The autonomic nervous system at high altitude

Preconditioning with Ginsenoside Rg3 mitigates cardiac injury induced by high-altitude hypobaric hypoxia exposure in mice by suppressing ferroptosis through inhibition of the RhoA/ROCK signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Ginseng has historically been utilized as a conventional herbal remedy and dietary supplement to enhance physical stamina and alleviate fatigue. The primary active component of Ginseng, Ginsenoside Rg3 (GS-Rg3), possesses diverse pharmacological properties including immune modulation and anti-inflammatory effects. Furthermore, GS-Rg3 has demonstrated efficacy in mitigating tissue and organ damage associated with metabolic disorders such as hypertension, hyperglycemia, and hyperlipidemia. Nevertheless, its potential impact on high-altitude cardiac injury (HACI) remains insufficiently explored.

AIM OF THE STUDY

The aim of this study was to examine the potential cardioprotective effects of Ginsenoside Rg3, and to investigate how Ginsenoside Rg3 preconditioning can enhance high-altitude cardiac injury by inhibiting the RhoA/ROCK pathway and ferroptosis in cardiac tissue. The findings of this study may contribute to the development of novel therapeutic strategies using traditional Chinese medicine for high-altitude cardiac injury, based on experimental evidence.

MATERIALS AND METHODS

A hypobaric hypoxia chamber was employed to simulate hypobaric hypoxia conditions equivalent to an altitude of 6000 m. Through a randomization process, groups of six male mice were assigned to receive either saline, Ginsenoside Rg3 at doses of 15 mg/kg or 30 mg/kg, or lysophosphatidic acid (LPA) at 1 mg/kg. The impact of Ginsenoside Rg3 on high altitude-induced arrhythmias was evaluated using electrocardiography. Cardiac pathology sections stained with hematoxylin and eosin were evaluated for damage, with the extent of cardiomyocyte damage observed via transmission electron microscopy. The impact of Ginsenoside Rg3 on high-altitude cardiac injury was investigated through analysis of serum biomarkers for cardiac injury (CK-MB, BNP), inflammatory cytokines (TNF, IL-6, IL-1β), reactive oxygen species (ROS) and glutathione (GSH). The expression levels of hypoxia and hypoxia-related proteins in myocardial tissues from each experimental group were assessed using Western blot analysis. Following a review of the existing literature, the traditional regulatory mechanisms of ferroptosis were examined. Immunofluorescence staining of cardiac tissues and Western blotting techniques were utilized to investigate the impact of Ginsenoside Rg3 on cardiomyocyte ferroptosis through the RhoA/ROCK signaling pathway under conditions of hypobaric hypoxia exposure.

RESULTS

Pre-treatment with Ginsenoside Rg3 improved high altitude-induced arrhythmias, reduced cardiomyocyte damage, decreased cardiac injury biomarkers and inflammatory cytokines, and lowered the expression of hypoxia-related proteins in myocardial tissues. Both Western blotting and immunofluorescence staining of cardiac tissues demonstrated that exposure to high-altitude hypobaric hypoxia results in elevated expression of ferroptosis and proteins related to the RhoA/ROCK pathway. Experimental validation corroborated that the role of the RhoA/ROCK signaling pathway in mediating ferroptosis.

CONCLUSIONS

The findings of our study suggest that preconditioning with Ginsenoside Rg3 may attenuate cardiac injury caused by high-altitude hypobaric hypoxia exposure in mice by inhibiting ferroptosis through the suppression of the RhoA/ROCK signaling pathway. These findings contribute to the current knowledge of Ginsenoside Rg3 and high-altitude cardiac injury, suggesting that Ginsenoside Rg3 shows potential as a therapeutic agent for high-altitude cardiac injury.

Changes in hypoxic and hypercapnic ventilatory responses at high altitude measured using rebreathing methods

Ventilatory responses to hypoxia and hypercapnia play a vital role in maintaining gas exchange homeostasis and in adaptation to high-altitude environments. This study investigates the mechanisms underlying sensitization of hypoxic and hypercapnic ventilatory response (HVR and HCVR, respectively) in individuals acclimatized to moderate high altitude (3,800 m). Thirty-one participants underwent chemoreflex testing using the Duffin-modified rebreathing technique. Measures were taken at sea level and after 2 days of acclimatization to high altitude. Ventilatory recruitment threshold (VRT), HCVR-Hyperoxia, HCVR-Hypoxia, and HVR were quantified. Acclimatization to high altitude resulted in increased HVR (P < 0.001) and HCVR-Hyperoxia (P < 0.001), as expected. We also observed that the decrease in VRT under hypoxic test conditions significantly contributed to the elevated HVR at high altitude since the change in VRT across hyperoxic and hypoxic test conditions was greater at high altitudes compared to baseline sea-level tests (P = 0.043). Pre-VRT, or basal, ventilation also increased at high altitudes (P < 0.001), but the change did not differ between oxygen conditions. Taken together, these data suggest that the increase in HVR at high altitude is at least partially driven by a larger decrease in the VRT in hypoxia versus hyperoxia at high altitude compared to sea level. This study highlights the intricacies of respiratory adaptations during acclimatization to moderate high altitude, shedding light on the roles of the VRT, baseline respiratory drive, and two-slope HCVR in this process. These findings contribute to our understanding of how human respiratory control responds to hypoxic and hypercapnic challenges at high altitude.NEW & NOTEWORTHY We report the first measurements of the hypoxic ventilatory response (HVR) after 2 days at high altitude using a CO2 rebreathing technique. We evaluated mechanisms by which the HVR becomes elevated with acclimatization (increased hypercapnic ventilatory response sensitivity in hypoxia, increased baseline respiratory drive in hypoxia, or lower ventilatory recruitment thresholds in hypoxia). For the first time, we report that decreases in the ventilatory recruitment threshold in hypoxia contribute to elevated HVR at high altitude.

Review of Athletic Guidelines for High-Altitude Training and Acclimatization

Ramchandani, Rashi, Ioana Tereza Florica, Zier Zhou, Aziz Alemi, and Adrian Baranchuk. Review of athletic guidelines for high-altitude training and acclimatization. High Alt Med Biol. 00:000-000, 2024. Introduction: Exposure to high altitude results in hypobaric hypoxia with physiological acclimatization changes that are thought to influence athletic performance. This review summarizes existing literature regarding implications of high-altitude training and altitude-related guidelines from major governing bodies of sports. Methods: A nonsystematic review was performed using PubMed and OVID Medline to identify articles regarding altitude training and guidelines from international governing bodies of various sports. Sports inherently involving training or competing at high altitude were excluded. Results: Important physiological compensatory mechanisms to high-altitude environments include elevations in blood pressure, heart rate, red blood cell mass, tidal volume, and respiratory rate. These responses can have varying effects on athletic performance. Governing sport bodies have limited and differing regulations for training and competition at high altitudes with recommended acclimatization periods ranging from 3 days to 3 weeks. Discussion: Physiological changes in response to high terrestrial altitude exposure can have substantial impacts on athletic performance. Major sport governing bodies have limited regulations and recommendations regarding altitude training and competition. Existing guidelines are variable and lack substantial evidence to support recommendations. Additional studies are needed to clarify the implications of high-altitude exposure on athletic ability to optimize training and competition.

The cardiovascular system at high altitude: A bibliometric and visualization analysis

BACKGROUND

When exposed to high-altitude environments, the cardiovascular system undergoes various changes, the performance and mechanisms of which remain controversial.

AIM

To summarize the latest research advancements and hot research points in the cardiovascular system at high altitude by conducting a bibliometric and visualization analysis.

METHODS

The literature was systematically retrieved and filtered using the Web of Science Core Collection of Science Citation Index Expanded. A visualization analysis of the identified publications was conducted employing CiteSpace and VOSviewer.

RESULTS

A total of 1674 publications were included in the study, with an observed annual increase in the number of publications spanning from 1990 to 2022. The United States of America emerged as the predominant contributor, while Universidad Peruana Cayetano Heredia stood out as the institution with the highest publication output. Notably, Jean-Paul Richalet demonstrated the highest productivity among researchers focusing on the cardiovascular system at high altitude. Furthermore, Peter Bärtsch emerged as the author with the highest number of cited articles. Keyword analysis identified hypoxia, exercise, acclimatization, acute and chronic mountain sickness, pulmonary hypertension, metabolism, and echocardiography as the primary research hot research points and emerging directions in the study of the cardiovascular system at high altitude.

CONCLUSION

Over the past 32 years, research on the cardiovascular system in high-altitude regions has been steadily increasing. Future research in this field may focus on areas such as hypoxia adaptation, metabolism, and cardiopulmonary exercise. Strengthening interdisciplinary and multi-team collaborations will facilitate further exploration of the pathophysiological mechanisms underlying cardiovascular changes in high-altitude environments and provide a theoretical basis for standardized disease diagnosis and treatment.

Effect of ubiquinol on electrophysiology during high-altitude acclimatization and de-acclimatization: A substudy of the Shigatse CARdiorespiratory fitness (SCARF) randomized clinical trial

BACKGROUND

High-altitude exposure changes the electrical conduction of the heart. However, reports on electrocardiogram (ECG) characteristics and potent prophylactic agents during high-altitude acclimatization and de-acclimatization are inadequate. This study aimed to investigate the effects of ubiquinol on electrophysiology after high-altitude hypoxia and reoxygenation.

METHODS

The study was a prospective, randomized, double-blind, placebo-controlled trial. Forty-one participants were randomly divided into two groups receiving ubiquinol 200 mg daily or placebo orally 14 days before flying to high altitude (3900 m) until the end of the study. Cardiopulmonary exercise testing was performed at baseline (300 m), on the third day after reaching high altitude, and on the seventh day after returning to baseline.

