Arterial oxygen saturation in Tibetan and Han infants born in Lhasa, Tibet

Travel to high altitude during pregnancy: frequently asked questions and recommendations for clinicians

The effects of altitude on pregnancy have been extensively studied in high altitude residents, but there is a lack of knowledge concerning the pregnant altitude visitor. Exposure to hypoxia results in physiologic responses which act to preserve maternal and fetal oxygenation. However, these reactions are limited and maternal/fetal complications may be observed, especially in association with exercise. Certain pre-existing conditions or risk factors of hypertension/preeclampsia and/or fetal growth restriction are contra-indications for traveling to high altitude, especially after 20 weeks. The acclimatization process has to be respected to avoid acute mountain sickness without taking drugs, and at least a few days of acclimatization are required before exercising.

Altitude, oxygen and the definition of bronchopulmonary dysplasia

OBJECTIVE

The definition of bronchopulmonary dysplasia (BPD) among very-low birth weight (VLBW) infants is based upon oxygen requirement at 36 weeks gestation, but oxygen may be required at altitude because of hypoxia. This study determined the effect of altitude on BPD rates.

STUDY DESIGN

For 63 VLBW infants at high altitude, oxygen concentrations were measured by a hood oxygenation test (HOT) and BPD rates were determined with altitude adjustment.

RESULT

BPD rates before and after altitude adjustment were 71.8 and 26.7%, respectively. Of oxygen-dependent infants analyzed by HOT, 33.3% needed room air. HOT oxygen requirement correlated with gestational age of last apnea episode (r=0.42, P<0.001).

CONCLUSION

Although BPD rates may be adjusted for altitude with the HOT, the test does not accurately predict clinical oxygen need. Persistent requirement for supplemental oxygen beyond that needed in the HOT may be partially due to immaturity of respiratory control mechanisms.

Microtia: epidemiology and genetics

Microtia is a congenital anomaly of the ear that ranges in severity from mild structural abnormalities to complete absence of the ear, and can occur as an isolated birth defect or as part of a spectrum of anomalies or a syndrome. Microtia is often associated with hearing loss and patients typically require treatment for hearing impairment and surgical ear reconstruction. The reported prevalence varies among regions, from 0.83 to 17.4 per 10,000 births, and the prevalence is considered to be higher in Hispanics, Asians, Native Americans, and Andeans. The etiology of microtia and the cause of this wide variability in prevalence are poorly understood. Strong evidence supports the role of environmental and genetic causes for microtia. Although some studies have identified candidate genetic variants for microtia, no causal genetic mutation has been confirmed. The application of novel strategies in developmental biology and genetics has facilitated elucidation of mechanisms controlling craniofacial development. In this paper we review current knowledge of the epidemiology and genetics of microtia, including potential candidate genes supported by evidence from human syndromes and animal models. We also discuss the possible etiopathogenesis in light of the hypotheses formulated to date: Neural crest cells disturbance, vascular disruption, and altitude.

Mean oxygen saturation in well neonates at altitudes between 4498 and 8150 feet

PURPOSE

Examine changes in oxygen saturation in well neonates at altitudes from 4498 to 8150 feet with serial measurements at 12 to 24 hours of age, 36 to 48 hours, and, if still hospitalized, at 60 to 72 hours.

SUBJECTS

Convenience sample of well newborn infants meeting inclusion criteria of normal cardiopulmonary status (centrally pink with adequate perfusion) and no respiratory distress (absence of grunting, retracting, nasal flaring, or tachypnea-respiration ≤ 60/minute).

DESIGN

Nonexperimental, longitudinal, descriptive study.

METHODS

Using Masimo Radical SET monitors the SpO2 values were recorded from infant's right upper extremity to obtain a preductal measurement and then from left lower extremity for postductal measurement at study intervals.

OUTCOME MEASURE

SpO2 values.

RESULTS

The well neonates' birth weights ranged from 1835 to 4740 g [corrected], with 94.3% classified as term and 5.7% classified as preterm. At the data collection intervals based on hours of life, mean SpO2 readings at 4498 feet were 95% to 96.67%, at 6800 feet were 93.91% to 95.36%, at 7851 feet were 91.80% to 94.37%, at 7890 feet were 93.44% to 96.10%, and at 8150 feet were 93.69% to 96.25%. SpO2 readings at sites at or above 6800 feet were significantly lower than those at 4498 feet. No significant differences were noted for sleep state or season. Significant differences were noted in the first and second lower extremity readings between preterm and term neonates, with preterm SpO2 readings higher than term readings.

CONCLUSIONS

Mean oxygen saturation levels for well neonates born at higher altitudes are lower than those born at 4498 feet. Neonates born at or above 6800 feet exhibit "normal" oxygen saturation levels between 91% to 96% rather than the expected 97% found at sea level. These reference values for varying altitudes can guide clinicians to avoid hypoxemia or hyperoxia. If routine oxygen saturation screening for detection of critical congenital heart defects is implemented, these results will provide clinicians the mean values specific for additional altitudes, thus preventing unnecessary interventions when results are lower than the expected 97%.

Awake and asleep oxygen saturations in infants with chronic neonatal lung disease

AIM

There is uncertainty about the best method of withdrawing supplemental oxygen in babies with chronic neonatal lung disease (CNLD). Some authors advocate withdrawal of oxygen in the day, but continuing supplementation during sleep, based on early work suggesting that oxygen saturations are lower during sleep, which did not accord with our clinical impression. We re-examined the hypothesis that babies have lower saturations while asleep.

METHODS

We studied infants with CNLD during the day, while awake and asleep. We recorded video with simultaneous real-time capture of oxygen saturation (SpO2), heart rate and plethysmographic waveform from pulse oximetry. Behavioural state was scored using observation and video and classified as awake (feeding, active or quiet) or sleep.

RESULTS

Thirteen infants had analysable data, although one had strikingly lower SpO2 values while awake and was excluded from analysis. The infants had a median gestation of 26 weeks and were studied at a median (range) postmenstrual age of 66 (37-130) weeks, for 229 (89-330) min. Mean SpO2 was 97.6% during sleep and 97.0% awake (p=0.011).

CONCLUSION

Babies with CNLD have lower oxygen saturation while awake. There is no physiological justification for increasing oxygen during sleep, or withdrawing selectively during the daytime, although larger studies are needed to confirm this finding.

