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PubMed2000

[Classification of altitude decompression sickness].

The article is devoted to the discussion of principles of and approaches to classification of altitude decompression sickness (DCS), one of the most methodically formidable aspects of the problem. Based on his own multiyear experience in altitude DCS investigations and critical review of literature, the author reasons his concept of clinical classification of altitude DCS. The author's concept places emphasis on obligatory consideration of three stages in DCS development: A--pre-disease (the premorbid syndrome), B--uncomplicated (light) and C--complicated (severe) forms. The objective sign of the premorbid state is "silent" gas bubbles in organism detectable by ultrasonic devices. Signs of uncomplicated altitude DCS are musculoarticular pains, local edema and skin itching. Complicated altitude DCS is diagnosed by systemic (respiratory, neurological and cardiovascular) disorders.

Altitude Sickness↗
PubMed2002

Non-invasive measurement of pulmonary artery pressure in humans with simulated altitude-induced venous gas emboli.

BACKGROUND: Decompression to simulated altitude causes super-saturation of nitrogen desolved in body tissues and can result in venous gas emboli (VGE), which are usually "cleared" in the lung. Large intravenous boli of air administered to animals increase pulmonary artery pressure (PAP), and may induce cross-over of gas to the left side of the heart (creating dangerous arterial gas emboli). This study was conducted to determine whether high VGE grades induced at simulated altitude elevate PAP in humans. METHODS: Eight human subjects with subclinical tricuspid regurgitation were exposed to simulated altitude of > or = 24,000 ft (7315 m) for up to 4 h. Systolic PAP was derived from Doppler ultrasound echo imaging measurements of peak flow velocity of the regurgitant jet. VGE was rated using the Spencer scale. A technique of "bubble titration" was employed with changes in exercise and altitude to maintain sufficient bubbles without decompression sickness. RESULTS: All subjects developed grade III-IV VGE, but 3 developed decompression sickness, resulting in earlier termination. Pre-exposure systolic PAP averaged 24.4 +/- 1.3 (SE) mm Hg. After 1, 2, 3 and 4 h, systolic PAP was 23.7 +/- 1.2 (n = 8), 23.4 +/- 1.1 (n = 8), 23.3 +/- 1.0 (n = 6), and 25.9 +/- 0.6 (n = 5) mm Hg, respectively. Systolic PAP remained unchanged, in spite of bubble grades III-IV for up to 4 h. CONCLUSION: As systolic PAP did not increase with hypobaric exposures that created substantial VGE, the bubble loading was not sufficient to overwhelm the lung clearing capacity. The risk of high PAP resulting in VGE cross-over is low during typical operational altitude exposures.

Aerospace Medicine↗
PubMed1975

[Certain hemodynamic indicators during rest and after intensive physical exercise at high altitude].

For 5 years 364 normal males, aged 19--25, were studied at the altitude of 3800--4200 m, along with local inhabitants of the mountain region; the hemodynamic shifts and arterial blood oxygenation were studied with the base metabolism conditions preserved both at rest, and after intensive physical exercises performed according to the step-test method with the maximum tempo of the work (cardiological motion test, WHO, 1967). The initial reaction of the cardiovascular system to the high altitude conditions manifested itself in an increased stroke volume and cardiac output, of the volume speed of blood ejection, of the cardiac index in a decrease of the total peripheral resistance and oxygen saturation of the arterial blood. This reaction was interpreted as a compensatory one. In the course of acclimatizing, the cardiac output and the pulse amplitude of the arterial pressure gradually decreased, and the total peripheral resistance increased. These hemodynamic changes must be of an adaptative nature. The maximum physical workload caused a distinct intensification of the circulatory reactions, especially in those living for considerable periods of time at high altitude and in local inhabitants. The general state of the examined remained good. Hence, these persons have a considerable reserve of functional capacities of their cardiovascular system, and can perform hard muscle work at high altitude. Individuals staying at high altitude for only short periods of time react to intensive physical workloads by a less distinct intensification of the contractile capacity of the heart and by a sharp decrease of blood oxygenation, considerable acceleration of the heart rate and respiration rate, as well as by a deterioriation of their general state. Such muscular efforts cause overloading of the heart only in persons with a short-term acclimatizing.

