Since the beginning of the Himalayan climbing era, the anecdotal extraordinary physical performance at high altitude of Sherpas and Tibetans has intrigued scientists interested in altitude adaptation. These ethnic groups may have been living at high altitude for longer than any other population, and the hypothesis of a possible evolutionary genetic adaptation to altitude makes sense. Reviewed here is the evidence as to whether Tibetans are indeed better adapted for life and work at high altitude as compared to other populations and, if so, whether this better adaptation might be inborn. Tibetans, compared to lowlanders, maintain higher arterial oxygen saturation at rest and during exercise and show less loss of aerobic performance with increasing altitude. Tibetans have greater hypoxic and hypercapnic ventilatory responsiveness, larger lungs, better lung function, and greater lung diffusing capacity than lowlanders. Blood hemoglobin concentration is lower in Tibetans than in lowlanders or Andeans living at similar altitudes. Tibetans develop only minimal hypoxic pulmonary hypertension and have higher levels of exhaled nitric oxide than lowlanders or Andeans. Tibetans' sleep quality at altitude is better and they desaturate less at night. Several of these findings are also found in Tibetans born at low altitude when exposed for the first time to high altitude once adult. In conclusion, Tibetans indeed seem better adapted to life and work at high altitude, and this superior adaptation may very well be inborn, even though its exact genetic basis remains to be elucidated.
750 mg per day of acetazolamide in the prevention of acute mountain sickness (AMS), as recommended in the meta-analysis published in 2000 in the British. Medical Journal, may be excessive and is controversial. To determine if the efficacy of low-dose acetazolamide 125 mg bd (250 mg), as currently used in the Himalayas, is significantly different from 375 mg bd (750 mg) of acetazolamide in the prevention of AMS, we designed a prospective, double-blind, randomized, placebo-controlled trial. The participants were sampled from a diverse population of (non-Nepali) trekkers at Namche Bazaar (3440 m) in Nepal on the Everest trekking route as they ascended to study midpoints (4280 m/4358 m) and the endpoint, Lobuje (4928 m), where data were collected. Participants were randomly assigned to receive 375 mg bd of acetazolamide (82 participants), 125 mg bd of acetazolamide (74 participants), or a placebo (66 participants), beginning at 3440 m for up to 6 days as they ascended to 4928 m. The results revealed that composite AMS incidence for 125 mg bd was similar to the incidence for 375 mg bd (24% vs. 21%, 95% confidence interval, -12.6%,19.8%), in contrast to significantly greater AMS (51%) observed in the placebo group (95% confidence interval for differences: 8%, 46%; 12%, 49% for low and high comparisons, respectively). Both doses of acetazolamide improved oxygenation equally (82.9% for 250 mg daily and 82.8% for 750 mg daily), while placebo endpoint oxygen saturation was significantly less at 80.7% (95% confidence interval for differences: 0.5%, 3.9% and 0.4%, 3.7% for low and high comparisons, respectively). There was also more paresthesia in the 375-mg bd group (p < 0.02). We conclude that 1.25 mg bd of acetazolamide is not significantly different from 375 mg bd in the prevention of AMS; 125 mg bd should be considered the preferred dosage when indicated for persons ascending to altitudes above 2500 m.
