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At least 811 records · Page 45Linked to original sources
PubMed2000

Acclimatization to altitude and normoxic training improve 400-m running performance at sea level.

To investigate the benefits of 'living high and training low' on anaerobic performance at sea level, eight 400-m runners lived for 10 days in normobaric hypoxia in an altitude house (oxygen content = 15.8%) and trained outdoors in ambient normoxia at sea level. A maximal anaerobic running test and 400-m race were performed before and within 1 week of living in the altitude house to determine the maximum speed and the speeds at different submaximal blood lactate concentrations (3, 5, 7, 10 and 13 mmol x l(-1)) and 400-m race time. At the same time, ten 400-m runners lived and trained at sea level and were subjected to identical test procedures. Multivariate analysis of variance indicated that the altitude house group but not the sea-level group improved their 400-m race time during the experimental period (P < 0.05). The speeds at blood lactate concentrations of 5-13 mmol x l(-1) tended to increase in the altitude house group but the response was significant only at 5 and 7 mmol x l(-1) (P < 0.05). Furthermore, resting blood pH was increased in six of the eight altitude house athletes from 0.003 to 0.067 pH unit (P < 0.05). The results of this study demonstrate improved 400-m performance after 10 days of living in normobaric hypoxia and training at sea level. Furthermore, the present study provides evidence that changes in the acid-base balance and lactate metabolism might be responsible for the improvement in sprint performance.

Acclimatization↗
PubMedDate not supplied

The importance of socioeconomic and nutritional conditions rather than altitude on the physical growth of prepubertal Andean highland boys.

The aim of this work was to study the effect of hypoxic stress on the physical growth of prepubertal Bolivian boys (10-11.5 years of age) of the same socioeconomic and nutritional conditions. The subjects consisted of 143 boys living in La Paz (altitude 3600 m, n = 67) and Santa Cruz de la Sierra (altitude 420 m, n = 76). Among the boys studied at high altitude, 23 were from a high socioeconomic background (HA1) and 44 from a low socioeconomic background (HA2). The group studied at low altitude consisted of 47 boys from a high socioeconomic background (LA1) and 29 from a low socioeconomic background (LA2). A scientific evaluation of the nutritional status of the boys was realized from specific anthropometric characteristics (height, body weight, upper arm muscle circumference, body fat mass and body mass index) and haematological (haematocrit, haemoglobin, serum iron, serum ferritin, red cell protoporphyrin, transferrin saturation) and biochemical (total serum protein, albumin and prealbumin) parameters. At high as at low altitudes, the biometric characteristics of boys from a low socioeconomic background were significantly lower than those of boys from a high socioeconomic background. The physical growth of HA2 and LA2 boys was delayed by approximately 2 years. All the boys had biochemical and haematological parameters within the normal range. Boys from a low socioeconomic background were considered as marginally undernourished and those from a high socioeconomic background as well-nourished. Within the same socioeconomic class there was no nutritional difference between highland and lowland boys. Similarly, and this is the most important feature of this study, there was no difference for the overall biometric characteristics between highland and lowland boys of the same socioeconomic and nutritional status. Therefore, it appears that when socioeconomic and nutritional conditions are taken into account, there is no effect of hypoxic stress on the physical growth of prepubertal Andean highland boys.

Altitude↗
PubMedDate not supplied

Anthropometric comparison between high- and low-altitude Saudi Arabians.

Measurements of weight, height, mid-upper arm circumference, mid-upper arm muscle circumference and skinfold thickness over the triceps region were made in 437 high-altitude residents (3150m above sea level) aged 16-60 years and 468 low-altitude residents (500 m above sea level) aged 16-60 years in southern Saudi Arabia. Compared with low-altitude residents, high-altitude residents were found to be significantly heavier and taller, but to have nearly similar mid-upper arm circumference, mid-upper arm muscle circumference and triceps skinfold thickness. Estimates of body fat have been made from the triceps skinfold measurements. No significant difference in the percentage of fat was detected between high- and low-altitude residents. When fat mass (kg) and fat mass index (fat mass (kg)/height in m2) were considered, similar trends were found between highland and lowland men only. Highland women showed significantly higher fat mass and fat mass index when compared with lowland women. These differences in physique between highland and lowland residents of southern Saudi Arabia may be attributed to the effect of environmental factors, possibly the hot climate and parasitic infections prevalent in lowland areas, in addition to the higher physical activity observed in lowland women.

Adolescent↗
PubMed2000

Inhibition of interferon, cytokine, and lymphocyte proliferative responses in elite swimmers with altitude exposure.