Long-term exposure to high-altitude chronic hypoxia during gestation induces neonatal pulmonary hypertension at sea level

We determined whether postnatal pulmonary hypertension induced by 70% of pregnancy at high altitude (HA) persists once the offspring return to sea level and investigated pulmonary vascular mechanisms operating under these circumstances. Pregnant ewes were divided into two groups: conception, pregnancy, and delivery at low altitude (580 m, LLL) and conception at low altitude, pregnancy at HA (3,600 m) from 30% of gestation until delivery, and return to lowland (LHL). Pulmonary arterial pressure (PAP) was measured in vivo. Vascular reactivity and morphometry were assessed in small pulmonary arteries (SPA). Protein expression of vascular mediators was determined. LHL lambs had higher basal PAP and a greater increment in PAP after N(G)-nitro-L-arginine methyl ester (20.9 ± 1.1 vs. 13.7 ± 0.5 mmHg; 39.9 ± 5.0 vs. 18.3 ± 1.3 mmHg, respectively). SPA from LHL had a greater maximal contraction to K(+) (1.34 ± 0.05 vs. 1.16 ± 0.05 N/m), higher sensitivity to endothelin-1 and nitroprusside, and persistence of dilatation following blockade of soluble guanylate cyclase. The heart ratio of the right ventricle-to-left ventricle plus septum was higher in the LHL relative to LLL. The muscle area of SPA (29.3 ± 2.9 vs. 21.1 ± 1.7%) and the protein expression of endothelial nitric oxide synthase (1.7 ± 0.1 vs. 1.1 ± 0.2), phosphodiesterase (1.4 ± 0.1 vs. 0.7 ± 0.1), and Ca(2+)-activated K(+) channel (0.76 ± 0.16 vs. 0.30 ± 0.01) were greater in LHL compared with LLL lambs. In contrast, LHL had decreased heme oxygenase-1 expression (0.82 ± 0.26 vs. 2.22 ± 0.44) and carbon monoxide production (all P < 0.05). Postnatal pulmonary hypertension induced by 70% of pregnancy at HA promotes cardiopulmonary remodeling that persists at sea level.

High-altitude disorders: pulmonary hypertension: pulmonary vascular disease: the global perspective

Globally, it is estimated that > 140 million people live at a high altitude (HA), defined as > 2,500 m (8,200 ft), and that countless others sojourn to the mountains for work, travel, and sport. The distribution of exposure to HA is worldwide, including 35 million in the Andes and > 80 million in Asia, including China and central Asia. HA stress primarily is due to the hypoxia of low atmospheric pressure, but dry air, intense solar radiation, extreme cold, and exercise contribute to acute and chronic disorders. The acute disorders are acute mountain sickness (also known as soroche), HA cerebral edema, and HA pulmonary edema (HAPE). Of these, HAPE is highly correlated with acute pulmonary hypertension. The first chronic syndrome described in HA dwellers in Peru was chronic mountain sickness (Monge disease), which has a large component of relative hypoventilation and secondary erythrocytosis. The prevalence of chronic mountain sickness in HA dwellers ranges from 1.2% in native Tibetans to 5.6% in Chinese Han; 6% to 8% in male residents of La Paz, Bolivia; and 15.6% in the Andes. Subacute mountain sickness is an exaggerated pulmonary hypertensive response to HA hypoxia occurring over months, most often in infants and very young children. Chronic pulmonary hypertension with heart failure but without hypoventilation is seen in Asia. Not only does HA pulmonary hypertension exact health consequences for the millions affected, but also the mechanisms of disease relate to pulmonary hypertension associated with multiple other disorders. Genetic understanding of these disorders is in its infancy.

Sequencing of 50 human exomes reveals adaptation to high altitude

Residents of the Tibetan Plateau show heritable adaptations to extreme altitude. We sequenced 50 exomes of ethnic Tibetans, encompassing coding sequences of 92% of human genes, with an average coverage of 18x per individual. Genes showing population-specific allele frequency changes, which represent strong candidates for altitude adaptation, were identified. The strongest signal of natural selection came from endothelial Per-Arnt-Sim (PAS) domain protein 1 (EPAS1), a transcription factor involved in response to hypoxia. One single-nucleotide polymorphism (SNP) at EPAS1 shows a 78% frequency difference between Tibetan and Han samples, representing the fastest allele frequency change observed at any human gene to date. This SNP's association with erythrocyte abundance supports the role of EPAS1 in adaptation to hypoxia. Thus, a population genomic survey has revealed a functionally important locus in genetic adaptation to high altitude.

The impact of altitude on infant health in South America

Several studies report that altitude reduces birth weight. However, much remains unknown about effects in various altitude ranges and about the heterogeneity in altitude effects by fetal health endowments. This study estimates the effects of altitude in South America on the means and quantiles of birth weight and gestational age separately for two large samples born at altitude ranges of 5 to 1,280 m and 1,854 to 3,600 m. The study finds significant negative altitude effects on birth weight and gestational age in the low-altitude sample and on birth weight in the high-altitude sample. Altitude effects are larger for infants with very low fetal health endowments. The study finds differences in the effects of several inputs such as socioeconomic status and maternal fertility history and health between the two altitude samples. The study highlights the importance of adverse altitude effects on infant health when evaluating the costs and returns of policies that change the number of individuals who reside at higher altitude in both low and high altitude ranges.

Efeitos da exposição à altitude sobre os aspectos neuropsicológicos: uma revisão da literatura

OBJETIVO: Discutir os efeitos da exposição à altitude sobre as funções neuropsicológicas. MÉTODO: Foi realizada uma revisão de literatura usando como fonte de pesquisa artigos indexados no Pubmed, no período de 1921 a 2008, utilizando as palavras-chave "cognition and hypoxia", "hypoxia and neuropsychology", "acute hypoxia", "chronic hypoxia" e "acclimatization and hypoxia", além de livros específicos do assunto. DISCUSSÃO: Os efeitos agudos e crônicos da hipóxia podem alterar inúmeras funções neuropsicológicas em diferentes altitudes, decorrentes de alterações fisiológicas que resultam da diminuição parcial de oxigênio (O2), que podem levar as alterações neuropsicológicas, como atenção, memória, tomada de decisão e demais funções executivas, em indivíduos expostos a grandes altitudes. CONCLUSÃO: Indivíduos que se expõem às grandes altitudes devem utilizar suplementação de O2 e prática de aclimatização, entre outras estratégias para minimizar os efeitos negativos da hipóxia nos aspectos neuropsicológicos.