RESULTS

Acute high-altitude exposure prolonged resting ventricular repolarization, represented by increased corrected QT interval (455.9 ± 23.4 vs. 427.1 ± 19.1 ms, P < 0.001) and corrected Tpeak-Tend interval (155.5 ± 27.4 vs. 125.3 ± 21.1 ms, P < 0.001), which recovered after returning to low altitude. Ubiquinol supplementation shortened the hypoxia-induced extended Tpeak-Tend interval (-7.7 ms, [95% confidence interval (CI), -13.8 to -1.6], P = 0.014), Tpeak-Tend /QT interval (-0.014 [95% CI, -0.027 to -0.002], P = 0.028), and reserved maximal heart rate (11.9 bpm [95% CI, 3.2 to 20.6], P = 0.013) during exercise at high altitude. Furthermore, the decreased resting amplitude of the ST-segment in the V3 lead was correlated with decreased peak oxygen pulse (R = 0.713, P < 0.001) and maximum oxygen consumption (R = 0.595, P < 0.001).

CONCLUSIONS

Our results illustrated the electrophysiology changes during high-altitude acclimatization and de-acclimatization. Similarly, ubiquinol supplementation shortened the prolonged Tpeak-Tend interval and reserved maximal heart rate during exercise at high altitude.

REGISTRATION

URL: www.chictr.org.cn; Unique identifier: ChiCTR2200059900.

Effect of short-term exposure to high-altitude hypoxic climate on feed-intake, blood glucose level and physiological responses of native and non-native goat

The exposure to high altitude and cold stress poses challenges in maintaining normal physiological standards and body homeostasis in non-native animals. To enhance our understanding of the physiology of native and non-native goats in high-altitude environments, we conducted a comparative study to examine the impact of natural hypoxic and cold stress conditions on their feed intake (FIT) and associated changes in physiological responses, including plasma glucose concentration (PGC). The study took place at an altitude of 3505.2 m above mean sea level and involved twenty-two healthy females from two different breeds of goats. This study was conducted over a period of 56 days after the arrival of non-native Black Bengal goats (BBN) and compared with native Changthangi (CHAN) goats. Both groups were extensively reared in a natural high-altitude and cold-stress environment in Leh, India, and were subjected to defined housing and management practices. The parameters evaluated included FIT, PGC, respiration rate, heart rate, pulse rate, and rectal temperature. High altitudes had a significant (p < 0.05) impact on FIT, PGC, respiration rate, heart rate, pulse rate, and rectal temperature in BBN, whereas these parameters remained stable in CHAN throughout the study period. Additionally, the detrimental effects of high-altitude stress were more pronounced in non-native goats compared to native goats. These findings suggest that physiological responses in non-native goats tend to stabilize after an initial period of adverse effects in high-altitude environments. Based on the physiological responses and glucose concentration, it is recommended to pay special attention to the nutrition of non-native goats for up to the third week (21 days) after their arrival in high-altitude areas.

Cardiovascular physiology and pathophysiology at high altitude

Oxygen is vital for cellular metabolism; therefore, the hypoxic conditions encountered at high altitude affect all physiological functions. Acute hypoxia activates the adrenergic system and induces tachycardia, whereas hypoxic pulmonary vasoconstriction increases pulmonary artery pressure. After a few days of exposure to low oxygen concentrations, the autonomic nervous system adapts and tachycardia decreases, thereby protecting the myocardium against high energy consumption. Permanent exposure to high altitude induces erythropoiesis, which if excessive can be deleterious and lead to chronic mountain sickness, often associated with pulmonary hypertension and heart failure. Genetic factors might account for the variable prevalence of chronic mountain sickness, depending on the population and geographical region. Cardiovascular adaptations to hypoxia provide a remarkable model of the regulation of oxygen availability at the cellular and systemic levels. Rapid exposure to high altitude can have adverse effects in patients with cardiovascular diseases. However, intermittent, moderate hypoxia might be useful in the management of some cardiovascular disorders, such as coronary heart disease and heart failure. The aim of this Review is to help physicians to understand the cardiovascular responses to hypoxia and to outline some recommendations that they can give to patients with cardiovascular disease who wish to travel to high-altitude destinations.

Efficacy of Sildenafil on healthy humans in high‑altitude hypoxia at rest and during exercise: A meta‑analysis

The current meta-analysis aimed to fully evaluate the efficacy of Sildenafil in healthy humans at different altitudes, focusing on echocardiographic and hemodynamic parameters. Relevant studies were retrieved from the Cochrane, Embase and PubMed databases. Odds ratios (OR) were determined for dichotomous data and weighted mean differences with 95% confidence intervals (CIs) for continuous data. A total of 16 RCTs were included in the current meta-analysis. Short-term treatment with Sildenafil significantly elevated resting heart rate (P<0.01) at altitudes <4,000 meters. No significant differences in heart rate were observed between the Sildenafil and placebo groups at rest and during exercise at an altitude of >4,000 meters (P>0.05). Sildenafil improved resting cardiac output at an altitude of >5,000 meters (P<0.01) and exercising arterial oxygen saturation at <4,000 meters (P<0.01). Sildenafil reduced resting pulmonary artery systolic pressure (PASP) at altitudes >4,000 meters (P<0.01) and exercising PASP at altitudes >5,000 meters (P<0.01). Therefore, Sildenafil efficacy in healthy humans with high-altitude hypoxia is related to altitude and rest or exercise.

The importance of personalization in high altitude protocols for hematologic and metabolic benefits in sports: A multi-dimensional N-of-1 case study

The hematologic and metabolic benefits of high altitude exposure have been extensively studied in athletes due to their promising performance enhancing effects. However, despite the increased research and development of various high altitude protocols for achieving peak performance, the reproducibility of the results at the individual level remains sparse. To systematically address this limitation and establish a more effective method to achieve consistent results at the individual level, we conducted a multi-dimensional study of one elite endurance athlete in two Phases. In Phase 1, we applied the standard protocol of LHTH (Live-High-Train-High) using a commercially available, at-home, normobaric, high altitude simulation tent under the SHTL (Sleep-High-Train-Low) model. Then, we developed the athlete's personalized protocol for peak hematologic parameters during their off-season. This protocol determined the exact total high altitude exposure time required to achieve peak hematologic parameters, which in the case of this athlete, amounted to 45 nights with approximately 8hrs per night. In Phase 2, we replicated the Phase 1 protocol during the athlete's in-season and observed the same or even higher hematologic and metabolic benefits compared to Phase 1. During both phases, we collected thousands of multi-dimensional data points to ensure that the athlete's lifestyle and environmental factors remained stable, and to increase the likelihood that physiological changes resulted primarily from the high altitude exposure. The data trends in both Phases validated that, for this athlete, hematologic measures such as red blood cell count, hematocrit, and hemoglobin, as well as electrolyte content, body weight and gut microbiome composition improved to their personal best values after a total of approximately 15 days of high altitude exposure (45 nights with roughly 8hrs per night totaling 360hrs or 15days). These improvements did not occur after the 21 days recommended by the LHTH protocol highlighting the significance of personalization in high altitude protocols that are designed for peak performance parameters. Therefore, to maximize the benefits in hematologic and other metabolic values and thus increase muscle oxygen supply and peak aerobic capacity through high altitude exposure, each athlete may require a unique total duration of high altitude exposure tailored to their individual physiology. This duration must be determined by their specific response in hematologic peaking. Therefore, initially establishing a personalized protocol for an athlete by determining their required total duration of high altitude exposure for peak hematologic values during their off-season and applying this protocol during their in-season phase may lead to more successful and reproducible benefits compared to following a generalized protocol alone.

Baroreflex sensitivity is blunted in hypoxia independently of changes in inspired carbon dioxide pressure in prematurely born male adults

Premature birth may result in specific cardiovascular responses to hypoxia and hypercapnia, that might hamper high-altitude acclimatization. This study investigated the consequences of premature birth on baroreflex sensitivity (BRS) under hypoxic, hypobaric and hypercapnic conditions. Seventeen preterm born males (gestational age, 29 ± 1 weeks), and 17 age-matched term born adults (40 ± 0 weeks) underwent consecutive 6-min stages breathing different oxygen and carbon dioxide concentrations at both sea-level and high-altitude (3375 m). Continuous blood pressure and ventilatory parameters were recorded in normobaric normoxia (NNx), normobaric normoxic hypercapnia (NNx + CO2 ), hypobaric hypoxia (HHx), hypobaric normoxia (HNx), hypobaric normoxia hypercapnia (HNx + CO2 ), and hypobaric hypoxia with end-tidal CO2 clamped at NNx value (HHx + clamp). BRS was assessed using the sequence method. Across all conditions, BRS was lower in term born compared to preterm (13.0 ± 7.5 vs. 21.2 ± 8.8 ms⋅mmHg-1 , main group effect: p < 0.01) participants. BRS was lower in HHx compared to NNx in term born (10.5 ± 4.9 vs. 16.0 ± 6.0 ms⋅mmHg-1 , p = 0.05), but not in preterm (27.3 ± 15.7 vs. 17.6 ± 8.3 ms⋅mmHg-1 , p = 0.43) participants, leading to a lower BRS in HHx in term born compared to preterm (p < 0.01). In conclusion, this study reports a blunted response of BRS during acute high-altitude exposure without any influence of changes in inspired CO2 in healthy prematurely born adults.