To determine the immunologic consequences of athletic training at altitude, blood samples were taken at rest from 10 swimmers and 8 control nontraining but altitude-exposed members of the 1996 Australian Olympic Swimming Team, near the start and completion of a 21-day training camp at 2102 m. Blood leukocyte numbers dropped in both groups (p < 0.05), with the decrease greater in the swimmers (-38% swimmers, -3% controls). Concanavalin A (ConA)-induced blastogenesis decreased in both groups (p < 0.01), but the drop was greater in the control group (-32% swimmers, -56% controls, p < 0.05). Lipopolysaccharide (LPS)-induced blastogenesis more than doubled in both groups (281% swimmers, 249% controls, p < 0.01). Increases in mitogen-induced interleukin-1beta (IL-1beta), IL-4, and interferon-gamma (IFN-gamma) production and a decrease in IL-2 levels were observed in both groups after altitude exposure (all p < 0.05). The percentage of cells expressing HLA-DR fell (-33% swimmers, -20% controls, p < 0.01), whereas those expressing CD-4 expression increased (16% swimmers only, p < 0.01). Although training at medium-level altitude alters some immunologic parameters, the training-induced changes may be secondary to those induced by altitude alone.

Adaptation, Physiological↗
PubMed2000

Hematological parameters in high altitude residents living at 4,355, 4,660, and 5,500 meters above sea level.

There have been a number of reports describing the hematological indicators of Andean residents living at altitudes above 4,000 m, but several confounding factors have made the published results difficult to interpret. To clear up the effect of hypoxia on hemoglobin concentration (Hb, g/dL), hematocrit (Hct, %) and red blood cell concentration (RBC, cells/microL), this publication describes and analyzes these variables in children, men, and women from three large and homogeneous populations living at 4,355 m (n = 151), 4,660 m (n = 400), and 5,500 m (n = 273) in the Southern Peruvian Andes. Hb, Hct, and RBC increase with age in men (p < 0.001), as well as in women (p < 0.001) at the three altitudes of the study. In children (boys and girls) living at 5,500, Hb increases 11% when compared with children living at 4,355 m, and in adults, Hb increases 9.6% when comparing the same altitudes. The maximum percentage increase in Hb with age was 5.6% at 5,500 m, in men and 3.2% at 4,355 m, in women. The average percentage of difference for the Hb concentration between adult men and women is 6.6% at 4,355 m, 9.8% at 4,660 m, and 11.6% at 5,500 m. The differences in Hb concentration between men and women can only be seen after puberty. Finally, Hb is higher in older than younger women, which confirms the role of menopause in the development of erythremia. The result of this analysis reinforces the notion that Hb and Hct seem to be stable and useful parameters for acclimatization only at moderate altitudes; with aging or with increasing altitude, they may become excessive and lose their efficiency to protect the venous oxygen pressure.

Acclimatization↗
PubMed2001

Assessment of high altitude tolerance in healthy individuals.

The most reliable prediction of high altitude tolerance can be derived from the clinical history of previous comparable exposures. Unfortunately, there are no reliable tests for prediction prior to first-time ascents. Although susceptibility to AMS is usually associated with a low hypoxic ventilatory response (HVR), there is too much overlap with the range of normal values, which precludes measuring HVR or O(2) saturation during brief hypoxia for reliable identification of susceptibility to AMS. A low HVR and an exaggerated rise in pulmonary artery pressure with (prolonged) hypoxia, or exercise in normoxia, are markers of susceptibility to high altitude pulmonary edema (HAPE). These tests can not be recommended for routinely determining high altitude tolerance because the prevalence of susceptibility to HAPE is low and because specificity and sensitivity of these tests are not sufficiently established. On the other hand, HAPE may be avoided in susceptible individuals by ascent rates of 300 m per day above an altitude of 2000 m. Since prediction of risk of mountain sickness is difficult, it is important during the physician consultation prior to ascent to consider the altitude profile, the type of ascent, the performance capacity, the history of previous exposures, and the medical infrastructure of the area.

Acclimatization↗
PubMed2003

Cardiopulmonary function in high altitude residents of Ladakh.