Rupert, Jim L., and Michael S. Koehle. Evidence for a genetic basis for altitude-related illness. High Alt. Med. Biol. 7:150-167, 2006.-Altitude-related illnesses are a family of interrelated pulmonary, cerebral, hematological, and cardiovascular medical conditions associated with the diminished oxygen availability at moderate to high altitudes. The acute forms of these debilitating and potentially fatal conditions, which include acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE), often develop in incompletely acclimatized lowlanders shortly after ascent, whereas, the chronic conditions, such as chronic mountain sickness (CMS) and high altitude pulmonary hypertension (HAPH), usually afflict native or long-term highlanders and may reflect a loss of adaptation. Anecdotal reports of particularly susceptible people or families are frequently cited as evidence that certain individuals have an innate susceptibility (or resistance) to developing these conditions and, in recent decades, there have been a number of studies designed to characterize the physiology of individuals predisposed to these conditions, as well as to identify the specific genetic variants that contribute to this predisposition. This paper reviews the epidemiological evidence for a genetic component to the various forms of altitude-related illness, such as innate susceptibility, familial clustering, and patterns of population susceptibility, as well as the molecular evidence for specific genetic risk factors. While the evidence supports some role for genetic background in the etiology of altitude-related illness, limitations in individual studies and a general lack of corroborating research limit the conclusions that can be drawn about the extent of this contribution and the specific genes or pathways involved. The paper closes with suggestions for future work that could support and expand on previous studies, as well as provide new insights.
Some studies have found different distribution patterns for the lipid profile of high altitude populations, having found the majority of them a more favorable one in these subjects. The objective of this study is to describe the lipid profile of a high altitude population and relate it to the waist circumference, body mass index, gender, and age. A descriptive study was done in an adult population, 30 yr old and above, of the town of San Pedro de Cajas (SPC), Peru, located at 4100 m (13,450 ft) above sea level. One hundred and two representative individuals (38 males and 64 females) were included. HDL cholesterol and triglyceride means were elevated, whereas total cholesterol means were average, and LDL cholesterol means were low. The BMI mean was 25.4 +/- 3.7. We observed a high prevalence of hypercholesterolemia (34.3%) and hypertriglyceridemia (53.9%) in both genders. Higher prevalences of low HDL (45.3%), abnormal waist circumference (64%), and obesity (14.1%) were found in women (p < 0.001). A higher prevalence of low HDL in overweight/ obese (74.2%) and abnormal waist circumference (77.4%) subjects was evident (p < 0.001). We found high prevalences of hypercholesterolemia and hypertriglyceridemia for both genders and important prevalences of risk factors for cardiovascular disease and coronary heart disease, such as hypertriglyceridemia, low HDL, abnormal waist circumference, and obesity, in high altitude natives, especially in women.
The Sherpas' adaptation to high altitude has been hypothesized as being due to a genetic basis since the beginning of the last century, but this has yet to be demonstrated. We randomly enrolled 105 Sherpas in Namche Bazaar (3440 m) and 111 non-Sherpa Nepalis in Kathmandu (1330 m) in Nepal. The genotypes of Glu298Asp and eNOS4b/a polymorphisms of the endothelial nitric oxide synthase (eNOS) gene were identified. The metabolites of nitric oxide (NO,: nitrite and nitrate) in serum were measured. The frequencies of the Glu and eNOS4b alleles were significantly higher in Sherpas (Glu: 87.5%; eNOS4b: 96.7%) than in non-Sherpas (Glu: 77.9%, p = 0.036; eNOS4b: 90.5%, p = 0.009). In addition, the combination of the wild types of Glu298GIu and eNOS4blb was significantly greater in Sherpas (66.7%) than non-Sherpas (47.7%, p = 0.008). However, the serum NO, was significantly lower in Sherpas (53.2 +/- 4.6 mu mol/L) than in non-Sherpas (107.3 +/- 9.0 mu mol/L, p < 0.0001). The wild alleles of the Glu298Asp and eNOS4b/a polymorphisms of the eNOS gene may be a benefit for the Sherpas, adaptation to high altitude. The nitric oxide metabolites (NOx) in serum vary individually, thus it is not a reliable indicator for endogenous nitric oxide production.