Acclimatization↗
PubMed2002

Pulmonary decompression sickness at altitude: early symptoms and circulating gas emboli.

INTRODUCTION: Pulmonary altitude decompression sickness (DCS) is a rare condition. 'Chokes' which are characterized by the triad of substernal pain, cough, and dyspnea, are considered to be associated with severe accumulation of gas bubbles in the pulmonary capillaries and may rapidly develop into a life-threatening medical emergency. This study was aimed at characterizing early symptomatology and the appearance of venous gas emboli (VGE). METHODS: Symptoms of simulated-altitude DCS and VGE (with echo-imaging ultrasound) were analyzed in 468 subjects who participated in 22 high altitude hypobaric chamber research protocols from 1983 to 2001 at Brooks Air Force Base, TX. RESULTS: Of 2525 subject-exposures to simulated altitude, 1030 (41%) had symptoms of DCS. Only 29 of those included DCS-related pulmonary symptoms. Of these, only 3 subjects had all three pulmonary symptoms of chokes; 9 subjects had two of the pulmonary symptoms; and 17 subjects had only one. Of the 29 subject-exposures with pulmonary symptoms, 27 had VGE and 21 had severe VGE. The mean onset times of VGE and symptoms in the 29 subject-exposures were 42 +/- 30 min and 109 +/- 61 min, respectively. In 15 subjects, the symptoms disappeared during recompression to ground level followed by 2 h of oxygen breathing. In the remaining 14 cases, the symptoms disappeared with immediate hyperbaric oxygen treatment. CONCLUSIONS: Pulmonary altitude DCS or chokes is confirmed to be a rare condition. Our data showed that when diagnosed early, recompression to ground level pressure and/or hyperbaric oxygen treatment was 100% successful in resolving the symptoms.

Adult↗
PubMed2003

Gender not a factor for altitude decompression sickness risk.

INTRODUCTION: Early, retrospective reports of the incidence of altitude decompression sickness (DCS) during altitude chamber training exposures indicated that women were more susceptible than men. We hypothesized that a controlled, prospective study would show no significant difference. METHODS: We conducted 25 altitude chamber decompression exposure profiles. A total of 291 human subjects, 197 men and 94 women, underwent 961 exposures to simulated altitude for up to 8 h, using zero to 4 h of preoxygenation. Throughout the exposures, subjects breathed 100% oxygen, rested or performed mild or strenuous exercise, and were monitored for precordial venous gas emboli (VGE) and DCS symptoms. RESULTS: No significant differences in DCS incidence were observed between men (49.5%) and women (45.3%). However, VGE occurred at significantly higher rates among men than women under the same exposure conditions, 69.3% and 55.0% respectively. Women using hormonal contraception showed significantly greater susceptibility to DCS than those not using hormonal contraception during the latter two weeks of the menstrual cycle. Significantly higher DCS incidence was observed in the heaviest men, in women with the highest body fat, and in subjects with the highest body mass indices and lowest levels of fitness. CONCLUSION: No differences in altitude DCS incidence were observed between the sexes under our test conditions, although men developed VGE more often than women. Age and height showed no significant influence on DCS incidence, but persons of either sex with higher body mass index and lower physical fitness developed DCS more frequently.

Aerospace Medicine↗
PubMed1976

Ethnic variations in psychological performance under altitude stress.

Sea-level performance of 120 subjects equally drawn from Gorkha, Madrasi, and Rajput groups was compared with that at an altitude of 4,000 m after 10 months' stay. Alterations in concentration, eye-hand coordination, anxiety, depression, and social interaction were recorded to ascertain ethnic differences in withstanding the altitude stress. Results showed a uniform fall in the scores for eye-hand coordination and social interaction at altitude for the three ethnic groups. However, the effects on concentration, anxiety, and depression were differential for these groups indicating a better toleration of altitude stress by Gorkhas. Climatic similarity between the region of natural habitat of Gorkhas and altitude environment has been suggested to be responsible for their better performance over the other two groups.

