Effect Of High-altitude Exposure Research Articles

Effect of High-Altitude Exposure on the Heart

High altitude brings a great physiological change in human beings, both during short-term exposure and in lifelong residents, especially in the cardiovascular system. Hypoxia notably induces pulmonary vasoconstriction, thus resulting in a moderate increase in pulmonary arterial pressure. Acclimatized inhabitants exhibit lower pulmonary pressure and better exercise capacity than lowlanders during short-term high-altitude exposure. Rapid ascent to high altitude without adequate acclimatization can cause high-altitude pulmonary edema in susceptible individuals, with a rapid increase in pulmonary pressure. Cardiac output increases initially following acute high-altitude exposure and returns to normal as at sea level after a few days of acclimatization. Ventricular volumes at high altitude change consistently with decreases in plasma volume. Left ventricular systolic function is enhanced after acute high-altitude exposure and during chronic acclimatization. However, there are controversies on whether right ventricular systolic function is preserved or decreases after high-altitude exposure, probably due to variable hypoxic pulmonary vasoconstriction. High altitude induces altered ventricular diastolic patterns. Recently, a new perspective has emerged, whereby ventricular intrinsic relaxation is not impaired, as assessed by untwisting through speckle-tracking imaging. Persistent hypoxic pulmonary hypertension probably induced right ventricular dilation and hypertrophy, and even right heart failure, described as high-altitude heart diseases. Descent to lower altitude should be the best treatment for them, and potential pharmacological agents majorly focus on the inhabitation of pulmonary vasoconstriction, such as phosphodiesterase-5 inhibitors and endothelin receptor antagonists. Evidence on the risks of high-altitude exposure for patients with previous cardiovascular diseases is limited, and thus they should be prudent when ascending to high altitude. Further randomized large-scale studies are needed to explore cardiac performance at high altitudes and provide more evidence for the prevention and clinical management of medical complications at high altitude.

POS-256 EFFECTS OF HIGH ALTITUDE EXPOSURE ON SERUM HEMOGLOBIN LEVELS IN PATIENTS WITH CHRONIC KIDNEY DISEASE ON HEMODIALYSIS

In recent years, the study of the physiological mechanisms related to the hypoxia-inducible factor (HIF) has allowed the development of new therapeutic alternatives for the management of this condition, however, the particularities of the function of this molecule in high altitude environments are not well elucidated, although there are data on a lower prevalence of anemia in native high altitude patients with chronic kidney disease (CKD) on hemodialysis (HD), there is no information about the effect of high altitude exposure in those from low places.

Assessment of right atrial dyssynchrony by 2D speckle-tracking in healthy young men following high altitude exposure at 4100 m.

BackgroundHigh altitude exposure induces overload of right-sided heart and may further predispose to supraventricular arrhythmia. It has been reported that atrial mechanical dyssynchrony is associated with atrial arrhythmia. Whether high altitude exposure causes higher right atrial (RA) dyssynchrony is still unknown. The aim of study was to investigate the effect of high altitude exposure on right atrial mechanical synchrony.MethodsIn this study, 98 healthy young men underwent clinical examination and echocardiography at sea level (400 m) and high altitude (4100 m) after an ascent within 7 days. RA dyssynchrony was defined as inhomogeneous timing to peak strain and strain rate using 2D speckle-tracking echocardiography.ResultsFollowing high altitude exposure, standard deviation of the time to peak strain (SD-TPS) [36.2 (24.5, 48.6) ms vs. 21.7 (12.9, 32.1) ms, p<0.001] and SD-TPS as percentage of R–R’ interval (4.6 ± 2.1% vs. 2.5 ± 1.8%, p<0.001) significantly increased. Additionally, subjects with higher SD-TPS (%) at high altitude presented decreased right ventricular global longitudinal strain and RA active emptying fraction, but increased RA minimal volume index, which were not observed in lower group. Multivariable analysis showed that mean pulmonary arterial pressure and tricuspid E/A were independently associated with SD-TPS (%) at high altitude.ConclusionOur data for the first time demonstrated that high altitude exposure causes RA dyssynchrony in healthy young men, which may be secondary to increased pulmonary arterial pressure. In addition, subjects with higher RA dyssynchrony presented worse RA contractile function and right ventricular performance.