Wu, Tianyi, Shouquan Ding, Jinliang Liu, Jianhou Jia, Ruichen Dai, Baozhu Liang, Jizhui Zhao, and Detang Qi. Ataxia: an early indicator in high altitude cerebral edema. High Alt. Med. Biol. 7:275-280, 2006.-As a result of industrial development in the western region of China, in 2001 the Chinese government decided to build Qinghai-Tibetan Railway. The new railroad stretches 1118 km from Golmud (2808 m) to Lhasa (3658 m), with more than three-quarter of the distance above 4000 m, through the Mt. Kun Lun and Tanggula ranges. From the beginning of the project on June, 29, 2001, to the end of the year of 2003, about 74,735 construction workers worked in the harsh climate, in adverse circumstances and a low-barometric-pressure environment. The construction provided an opportunity for the investigation and study of acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE). These altitude illnesses were very common in the construction workers. From July 1, 2001, to October 31, 2003, the overall incidence of AMS, HAPE, and HACE in the total workers was approximately 45%-95%, 0.49%, and 0.26%, respectively. Altitude illnesses were studied at two hospitals near the construction site. One hospital is located on the Fenghuoshan (Mt. Wind-gap) at an altitude of 4779 m (PB 428 torr), and the second hospital is situated in the Kekexili area at an altitude of 4505 m (PB 440 torr). Kekexili is a sparsely populated zone because the weather conditions are very bad all year round. These two hospitals received patients from the construction sites, where workers were working at altitudes between 4464 and 4905 m. A total of 8014 workers were treated at Fenghuoshan and 5488 were in Kekexili over the past 3 years. According to local guidance about proper medical care, workers ascending to high altitude should be examined physically, complete an AMS questionnaire, and be monitored for ataxia as an early warning sign of the impending, more serious aspects of HACE. The onset of HACE is frequently characterized by an ataxic gait, as reported since the middle of the 20th century (Gray et al., 1971; Wilson, 1973; Houston and Dickinson, 1975; Dickinson, 1979; Clarke, 1988; Hackett and Oelz, 1992; Hackett, 2002; Hackett and Roach, 2004). However, there are no detailed analyses of ataxia in HACE. This paper considers the relation between ataxia and HACE and its frequency, significance, and importance.
Koehle, Michael S., Pei Wang, Jordan A. Guenette, and Jim L. Rupert. No association between variants in the ACE and angiotensin II receptor I genes and acute mountain sickness in Nepalese pilgrims to the Janai Purnima Festival at 4380 m. High Alt. Med. Biol. 7:281-289, 2006.-Acute mountain sickness (AMS) causes significant morbidity among visitors to altitude. The primary contributors to developing AMS are altitude and rate of ascent; however, the substantial variation in susceptibility between individuals has led a number of investigators to propose that there may be genetic predilection to the disease. The ACE I/D polymorphism has been shown to predict performance among elite mountaineers. This study compares genotype and allele frequencies at the ACE I/D locus, two other loci in the ACE gene, and one locus in the angiotensin-2 receptor gene between individuals who did, or did not, express signs of AMS while attending a high altitude religious festival in Nepal (4380 m). Subjects (80 males, 23 females) were recruited and genotyped. All subjects were Nepalese. Forty-four of the subjects had been diagnosed with AMS by physicians at a high altitude health camp; the rest were free from altitude illness. All subjects were genotyped at polymorphic loci in the genes encoding angiotensin converting enzyme (ACE) and angiotensin II receptor type I gene (AGTRI). The polymorphisms examined were two single nucleotide polymorphisms (SNPs) in ACE (ACE(A-240T), dbSNP rs4291; and ACE(A2350G), dbSNP rs4343), the intronic Alu insertion in ACE (ACE I/D), and the SNP ATR(A1166C), (dbSNP rsl7231380) in AGTR1d. All polymorphisms in ACE were found to be in linkage disequilibrium. No significant associations were found between AMS incidence and any of the alleles, suggesting that variants at these loci do not contribute to susceptibility to AMS in this population.