We studied residents of high altitude in Ladakh, India, to determine the effects of altitude, age, gender, and ethnicity on gas exchange and pulmonary function. Physical examinations, including pulse oximetry, hemoglobin concentration, end-tidal PCO2, and pulmonary function, were conducted on resting Ladakhi and Tibetan subjects at altitudes of 3300, 4200, and 4500 m. A total of 574 men and women, ranging in age from 17 to 82, were studied. At 3300 m, Ladakhis had higher heart rates than Tibetans in both genders and higher PETCO2 in women. Above 4000 m, 21 of the 141 men studied (15%) had Hb concentrations higher than 20 g/dL, with one confirmed case of Monge's disease. There was no gender difference in SaO2 at any altitude except for pregnant women. At 4600 m, Tibetans had significantly higher peak flows and lower PETCO2 than Ladakhis. Ladakhi men had higher diastolic BP than women (91 vs. 81), with no difference in systolic BP. There was no gender difference in BP for Tibetans. An important spirometry finding for both groups was high air flows, with mid-maximal expiratory flow (MMEF) at 130% to 150% of predicted values, compared with 85% for sojourner controls, and FEV1/FVC at 115%, compared with sojourner controls at 98%. Improved lung mechanics may be an important adaptation to the lifelong sustained increase in resting ventilation as well as to indoor biomass smoke and outdoor dust exposure of these populations at high altitude.

Acclimatization↗
PubMed2004

Physiological basis for recommendations regarding exercise during pregnancy at high altitude.

Although exercise during pregnancy has been shown to be safe and is now recommended by the American College of Obstetricians and Gynecologists and the Society of Obstetricians and Gynaecologists of Canada for all healthy women, little is known about the combined effects of high altitude and exercise during pregnancy. Due to a paucity of experimental data, recommendations regarding exercise during pregnancy at elevations >/=1600 m must be based on synthesis of available information regarding the independent effects of high altitude and exercise on uteroplacental oxygen delivery. Maternal hyperventilation and elevated blood hemoglobin concentration maintain resting arterial oxygen content at or above sea-level values. During exercise, however, arterial hemoglobin saturation falls, lowering the oxygen content. Resting uterine artery blood flow is lower in residents at 3100 m than at 1600 m, and flow is likely to decrease further during exercise, in proportion to the intensity and duration. The combined reduction in arterial oxygen content and uterine artery flow suggest that fetal oxygen delivery is compromised during exercise at altitude. Anemia, which should be defined according to altitude-adjusted criteria, will further diminish oxygen delivery. Clinicians may wish to monitor patient hemoglobin concentration more frequently and adopt a more conservative stance regarding exercise during pregnancy for both residents and visitors of altitudes >/=1600 m.

Altitude↗
PubMed2004

Proportional assist ventilation reduces the work of breathing during exercise at moderate altitude.

Reducing the work of breathing (WOB) during exercise and thus the oxygen required solely for ventilation may be an option to increase the oxygen available for nonventilatory physiological tasks at altitude. This study evaluated whether pressure support ventilation (PSV) and proportional assist ventilation (PAV) may partially reduce WOB during exercise at altitude. Seven volunteers breathing with either PSV or PAV or without support (control) were examined for WOB, inspiratory pressure time product (iPTP), and (O(2)) before and during pedaling at 160 W for 4 min on an ergometer at an altitude of 2860 m, where barometric pressure and oxygen partial pressure are approximately 30% less than at sea level. PSV and PAV reduced WOB from 4.5 +/- 0.9 J/L(-1)/min(-1) during unsupported breathing to 3.7 +/- 0.4 (p < 0.05) and 3.2 +/- 0.7 (p < 0.01), respectively. iPTP was reduced during PAV (570 +/- 151 cm H(2)O/sec/min(-1), p < 0.01), but not during PSV (727 +/- 116, p = 0.58) compared with unsupported ventilation during exercise (763 +/- 90). During PSV and PAV breathing, higher arterial oxygen saturations (84 +/- 2%, p < 0.05, and 86 +/- 1%, p < 0.01, respectively) were observed compared with control (80 +/- 3%), indicating that PSV and PAV attenuated hypoxemia during exercise at altitude. Total body (O(2)), however, was not reduced during PSV or PAV. In conclusion, both PSV and PAV reduced the WOB during exercise at altitude, but only PAV reduces iPTP. Both modes reduce hypoxemia, which may be due to higher alveolar ventilation or decreased ventilation-perfusion heterogeneity compared to unsupported breathing.

Adult↗
PubMed1995

Selections from current literature: the traveller to high altitude.

AMS is a preventable disease about which travellers are frequently uninformed and one which physicians may wrongfully assume is limited to the population of ultra high altitude adventurers. These studies on incidence, while not without flaws, point out the frequency of AMS, as well as its significant incidence at moderate and commonly frequented altitudes. The current literature does not fully answer questions about incidence at moderate altitudes, nor about the full effects of altitude on children. Certainly AMS is not a rare complication of travel to altitudes and may indeed be under-recognized and under-treated. Both acetazolamide and dexamethasone provide adequate prophylaxis, and the choice of medications can be to some extent based on experience and patient profile. The best prophylaxis is a slow stepwise ascent, and the best treatment descent. The availability of medications for the amelioration or prevention of symptoms, and succinct advice on prevention by travel planning will make many of our patients' holidays more enjoyable and business trips more productive.

