Effects Of Acute Normobaric Hypoxia Research Articles

The effects of acute normobaric hypoxia on standing balance while dual-tasking with and without visual input.

To investigate the influence of acute normobaric hypoxia on standing balance under single and dual-task conditions, both with and without visual input. 20 participants (7 female, 20-31years old) stood on a force plate for 16, 90-s trials across four balance conditions: single-task (quiet stance) or dual-task (auditory Stroop test), with eyes open or closed. Trials were divided into four oxygen conditions where the fraction of inspired oxygen (FIO2) was manipulated (normoxia: 0.21 and normobaric hypoxia: 0.16, 0.145 and 0.13 FIO2) to simulate altitudes of 1100, 3,400, 4300, and 5200m. Participants breathed each FIO2 for ~ 3min before testing, which lasted an additional 7-8min per oxygen condition. Cardiorespiratory measures included heart rate, peripheral blood oxygen saturation, and pressure of end tidal (PET) CO2 and O2. Center of pressure measures included total path length, 95% ellipse area, and anteroposterior and mediolateral velocity. Auditory Stroop test performance was measured as response accuracy and latency. Significant decreases in oxygen saturation and PETO2, and increased heart rate were observed between normoxia and normobaric hypoxia (P < 0.0001). Total path length was higher at 0.13 compared to 0.21 FIO2 for the eyes closed no Stoop test condition (P = 0.0197). No other significant differences were observed. These findings suggest that acute normobaric hypoxia has a minimal impact on standing balance and does not influence auditory Stroop test or dual-task performance. Further investigation with longer exposure is required to understand the impact and time course of normobaric hypoxia on standing balance.

Independent, additive and interactive effects of acute normobaric hypoxia and cold on submaximal and maximal endurance exercise.

To evaluate the independent and combined effects of hypoxia (FiO2 = 13.5%) and cold (-20°C) on physiological and perceptual responses to endurance exercise. 14 trained male subjects ( O2max: 64 ± 5mL/kg/min) randomly performed a discontinuous maximal incremental test to exhaustion on a motorized treadmill under four environmental conditions: Normothermic-Normoxia (N), Normothermic-Hypoxia (H), Cold-Normoxia (C) and Cold-Hypoxia (CH). Performance and physiological and perceptual responses throughout exercise were evaluated. Maximal WorkLoad (WL) and WL at lactate threshold (LT) were reduced in C (-2.3% and -3.5%) and H (-18.0% and -21.7%) compared to N, with no interactive (p = 0.25 and 0.81) but additive effect in CH (-21.5% and -24.6%). Similarly, HRmax and Vemax were reduced in C (-3.2% and -14.6%) and H (-5.0% and -7%), showing additive effects in CH (-7.7% and -16.6%). At LT, additive effect of C (-2.8%) and H (-3.8%) on HR reduction in CH (-5.7%) was maintained, whereas an interactive effect (p = 0.007) of the two stressors combined was noted on Ve (C: -3.1%, H: + 5.5%, CH: -10.9%). [La] curve shifted on the left in CH, displaying an interaction effect between the 2 stressors on this parameter. Finally, RPE at LT was exclusively reduced by hypoxia (p < 0.001), whereas TSmax is synergistically reduced by cold and hypoxia (interaction p = 0.047). If compared to single stress exposure, exercise performance and physiological and perceptual variables undergo additive or synergistic effects when cold and hypoxia are combined. These results provide new insight into human physiological responses to extreme environments.

SALIFEN PREVENTS PERINATAL HYPOXIA-INDUCED COGNITIVE IMPAIRMENTS AND CHANGES IN GABA&lt;sub&gt;B&lt;/sub&gt; RECEPTOR EXPRESSION IN THE RAT NEOCORTEX

We have studied the effects of acute normobaric hypoxia in the early postnatal period of the development (the 2nd postnatal day) on learning and memory abilities and the expression of GABAB receptors in the neocortex (medial prefrontal cortex) in adolescent rats (the 55–60th postnatal day), as well as the possibility of correction of the revealed impairments by GABA derivative salifen. It was shown that perinatal hypoxia disrupts task acquisition and consolidation in the novel object recognition test, impairs passive avoidance performance, and also reduces spatial learning abilities in the Morris water maze. Western blotting analysis revealed increased levels of GABAB receptor protein in the medial prefrontal cortex of the rats following the exposure to perinatal hypoxia. Post-hypoxic daily salifen injections over 14 days at a dose of 15 mg/kg improved cognitive abilities in rats, and also normalized GABAB receptor content in the rat medial prefrontal cortex. The results of the present research are of considerable significance for solution of applied problem of neonatology – the search for effective drug candidates for the pharmacological correction of the impacts of perinatal hypoxia.