Central Corneal Thickness of Healthy Lowlanders at High Altitude: A Systematic Review and Meta-Analysis

ABSTRACTPurpose: Central corneal thickness, a marker of corneal hydration and metabolism, was reported to increase at high elevations. This study aimed to assess the effect of chronic high-altitude exposure on the central corneal thickness of healthy lowlanders with unoperated corneas, and determine if a relationship exists between exposure time and corneal edema formation.Materials and Methods: The PubMed, Embase, Scopus, Cochrane Library, and Airiti Library databases were searched up to 2017 January 31 for prospective cohort studies performed above 2500 m in healthy lowlanders with measurements of the central corneal thickness. Subjects with prior eye surgery, contact lens, and non-hypobaric hypoxic exposure were excluded.Results: Seven studies of 207 adults were included. The pooled effect of high-altitude exposure on the central corneal thickness for < 12 hours, 3–5 days, 6–7 days, and > 10 days was a mean difference of 13.4 (95% confidence interval: 5.1–21.6) μm with moderate heterogeneity (p < 0.05, I2 = 59%), 19.3 (95% confidence interval: 9.7–29) μm with low heterogeneity (p = 0.88, I2 = 0%), 20.4 (95% confidence interval: 10.3–30.5) μm with low heterogeneity (p = 0.73, I2 = 0%), and 30.8 (95% confidence interval: 20.4–41.2) μm with low heterogeneity (p = 0.69, I2 = 0%), respectively. Baseline differences between pre-exposure and post-exposure were not statistically significant. Regression analysis revealed a significant linear relation between high-altitude exposure time and corneal edema formation that exceeded 5% after 10 days.Conclusions: High-altitude exposure induces central corneal thickening with significant linear progression over time, whereas it takes over 10 days to reach clinical significance in healthy lowlanders with unoperated corneas, and changes in central corneal thickness are reversible after descent to lower elevations.

Effect of High Altitude Exposure on Intraocular Pressure Using Goldmann Applanation Tonometry.

The aim of the study was to quantify changes of intraocular pressure (IOP) during exposure to 4559 m using the state-of-the-art method of Goldmann applanation tonometry for IOP measurement and to detect correlations between IOP and acute mountain sickness (AMS) in a prospective manner. IOP was measured using a Goldmann applanation tonometer AT 900® (Haag-Streit, Switzerland) and central corneal thickness (CCT) with the anterior segment module of a Spectralis™ HRA+OCT® device (Heidelberg Engineering, Germany) at baseline and high altitude. Assessment of AMS was performed using the Lake Louise and AMS-C questionnaires, and Pearson's correlation coefficient was calculated for association between IOP and AMS. Raw IOP values at high altitude were not significantly changed compared to baseline. IOP adjusted to the increase in CCT at high altitude, which is known to alter IOP levels, showed a significant reduction for corrected IOP values on day 3 of exposure (morning -2.1 ± 1.2 mmHg; evening -2.3 ± 1.1 mmHg; p < 0.05). No correlation of IOP with AMS or clinical parameters (heart rate and SpO2) at high altitude was noted. IOP showed a significant reduction of IOP levels when corrected for increased CCT values at high altitude. Furthermore, the prospective measurement of IOP is not useful in diagnosing AMS or for the prediction of more severe high altitude related illnesses as the decrease in IOP and symptoms of AMS do not correlate during altitude exposure.

Going High with Heart Disease: The Effect of High Altitude Exposure in Older Individuals and Patients with Coronary Artery Disease.