Acclimatization↗
PubMed1976

[Altitude adaptation. Biological problems in the context of the environment].

The following part of the description of adaptation to high altitude describes the geographical specifities of the relevant regions of the world. There are several factors which require an adaptive answer, such as hypoxia, temperature, terrain, nutrition etc. The terms of genetically determined and of individual adaptation are discussed, with special consideration of a duration of settlement in the main altitude regions of about ten thousand years, as well as the principles of adaptation in general, including the phenomenon of maladaptation. The problem of adaptation of animals to high altitude is reviewed in short especially in regard to mammals. The differential fertility proves to be most important in the survival of a species in high altitude as well as the individual adaptability, is the fitness which makes high altitude tolerable to newcomers.

Acclimatization↗
PubMed2003

[Effect of nitroglycerin on vasodilation at high altitude].

After more than centenary successful use of nitroglycerin in clinical practice, scientists revealed that its medicinal effect is based on release of potent vasodilator nitric oxide (NO). Moreover, the experiments showed that NO plays an important role in hypoxia vasodilator mechanisms. Since nitroglycerin is an exogenous NO donor and moderate hypoxia facilitates release of endogenous NO, we suggested that nitroglycerin effects are changed in high altitude. To examine this suggestion, we have carried out a standard nitroglycerin test for healthy volunteers living in high and low altitude areas. Comparison of obtained results showed that the use of oral nitroglycerin in high altitude areas is accompanied with significant prolonged decrease in blood pressure and total vascular resistance. So, we first found that high altitude hypoxia strengthens and extends nitroglycerin-induced peripheral vasodilation in healthy subjects. This effect might be caused by additive vasodilator effect of nitroglycerin and moderate hypoxia. This data should be taken into account when prescribing exogenous and endogenous NO donors to treat patients in high altitude areas.

Adaptation, Physiological↗
PubMed1992

[Digestive physiology and pathology in high altitude].

In the high altitude environment the oxygen and air density are decreased, the temperature and humidity are low, there es an increase in radioactivity. These environmental factors influence on the human body; it has been known for many years that people born and living at high altitude have different morphological and physiological characteristic than those at low altitude. The digestive mechanism for adaptation or acclimation to high altitude has interested physiologist and clinicians for many years. The objective of this article is to present a brief overview of the digestive physiology and pathology in the high altitude.

Altitude↗
PubMed1998

[Altitude exposure induces hypoxic preconditioning of the heart].

Under in vitro conditions, the resistance to ischemia may be improved by hypoxic preconditioning. This study was designed to test the hypothesis, that hypoxic preconditioning can also be induced in vivo by exposure of an intact animal to simulated high altitude. Male Wister rats (n = 48) were exposed for 60 minutes to simulated high altitude at 3000 m or 5000 m above sea level in a hypobaric chamber. 30, 150 or 300 min following exposure, hearts were excised and perfused aerobically in the working heart model prior to 45 minutes of global ischemia at 30 degrees C and subsequent normothermic reperfusion. For control, hearts of unexposed rats were either preconditioned by one cycle of 5 minutes of normothermic ischemia and reperfusion prior to subsequent ischemia or (n = 8) or not (n = 8). Postischemic measurements included functional parameters such as aortic flow, maximum developed left ventricular pressure, creatine kinase leakage from collected samples of the coronary effluent and the morphometric assessment of the area of myocardium at risk. When compared to non-preconditioning, ischemic preconditioning significantly improved the recovery of aortic flow, left ventricular systolic pressure and reduced the postischemic creatine kinase leakage. Likewise, exposure to a simulated high altitude at 3000 m above sea level significantly improved the recovery of aortic flow and reduced creatinkinase leakage when the time interval between exposure to simulated high altitude and perfusion was set to 150 minutes. Further increase in hypoxic stress (5000 m above sea level) or the reduction of this time interval to 30 minutes reduced postischemic recovery of hearts. The exposure of an intact organism to simulated high altitude can improve the resistance of the heart to ischemia by hypoxic preconditioning. The induction of this beneficial effect depends on the level of hypoxic stress and the time interval between preconditioning and subsequent ischemia.

