Reference values for oxygen saturation from sea level to the highest human habitation in the Andes in acclimatised persons

The relationship between altitude and BMI varies across low- and middle-income countries

OBJECTIVES

Studies suggest that living at high altitude decreases obesity risk, but this research is limited to single-country analyses. We examine the relationship between altitude and body mass index (BMI) among women living in a diverse sample of low- and middle-income countries.

MATERIALS AND METHODS

Using Demographic and Health Survey data from 1 583 456 reproductive age women (20-49 years) in 54 countries, we fit regression models predicting BMI and obesity by altitude controlling for a range of demographic factors-age, parity, breastfeeding status, wealth, and education.

RESULTS

A mixed-effects model with country-level random intercepts and slopes predicts an overall -0.162 kg/m2 (95% CI -0.220, -0.104) reduction in BMI and lower odds of obesity (OR 0.90, 95% CI 0.87, 0.95) for every 200 m increase in altitude. However, countries vary dramatically in whether they exhibit a negative or positive association between altitude and BMI (34 countries negative, 20 positive). Mixed findings also arise when examining odds of obesity.

DISCUSSION

We show that past findings of declining obesity risk with altitude are not universal. Increasing altitude predicts slightly lower BMIs at the global level, but the relationship within individual countries varies in both strength and direction.

A new algorithm DEtectS critical Congenital Heart Disease at different altitudes: ANDES-CHD study

BACKGROUND

Neonatal pulse oximetry screening (POS) algorithms for critical congenital heart disease (CCHD) have contributed towards decreasing neonatal mortality but cannot be applied at high altitudes. New POS algorithms at high altitudes are needed.

METHODS

This observational, prospective study included newborns born at different altitudes from 0 to 4380 meters above the sea level in Peru. Healthy newborns underwent neonatal preductal and postductal oximetry, echocardiography and telephonic follow-up up to 12 months of age. Newborns with CCHD underwent preductal and postductal oximetry at the time of telemedicine evaluation while located at the high-altitude hospital where they were born, and their diagnoses were confirmed with echocardiography locally or after arriving to the referral center. Two new algorithms were designed using clinically accepted neonatal oximetry cutoffs or the 5th and 10th percentiles for preductal and postductal oximetry values.

RESULTS

A total of 502 healthy newborns and 15 newborns with CCHD were enrolled. Echocardiography and telephonic follow-up were completed in 227 (45%) and 330 healthy newborns (65%), respectively. The algorithm based on clinically accepted cutoffs had a sensitivity of 92%, specificity of 73% and false positive rate of 27% The algorithm based on the 5th and 10th percentiles had a sensitivity of 80%, specificity of 88% and false positive rate of 12%.

CONCLUSIONS

Two algorithms that detect CCHD at different altitudes had adequate performance but high false positive rates.

Evaluation of colour vision impairment during acute hypobaric hypoxia in aviation medicine: a randomized controlled trial

The digitization of aircraft cockpits places high demands on the colour vision of pilots. The present study investigates colour vision changes upon acute exposure to hypobaric hypoxia. The digital Waggoner Computerized Color Vision Test and the Waggoner D-15 were performed by 54 healthy volunteers in a decompression chamber. Respective altitude levels were sea level, 10,000 or 15,000 ft for exposure periods of 15 and 60 min, respectively. As for 60 min of exposure a significant decrease in colour perception was found between subjects at 15,000 ft as compared to the control group as well as between subjects at 15,000 ft as compared to subjects at 10,000 ft. No significant difference was found in the comparison within the 15,000 ft groups across time points pre-, peri-, and post-exposure. Thus, pilots appear to experience only minor colour vision impairment up to an exposure altitude of 15,000 ft over 60 min of exposure.

Performance of oxygenation indices and risk scores to predict invasive mechanical ventilation and mortality in COVID-19

BACKGROUND

Information on the performance of oxygenation indices (OIs) and risk scores in patients requiring invasive mechanical ventilation (IMV) is limited. We determine the performance of the OIs and risk scores in hospitalized patients with COVID-19 to predict the requirement of IMV and death at 28 days after admission.

METHODS

A retrospective study of diagnostic tests in patients admitted to the emergency department, hospitalization, and intensive care unit diagnosed with COVID-19. The receiver operating characteristic curve (ROC-curve) were built with the OIs and risk scores to predict IMV and mortality.

RESULTS

A total of 1402 subjects entered the final analysis, of whom 19.5% (274/1402) received IMV and 23.0% (323/1402) died at 28 days. The ROC-curve of the delta PaO2/FiO2 ratio for the requirement of IMV and mortality at 28-day was 0.589 (95% CI: 0.546-0.632) and 0.567 (95% CI: 0.526-0.608), respectively. PaO2/FiO2 ≤ 300 shows a ROC curve of 0.669 (95% CI: 0.628-0.711) to predict IMV. PaO2/FiO2 ≤ 300 and 4 C mortality score in mortality at 28 days showed an ROC-curve of 0.624 (95% CI: 0.582-0.667) and 0.706 (95% CI: 0.669-0.742), respectively.

CONCLUSION

PaO2/FiO2 ≤ 300, 4 C mortality score ≥ 8, SOFA score ≥ 4 y SaO2/FiO2 ≤ 300 were weak predictors of the IMV requirement from admission, and 4 C mortality score ≥ 8 was weak predictors of the mortality from admission in patients with pulmonary involvement by COVID-19.

External validation of clinical severity scores to guide referral of paediatric acute respiratory infections in resource-limited primary care settings

Accurate and reliable guidelines for referral of children from resource-limited primary care settings are lacking. We identified three practicable paediatric severity scores (the Liverpool quick Sequential Organ Failure Assessment (LqSOFA), the quick Pediatric Logistic Organ Dysfunction-2, and the modified Systemic Inflammatory Response Syndrome) and externally validated their performance in young children presenting with acute respiratory infections (ARIs) to a primary care clinic located within a refugee camp on the Thailand-Myanmar border. This secondary analysis of data from a longitudinal birth cohort study consisted of 3010 ARI presentations in children aged ≤ 24 months. The primary outcome was receipt of supplemental oxygen. We externally validated the discrimination, calibration, and net-benefit of the scores, and quantified gains in performance that might be expected if they were deployed as simple clinical prediction models, and updated to include nutritional status and respiratory distress. 104/3,010 (3.5%) presentations met the primary outcome. The LqSOFA score demonstrated the best discrimination (AUC 0.84; 95% CI 0.79-0.89) and achieved a sensitivity and specificity > 0.80. Converting the scores into clinical prediction models improved performance, resulting in ~ 20% fewer unnecessary referrals and ~ 30-50% fewer children incorrectly managed in the community. The LqSOFA score is a promising triage tool for young children presenting with ARIs in resource-limited primary care settings. Where feasible, deploying the score as a simple clinical prediction model might enable more accurate and nuanced risk stratification, increasing applicability across a wider range of contexts.

