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PubMed2003

Low prevalence and increased household clustering of Mycobacterium tuberculosis infection in high altitude villages in Peru.

Anecdotal historical evidence suggests that tuberculosis was uncommon at high altitude, but whether transmission is affected by high altitude is not known. To test whether high altitude lowers infection by Mycobacterium tuberculosis, the prevalence of tuberculin skin test (TST) positivity was compared between two high altitude villages (3,340 meters [10,960 feet] and 3,500 meters [11,480 feet]) and three sea-level sites in Peru. High altitude villages had lower TST-positive prevalence rates (5.7% and 6.8%) than sea level areas (25-33%), and the difference remained significant (odds ratio = 4.5-6.0) after adjusting for age, education, bacille Calmette-Guerin vaccination, and contact with tuberculosis patients. The TST-positive individuals clustered within highland families more than within sea level families. These data suggest that prevention and control efforts targeted to families may be more effective at high altitude. The mechanism by which TST-positivity prevalence is decreased at high altitude is unknown, but may reflect relative hypoxia, low humidity, or an increased ultraviolet effect.

Adolescent↗
PubMed2003

The risk of altitude decompression sickness at 12,000 m and the effect of ascent rate.

INTRODUCTION: Loss of aircraft cabin pressurization can result in very rapid decompression rates. The literature contains reports of increased or unchanged levels of altitude decompression sickness (DCS) resulting from increasing the rate of decompression. We conducted two prospective exposure profiles to quantify the DCS risk at 12,192 m (40,000 ft), and to determine if there was a greater DCS hazard associated with a much higher rate of decompression than typically used during past DCS studies. METHODS: The 63 human subjects participated in 80 altitude chamber decompression exposures to a simulated altitude of 12,192 m (2.72 psia; 18.75 kPa) for 90 min, following preoxygenation with 100% oxygen for 90 min. Half of the subject-exposures involved an 8-min decompression (1,524 mpm; 5,000 fpm) and the other half experienced a 30-s decompression (mean of 24,384 mpm; 80,000 fpm). Throughout each ascent and exposure, subjects were seated at rest and breathed 100% oxygen. At altitude, they were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS: The higher decompression rate yielded 55.0% DCS and 72.5% VGE and the lower rate produced 47.5% DCS and 65.0% VGE. Chi square and log rank tests based on the Kaplan-Meier analyses indicated no difference in the incidence or onset rate of DCS or VGE observed during the two profiles. CONCLUSION: Decompression rate to altitude up to 24,384 mpm was found not to have an effect on DCS risk at altitude. However, research is needed to define the DCS risk with decompression rates greater than 24,384 mpm. It was also found that the onset time to DCS symptoms decreases as altitude increases.

Adult↗
PubMed2003

[Comparative evaluation of cardiac hemodynamics and endothelium-dependent reactive hyperemia in people with arterial hypertension living in high-altitude and plain areas].

AIM: To reveal the specific features of cardiac hemodynamics and endothelial function in high-altitude native dwellers with arterial hypertension (AH). MATERIALS AND METHODS: 90 native dwellers from high-altitude and plain areas, who had Stages I and II AH, were examined. To assess cardiac contractility, central and peripheral hemodynamics, the authors used electrocardiography, echocardiography, tetrapolar impedance rheoplethysmography. The functional status of the endothelium was evaluated by the reproduction of endothelium-dependent reactive hyperthermia in the antebrachial vessels. RESULTS: The patients with Stages I and II AH who live in high-altitude area have been found to have less pronounced peripheral vasocontriction due to the less suppression of pump and contractile functions of the heart. Total peripheral resistance in high-altitude dwellers with Stage II AH is practically similar to that in plain inhabitants with Stage I AH. The extended vasodilator reserve in high-altitude inhabitants with AH is also shown by the data obtained in the reproduction of reactive hyperemia in the antebrachial vessels. A less marked decrease in this vascular reaction in patients with AH who live in high-altitude areas may be due to additional production and/or release of nitric oxide in order to increase the vasodilator reserve in moderate hypoxia. CONCLUSION: The course of AH in high-altitude dwellers is marked by less suppression of cardiac pump and contractile functions and less peripheral vasoconstriction. This may be accounted for by compensatory activation of endothelial vasodilator mechanisms aimed at preserving adequate tissue perfusion and at optimally providing the body with oxygen in moderate hypoxia.