Vargas P., Enrique, and Hilde Spielvogel. Chronic mountain sickness, optimal hemoglobin, and heart disease. High Alt. Med. Biol. 7:138-149, 2006.-For the male inhabitants of La Paz, Bolivia (3200-4100 m), and other high altitude regions in America and Asia, chronic mountain sickness (CMS) is a major health problem. Since CMS was first described by Carlos Monge in the Peruvian Andes in 1925, numerous research papers have been devoted to this topic, but many unanswered questions still exist with respect to the beginning of the disease and its cause(s). The experience with CMS has shown that an excessively high hemoglobin concentration is not favorable for high altitude acclimatization, and the hypothesis of theoretically "optimal" hematocrit and "optimal" hemoglobin has been made. The calculated optimal hemoglobin concentration of 14.7 g/dL for resting men in the Andes is discussed as theoretical and not applicable in real life. The most frequent congenital and acquired heart diseases are discussed, such as patent ductus, atrial septum defect, ventricle septum defect among congenital heart diseases and the still very frequent rheumatic valve cardiopathies and Chagas disease as acquired cardiopathies. Among the typical acquired heart diseases of the high altitude dweller, special attention is given to chronic cor pulmonale as a consequence of severe CMS with pulmonary hypertension.
Fabiola Leon-Velarde and Jean-Paul Richalet. Respiratory control in residents at high altitude: physiology and pathophysiology. High Alt. Med. Biol. 7:125-137, 2006.-Highland population (HA) from the Andes, living above 3000 in, have a blunted ventilatory response to increasing hypoxia, breathe less compared to acclimatized newcomers, but more, compared to sea-level natives at sea level. Subjects with chronic mountain sickness (CMS) breathe like sea-level natives and have excessive erythrocytosis (EE). The respiratory stimulation that arises through the peripheral chemoreflex is modestly less in the CMS group when compared with the HA group at the same P-ETO2. With regard to CO2 sensitivity, CMS subjects seem to have reset their central CO2 chemoreceptors to operate around the sea-level resting P-ETCO2. Acetazolamide, an acidifying drug that increases the chemosensitivity of regions in the brain stem that contain CO2/H+-sensitive neurons, partially reverses this phenomenon, thus, providing CMS subjects with the possibility to have high CO2 changes, despite small changes in ventilation. However, the same type of adjustments of the breathing pattern established for Andeans has not been found necessarily in Asian humans and/or domestic animals nor in the various high altitude species studied. The differing time frames of exposure to hypoxia among the populations, as well as the reversibility of the different components of the respiratory process at sea level, provide key concepts concerning the importance of time at high altitude in the evolution of an appropriate breathing pattern.
Greksa, Lawrence P. Growth and development of Andean high altitude residents. High Alt. Med. & Biol. 7:116-124, 2006.-Growth and development under conditions of chronic hypoxia result in a different pattern of growth in Andean highlanders than in lowlanders. Growth at high altitude results in a small (I to 4 cm) delay in linear growth, with most, if not all, of the delay probably established at or soon after birth. It also results in an enhancement of lung volumes, particularly residual volume, which is 70%-80% larger in highland than lowland children, on average, with the magnitude of the increase being positively related to age. In addition, growth and development under conditions of chronic hypoxia result in a blunted ventilatory response to hypoxia, a 4% to 5% reduction in Sa(O2), and a substantial increase in pulmonary diffusing capacity. Andean highlanders have V-O2 max Similar to that of lowlanders at low altitude, suggesting that they have successfully adapted to their hypoxic environment. It is likely that both developmental and genetic factors influence most, if not all, components of the cardiorespiratory system of Andean highlanders, but the relative importance of each is not clear.