Rat strain differences in pulmonary artery smooth muscle Ca(2+) entry following chronic hypoxia

Effects of chronic hypoxia (CH) on store- and receptor-operated Ca(2+) entry (SOCE, ROCE) in pulmonary vascular smooth muscle (VSM) are controversial, although whether genetic variation explains such discrepancies in commonly studied rat strains is unclear. Since protein kinase C (PKC) can inhibit Ca(2+) permeable nonselective cation channels, we hypothesized that CH differentially alters PKC-dependent inhibition of SOCE and ROCE in pulmonary VSM from Sprague-Dawley and Wistar rats. To test this hypothesis, we examined SOCE and endothelin-1 (ET-1)-induced ROCE in endothelium-disrupted, pressurized pulmonary arteries from control and CH Sprague-Dawley and Wistar rats. Basal VSM Ca(2+) was elevated in CH Wistar, but not Sprague-Dawley, rats. Further, CH attenuated SOCE in VSM from Sprague-Dawley rats, while augmenting this response in Wistar rats. CH reduced ROCE in arteries from both strains. PKC inhibition restored SOCE in CH Sprague-Dawley arteries to control levels, while having no effect on SOCE in Wistar arteries or on ROCE in either strain. We conclude that effects of CH on pulmonary VSM SOCE are strain dependent, whereas inhibitory effects of CH on ROCE are strain independent. Further, PKC inhibits SOCE following CH in Sprague-Dawley, but not Wistar, rats but does not contribute to ET-1-induced ROCE in either strain.

Different adaptation patterns of antioxidant system in natives and sojourners at high altitude

Comparative studies on the adaptation pattern of antioxidant status among high altitude natives and acclimatized sojourners are very scanty. The aim of the present study was to compare the differences in antioxidant profile between two groups of active male volunteers, i.e. native highlanders (HAN, n=66) in their natural hypoxic environment with that of sojourners (SOJ, n=81) from sea level (SL) after 4 weeks of stay at an altitude of 4560m. Blood samples of SOJ were collected at SL and HA. Same was collected from HAN once at HA. HAN had significantly higher SOD activity and significantly lower catalase, GPX and GR activities than SOJ at HA. Ratio of GSH/GSSG was also significantly higher in HAN than SOJ at HA. In SOJ, antioxidant profile showed an upregulation after HA stay but it was not effective to reduce the levels of oxidative stress markers. Therefore, it can be stated that lifelong exposure to hypoxia has beneficial adaptive effects on antioxidant system in HAN. Similarly, acclimatization to HA also has beneficial preconditioning effects on antioxidant system in SOJ, but, may not be sufficient to ameliorate oxidative stress completely. Transient increase in metabolic rate due to hypoxia may be a causative factor for excess free radical generation among sojourners at HA.

Mortality on Mount Everest, 1921-2006: descriptive study

OBJECTIVE

To examine patterns of mortality among climbers on Mount Everest over an 86 year period.

DESIGN

Descriptive study.

SETTING

Climbing expeditions to Mount Everest, 1921-2006.

PARTICIPANTS

14,138 mountaineers; 8030 climbers and 6108 sherpas.

MAIN OUTCOME MEASURE

Circumstances of deaths.

RESULTS

The mortality rate among mountaineers above base camp was 1.3%. Deaths could be classified as involving trauma (objective hazards or falls, n=113), as non-traumatic (high altitude illness, hypothermia, or sudden death, n=52), or as a disappearance (body never found, n=27). During the spring climbing seasons from 1982 to 2006, 82.3% of deaths of climbers occurred during an attempt at reaching the summit. The death rate during all descents via standard routes was higher for climbers than for sherpas (2.7% (43/1585) v 0.4% (5/1231), P<0.001; all mountaineers 1.9%). Of 94 mountaineers who died after climbing above 8000 m, 53 (56%) died during descent from the summit, 16 (17%) after turning back, 9 (10%) during the ascent, 4 (5%) before leaving the final camp, and for 12 (13%) the stage of the summit bid was unknown. The median time to reach the summit via standard routes was earlier for survivors than for non-survivors (0900-0959 v 1300-1359, P<0.001). Profound fatigue (n=34), cognitive changes (n=21), and ataxia (n=12) were the commonest symptoms reported in non-survivors, whereas respiratory distress (n=5), headache (n=0), and nausea or vomiting (n=3) were rarely described.

CONCLUSIONS

Debilitating symptoms consistent with high altitude cerebral oedema commonly present during descent from the summit of Mount Everest. Profound fatigue and late times in reaching the summit are early features associated with subsequent death.

Comparison of maternal and newborn outcomes of Tibetan and Han Chinese delivering in Lhasa, Tibet

AIM

To compare maternal and neonatal outcomes of Tibetan and Han Chinese women delivering vaginally at high altitude (3650 meters) in Lhasa, Tibet Autonomous Region, People's Republic of China.

METHOD

Comparative analysis of data from a prospective observational study of Tibetan (n = 938) and Han Chinese (n = 146) women delivering at three hospitals between January 2004 and May 2005.

RESULTS

Han Chinese women had higher rates of pre-eclampsia/gestational hypertension than Tibetan women, (10.3% vs 5.9%, P = 0.04). There was no difference in rates of postpartum hemorrhage between Tibetan and Han women (12.8% vs 17.1%, P = 0.15). Han newborns weighed significantly less than Tibetan newborns (P < 0.01), and were twice as likely to be small for gestational age, (24.5% vs 11.6%, P < 0.01). Tibetan newborns were less likely to have poor neonatal outcomes than Han newborns (P < 0.01).

CONCLUSION

In high altitude deliveries in Tibet, adverse outcomes were significantly more common among Han Chinese.

