Postnatal cardiopulmonary adaptations to high altitude

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

Respiratory physiology at high altitude and considerations for pediatric patients

Over 150 million people, including many children, live at high altitude (>2500 m) with the majority residing in Asia and South America. With increases in elevation, the partial pressure of oxygen (pO2) is reduced, resulting in a hypobaric hypoxic environment. Fortunately, humans have evolved adaptive processes which serve to acclimate the body to such conditions. These mechanisms, occurring along a specific time course, result in tachypnea, tachycardia, diuresis, and hematopoiesis, and a shift in the oxygen dissociation curve favoring an increased affinity for oxygen. These, along with other physiological effects, including increased pulmonary vascular resistance, alterations in cerebral blood flow, and changes in sensitivity to opioids, must be considered when administering anesthesia at high altitudes. Susceptible individuals or those who ascend too quickly may outpace the body's ability to acclimate resulting in one or more forms of high-altitude sickness ranging from the milder acute mountain sickness to the more serious conditions of high-altitude pulmonary edema and cerebral edema, either of which can be life-threatening if not promptly recognized and treated. Since the adaptive mechanisms for acclimatization greatly affect the cardiopulmonary systems, patients with underlying health issues such as sleep apnea, congenital heart disease, and asthma may have susceptibilities and warrant special consideration. Clinicians should have an understanding of the physiologic adaptations, anesthetic considerations, and special concerns in these populations in order to offer the best care possible.

Pulse oximetry in neonates at high altitudes: a modified Colorado protocol

Pulse oximetry for detecting critical CHD produces more false positive tests at high altitudes than at sea level, because at altitude the average resting saturation is lower and the variability is higher. This increases diagnostic difficulties, especially in small isolated communities without paediatric echocardio-graphy, and requires expensive transport to a regional medical centre. One way of reducing diagnostic errors is to measure arterial oxygen saturation while the infant is breathing 100% oxygen. In the absence of right-to-left shunting through the heart, the ductus, or the lungs, arterial oxygen tension will exceed 150 mmHg and arterial oxygen saturation will be 100%. With right-to-left shunting, arterial oxygen tension will be <100 mmHg, and thus <96% (usually much lower).

Adaptation to Life in the High Andes: Nocturnal Oxyhemoglobin Saturation in Early Development

STUDY OBJECTIVES

Physiological adaptation to high altitude hypoxia may be impaired in Andeans with significant European ancestry. The respiratory 'burden' of sleep may challenge adaptation, leading to relative nocturnal hypoxia. Developmental aspects of sleep-related breathing in high-altitude native children have not previously been reported. We aimed to determine the influence of development on diurnal-nocturnal oxyhemoglobin differences in children living at high altitude.

METHODS

This was a cross-sectional, observational study. Seventy-five healthy Bolivian children aged 6 mo to 17 y, native to low altitude (500 m), moderate high altitude (2,500 m), and high altitude (3,700 m) were recruited. Daytime resting pulse oximetry was compared to overnight recordings using Masimo radical oximeters. Genetic ancestry was determined from DNA samples.

RESULTS

Children had mixed European/Amerindian ancestry, with no significant differences between altitudes. Sixty-two participants had ≥ 5 h of nocturnal, artifact-free data. As predicted, diurnal mean oxyhemoglobin saturation decreased across altitudes (infants and children, both P < 0.001), with lowest diurnal values at high altitude in infants. At high altitude, there was a greater drop in nocturnal mean oxyhemoglobin saturation (infants, P < 0.001; children, P = 0.039) and an increase in variability (all P ≤ 0.001) compared to low altitude. Importantly, diurnal to nocturnal altitude differences diminished (P = 0.036), from infancy to childhood, with no further change during adolescence.

CONCLUSIONS

Physiological adaptation to high-altitude living in native Andeans is unlikely to compensate for the significant differences we observed between diurnal and nocturnal oxyhemoglobin saturation, most marked in infancy. This vulnerability to sleep-related hypoxia in early childhood has potential lifespan implications. Future studies should characterize the sleep- related respiratory physiology underpinning our observations.

Congenital heart disease and pulmonary arterial hypertension in South America (2013 Grover Conference series)

South America is a territory of 17,819,100 km(2), where ∼388 million people live in 13 countries. In the region, access to medical assistance (e.g., for treatment of cardiovascular disorders) is relatively easy in metropolitan areas but difficult in remote places such as the Andes and the Amazon. Altitudes up to ∼6,700 m influence the prevalence of congenital heart disease (CHD) and pulmonary arterial hypertension (PAH). In tertiary centers, CHD is now treated earlier in life but remains an important etiology of PAH. In adolescents and adults with PAH assisted at institutions devoted to treatment of cardiovascular disorders, the relative frequency of PAH-CHD (∼50%-60%) is even higher than that of idiopathic PAH. In one big tertiary center in São Paulo, Brazil, the prevalence of advanced PAH in children and adults with CHD is 1.2% and 4.2%, respectively. In young patients with cardiac septal defects (aged up to 2 years), pulmonary vascular abnormalities are a matter of concern in the decision about operability in 4.9% of cases. Access to specific PAH drugs is not uniform in South America, being unrealistic in remote places. In big cities, there are real possibilities for management of complex CHD, neonatal disorders, and even cardiac transplantation. Research activities have been implemented at clinical, translational, and basic levels. However, because of social and economic inequalities and political issues, access to best standards of medical care remains a problem in the region as a whole.