Levine, Benjamin D. Going high with heart disease: The effect of high altitude exposure in older individuals and patients with coronary artery disease. High Alt Med Biol 16:89-96, 2015.--Ischemic heart disease is the largest cause of death in older men and women in the western world (Lozano et al., 2012 ; Roth et al., 2015). Atherosclerosis progresses with age, and thus age is the dominant risk factor for coronary heart disease in any algorithm used to assess risk for cardiovascular events. Subclinical atherosclerosis also increases with age, providing the substrate for precipitation of acute coronary syndromes. Thus the risk of high altitude exposure in older individuals is linked closely with both subclinical and manifest coronary heart disease (CHD). There are several considerations associated with taking patients with CHD to high altitude: a) The reduced oxygen availability may cause or exacerbate symptoms; b) The hypoxia and other associated environmental conditions (exercise, dehydration, change in diet, thermal stress, emotional stress from personal danger or conflict) may precipitate acute coronary events; c) If an event occurs and the patient is far from advanced medical care, then the outcome of an acute coronary event may be poor; and d) Sudden death may occur. Physicians caring for older patients who want to sojourn to high altitude should keep in mind the following four key points: 1). Altitude may exacerbate ischemic heart disease because of both reduced O2 delivery and paradoxical vasoconstriction; 2). Adverse events, including acute coronary syndromes and sudden cardiac death, are most common in older unfit men, within the first few days of altitude exposure; 3). Ensuring optimal fitness, allowing for sufficient acclimatization (at least 5 days), and optimizing medical therapy (especially statins and aspirin) are prudent recommendations that may reduce the risk of adverse events; 4). A graded exercise test at sea level is probably sufficient for most clinical decision making and will allow for assessment of exercise capacity, and provocable ischemia. Given these considerations, most older individuals with CHD should be able to tolerate exposure to high altitude safely, and with minimal increased risk.

Sleep quality changes in insomniacs and non-insomniacs after acute altitude exposure and its relationship with acute mountain sickness

ObjectiveWe aimed to observe the changes in subjective sleep quality among insomniacs and non-insomniacs after acute ascending to 3,700 m and its possible relationship with acute mountain sickness (AMS).MethodsA total of 600 adult men were recruited. Subjects’ subjective sleep quality was evaluated by the Athens Insomnia Scale. AMS was assessed using the Lake Louise scoring system. Arterial oxygen saturation was measured.ResultsDespite insomnia resolution in only a few subjects, the prevalence of insomnia among insomniacs remained stable at 90% after rapid ascent to 3,700 m. However, among non-insomniacs, the prevalence of insomnia sharply increased to 32.13% in the first day of altitude exposure and progressively reduced to 4.26% by the 60th day of altitude stay. Moreover, the prevalences of insomnia symptoms decreased more markedly from day 1 to day 60 at 3,700 m among non-insomniacs than among insomniacs. At 3,700 m, the prevalence of AMS among insomniacs was 79.01%, 60.49%, and 32.10% on the first, third, and seventh days, respectively, which was significantly higher than that among non-insomniacs. Multivariate regression revealed that elevated Athens Insomnia Scale scores are an independent risk factor for AMS (adjusted odds ratio 1.388, 95% confidence interval: 1.314–1.464, P<0.001), whereas high arterial oxygen saturation and long duration of altitude exposure are protective factors against AMS.ConclusionOur results suggest that the effect of high-altitude exposure on subjective sleep quality is more marked, but disappears more quickly, among non-insomniacs than among insomniacs, whereas AMS is especially common among insomniacs. Moreover, poor subjective sleep quality is a risk factor for AMS.

Effect of high altitude exposure on the hemodynamics of the bidirectional Glenn physiology: Modeling incremented pulmonary vascular resistance and heart rate

The considerable blood mixing in the bidirectional Glenn (BDG) physiology further limits the capacity of the single working ventricle to pump enough oxygenated blood to the circulatory system. This condition is exacerbated under severe conditions such as physical activity or high altitude. In this study, the effect of high altitude exposure on hemodynamics and ventricular function of the BDG physiology is investigated. For this purpose, a mathematical approach based on a lumped parameter model was developed to model the BDG circulation. Catheterization data from 39 BDG patients at stabilized oxygen conditions was used to determine baseline flows and pressures for the model. The effect of high altitude exposure was modeled by increasing the pulmonary vascular resistance (PVR) and heart rate (HR) in increments up to 80% and 40%, respectively. The resulting differences in vascular flows, pressures and ventricular function parameters were analyzed. By simultaneously increasing PVR and HR, significant changes (p <0.05) were observed in cardiac index (11% increase at an 80% PVR and 40% HR increase) and pulmonary flow (26% decrease at an 80% PVR and 40% HR increase). Significant increase in mean systemic pressure (9%) was observed at 80% PVR (40% HR) increase. The results show that the poor ventricular function fails to overcome the increased preload and implied low oxygenation in BDG patients at higher altitudes, especially for those with high baseline PVRs. The presented mathematical model provides a framework to estimate the hemodynamic performance of BDG patients at different PVR increments.