The severity of acute hypoxaemia determines distinct changes in intracortical and spinal neural circuits

The purpose of this study was to examine how two common methods of continuous hypoxaemia impact the activity of intracortical circuits responsible for inhibition and facilitation of motor output, and spinal excitability. Ten participants were exposed to 2 h of hypoxaemia at 0.13 fraction of inspired oxygen (F I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol) and 80% of peripheral capillary oxygen saturation (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol) using a simulating altitude device on two visits separated by a week. Using transcranial magnetic and peripheral nerve stimulation, unconditioned motor evoked potential (MEP) area, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), and F-wave persistence and area were assessed in the first dorsal interosseous (FDI) muscle before titration, after 1 and 2 h of hypoxic exposure, and at reoxygenation. The clamping protocols resulted in differing reductions inS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ by 2 h (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol: 81.9 ± 1.3%,F I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol: 90.6 ± 2.5%). Although unconditioned MEP peak to peak amplitude and area did not differ between the protocols, SICI duringF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping was significantly lower at 2 h compared toS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping (P = 0.011) and baseline (P < 0.001), whereas ICF was higher throughout theF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping compared toS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping (P = 0.005). Furthermore, a negative correlation between SICI andS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ (rrm  = -0.56, P = 0.002) and a positive correlation between ICF andS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ (rrm  = 0.69, P = 0.001) were determined, where greater reductions inS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ correlated with less inhibition and less facilitation of MEP responses. Although F-wave area progressively increased similarly throughout the protocols (P = 0.037), persistence of responses was reduced at 2 h and reoxygenation (P < 0.01) during theS p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol compared to theF I O 2 ${F_{{\mathrm{I}}{{\mathrm{O}}_{\mathrm{2}}}}}$ clamping protocol. After 2 h of hypoxic exposure, there is a reduction in the activity of intracortical circuits responsible for inhibiting motor output, as well as excitability of spinal motoneurones. However, these effects can be influenced by other physiological responses to hypoxia (i.e., hyperventilation and hypocapnia). NEW FINDINGS: What is the central question of this study? How do two common methods of acute hypoxic exposure influence the excitability of intracortical networks and spinal circuits responsible for motor output? What is the main finding and its importance? The excitability of spinal circuits and intracortical networks responsible for inhibition of motor output was reduced during severe acute exposure to hypoxia at 2 h, but this was not seen during less severe exposure. This provides insight into the potential cause of variance seen in motor evoked potential responses to transcranial magnetic stimulation (corticospinal excitability measures) when exposed to hypoxia.

Pulse oximetry values from 33,080 participants in the Apple Heart & Movement Study

Wearable devices that include pulse oximetry (SpO₂) sensing afford the opportunity to capture oxygen saturation measurements from large cohorts under naturalistic conditions. We report here a cross-sectional analysis of 72 million SpO₂ values collected from 33,080 individual participants in the Apple Heart and Movement Study, stratified by age, sex, body mass index (BMI), home altitude, and other demographic variables. Measurements aggregated by hour of day into 24-h SpO₂ profiles exhibit similar circadian patterns for all demographic groups, being approximately sinusoidal with nadir near midnight local time, zenith near noon local time, and mean 0.8% lower saturation during overnight hours. Using SpO₂ measurements averaged for each subject into mean nocturnal and daytime SpO₂ values, we employ multivariate ordinary least squares regression to quantify population-level trends according to demographic factors. For the full cohort, regression coefficients obtained from models fit to daytime SpO₂ are in close quantitative agreement with the corresponding values from published reference models for awake arterial oxygen saturation measured under controlled laboratory conditions. Regression models stratified by sex reveal significantly different age- and BMI-dependent SpO₂ trends for females compared with males, although constant terms and regression coefficients for altitude do not differ between sexes. Incorporating categorical variables encoding self-reported race/ethnicity into the full-cohort regression models identifies small but statistically significant differences in daytime SpO₂ (largest coefficient corresponding to 0.13% lower SpO₂, for Hispanic study participants compared to White participants), but no significant differences between groups for nocturnal SpO₂. Additional stratified analysis comparing regression models fit independently to subjects in each race/ethnicity group is suggestive of small differences in age- and sex-dependent trends, but indicates no significant difference in constant terms between any race/ethnicity groups for either daytime or nocturnal SpO₂. The large diverse study population and study design employing automated background SpO₂ measurements spanning the full 24-h circadian cycle enables the establishment of healthy population reference trends outside of clinical settings.

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

A study of survival strategies for improving acclimatization of lowlanders at high-altitude

Human Acclimatization and therapeutic approaches are the core components for conquering the physiological variations at high altitude (≥2500 m) exposure. The declined atmospheric pressure and reduced partial pressure of oxygen at high altitudes tend to decrease the temperature by several folds. Hypobaric hypoxia is a major threat to humanity at high altitudes, and its potential effects include altitude mountain sickness. On severity, it may lead to the development of conditions like high-altitude cerebral edema (HACE) or high-altitude pulmonary edema (HAPE) and cause unexpected physiological changes in the healthy population of travelers, athletes, soldiers, and low landers while sojourning at high altitude. Previous investigations have been done on long-drawn-out acclimatization strategies such as the staging method to prevent the damage caused by high-altitude hypobaric Hypoxia. Inherent Limitations of this strategy hamper the daily lifestyle and time consuming for people. It is not suitable for the rapid mobilization of people at high altitudes. There is a need to recalibrate acclimatization strategies for improving health protection and adapting to the environmental variations at high altitudes. This narrative review details the geographical changes and physiological changes at high altitudes and presents a framework of acclimatization, pre-acclimatization, and pharmacological aspects of high-altitude survival to enhance the government efficacy and capacity for the strategic planning of acclimatization, use of therapeutics, and safe de-induction from high altitude for minimizing the life loss. It's simply too ambitious for the importance of the present review to reduce life loss, and it can be proved as the most essential aspect of the preparatory phase of high-altitude acclimatization in plateau regions without hampering the daily lifestyle. The application of pre-acclimatization techniques can be a boon for people serving at high altitudes, and it can be a short bridge for the rapid translocation of people at high altitudes by minimizing the acclimatization time.