Study on the dynamic effects of plateau hypoxic and cold environment on the thermal adaptation of short-term sojourners in Xizang

The plateau hypoxic environment can affect the thermoregulation process of the human body, and due to the different acclimatization ability to the hypoxic environment, the thermal requirements among the people who enter Xizang at different times may be different. Accordingly, this study aims to clarify how plateau hypoxic environments influence the physiological and subjective responses of people entering Xizang at different times. And field experiments were conducted in Xi'an and Lhasa, respectively, to compare the thermal responses and oxygen responses of the subjects under different temperature conditions on the plain, the first day of entering Xizang and the 15th day of entering Xizang. The results showed that under the hypoxic environment, the thermal sensation of the subjects decreased. With the extension of the time entering Xizang, the influence of the hypoxic environment on thermal comfort was gradually weakened, but under the low temperature environment, the effect of hypoxia on thermal response was not significantly reduced. The results of this study can help to reveal how plateau hypoxic environments affect human thermal comfort and provide a theoretical basis for the design of indoor thermal environment parameters suitable for sojourners entering Xizang at different times.

Landscape genomics reveals adaptive divergence of indigenous sheep in different ecological environments of Xinjiang, China

Sheep are important livestock animals that have evolved under various ecological pressures. Xinjiang is a region with diverse and harsh environments that have shaped many local sheep breeds with unique characteristics and environmental adaptability. However, these breeds are losing ecological flexibility due to the promotion of intensive farming practices. Here we sequenced 14 local sheep breeds from Xinjiang and analyzed their genetic structure and gene flow with other sheep breeds from neighboring regions. The Tibetan Plateau was the geographic origin of Xinjiang native sheep evolution. We performed genome-environment association analysis and identified Bio9: Mean Temperature of Driest Quarter and Bio15: Precipitation Seasonality as the key environmental factors affecting Xinjiang local sheep and the key genes involved in their survival and adaptation. We classified Xinjiang native sheep breeds into six groups based on their differential genes by pairwise selective sweep analysis and Community Network Analysis. We analyzed transcriptome expression data of 832 sheep tissues and detected tissue-specific enrichment of six group-specific genes in different biological systems. Our results revealed the genetic basis of year-round estrus, drought tolerance, hypoxia resistance, and cold tolerance traits of Xinjiang sheep breeds. Moreover, we proposed conservation strategies for Xinjiang local sheep breeds and provided theoretical guidance for breeding new sheep breeds under global extreme environments.

New strategy for rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments

High-altitude hypoxic environments have critical implications on cardiovascular system function as well as blood pressure regulation. Such environments place patients with hypertension at risk by activating the sympathetic nervous system, which leads to an increase in blood pressure. In addition, the high-altitude hypoxic environment alters the in vivo metabolism and antihypertensive effects of antihypertensive drugs, which changes the activity and expression of drug-metabolizing enzymes and drug transporters. The present study reviewed the pharmacodynamics and pharmacokinetics of antihypertensive drugs and its effects on patients with hypertension in a high-altitude hypoxic environment. It also proposes a new strategy for the rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments. The increase in blood pressure on exposure to a high-altitude hypoxic environment was mainly dependent on increased sympathetic nervous system activity. Blood pressure also increased proportionally to altitude, whilst ambulatory blood pressure increased more than conventional blood pressure, especially at night. High-altitude hypoxia can reduce the activities and expression of drug-metabolizing enzymes, such as CYP1A1, CYP1A2, CYP3A1, and CYP2E1, while increasing those of CYP2D1, CYP2D6, and CYP3A6. Drug transporter changes were related to tissue type, hypoxic degree, and hypoxic exposure time. Furthermore, the effects of high-altitude hypoxia on drug-metabolism enzymes and transporters altered drug pharmacokinetics, causing changes in pharmacodynamic responses. These findings suggest that high-altitude hypoxic environments affect the blood pressure, pharmacokinetics, and pharmacodynamics of antihypertensive drugs. The optimal hypertension treatment plan and safe and effective medication strategy should be formulated considering high-altitude hypoxic environments.

Pretreatment with Notoginsenoside R1 attenuates high-altitude hypoxia-induced cardiac injury via activation of the ERK1/2-P90RSK-Bad signaling pathway in rats

High-altitude cardiac injury (HACI) is one of the common tissue injuries caused by high-altitude hypoxia that may be life threatening. Notoginsenoside R1 (NG-R1), a major saponin of Panax notoginseng, exerts anti-oxidative, anti-inflammatory, and anti-apoptosis effects, protecting the myocardium from hypoxic injury. This study aimed to investigate the protective effect and molecular mechanism of NG-R1 against HACI. We simulated a 6000 m environment for 48 h in a hypobaric chamber to create a HACI rat model. Rats were pretreated with NG-R1 (50, 100 mg/kg) or dexamethasone (4 mg/kg) for 3 days and then placed in the chamber for 48 h. The effect of NG-R1 was evaluated by changes in Electrocardiogram parameters, histopathology, cardiac biomarkers, oxidative stress and inflammatory indicators, key protein expression, and immunofluorescence. U0126 was used to verify whether the anti-apoptotic effect of NG-R1 was related to the activation of ERK pathway. Pretreatment with NG-R1 can improve abnormal cardiac electrical conduction and alleviate high-altitude-induced tachycardia. Similar to dexamethasone, NG-R1 can improve pathological damage, reduce the levels of cardiac injury biomarkers, oxidative stress, and inflammatory indicators, and down-regulate the expression of hypoxia-related proteins HIF-1α and VEGF. In addition, NG-R1 reduced cardiomyocyte apoptosis by down-regulating the expression of apoptotic proteins Bax, cleaved caspase 3, cleaved caspase 9, and cleaved PARP1 and up-regulating the expression of anti-apoptotic protein Bcl-2 through activating the ERK1/2-P90RSK-Bad pathway. In conclusion, NG-R1 prevented HACI and suppressed apoptosis via activation of the ERK1/2-P90RSK-Bad pathway, indicating that NG-R1 has therapeutic potential to treat HACI.

Moderate Aerobic Exercise Reduces the Detrimental Effects of Hypoxia on Cardiac Autonomic Control in Healthy Volunteers

Physical inactivity increases cardiometabolic risk through a variety of mechanisms, among which alterations of immunological, metabolic, and autonomic control systems may play a pivotal role. Physical inactivity is frequently associated with other factors that may further worsen prognosis. The association between physical inactivity and hypoxia is particularly interesting and characterizes several conditions—whether physiological (e.g., residing or trekking at high altitude and space flights) or pathological (e.g., chronic cardiopulmonary diseases and COVID-19). In this randomized intervention study, we investigated the combined effects of physical inactivity and hypoxia on autonomic control in eleven healthy and physically active male volunteers, both at baseline (ambulatory) conditions and, in a randomized order, hypoxic ambulatory, hypoxic bedrest, and normoxic bedrest (i.e., a simple experimental model of physical inactivity). Autoregressive spectral analysis of cardiovascular variabilities was employed to assess cardiac autonomic control. Notably, we found hypoxia to be associated with an impairment of cardiac autonomic control, especially when combined with bedrest. In particular, we observed an impairment of indices of baroreflex control, a reduction in the marker of prevalent vagal control to the SA node, and an increase in the marker of sympathetic control to vasculature.

Night-Time Heart Rate Variability during an Expedition to Mt Everest: A Case Report

Mt Everest has been gaining popularity from casual hiking athletes, climbers, and ultra-endurance marathon runners. However, living and sleeping at altitude increases the risk of injury and illness. This is because travel to high altitudes adversely affects human physiology and performance, with unfavourable changes in body composition, exercise capacity, and mental function. This is a case report of a climber who reached the summit of Mt Everest from the north side. During his 40-day expedition, we collected sleep quality data and night-time heart rate variability. During the night inside the tent, the air temperature ranged from -12.9 to 1.8 °C (-5.8 ± 4.9 °C) and the relative humidity ranged from 26.1 to 78.9% (50.7 ± 16.9%). Awake time was 17.1 ± 6.0% of every sleep-time hour and increased with altitude (r = 0.42). Sleep time (r = -0.51) and subjective quality (r = 0.89) deteriorated with altitude. Resting heart rate increased (r = 0.70) and oxygen saturation decreased (r = -0.94) with altitude. The mean NN, RMSSD, total power, LF/HF, and SD1 and SD2 were computed using the NN time series. Altitude reduced the mean ΝΝ (r = -0.73), RMSSD (r = -0.31), total power (r = -0.60), LF/HF ratio (r = -0.40), SD1 (r = -0.31), and SD2 (r = -0.70). In conclusion, this case report shows that sleeping at high altitudes above 5500 m results in progressively reduced HRV, increased awakenings, as well as deteriorated sleep duration and subjective sleep quality. These findings provide further insight into the effects of high altitude on cardiac autonomic function and sleep quality and may have implications for individuals who frequently spend time at high altitudes, such as climbers.

A systematic review of electrocardiographic changes in populations temporarily ascending to high altitudes

High altitudes can cause hypobaric hypoxia, altering human physiology and the corresponding electrocardiogram (ECG). As part of the Altitude Nondifferentiated ECG Study (ANDES), this paper reviews ECG changes in subjects ascending to high altitudes. This review was conducted following PRISMA guidelines. PubMed, EMBASE, OVID Medline, and Web of Science were searched. 19 studies were ultimately included. Notable ECG changes at high altitudes include T wave inversion in the precordial leads and rightward QRS axis deviation in leads I, II and aVF. Less common findings were increases in P wave amplitude, QRS amplitude, and QTc interval. These ECG deviations typically self-resolved within 2-6 weeks following return to sea level. Consideration must be taken when interpreting ECG changes in individuals during ascent to, at, or upon return from high altitudes. Further large-scale studies are needed to elucidate temporal and altitude-dependent ECG patterns and establish reference standards for clinicians.