Abnormal energy regulation in early life: childhood gene expression may predict subsequent chronic mountain sickness

BACKGROUND

Life at altitude depends on adaptation to ambient hypoxia. In the Andes, susceptibility to chronic mountain sickness (CMS), a clinical condition that occurs to native highlanders or to sea level natives with prolonged residence at high altitude, remains poorly understood. We hypothesized that hypoxia-associated gene expression in children of men with CMS might identify markers that predict the development of CMS in adults. We assessed distinct patterns of gene expression of hypoxia-responsive genes in children of highland Andean men, with and without CMS.

METHODS

We compared molecular signatures in children of highland (HA) men with CMS (n = 10), without CMS (n = 10) and in sea level (SL) children (n = 20). Haemoglobin, haematocrit, and oxygen saturation were measured. Gene expression in white cells was assessed at HA and then, in the same subjects, within one hour of arrival at sea level.

RESULTS

HA children showed higher expression levels of genes regulated by HIF (hypoxia inducible factor) and lower levels of those involved in glycolysis and in the tricarboxylic acid (TCA) cycle. Pyruvate dehydrogenase kinase 1(PDK1) and HIF prolyl hydroxylase 3 (HPH3) mRNA expressions were lowest in children of CMS fathers at altitude. At sea level the pattern of gene expression in the 3 children's groups was indistinguishable.

CONCLUSION

The molecular signatures of children of CMS patients show impaired adaptation to hypoxia. At altitude children of CMS fathers had defective coupling between glycolysis and mitochondria TCA cycle, which may be a key mechanism/biomarker for adult CMS. Early biologic markers of disease susceptibility in Andeans might impact health services and social planning.

Positive pressure ventilation: what is the real cost?

Positive pressure ventilation is a radical departure from the physiology of breathing spontaneously. The immediate physiological consequences of positive pressure ventilation such as haemodynamic changes are recognized, studied, and understood. There are other significant physiological interactions which are less obvious, more insidious, and may only produce complications if ventilation is prolonged. The interaction of positive pressure with airway resistance and alveolar compliance affects distribution of gas flow within the lung. The result is a wide range of ventilation efficacy throughout different areas of the lung, but the pressure differentials between alveolus and interstitium also influence capillary perfusion. The hydrostatic forces across the capillaries associated with the effects of raised venous pressures compound these changes resulting in interstitial fluid sequestration. This is increased by impaired lymphatic drainage which is secondary to raised intrathoracic pressure but also influenced by raised central venous pressure. Ventilation and PEEP promulgate further physiological derangement. In theory, avoiding these physiological disturbances in a rested lung may be better for the lung and other organs. An alternative to positive pressure ventilation might be to investigate oxygen supplementation of a physiologically neutral and rested lung. Abandoning heroic ventilation would be a massive departure from current practice but might be a more rationale approach to future practice.

Chronic hypoxia and rat lung development: analysis by morphometry and directed microarray

It is unclear how sublethal hypoxia affects lung development. To investigate the effects of chronic hypoxia on postnatal lung remodeling, we treated neonatal rats with FIO2 of 0.12 for 10 d and analyzed lung development by morphometry and gene expression by DNA microarray. Our results showed the neonatal rats exposed to hypoxia reduced body weight by 42% and wet lung weight by 32% compared with the neonatal rats exposed to normoxia. In the neonatal rats exposed to hypoxia, the radial alveolar counts were decreased to 5.6 from 7.9 and the mean linear intercepts were increased to 56.5 mum from 38.2 mum. In DNA microarray analysis, approximately half of probed genes were unknown. Chronic hypoxia significantly regulated expression of genes that are involved in pathogenesis of pulmonary hypertension and postnatal lung remodeling. Chemokine ligand 12, jagged 2 were among those upregulated; c-kit, ephrin A1, and Hif-2alpha were among those downregulated. The altered expression of those genes was correlated with the lung development and remodeling.

Adaptation to high altitude in Sherpas: association with the insertion/deletion polymorphism in the Angiotensin-converting enzyme gene

OBJECTIVE

Sherpas are well-known for their physical strength at high altitudes. They adapt to high altitude so well that little acute or chronic mountain sickness has been documented in them. The possible genetic basis for this adaptation is, however, unclear. The objective of this study was to elucidate the genetic background underlying this characteristic among Sherpas with respect to the angiotension-converting enzyme (ACE) gene.

METHODS

We enrolled 105 Sherpa volunteers in Namche Bazaar (3440 meters) and 111 non-Sherpa Nepalese volunteers in Kathmandu Valley (1330 meters) in Nepal. Information about high-altitude exposure and physiological phenotypes was obtained via fieldwork investigation. The genotype of the insertion/deletion (I/D) polymorphism in the ACE gene was identified by polymerase chain reaction. Serum ACE activity was also measured.

RESULTS

The distribution of the I dominant genotype (II & ID) and the I allelic frequency were significantly more prevalent in Sherpas (II & ID: 94.3%, I allele: 73.3%) than in non-Sherpas (II & ID: 85.6%, P = .035; I allele: 64.0%, P = .036). Moreover, despite residing at high altitude, the circulating ACE levels of Sherpas were statistically similar to those of non-Sherpas at low altitudes (Sherpas: 14.5 +/- 0.4 IU/L/37 degrees C; non-Sherpas: 14.7 +/- 0.4 IU/L/37 degrees C; P = .755).

CONCLUSIONS

These findings suggest that the overrepresented I allele of the ACE gene in Sherpas might be one of the fundamental genetic factors responsible for maintaining physiological low-altitude ACE activity at high altitude, which may have an advantageous physiological role in adapting to a high-altitude environment.

Outcome of hospital deliveries of women living at high altitude: a study from Lhasa in Tibet

AIM

To describe rates of neonatal mortality, low birthweight (LBW), preterm birth and small for gestational age (SGA), and relate outcome to ethnicity and perinatal risk factors of liveborn infants of hospital deliveries in Lhasa. The differences in these variables between ethnic Tibetans and non-Tibetans were also studied.

METHODS

Data were prospectively collected on the outcome of all liveborn infants born in four hospitals in the urban area of Lhasa, Tibet, in 2005.