DSC MRI in the human brain using deoxyhemoglobin and gadolinium-Simulations and validations at 3T

INTRODUCTION

Dynamic susceptibility contrast (DSC) MRI allows clinicians to determine perfusion parameters in the brain, such as cerebral blood flow, cerebral blood volume, and mean transit time. To enable quantification, susceptibility changes can be induced using gadolinium (Gd) or deoxyhemoglobin (dOHb), the latter just recently introduced as a contrast agent in DSC. Previous investigations found that experimental parameters and analysis choices, such as the susceptibility amplitude and partial volume, affect perfusion quantification. However, the accuracy and precision of DSC MRI has not been systematically investigated, particularly in the lower susceptibility range.

METHODS

In this study, we compared perfusion values determined using Gd with values determined using a contrast agent with a lower susceptibility-dOHb-under different physiological conditions, such as varying the baseline blood oxygenation and/or magnitude of hypoxic bolus, by utilizing numerical simulations and conducting experiments on healthy subjects at 3T. The simulation framework we developed for DSC incorporates MRI signal contributions from intravascular and extravascular proton spins in arterial, venous, and cerebral tissue voxels. This framework allowed us to model the MRI signal in response to both Gd and dOHb.

RESULTS AND DISCUSSION

We found, both in the experimental results and simulations, that a reduced intravascular volume of the selected arterial voxel, reduced baseline oxygen saturation, greater susceptibility of applied contrast agent (Gd vs. dOHb), and/or larger magnitude of applied hypoxic bolus reduces the overestimation and increases precision of cerebral blood volume and flow. As well, we found that normalizing tissue to venous rather than arterial signal increases the accuracy of perfusion quantification across experimental paradigms. Furthermore, we found that shortening the bolus duration increases the accuracy and reduces the calculated values of mean transit time. In summary, we experimentally uncovered an array of perfusion quantification dependencies, which agreed with the simulation framework predictions, using a wider range of susceptibility values than previously investigated. We argue for caution when comparing absolute and relative perfusion values within and across subjects obtained from a standard DSC MRI analysis, particularly when employing different experimental paradigms and contrast agents.

Temporary hypoxemia at high altitude in an intensive care unit physician

A 42-year-old pediatric intensive care unit physician traveled to Nepal and took a helicopter trip to Everest Base Camp. The helicopter reached an altitude of 5500 m during flight and descended at different destinations with varying altitudes. At Hotel Everest View at 3820 m, his oxygen saturation was 79%. He had mild tachypnea and deep breathing but was able to walk around, jump, and take photographs. He returned to Kathmandu (altitude, 1324 m) without using any supplemental oxygen during the entire trip. Based on calculations with the alveolar gas equation, he observed that he and his fellow passengers probably had hypoxemia during the trip. In summary, temporary hypoxemia associated with high altitude in healthy individuals without cardiorespiratory compromise may not require oxygen therapy. In contrast, intensive care unit patients who have respiratory failure may have similar oxygen saturation levels but may require oxygen therapy and mechanical ventilation. The oxygen saturation level must be interpreted in consideration of the clinical scenario before deciding about the need for oxygen therapy.

Oxygen saturation targets for adults with acute hypoxemia in low and lower-middle income countries: a scoping review with analysis of contextual factors

Knowing the target oxygen saturation (SpO₂) range that results in the best outcomes for acutely hypoxemic adults is important for clinical care, training, and research in low-income and lower-middle income countries (collectively LMICs). The evidence we have for SpO₂ targets emanates from high-income countries (HICs), and therefore may miss important contextual factors for LMIC settings. Furthermore, the evidence from HICs is mixed, amplifying the importance of specific circumstances. For this literature review and analysis, we considered SpO₂ targets used in previous trials, international and national society guidelines, and direct trial evidence comparing outcomes using different SpO₂ ranges (all from HICs). We also considered contextual factors, including emerging data on pulse oximetry performance in different skin pigmentation ranges, the risk of depleting oxygen resources in LMIC settings, the lack of access to arterial blood gases that necessitates consideration of the subpopulation of hypoxemic patients who are also hypercapnic, and the impact of altitude on median SpO₂ values. This process of integrating prior study protocols, society guidelines, available evidence, and contextual factors is potentially useful for the development of other clinical guidelines for LMIC settings. We suggest that a goal SpO₂ range of 90-94% is reasonable, using high-performing pulse oximeters. Answering context-specific research questions, such as an optimal SpO₂ target range in LMIC contexts, is critical for advancing equity in clinical outcomes globally.

Validity of the ROX index in predicting invasive mechanical ventilation requirement in pneumonia

Background

The ROX index (Respiratory rate-OXygenation) has been described as a prediction tool to identify the need for invasive mechanical ventilation (IMV) in community-acquired pneumonia (CAP) with acute hypoxaemic respiratory failure treated with high-flow nasal cannula in order to avoid delay of a necessary intubation. However, its use in predicting the need for ventilatory support in hospitalised patients with CAP has not been validated.

Methods

This is a retrospective cohort study including subjects with CAP treated in the general ward, emergency service or intensive care unit of a third-level centre in Cundinamarca, Colombia, between January 2001 and February 2020. The ROX index was estimated as the ratio of oxygen saturation/fraction of inspired oxygen to respiratory rate.

Results

A total of 895 patients were included, of whom 93 (10%) required IMV. The ROX index proved to be a good predictor, presenting an area under the curve of receiver operating characteristics (AUROC) of 0.733 (95% CI 0.671 to 0.795, p<0.001) when determined by pulse oximetry and an AUROC of 0.779 (95% CI 0.699 to 0.859, p<0.001) when estimated by arterial blood gas (ABG) parameters, with an intraclass correlation of 0.894. The estimated cut-off point was 14.8; a score less than 14.8 indicates high risk of requiring IMV.