Acetazolamide↗
PubMed1979

Altitude and ischemic heart disease in tricultural New Mexico: an example of confounding.

The relationship of male white ischemic heart disease (IHD) death rates to altitude falls to negligible levels when New Mexico populations are separated into Hispanic and Anglo. Low rates of IHD mortality characterize Hispanic males in New Mexico regardless of altitude. In comparison, New Mexico Anglo males have rates near the US average. The variable showing the most consistent positive relationship with altitude is per cent Hispanic. Mortimer et al. (N Engl J Med 296:581--587, 1977) reported a reduction in coronary heart disease mortality in New Mexico white males with an increase in altitude. The current authors claim that this is an example of confounding. They find that the relationship between IHD mortality and altitude is largely due to the intervening variable, per cent Hispanic. Ethnicity demands major attention in epidemiologic studies in tricultural New Mexico.

Altitude↗
PubMed1983

Associations among cataract prevalence, sunlight hours, and altitude in the Himalayas.

The relationship between cataract prevalence, altitude, and sunlight hours was investigated in a large national probability sample survey of 105 sites in the Himalayan kingdom of Nepal, December 1980 through April 1981. Cataract of senile or unknown etiology was diagnosed by ophthalmologists in 873 of 30,565 full-time life-long residents of survey sites. Simultaneously, the altitude of sites was measured using a standard mountain altimeter. Seasonally adjusted average daily duration of sunlight exposure for each site was calculated by a method which took into account latitude and obstructions along the skyline. Age- and sex-standardized cataract prevalence was 2.7 times higher in sites at an altitude of 185 meters or less than in sites over 1000 meters. Cataract prevalence was negatively correlated with altitude (r = -0.533, p less than 0.0001). However, a positive correlation between cataract prevalence and sunlight was observed (r = 0.563, p less than 0.0001). Sites with an average of 12 hours of sunlight exposure had 3.8 times as much cataract as sites with an average of only seven hours of exposure. Sunlight was blocked from reaching certain high altitude sites by tall neighboring mountains.

Adolescent↗
PubMed1994

Cardiovascular neural regulation during and after prolonged high altitude exposure.

Eight young healthy male subjects, members of a Himalayan expedition, underwent 24 h Holter monitoring before departure, after 1 and 4 weeks at high altitude (5000 m) and after return to sea level. At high altitude, the circadian reciprocal changes in low and high frequency (LF, HF) were absent, with no significant reduction in the LF to HF ratio over the 24 h; moreover, the proportion of adjacent R-R intervals that differed by more than 50 ms (pNN50) decreased significantly and remained lower after return to sea level. Urine catecholamines increased at high altitude, but only norepinephrine, after 1 week of exposure, rose significantly. Upon return to sea level the density, but not the affinity, of [alpha]2-adrenergic receptors on platelets decreased significantly compared to pre-expedition values. At high altitude increased sympathetic activity was indicated by elevation of urine norepinephrine and by the loss of circadian rhythm in spectral components. The simultaneous reduction of HF and pNN50 demonstrated decreased vagal tone. The persistence of increased sympathetic activity could explain the downregulation of adrenergic receptors after prolonged high altitude exposure.

Adult↗
PubMed2005

Normal values of pulse oximetry in newborns at high altitude.

The aim of the study was to establish normal values of pulse oximetry saturation, respiratory rate, heart rate, and blood pressure in healthy newborns at high altitude. Vital signs and oximetry saturation readings were collected from healthy term newborns at birth, at 1 h, and at 24 h of life. These were analyzed and compared with reference ranges at sea level. This study was carried out at altitudes of 1640 m above sea level in Taif city, Saudi Arabia. A total of 6011 term newborns were examined at birth and 1 h and 4274 were examined at 24 h of life. At birth, the mean SpO(2) was 68.6 per cent and 60.3 per cent from the right upper and lower limbs, respectively. Mean SpO(2) was 94.3 per cent and 95.4 per cent at the age of 1 and 24 h, respectively. These values were significantly lower than those reported at sea level. The mean respiratory rate, heart rate, and mean blood pressure at 24 h were 45.7/min, 149.7/min, and 46.9 mmHg, respectively. It is concluded that pulse oximetry saturation for newborn babies is lower at higher altitudes than at sea level. This effect is observable at altitudes of 1600 m above sea level. Cut-off levels lower than those used at sea level should be adopted when dealing with newborns living at high altitudes.