Farias, Jorge G., Jorge Osorio, Gustavo Soto, Julio Brito, Patricia Siques, and Juan G. Reyes. Sustained acclimatization in Chilean mine workers subjected to chronic intermittent hypoxia. High Alt. Med. Biol. 7:302-306, 2006-We wanted to know if sea-level mine workers exposed previously to chronic intermittent hypoxia reached a steady acclimatization at 36 months under hypobaric hypoxia. An intermittently exposed group of mine workers (IE, n = 25) were subjected to submaximal exercise (100 W) at 4500 m. Their systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and hemoglobin oxygen saturation (HbSatO(2)) were monitored. Two comparison groups of unacclimatized sea-level workers (n = 17) were studied. A nonexposed group (NE) performed 5 min of submaximal exercise at sea level. Some kind of exercise was performed both by an acutely exposed group (AE) and IE group at 4500 m. No statistical differences were found for HR, SBP, and DBP (p > 0.05) during exercise between IE and AE groups. Resting HbSatO(2) of IE (87 +/- 6%) was lower than NE (97 +/- 3%) (p < 0.05), but was higher than AE (82 +/- 4%) (p < 0.05). In the exercise condition, HbSatO(2) of IE (85 +/- 5%) was lower than NE (95 +/- 3%) (p < 0.05), but was higher than AE (76 +/- 2%) (p < 0.05). These responses were maintained through the 6 months of the study period. Thus, mine workers subjected to intermittent hypobaric condition for 3 years showed a good degree of acclimatization that was maintained through time.
Previous studies have reported that glucose tolerance can be improved by short-term altitude living and activity. However, not all literature agrees that insulin sensitivity is increased at altitude. The present study investigated the effect of a 25-day mountaineering activity on glucose tolerance and its relation to serum levels of dehydroepiandrosterone-sulfate (DHEA-S) and tumor necrosis factor-alpha (TNF-alpha) in 12 male subjects. On day 3 at altitude, we found that serum DHEA-S was reduced in the subjects with initially greater DHEA-S value, whereas the subjects with initially lower DHEA-S remained unchanged. To further elucidate the role of DHEA-S in acclimatization to mountaineering activity, all subjects were then divided into lower and upper halves according to their sea-level DHEA-S concentrations: low DHEA-S (n = 6) and high DHEA-S groups (n = 6). Glucose tolerance, insulin level, and the normal physiologic responses to altitude exposure, including hematocrit, hemoglobin, erythropoietin (EPO), and cortisol were measured. We found that glucose and insulin concentrations on an oral glucose tolerance test were significantly lowered by the mountaineering activity only in the high DHEA-S group. Similarly, hematocrit and hemoglobin concentration in altitude were increased only in the high DHEA-S group. In contrast, the low DHEA-S subjects exhibited an EPO value at sea level and altitude greater than the high DHEA-S group, suggesting an EPO resistance. The findings of the study imply that DHEA-S is essential for physiologic acclimatization to mountaineering challenge.
Vuyk, Jaap, Jan Van Den Bos, Kees Terhell, Rene De Bos, Ad Vletter, Pierre Valk, Martie Van. Beuzekom, Jack Van Kleef, and Albert Dahan. Acetazolamide improves cerebral oxygenation during exercise at high altitude. High Alt. Med. Biol. 7:290-301, 2006.-Acute mountain sickness is thought to be triggered by cerebral hypoxemia and be prevented by acetazolamide (Actz). The effect of Actz on cerebral oxygenation at altitude remains unknown. In 16 members of the 2005 Dutch Cho Oyu (8201 m, Tibet) expedition, the influence of Actz and exercise (750 mg PO daily) on heart rate, peripheral and regional cerebral oxygen saturation (Sa(O2) and rS(O2)). the Lake Louise score (LLS), and psychornotor function were studied at 0 m 14 days prior to the expedition, after arrival at 3,700 m on day 3, after arrival at 5700 m on day 29, and again at 5700 m before the end of the expedition on day 51. After arrival at 3700 m, the LLS of the climbers taking Actz (n = 8) was significantly lower compared to those who did not take Actz (n = 8): 0.75 +/- 1.0 versus 2.9 +/- 2.0, p < 0.05 (ANOVA). High LLSs were associated with low rS(O2) values in rest and exercise (p < 0.01 and p < 0.001). With altitude, resting Sa(O2) and resting rS(O2) decreased significantly (p < 0.001), irrespective of Actz use. Exercise at 3700 In and 5700 m reduced Sa(O2) and rS(O2) even further compared to rest (p, < 0.001), although at 3700 m the rS02 was preserved better in those who took Actz (55.3 +/- 4.3% versus 47.9 +/- 5.7%, p < 0.05). Irrespective of Actz use, with altitude, the percentage of omissions in the vigilance and tracking test increased while the climbers' scores on vigor decreased (p < 0.05). In conclusion, at altitude, exercise-induced reduction in cerebral oxygenation is less in climbers on Actz compared to climbers not taking Actz. This effect is nullified after several weeks at altitude due to acclimatization in climbers not taking Actz.