The effects of acute normobaric hypoxia on vestibular-evoked balance responses in humans.

Hypoxia influences standing balance and vestibular function. The purpose here was to investigate the effect of hypoxia on the vestibular control of balance. Twenty participants (10 males; 10 females) were tested over two days (normobaric hypoxia and normoxia). Participants stood on a force plate (head rotated leftward) and experienced random, continuous electrical vestibular stimulation (EVS) during trials of eyes open (EO) and closed (EC) at baseline (BL), after 5 (H1), 30 (H2) and 55-min (H3) of hypoxia, and 10-min into normoxic recovery (NR). Vestibular-evoked balance responses were quantified using cumulant density, coherence, and gain functions between EVS and anteroposterior forces. Oxyhemoglobin saturation, end-tidal oxygen and carbon dioxide decreased for H1-3 compared to BL; however, end-tidal carbon dioxide remained reduced at NR with EC (p≤0.003). EVS-AP force peak-to-peak amplitude was lower at H3 and NR than at BL (p≤0.01). At multiple frequencies, EVS-AP force coherence and gain estimates were lower at H3 and NR than BL for females; however, this was only observed for coherence for males. Overall, vestibular-evoked balance responses are blunted following normobaric hypoxia >30 min, which persists into NR and may contribute to the reported increases in postural sway.

Independent effects of acute normobaric hypoxia and hypobaric hypoxia on human physiology

The purpose of this study was to examine the effects of acute normobaric (NH, decreased FiO2) and hypobaric (HH, 4200 m ascent) hypoxia exposures compared to sea level (normobaric normoxia, NN). Tissue oxygenation, cardiovascular, and body fluid variables measured during rest and a 3-min step-test following 90-min exposures (NH, HH, NN). Muscle oxygenated hemoglobin (O2Hb) decreased, and muscle deoxygenated hemoglobin (HHb) increased environmentally independent from rest to exercise (p < 0.001). During exercise, brain O2Hb was lower at HH compared to NN (p = 0.007), trending similarly with NH (p = 0.066), but no difference between NN and NH (p = 0.158). During exercise, HR at NH (141 ± 4 beats·min−1) and HH (141 ± 3 beats·min−1) were higher than NN (127 ± 44 beats·min−1, p = 0.002), but not each other (p = 0.208). During exercise, stroke volume at HH (109.6 ± 4.1 mL·beat−1) was higher than NH (97.8 ± 3.3 mL·beat−1) and NN (99.8 ± 3.9 mL·beat−1, p ≤ 0.010) with no difference between NH and NN (p = 0.481). During exercise, cardiac output at NH (13.8 ± 0.6 L) and HH (15.5 ± 0.7 L) were higher than NN (12.6 ± 0.5 L, p ≤ 0.006) with HH also higher than NH (p = 0.001). During acute hypoxic stimuli, skeletal muscle maintains oxygenation whereas the brain does not. These differences may be mediated by environmentally specific cardiovascular compensation. Thus, caution is advised when equating NH and HH.

Acupuncture Effects on Cerebral Blood Flow during Normoxia and Normobaric Hypoxia: Results from a Prospective Crossover Pilot Study

Cerebral blood flow (CBF) is significantly influenced by exposure to hypoxia, both hypobaric and normobaric. Alterations in cerebral blood flow can play a crucial role in the pathogenesis of acute mountain sickness (AMS) and its symptoms, especially headache, dizziness, and nausea. Acupuncture has been proven to be effective in treating some cerebrovascular disorders and PC6 Nei Guan stimulation seems to enhance cerebral blood flow. Therefore, we have hypothesized that PC6 Nei Guan stimulation could affect CBF in acute hypoxia and could be used to contrast AMS symptoms. We evaluated blood flow in the middle cerebral artery (MCA) in normoxia, after 15 min in normobaric hypoxia (fraction of inspired oxygen (FiO2) 14%, corresponding to 3600 m a.s.l.) in basal conditions, and after PC6 Nei Guan stimulation, both by needle and by pressure. No comparisons with other acupuncture points and sham acupuncture were done. PC6 stimulation seemed to counteract the effects of acute normobaric hypoxia on end-diastolic velocity (EDV) in MCA, especially after acupuncture, and significantly reduced systolic and diastolic blood pressure. A rebalance of CBF could control some AMS symptoms, but further studies are necessary.

