed, and naproxen-treated altitude-exposed rats after intermittent exposure of 8 h/d for 6 consecutive days to a simulated high altitude of 6,100 m (barometric pressure 349 +/- 3 mmHg). Arterial blood oxygen saturation was reduced in altitude-exposed rats, but increased significantly to near control level in naproxen-treated rats. On the other hand, 2,3-diphosphoglycerate in erythrocytes increased in altitude-exposed rats, but naproxen prevented this increase. The red blood cell count, hemoglobin concentration and hematocrit ratio were reduced significantly in drug-treated altitude-exposed rats when compared to the altitude-exposed group (without drug). Red cell mass was increased in the altitude-exposed group in comparison with control. Both red cell mass and mean corpuscular volume of altitude-exposed rats were shifted towards the control value when they were treated with naproxen. Drug-treated high altitude-exposure reduced the thiocyanate space, intracellular fluid volume and total body water content compared to drug-treated control rats. On the other hand, thiocyanate space and total body water content were increased significantly in drug-treated control rats in comparison with the control group.

Altitude↗
PubMed2001

[Altitude and the autonomic nervous system].

Ascent to high altitudes arouses the sympathetic nervous system in non-acclimatized healthy humans. Such activation is provoked by hypobaric hypoxia combined with other stressors. While this is an adaptive response, it also contributes to the general physical deterioration consequent to prolonged exposure to high altitudes, and is even implied in specific syndromes: acute mountain sickness, high altitude pulmonary edema (HAPE), and high altitude cerebral edema. Muscular sympathetic nervous activity increases at simulated high altitudes (hypoxic mixture or hypobaric chamber), and HAPE-susceptible subjects show an exaggerated response. Increases in plasma and urinary catecholamines take several days to appear: they are observed rarely at simulated altitudes but frequently on the field. Heart rate variability decreases at high altitudes, particularly in subjects suffering from acute mountain sickness. The low frequency component has been described in healthy subjects as increased or decreased, but is reduced in sympatomatic subjects; increases in the low frequency/high frequency ratio are reported in all studies. Few and discordant data are available regarding baroreflex sensitivity at high altitudes. Some (past and present) authors regard parasympathetic fitness as a defense against illness at high altitudes. Current guidelines advise against high altitude exposure for cardiac patients in whom sympathetic arousal would be too risky.

Altitude↗
PubMed2002

Plasma nitrite/nitrate and erythropoietin levels in cross-country skiers during altitude training.

BACKGROUND: The aim of this study was to evaluate the effects of training at altitude on plasma nitrite/nitrate and erythropoietin levels since previously it has been reported an interaction of the NO/cGMP system in erythropoietin production. METHODS: Nine physically trained cross-country male skiers, usually living at 800-1200 m altitude, underwent 6 days of intensive training at a moderate altitude of 3100 m preceeded by 2 days of acclimatisation. Six team-managers, selected as controls, did not undergo any regular physical activity in the last 5 years and during the altitude period. Haematological parameters, erythropoietin and nitrite/nitrate were measured prior to reach the place at altitude, at the end of the period at moderate altitude and 7 days after returning at home. RESULTS: Haematocrit significantly increased in controls after 8 days at altitude. Erythropoietin levels significantly increased after the intensive altitude training only in trained subjects (13.1+/-1.7 vs 6.7+/-1.7 mU x ml-1, p<0.001). Nitrite/nitrate baseline values were significantly higher in trained subjects compared to untrained (49.9+/-17.9 vs 25.4+/-2.8 micromol x l(-1), p<0.01); the altitude period significantly increased nitrite/nitrate levels, in untrained subjects, to the same values observed in trained subjects under control conditions (47.0+/-10.3 micromol x l(-1)). CONCLUSIONS: In our experimental conditions we demonstrated the influence of hypoxia on Epo levels in athletes sustaining a short-term training and the role of a regular physical activity (partly independent from altitude hypoxia) on NO production.

Adult↗
PubMed2003

[Study of diagnostic criteria of acute respiratory distress syndrome and multiple organ dysfunction syndrome at high altitude: revised draft of the diagnostic criteria of high acute respiratory distress syndrome drawn in Lanzhou conference].