Marconi, Claudio, Mauro Marzorati, and Paolo Cerretelli. Work capacity of permanent residents of high altitude. High Alt. Med. Biol. 7:105-115, 2006.-Tibetan and Andean natives at altitude have allegedly a greater work capacity and stand fatigue better than acclimatized lowlanders. The principal aim of the present review is to establish whether convincing experimental evidence supports this belief and, should this be the case, to analyze the possible underlying mechanisms. The superior work capacity of high altitude natives is not based on differences in maximum aerobic power (V-O2 peak, mL kg(-1) min(-1)). In fact, average V-O2 (peak) of both Tibetan and Andean natives at altitude is only slightly, although not significantly, higher than that of Asian or Caucasian lowlanders resident for more than 1 yr between 3400 and 4700 in (Tibetans, n = 152, vs. Chinese Hans, n = 116: 42.4 +/- 3.4 vs. 39.2 +/- 2.6 mL kg(-1)min(-1), mean +/- SE; Andeans, n = 116, vs. Caucasians, n = 70: 47.1 +/- 1.7 vs. 41.6 +/- 1.2 mL kg(-1)min(-1)). However, compared to acclimatized lowlanders, Tibetans appear to be characterized by a better economy of cycling, walking, and running on a treadmill. This is possibly due to metabolic adaptations, such as increased muscle myoglobin content and antioxidant defense. All together, the latter changes may enhance the efficiency of the muscle oxidative metabolic machinery, thereby supporting a better prolonged submaximal performance capacity compared to lowlanders, despite equal V-O2 (peak). With regard to Andeans, data on exercise efficiency is scanty and controversial and, at present, no conclusion can be drawn as to the origin of their superior performance.
Previous genetic association studies in high-risk subjects have suggested that polymorphisms in the gene encoding endothelial nitric oxide synthase (eNOS) may be associated with susceptibility to high altitude pulmonary edema (HAPE). We aimed to determine whether eNOS polymorphisms influence systolic pulmonary artery pressure measurements (PASP) in healthy trekkers ascending to high altitude. We examined two polymorphisms of the eNOS gene in Caucasian volunteers: Glu298Asp variant and 27-base pair (bp) variable number of tandem repeats polymorphism (27-bp VNTR). In 33 subjects, the relationships between polymorphisms and absolute pulmonary artery systolic pressure measurements (PASP), determined by echocardiography, were assessed at sea level and 1, 3, and 7 days after acute ascent by vehicle transport to 5200 m. As expected, there was a significant rise in pulmonary artery pressure on ascent to high altitude. By contrast, at sea level and at each time point at high altitude, no difference was found in mean PASP according to eNOS polymorphism. We found no association of Glu298Asp and 27-bp VNTR polymorphisms in the eNOS gene with PASP in a population of healthy trekkers at low or high altitude.