Effect of acute normobaric hypoxia on passively simulated illusions: A double-blind randomized study

Introduction: Number of accidents in the past four decades in rotary wing flying in high altitude areas in the Indian Air Force have been attributed to spatial disorientation (SD) or hypoxia or both. Although the two aviation stressors; hypoxia and SD, have been studied independently, literature is scant on the combined effects of the two notorious factors in military aviation. Material and Methods: In a double-blind randomized control design, 32 healthy volunteers divided into two groups (hypoxia group and normoxia group) of 16 subjects each, participated in the study. Subjects in the hypoxia group were exposed to normobaric hypoxia with pre-mixed gases in cylinders with nitrox gas (simulating altitude of 22,000 ft) and the normoxia group was exposed to normal air. Autokinesis time (AT) and vestibular adaptation time (VAT) during acceleration and deceleration, in both clockwise and counter-clockwise turns, were studied as surrogates for SD in both hypoxia group and normoxia group in Disorientation Simulator. Results: Mean AT showed a statistically significant decrease (t = −2.2, P = 0.039) in hypoxia group compared to normoxia group. Similarly, a statistically significant reduction (F = 5.989, P = 0.016) in mean VAT was observed in in hypoxia group compared to normoxia group. There was no significant difference in the VAT in clockwise and counter-clockwise yaw rotation in both the groups. Conclusion: A significant reduction in AT indicates that hypoxia may increase the onset of autokinesis early. The changes in VAT in hypoxic conditions bring out a possible effect of hypoxia on the adaptability of the vestibular system in the angular motion environment.

P 61. Effects of acute normobaric hypoxia on memory and attention in young adults

Objective. An increasing number of sea-level residents takes part in alpine sports such as trekking or skiing. This has inspired a growing research interest on the effects of high altitude and hypoxic conditions on cognition. The aim of this study was to assess the effects of an acute normobaric hypoxia intervention (90 minutes) on cognition in healthy young adults. Methods . Twenty-five healthy, high-altitude-naive adults (25,8 ± 3,3 years; 15 females) were analysed in a randomized cross-over study. Participants received one acute normobaric hypoxic and one normobaric normoxic intervention separated by at least 2 weeks. Heart frequency and saturation of arterial blood oxygenation (SaO2) were continuously monitored while participants lay down for 120 minutes. After 30 minutes, either normobaric hypoxia (SaO2 of 80-85%) or normobaric normoxia was applied for the following 90 minutes. Cognitive parameters related to working memory and sustained attention (d2-Test, N-Back and Digit Span Test) were collected before and after each intervention session. Results . Normobaric hypoxia led to a significant decrease of SaO2 compared to normobaric normoxia (82,7 ± 4,3% vs. 98,1 ± 0,5%, p < .001). Regarding cognitive parameters, no significant time × group interactions were observed. Post hoc t-tests revealed a significant improvement in the d2-Test in both groups. Conclusion . In contrast to previous studies (Malle et al., 2013; Pilmanis, Balldin & Fischer, 2016; Ochi et al., 2018) our results indicate that acute normobaric hypoxia has no effects on working memory and sustained attention. One potential explanation for the absence of effects is the short duration and/or the rather high O2 concentration of the hypoxic condition. In this regard, Ochi et al. have found dose-dependent effects of hypoxia on cognition with the most pronounced results under the severe condition (5000 m). Future studies are needed that investigate dose-response mechanisms of acute hypoxia on cognition.