Altitude↗
PubMed2003

[Study on the hemoglobin levels of children under the age of three years and the prevalence of anemia at high altitude in Tibet of China].

OBJECTIVE: To study the hemoglobin status of children under the age of three years and the prevalence of anemia at high altitude. METHODS: Cross-sectional study and randomly sampling were used. Blood was collected on tip of finger and the level of hemoglobin was measured using B-Hemoglobin photometer. We adjusted the hemoglobin based on altitude, using three methods of CDC, Direen's and Dallman's and then estimated the prevalence of anemia. RESULTS: (1) 1 127 children were examined. The findings indicated that the average hemoglobin was about 120 g/L. There was no significant difference for Hb between boys and girls. Urban children had a higher hemoglobin level (123.3 g/L) than rural children (119.9 g/L). Analysis of covariance indicated that, after controlling the factor of altitude, the mean content of hemoglobin of rural children was lower than that of urban children and hemoglobin varied among districts. (2) Different method used for correction of hemoglobin caused different prevalence rates of anemia but they were higher than un-corrected prevalences: 90.4% for CDC method, 72.3% for Dirren's method and 65.0% for Dallman's method respectively. CONCLUSION: Higher altitude seemed to affect the levels of hemoglobin significantly. The prevalence of anemia in children might be higher, but current hemoglobin correction methods might not be suitable for correcting hemoglobin of Tibetan children. So we suggested that it was imperative to establish a relationship between altitude and hemoglobin of Tibetan children.

Age Factors↗
PubMed1992

Training at moderate altitude: iron status of elite male swimmers.

Laboratory evidence of suboptimal iron status is endemic in chronically training athletes, yet the importance of low serum ferritin values to athletic performance is unclear. The purpose of this study was to monitor iron status in nine male elite swimmers during and after a 3-week training camp at 2225 m altitude. Values for hemoglobin, hematocrit, serum iron, serum transferrin, and transferrin saturation were within the normal range and remained unchanged over the 54-day monitoring period. Serum ferritin level was significantly decreased by day 13 and continued to decline over the period at altitude. Significant recovery was observed by day 35, by which the workload and altitude were reduced. Reticulocyte counts were raised above normal values by the fifth day at altitude and remained elevated for the duration of the study, indicating increased erythropoiesis. In contrast, neither ferritin levels nor reticulocyte counts were changed in six of the nine subjects after 1 month's training at 1000 m. Food histories revealed dietary iron intakes two to three times as great as the recommended dietary allowance for iron. The draw on body iron reserves observed in this study over the heavy training period at moderate altitude indicates that adequate iron stores are necessary to provide a reservoir of iron during periods of increased iron utilization or loss. Further work is required to elucidate the sources and endpoints of the observed iron flux.

Adult↗
PubMed2004

Renin angiotensin aldosterone system and ACE I/D gene polymorphism in high-altitude pulmonary edema.

INTRODUCTION: People who visit high altitude are exposed to a stressful environment, and many of them suffer from altitude-induced conditions, including high altitude pulmonary edema (HAPE). We investigated the renin angiotensin aldosterone system (RAAS) and the possible association of angiotensin converting enzyme (ACE) insertion/deletion (I/D) gene polymorphism in the development of HAPE in Indian men. METHODS: Subjects were all low-altitude natives: 19 men who developed HAPE within 1-3 d of arrival at 3000 to 3800 m (patients); and 20 age-matched men who did not develop HAPE during a period of a month or more at > or = 3500 m (controls). We recorded the arterial oxygen saturation (Sao2), heart rate (HR), and blood pressure (BP) of both groups and measured their levels of plasma renin activity (PRA), ACE, aldosterone, and serum electrolytes. Polymerase chain reaction was used to investigate a 287 base pair alu repeat sequence I/D polymorphism in the ACE gene. RESULTS: Compared with controls, patients showed a significantly lower Sao2 and a higher HR. They also had significantly higher plasma PRA, aldosterone, ACE, and serum sodium (Na+) and potassium (K+). No significant difference was observed in ACE I/D allele frequencies. DISCUSSION: The results suggested that RAAS is involved in the development of HAPE in low-altitude natives, but there is no association of ACE I/D gene polymorphism with HAPE.