RESULT

A total of 2540 liveborn infants were recorded. The rates of LBW, preterm birth and SGA were 13.6%, 5.7% and 22.2%, respectively. Neonatal mortality rate was 42/1000 for the infants born alive in the hospitals. Lower GA, vaginal delivery, foetal distress and lack of prenatal care, but not ethnicity, were associated with increased risk of death in multivariate logistic regression. Tibetans had higher BW and lower rates of LBW, SGA, need of oxygen supplementation and maternal hypertension, but higher rates of foetal distress, caesarean section, multiple births and low Apgar scores.

CONCLUSION

This study provided a profile of perinatal-neonatal care of hospital newborn infants in Lhasa, Tibet. The rates of neonatal mortality, LBW and SGA were high. The findings suggest ethnic differences in perinatal-neonatal adaptation to high altitude.

Role of platelet-activating factor in pulmonary vascular remodeling associated with chronic high altitude hypoxia in ovine fetal lambs

Platelet-activating factor (PAF) is implicated in pathogenesis of chronic hypoxia-induced pulmonary hypertension in some animal models and in neonates. Effects of chronic hypoxia on PAF receptor (PAF-R) system in fetal pulmonary vasculature are unknown. We investigated the effect of chronic high altitude hypoxia (HAH) in fetal lambs [pregnant ewes were kept at 3,801 m (12,470 ft) altitude from ∼35 to 145 days gestation] on PAF-R-mediated effects in the pulmonary vasculature. Age-matched controls were kept at sea level. Intrapulmonary arteries were isolated, and smooth muscle cells (SMC-PA) were cultured from HAH and control fetuses. To determine presence of pulmonary vascular remodeling, lung tissue sections were subjected to morphometric analysis. Percentage medial wall thickness was significantly increased ( P < 0.05) in arteries at all levels in the HAH lambs. PAF-R protein expression studied by immunocytochemistry and Western blot analysis on lung tissue SMC-PA demonstrated greater PAF-R expression in HAH lambs. PAF-R binding (femtomoles per 106cells) in HAH SMC-PA was 90.3 ± 4.08 and 66% greater than 54.3 ± 4.9 in control SMC-PA. Pulmonary arteries from HAH fetuses synthesized >3-fold PAF than vessels from controls. Compared with controls SMC-PA of HAH lambs demonstrated 139% and 40% greater proliferation in 10% FBS alone and with 10 nM PAF, respectively. Our data demonstrate that exposure of ovine fetuses to HAH will result in significant upregulation of PAF synthesis, PAF-R expression, and PAF-R-mediated effects in pulmonary arteries. These findings suggest that increased PAF-R protein expression and increased PAF binding contribute to pulmonary vascular remodeling in these animals and may predispose them to persistent pulmonary hypertension after birth.

The role of oxygen in prenatal growth: studies in the chick embryo

The compelling evidence linking small size at birth with later cardiovascular disease has renewed and amplified scientific and clinical interests into the determinants of fetal growth. It is accepted that genes and nutrition control fetal growth; however, prior to this study, it had been impossible to isolate the effect of increases and decreases in fetal oxygenation on the regulation of prenatal growth. We investigated the role of oxygen in the control of fetal growth in the chicken because in contrast to mammals, the effects on the fetus of changes in oxygenation could be isolated, by assessing them directly without alteration to the maternal or placental physiology or maternal nutrition during development. The data show that incubation at high altitude of fertilized eggs laid by sea level hens markedly restricted fetal growth. Incubation at high altitude of fertilized eggs laid by high altitude hens also restricted fetal growth, but to a lesser extent compared to eggs laid by sea level hens. By contrast, incubation at sea level of fertilized eggs laid by high altitude hens not only restored, but enhanced, fetal growth relative to sea level controls. Incubation at high altitude of sea level eggs with oxygen supplementation completely prevented the high altitude-induced fetal growth restriction. Thus, fetal oxygenation, independent of maternal nutrition during development, has a predominant role in the control of fetal growth. Further, prolonged high altitude residence confers protection against the deleterious effects of hypoxia on fetal growth.

Tradeoffs between oxygen and energy in tibial growth at high altitude

Some studies of high altitude populations argue that stature reduction results from caloric, rather than hypoxic, stress. However, tradeoff models of oxygen and glucose metabolism predict that in hypoxemia, glucose metabolism will be downregulated. We used tradeoff assumptions in two hypotheses: First, that hypoxia targets leg segment growth differentially, and second, that proportions of leg segments partition the impact of high altitude into hypoxemic and energetic components. A group of 113 Han and Tibetan middle school children at 3100 m aged 8 to 11 were measured for segment anthropometries, skinfolds, vital capacity, blood oxygen saturation, and percent body fat. MANOVA showed that Tibetan children were significantly larger and fatter than Han children. Independent of ethnicity or caloric status, absolute and relative tibia length was significantly reduced in children with lower blood oxygen saturation. Height, chest circumference, sitting height, tibia length, and ankle diameter were greatest in fatter children, independent of ethnicity or blood oxygen. For children of either ethnicity with the lowest blood oxygen, size as well as proportion was impacted. These results support the tradeoff model. Caloric reserves and ethnicity independently affect total skeletal size. Oxygen saturation and ethnicity affect leg proportions. In hypoxemia, body fat has less impact on growth than when ample oxygen is present. Therefore, we should qualify the claim that size in high altitude populations stems from nutritional stress. The findings also suggest that decanalization may have different meanings and outcomes depending on which body segments contribute to the effect.

High-altitude ancestry protects against hypoxia-associated reductions in fetal growth

OBJECTIVE

The chronic hypoxia of high-altitude (>/=2500 m) residence has been shown to decrease birth weight in all populations studied to date. However, multigenerational high-altitude populations appear protected relative to newcomer groups. This study aimed to determine whether such protection exists independently of other factors known to influence fetal growth and whether admixed populations (ie, people having both high- and low-altitude ancestry) show an intermediate level of protection.

DESIGN

3551 medical records from consecutive deliveries to Andean, European or Mestizo (ie, admixed) women at low, intermediate or high altitudes in Bolivia were evaluated for maternal characteristics influencing fetal growth as measured by birth weight and the frequency of small for gestational age births (SGA or </=10th percentile birth weight for gestational age and sex). Two-way analysis of variance and chi(2) tests were used to compare maternal and infant characteristics. The effects of ancestry or altitude on SGA and birth weight were assessed using logistic or linear regression models, respectively.