Exposure to acute normobaric hypoxia results in adaptions of both the macro- and microcirculatory system

Although acute hypoxia is of utmost pathophysiologic relevance in health and disease, studies on its effects on both the macro- and microcirculation are scarce. Herein, we provide a comprehensive analysis of the effects of acute normobaric hypoxia on human macro- and microcirculation. 20 healthy participants were enrolled in this study. Hypoxia was induced in a normobaric hypoxia chamber by decreasing the partial pressure of oxygen in inhaled air stepwisely (pO2; 21.25 kPa (0 k), 16.42 kPa (2 k), 12.63 kPa (4 k) and 9.64 kPa (6 k)). Macrocirculatory effects were assessed by cardiac output measurements, microcirculatory changes were investigated by sidestream dark-field imaging in the sublingual capillary bed and videocapillaroscopy at the nailfold. Exposure to hypoxia resulted in a decrease of systemic vascular resistance (p < 0.0001) and diastolic blood pressure (p = 0.014). Concomitantly, we observed an increase in heart rate (p < 0.0001) and an increase of cardiac output (p < 0.0001). In the sublingual microcirculation, exposure to hypoxia resulted in an increase of total vessel density, proportion of perfused vessels and perfused vessel density. Furthermore, we observed an increase in peripheral capillary density. Exposure to acute hypoxia results in vasodilatation of resistance arteries, as well as recruitment of microvessels of the central and peripheral microcirculation. The observed macro- and microcirculatory effects are most likely a result from compensatory mechanisms to ensure adequate tissue oxygenation.

Effects of Acute Normobaric Hypoxia on Memory Interference.

Purpose: Previous research has evaluated the effects of acute hypoxia exposure on cognitive function, notably executive function. No studies, to date, have evaluated the effects of acute hypoxia exposure on memory interference, which was the purpose of this experiment. Methods: A within-subjects, counterbalanced experimental design was employed, with condition (hypoxia vs. normoxia) and time (immediate vs. delayed) being the independent variables. Participants (N = 21; Mage = 21.0 years) completed two laboratory visits, involving 30 min of exposure to either hypoxia (FIO2 = 0.12) or normoxia (FIO2 = 0.21). Following this, they completed a memory interference task (AB/AC paradigm), assessing immediate and delayed proactive and retroactive interference. Results: For retroactive interference, we observed a significant main effect for condition, F(1, 20) = 5.48, p = 0.03, ƞ2 = 0.10, condition by time interaction, F(1, 20) = 4.96, p = 0.03, ƞ2 = 0.01, but no main effect for time, F(1, 20) = 1.75, p = 0.20, ƞ2 = 0.004. Conclusion: Our results demonstrate that acute hypoxia exposure was facilitative in reducing memory interference. We discuss these findings in the context of the potential therapeutic effects of acute hypoxia exposure on synaptic plasticity.

Effects of Acute Normobaric Hypoxia on Non-linear Dynamics of Cardiac Autonomic Activity During Constant Workload Cycling Exercise.

AimMeasurements of Non-linear dynamics of heart rate variability (HRV) provide new possibilities to monitor cardiac autonomic activity during exercise under different environmental conditions. Using detrended fluctuation analysis (DFA) technique to assess correlation properties of heart rate (HR) dynamics, the present study examines the influence of normobaric hypoxic conditions (HC) in comparison to normoxic conditions (NC) during a constant workload exercise.Materials and MethodsNine well trained cyclists performed a continuous workload exercise on a cycle ergometer with an intensity corresponding to the individual anaerobic threshold until voluntary exhaustion under both NC and HC (15% O2). The individual exercise duration was normalized to 10% sections (10–100%). During exercise HR and RR-intervals were continuously-recorded. Besides HRV time-domain measurements (meanRR, SDNN), fractal correlation properties using short-term scaling exponent alpha1 of DFA were calculated. Additionally, blood lactate (La), oxygen saturation of the blood (SpO2), and rating of perceived exertion (RPE) were recorded in regular time intervals.ResultsWe observed significant changes under NC and HC for all parameters from the beginning to the end of the exercise (10% vs. 100%) except for SpO2 and SDNN during NC: increases for HR, La, and RPE in both conditions; decreases for SpO2 and SDNN during HC, meanRR and DFA-alpha1 during both conditions. Under HC HR (40–70%), La (10–90%), and RPE (50–90%) were significantly-higher, SpO2 (10–100%), meanRR (40–70%), and DFA-alpha1 (20–60%) were significantly-lower than under NC.ConclusionUnder both conditions, prolonged exercise until voluntary exhaustion provokes a lower total variability combined with a reduction in the amplitude and correlation properties of RR fluctuations which may be attributed to increased organismic demands. Additionally, HC provoked higher demands and loss of correlation properties at an earlier stage during the exercise regime, implying an accelerated alteration of cardiac autonomic regulation.