The effects of normobaric and hypobaric hypoxia on cognitive performance and physiological responses: A crossover study

This partially randomised controlled, crossover study sought to investigate the effects of normobaric hypoxia (NH) and hypobaric hypoxia (HH) on cognitive performance, the physiological response at rest and after a 3-min step-test. Twenty healthy participants (10 females and 10 males, 27.6±6.2yrs, 73.6±13.7kg, 175.3±8.9cm) completed a cognitive performance test, followed by the modified Harvard-step protocol, in four environments: normobaric normoxia (NN; PiO2: 146.0±1.5mmHg), NH (PiO2: 100.9±1.3mmHg), HH at the first day of ascent (HH1: PiO2 = 105.6±0.4mmHg) and HH after an overnight stay (HH2: PiO2 = 106.0±0.5mmHg). At rest and/or exercise, SpO2, NIRS, and cardiovascular and perceptual data were collected. The cerebral tissue oxygenation index and the cognitive performance (throughput, accuracy, and reaction time) were not different between the hypoxic conditions (all p>0.05). In NH, SpO2 was higher compared to HH1 (ΔSpO2 NH vs HH1: 1.7±0.5%, p = 0.003) whilst heart rate (ΔHR NH vs HH2: 5.8±2.6 bpm, p = 0.03) and sympathetic activation (ΔSNSi NH vs HH2: 0.8±0.4, p = 0.03) were lower in NH compared to HH2. Heart rate (ΔHR HH1 vs HH2: 6.9±2.6 bpm, p = 0.01) and sympathetic action (ΔSNSi HH1 vs HH2: 0.9±0.4, p = 0.02) were both lower in HH1 compared to HH2. In conclusion, cognitive performance and cerebral oxygenation didn’t differ between the hypoxic conditions. SpO2 was only higher in NH compared to HH1. In HH2, heart rate and sympathetic activation were higher compared to both NH and HH1. These conclusions account for a PiO2 between 100–106 mmHg.

Sex differences during a cold-stress test in normobaric and hypobaric hypoxia: A randomized controlled crossover study

Cold and hypoxia are two stressors that are frequently combined and investigated in the scientific literature. Despite the growing literature regarding normobaric hypoxia (NH) and hypobaric hypoxia (HH), responses between females and males are less often evaluated. Therefore, this study aims to investigate the physiological sex differences following a cold-stress test under normoxia, normobaric- and hypobaric hypoxia. A total of n = 10 females (24.8 ± 5.1 years) and n = 10 males (30.3 ± 6.3 years) from a university population volunteered for this study. The cold-stress test (CST) of the right hand (15°C for 2 min) was performed using a randomised crossover design in normobaric normoxia, NH and HH. The change (∆) from baseline to post-CST up to 15 min was analysed for cutaneous vascular conductance (CVC) and the hands’ skin temperature, whilst the mean values across time (post-CST up to 15 min) were assessed for peripheral oxygen saturation (SpO₂), thermal sensation- and comfort. Pressure pain threshold (PPT) was assessed after the post-CST 15 min period. The hands’ skin temperature drop was higher (p = 0.01) in the female group (∆3.3 ± 1.5°C) compared to the male group (∆1.9 ± 0.9°C) only in NH. Females (−0.9 ± 0.5) rated this temperature drop in NH to feel significantly colder (p = 0.02) compared to the males (−0.2 ± 0.7). No differences were observed between sexes in NN, NH, and HH for ∆CVC, SpO₂, thermal comfort and PPT. In conclusion, females and males show similar reactions after a CST under normoxia and hypoxia. Sex differences were observed in the local skin temperature response and thermal sensation only in NH.

The Effect of High-Altitude Acclimatisation on Ultra-Short Heart Rate Variability

Introduction

High-altitude (HA) exposure affects heart rate variability (HRV) and has been inconsistently linked to acute mountain sickness (AMS). The influence of increasing HA exposure on ultra-short HRV and its relationship to gold standard HRV measures at HA has not been examined.

Methods

This was a prospective observational study of adults aged ≥ 18 years undertaking a HA trek in the Dhaulagiri region of the Himalayas. Cardiac inter-beat-intervals were obtained from a 10-s recording of supra-systolic blood pressure (Uscom BP⁺ device) immediately followed by 300 s single lead ECG recording (CheckMyHeart device). HRV was measured using the RMSSD (root mean square of successive differences of NN intervals) at sea level (SL) in the United Kingdom and at 3,619, 4,600, and 5,140 m at HA. Oxygen saturations (SpO₂) were measured using finger-based pulse oximetry. The level of agreement between the 10 and 300 s RMSSD values were examined using a modified Bland–Altman relative-difference analysis.

Results

Overall, 89 participants aged 32.2 ± 8.8 years (range 18–56) were included of which 70.8% were men. HA exposure (SL vs. 3,619 m) was associated with an initial increase in both 10 s (45.0 [31.0–82.0]) vs. 58.0 [33.0–119.0] ms) and 300 s (45.67 [33.24–70.32] vs. 56.48 [36.98–102.0] ms) in RMSSD. Thereafter at 4,600 and 5,140 m both 10 and 300 s RMSSD values were significantly lower than SL. From a total of 317 paired HRV measures the 10 and 300 s RMSSD measures were moderately correlated (Spearman r = 0.66; 95% CI: 0.59–0.72; p < 0.0001). The median difference (bias) in RMSSD values (300 s − 10 s) was −2.3 ms with a lower and upper limit of agreement of −107.5 and 88.61 ms, respectively with no differences with altitude. Overall, 293/317 (92.4%) of all paired HRV values fell within the 95% CI limits of agreement. Neither HRV method was predictive of AMS.

Conclusion

Increasing HA affects ultra-short HRV in a similar manner to gold-standard 300 s. Ultra-short HRV has a moderate agreement with 300 s measurements. HRV did not predict AMS.

A systematic review of electrocardiographic changes in healthy high-altitude populations

High-altitude environments are characterized by decreased atmospheric pressures at which individuals exhibit a reduced volume of maximal oxygen uptake and arterial partial pressure of oxygen, both of which lead to hypobaric hypoxia. While acute exposure may temporarily offset cardiovascular homeostasis in sea-level residents, native highlanders have become accustomed to these high-altitude conditions and often exhibit variations in normal ECG parameters. As part of the "Altitude Non-differentiated ECG Study" (ANDES) project, this paper aims to systematically review the available literature regarding ECG changes in healthy highlander populations. After searching the PubMed, Medline, and Embase databases, 286 abstracts were screened, of which 13 full-texts were ultimately included. This process was completed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Major ECG deviations in native healthy highlanders include right QRS axis deviation, right ventricular hypertrophy signs, and more prevalent T-wave inversion in the right precordial leads. Notably, they exhibit a prolonged QTc compared to sea-level residents, although within normal limits. Evidence about increased P-wave amplitude or duration, variations in PR interval, or greater prevalence of complete right bundle branch block is not conclusive. This review provides ECG reference standards that can be used by clinicians, who should be aware of the effects of high-altitude residence on cardiovascular health and how these may change according to age, ethnicity, and other factors.

Adrenergic control of the cardiovascular system in deer mice native to high altitude

Studies of animals native to high altitude can provide valuable insight into physiological mechanisms and evolution of performance in challenging environments. We investigated how mechanisms controlling cardiovascular function may have evolved in deer mice (Peromyscus maniculatus) native to high altitude. High-altitude deer mice and low-altitude white-footed mice (P. leucopus) were bred in captivity at sea level, and first-generation lab progeny were raised to adulthood and acclimated to normoxia or hypoxia. We then used pharmacological agents to examine the capacity for adrenergic receptor stimulation to modulate heart rate (f_H) and mean arterial pressure (P_mean) in anaesthetized mice, and used cardiac pressure-volume catheters to evaluate the contractility of the left ventricle. We found that highlanders had a consistently greater capacity to increase f_H via pharmacological stimulation of β₁-adrenergic receptors than lowlanders. Also, whereas hypoxia acclimation reduced the capacity for increasing P_mean in response to α-adrenergic stimulation in lowlanders, highlanders exhibited no plasticity in this capacity. These differences in highlanders may help augment cardiac output during locomotion or cold stress, and may preserve their capacity for α-mediated vasoconstriction to more effectively redistribute blood flow to active tissues. Highlanders did not exhibit any differences in some measures of cardiac contractility (maximum pressure derivative, dP/dt_max, or end-systolic elastance, E_es), but ejection fraction was highest in highlanders after hypoxia acclimation. Overall, our results suggest that evolved changes in sensitivity to adrenergic stimulation of cardiovascular function may help deer mice cope with the cold and hypoxic conditions at high altitude.

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High-altitude deer mice have evolved increased aerobic capacity in hypoxia.

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Cardiovascular regulation was examined in normoxia and chronic hypoxia.

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Highland mice had increased capacity for β₁-adrenergic stimulation of heart rate.

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Hypoxia reduced vascular α-adrenergic sensitivity in lowland but not highland mice.

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Cardiac ejection fraction was elevated in highland mice in chronic hypoxia.

Similar Supine Heart Rate Variability Changes During 24-h Exposure to Normobaric vs. Hypobaric Hypoxia

Purpose: This study aimed to investigate the differences between normobaric (NH) and hypobaric hypoxia (HH) on supine heart rate variability (HRV) during a 24-h exposure. We hypothesized a greater decrease in parasympathetic-related parameters in HH than in NH.