The aim of this study was to evaluate the effects of two periods of intermittent exposure to hypoxia (428 torr) in rats over 12 months. The conditions of CIH4X4 (4 days in hypoxia, 4 days in normoxia, n = 50) and CIH2X2 (2 days in hypoxia, 2 days in normoxia, n = 50) were selected for simulating in this animal model the chronic-intermittent exposure to high altitudes experienced by Andean miners. We assessed mortality, weight, hematological parameters, and time course of resting heart rate and systolic blood pressure. In general, mortality increased during the first month, with a tendency to stabilize during exposure; it was associated with lower weights and with higher hematocrit levels, making these possible predictor factors. Intermittence produced an increase in hematocrit and hemoglobin concentrations as previously seen in most hypoxic models, compared with normoxia (NX, n = 30), but attained lower levels compared with chronic hypoxia (CH, n = 28). CIH4 X 4 and CIH2 X 2 had similar sustained elevations of systolic blood pressure (171 +/- 3 and 174 +/- 2 mmHg, respectively) versus the basal level (163 +/- 3; 163 +/- 3 mmHg), whereas CH did not. Heart rate suffered an equally sustained decrease in all exposed groups (343 +/- 14 beats/min). Exposure to chronic-intermittent hypoxia led to a mild polycythemia and to a decrease in heart rate. The effects of hypoxia were already evident during the first month of exposure and attained a more pronounced expression and stabilization during the third month.
Windsor, Jeremy S., and George W. Rodway. Supplemental oxygen and sleep at altitude. High Alt. Med. Biol. 7:307-311, 2006.-The purpose of this study was to examine the effect supplemental oxygen has on the respiratory and cardiovascular system of a mountaineer during sleep at high altitude by using a novel ambulatory, multisensor, continuous monitoring device. Supplemental oxygen was administered to a healthy subject via a nasal demand system (0, 16.7, 33.3, or 50 mL/sec per pulse dose delivered over 1 sec) during the first three nights of sleep at 4900 and 5700 m. Increases in pulse dose resulted in a consistent rise in Sa(O2) and a fall in minute ventilation (p < 0.05). The 50-mL pulse dose resulted in the greatest changes, with an increase in Sa02 from 68.5% to 81% (p < 0.05) and a fall in minute ventilation from 13.1 to 10.9 L/min (p < 0.05) being noted. Changes in Sa(O2) and minute ventilation also coincided with a fall in apnea/hypopnea index (AHI). At 4900 rn the AHI fell from 12.5-52.3 (breathing air) to 0-7.5 (50mL oxygen pulse), whereas at 5700 m a decrease from 49.1-80.4 to 3.5-10.0 was observed. No changes in respiratory rate or heart rate were identified when different pulse doses were compared (p < 0.05). The multisensor monitoring device proved to be a highly effective system, demonstrating marked improvements in Sa(O2), tidal volume, and AHI in our participant when supplemental oxygen was administered via a nasal demand system.
Reduced blood flow to the gut may contribute to weight loss and gastrointestinal symptoms of acute mountain sickness (AMS) at altitude. A study in humans tested the hypothesis that acute hypobaric hypoxia (ALT) would attenuate the normal postprandial hyperemia in the superior mesenteric artery (Q(SM)). Blood pressure, cardiac output (CO), and Q(SM) were measured with previously validated noninvasive Doppler ultrasonic flowmetry in 9 (3 women) healthy young adults (mean age: 23; range: 18-33 yr) residing at 1700 m. Baseline measurements were made after 2 h at ALT in a chamber at 430 mmHg (approximate to 4800 m = 15,750 ft) after 10-12-h fasting, and the next day the control (CON) measurements were made at 615 mmHg (1850 m). Postprandial measurements were made 45 to 60 min after ingesting a 1000-cal liquid meal under both conditions. At ALT, 5 of the 9 subjects had AIMS by the Lake Louise score criteria of headache >= 1 and total score >= 3. ALT significantly reduced fasting, baseline Q(SM) relative to CON by 15%, and increased CO by 16%. The postprandial CO increase was not different between ALT and CON, but Q(SM) increased 115% at CON, but only 75% at ALT, the attenuation being significant (p < 0.006). Neither the diminution of fasting QSM at ALT nor the attenuation of the postprandial increase in Q(SM) correlated significantly with AMS symptom scores. These results suggest that baseline and postprandial gut blood flow are altered during acute altitude exposure because of increased intestinal sympathetic tone, inferred from increased local resistance, and may be related to reduced energy intake if sustained during prolonged exposure.