OBJECTIVE: To compare the difference of the diagnostic parameters of acute respiratory distress syndrome/multiple organ dysfunction syndrome (ARDS/MODS) at high altitude (H-ARDS/MODS) with that on plains and reevaluate the practicality and feasibility of the diagnostic criteria of H-ARDS (Lanzhou conference, 1999). METHODS: Three hundred and sixty cases with relatively complete data were divided into three groups according to their originating altitude: control group on plains (CG, n=93), high altitude group 1 at the altitude of 1,517 m (H1G, n=223), high altitude group 2 at the altitude of 2,261-2,400 m (H2G, n=44). The ARDS/MODS scorings of the three groups were carried out according to the diagnostic criteria of Lushan Conference, Marshall (1995) and Lanzhou criteria drafted by the authors and the receiver operating characteristic curves (ROC curve) were made to predict the outcome of MODS. RESULTS: In CG group, the area of ROC, the susceptibility and specificity were 0.823, 0.833, 0.731, respectively according to Lushan criteria, which were better than those (0.815, 0.767, 0.763) according to Marshall criteria. Then in group H2G, the area of ROC, the susceptibility and specificity according to Lushan criteria were lower than those according to Marshall criteria: 0.855, 0.583, 0.969 vs 0.914, 1.000, 0.657. The optimum cutoff points of partial pressure of oxygen in artery (PaO(2))/fractional concentration of inspired oxygen (FiO(2)) were 198.32 mmHg, 131.50 mmHg and 97.58 mmHg in group CG, H1G and H2G. CONCLUSION: (1) There are significant differences between the diagnostic criteria of ARDS at high altitude and that on plains. The altitude of 1 517 m would be an important border line in diagnosing H-ARDS. (2) The drafted diagnostic criteria of ARDS at high altitude are feasible and practical in this region, but the range of the parameters is still wide, which need to be properly amended. (3) The changing tendency of the parameters of MODS at high altitude is different from that on plains, but the amount of sample needs to be accumulated further and the Lanzhou criteria needs to be perfected.

Age Factors↗
PubMed2004

Hemoglobin, altitude and birth weight: does maternal anemia during pregnancy influence fetal growth?

OBJECTIVE: To investigate the relationship between maternal hemoglobin concentration, altitude and birth weight. STUDY DESIGN: Birth weights in 235 term pregnancies were investigated for their dependence on maternal hemoglobin concentration after other maternal and pregnancy-specific influences on fetal weight were taken into account. The additional predictive value of hemoglobin concentration on birth weight was assessed using multiple regression. Using published data, the relationship of hemoglobin concentration to altitude was determined, as was the effect of increasing altitude on birth weight. The quantitative effect of hemoglobin concentration on birth weight was correlated with the effect of altitude on hemoglobin concentration to assess whether this could account for the known decrease in birth weight with increasing altitude. RESULTS: Birth weights ranged from 2,220 to 4,850 g (mean, 3,505+/-443), and hemoglobin concentrations ranged from 9.3 to 13.5 g/dL (mean, 11.6+/-0.8). Apart from other known predictive variables, the variation in maternal hemoglobin concentrations at constant altitude independently explained 2.6% of the variance in birth weight (r=-.18, P=.003). Term birth weight was reduced by 89 g for each 1.0 g/dL increase in hemoglobin concentration (P<.01). For every 1,000-m increase in altitude, hemoglobin concentration increased by 1.52 g/dL and birth weight decreased by 117 g. CONCLUSION: Birth weight correlates negatively with maternal hemoglobin concentration. This is consistent with the well-known effect of high-altitude exposure during pregnancy, which increases both hematocrit and blood viscosity and lowers birth weight. The quantitative effect on birth weight of increasing maternal hemoglobin concentration at constant altitude is within 13% of the change in birth weight that can be attributed to the change in hemoglobin concentration associated with increases in altitude.

Adult↗
PubMed1988

Hemodynamic and sympathoadrenal responses to altitude in humans: effect of dexamethasone.