Adult↗
PubMed2004

The impact of altitude on mortality from tuberculosis and pneumonia.

OBJECTIVE: To examine the association between altitude and mortality from tuberculosis (TB) and pneumonia-influenza in Mexico. DESIGN: We analysed specific causes of death in Mexico according to death certificates for the period 1993-1997, totalling over 2,700,000 deaths and including nearly 23,000 attributed to TB and 115,000 to pneumonia and influenza. Thirty population subgroups were formed based on altitude of residence (six categories) and level of poverty (five categories). The effect of altitude on mortality was estimated through Poisson regression models, with adjustment for age, gender and socioeconomic status. RESULTS: Adjusted death rates for TB decreased with altitude and increased for pneumonia-influenza. Compared to people living below 500 m above sea level, those living between 2000 and 2499 m had a 58% mortality rate for TB and a three-fold increase in mortality due to pneumonia-influenza, despite adjustment for poverty, age and gender. CONCLUSION: The mortality rate for TB based on death certificates decreases with altitude of residence, whereas the opposite is observed for pneumonia and influenza.

Adolescent↗
PubMed2004

Effect of altitude on the frequency of pulmonary tuberculosis.

SETTING: Pulmonary tuberculosis (PTB) incidence greatly varies around the world, a phenomenon usually attributed to socio-economic factors or health service availability. A recent study, however, indicated that PTB was inversely related to altitude. OBJECTIVE: To evaluate factors associated with PTB notification rates in Mexico. METHODS: Annual notification rates (1998-2002) of PTB in each of the 32 Mexican states were analysed, and likely factors were assessed through correlation and multiple regression analyses. RESULTS: Most variables lacked association with PTB rates, including percentage of population aged > or = 65 years, population density, percentage of population with < or = 2 minimum salaries, percentage of population with social security, level of education, diabetes incidence, percentage of immigration, percentage of rural population and a global marginalisation index. Only altitude above sea level correlated with tuberculosis incidence (r = -0.74, P < 0.0001). Likewise, in the multiple regression analysis only altitude reached a statistically significant association. CONCLUSION: Our results showed that altitude had a strong inverse relationship to PTB notification rates in Mexico, which might be related to the well known changes in alveolar oxygen pressure at different altitudes. Interestingly, several factors traditionally considered as predisposing conditions for the development of PTB did not correlate with the disease.

Adolescent↗
PubMed2005

Nephropathy and retinopathy in type 2 diabetic patients living at moderately high altitude and sea level.

BACKGROUND: High-altitude-induced hypoxia results in various diseases, such as chronic mountain sickness and high altitude retinal edema, and may affect severity and incidence of some cardiovascular diseases. In order to evaluate the effects of moderately high altitude on diabetic nephropathy and retinopathy, a cross-sectional study was planned. MATERIAL METHOD: Long-term type II diabetic residents of sea level (n=75, 38 male, 37 female, mean age 51.9+/-10.5 in Trabzon and Zonguldak cities) and moderately high altitude (h = 1,727 m, n = 73, 28 male, 45 female, mean age 48.3+/-12.1, Van city) were compared. RESULTS: No difference was observed in terms of age, gender, diabetes duration, body mass index, smoking, systolic, diastolic, and mean arterial blood pressure values, serum glucose levels, cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, hemoglobin, HbA1C, hypertension control, or blood pressure medications and retinopathy incidence. Mean 24 h protein excretion (210.0+/-139.9, 127.8+/-112.1 mg; P=0.00), proteinuria prevalence (57.5% versus 33.3%, p=0.003), and serum creatinine levels (1.04+/-0.22 versus 0.84+/-0.21, p = 0.00) were significantly higher in the highlanders, glomerular filtration rate (GFR) was significantly lower in sea level (SL) patients (90.9+/-26.5 versus 83+/-21.1, p=0.05). CONCLUSION: Tendency to diabetic nephropathy as indicated by higher proteinuria and creatinine levels is increased among type 2 diabetic patients living at moderately high altitude. Prospective studies are needed to confirm these findings.