No effect of acute normobaric hypoxia on plasma triglyceride levels in fasting healthy men.

Circulating fatty acids are a major systemic energy source in the fasting state as well as a determinant of hepatic triglycerides (TG)-rich very-low-density lipoprotein production. Upon acute hypoxia, sympathetic arousal induces adipose tissue lipolysis, resulting in an increase in circulating nonesterified fatty acids (NEFA). Animal studies suggest that TG clearance may also be strongly reduced under hypoxia, though this effect has been shown to be dependent on temperature. Whether the hypoxia-induced rise in blood fatty acid concentrations affects fasting TG levels in humans under thermoneutral conditions remains unknown. TG, NEFA, and glycerol levels were measured in fasted healthy young men (n = 10) exposed for 6 h to either normoxia (ambient air) or acute hypoxia (fraction of inspired oxygen = 0.12) in a randomized, crossover design. Participants were casually clothed and rested in front of a fan in an environmental chamber maintained at 28 °C during each trial. Under hypoxia, a significantly greater increase in NEFA occurred (condition × time interaction, p = 0.049) and glycerol levels tended to be higher (condition × time, p = 0.104), suggesting an increase in adipose tissue lipolysis. However, plasma TG levels did not change over time and did not differ between the normoxia and hypoxia conditions. In conclusion, acute exposure to normobaric hypoxia under thermoneutral condition in healthy men during fasting state increased lipolysis without affecting circulating TG.

Behavior Disorders Caused by Perinatal Hypoxia in Juvenile Rats and Their Correction with GABA Derivative.

We studied the effects of acute normobaric hypoxia on postnatal day 2 (model of preterm pregnancy) on reflex activity and behavior of juvenile male Wistar rats and the possibility of correction of behavioral deficit by administration of GABA derivative Salifen after hypoxia. It is shown, that perinatal hypoxia impaired righting reflex and forelimb grip strength and increased motor activity in juvenile male rats. Administration of Salifen for 14 days in a dose of 15 mg/kg improved reflex activity and behavior of rats, which indicates the prospect of further study of the therapeutic efficacy of this drug on models of neonatal encephalopathy.

Physiological and Cognitive Effects of Acute Normobaric Hypoxia and Modulations from Oxygen Breathing.

The emergence of normobaric devices for hypoxia awareness training makes crucial the study of physiological and cognitive effects induced by acute normobaric hypoxia (NH) exposure. Our study aimed to 1) investigate the effects of acute NH exposure on physiological variables and working memory; and 2) investigate the physiological and cognitive effects of oxygen breathing before and after acute NH exposure. There were 86 healthy men who were randomized into 4 groups: the Normoxia-Air group (N = 23), whose subjects were breathing air; the Hypoxia-Air group (N = 22), where NH exposure was preceded and followed by air breathing; the Normoxia-O₂group (N = 21), whose protocol was similar to the Normoxia-Air group, except with the addition of 100% O₂breathing periods; and the Hypoxia-O₂group (N = 20), whose participants were exposed to 100% O₂before and after NH exposure. Working memory was assessed with the Paced Auditory Serial Addition Test. Peripheral oxygen saturation (Spo₂), heart rate (HR), and electroencephalogram (EEG) were recorded. Acute NH exposure induced a classical physiological response (i.e., decreased Spo₂and increased HR), but not identical to the well-described physiological response to acute hypobaric hypoxia. Acute NH also caused a strong impairment in working memory. Oxygen breathing following NH exposure induced a slowing in the EEG associated with a worsening of working memory performance. Acute NH exposure revealed a good surrogate for the classical hypobaric chamber for refresher hypoxia awareness training. Because the association between hypoxia and hyperoxia seems deleterious for the brain, we suggest that NH exposure should be surrounded by air breathing.

A Meta-Analysis of Exhaled Nitric Oxide in Acute Normobaric Hypoxia.

