Energy Intake of Men With Excess Weight During Normobaric Hypoxic Confinement

Due to the observations of weight loss at high altitude, normobaric hypoxia has been considered as a method of weight loss in obese individuals. With this regard, the aim of the present study was to determine the effect of hypoxia per se on metabolism in men with excess weight. Eight men living with excess weight (125.0 ± 17.7 kg; 30.5 ± 11.1 years, BMI: 37.6 ± 6.2 kg⋅m–2) participated in a randomized cross-over study comprising two 10-day confinements: normobaric (altitude of facility ≃ 940 m) normoxia (NORMOXIA; PIO2 = 133 mmHg), and normobaric hypoxia (HYPOXIA). The PIO2 in the latter was reduced from 105 (simulated altitude of 2,800 m) to 98 mmHg (simulated altitude of 3,400 m over 10 days. Before, and at the end of each confinement, participants completed a meal tolerance test (MTT). Resting energy expenditure (REE), circulating glucose, GLP-1, insulin, catecholamines, ghrelin, peptide-YY (PYY), leptin, gastro-intestinal blood flow, and appetite sensations were measured in fasted and postprandial states. Fasting REE increased after HYPOXIA (+358.0 ± 49.3 kcal⋅day–1, p = 0.03), but not after NORMOXIA (−33.1 ± 17.6 kcal⋅day–1). Postprandial REE was also significantly increased after HYPOXIA (p ≤ 0.05), as was the level of PYY. Furthermore, a tendency for decreased energy intake was concomitant with a significant body weight reduction after HYPOXIA (−0.7 ± 0.2 kg) compared to NORMOXIA (+1.0 ± 0.2 kg). The HYPOXIA trial increased the metabolic requirements, with a tendency toward decreased energy intake concomitant with increased PYY levels supporting the notion of a hypoxia-induced appetite inhibition, that could potentially lead to body weight reduction. The greater postprandial blood-glucose response following hypoxic confinement, suggests the potential development of insulin resistance.

Right Ventricular Response to Acute Hypoxia Exposure: A Systematic Review

Background: Acute hypoxia exposure is associated with an elevation of pulmonary artery pressure (PAP), resulting in an increased hemodynamic load on the right ventricle (RV). In addition, hypoxia may exert direct effects on the RV. However, the RV responses to such challenges are not fully characterized. The aim of this systematic review was to describe the effects of acute hypoxia on the RV in healthy lowland adults.Methods: We systematically reviewed PubMed and Web of Science and article references from 2005 until May 2021 for prospective studies evaluating echocardiographic RV function and morphology in healthy lowland adults at sea level and upon exposure to simulated altitude or high-altitude.Results: We included 37 studies in this systematic review, 12 of which used simulated altitude and 25 were conducted in high-altitude field conditions. Eligible studies reported at least one of the RV variables, which were all based on transthoracic echocardiography assessing RV systolic and diastolic function and RV morphology. The design of these studies significantly differed in terms of mode of ascent to high-altitude, altitude level, duration of high-altitude stay, and timing of measurements. In the majority of the studies, echocardiographic examinations were performed within the first 10 days of high-altitude induction. Studies also differed widely by selectively reporting only a part of multiple RV parameters. Despite consistent increase in PAP documented in all studies, reports on the changes of RV function and morphology greatly differed between studies.Conclusion: This systematic review revealed that the study reports on the effects of acute hypoxia on the RV are controversial and inconclusive. This may be the result of significantly different study designs, non-compliance with international guidelines on RV function assessment and limited statistical power due to small sample sizes. Moreover, the potential impact of other factors such as gender, age, ethnicity, physical activity, mode of ascent and environmental factors such as temperature and humidity on RV responses to hypoxia remained unexplored. Thus, this comprehensive overview will promote reproducible research with improved study designs and methods for the future large-scale prospective studies, which eventually may provide important insights into the RV response to acute hypoxia exposure.