Methods: A pooling of original data from forty-one healthy lowland trained men was analyzed. They were exposed to altitude either in NH (F_IO₂ = 15.7 ± 2.0%; PB = 698 ± 25 mmHg) or HH (F_IO₂ = 20.9%; PB = 534 ± 42 mmHg) in a randomized order. Pulse oximeter oxygen saturation (S_pO₂), heart rate (HR), and supine HRV were measured during a 7-min rest period three times: before (in normobaric normoxia, NN), after 12 (H12), and 24 h (H24) of either NH or HH exposure. HRV parameters were analyzed for time- and frequency-domains.

Results: S_pO₂ was lower in both hypoxic conditions than in NN and was higher in NH than HH at H24. Subjects showed similarly higher HR during both hypoxic conditions than in NN. No difference in HRV parameters was found between NH and HH at any time. The natural logarithm of root mean square of the successive differences (LnRMSSD) and the high frequency spectral power (HF), which reflect parasympathetic activity, decreased similarly in NH and HH when compared to NN.

Conclusion: Despite S_pO₂ differences, changes in supine HRV parameters during 24-h exposure were similar between NH and HH conditions indicating a similar decrease in parasympathetic activity. Therefore, HRV can be analyzed similarly in NH and HH conditions.

Duration at high altitude influences the onset of arrhythmogenesis during apnea

PURPOSE

Autonomic control of the heart is balanced by sympathetic and parasympathetic inputs. Excitation of both sympathetic and parasympathetic systems occurs concurrently during certain perturbations such as hypoxia, which stimulate carotid chemoreflex to drive ventilation. It is well established that the chemoreflex becomes sensitized throughout hypoxic exposure; however, whether progressive sensitization alters cardiac autonomic activity remains unknown. We sought to determine the duration of hypoxic exposure at high altitude necessary to unmask cardiac arrhythmias during instances of voluntary apnea.

METHODS

Measurements of steady-state chemoreflex drive (SS-CD), continuous electrocardiogram (ECG) and SpO₂ (pulse oximetry) were collected in 22 participants on 1 day at low altitude (1045 m) and over eight consecutive days at high-altitude (3800 m). SS-CD was quantified as ventilation (L/min) over stimulus index (P_ETCO₂/SpO₂).

RESULTS

Bradycardia during apnea was greater at high altitude compared to low altitude for all days (p < 0.001). Cardiac arrhythmias occurred during apnea each day but became most prevalent (> 50%) following Day 5 at high altitude. Changes in saturation during apnea and apnea duration did not affect the magnitude of bradycardia during apnea (ANCOVA; saturation, p = 0.15 and apnea duration, p = 0.988). Interestingly, the magnitude of bradycardia was correlated with the incidence of arrhythmia per day (r = 0.8; p = 0.004).

CONCLUSION

Our findings suggest that persistent hypoxia gradually increases vagal tone with time, indicated by augmented bradycardia during apnea and progressively increased the incidence of arrhythmia at high altitude.

TMT-Based Plasma Proteomics Reveals Dyslipidemia Among Lowlanders During Prolonged Stay at High Altitudes

Acute exposure to high altitude perturbs physiological parameters and induces an array of molecular changes in healthy lowlanders. However, activation of compensatory mechanisms and biological processes facilitates high altitude acclimatization. A large number of lowlanders stay at high altitude regions from weeks to months for work and professional commitments, and thus are vulnerable to altitude-associated disorders. Despite this, there is a scarcity of information for molecular changes associated with long-term stay at high altitudes. In the present study, we evaluated oxygen saturation (SpO₂), heart rate (HR), and systolic and diastolic blood pressure (SBP and DBP) of lowlanders after short- (7 days, HA-D7) and long-term (3 months, HA-D150) stay at high altitudes, and used TMT-based proteomics studies to decipher plasma proteome alterations. We observed improvements in SpO₂ levels after prolonged stay, while HR, SBP, and DBP remained elevated as compared with short-term stay. Plasma proteomics studies revealed higher levels of apolipoproteins APOB, APOCI, APOCIII, APOE, and APOL, and carbonic anhydrases (CA1 and CA2) during hypoxia exposure. Biological network analysis also identified profound alterations in lipoprotein-associated pathways like plasma lipoprotein assembly, VLDL clearance, chylomicron assembly, chylomicron remodeling, plasma lipoprotein clearance, and chylomicron clearance. In corroboration, lipid profiling revealed higher levels of total cholesterol (TC), triglycerides (TGs), low-density lipoprotein (LDL) for HA-D150 whereas high density lipoproteins (HDL) levels were lower as compared with HA-D7 and sea-level indicating dyslipidemia. We also observed higher levels of proinflammatory cytokines IL-6, TNFα, and CRP for HA-D150 along with oxidized LDL (oxLDL), suggesting vascular inflammation and proartherogenic propensity. These results demonstrate that long-term stay at high altitudes exacerbates dyslipidemia and associated disorders.

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.

An observational study of sleep characteristics in elite endurance athletes during an altitude training camp at 1800 m

OBJECTIVES

To observe changes in sleep from baseline and during an altitude training camp in elite endurance athletes.

DESIGN

Prospective, observational.

SETTING

Baseline monitoring at <500 m for 2 weeks and altitude monitoring at 1800 m for 17-22 days.

PARTICIPANTS

Thirty-three senior national-team endurance athletes (mean age 25.8 ± S.D. 2.8 years, 16 women).

MEASUREMENTS

Daily measurements of sleep (using a microwave Doppler radar at baseline and altitude), oxygen saturation (SpO₂), training load and subjective recovery (at altitude).

RESULTS

At altitude vs. baseline, sleep duration (P = .036) and light sleep (P < .001) decreased, while deep sleep (P < .001) and respiration rate (P = .020) increased. During the first altitude week vs. baseline, deep sleep increased (P = .001). During the first vs. the second and third altitude weeks, time in bed (P = .005), sleep duration (P = .001), and light sleep (P < .001) decreased. Generally, increased SpO₂ was associated with increased deep sleep while increased training load was associated with increased respiration rate.

CONCLUSION

This is the first study to document changes in sleep from near-sea-level baseline and during a training camp at 1800 m in elite endurance athletes. Ascending to altitude reduced total sleep time and light sleep, while deep sleep and respiration rate increased. SpO₂ and training load at altitude were associated with these responses. This research informs our understanding of the changes in sleep occurring in elite endurance athletes attending training camps at competition altitudes.

A sex-specific evolutionary interaction between ADCY9 and CETP

Pharmacogenomic studies have revealed associations between rs1967309 in the adenylyl cyclase type 9 (ADCY9) gene and clinical responses to the cholesteryl ester transfer protein (CETP) modulator dalcetrapib, however, the mechanism behind this interaction is still unknown. Here, we characterized selective signals at the locus associated with the pharmacogenomic response in human populations and we show that rs1967309 region exhibits signatures of positive selection in several human populations. Furthermore, we identified a variant in CETP, rs158477, which is in long-range linkage disequilibrium with rs1967309 in the Peruvian population. The signal is mainly seen in males, a sex-specific result that is replicated in the LIMAA cohort of over 3400 Peruvians. Analyses of RNA-seq data further suggest an epistatic interaction on CETP expression levels between the two SNPs in multiple tissues, which also differs between males and females. We also detected interaction effects of the two SNPs with sex on cardiovascular phenotypes in the UK Biobank, in line with the sex-specific genotype associations found in Peruvians at these loci. We propose that ADCY9 and CETP coevolved during recent human evolution due to sex-specific selection, which points toward a biological link between dalcetrapib’s pharmacogene ADCY9 and its therapeutic target CETP.

Yogic breathing in hypobaric environment: breathing exercising and its effect on hypobaric hypoxemia and heart rate at 3,650-m elevation

High altitude sojourn is a risk factor for hypobaric hypoxemia and subsequent altitude sickness. The aim of this study was to analyze the effect of new type of yogic breathing—Maheshwarananda’s new Modified Bhujangini Pranayama performed by active yoga practitioners—on the arterial haemoglobin saturation of oxygen (measured by the pulse oximetry - SpO₂) and the heart rate compared to normal spontaneous resting breathing. A pilot prospective study was conducted in the Himalayas at an altitude of 3,650 m. We monitored SpO₂ and pulse rate in 34 experienced yoga practitioners. Within the 3 measurement days at the altitude of 3,650 m, the mean value of SpO₂ increased from 89.11± 4.78 to 93.26±4.44 (P<0.001) after the yogic breathing exercise. No significant changes were observed in pulse rate (P<0.230) measured before and after yogic breathing. The new Yogic breathing—Maheshwarananda’s Modified Bhujangini Pranayama—is increasing the arterial haemoglobin saturation compared to normal resting spontaneous breathing. The heart rate was not affected by this type of yogic breathing.