The effect of hypoxia on the exhaled nitric oxide (NO) of humans is unresolved. Many studies have measured the fraction of exhaled NO (FENO) or the partial pressure of exhaled NO (PENO) in normobaric and hypobaric hypoxia, with differing results. To better understand NO physiology and altitude acclimatization, we employed a random effects meta-analysis to determine the effect of acute normobaric hypoxia on the PENO of humans. A total of 93 subjects from 7 published studies (with 9 groups) were included. The median duration of exposure was 30 min and the mean hypoxic PIo2 was 95 (SD=10) mmHg. The weighted standardized mean difference (SMD) in PENO measured at baseline and during an acute exposure to normobaric hypoxia was not significantly different from zero (SMD=0.09; 95% CI=-0.17, 0.34; z=0.65). Based on this meta-analysis, acute normobaric hypoxia does not affect the PENO measured from the mouths of humans. This result should be considered for interpretations of high-altitude (and hypobaric) measurements of exhaled NO. As the PENO is a potential biomarker for altitude-illness susceptibility, recognizing that normobaric hypoxia does not affect the PENO will be important for understanding previous associations between low exhaled NO and poor acclimatization to hypoxia.

Predicting the Effects of Acute Normobaric Hypoxia on Exercise Performance from Physiological Measurements at Rest.

Predicting the Effects of Acute Normobaric Hypoxia on Exercise Performance from Physiological Measurements at Rest.

Effects of Exercise and Hypoxia on Heart Rate Variability and Acute Mountain Sickness

Acute mountain sickness (AMS) is a common condition among non-acclimatized individuals ascending to high altitude. Exercise, a characteristic feature of hiking and mountaineering, has been suggested to exacerbate AMS prevalence and to cause modifications of the autonomic nervous system. A reduction of the heart rate variability (HRV) is a common finding during acute hypoxia, however characteristics of HRV during exercise in subjects suffering from AMS are unknown. Therefore, the aim of the present study was to investigate the effects of acute normobaric hypoxia (FiO2=11.0% ≙ 5 500 m) at rest (PHE) and during exercise (AHE) on the cardiac autonomic function and the development of AMS in 20 healthy, male individuals. HRV recordings were performed during normoxia and after 2, 4, 6 and 8 h in hypoxia during PHE and AHE, respectively. AMS was assessed using the Lake Louise Score. During PHE 50% of participants developed AMS and 70% during AHE (p=0.22). The analysis of HRV data showed a significant reduction of total power (TP), high frequency (HF) and low frequency (LF) components and an increase of the LF:HF ratio during PHE, however without further modification during AHE. Exercise did not increase AMS prevalence or severity, but increased "non-gastrointestinal" symptoms including headache, fatigue and dizziness. HRV indices were not related to the overall incidence of AMS or the development of "non-gastrointestinal" symptoms but we detected significant correlations between gastrointestinal complaints and HRV components. Thus, we suggest that the cardiac autonomic modulation during acute normobaric hypoxia does not play an important role in the development of AMS, but seems to be related to gastrointestinal complaints at high altitude. However, the influence of moderate exercise on HRV and AMS is minor, only "non-GI" symptoms seem to be exacerbated when exercise is applied.

The Effect of Acute Normobaric Hypoxia On Heart Rate And Mean Arterial Pressure at Rest, During annd Post Exercise

BACKGROUND: Hypoxia is a potent stressor that induces various physiological changes. Although modifications in autonomic regulation and vascular tone are responses to hypoxia, changes in heart rate and blood pressure may vary depending on individual characteristics, severity of hypoxia and exercise intensity and duration. PURPOSE: The purpose of the current study was to determine the effect of acute normobaric hypoxia on heart rate and mean arterial pressure at rest, during and post-exercise in middle-aged males. METHODS: Eight apparently healthy (35.9 ± 5.7 ml·kg-1·min-1), middle-aged (40.5 ± 2 yr) males volunteered to participate in the present investigation. Participants reported to the exercise physiology laboratory on three separate occasions. On the first visit, subjects underwent a graded exercise test (Excalibur 1300W cycle ergometer) to determine maximal oxygen consumption. The next two visits were separated by a one week washout period. Participants underwent normoxia with exercise (NE) and hypoxia with exercise (HE) in a hypoxia (20.9% vs. 12.5% O2) chamber (Colorado Altitude Training, Louisville, CO) including 2hr baseline, 1h low intensity cycling (50% of hypoxic VO2max) and 2h recovery. Heart rate (HR) measures were obtained every 10 min, and mean arterial pressure (MAP) measures were obtained every 30min throughout the experimental trials. RESULTS: A repeated measures ANOVA revealed a trial (NE and HE) by time interaction for heart rate (p<0.01), and a pair-sample t-test demonstrated that the difference in post exercise HR between HE and NE is greater than pre exercise (p<0.05). MAP demonstrated a trial by time interaction (p<0.05); MAP decreased greater in hypoxia than normoxia post exercise. CONCLUSION: These data suggest that normobaric hypoxia causes a differential hemodynamic response from normoxia in apparently healthy middle aged males at rest and post-exercise.