Acclimatization↗
PubMed1992

Effects of high altitude and exercise on marksmanship.

The effects of exercise and high altitude (3,700 m to 4,300 m) on marksmanship accuracy and sighting time were quantified in 16 experienced marksmen. Subjects dry-fired a disabled rifle equipped with a laser-based system from a free-standing position. The 2.3-cm circular target was at a distance of 5 m. Marksmanship was assessed under the following conditions: 1) at rest at sea level; 2) immediately after a 21-km run/walk ascent from 1,800 m to 4,300 m elevation; 3) at rest during days 1 to 3 at altitude; 4) at rest during days 14 to 16 at altitude; and 5) immediately after a second ascent after 17 d at altitude. Exercise reduced marksmanship accuracy (p less than 0.05) but did not affect sighting time. Acute altitude exposure reduced marksmanship accuracy, and decreased sighting time (p less than 0.05). However, after residence at altitude, accuracy and sighting time at rest returned to sea level values. Exercise and acute altitude exposure had similar but independent detrimental effects on marksmanship.

Adolescent↗
PubMed2005

Sinus vein thrombosis following exposure to simulated high altitude.

A relation exists between high altitude exposure and a hypercoagulable state, the nature of which is not entirely clear. This has been mostly reported in mountain climbers. We report a 19-yr-old female, working as a high-altitude chamber instructor, who presented with severe frontal headaches which persisted for a month following routine high altitude chamber training. The patient was in generally good health and was using oral contraceptives for 3 yr prior to the event. Due to the unremitting nature of the symptoms, the patient was admitted to a neurology department, and computerized tomography (CT) and magnetic resonance imaging (MRI) were performed. Sagittal and transverse sinus vein thrombosis were diagnosed and anticoagulant therapy was initiated (low molecular weight heparin followed by warfarin). Following treatment, a slow symptomatic improvement was observed, and the patient was discharged. On discharge, it was recommended she continue oral anticoagulant therapy (warfarin). A complete coagulation screening panel was performed, which was negative. Although the relation between high altitude exposure and a hypercoagulable state is well known, this is the first time a case of sinus vein thrombosis has been reported after high altitude chamber training. Careful history and closely monitored medical follow-up should be performed on all designated staff exposed to simulated altitude. Even though there is no conclusive evidence regarding it, we suggest, as a matter of caution, that women using oral contraceptives should consider their risks before deciding to undertake exposure to simulated altitude in chambers. Literature review and detailed recommendations for prevention are provided.

Adult↗
PubMed2006

Effects of gender and altitude on short-term heart rate variability in children.

OBJECTIVE: We aimed to study short-term heart rate variability (HRV) in 113 apparently healthy children permanent residents of moderate altitudes, the effects of gender and altitude. METHODS: Children were assigned into 3 groups according with altitude of residence: Group 1--1650 m/a/s/l (n=38), Group 2--1740 m/a/s/l (n=36) and Group 3--2030 m/a/s/l (n=39). All children underwent short-term electrocardiographic recordings with spectral analysis of HRV at rest and during standing. Statistical analysis was performed using multivariate ANOVA analysis. RESULTS: Heart rate variability analysis showed significant increase in SDNN, high frequency and total powers in parallel with increase of the altitude of residence (p<0.0001, p<0.03 and p<0.01, respectively). The magnitude of the HRV response to posture did not differ between groups except index of sympathetic modulation, LFNU, which rose to a significantly lesser degree (F=3.45, p<0.03) in Group 3, as compared with Group 1 and 2. Girls had lower HRV as compared with boys. CONCLUSION: Thus, in apparently healthy children, residents of moderate altitudes, increase in altitude levels is accompanied by higher overall variability and parasympathetic modulation of the sinus node and lower sympathetic response to posture. Heart rate variability in children, residents of moderate altitudes is also dependent of gender, resembling similar relationship in inhabitants of sea level.