Developmental functional adaptation to high altitude: review

Various approaches have been used to understand the origins of the functional traits that characterize the Andean high-altitude native. Based on the conceptual framework of developmental functional adaptation which postulates that environmental influences during the period of growth and development have long lasting effects that may be expressed during adulthood, we initiated a series of studies addressed at determining the pattern of physical growth and the contribution of growth and development to the attainment of full functional adaptation to high-altitude of low and high altitude natives living under rural and urban conditions. Current research indicate that: (a) the pattern of growth at high altitude due to limited nutritional resources, physical growth in body size is delayed but growth in lung volumes is accelerated because of hypoxic stress); (b) low-altitude male and female urban natives can attain a full functional adaptation to high altitude by exposure to high-altitude hypoxia during the period of growth and development; (c) both experimental studies on animals and comparative human studies indicate that exposure to high altitude during the period of growth and development results in the attainment of a large residual lung volume; (d) this developmentally acquired enlarged residual lung volume and its associated increase in alveolar area when combined with the increased tissue capillarization and moderate increase in red blood cells and hemoglobin concentration contributes to the successful functional adaptation of the Andean high-altitude native to hypoxia; and (e) any specific genetic traits that are related to the successful functional adaptation of Andean high-altitude natives have yet to be identified.

Evaluation of cardiac function in healthy children native to 1890 metres

OBJECTIVE

The aim of the study is, by comparing cardiac parameters between children native to 1890 metres with children living at sea level, to find out whether there is any impairment in cardiac function related to that altitude.

METHODS

Electrocardiographic, conventional, and tissue Doppler echocardiographic parameters were compared in 42 healthy children native to 1890 metres, and in 21 healthy age and gender matched children living at sea level. Plasma haemoglobin level and oxygen saturation measured by pulse oxymeter were also obtained from all patients.

RESULTS

Haemoglobin levels were higher, and oxygen saturation levels were lower in children native to 1890 metres. Conventional echocardiographic parameters and mitral annular myocardial parameters were all similar between children native to 1890 metres and children living at sea level. Tricuspid lateral annular early diastolic velocity and the ratio of early-to-late diastolic velocity were significantly lower and tricuspid lateral annular izovolumetric relaxation time was significantly higher in children native to 1890 metres than children living at sea level.

CONCLUSION

Children living at 1890 metres of altitude predispose to asymptomatic right ventricular diastolic dysfunction or otherwise they remain as healthy children.

Arterial blood gas parameters of normal foals born at 1500 metres elevation

REASONS FOR PERFORMING STUDY

Arterial blood gas analysis is widely accepted as a diagnostic tool to assess respiratory function in neonates. To the authors' knowledge, there are no published reports of arterial blood gas parameters in normal neonatal foals at altitude.

OBJECTIVE

To provide information on arterial blood gas parameters of normal foals born at 1500 m elevation (Fort Collins, Colorado) in the first 48 h post partum.

HYPOTHESIS

Foals born at 1500 m will have lower PaO2 and PaCO2 than foals born at sea level due to low inspired oxygen and compensatory hyperventilation occurring at altitude.

METHODS

Sixteen foals were studied. Arterial blood gas analysis was performed within 1 h of foaling and subsequent samples were evaluated at 3, 6, 12, 24 and 48 h post partum. Data were compared to those previously reported in healthy foals born near sea level.

RESULTS

Mean PaO2 was 53.0 mmHg (7.06 kPa) within 1 h of foaling, rising to 67.5 mmHg (9.00 kPa) at 48 h post partum. PaCO2 was 44.1 mmHg (5.88 kPa) within one hour of foaling, falling to 38.3 mmHg (5.11 kPa) at 48 h. Both PaO2 and PaCO2 were significantly lower in foals born at 1500 m elevation than those near sea level at several time points during the first 48 h.

CONCLUSIONS AND POTENTIAL RELEVANCE

Foals at 1500 m elevation undergo hypobaric hypoxia and compensatory hyperventilation in the first 48 h. Altitude specific normal arterial blood values are an important reference for veterinarians providing critical care to equine neonates.

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.