Conclusion

The ROX index is a good predictor of IMV in hospitalised patients with CAP. It presents good performance when calculated through pulse oximetry and can replace the one calculated by ABG.

Hyperoxia Reprogrammes Microvascular Endothelial Cell Response to Hypoxia in an Organ-Specific Manner

Organ function relies on microvascular networks to maintain homeostatic equilibrium, which varies widely in different organs and during different physiological challenges. The endothelium role in this critical process can only be evaluated in physiologically relevant contexts. Comparing the responses to oxygen flux in primary murine microvascular EC (MVEC) obtained from brain and lung tissue reveals that supra-physiological oxygen tensions can compromise MVEC viability. Brain MVEC lose mitochondrial activity and undergo significant alterations in electron transport chain (ETC) composition when cultured under standard, non-physiological atmospheric oxygen levels. While glycolytic capacity of both lung and brain MVEC are unchanged by environmental oxygen, the ability to trigger a metabolic shift when oxygen levels drop is greatly compromised following exposure to hyperoxia. This is particularly striking in MVEC from the brain. This work demonstrates that the unique metabolism and function of organ-specific MVEC (1) can be reprogrammed by external oxygen, (2) that this reprogramming can compromise MVEC survival and, importantly, (3) that ex vivo modelling of endothelial function is significantly affected by culture conditions. It further demonstrates that physiological, metabolic and functional studies performed in non-physiological environments do not represent cell function in situ, and this has serious implications in the interpretation of cell-based pre-clinical models.

Post-fatigue ability to activate muscle is compromised across a wide range of torques during acute hypoxic exposure

The purpose of this study was to assess how severe acute hypoxia alters the neural mechanisms of muscle activation across a wide range of torque output in a fatigued muscle. Torque and electromyography responses to transcranial and motor nerve stimulation were collected from 10 participants (27 years ± 5 years, 1 female) following repeated performance of a sustained maximal voluntary contraction that reduced torque to 60% of the pre‐fatigue peak torque. Contractions were performed after 2 h of hypoxic exposure and during a sham intervention. For hypoxia, peripheral blood oxygen saturation was titrated to 80% over a 15‐min period and remained at 80% for 2 h. Maximal voluntary torque, electromyography root mean square, voluntary activation and corticospinal excitability (motor evoked potential area) and inhibition (silent period duration) were then assessed at 100%, 90%, 80%, 70%, 50% and 25% of the target force corresponding to the fatigued maximal voluntary contraction. No hypoxia‐related effects were identified for voluntary activation elicited during motor nerve stimulation. However, during measurements elicited at the level of the motor cortex, voluntary activation was reduced at each torque output considered (P = .002, η_p² = .829). Hypoxia did not impact the correlative linear relationship between cortical voluntary activation and contraction intensity or the correlative curvilinear relationship between motor nerve voluntary activation and contraction intensity. No other hypoxia‐related effects were identified for other neuromuscular variables. Acute severe hypoxia significantly impairs the ability of the motor cortex to voluntarily activate fatigued muscle across a wide range of torque output.

Use of High-Flow Nasal Cannula in Patients With Pneumonia and Hypoxemic Respiratory Failure at Altitudes Above 2600 m: What Is the Best Predictor of Success?

Introduction: The use of high-flow nasal cannulas (HFNC) in patients with hypoxemic ventilatory failure reduces the need for mechanical ventilation and does not increase mortality when intubation is promptly applied. The aim of the study is to describe the behavior of HFNC in patients who live at high altitudes, and the performance of predictors of success/failure of this strategy. Methods: Prospective multicenter cohort study, with patients aged over 18 years recruited for 12 months in 2020 to 21. All had a diagnosis of hypoxemic respiratory failure secondary to pneumonia, were admitted to intensive care units, and were receiving initial management with a high-flow nasal cannula. The variables assessed included need for intubation, mortality in ICU, and the validation of SaO2, respiratory rate (RR) and ROX index (IROX) as predictors of HFNC success / failure. Results: One hundred and six patients were recruited, with a mean age of 59 years and a success rate of 74.5%. Patients with treatment failure were more likely to be obese (BMI 27.2 vs 25.5; OR: 1.03; 95% CI: .95-1.1) and had higher severity scores at admission (APACHE II 12 vs 20; OR 1.15; 95% CI: 1.06-1.24). Respiratory rates after 12 (AUC .81 CI: .70-.92) and 18 h (AUC .85 CI: .72-0.90) of HFNC use were the best predictors of failure, performing better than those that included oxygenation. ICU mortality was higher in the failure group (6% vs 29%; OR 8.8; 95% CI:1.75-44.7). Conclusions: High-flow oxygen cannula therapy in patients with hypoxemic respiratory failure living at altitudes above 2600 m is associated with low rates of therapy failure and a reduced need for mechanical ventilation in the ICU. The geographical conditions and secondary physiological changes influence the performance of the traditionally validated predictors of therapy success. Respiratory rate <30 proved to be the best indicator of early success of the device at 12 h of use.

Severe acute hypoxia impairs recovery of voluntary muscle activation after sustained submaximal elbow flexion