Exposure to Hypobaric Hypoxia and Reoxygenation Induces Transient Anxiety-Like Behavior in Rat

Chronic exposure to hypobaric hypoxia (HH) causes memory impairment and prolonged state of mental confusion. However, effect of high altitude exposure on mood state and its underlying mechanisms have been poorly studied. Present study was undertaken to investigate the mood state alteration following chronic exposure to HH. Male Sprague Dawley rats were divided into five groups and exposed to hypoxia for 3, 7, 14 and 21 days in an animal decompression chamber at an altitude of 25,000ft. Anxiety-and depression-like behaviors were assessed by using various mazes along with changes in serotonin and glutamate level. Our study revealed a decrease in exploratory, grooming and rearing behavior in open field test following initial exposure to HH for 7 days without affecting the locomotory behavior. Initial exposure to HH-decreased time spent in open arm of elevated plus maze indicating induction of anxiety-like behavior which normalized on prolonged hypoxic exposure for 21 days. Hypoxic exposure for 7 days induced anhedonia and increased despair behavior in rat while there was steady improvement in these behaviors when exposed for 21 days. Decrease in serotonin level was noted in hippocampus along with elevated corticosterone and glutamate level which gradually decreased on prolonged exposure to HH. These findings suggest that initial exposure to HH increases transient anxiety-like behavior in rats followed by gradual improvement in mood state on prolonged exposure. Further, the study also indicates the involvement of serotonergic system in mood state alteration at high altitude following chronic exposure and reoxygenation.

High altitude induced anorexia: Effect of changes in leptin and oxidative stress levels

High altitude (HA) exposure usually leads to a significant weight loss in non-acclimatized humans. Anorexia is believed to be the main cause of this body weight loss. Appetite regulatory peptides, i.e. leptin and neuropeptide Y play a key role in food intake and energy homeostasis. Recent studies suggests increased oxidative stress during HA exposure. In present study effect of HA exposure on levels of leptin and NPY was evaluated along with N-acetyl cysteine (NAC) and vitamin E supplementation in relation to food intake and body weight changes. The study was conducted on 30 healthy male volunteers (age 19 – 29 years). Subjects were divided randomly into three groups of 10 each. Group 1 (placebo) supplemented with 400 mg of calcium gluconate, group 2 and 3 were supplemented with 400 mg of NAC and 400 mg vitamin E, respectively per day. The study was conducted at low altitude (320 m, Phase I), at HA 3600 m (Phase II) and at an altitude of 4580 m (Phase III). On HA exposure significant reduction in plasma leptin levels was observed in all the groups on day 2 (Phase II) along with decrease in food intake and reduction in body weight. Statistically significant increase in blood malondialdehyde (MDA) levels was seen in all the groups on HA exposure (Phase II, Day 2), but the maximum increase was in case of placebo group (65.1%) on day 2 (Phase II) in comparison to low altitude values. The decrease in energy intake was almost same in all the groups indicating that antioxidant supplementation did not provide any protection against HA anorexia. From the study, it may be concluded that leptin and oxidative stress possibly are not the key players for HA anorexia.

Effect of high altitude exposure on spermatogenesis and epididymal sperm count in male rats

Effect of high altitude exposure on spermatogenesis and epididymal sperm count in male rats

Effect of high altitude exposure on spermatogenesis and epididymal sperm count in male rats.

The present study was designed to determine the effect of exposure to high altitude on spermatogenesis using transillumination technique and sperm count in male rats. In addition, the effect of oral intubation for intragastric administration of vehicle on testicular parameters in adult male rats in a schedule of 42 days was assessed. Male rats were exposed to Cerro de Pasco (Peru) at 4340 m for 3, 7, 14, 21, 28, 35 and 42 days resulting in a modification of the pattern of the seminiferous tubule stages. At day 3, stages I, IV-V, VI, VII and IX-XI were relatively shorter at high altitude than at sea level. At day 7, stages VIII, IX-XI, XII and XIII-XIV were reduced. At day 14, stages VII, VIII and IX-XI were reduced. At day 21 and 28, stages VIII, XII and XIII-XIV were significantly increased at high altitude. At day 35 an increase in stage XIII-XIV was observed. At day 42, stages II-III, IX-XI and XII were significantly increased at high altitude. Epididymal sperm count was significantly reduced at day 7 of exposure to high altitude and maintained low levels with respect to sea level up to 42 days. In conclusion, high altitude exposure affects spermatogenesis, particularly onset of mitosis and spermiation. This in turn affects epididymal sperm count.