Hypoxia Conditioning for High-Altitude Pre-acclimatization

Purpose Main purposes of pre-acclimatization by hypoxia conditioning (HC) are the prevention of high-altitude illnesses and maintenance of aerobic exercise performance. However, robust evidence for those effects or evidence-based guidelines for exposure strategies, including recommendations to ensure safety, are largely lacking. Therefore, we summarize the current knowledge on the physiology of acclimatization to hypoxia and HC with the aim to derive implications for pre-acclimatization strategies before going on high-altitude treks and expeditions. Methods Based on the literature search and personal experience, core studies and important observations have been selected in order to present a balanced view on the current knowledge of high-altitude illnesses and the acclimatization process, specifically focusing on pre-acclimatization strategies by HC. Results and Conclusions It may be concluded that in certain cases even short periods (e.g., 7 h) of pre-acclimatization by HC are effective, but longer periods (e.g., > 60 h) are needed to elicit more robust effects. About 300 h of HC (intermittently applied) may be the optimal preparation for extreme altitude sojourns, although every additional hour spent in hypoxia may confer further benefits. The inclusion of hypobaric exposures (i.e., real altitude) in pre-acclimatization protocols could further increase their efficacy. The level of simulated altitude is progressively increased or individually adjusted ideally. HC should not be terminated earlier than 1–2 weeks before altitude sojourn. Medical monitoring of the pre-acclimatization program is strongly recommended.

Hearing Aids Performance in Hypobaric Environments

OBJECTIVE: High altitudes imply exposure to a decreased ambient air pressure. Such a situation may also alter the performance of acoustic transducers using vibrating diaphragms due to air rarefaction. This study aimed at analyzing the performance at high altitude of hearing aids (HAs) where mechano-electric and electro-mechanic transducers are used. METHODS: A hypobaric chamber was used to perform two separated experimental sessions. In the first one two commercial models of HAs were exposed to a simulated altitude of 25,000 ft (7620 m) and to a subsequent rapid decompression profile, with a rapid climb (< 3 s) from 8000 (2438 m) to 25,000 ft. The second session separately analyzed the performance of microphone and receiver at an altitude of 9000 and 15,000 ft (2743 and 4572 m). Before and after the first session, the HAs were tested with an electronic ear while a dedicated recording system was used in the second session. RESULTS: No HA damage or dysfunction was detected during the first session. In the second one, the microphone showed a mild decrease of its output, while the receiver exhibited a much higher reduction of its output. CONCLUSION: Our findings highlight the safe use of HAs even under extreme environmental pressure changes. For altitudes exceeding 10,000 ft (3048 m), a recalibration of the HAs output via a dedicated program may be suggested. Lucertini M, Sanjust F, Manca R, Cerini L, Lucertini L, Sisto R. Hearing aids performance in hypobaric environments. Aerosp Med Hum Perform. 2021; 92(9):738743.

Effects of Acute Hypoxia on Lactate Thresholds and High-Intensity Endurance Performance—A Pilot Study

The present project compared acute hypoxia-induced changes in lactate thresholds (methods according to Mader, Dickhuth and Cheng) with changes in high-intensity endurance performance. Six healthy and well-trained volunteers conducted graded cycle ergometer tests in normoxia and in acute normobaric hypoxia (simulated altitude 3000 m) to determine power output at three lactate thresholds (PMader, PDickhuth, PCheng). Subsequently, participants performed two maximal 30-min cycling time trials in normoxia (test 1 for habituation) and one in normobaric hypoxia to determine mean power output (Pmean). PMader, PDickhuth and PCheng decreased significantly from normoxia to hypoxia by 18.9 ± 9.6%, 18.4 ± 7.3%, and 11.5 ± 6.0%, whereas Pmean decreased by only 8.3 ± 1.6%. Correlation analyses revealed strong and significant correlations between Pmean and PMader (r = 0.935), PDickhuth (r = 0.931) and PCheng (r = 0.977) in normoxia and partly weaker significant correlations between Pmean and PMader (r = 0.941), PDickhuth (r = 0.869) and PCheng (r = 0.887) in hypoxia. PMader and PCheng did not significantly differ from Pmean (p = 0.867 and p = 0.784) in normoxia, whereas this was only the case for PCheng (p = 0.284) in hypoxia. Although investigated in a small and select sample, the results suggest a cautious application of lactate thresholds for exercise intensity prescription in hypoxia.