RESULTS

Altitude decreased birth weight and increased SGA in all ancestry groups. Andean infants weighed more and were less often SGA than Mestizo or European infants at high altitude (13%, 16% and 33% respectively, p<0.01). After accounting for the influences of maternal hypertensive complications of pregnancy, parity, body weight, and number of prenatal visits, European relative to Andean ancestry increased the frequency of SGA at high altitude nearly fivefold.

CONCLUSIONS

Andean relative to European ancestry protects against altitude-associated reductions in fetal growth. The intermediate protection seen in the admixed (Mestizo) group is consistent with the influence of genetic or other Andean-specific protective characteristics.

Maternal and neonatal outcomes of hospital vaginal deliveries in Tibet

INTRODUCTION

To determine the outcomes of vaginal deliveries in three study hospitals in Lhasa, Tibet Autonomous Region (TAR), People's Republic of China (PRC), at high altitude (3650 m).

METHODS

Prospective observational study of 1121 vaginal deliveries.

RESULTS

Pre-eclampsia/gestational hypertension (PE/GH) was the most common maternal complication 18.9% (n=212), followed by postpartum hemorrhage (blood loss > or = 500 ml) 13.4%. There were no maternal deaths. Neonatal complications included: low birth weight (10.2%), small for gestational age (13.7%), pre-term delivery (4.1%) and low Apgar (3.7%). There were 11 stillbirths (9.8/1000 live births) and 19 early neonatal deaths (17/1000 live births).

CONCLUSION

This is the largest study of maternal and newborn outcomes in Tibet. It provides information on the outcomes of institutional vaginal births among women delivering infants at high altitude. There was a higher incidence of PE/GH and low birth weight; rates of PPH were not increased compared to those at lower altitudes.

High-altitude chronic hypoxia during gestation and after birth modifies cardiovascular responses in newborn sheep

Perinatal exposure to chronic hypoxia induces sustained pulmonary hypertension and structural and functional changes in both pulmonary and systemic vascular beds. The aim of this study was to analyze consequences of high-altitude chronic hypoxia during gestation and early after birth in pulmonary and femoral vascular responses in newborn sheep. Lowland (LLNB; 580 m) and highland (HLNB; 3,600 m) newborn lambs were cathetherized under general anesthesia and submitted to acute sustained or stepwise hypoxic episodes. Contractile and dilator responses of isolated pulmonary and femoral small arteries were analyzed in a wire myograph. Under basal conditions, HLNB had a higher pulmonary arterial pressure (PAP; 20.2 ± 2.4 vs. 13.6 ± 0.5 mmHg, P < 0.05) and cardiac output (342 ± 23 vs. 279 ± 13 ml·min−1·kg−1, P < 0.05) compared with LLNB. In small pulmonary arteries, HLNB showed greater contractile capacity and higher sensitivity to nitric oxide. In small femoral arteries, HLNB had lower maximal contraction than LLNB with higher maximal response and sensitivity to noradrenaline and phenylephrine. In acute superimposed hypoxia, HLNB reached higher PAP and femoral vascular resistance than LLNB. Graded hypoxia showed that average PAP was always higher in HLNB compared with LLNB at any Po2. Newborn lambs from pregnancies at high altitude have stronger pulmonary vascular responses to acute hypoxia associated with higher arterial contractile status. In addition, systemic vascular response to acute hypoxia is increased in high-altitude newborns, associated with higher arterial adrenergic responses. These responses determined in intrauterine life and early after birth could be adaptive to chronic hypoxia in the Andean altiplano.

Going to High Altitude with a Newborn Infant

Fetal life conditions the responses of a newborn infant to high altitude. The fetal circulation is characterized by high pulmonary vascular resistance and low pulmonary blood flow, as well as intra and extracardiac shunts that serve to route blood to and from the placenta and around the fetal lungs. At birth, rapid changes occur in the pulmonary circulation under normoxia; pulmonary vascular resistance falls, pulmonary blood flow increases dramatically, and the fetal shunts close functionally, then anatomically. Under conditions of hypoxia, the changes of circulatory transition occur more slowly, and pronounced hypoxia can cause a reversion to fetal circulatory patterns, albeit without the placenta to serve as the organ of oxygenation. Underlying medical conditions of newborn infants that combine exaggerated hypoxemia in response to high altitude hypoxia with an underlying predisposition to pulmonary hypertension can increase the likelihood of problems at high altitude. Awareness of risk factors and clinical signs of hypoxemia in newborn infants, as well as measurement of arterial oxygen saturation by pulse oximetry, can aid health professionals and parents in recognizing and preventing altitude-associated illness.

High-altitude physiology and pathophysiology: implications and relevance for intensive care medicine

Cellular hypoxia is a fundamental mechanism of injury in the critically ill. The study of human responses to hypoxia occurring as a consequence of hypobaria defines the fields of high-altitude medicine and physiology. A new paradigm suggests that the physiological and pathophysiological responses to extreme environmental challenges (for example, hypobaric hypoxia, hyper-baria, microgravity, cold, heat) may be similar to responses seen in critical illness. The present review explores the idea that human responses to the hypoxia of high altitude may be used as a means of exploring elements of the pathophysiology of critical illness.

Postnatal cardiopulmonary adaptations to high altitude

Postnatal cardiopulmonary adaptations to high altitude constitute a key component of any set of responses developed to face high altitude hypoxia. Such responses are required ultimately to meet the energy demands necessary for adequate functioning at cell and organism level. After a brief insight on general and cardiopulmonary comparative studies in growing and adult organisms, differences and possible explanations for varying cardiopulmonary pathology, pulmonary artery hypertension, persistent right ventricular predominance and subacute high altitude pulmonary hypertension in different populations of children living at high altitude are discussed. Potential long-term implications of early chronic hypoxic exposure on later diseases are also presented. It is hoped that this review will help the practicing physician working at high altitude to make informed decisions concerning individual pediatric patients, specifically with regard to diagnosis and management of altitude-related cardiopulmonary pathology. Finally, plausibility and the knowledge-base of public health interventions to reduce the risks posed by suboptimal or inadequate postnatal cardiopulmonary responses to high altitude are discussed.