Ethnic Differences on Cardiac Rhythms and Autonomic Nervous System Responses During a High-Altitude Trek: A Pilot Study Comparing Italian Trekkers to Nepalese Porters

Altitude hypoxia exposure results in increased sympathetic activity and heart rate due to several mechanisms. Recent studies have contested the validity of heart rate variability (HRV) analysis on sympathetic activity measurement. But the plethora of HRV metrics may provide meaningful insights, particularly if linked with cardiovascular and autonomic nervous system parameters. However, the population-specific nature of HRV and cardiorespiratory response to altitude hypoxia are still missing. Six Italian trekkers and six Nepalese porters completed 300 km of a Himalayan trek. The ECG analysis was conducted at baseline, and before (bBC) and after (aBC) the high-altitude (HA) circuit. Urine was collected before and after the expedition in Italians, for assessing catecholamines. Heart rate increased with altitude significantly (p < 0.001) in the Italian group; systolic (p = 0.030) and diastolic (p = 0.012) blood pressure, and mean arterial pressure (p = 0.004) increased with altitude. Instead, pulse pressure did not change, although the Nepalese group showed lower baseline values than the Italians. As expected, peripheral oxygen saturation decreased with altitude (p < 0.001), independently of the ethnic groups. Nepalese had a higher respiratory rate (p = 0.007), independent of altitude. The cardiac vagal index increased at altitude, from baseline to bBC (p = 0.008). Higuchi fractal dimension (HFD) showed higher basal values in the Nepalese group (p = 0.041), and a tendency for the highest values at bBC. Regarding the urinary catecholamine response, exposure to HA increased urinary levels, particularly of norepinephrine (p = 0.005, d = 1.623). Our findings suggest a better cardiovascular resilience of the Nepalese group when compared with Italians, which might be due to an intrinsic adaptation to HA, resulting from their job.

Fetal growth, high altitude, and evolutionary adaptation: a new perspective

Residence at high altitude is consistently associated with low birthweight among placental mammals. This reduction in birthweight influences long-term health trajectories for both the offspring and mother. However, the physiological processes that contribute to fetal growth restriction at altitude are still poorly understood, and thus our ability to safely intervene remains limited. One approach to identify the factors that mitigate altitude-dependent fetal growth restriction is to study populations that are protected from fetal growth restriction through evolutionary adaptations (e.g., high altitude-adapted populations). Here, we examine human gestational physiology at high altitude from a novel evolutionary perspective that focuses on patterns of physiological plasticity, allowing us to identify 1) the contribution of specific physiological systems to fetal growth restriction and 2) the mechanisms that confer protection in highland-adapted populations. Using this perspective, our review highlights two general findings: first, that the beneficial value of plasticity in maternal physiology is often dependent on factors more proximate to the fetus; and second, that our ability to understand the contributions of these proximate factors is currently limited by thin data from altitude-adapted populations. Expanding the comparative scope of studies on gestational physiology at high altitude and integrating studies of both maternal and fetal physiology are needed to clarify the mechanisms by which physiological responses to altitude contribute to fetal growth outcomes. The relevance of these questions to clinical, agricultural, and basic research combined with the breadth of the unknown highlight gestational physiology at high altitude as an exciting niche for continued work.

Association of age and blood pressure among 3.3 million adults: insights from China PEACE million persons project

OBJECTIVE

To assess the association between blood pressure (BP) with age and its heterogeneity across various sociodemographic subgroups in China.

METHODS

In this cross-sectional study, we analysed the data from nearly 3.3 million individuals aged 35-75 years from all 31 provinces in mainland China collected from September 2014 through August 2019. On the basis of possible combinations of eight characteristics and antihypertensive status, subgroups of at least 10 000 individuals were created and the age--blood pressure relationship was determined for each group.

RESULTS

The study included 3 291 058 participants (59.6% women), with a mean age of 55.8 ± 9.8 years. The prevalence of hypertension was 47.6%, of which 30.0% were taking antihypertensive medications. The mean SBP was 135.9 ± 20.2 mmHg. SBP increased at a mean unadjusted rate of 0.639 ± 0.001 mmHg/year. For 95% of the 25 145 subgroups, the SBP increased by 0.28--0.85 mmHg/year. The most common characteristics in the subgroups with the steepest association were female sex, rural area, low education, low-income family, Tibet region, and farmer occupation. The increase in SBP ranged from 0.13 to 0.41 mmHg/year for 95% of the treated subgroups and from 0.33 to 0.82 mmHg/year for 95% of the untreated subgroups.

CONCLUSION

Blood pressure is positively associated with age in this study, with almost three-fold variation across subgroups, indicating subgroup differences in biology, behaviour, or exposures. Antihypertension strongly blunts the association of age and blood pressure and diminishes the variation.

Post-exercise cardiac autonomic and cardiovascular responses to heart rate-matched and work rate-matched hypoxic exercise

Purpose

This study investigated the effect of performing hypoxic exercise at the same heart rate (HR) or work rate (WR) as normoxic exercise on post-exercise autonomic and cardiovascular responses.

Methods

Thirteen men performed three interval-type exercise sessions (5 × 5-min; 1-min recovery): normoxic exercise at 80% of the WR at the first ventilatory threshold (N), hypoxic exercise (FiO₂ = 14.2%) at the same WR as N (H-WR) and hypoxic exercise at the same HR as N (H-HR). Autonomic and cardiovascular assessments were conducted before and after exercise, both at rest and during active squat–stand manoeuvres (SS).

Results

Compared to N, H-WR elicited a higher HR response (≈ 83% vs ≈ 75%HRmax, p < 0.001) and H-HR a reduced exercise WR (− 21.1 ± 9.3%, p < 0.001). Cardiac parasympathetic indices were reduced 15 min after exercise and recovered within 60 min in N and H-HR, but not after H-WR (p < 0.05). H-WR altered cardiac baroreflex sensitivity (cBRS) both at rest and during SS (specifically in the control of blood pressure fall during standing phases) in the first 60 min after the exercise bout (p < 0.05). Post-exercise hypotension (PEH) did not occur in H-HR (p > 0.05) but lasted longer in H-WR than in N (p < 0.05).

Conclusions

Moderate HR-matched hypoxic exercise mimicked post-exercise autonomic responses of normoxic exercise without resulting in significant PEH. This may relate to the reduced WR and the limited associated mechanical/metabolic strain. Conversely, WR-matched hypoxic exercise impacted upon post-exercise autonomic and cardiovascular responses, delaying cardiac autonomic recovery, temporarily decreasing cBRS and evoking prolonged PEH.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04678-5.

Comparison of Sleep Disturbances Between Older Nursing Home Residents in High- and Low-Altitude Areas

BACKGROUND AND OBJECTIVE

This study compared sleep disturbances between older adults living in nursing home located in high- and low-altitude areas and explored the association between sleep disturbances and quality of life (QoL).

METHOD

In total, 207 participants living in a high-altitude area and 437 participants in a low-altitude area were included. Sleep disturbances (ie, difficulty in initiating sleep, difficulty in maintaining sleep, and early morning awakening) were measured using standardized questions. The independent demographic and clinical correlates of sleep disturbances in high-altitude area were examined using multiple logistic regression analyses. Each type of sleep disturbance was entered as the dependent variable separately, while those with significant group differences in the univariate analyses (ie, male gender, married status, age and depressive symptoms) were entered as independent variables.

RESULTS

The prevalence of any type of sleep disturbances in the whole sample was 26.09%, with 41.54% in the high-altitude area and 18.76% in the low-altitude area. Physical, psychological, social, and environmental QoL domains were negatively associated with sleep disturbances in high-altitude area. Multiple logistic regression analyses revealed that male gender and married status were less likely to have sleep disturbances, while those with more severe depressive symptoms were more likely to have sleep disturbances in high-altitude area.

CONCLUSION

Sleep disturbance is common among older nursing home residents in high-altitude areas. Considering the negative impact of sleep disturbance on QoL, regular screening and treatment strategies need to be developed directly for this population.

Shortening Work-Rest Durations Reduces Physiological and Perceptual Load During Uphill Walking in Simulated Cold High-Altitude Conditions

Fornasiero, Alessandro, Aldo Savoldelli, Federico Stella, Alexa Callovini, Lorenzo Bortolan, Andrea Zignoli, David A. Low, Laurent Mourot, Federico Schena, and Barbara Pellegrini. Shortening work-rest durations reduces physiological and perceptual load during uphill walking in simulated cold high-altitude conditions. High Alt Med Biol. 21:249-257, 2020. Background: We investigated the effects of two different work-rest durations on the physiological and perceptual responses to a simulated mountain hike in a cold hypoxic environment. Materials and Methods: Twelve healthy nonacclimatized active men (age 31.3 ± 5.3 years, body mass index 22.4 ± 1.5 kg/m2) completed a 80-minute work-matched intermittent exercise on a motorized treadmill (25% incline, fixed self-selected speed), in a simulated mountain environment (-25°C, FiO2 = 11%, ≈5000 m a.s.l.), wearing extreme cold weather gear, once with short (20 × 3 minutes walking with 1 minute rest; SHORT) and once with long (10 × 6 minutes walking with 2 minutes rest; LONG) work-rest durations. Heart rate (HR), pulse oxygen saturation (SpO2), rate of perceived exertion (RPE), and thermal sensation (TS) were assessed throughout the exercise protocols. Cardiac autonomic modulation was assessed before (PRE) and after exercise (POST) in supine position, as well as during standing resting periods by means of HR recovery (HRR) assessment. Results: SpO2 and TS were similar (p > 0.05) in SHORT and LONG protocols. HR and RPE were increased, and HRR reduced during LONG compared to SHORT (p < 0.05). Parasympathetic activity indices were reduced at POST after both protocols (p < 0.05), but to a lesser extent after SHORT (p < 0.05). Conclusions: Reduced work-rest durations are associated with improved perceptual responses and less perturbation of cardiac autonomic balance, compared to longer work-rest durations. Shorter exercise periods from more frequent breaks during hikes at high altitude may represent a valid strategy to limit the impact of exercise under extreme environmental conditions.

Minimal Influence of Hypobaria on Heart Rate Variability in Hypoxia and Normoxia

Introduction

The present study evaluated the putative effect of hypobaria on resting HRV in normoxia and hypoxia.