The purpose of this study was to determine how severe acute hypoxia alters neural mechanisms during, and following, a sustained fatiguing contraction. Fifteen participants (25 ± 3.2 years, six female) were exposed to a sham condition and a hypoxia condition where they performed a 10 min elbow flexor contraction at 20% of maximal torque. For hypoxia, peripheral blood oxygen saturation ( S p O 2 ) was titrated to 80% over a 15 min period and maintained for 2 h. Maximal voluntary contraction torque, EMG root mean square, voluntary activation, rating of perceived muscle fatigue, and corticospinal excitability (motor-evoked potential) and inhibition (silent period duration) were then assessed before, during and for 6 min after the fatiguing contraction. No hypoxia-related effects were identified for neuromuscular variables during the fatigue task. However, for recovery, voluntary activation assessed by motor point stimulation of biceps brachii was lower for hypoxia than sham at 4 min (sham: 89% ± 7%; hypoxia: 80% ± 12%; P = 0.023) and 6 min (sham: 90% ± 7%; hypoxia: 78% ± 11%; P = 0.040). Similarly, voluntary activation (P = 0.01) and motor-evoked potential area (P = 0.002) in response to transcranial magnetic stimulation of the motor cortex were 10% and 11% lower during recovery for hypoxia compared to sham, respectively. Although an S p O 2 of 80% did not affect neural activity during the fatiguing task, motor cortical output and corticospinal excitability were reduced during recovery in the hypoxic environment. This was probably due to hypoxia-related mechanisms involving supraspinal motor circuits. KEY POINTS: Acute hypoxia has been shown to impair voluntary activation of muscle and alter the excitability of the corticospinal motor pathway during exercise. However, little is known about how hypoxia alters the recovery of the motor system after performing fatiguing exercise. Here we assessed hypoxia-related responses of motor pathways both during active contractions and during recovery from active contractions, with transcranial magnetic stimulation and motor point stimulation of the biceps brachii. Fatiguing exercise caused reductions in voluntary activation, which was exacerbated during recovery from a 10 min sustained elbow flexion in a hypoxic environment. These results suggest that reductions in blood oxygen concentration impair the ability of motor pathways in the CNS to recover from fatiguing exercise, which is probably due to hypoxia-induced mechanisms that reduce output from the motor cortex.

Health Effects of Chronic Intermittent Hypoxia at a High Altitude among Chilean Miners: Rationale, Design, and Baseline Results of a Longitudinal Study

OBJECTIVES

This study aims to assess the health effects on mining workers of exposure to chronic intermittent hypoxia (CIH) at high- and very high-altitude mining compared with similar work at lower altitudes in Chile, and it also aims to constitute the baseline of a 5-year follow-up study.

METHODS

We designed a cross-sectional study to assess health conditions in 483 miners working at 2 levels of altitude exposure: 336 working at a very high or high altitude (HA; 247 above 3900-4400 m, and 89 at 3000-3900 m), and 147 below 2400 m. Subjects were randomly selected in two stages. First, a selection of mines from a census of mines in each altitude stratum was made. Secondly, workers with less than 2 years of employment at each of the selected mines were recruited. The main outcomes measured at the baseline were mountain sickness, sleep alterations, hypertension, body mass index, and neurocognitive functions.

RESULTS

Prevalence of acute mountain sickness (AMS) was 28.4% in the very high-altitude stratum (P = 0.0001 compared with the low stratum), and 71.7% experienced sleep disturbance (P = 0.02). The adjusted odds ratio for AMS was 9.2 (95% confidence interval: 5.2-16.3) when compared with the very high- and low-altitude groups. Motor processing speed and spatial working memory score were lower for the high-altitude group. Hypertension was lower in the highest-altitude subjects, which may be attributed to preoccupational screening even though this was not statistically significant.

CONCLUSIONS

Despite longer periods of acclimatization to CIH, subjects continue to present AMS and sleep disturbance. Compromise of executive functions was detected, including working memory at HA. Further rigorous research is warranted to understand long-term health impacts of high-altitude mining, and to provide evidence-based policy recommendations.

Cognitive and psychophysiological impact of surgical mask use during university lessons

The aim of the present study was to analyze the impact of surgical mask use in cognitive and psychophysiological response of university students during a lesson. We analyzed 50 volunteers university students (age 20.2 ± 2.9) in two 150 min lessons. i. personal class using a surgical mask and ii. online class with student at home without the mask. Blood oxygen saturation, heart rate and heart rate variability, mental fatigue and reaction time were measured before and immediately after both lectures. We found how both lesson produced an increase in mental fatigue, reaction time and autonomous sympathetic modulation, being heart rate significantly higher (77.7 ± 18.2 vs. 89.3 ± 11.2 bpm, not mask, mask respectively) and blood oxygen saturation significantly lower (98.4 ± 0.5 vs. 96.0 ± 1.8%, mask, not mask respectively) using the surgical mask. The use of surgical mask during a 150 min university lesson produced an increased heart rate and a decrease in blood oxygen saturation, not significantly affecting the mental fatigue perception, reaction time and time, frequency and nonlinear hear rate variability domains of students.

Rate-Pressure Product Responses to Static Contractions Performed at Various Altitudes

Simmonds, Michael J., Surendran Sabapathy, and Jean-Marc Hero. Rate-pressure product responses to static contractions performed at various altitudes. High Alt Med Biol. 22: 166-173, 2021. Background: Adventure tourism has led to an unprecedented number of individuals being exposed to altitude, including those with subclinical cardiometabolic disorders. The disproportionate hemodynamic challenge associated with small-muscle static activities is potentially dangerous at altitude as these may compound the risk for cardiac events. We thus examined the cardiovascular response to, and during recovery from, static exercise performed at altitude. Methods: Eighteen individuals completed this study at three altitudes (sea level; ∼1,500 m; ∼3,000 m) in central Nepal. At each altitude, individuals performed two handgrip contractions for 2 minutes at the same intensity (30% maximal voluntary contraction [MVC]), with two distinct recovery periods: during control recovery was completed quietly at rest, while during ischemic challenge recovery was conducted with a cuff occluding the upper limb. Results: Oxygen saturation decreased during ascent to 1,500 m (-2%) and 3,000 m (-8%), compared with sea level. Handgrip MVC was not affected by altitude, although heart rate at rest (∼70 beat/min), during static exercise (range ∼90-95 beat/min), and during recovery in both conditions (each ∼70 beat/min) was significantly increased by ∼15% at 3,000 m, but not 1,500 m. The magnitude of the muscle metaboreflex during recovery from static exercise was unaffected by altitude; however, the rate-pressure product was significantly elevated by ∼10% during and following static exercise at 3,000 m. Conclusions: A significant increase in the rate-pressure product during static exercise was observed at altitude, which persisted during recovery. Individuals at risk for cardiac events should use awareness of static contractions while at altitude, especially considering that stress induced by static exercise is additive to that of dynamic activities such as hiking.