Adaptation, Physiological↗
PubMed1991

Echocardiography shows persistent thickness of the wall of the right ventricle in infants at high altitude.

We have applied M-mode and two-dimensional echocardiography to infants living at high altitude in La Paz, Bolivia (3800m) and infants living at low altitude in Santa Cruz, Bolivia (400m). At low altitude, the thickness of the anterior wall of the right ventricle decreases during the first month of extrauterine life to a dimension which remains constant for the rest of infancy. At high altitude, the thickness of the anterior wall of the right ventricle at birth is similar to that found at low altitude but does not decrease in the succeeding twelve months. The ratio of the diameter of the aorta to that of the pulmonary artery was higher at low altitude in all age-groups. The observations are consistent with the persistence of a high pulmonary arterial pressure during infancy at high altitude.

Adaptation, Physiological↗
PubMed1989

Exercise performance of hemodialysis patients during short-term and prolonged exposure to altitude.

The work capacity of patients on maintenance hemodialysis is impaired even at normal inspiratory oxygen pressure. A further restriction can be expected when these patients are exposed to hypoxia at altitude, since most of the usual compensatory mechanisms required to adjust to this environment are impaired or even missing. We tested the tolerance of hemodialysis patients to hypoxia and measured work capacity, hematological, and cardiovascular parameters at rest and during incremental bicycle ergometry during 3-hour exposure to altitudes of 2,000 m and 3,000 m, and during 2 weeks of exposure to an altitude of 2,000 m and compared these data with prealtitude values or with data evaluated in a control group, respectively. In control tests the patients reached work loads at exercise termination of about 66% of age and sex-matched healthy controls, the reduction correlated well with the degree of anemia. During short-term altitude exposure to 2,000 m peak work performance remained unchanged in comparison to prealtitude tests, whereas at 3,000 m it was reduced by about 12%. During the 2-week stay at 2,000 m peak work loads increased significantly by 17% accompanied by an increase in peak oxygen uptake (+15%), blood lactate, heart rates (+10 min-1), and systolic blood pressure (+20 mmHg), whereas the diastolic pressure was comparable to prealtitude values. In another group of hemodialysis patients studied at low altitude under similar experimental conditions none of these parameters was changed. Our data show that during acute exposure to altitudes up to 2,000 m maximal work of hemodialysis patients is not reduced, but is restricted at altitudes higher than that.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1989

Propranolol and the compensatory circulatory responses to orthostasis at high altitude.

Tachycardia has been shown to be an important response involved in the maintenance of cardiac output during orthostasis at high altitude. This study was undertaken to determine if tachycardia, mediated by beta-adrenergic sympathetic stimulation, actually represents an essential response. Twelve young, healthy male subjects were administered either 80 mg propranolol (n = 6) or placebo (n = 6), t.i.d. at sea level and for 3 days (d) prior to and during the first 15 d of a 19-d altitude sojourn (On Treatment). Individuals were randomly assigned to each group. Upright tilt tests were performed at sea level and at high altitude during days 2, 7, and 15 On Treatment. Subjects were also tilt-tested at sea level and on day 19 of the altitude exposure without placebo or propranolol administration (Off Treatment). Heart rate, stroke volume, calf blood flow, and blood pressure were obtained during supine rest and after 12 min of 60 degrees tilt. We found no differences between groups in any of the circulatory measurements at sea level and altitude while Off Treatment. During the On Treatment phases at sea level and altitude, propranolol caused reductions in heart rate and blood pressure values in each position (p less than 0.05). Supine and upright cardiac output, however, were found not altered due to compensatory increases in stroke volume (p less than 0.05). We concluded that tachycardia, both at rest and during upright tilt at high altitude is important, but not essential to maintain cardiac output.

Adult↗
PubMed1986

Cardiovascular adaptation to exercise at high altitude.