Methods

Fifteen young pilot trainees were exposed to five different conditions in a randomized order: normobaric normoxia (NN, P_B = 726 ± 5 mmHg, F_IO₂ = 20.9%), hypobaric normoxia (HN, P_B = 380 ± 6 mmHg, F_IO₂≅40%), normobaric hypoxia (NH, P_B = 725 ± 4 mmHg, F_IO₂≅11%); and hypobaric hypoxia (HH at 3000 and 5500 m, HH3000 and HH5500, P_B = 525 ± 6 and 380 ± 8 mmHg, respectively, F_IO₂ = 20.9%). HRV and pulse arterial oxygen saturation (SpO₂) were measured at rest seated during a 6 min period in each condition. HRV parameters were analyzed (Kubios HVR Standard, V 3.0) for time (RMSSD) and frequency (LF, HF, LF/HF ratio, and total power). Gas exchanges were collected at rest for 10 min following HRV recording.

Results

SpO₂ decreased in HH3000 (95 ± 3) and HH5500 (81 ± 5), when compared to NN (99 ± 0). SpO₂ was higher in NH (86 ± 4) than HH5500 but similar between HN (98 ± 2) and NN. Participants showed lower RMSSD and total power values in NH and HH5500 when compared to NN. In hypoxia, LF/HF ratio was greater in HH5500 than NH, whereas in normoxia, LF/HF ratio was lower in HN than NN. Minute ventilation was higher in HH5500 than in all other conditions.

Discussion

The present study reports a slight hypobaric effect either in normoxia or in hypoxia on some HRV parameters. In hypoxia, with a more prominent sympathetic activation, the hypobaric effect is likely due to the greater ventilation stimulus and larger desaturation. In normoxia, the HRV differences may come from the hyperoxic breathing and slight breathing pattern change due to hypobaria in HN.

Baroreflex Modulation During Acute High-Altitude Exposure in Rats

Baroreflex (BR) control is critically dependent of sympathetic and parasympathetic modulation. It has been documented that during acute hypobaric hypoxia there is a BR control impairment, however, the effect of a natural hypoxic environment on BR function is limited and controversial. Therefore, the aim of this study was to determine the effect of acute High-Altitude exposure on sympathetic/parasympathetic modulation of BR control in normal rats. Male Sprague Dawley rats were randomly allocated into Sea-Level (n = 7) and High-Altitude (n = 5) (3,270 m above sea level) groups. The BR control was studied using phenylephrine (Phe) and sodium nitroprusside (SNP) through sigmoidal analysis. The autonomic control of the heart was estimated using heart rate variability (HRV) analysis in frequency domain. Additionally, to determine the maximum sympathetic and parasympathetic activation of BR, spectral non-stationary method analysis, during Phe (0.05 μg/mL) and SNP administration (0.10 μg/mL) were used. Compared to Sea-Level condition, the High-Altitude group displayed parasympathetic withdrawal (high frequency, 0.6-2.4 Hz) and sympathoexcitation (low frequency, 0.04-0.6 Hz). Regarding to BR modulation, rats showed a significant decrease (p < 0.05) of curvature and parasympathetic bradycardic responses to Phe, without significant differences in sympathetic tachycardic responses to SNP after High-Altitude exposure. In addition, the non-stationary analysis of HRV showed a reduction of parasympathetic activation (Phe) in the High-Altitude group. Our results suggest that acute exposure to High-Altitude produces an autonomic and BR control impairment, characterized by parasympathetic withdrawal after 24 h of high-altitude exposure.

Oxygen-Detecting Synaptic Device for Realization of Artificial Autonomic Nervous System for Maintaining Oxygen Homeostasis

Incorporation of various functions of a biological nervous system into electronic devices is an intriguing challenge in the realization of a human-like recognition and response system. Emerging artificial synaptic devices capable of processing electronic signals through neuromorphic functions operate such biomimetic systems similarly to biological nervous systems. Here, an oxygen-sensitive artificial synaptic device that simultaneously detects oxygen concentration and generates a synaptic signal is demonstrated. The device successfully achieves an interconversion between the excitatory and inhibitory modes of the synaptic current at various oxygen concentrations by virtue of an oxygen-sensitive trilayered organic double heterojunction. The oxygen-induced traps in the organic layer modulate the majority charge carrier from holes to electrons, and this modulation induces an interconversion between the excitatory and inhibitory modes according to the environmental oxygen condition. Finally, the proposed synaptic device is applied to the realization of a negative feedback system for regulation of oxygen homeostasis, which mimics the human autonomic nervous system. The oxygen-sensitive synaptic device proposed in this study is expected to open up new possibilities for the development of a biomimetic neural system that can respond appropriately to various environmental changes.

Alterations of Cardiovascular Complexity during Acute Exposure to High Altitude: A Multiscale Entropy Approach

Stays at high altitude induce alterations in cardiovascular control and are a model of specific pathological cardiovascular derangements at sea level. However, high-altitude alterations of the complex cardiovascular dynamics remain an almost unexplored issue. Therefore, our aim is to describe the altered cardiovascular complexity at high altitude with a multiscale entropy (MSE) approach. We recorded the beat-by-beat series of systolic and diastolic blood pressure and heart rate in 20 participants for 15 min twice, at sea level and after arrival at 4554 m a.s.l. We estimated Sample Entropy and MSE at scales of up to 64 beats, deriving average MSE values over the scales corresponding to the high-frequency (MSE_HF) and low-frequency (MSE_LF) bands of heart-rate variability. We found a significant loss of complexity at heart-rate and blood-pressure scales complementary to each other, with the decrease with high altitude being concentrated at Sample Entropy and at MSE_HF for heart rate and at MSE_LF for blood pressure. These changes can be ascribed to the acutely increased chemoreflex sensitivity in hypoxia that causes sympathetic activation and hyperventilation. Considering high altitude as a model of pathological states like heart failure, our results suggest new ways for monitoring treatments and rehabilitation protocols.

Spontaneous Recurrent Seizures Mediated Cardiac Dysfunction via mTOR Pathway Upregulation: A Putative Target for SUDEP Management

Background:

Alteration in electrophysiology, leading to cardiac dysfunction and subsequently a nontraumatic death is a complication of epilepsy known as “SUDEP” (Sudden Unexpected Death in Epilepsy).

Aims:

The present study was designed to understand the molecular changes and cardiac parameters during different phases of epileptogenesis in lithium-pilocarpine (Li-pilo) rat model of epilepsy.

Methods:

The animals were exposed to Li-pilo to induce Spontaneous Recurrent Seizures (SRS). Noninvasive blood pressure and electrocardiography was recorded at 7th, 28th and 75th day following pilocarpine administration, considered as latent, initial and late SRS phases, respectively. The serum biochemistry, cardiac histopathology, protein and mRNA expressions were studied, following electrocardiography on day 75.

Results:

The mean arterial pressure decreased during the latent phase, thereafter it progressively increased during the initial and the late SRS phases, as compared to the basal and the latent phase. Histopathological analysis of the heart sections indicated hypertrophy, degenerative changes and fibrous tissue deposition in epileptic animals, along with increased levels of lactate dehydrogenase and creatine kinase-MB in the serum. The expression of HIF-1α, phospho-S6, phospho-mTOR, TGF-β, collagen I and Na+/K+-ATPase α1 proteins, and mRNA levels of HIF-1α, mTOR, Rps6, Scn1b, Scn3b, Nav1.5 and TGF-β were increased in the cardiac tissue of epileptic animals, as compared to control.

Conclusion:

Our results conclusively showed that Li-pilo-induced SRS leads to cardiac dysfunction via mTOR pathway upregulation, thus suggested the regulatory control of mTOR pathway as a potential target for SUDEP management.

Whole-genome analysis identifying candidate genes of altitude adaptive ecological thresholds in yak populations

The domestic yak (Bos grunniens) is an iconic symbol of animal husbandry on the Qinghai-Tibet Plateau. Long-term domestication and natural selection have led to a wide distribution of yak, forming many ecological populations to adapt to the local ecological environment. High altitude is closely related to oxygen density, and it is an important environmental ecological factor for biological survival and livestock production. The aim of the present study was to perform a preliminary analysis to identify the candidate genes of altitude distribution adapted ecological thresholds in yak using next-generation sequence technology. A total of 15,762,829 SNPs were obtained from 29 yaks with high- and low-altitude distribution by genome-wide sequencing. According to the results of the selective sweep analysis with FST and ZHp, 21 candidate genes were identified. 14 genes (serine/threonine protein kinase TNNI3K, TEN1, DYM, ITPR1, ZC4H2, KNTC1, ADGRB3, CLYBL, TANGO6, ASCC3, KLHL3, PDE4D, DEPDC1B and AGBL4) were grouped into 32 Gene Ontology terms, and four genes (RPS6KA6, ITPR1, GNAO1 and PDE4D) annotated in 35 pathways, including seven environmental information processing and one environmental adaptation. Therefore, the novel candidate genes found in the current study do not only support new theories about high-altitude adaptation, but also further explain the molecular mechanisms of altitude adaptation threshold in yaks.

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.

Assessment of the impact of 10-day intermittent hypoxia on the autonomic control measured by heart rate variability

Purpose

The purpose of this study is to establish the alterations in the activity of the autonomic nervous system (ANS) via heart rate variability (HRV) in subjects exposed to 1 h of exogenous hypoxia for 10 consecutive days.

Methods

Twelve healthy non-smoker males at mean age of 29.8 ± 7.4 (mean ± SD) breathed hypoxic air delivered through hypoxicator (FiО2 = 12.3% ± 1.5%) for 1 h in 10 consecutive days. Pulse oximetry and electrocardiography were monitored during the visit and HRV was calculated for the entire 1-h hypoxic period.