Altitude exposure alters hemodynamics and sympathoadrenal function and elicits acute mountain sickness (AMS). Since dexamethasone prevents AMS and influences responsiveness to catecholamines, we studied hemodynamic and sympathoadrenal responses to 4,570 m simulated altitude in 8 subjects treated with dexamethasone or placebo. Mean pulse rates were less at altitude with dexamethasone (96.1 for placebo and 84.1 for dexamethasone; treatment-altitude interaction, p = 0.0045). Altitude led to a postural decline in mean arterial pressure (posture-altitude interaction, p = 0.0026), but this was not affected by dexamethasone. Dexamethasone reduced urinary epinephrine to a greater extent during altitude exposure (from 9.41 ng.mg-1 creatinine with placebo to 4.16 with dexamethasone) when compared with sea level (from 3.24 to 3.08). Urinary excretion of norepinephrine was unchanged at altitude. We conclude that acute altitude exposure is associated with stimulation of the adrenal medulla and not the sympathetic nervous system. Dexamethasone blocks the adrenal medullary response and blunts the pulse rate increase at altitude.

Adrenal Medulla↗
PubMedDate not supplied

Immunological survey in high altitude: effect on antibody production and the complement system.

In order to asses the effect of acute exposure to natural high altitude on some immunological mechanisms of mice, the primary response to SRBC was studied by the direct Hemolytic Plaque and Hemagglutination Tests. A control group was studied in Lima, Peru, 150 m. At high altitude (Ticlio, Peru, 4843 m), we found fewer spleen plaque-forming cells (PFC) and the maximal peak of PFC was delayed 1 day, as compared with the response at a lower altitude. Conversely, there was a higher serum concentration of 2-ME sensitive and resistant hemagglutinin antibodies at high altitude and the 19-S (2-ME sensitive) response was predominant during the first days at high altitude while the 7-S response was retarded. These results are interpreted as a stimulating effect of hypoxia on the 19-S antibody production rather than a cellular proliferation as far as the SRBC system is concerned. Serum concentrations of Igs G, M, A and the fraction C'3 of the Complement (B1C/B1A globulin) were determined in normal natives from three cities at different altitude levels: Morococha-Ticlio, 4680 m; La Oroya, 3700 m; and Tarma, 3051 m by the Radial Immunodiffusion Test. The serum concentration of C'3 was correlated with the total hemolytic activity of Complement (C'H50 method) in a group of natives from Morococha. The control group was of normal natives from Lima. No significant differences were found between resum concentration of Igs G, M and A in both groups, but there was a tendency for higher values of IgA at higher altitudes, and most sera in the high altitude group were above the normal IgG values for adults. The resum concentration of C'3 and the hemolytic activity of Complement were wound to be diminished in the high altitude group. These results are interpreted as an inhibitory effect of the altitude on the sequential activation and/or lysing capability rather than a reduction in the C'3 concentration.

Adult↗
PubMed1998

Risk factors of stroke at high and low altitude areas in Saudi Arabia.

BACKGROUND: The epidemiology of stroke at different geographical locations in the Kingdom of Saudi Arabia has not been adequately investigated. METHODS: In this study, clinical types and risk factors of stroke were compared among patients at low-altitude (Riyadh, 620 m) and high-altitude (Al Baha > 2000 m) areas using a case-control study design. One-hundred ninety recently diagnosed cases (109 from Riyadh and 81 from Al Baha) were verified and subjects were interviewed. An equal number of age- and sex-matched controls from the corresponding areas were also interviewed using a specific standard questionnaire. RESULTS: The frequency of thrombotic stroke at high altitude was 93.4% as compared to 79.3% at low altitude (P < 0.05). The odds ratios (OR) for the different risk factors at high and low altitudes, respectively, were: hypertension 4.4 and 2.1; diabetes mellitus: 2.7 and 1.9; ischemic heart disease (IHD): 2.4 and 1.9; atrial fibrillation: 3.9 and 3.3, and smoking: 2.3 and 2.5. The mean hematocrit values were 45.3% at high altitude and 41.0% for low altitude patients (P < 0.001) and its association with stroke at high altitude remained significant even after adjusting for age, gender and occupation. CONCLUSIONS: The study's finding of an increased frequency of thrombotic stroke at high altitude was explained by increased hematocrit which might have caused this in conjunction with other factors such as hypertension and IHD. Larger studies are recommended for better clarification of interaction between high altitude and other established risk factors not included in this study, such as sickle cell anemia and congenital heart diseases in young patients.