To exercise at high altitude means working in an environment with reduced atmospheric pressure. The oxygen tension of the inspired air is therefore decreased, that is, there is atmospheric hypoxia. Exercise increases oxygen requirements which must now be met in the face of this decreased oxygen driving pressure. The initial handicap is less complete oxygenation of blood within the lung. In an effort to preserve oxygen delivery, a greater volume of blood is circulated, that is, cardiac output is increased. However, this pattern of compensation is only temporary. Within days, hemoconcentration increases the oxygen-carrying capacity of the blood, and as a consequence, less cardiac output is required to maintain oxygen delivery. In fact, cardiac output decreases to levels lower than existed prior to ascent. This reduction in cardiac output results primarily from a decrease in stroke volume due to less venous return secondary to the smaller blood volume produced by hemoconcentration. The hypoxia of high altitude produces sustained stimulation of the sympathetic nervous system. Initially, this increases heart rate, but, with time, the responsiveness of the heart decreases, so the initial tachycardia may not be sustained. Other consequences of sympathetic stimulation include an increase in resting metabolic rate, a shift away from glycogen toward free fatty acids as primary energy sources, and bone marrow stimulation to increase red cell production. The parasympathetic nervous system may also be stimulated at high altitude, which may explain the reduction in maximum heart rate. Upon arrival at high altitude, aerobic working capacity is reduced. Although this may or may not be attenuated following adaptation, endurance capacity does seem to improve. Several parallels therefore emerge between adaptation to the hypoxia of high altitude and adaptation to the struggle for oxygen created by exercise training at low altitude. Sympathetic stimulation is common to both forms of hypoxic stress, and similar responses, particularly metabolic, result. Not surprisingly, then, exercise training provides an advantage to adaptation to high altitude.

Acclimatization↗
PubMed1987

Some effects of alcohol and simulated altitude on complex performance scores and breathalyzer readings.

Each of 17 men was trained on 7 tasks in the Multiple Task Performance Battery and then performed over a 2-week period in four experimental sessions: ground level with and without alcohol, and simulated altitude (12,500 ft), with and without alcohol. Subjects breathed appropriate gas mixtures through oxygen masks at both ground level and altitude. Alcohol doses of 100-proof vodka mixed with juice 2.2 ml X kg-1 of body weight. Results showed no differential effect of simulated altitude on breathalyzer readings (peaks averaged 78 mg % at 12,500 ft and 77 mg % at ground level). The best performance occurred at ground level under placebo conditions; the 12,500-ft simulated altitude produced some decrement for placebo scores. Alcohol at ground level resulted in significantly impaired performance during the morning sessions; the addition of altitude to the alcohol condition further depressed performance scores, but to about the same extent that placebo scores were depressed by altitude. Thus, there was no synergistic interactive effect of alcohol and altitude on either breathalyzer readings or performance scores.

Adult↗
PubMed1986

[Altitude edema in the Swiss Alps. Observations on the incidence and clinical course in 50 patients 1980-1984].

In the Swiss Alps 50 patients with high altitude edema (high altitude pulmonary edema and/or high altitude cerebral edema) had to be rescued by helicopter during the period 1980-1984. The development, clinical picture and clinical course have been analyzed retrospectively. The patients were 49 men and one woman, generally in good health and well trained. They had ascended from the low-lands to an altitude above 2500 m and subsequently climbed higher. The climbers developed symptoms of acute mountain sickness on the second to third day of high altitude exposure and had to be evacuated by air on the fourth to fifth day. 70% of the cases occurred in the Valais Alps and the rest in the region of the Bernese Alps and the Bernina. The highest incidence of high altitude edema was observed in the Capanna Margherita (4559 m), where one of 588 climbers who stayed overnight had to be air-rescued. This ratio was about one in 4000 mountaineers at the Finsteraarhorn hut (3050 m) and the Monte Rosa hut (2795 m). Evacuation by air was the most successful therapeutic measure and resulted in immediate amelioration of clinical symptoms in 16 patients. 34 climbers had to be admitted to local hospitals due to severe high altitude pulmonary and/or cerebral edema. The pulmonary edema was bilateral in two thirds of these patients and unilateral in one third. Arterial blood gases showed moderate to severe limitation of oxygen diffusion capacity. All patients recovered completely within a few days.