Vagal Threshold Determination during Incremental Stepwise Exercise in Normoxia and Normobaric Hypoxia

This study focuses on the determination of the vagal threshold (T_va) during exercise with increasing intensity in normoxia and normobaric hypoxia. The experimental protocol was performed by 28 healthy men aged 20 to 30 years. It included three stages of exercise on a bicycle ergometer with a fraction of inspired oxygen (FiO₂) 20.9% (normoxia), 17.3% (simulated altitude ~1500 m), and 15.3% (~2500 m) at intensity associated with 20% to 70% of the maximal heart rate reserve (MHRR) set in normoxia. T_va level in normoxia was determined at exercise intensity corresponding with (M ± SD) 45.0 ± 5.6% of MHRR. Power output at T_va (PO_th), representing threshold exercise intensity, decreased with increasing degree of hypoxia (normoxia: 114 ± 29 W; FiO₂ = 17.3%: 110 ± 27 W; FiO₂ = 15.3%: 96 ± 32 W). Significant changes in PO_th were observed with FiO₂ = 15.3% compared to normoxia (p = 0.007) and FiO₂ = 17.3% (p = 0.001). Consequentially, normoxic %MHRR adjusted for hypoxia with FiO₂ = 15.3% was reduced to 39.9 ± 5.5%. Considering the convenient altitude for exercise in hypoxia, PO_th did not differ excessively between normoxic conditions and the simulated altitude of ~1500 m, while more substantial decline of PO_th occurred at the simulated altitude of ~2500 m compared to the other two conditions.

Time course of neuromuscular responses to acute hypoxia during voluntary contractions

NEW FINDINGS

What is the central question of this study? How does acute hypoxia alter central and peripheral fatigue during brief and sustained maximal voluntary muscle contractions? What is the main finding and its importance? Perception of fatigue during muscle contractions was increased progressively for 2 h after hypoxic exposure. However, an increase in motor cortex excitability and a decrease in voluntary activation of skeletal muscle were observed across the entire protocol when performing brief (3 s) maximal contractions. These adaptations were abolished if the brief contraction was held for a duration of 20 s, which was presumably attributable to a successful redistribution of blood to overcome the reduced oxygen content.

ABSTRACT

Few studies have examined the time course of changes in the motor system after acute exposure to hypoxia. Thus, the purpose of this study was to examine how acute hypoxia affects corticospinal excitability, voluntary activation (VA) and the perception of fatigue during brief (3 s) and sustained (20 s) maximal voluntary contractions (MVCs). Fourteen healthy individuals (23 ± 2.2 years of age; four female) were exposed to hypoxia and sham conditions. During hypoxia, peripheral blood oxygen saturation was titrated over a 15 min period and remained at 80% during testing. Corticospinal excitability and VA were assessed before titration (Pre), 0, 1 and 2 h after. At each time point, the brief and sustained elbow flexion MVCs were performed. Motor evoked potentials (MEPs) were obtained using transcranial magnetic stimulation. Superimposed and resting twitches were obtained from motor point stimulation of biceps brachii to calculate the level of VA, and ratings of perceived fatigue were obtained with a modified CR-10 Borg scale. A condition-by-time interaction was detected for the CR-10 Borg scale, whereby perception of fatigue increased progressively throughout the hypoxia protocol. However, main effects of MEP area and VA indicated that corticospinal excitability increased, and VA of the biceps brachii decreased, throughout the hypoxia protocol. Given that these changes in MEP area and VA were seen only when performing the brief MVCs (and not during the sustained MVCs), performing longer contractions might overcome reduced oxygen content by redirecting blood flow to active areas of the motor system.

Effect of altitude on mortality of end-stage renal disease patients on hemodialysis in Peru

Background

In Latin America, the prevalence of end-stage kidney disease (ESKD) has risen tremendously during the last decade. Previous studies have suggested that receiving dialysis at high altitude confers mortality benefits; however, this effect has not been demonstrated at >2000 m above sea level (masl) or in developing countries.

Methods

This historical cohort study analyzed medical records from six Peruvian hemodialysis (HD) centers located at altitudes ranging from 44 to 3827 masl. Adult ESKD patients who started maintenance HD between 2000 and 2010 were included. Patients were classified into two strata based on the elevation above sea level of their city of residence: low altitude (<2000 masl) and high altitude (≥2000 masl). Death from any cause was collected from national registries and Cox proportional hazards models were built.

Results

A total of 720 patients were enrolled and 163 (22.6%) resided at high altitude. The low-altitude group was significantly younger, more likely to have diabetes or glomerulonephritis as the cause of ESKD and higher hemoglobin. The all-cause mortality rate was 84.3 per 1000 person-years. In the unadjusted Cox model, no mortality difference was found between the high- and low-altitude groups {hazard ratio [HR] 1.20 [95% confidence interval (CI) 0.89-1.62]}. After multivariable adjustment, receiving HD at high altitude was not significantly associated with higher mortality, but those with diabetes as the cause of ESKD had significantly higher mortality [HR 2.50 (95% CI 1.36-4.59)].

Conclusions

In Peru, patients receiving HD at high altitudes do not have mortality benefits.

A factorial cluster-randomised controlled trial combining home-environmental and early child development interventions to improve child health and development: rationale, trial design and baseline findings

Background

Exposure to unhealthy environments and inadequate child stimulation are main risk factors that affect children’s health and wellbeing in low- and middle-income countries. Interventions that simultaneously address several risk factors at the household level have great potential to reduce these negative effects. We present the design and baseline findings of a cluster-randomised controlled trial to evaluate the impact of an integrated home-environmental intervention package and an early child development programme to improve diarrhoea, acute respiratory infections and childhood developmental outcomes in children under 36 months of age living in resource-limited rural Andean Peru.

Methods

We collected baseline data on children’s developmental performance, health status and demography as well as microbial contamination in drinking water. In a sub-sample of households, we measured indoor kitchen 24-h air concentration levels of carbon monoxide (CO) and fine particulate matter (PM_2.5) and CO for personal exposure.

Results

We recruited and randomised 317 children from 40 community-clusters to four study arms. At baseline, all arms had similar health and demographic characteristics, and the developmental status of children was comparable between arms. The analysis revealed that more than 25% of mothers completed primary education, a large proportion of children were stunted and diarrhoea prevalence was above 18%. Fifty-two percent of drinking water samples tested positive for thermo-tolerant coliforms and the occurrence of E.coli was evenly distributed between arms. The mean levels of kitchen PM_2.5 and CO concentrations were 213 μg/m³ and 4.8 ppm, respectively.