Results

Comparing the last hypoxic visit to the first, subjects had higher standard deviation of normal-to-normal interbeat intervals (SDNNs) (65.7 ± 32.5 vs. 81.1 ± 32.0 ms, p = 0.013) and root mean square of successive R–R interval difference (RMSSD) (58.1 ± 30.9 vs. 76.5 ± 34.6 ms, p = 0.029) as well as higher lnTotal power (8.1 ± 1.1 vs. 8.5 ± 0.9 ms2, p = 0.015) and high frequency (lnHF) (6.8 ± 1.3 vs. 7.5 ± 1.2 ms2, p = 0.05) and lower LF/HF (2.4 ± 1.4 vs. 1.5 ± 1.0, p = 0.026). Changes in saturation (87.0 ± 7.1 vs. 90.8 ± 5.0%, p = 0.039) and heart rate (67.1 ± 8.9 vs. 62.5 ± 6.0 beats/min, p = 0.040) were also observed.

Conclusions

Intermittent hypoxic training consisting of 1-h hypoxic exposure for 10 consecutive days could diminish the effects of acute exogenous hypoxia on the ANS characterized by an increased autonomic control (SDNN and total power) with augmentation of the parasympathetic nervous system activity (increased RMSSD and HF and decreased LF/HF). Therefore, it could be applied as a pre-acclimatization technique aiming at an increase in the autonomic control and oxygen saturation in subjects with upcoming sojourn to high altitude.

The Process of Acclimation to Chronic Hypoxia Leads to Submandibular Gland and Periodontal Alterations: An Insight on the Role of Inflammatory Mediators

The exposition to hypoxia is a stressful stimulus, and the organism develops acclimation mechanisms to ensure homeostasis, but if this fails, it leads to the development of pathological processes. Considering the large number of people under hypoxic conditions, it is of utmost importance to study the mechanisms implicated in hypoxic acclimation in oral tissues and the possible alteration of some important inflammatory markers that regulate salivary and periodontal function. It is the aim of the present study to analyze submandibular (SMG) and periodontal status of animals chronically exposed to continuous (CCH) or intermittent (CIH) hypoxia in order to elucidate the underlying molecular mechanisms that may lead to hypoxic acclimation. Adult Wistar rats were exposed to CCH or CIH simulating 4200 meters of altitude during 90 days. Salivary secretion was decreased in animals exposed to hypoxia, being lower in CIH, together with increased prostaglandin E₂ (PGE₂) content, TBARS concentration, and the presence of apoptotic nuclei and irregular secretion granules in SMG. AQP-5 mRNA levels decreased in both hypoxic groups. Only the CCH group showed higher HIF-1α staining, while CIH alone exhibited interradicular bone loss and increased concentration of the bone resorption marker CTX-I. In summary, animals exposed to CIH show a worse salivary secretion rate, which related with higher levels of PGE₂, suggesting a negative role of this inflammatory mediator during hypoxia acclimation. We link the weak immunorreactivity of HIF-1α in CIH with improper hypoxia acclimation, which is necessary to sustaining SMG physiology under this environmental condition. The alveolar bone loss observed in CIH rats could be due mainly to a direct effect of PGE₂, as suggested by its higher content in gingival tissue, but also to the indirect effect of hyposalivation. This study may eventually contribute to finding therapeutics to treat the decreased salivary flow, improving in that way oral health.

Voice Stress Analysis: A New Framework for Voice and Effort in Human Performance

People rely on speech for communication, both in a personal and professional context, and often under different conditions of physical, cognitive and/or emotional load. Since vocalization is entirely integrated within both our central (CNS) and autonomic nervous system (ANS), a mounting number of studies have examined the relationship between voice output and the impact of stress. In the current paper, we will outline the different stages of voice output, i.e., breathing, phonation and resonance in relation to a neurovisceral integrated perspective on stress and human performance. In reviewing the function of these three stages of voice output, we will give an overview of the voice parameters encountered in studies on voice stress analysis (VSA) and review the impact of the different types of physiological, cognitive and/or emotional load. In the section "Discussion," with regard to physical load, a competition for ventilation processes required to speak and those to meet metabolic demand of exercised muscles is described. With regard to cognitive and emotional load, we will present the "Model for Voice and Effort" (MoVE) that comprises the integration of ongoing top-down and bottom-up activity under different types of load and combined patterns of voice output. In the MoVE, it is proposed that the fundamental frequency (F0) values as well as jitter give insight in bottom-up/arousal activity and the effort a subject is capable to generate but that its range and variance are related to ongoing top-down processes and the amount of control a subject can maintain. Within the MoVE, a key-role is given to the anterior cingulate cortex (ACC) which is known to be involved in both the equilibration between bottom-up arousal and top-down regulation and vocal activity. Moreover, the connectivity between the ACC and the nervus vagus (NV) is underlined as an indication of the importance of respiration. Since respiration is the driving force of both stress and voice production, it is hypothesized to be the missing-link in our understanding of the underlying mechanisms of the dynamic between speech and stress.

Uncertainty in heart rate complexity metrics caused by R-peak perturbations

Heart rate complexity (HRC) is a proven metric for gaining insight into human stress and physiological deterioration. To calculate HRC, the detection of the exact instance of when the heart beats, the R-peak, is necessary. Electrocardiogram (ECG) signals can often be corrupted by environmental noise (e.g., from electromagnetic interference, movement artifacts), which can potentially alter the HRC measurement, producing erroneous inputs which feed into decision support models. Current literature has only investigated how HRC is affected by noise when R-peak detection errors occur (false positives and false negatives). However, the numerical methods used to calculate HRC are also sensitive to the specific location of the fiducial point of the R-peak. This raises many questions regarding how this fiducial point is altered by noise, the resulting impact on the measured HRC, and how we can account for noisy HRC measures as inputs into our decision models. This work uses Monte Carlo simulations to systematically add white and pink noise at different permutations of signal-to-noise ratios (SNRs), time segments, sampling rates, and HRC measurements to characterize the influence of noise on the HRC measure by altering the fiducial point of the R-peak. Using the generated information from these simulations provides improved decision processes for system design which address key concerns such as permutation entropy being a more precise, reliable, less biased, and more sensitive measurement for HRC than sample and approximate entropy.

Effects of training and competition on the sleep of elite athletes: a systematic review and meta-analysis

Objectives

To characterise the sleep of elite athletes and to identify factors associated with training and competition that negatively affect sleep.

Design

Prognosis systematic review.

Data sources

Three databases (PubMed, SCOPUS and SPORTDiscus) were searched from inception to 26 February 2018.

Eligibility criteria for selecting studies

Included studies objectively reported total sleep time (TST) and/or sleep efficiency (SE) in elite athletes. Studies were required to be observational or to include an observational trial.

Results

Fifty-four studies were included. During training, many studies reported athletes were unable to achieve TST (n=23/41) and/or SE (n=16/37) recommendations. On the night of competition, most studies reported athletes were unable to achieve TST (n=14/18) and/or SE (n=10/16) recommendations. TST was shorter (60 min) the night of competition compared with previous nights. SE was lower (1%) the night of competition compared with the previous night. TST was shorter the night of night competition (start ≥18:00; 80 min) and day competition (20 min) compared with the previous night. SE was lower (3%–4%) the night of night competition but unchanged the night of day competition compared with previous nights. Early morning training (start <07:00), increases in training load (>25%), late night/early morning travel departure times, eastward air travel and altitude ascent impaired sleep.

Conclusion

Athletes were often unable to achieve sleep recommendations during training or competition periods. Sleep was impaired the night of competition compared with previous nights. Early morning training, increases in training load, travel departure times, jet lag and altitude can impair athletes’ sleep.

PROSPERO registration number

CRD42017074367.

Delayed parasympathetic reactivation and sympathetic withdrawal following maximal cardiopulmonary exercise testing (CPET) in hypoxia

PURPOSE

This study investigated the effects of acute hypoxic exposure on post-exercise cardiac autonomic modulation following maximal cardiopulmonary exercise testing (CPET).

METHODS

Thirteen healthy men performed CPET and recovery in normoxia (N) and normobaric hypoxia (H) (FiO₂ = 13.4%, ≈ 3500 m). Post-exercise cardiac autonomic modulation was assessed during recovery (300 s) through the analysis of fast-phase and slow-phase heart rate recovery (HRR) and heart rate variability (HRV) indices.

RESULTS

Both short-term, T30 (mean difference (MD) 60.0 s, 95% CI 18.2-101.8, p = 0.009, ES 1.01), and long-term, HRRt (MD 21.7 s, 95% CI 4.1-39.3, p = 0.020, ES 0.64), time constants of HRR were higher in H. Fast-phase (30 and 60 s) and slow-phase (300 s) HRR indices were reduced in H either when expressed in bpm or in percentage of HR_peak (p < 0.05). Chronotropic reserve recovery was lower in H than in N at 30 s (MD - 3.77%, 95% CI - 7.06 to - 0.49, p = 0.028, ES - 0.80) and at 60 s (MD - 7.23%, 95% CI - 11.45 to - 3.01, p = 0.003, ES - 0.81), but not at 300 s (p = 0.436). Concurrently, Ln-RMSSD was reduced in H at 60 and 90 s (p < 0.01) but not at other time points during recovery (p > 0.05).

CONCLUSIONS

Affected fast-phase, slow-phase HRR and HRV indices suggested delayed parasympathetic reactivation and sympathetic withdrawal after maximal exercise in hypoxia. However, a similar cardiac autonomic recovery was re-established within 5 min after exercise cessation. These findings have several implications in cardiac autonomic recovery interpretation and in HR assessment in response to high-intensity hypoxic exercise.