Peruvian contributions to the study on human reproduction at high altitude: from the chronicles of the Spanish conquest to the present

Humans have lived in the Peruvian Andes for about 12,000 years providing adequate time for adaptation to high altitude to have occurred. The arrival of the Spanish conquistadors in the 16th century potentially altered this process through genetic admixture. Early records revealed a potential for reduced fertility and a high perinatal and neonatal mortality amongst the early Spanish inhabitants who settled at high altitude when compared to the native Inca population. It appears that fertility is reduced during acute exposure at high altitude but is normal in populations born and living at high altitude. On the other hand, perinatal and neonatal mortality is presently still high at elevated altitudes, even after taking into account socio-economic status. The rates of perinatal and neonatal mortality are, however, lower in populations that have resided at high altitude for longer; populations inhabiting the southern Andes have a longer antiquity at high altitude and lower rates of fetal and neonatal deaths than those in the central Andes with a shorter residence at high altitude. Clearly, antiquity and genetics are important components in determining survival and quality of life at high altitude.

Population genetic aspects and phenotypic plasticity of ventilatory responses in high altitude natives

Highland natives show unique breathing patterns and ventilatory responses at altitude, both at rest and during exercise. For many ventilatory traits, there is also significant variation between highland native groups, including indigenous populations in the Andes and Himalaya, and more recent altitude arrivals in places like Colorado. This review summarizes the literature in this area with some focus on partitioning putative population genetic differences from differences acquired through lifelong exposure to hypoxia. Current studies suggest that Tibetans have high resting ventilation (V (E)), and a high hypoxic ventilatory response (HVR), similar to altitude acclimatized lowlanders. Andeans, in contrast, show low resting V (E) and a low or "blunted" HVR, with little evidence that these traits are acquired via lifelong exposure. Resting V (E) of non-indigenous altitude natives is not well documented, but lifelong hypoxic exposure almost certainly blunts HVR in these groups through decreased chemosensitivity to hypoxia in a process known as hypoxic desensitization (HD). Together, these studies suggest that the time course of ventilatory response, and in particular the origin or absence of HD, depends on population genetic background i.e., the allele or haplotype frequencies that characterize a particular population. During exercise, altitude natives have lower V (E) compared to acclimatized lowland controls. Altitude natives also have smaller alveolar-arterial partial pressure differences P(AO2) - P(aO2) during exercise suggesting differences in gas exchange efficiency. Small P(AO2) - P(aO2) in highland natives of Colorado underscores the likely importance of developmental adaptation to hypoxia affecting structural/functional aspects of gas exchange with resultant changes in breathing pattern. However, in Andeans, at least, there is also evidence that low exercise V (E) is determined by genetic background affecting ventilatory control independent of gas exchange. Additional studies are needed to elucidate the effects of gene, environment, and gene-environment interaction on these traits, and these effects are likely to differ widely between altitude native populations.

High altitude and early childhood growth retardation: new evidence from Tibet

OBJECTIVE

To assess possible effect of high altitude on early childhood growth in Tibet.

METHOD

A cross-sectional survey on child health and nutrition was conducted in Tibet with stratified multistage cluster random sampling technique. Height and weight status of Tibetan children <36 months of age was measured. A questionnaire was administered to mothers of children for information on family background, child feeding practice and health care and maternal care. A total of 1458 children with complete information were used for analysis. A logistic regression model was used to control for selected potential confounding factors and then observed altitude effect on growth of Tibetan children.

RESULTS

Positive association of stunting with altitude was observed for each age group, even after controlling for selected potential affecting factors. Children above 3500 m had two to six times risk of getting stunting compared with those at 3000 m when socioeconomic and other factors were controlled. Effect of altitude on underweight was observed only among children <24 months old and significant increase in odds ratio appeared only above 4000 m after controlling for those confounding factors. Indicator of wasting was not related to altitude.

CONCLUSIONS

Altitude might result in a delay in height of younger Tibetan children, independent of socioeconomic and other factors operating through nutrition and disease, and took adverse effect persistently through birth to 3 years old. Its adverse effect on weight could be limited. For comparison and assessment of nutritional status of Tibetan children, the effect of altitude on growth should be taken into account.

A Comparative Analysis of Arterial Oxygen Saturation among Tibetans And Han Born And Raised at High Altitude

This study compares resting arterial oxygen saturation as measured by pulse oximetry (Sp(O2)) among 818 Tibetans and 668 Han who were born and raised at altitudes between 3200 and 4300 m in Qinghai Province, Western China. Both Tibetans and Han show an increase in Sp(O2) values between the ages of 5 and 19 yr, and both groups show a decline after the third decade. However, mean, age-adjusted Sp(O2) values at rest do not differ significantly among growing Tibetans and Han aged 5 through 19 yr or among Tibetans and Han aged 20 through 51 yr. Therefore, the results of this study do not support the hypothesis that indigenous groups possess a superior arterial saturation while awake and at rest compared to lowlanders who have been born and raised at high altitude. Differences between adult Tibetan males and females approach statistical significance (females show higher values than males), while differences between adult Han males and females are not statistically significant. A review of the literature indicates that substantial interstudy variation exists in resting Sp(O2) values among Tibetans residing at high altitudes (between 2% and 4%, depending on the age of individuals measured) and may reflect differences in sample size, health of participants, instruments, probe location, and measurement protocols.

Cross-sectional study of electrocardiographic pattern in healthy children resident at high altitude

Electrocardiographic studies have reported persistent right ventricle predominance in high altitude children as an adaptive response. No information was provided on ethnicity and environmental factors in those studies. We assessed the electrocardiographic characteristics in healthy high altitude children with mixed ancestry and relatively high mobility to lower altitudes. A cross-sectional study of 321 children aged 2 months through 19 years old and living at high altitude (Tintaya, Peru, 4,100 m) was conducted. Standard 12-lead electrocardiography was performed. Information was obtained on ethnicity, medical history, place and altitude of pregnancy and birth, mobility of children and their parents and grandparents to lower altitudes, and housing conditions. A medical examination, echocardiography, hemoglobin, oxygen saturation, and anthropometric measurements were performed. Means between sexes were compared through Mann-Whitney test for independent samples not normally distributed. Potentially influential variables on electrocardiographic values were controlled through a general linear model. Electrocardiographic parameters including QRS axis, RV1, RSV1, RV1SV5, RSV5, RSV6, and SV1RV5 did not show a right predominance pattern at any age. Values were within sea level norms. None of the genetic or environmental factors controlled showed a consistent influence on the electrocardiographic variables. Our study showed an electrocardiographic pattern similar to that of sea level in high altitude children with some degree of high-altitude ancestry, comparatively well-nourished and with relatively high mobility to low altitudes.