Serum glucose level in severe acute exogenous normobaric hypoxia in humans at rest

The study of the effect of acute normobaric hypoxia, which was simulated by inhalation of the oxygen-nitrogen mixture containing 8% of oxygen, which corresponds to its partial pressure at an altitude of 7000 m above sea level, was conducted in a group of apparently healthy men (aged 19–23 years, n = 10). The biochemical analysis during the test included determining the glucose, pyruvate, and lactate levels in venous blood; the hemoglobin content, pH, hematocrit, partial oxygen and carbon dioxide pressures, and hemoglobin saturation with oxygen. It was shown that, at the fifth minute of hypoxia, the serum glucose level decreased significantly (p < 0.05) compared to the background. However, on the whole, the maximal glucose level decrease was 0.76 mM, and the lowest individual parameter values did not decrease below 4.0 mM. The serum glucose level was restored to the background values at the tenth minute of testing. It was suggested that the syncopal form of altitude hypoxia in humans is unlikely to be linked to the development of hypoglycemia.

Trained Women Demonstrate Greater Preservation Of Peak Exercise Capacity During Acute Hypoxia Than Trained Men

The lower hemoglobin concentration and consequent lower arterial oxygen content in women compared to men may result in gender differences in the physiological response to acute hypoxia. However, very few reports of direct gender comparisons in the physiological response to acute hypoxia are available to date and indirect comparisons between studies exclusively of men or women are largely equivocal. PURPOSE: To determine the effects of acute normobaric hypoxia on cardiovascular hemodynamics at rest and during maximal exercise in endurance trained men and women. METHODS: Peak exercise capacity (Wpeak) at sea level (SL) and normobaric hypoxia (NH, 12.8% FIO2, ∼3900 m) was determined for 20 male (26 ± 1 yr, 56.6 ± 1.2 ml/kg/min VO2peak, mean ± SE) and 15 female (25 ± 1 yr, 45.3 ± 1.2 ml/kg/min VO2peak) trained cyclists and triathletes at least 48 h apart. At rest and during exercise, heart rate (HR), stroke volume (SV), and cardiac output (Q) were measured continuously by noninvasive impedance cardiography while arterial oxygen saturation (SaO2) was measured by pulse oximetry. RESULTS: HR, SV, and Q at rest did not change from SL to NH in men or women and both genders demonstrated similar reductions in SaO2 at rest (96 ± 1 to 85 ± 1%, p < 0.05). Wpeak was significantly reduced from SL to NH in both men (325 ± 8 to 250 ± 6 W, p < 0.05) and women (245 ± 7 to 201 ± 6 W, p < 0.05), but the relative decrease in Wpeak from SL to NH was significantly greater in men than women (-22.7 ± 0.9 vs. -17.5 ± 1.5%, p < 0.05). Peak Q was similarly reduced in both genders from SL to NH (-9.5 ± 3.6%, p < 0.05), while peak SV did not change and peak HR was reduced in men more than women (-7.3 ± 0.7% vs. -4.9 ± 0.8%, p < 0.05). SaO2 at peak was similarly reduced in men (94 ± 1 to 71 ± 2%, p < 0.05) and women (94 ± 1 to 72 ± 2%, p < 0.05) from SL to NH. CONCLUSION: Endurance trained women appear to be more capable of preserving peak exercise capacity during acute NH than endurance trained men despite similar decrements in Q and SaO2. Supported by the World Anti-Doping Agency