Huicho, Luis, and Susan Niermeyer. Cardiopulmonary pathology among children resident at high altitude in Tintaya, Peru: A cross-sectional study. High Alt. Med. Biol. 7:168-179, 2006.-Symptomatic high-altitude pulmonary hypertension and structural cardiac abnormalities related to high altitude have been reported previously. However, their true prevalence has not been systematically determined. We assessed clinical indicators of cardiovascular health or disease and correlated them with anatomic and physiologic cardiovascular features in preschool and schoolchildren living at 4000 m. We also estimated the prevalence of cardiovascular problems in the population, with emphasis on symptomatic high altitude pulmonary hypertension and structural cardiopathies. Three hundred and twenty-six children residents of Tintaya, Peru, were cross-sectionally studied. Methods included structured interviews, anthropometry and physical examination, arterial oxygen saturation, hemoglobin determination, electrocardiography, and echocardiography. The prevalence of structural cardiac problems was 1.5%, with less than 1% possibly attributable to high altitude. All children with structural cardiac abnormalities were identified by a focused physical exam prior to echocardiography. None were identified by the health interview. No symptomatic high altitude pulmonary hypertension was identified in the absence of underlying structural anomalies. The prevalence of structural cardiac problems was consistent with data from sea level. Active monitoring of the health status of a pediatric population at high altitude is valuable in the timely detection of cardiac abnormalities. Although our study children enjoyed generally excellent health, comparative, longitudinal studies are warranted to determine the incidence of high altitude cardiopulmonary problems and to identify risk factors and early markers for later disorders associated to life at high altitude. Our findings are applicable to children with some degree of high altitude genetic background and high mobility patterns to lower altitudes and living in comparatively good nutritional and socioeconomic conditions.
Droma, Yunden, Masayuki Hanaoka, Buddha Basnyat, Amit Arjyal, Pritam Neupane, Anil Pandit, Dependra Sharma, and Keishi Kubo. Symptoms of acute mountain sickness in Sherpas exposed to extremely high altitude. High Alt. Med. Biol. 7:312-314, 2006.-The aim of this fieldinterview was to investigate the current state of affairs concerning acute mountain sickness (AMS) in high-altitude residents, specifically the Sherpas at 3440 m above sea level, when they are exposed rapidly to altitudes significantly higher than their residing altitudes. Out of 105 Sherpas (44 men and 61 women, 31.2 +/- 0.8 yr), 104 had mountain-climbing experiences to 5701.4 +/- 119.1m altitude in average 3.5 times each year. On the other hand, only 68 out of 111 non-Sherpas (29.9 +/- 0.8 yr) had experience of 1.4 +/- 1.5 climbs to an average 2688.6 +/- 150.4-m altitude in their mountaineering histories (p < 0.0001). Among the 104 Sherpas, 45 (43.3%) complained of at least one AMS symptom (headache, gastrointestinal symptoms, weakness, dizziness, and difficulty sleeping) in their experiences of mountaineering at an average 5518.9 +/- 195.9-m altitude. And 16 out of the 68 non-Sherpas (23.5%) reported the AMS symptoms at a mean altitude of 2750.0 +/- 1288.8 m. Moreover, we also noticed that the Sherpa women showed a significantly higher Sa(O2) (93.9 +/- 0.2%) than did Sherpa men (92.4 +/- 0.3%, p = 0.0001) at an altitude of 3440 m. The brief field interview evidenced that Sherpas might suffer from AMS when exposed to altitudes significantly higher than their residing altitude.