Adult↗
PubMed2006

Patent foramen ovale and high-altitude pulmonary edema.

CONTEXT: Individuals susceptible to high-altitude pulmonary edema (HAPE) are characterized by exaggerated pulmonary hypertension and arterial hypoxemia at high altitude, but the underlying mechanism is incompletely understood. Anecdotal evidence suggests that shunting across a patent foramen ovale (PFO) may exacerbate hypoxemia in HAPE. OBJECTIVE: We hypothesized that PFO is more frequent in HAPE-susceptible individuals and may contribute to more severe arterial hypoxemia at high altitude. DESIGN, SETTING, AND PARTICIPANTS: Case-control study of 16 HAPE-susceptible participants and 19 mountaineers resistant to this condition (repeated climbing to peaks above 4000 m and no symptoms of HAPE). MAIN OUTCOME MEASURES: Presence of PFO determined by transesophageal echocardiography, estimated pulmonary artery pressure by Doppler echocardiography, and arterial oxygen saturation measured by pulse oximetry in HAPE-susceptible and HAPE-resistant participants at low (550 m) and high altitude (4559 m). RESULTS: The frequency of PFO was more than 4 times higher in HAPE-susceptible than in HAPE-resistant participants, both at low altitude (56% vs 11%, P = .004; odds ratio [OR], 10.9 [95% confidence interval {CI}, 1.9-64.0]) and high altitude (69% vs 16%, P = .001; OR, 11.7 [95% CI, 2.3-59.5]). At high altitude, mean (SD) arterial oxygen saturation prior to the onset of pulmonary edema was significantly lower in HAPE-susceptible participants than in the control group (73% [10%] vs 83% [7%], P = .001). Moreover, in the HAPE-susceptible group, participants with a large PFO had more severe arterial hypoxemia (65% [6%] vs 77% [8%], P = .02) than those with smaller or no PFO. CONCLUSIONS: Patent foramen ovale was roughly 4 times more frequent in HAPE-susceptible mountaineers than in participants resistant to this condition. At high altitude, HAPE-susceptible participants with a large PFO had more severe hypoxemia. We speculate that at high altitude, a large PFO may contribute to exaggerated arterial hypoxemia and facilitate HAPE.

Adult↗
PubMed1996

Metabolic responses during initial days of altitude acclimatization in the eastern Himalayas.

The study was carried out on 16 men (aged 20-30 years) to evaluate daily metabolic responses during the early phase of altitude acclimatization at moderate altitudes between 3100 and 4200 m in the Eastern Himalayas. Resting (R) and submaximal exercise (E) oxygen consumption (IVO2) at 100 W at sea level (SL) were 3.25 (SEM 0.15) and 20.31 (SEM 0.77) ml/kg per min respectively. On day 1 at 3110 m both R and E IVO2 decreased (P < 0.001) and subsequently remained constant. At 3445 m these values tended to increase over the 3110 m values but were lower than the SL values. At 4177 m the decline in IVO2 was significantly greater (P < 0.01) than at the preceding altitudes. Pulmonary ventilation (IVE) increased consistently (P < 0.001) with increase in altitude. The arterial oxygen saturation (SaO2) at different altitudes was lower (P < 0.001) than SL values. The cardiac frequency (fC) at R and E was higher (P < 0.001) at altitude; the values at 3110 and 3445 m were significantly lower (P < 0.001) than at 4177 m. Blood pressure (BP) increased (P < 0.001) on the first day at each altitude. The systolic BP tended to decline towards SL values but the diastolic BP remained high (P < 0.001) throughout. The resting blood lactic acid concentration, [la-]bl, showed a decline (P < 0.001) only at 4177 m. The [la-]bl at E was similar at 3110 and 3445 m but was higher (P < 0.01) at 4177 m. These observations suggest that acclimatization to a mid-altitude of 3445 m can be safely avoided where rapid ascent to higher altitude is required.

Acclimatization↗