Changes of Plasma Level of Neurotensin, Somatostatin, and Dynorphin A in Pilots under Acute Hypoxia

This study examined the effect of high-altitude exposure on the plasma levels of certain peptides in the regulation of heart and blood vessels. The plasma levels of dynorphin A, neurotensin, and somatostatin were measured in 30 pilots before and after exposure to hypoxia in an altitude chamber. The results showed that plasma concentrations of the three peptides were increased significantly after exposure to hypoxia. In the test group, 18 pilots lived on a plateau (1,725 m above sea level); the other 12 pilots lived on a plain (208 m above sea level). When exposed to hypoxia, the three peptides increased significantly in the plateau group, but in the plain group, neurotensin and dynorphin A increased but somatostatin had no significant change. These results indicate that these peptides might participate in the regulation of cardiovascular activities under hypoxia.

Effect of high-altitude exposure in the elderly: the Tenth Mountain Division study.

More than 5 million people/year over age 60 visit high altitude, which may exacerbate underlying cardiac or pulmonary disease. We hypothesized that the elderly would exhibit an impaired functional capacity at altitude, with increased myocardial ischemia compared with sea level (SL). Twenty veterans (68+/-3 years) were studied at (1) SL, (2) acute simulated altitude to 2500 m, and (3) after 5 days of acclimatization to 2500 m. With acute altitude, PaO2 and oxyhemoglobin saturation decreased and pulmonary artery pressure increased 43%, associated with sympathetic activation. VO2peak decreased 12% acutely but normalized after acclimatization. The best predictor of VO2peak with acute altitude was VO2peak at SL (r=.94). The double product that induced 1-mm ST depression during exercise with acute altitude was 5% less than SL but normalized after acclimatization. One patient with severe coronary disease sustained a myocardial infarction after an exercise test. Moderate altitude exposure in the elderly is associated with hypoxemia, sympathetic activation, and pulmonary hypertension resulting in a reduced exercise capacity that is predictable based on exercise performance at SL. Patients with coronary artery disease who are well compensated at SL do well at moderate altitude, although acutely ischemia may be provoked at modestly lower myocardial and systemic work rates. The elderly acclimatize well with normalization of SL performance after 5 days. A prudent policy would be for elderly individuals, particularly those with coronary artery disease, to limit their activity during the first few days at altitude to allow this acclimatization process to occur.

The effects of hypobaric hypoxia (50.6 kPa) on blood components in guinea-pigs

One hundred and five male (Hartley) guinea-pigs weighing 350-380 g and 30 splenectomized guinea-pigs were exposed to simulated hypobaric hypoxia of 50.6 kPa (equal to an altitude of 5486 m) for 14 days. The partial pressure of oxygen was set at half that at sea level. The white blood cell count increased significantly on day 3 of the simulated high altitude experiment but returned to normal on day 7, whereas the red blood cell count increased continuously. To study the effect of high altitude exposure on platelets, the platelet count in the splenectomized group was compared to that in a non-splenectomized group. Investigation of the resistance of red blood cell membranes to osmotic pressure under hypobaric conditions revealed a shift of the onset of haemolysis in the hyperosmotic direction. These findings may help to increase our understanding of the biochemical mechanisms of adaptation to hypobaric hypoxia.

Mountaineering accidents in the Sierra Nevada.

Two hundred and fifteen mountaineering accidents occurred in the Sierra Nevada over a 5-year period in climbers on Class V routes. Patients were evaluated for: climbing preparation and training, first aid experience, altitude acclimatization, age, anatomical site of injuries, and cause of the injury. Consideration as to evacuation procedure was also given. The effect of high altitude exposure impairs judgment and muscular coordination and implies poor acclimatization. Acute mountain sickness and hypothermia were documented in 104 patients, the majority of whom sustained injuries resulting from judgmental errors. Ninety-four injuries involved the ankle and lower tibia, an incidence similar to that seen in alpine skiing a decade ago. There were 17 deaths resulting most frequently from head injuries. Few climbers had formal training in basic mountain medicine which was reflected in the poor assessment and management of injuries, with an unnecessary reliance upon others for evacuation. Morbidity and mortality may be lessened by proper climbing preparation--instruction in mountaineering techniques as well as basic mountain medicine--and by prevention of acute mountain sickness and cold injury.