Genetic contribution of the endothelial nitric oxide synthase gene to high altitude adaptation in sherpas

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( x ): 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 Glu298Glu and eNOS4b/b was significantly greater in Sherpas (66.7%) than non-Sherpas (47.7%, p = 0.008). However, the serum NO( x ) was significantly lower in Sherpas (53.2 +/- 4.6 micromol/L) than in non-Sherpas (107.3 +/- 9.0 micromol/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 (NO( x )) in serum vary individually, thus it is not a reliable indicator for endogenous nitric oxide production.

High Altitude Adaptation in Tibetans

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.

Human behaviour and development under high-altitude conditions

Although we are far from a universally accepted pattern of impaired function at altitude, there is evidence indicating motor, perceptual, memory and behavioural deficits in adults. Even relatively low altitudes (2500 m) may delay reaction time, and impair motor function. Extreme altitude exposure (>5000 m) may result in more pronounced impairment that can persist after returning to the lowlands. Research into the effects of altitude exposure earlier in development is lacking by comparison. Un-acclimatized children can suffer from acute mountain sickness, and, in native populations born at altitude, subtle cognitive and behavioural deficits suggest incomplete adaptation to hypoxia. The study of neurobehavioural functioning at altitude may provide important information about the effects of clinical hypoxia on the human brain and behavioural development.

Oxygen saturation trends immediately after birth

OBJECTIVE

To describe the changes in oxygen saturation (SpO2) in healthy infants during the first 10 minutes of life.

STUDY DESIGN

In this observational study, infants > or = 35 weeks gestation at birth who did not require supplemental oxygen had continuous recordings taken of the preductal SpO2 over the first 10 minutes of life.

RESULTS

A total of 115 infants were analyzed. On average, infants delivered by cesarean delivery had a 3% lower SpO2 than infants delivered by vaginal delivery (95% confidence interval [CI] = -5.8 to -0.7; P = .01). Infants born by cesarean delivery also took longer (risk ratio, 1.79) to reach a stable SpO2 > or = 85% (95% CI = 1.02 to 3.14; P = .04). At 5 minutes of age, median SpO2 values (interquartile range) were 87% (80% to 95%) for infants delivered vaginally and 81% (75% to 83%) for those delivered through cesarean section. The median SpO2 did not reach 90% until 8 minutes of age in either group.

CONCLUSIONS

The process of transitioning to a normal postnatal oxygen saturation requires more than 5 minutes in healthy newborns breathing room air.

Consensus statement on chronic and subacute high altitude diseases

This is an international consensus statement of an ad hoc committee formed by the International Society for Mountain Medicine (ISMM) at the VI World Congress on Mountain Medicine and High Altitude Physiology (Xining, China; 2004) and represents the committee's interpretation of the current knowledge with regard to the most common chronic and subacute high altitude diseases. It has been developed by medical and scientific authorities from the committee experienced in the recognition and prevention of high altitude diseases and is based mainly on published, peer-reviewed articles. It is intended to include all legitimate criteria for choosing to use a specific method or procedure to diagnose or manage high altitude diseases. However, the ISMM recognizes that specific patient care decisions depend on the different geographic circumstances involved in the development of each chronic high altitude disease. These guidelines are established to inform the medical services on site who are directed to solve high altitude health problems about the definition, diagnosis, treatment, and prevention of the most common chronic high altitude diseases. The health problems associated with life at high altitude are well documented, but health policies and procedures often do not reflect current state-of-the-art knowledge. Most of the cases of high altitude diseases are preventable if on-site personnel identify the condition and implement appropriate care.

Arterial oxygen saturation in healthy newborns delivered at term in Cerro de Pasco (4340 m) and Lima (150 m)

BACKGROUND

High altitude is associated with both low pulse oxygen saturation at birth and more pre-term deliveries. The present study was performed to determine pulse oxygen saturation in newborns at term in Cerro de Pasco (4340 m) and Lima (150 m) to test the hypothesis that low pulse oxygen saturation at birth at high altitudes was not observed at term deliveries.

METHODS

The present study was designed to determine pulse oxygen saturation values through 1 minute to 24 hours and values of Apgar score at 1 and 5 minutes in newborns delivered at term in Cerro de Pasco (4340 m) and Lima (150 m). Pulse oxygen saturation was recorded in 39 newborns from Cerro de Pasco (4340 m) and 131 from Lima (150 m) at 1, 2, 3, 4, 5, 10, 15, 30 minutes and 1, 2, 8 and 24 hours after delivery. Apgar score was assessed at 1 and 5 minutes after birth. Neurological score was assessed at 24 h of birth by Dubowitz exam.

RESULTS

Pulse oxygen saturation increased significantly from 1 to 15 min after birth at sea level and from 1 to 30 minutes at Cerro de Pasco. Thereafter, it increased slightly such that at 30 min at sea level and at 60 minutes in Cerro de Pasco it reached a plateau up to 24 hours after birth. At all times, pulse oxygen saturation was significantly higher at sea level than at high altitude (P < 0.01). At 1 minute of life, pulse oxygen saturation was 15% lower at high altitude than at sea level. Apgar score at 1 minute was significantly lower at high altitude (P < 0.05). Neurological score at 24 hours was also lower at high altitude than at sea level. Head circumference, and Apgar score at 5 minutes were similar at sea level and at high altitude (P:NS). Incidence of low birth-weight (<2500 g) at high altitude (5.4%) was similar to that observed at sea level (2.29%) (P:NS). Incidences of low pulse oxygen saturation (<30%), low Apgar score at first minute (<7) and low neurological score at 24 h (<19) were significantly higher at high altitude than at sea level (P < 0.0001; P < 0.0001; and P < 0.001, respectively).

CONCLUSION

From these analyses may be concluded that pulse oxygen saturation at 4340 m was significantly low despite the fact that births occurred at term. Apgar scores at first minute and neurological scores were also lower at high altitudes.