Adult↗
PubMed2005

Altitude training experiences and perspectives: survey of 67 professional pilots.

INTRODUCTION: Pilots and crewmembers of flights exceeding 7620 m/mean sea level (msl) are required to complete ground training in high-altitude physiology, including hypoxia training. However, regulations do not require altitude chamber training (ACT). METHOD: An anonymous questionnaire concerning their experiences and perceptions of hypoxia training was filled out by 67 pilots attending an aviation safety conference. All pilots had logged professional business flight hours in the previous 6 mo. RESULTS: There were 62 pilots who reported receiving hypoxia training, and of these, 71% reported having initial ACT. Most of the pilots surveyed agreed that all pilots should receive introductory hypoxia training (92%), recurrent hypoxia training (86%), initial ACT (85%), and recurrent ACT (70%). Initial ACT received lower endorsements for private (32%) or recreational (10%) pilots than for commercial (74%) and air transport (90%) pilots. When asked if ACT should be based on the altitude capability of an aircraft, 59% responded affirmatively. Apparently, the perceived need for ACT was based on the likelihood of flying at higher altitudes and not simply the level of certification. When asked if the current regulations (i.e., not requiring ACT) addressing high-altitude flying (above 7620 m/msl) are sufficient, 52% of the current sample disagreed or strongly disagreed. DISCUSSION: Generally, these professional pilots perceived that pilot training should include introductory hypoxia training, recurrent hypoxia training, and ACT. Exceptions were initial ACT for recreational pilots and private pilots. Generalizability of these results may be affected by the specificity and size of the sample. Distributing the survey to a wider audience of pilots would provide additional information regarding perceptions of hypoxia training.

Adult↗
PubMed2005

Altitude negates the benefits of aerobic training on the vascular adaptations in rats.

INTRODUCTION: This study questioned the effect of living and training at moderate altitude on aortic vasoreactivity. Considering that chronic hypoxia exposure and endurance training are able to generate opposite effects on the systemic vascular reactivity, it was hypothesized that endurance training benefits on the vascular function could be limited by chronic hypoxia. METHODS: Sea-level native rats were randomly assigned to N (living in normoxia), NT (living and training 5 d.wk for 5 wk in normoxia), CH (living in hypoxia, 2800 m), and CHT (living and training 5 d.wk for 5 wk in hypoxia, 2800 m) groups. Concentration response curves to epinephrine, norepinephrine, endothelin-1, acetylcholine, and sodium nitro-prusside were assessed on aortic isolated rings. Left ventricular resting and maximal (during Tyrode's infusion) stroke volumes were evaluated by Doppler-echocardiography and used as indexes of chronic aortic volume overload. RESULTS: The main finding was that favorable aortic vasoreactivity adaptations consecutive to sea-level training were not observed when training was conducted at altitude. An improvement in the endothelium-dependent vasorelaxation (maximal relaxation, R(max), N = 60.4 +/- 10.0 vs NT = 91.7 +/- 3.2%; P < 0.05) and a reduced sensitivity to ET-1 were observed in NT rats. Such an enhancement in endothelium-dependent vasorelaxation was not found in CHT rats (R(max): 48.4 +/- 7.8%). Moreover, a higher sensitivity to ET-1 was reported in this group. Altitude-induced limitation in aortic blood flow and shear stress could play a major role in the explanation of these specific altitude-training adaptations. CONCLUSION: If extrapolated to the peripheral vascular bed, our results have practical significance for aerobic performance as aortic vasoreactivity adaptations after altitude training could contribute to limit blood delivery to exercising muscles.

Adaptation, Physiological↗