Adult↗
PubMed1985

Migration of the elderly from high altitudes in Colorado.

The reason for the reported decline in the proportion of elderly (greater than 60 years) persons at high (greater than 2,456 m) compared with low altitude (less than 1,376 m) in Colorado was unknown. We hypothesized that adverse effects of high altitude on the elderly, particularly those with heart and lung diseases, prompted their migration to lower elevations. Colorado census data indicated that selective out-migration occurred from high to low altitude among the elderly. Interviews (n = 833) in high- and low-altitude Colorado towns revealed that the elderly were unique in that they moved down for reasons of poor health and that for the majority (81%) ill health meant heart and lung diseases. Elderly migrants from high altitude reported heart and lung diseases more frequently than those remaining and cited improvement in symptoms at low altitude. We suggest that symptoms of heart and lung disease are exacerbated with advancing age at high altitude and influence choice of residence.

Aged↗
PubMed1983

Hemorrhagic tolerance of rats at sea level after acute exposure to high altitude.

Exposure of rats to a simulated altitude of 5,000 m for 1 and 3 d caused increases in hematocrit (Hct) and in hemoglobin (Hb) concentration and a decrease in total plasma volume (TPV) in comparison with sea level control animals. Total blood volume (TBV) was decreased after 1 d of exposure to altitude but returned to normal in 3 d of altitude exposure. The sea level hemorrhagic tolerance was measured in all animal groups by determining the bleeding volume which resulted in death following cannulation under anesthesia. This was recorded as a bleeding volume index (BVI), the total volume of blood lost per 100 g of body weight. The mean BVI decreased in 1-d altitude rats, but not in 3-d altitude rats. Changes in mean arterial blood pressure and Hct during bleeding were recorded. The decreased hemorrhagic tolerance was suggested to be due in part to a decreased TBV and to a loss in arterial blood pressure (BP) regulatory capability after severe hemorrhage. The results of the present study for acutely altitude-exposed rats are opposite to those of a previous study for chronically altitude-exposed rats in which BVI, TBV, and the ability for arterial BP regulation were increased.

Acclimatization↗
PubMedDate not supplied

[Factors influencing the house dust mite population IV. Altitude].

A study has been carried out on house-dust mites present in the buildings of 3 towns in Catalunya (Spain), with different altitudes: Reus (altitude, 76 m); L'Ametlla (altitude, 321 m); and Puigcerdá (altitude, 1.202 m). The period studied was between october, 1975 and september 1976. From this study, a negative correlation has been observed between the number of mites in house dust and the altitude of the town. This supports the results obtained by other authors. The decrease in the number of mites with increases in altitude is due to a decrease in the number of mites belonging to the Pyroglyphidae family. This family was present in all samples of house-dust studied, and generally in a greater number than other groups of mites. Of the three species of Pyroglyphidae more frequently present in house dust (Dermatophagoides pteronyssinus, D. farinae and Euroglyphus maynei), D. pternyssinus was the most abundant as well as the most affected variations of R.H and temperature resulting from the variations of the altitude. D. farinae and E. maynei were found in low levels suggesting inadequate conditions of temperature and R.H. in the houses studied. Even if E. maynei was the most abundant species in Puigcerdá, this is due more to the decreased incidence of D. pteronyssinus than to an increase in the number of E. maynei.

Altitude↗
PubMed1994

Coronary heart disease at altitude.