Conclusions

The trial arms are balanced with respect to most baseline characteristics, such as household air and water pollution, and child development. These results ensure the possible estimation of the trial effectiveness. This trial will yield valuable information for assessing synergic, rational and cost-effective benefits of the combination of home-based interventions.

Trial Registry

ISRCTN-26548981.

Effects of high altitude on respiratory rate and oxygen saturation reference values in healthy infants and children younger than 2 years in four countries: a cross-sectional study

BACKGROUND

In resource-limited settings, pneumonia diagnosis and management are based on thresholds for respiratory rate (RR) and oxyhaemoglobin saturation (SpO2) recommended by WHO. However, as RR increases and SpO2 decreases with elevation, these thresholds might not be applicable at all altitudes. We sought to determine upper thresholds for RR and lower thresholds for SpO2 by age and altitude at four sites, with altitudes ranging from sea level to 4348 m.

METHODS

In this cross-sectional study, we enrolled healthy children aged 0-23 months who lived within the study areas in India, Guatemala, Rwanda, and Peru. Participants were excluded if they had been born prematurely (<37 weeks gestation); had a congenital heart defect; had history in the past 2 weeks of overnight admission to a health facility, diagnosis of pneumonia, antibiotic use, or respiratory or gastrointestinal signs; history in the past 24 h of difficulty breathing, fast breathing, runny nose, or nasal congestion; and current runny nose, nasal congestion, fever, chest indrawing, or cyanosis. We measured RR either automatically with the Masimo Rad-97, manually, or both, and measured SpO2 with the Rad-97. Trained staff measured RR in duplicate and SpO2 in triplicate in children who had no respiratory symptoms or signs in the past 2 weeks. We estimated smooth percentiles for RR and SpO2 that varied by age and site using generalised additive models for location, shape, and scale. We compared these data with WHO RR and SpO2 thresholds for tachypnoea and hypoxaemia to determine agreement.

FINDINGS

Between Nov 24, 2017, and Oct 10, 2018, we screened 2027 children for eligibility. 335 were ineligible, leaving 1692 eligible participants. 30 children were excluded because of missing values and 92 were excluded because of measurement or data entry errors, leaving 1570 children in the final analysis. 404 participants were from India (altitude 1-919 m), 389 were from Guatemala (1036-2017 m), 341 from Rwanda (1449-1644 m), and 436 from Peru (3827-4348 m). Mean age was 7·2 months (SD 7·2) and 796 (50·7%) of 1570 participants were female. Although average age was mostly similar between settings, the average participant age in Rwanda was noticeably younger, at 5·5 months (5·9). In the 1570 children included in the analysis, mean RR was 31·9 breaths per min (SD 7·1) in India, 41·5 breaths per min in Guatemala (8·4), 44·0 breaths per min in Rwanda (10·8), and 48·0 breaths per min in Peru (9·4). Mean SpO2 was 98·3% in India (SD 1·5), 97·3% in Guatemala (2·4), 96·2% in Rwanda (2·6), and 89·7% in Peru (3·5). Compared to India, mean RR was 9·6 breaths per min higher in Guatemala, 12·1 breaths per min higher in Rwanda, and 16·1 breaths per min higher in Peru (likelihood ratio test p<0·0001). Smooth percentiles for RR and SpO2 varied by site and age. When we compared age-specific and site-specific 95th percentiles for RR and 5th percentiles for SpO2 against the WHO cutoffs, we found that the proportion of false positives for tachypnoea increased with altitude: 0% in India (95% CI 0-0), 7·3% in Guatemala (4·1-10·4), 16·8% in Rwanda (12·9-21·1), and 28·9% in Peru (23·7-33·0). We also found a high proportion of false positives for hypoxaemia in Peru (11·6%, 95% CI 7·0-14·7).

INTERPRETATION

WHO cutoffs for fast breathing and hypoxaemia overlap with RR and SpO2 values that are normal for children in different altitudes. Use of WHO definitions for fast breathing could result in misclassification of pneumonia in many children who live at moderate to high altitudes and show acute respiratory signs. The 5th percentile for SpO2 was in reasonable agreement with the WHO definition of hypoxaemia in all regions except for Peru (the highest altitude site). Misclassifications could result in inappropriate management of paediatric respiratory illness and misdirection of potentially scarce resources such as antibiotics and supplemental oxygen. Future studies at various altitudes are needed to validate our findings and recommend a revision to current guidelines. Substantiating research in sick children is still needed.

FUNDING

US National Institutes of Health, Bill & Melinda Gates Foundation.

Revised threshold values for neonatal oxygen saturation at mild and moderate altitudes

AIM

The aim of this study was to determine reference values for oxygen saturation (SpO₂ ) in neonates at mild and moderate altitudes.

METHODS

Our study included 41 097 consecutively born, asymptomatic neonates from 35 hospitals, located in Yunnan, China, with altitudes ranging from 267 to 2202 m. Pre-and post-ductal SpO₂ of each neonate was measured at 24 hours of age and before hospital discharge. All study participants, according to the altitude of birth, were categorised into three groups: low (0-500 m), mild (500-1500 m) and moderate altitude (1500-2500 m).

RESULTS

Every 1000-m increase in altitude was associated with a 1.54 per cent decrease in mean SpO₂ . The means of pre-ductal SpO₂ at low, mild and moderate groups were 97.9%, 96.4% and 95.5%, respectively. We used the 2.5th percentile of SpO₂ distribution as the cut-off for neonatal SpO₂ screening and defined new cut-off values of ≤93% for mild altitudes, ≤92% for moderate altitudes and no adjustment for low altitudes.

CONCLUSION

We recommend revised cut-off values for neonatal SpO₂ at mild and moderate altitudes and provide new values for paediatricians to refer to when screening neonates for severe congenital heart or lung diseases.

[Factors associated to high-flow nasal cannula treatment failure in pediatric patients with respiratory failure in two pediatric intensive care units at high altitude]

INTRODUCTION

Acute respiratory failure is the leading cause of hospitalization in pediatrics. High-flow nasal cannulas (HFNCs) offer a new alternative, but the evidence and indications are still debated. The performance of HFNCs at high altitude has not been described to date.