Altitude↗
PubMed1994

Changes in human respiratory sensation induced by acute high altitude hypoxia.

Respiratory sensation was studied in European low-landers at an altitude of 4382 m after a helicopter flight in order to investigate the acute and prolonged effects of high altitude hypoxia. At rest the ability to detect four inspiratory resistive loads can be used to create a sensitivity index P(A) without taking the response bias (B) into account, based on the Sensory Decision Theory. In 6 subjects respiratory sensitivity increased significantly under acute and prolonged hypoxia after 3-4 days of high altitude exposure. The respiratory sensitivity increased with the hyperventilation and mouth pressure increase induced by hypoxia. Hypoxia might also have feedback effects on the peripheral and central nervous integration of the respiratory sensation stimuli. One subject suffering from acute mountain sickness showed a severe decrease in his sensitivity index P(A) under hypoxic conditions, while the parameters of his cardiorespiratory function evolved in the same classical way as the other subjects who adapted well to altitude hypoxia. The increase in respiratory sensation may be the first necessary step in altitude acclimatization and might serve as a useful marker of this adaptation.

Altitude Sickness↗
PubMed2002

Unchanged cerebral blood flow and oxidative metabolism after acclimatization to high altitude.

The authors investigated the effect of acclimatization to high altitude on cerebral blood flow and oxidative metabolism at rest and during exercise. Nine healthy, native sea-level residents were studied 3 weeks after arrival at Chacaltaya, Bolivia (5,260 m) and after reacclimatization to sea level. Global cerebral blood flow at rest and during exercise on a bicycle ergometer was measured by the Kety-Schmidt technique. Cerebral metabolic rates of oxygen, glucose, and lactate were calculated by the Fick principle. Cerebral function was assessed by a computer-based measurement of reaction time. At high altitude at rest, arterial carbon dioxide tension, oxygen saturation, and oxygen tension were significantly reduced, and arterial oxygen content was increased because of an increase in hemoglobin concentration. Global cerebral blood flow was similar in the four conditions. Cerebral oxygen delivery and cerebral metabolic rates of oxygen and glucose also remained unchanged, whereas cerebral metabolic rates of lactate increased slightly but nonsignificantly at high altitude during exercise compared with high altitude at rest. Reaction time was unchanged. The data indicate that cerebral blood flow and oxidative metabolism are unaltered after high-altitude acclimatization from sea level, despite marked changes in breathing and other organ functions.

Acclimatization↗
PubMed2001

Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.

OBJECTIVE: To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia. DESIGN: We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO2), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5,000 m, in a hypobaric chamber). METHODS: We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during 'complete yogic breathing' (slow diaphragmatic + thoracic breathing, approximately 5 breaths/min) in yoga trainees, or simple slow breathing in controls. RESULTS: At baseline %SaO2, VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO2 decreased in all subjects (P< 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P< 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 +/- 45 to 770 +/- 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 +/- 0.5 to 3.2 +/- 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 +/- 0.31 to 3.07 +/- 0.24 In-mmHg2, P< 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing. No effect of altitude was seen on stimulation of carotid baroreceptors in both groups. CONCLUSIONS: Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia.

Adult↗
PubMed1996

Association of pulmonary artery size on chest radiograph with residence at elevated altitudes.

Mean pulmonary artery pressure (PAP) has been demonstrated to correlate with measures of pulmonary artery size. We tested the hypothesis that residence at elevated altitudes, a determinant of mean PAP, can be associated with increases in pulmonary artery size on chest radiographs from healthy adults. The study population consisted of three groups of asymptomatic, nonsmoking adults without hazardous respiratory exposures living at altitudes approximating 0 m (group 1, n = 197), 1,400 m (group 2, n = 145), and 2,600 m above sea level (group 3, n = 196). The width of the right descending pulmonary artery (RDPA) was measured at its widest diameter before bifurcation. In a multivariate regression model, significant associations were detected between RDPA width and residence at elevated altitudes (F = 13.84, p = 0.0002), age (F = 32.49, p < 0.0001), and gender (F = 56.10, p < 0.0001), with 36% of the variability of the measure determined by these three variables (r2 = 0.36). Mean RDPA width increased as altitude at residence increased. Larger mean values were noted among older individuals and males. We conclude that residence at altitudes of 1,400 and 2,600 m above sea level is associated with increases in pulmonary artery size on chest radiograph.

Adolescent↗