Variability in venous gas emboli following the same dive at 3,658 meters

Exposure to a reduction in ambient pressure such as in high-altitude climbing, flying in aircrafts, and decompression from underwater diving results in circulating vascular gas bubbles (i.e., venous gas emboli [VGE]). Incidence and severity of VGE, in part, can objectively quantify decompression stress and risk of decompression sickness (DCS) which is typically mitigated by adherence to decompression schedules. However, dives conducted at altitude challenge recommendations for decompression schedules which are limited to exposures of 10,000 feet in the U.S. Navy Diving Manual (Rev. 7). Therefore, in an ancillary analysis within a larger study, we assessed the evolution of VGE for two hours post-dive using echocardiography following simulated altitude dives at 12,000 feet. Ten divers completed two dives to 66 fsw (equivalent to 110 fsw at sea level by the Cross correction method) for 30 minutes in a hyperbaric chamber. All dives were completed following a 60-minute exposure at 12,000 feet. Following the dive, the chamber was decompressed back to altitude for two hours. Echocardiograph measurements were performed every 20 minutes post-dive. Bubbles were counted and graded using the Germonpré and Eftedal and Brubakk method, respectively. No diver presented with symptoms of DCS following the dive or two hours post-dive at altitude. Despite inter- and intra-diver variability of VGE grade following the dives, the majority (11/20 dives) presented a peak VGE Grade 0, three VGE Grade 1, one VGE Grade 2, four VGE Grade 3, and one VGE Grade 4. Using the Cross correction method for a 66-fsw dive at 12,000 feet of altitude resulted in a relatively low decompression stress and no cases of DCS.

Effect of altitude on the emission characteristics of a DI diesel engine

To evaluate the effects of altitude on common rail electronic-controlled diesel engine, an experiment was carried out on a test bench with the simulated altitude system. The results indicated that the emissions of CO and Soot increased, while the impact of altitude on NOx varied based on the specific loads and speed when altitude increased from 0m to 4000m. The increment rate of CO and Soot increased with altitude, and the impact of altitude was greater on CO and Soot than those of NOX. The average emissions of CO and Soot increased with altitude, while the average emission NOx first increased at 1000m then decreased with altitude. The average increasing rate of CO ,Soot and NOx was 14.5%~59.5%, 13.4%~25.6% , -5.6%~0.5% respectively.

Effect of Dark Chocolate Supplementation on Tissue Oxygenation, Metabolism, and Performance in Trained Cyclists at Altitude

Dark chocolate (DC) is high in flavonoids and has been shown to increase nitric oxide in the blood. Increased nitric oxide has the potential to improve delivery of oxygen to muscle, especially in hypoxic conditions, such as altitude. Our aim was to assess the impact of DC supplementation on cycling performance at altitude. Twelve healthy, trained cyclists (n = 2 females, n = 10 males; age = 35 [12] years; height = 177 [7] cm; mass = 75.2 [11.0] kg; VO2max = 55 [6] ml·kg−1·min−1) were randomized to supplement with 60 g of DC or placebo twice per day for 14 days in a double-blind crossover study. After the 2 weeks of supplementation, the participants attended a laboratory session in which they consumed 120 g of DC or placebo and then cycled for 90 min at 50% peak power output, followed immediately by a 10-km time trial (TT) at simulated altitude (15% O2). The plasma concentration of blood glucose and lactate were measured before and at 15, 30, 60, and 90 min during the steady-state exercise and post TT, while muscular and prefrontal cortex oxygenation was measured continuously throughout exercise using near-infrared spectroscopy. DC resulted in a higher concentration of blood glucose (5.5 [0.5] vs. 5.3 [0.9] mmol/L) throughout the trial and lower blood lactate concentration following the TT (7.7 [1.92] vs. 10.0 [4.6] mmol/L) compared with the placebo. DC had no effect on the TT performance (19.04 [2.16] vs. 19.21 ± 1.96 min) or oxygenation status in either the prefrontal cortex or muscle. The authors conclude that, although it provided some metabolic benefit, DC is not effective as an ergogenic aid during TT cycling at simulated altitude.

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

This study focuses on the determination of the vagal threshold (Tva) 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. Tva level in normoxia was determined at exercise intensity corresponding with (M ± SD) 45.0 ± 5.6% of MHRR. Power output at Tva (POth), 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 POth 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, POth did not differ excessively between normoxic conditions and the simulated altitude of ~1500 m, while more substantial decline of POth occurred at the simulated altitude of ~2500 m compared to the other two conditions.