In the past, it has been assumed that some basic physiologic responses to altitude, exposure in coronary patients are comparable to those in normal young subjects. In fact there are similar changes in sympathetic activation, heart rate, and blood pressure early after ascent, with decrements in plasma volume, cardiac output, and stroke volume as acclimatization proceeds. These responses are described, and experience with coronary patients is reviewed. During the 1st 2 to 3 days at altitude, coronary patients are at greatest risk of untoward events. Gradual rather than abrupt ascent, a moderate degree of physical conditioning, early limitation of activity to a level tolerated at low altitude for somewhat less), and attention to blood pressure control all appear to have protective effects. Ascent to moderate altitude appears to entail little risk in coronary patients who are asymptomatic or have moderate exercise tolerance, provided that the above precautions are observed and that activity does not exceed levels at lower altitude. If activity is to be increased, pre-ascent treadmill exercise testing or Holter monitor data secured under conditions comparable to those anticipated at altitude may provide reasonable guidelines. For coronary patients previously evaluated and known to be in a high-risk category, indications for ascent should be examined more critically, and precautionary measures should be more rigorous. Advice for patients with known coronary disease who may desire to trek at very high altitude must involve individual evaluation, and guidelines remain elusive.

Altitude↗
PubMed1977

Changes in orthostatic tolerance in man at an altitude of 3500 meters.

Orthostatic tolerance was measured in 20 lowlander Indian soldiers (sojourners) by recording responses of heart rate (HR), blood pressure (BP) and mean skin temperature (Tsk) to 70 degrees head-up passive tilt, initially at Delhi (260 m altitude) and thereafter at 3500 m at weekly intervals for 3 weeks. For comparison, observations were also made once on 10 acclimatized lowlanders (AL) and 10 high-altitude natives (HAN) at the same altitude. Among sojourners, the percentage of subjects showing orthostatic intolerance (OI) during tilt increased at high altitude in the first and second weeks; six subjects fainted in the first week as compared to one who fainted at sea level (SL). There was no incidence of fainting among AL or HAN and the percentage of subjects showing OI was very small. The magnitude of cardio-acceleration to tilt was higher in sojourners at high altitude (HA) and relatively less in AL and HAN. The systolic BP during tilt showed no change at SL or during the first and second weeks of stay at altitude in sojourners, but in third week showed a mild rise and was comparable to the responses of AL and HAN. The diastolic BP during tilt always showed a rise, although it was of a higher magnitude during the second and third weeks in sojourners as well as in AL and HAN. There was a fall in Tsk during tilt, which was of a lesser magnitude at HA. It has been concluded that there is a reduced orthostatic tolerance at higher altitude during the first week, due to hypocapnia, after which it is improved as a result of relative sympathetic hyperactivity and adaptation of the vasomotor centre to reduced PaCO2 level.

Adaptation, Physiological↗
PubMed1999

Sleep and Breathing in Recreational Climbers at an Altitude of 4200 and 6400 Meters: Observational Study of Sleep and Patterning of Respiration During Sleep in a Group of Recreational Climbers.

Background: The increasing popularity of mountain climbing will result in greater numbers of the general population being at risk for the disturbances known to occur with altitude exposure. Methods: Observations of sleep and breathing were made in 6 healthy travellers (5 males and 1 female, 38 to 62 years of age) before, during, and after a recreational climb. We modified a portable seven channel polygraph to record sleep state, oxygen saturation, respiratory movements, body position, and oronasal airflow 4 weeks prior to the expedition at home (500m), at base camp (4200m) and in 3 climbers at 6400m. All had a repeat study at 500m altitude 4 weeks after the expedition. Results: For the group, the total number of obstructive apneas and hypopneas (OA/H) at night increased from 36 at home to 68 at base camp over a one night recording. Separately counted central apneas and hypopneas (CA/CS) increased from 6.7 to 45. In one climber, who had a history of recurrent snoring and observed apneas at home, the number of apneas increased from 201 at 4200m to 322 at 6400m, whereas in 2 climbers measured at 6400m, all apneas decreased. The total sleep time (TST) increased in all 6 climbers by 10% at base camp in comparison to home records. In the 3 climbers attaining an altitude of 6400m, the REM (rapid eye movement) sleep declined by 10% compared to the record at 4200m. Conclusion: Respiratory disturbances at low altitude are amplified by exposure to high and extreme altitude. In those without symptoms of sleep apnea, significant physiologic alterations will occur at high altitude but at extreme altitude regular ventilation is re-established.

Journal Article↗