OBJECTIVE

To describe the use of HFNCs in pediatric patients admitted with respiratory failure and explore the factors associated with treatment failure.

METHODOLOGY

A prospective cohort study was carried out in patients between 1 month and 18 years of age managed with HFNCs. The demographic and treatment response data were recorded at baseline and after 1, 6 and 24hours. The number of failures was determined, as well as the length of stay, complications and mortality. Patients with treatment failure were compared with the rest.

RESULTS

A total of 539 patients were enrolled. Infants (70.9%) of male sex (58.4%) and airway diseases such as asthma and bronchiolitis (61.2%) were more frequent. There were 53 failures (9.8%), with 21 occurring in the first 24hours. The median length of stay was 4 days (IQR 4); there were 5 deaths (0.9%) and 13 adverse events (epistaxis) (2.2%). Improvement was observed in vital signs and severity over time, with differences in the group that failed, but without interactions. The final logistic model established an independent relationship of failure between the hospital (OR 2.78, 95%CI 1.48-5.21) and the initial respiratory rate (OR 1.56, 95%CI 1.21-2.01).

CONCLUSIONS

HFNCs afford good clinical response, with few complications and a low failure rate. The differences found between institutions suggest a subjective relationship in the decision of therapy failure.

Physiologically driven, altitude-adaptive model for the interpretation of pediatric oxygen saturation at altitudes above 2,000 m a.s.l

Measuring peripheral oxygen saturation (SpO2) with pulse oximeters at the point of care is widely established. However, since SpO2 is dependent on ambient atmospheric pressure, the distribution of SpO2 values in populations living above 2000 m a.s.l. is largely unknown. Here, we propose and evaluate a computer model to predict SpO2 values for pediatric permanent residents living between 0 and 4,000 m a.s.l. Based on a sensitivity analysis of oxygen transport parameters, we created an altitude-adaptive SpO2 model that takes physiological adaptation of permanent residents into account. From this model, we derived an altitude-adaptive abnormal SpO2 threshold using patient parameters from literature. We compared the obtained model and threshold against a previously proposed threshold derived statistically from data and two empirical data sets independently recorded from Peruvian children living at altitudes up to 4,100 m a.s.l. Our model followed the trends of empirical data, with the empirical data having a narrower healthy SpO2 range below 2,000 m a.s.l. but the medians never differed more than 2.3% across all altitudes. Our threshold estimated abnormal SpO2 in only 17 out of 5,981 (0.3%) healthy recordings, whereas the statistical threshold returned 95 (1.6%) recordings outside the healthy range. The strength of our parametrized model is that it is rooted in physiology-derived equations and enables customization. Furthermore, as it provides a reference SpO2, it could assist practitioners in interpreting SpO2 values for diagnosis, prognosis, and oxygen administration at higher altitudes.NEW & NOTEWORTHY Our model describes the altitude-dependent decrease of SpO2 in healthy pediatric residents based on physiological equations and can be adapted based on measureable clinical parameters. The proposed altitude-specific abnormal SpO2 threshold might be more appropriate than rigid guidelines for administering oxygen that currently are only available for patients at sea level. We see this as a starting point to discuss and adapt oxygen administration guidelines.

Values of heart rate at rest in children and adults living at different altitudes in the Andes

Introduction

The heart rate (HR) is useful for the monitoring of patients, but almost no studies have been found which describe their variations according to different geographic locales and altitudes using centiles in children and adults.

Methodology

Descriptive, cross-sectional study of secondary data. Measurements were taken with a calibrated pulse oximeter; our participants resided in host cities for more than 2 months and underwent clinical evaluations by physicians. The results were categorized according to their age group and the altitude of residence using centile charts.

Results

Our sample size consisted of 6,289 subjects across different villages in Peru. Using Pearson correlation between HR and altitude, it was found in the group of patients aged 1–5 years, a coefficient of -0.118 (p value = 0.012), in the group of patients aged 6–17, 0.047 (p value = 0.025), in the group of patients aged 18–50, -0.044 (p value = 0.041) and for the group of patients aged 51–80, 0.042 (p value = 0.256). In the groups of 1–5, 6–17 and 18–50 years of age, the variations were negligible but statistically significant due to our large sample size. When all of the data was evaluated, HR values were also found to have negligible variations according to the residence altitude, with a Pearson coefficient of -0.033 (p value = 0.009). Centiles charts were used to describe the distribution of HR for different age groups by altitude of residence.

Conclusion

There are minimal variations of the HR according to the altitude of residence in all age groups.

Education, Altitude, and Humidity Can Interactively Explain Spatial Discrepancy and Predict Short Stature in 213,795 Chinese School Children

Backgrounds and Objectives: The north-south height distinctions in Chinese children suggest that some geographical-climatic factors could determine height variation of short stature. In a national health survey, we aimed to explore the spatial distribution of short stature on city scales, and detect its socio-economic and geographical-climatic factors. Methods: Data on the prevalence of short stature were obtained from a 2014 cross-sectional survey of China (CNSSCH). In total, 213,795 Han Chinese students aged 7-18 years, from 106 cities across 30 provinces, were included. Both China and World Health Organization (WHO) growth references were adopted to define short stature. Results: A spatial clustering was apparent in the distribution of short stature. After multivariable adjustment, altitude and humidity significantly increased the risk of high prevalence in short stature, according to the WHO (odds ratio [OR] = 1.61 and 1.26, 95% confidence interval [CI]: 1.20-2.17 and 1.03-1.54) and China (OR = 1.54 and 1.26; 95% CI: 1.15-2.05 and 1.02-1.55) growth references. Additionally, education significantly decreased the risk of high prevalence in short stature according to the WHO (OR = 0.40; 95% CI: 0.22-0.74) and China (OR = 0.42; 95% CI: 0.22-0.77) growth references. Combining both altitude >400 m and education <9 years, as well as education <9 years and humidity >70%, received the largest effect-size estimate, and significance retained after multivariable adjustment. Conclusions: Our findings indicate that high altitude and humidity increased the risk of high prevalence in short stature, high education was associated with low prevalence. Additionally, we observed possible interactions between education and altitude/humidity. They may interactively explain spatial discrepancy and predict short stature in Chinese school children. Further validations are necessary.