Steady-state cerebral blood flow regulation at altitude: interaction between oxygen and carbon dioxide

Fifteen-minute consultation: A guide to paediatric post-resuscitation care following return of spontaneous circulation

Paediatric resuscitation is a key skill for anyone in medicine who is involved in the care of children. Basic and advance paediatric life support courses are crucial in teaching those skills nationwide in a way that is memorable, protocolised and standardised. These courses are vital in the dissemination and upkeep of both theoretical and practical knowledge of paediatric resuscitation, with their primary aim being the return of spontaneous circulation. While sustaining life is important, preserving a life with quality, one with good functional and neurological outcomes should be the gold standard of any resuscitative attempt. Good neurological outcomes are dependent, in large part, on how well the postresuscitation stage is managed. This stage does not start in the intensive care unit, it starts at the point at which spontaneous circulation has been reinstated. The aim of this paper is to provide a basic overview of the main strategies that should be followed in order to minimise secondary brain injury after successful resuscitation attempts.

Hemorrhage at high altitude: impact of sustained hypobaric hypoxia on cerebral blood flow, tissue oxygenation, and tolerance to simulated hemorrhage in humans

With ascent to high altitude (HA), compensatory increases in cerebral blood flow and oxygen delivery must occur to preserve cerebral metabolism and consciousness. We hypothesized that this compensation in cerebral blood flow and oxygen delivery preserves tolerance to simulated hemorrhage (via lower body negative pressure, LBNP), such that tolerance is similar during sustained exposure to HA vs. low altitude (LA). Healthy humans (4F/4 M) participated in LBNP protocols to presyncope at LA (1130 m) and 5-7 days following ascent to HA (3800 m). Internal carotid artery (ICA) blood flow, cerebral delivery of oxygen (CDO2) through the ICA, and cerebral tissue oxygen saturation (ScO2) were determined. LBNP tolerance was similar between conditions (LA: 1276 ± 304 s vs. HA: 1208 ± 306 s; P = 0.58). Overall, ICA blood flow and CDO2 were elevated at HA vs. LA (P ≤ 0.01) and decreased with LBNP under both conditions (P < 0.0001), but there was no effect of altitude on ScO2 responses (P = 0.59). Thus, sustained exposure to hypobaric hypoxia did not negatively impact tolerance to simulated hemorrhage. These data demonstrate the robustness of compensatory physiological mechanisms that preserve human cerebral blood flow and oxygen delivery during sustained hypoxia, ensuring cerebral tissue metabolism and neuronal function is maintained.

PaCO2 Association with Outcomes of Patients with Traumatic Brain Injury at High Altitude: A Prospective Single-Center Cohort Study

BACKGROUND

Partial pressure of carbon dioxide (PaCO2) is generally known to influence outcome in patients with traumatic brain injury (TBI) at normal altitudes. Less is known about specific relationships of PaCO2 levels and clinical outcomes at high altitudes.

METHODS

This is a prospective single-center cohort of consecutive patients with TBI admitted to a trauma center located at 2600 m above sea level. An unfavorable outcome was defined as a Glasgow Outcome Scale-Extended (GOSE) score < 4 at the 6-month follow-up.

RESULTS

We had a total of 81 patients with complete data, 80% (65/81) were men, and the median (interquartile range) age was 36 (25-50) years. Median Glasgow Coma Scale (GCS) score on admission was 9 (6-14); 49% (40/81) of patients had severe TBI (GCS 3-8), 32% (26/81) had moderate TBI (GCS 12-9), and 18% (15/81) had mild TBI (GCS 13-15). The median (interquartile range) Abbreviated Injury Score of the head (AISh) was 3 (2-4). The frequency of an unfavorable outcome (GOSE < 4) was 30% (25/81), the median GOSE was 4 (2-5), and the median 6-month mortality rate was 24% (20/81). Comparison between patients with favorable and unfavorable outcomes revealed that those with unfavorable outcome were older, (median age 49 [30-72] vs. 29 [22-41] years, P < 0.01), had lower admission GCS scores (6 [4-8] vs. 13 [8-15], P < 0.01), had higher AISh scores (4 [4-4] vs. 3 [2-4], P < 0.01), had higher Acute Physiology and Chronic Health disease Classification System II scores (17 [15-23] vs. 10 [6-14], P < 0.01), had higher Charlson scores (0 [0-2] vs. 0 [0-0], P < 0.01), and had higher PaCO2 levels (mean 35 ± 8 vs. 32 ± 6 mm Hg, P < 0.01). In a multivariate analysis, age (odds ratio [OR] 1.14, 95% confidence interval [CI] 1.1-1.30, P < 0.01), AISh (OR 4.7, 95% CI 1.55-21.0, P < 0.05), and PaCO2 levels (OR 1.23, 95% CI 1.10-1.53, P < 0.05) were significantly associated with the unfavorable outcomes. When applying the same analysis to the subgroup on mechanical ventilation, AISh (OR 5.4, 95% CI 1.61-28.5, P = 0.017) and PaCO2 levels (OR 1.36, 95% CI 1.13-1.78, P = 0.015) remained significantly associated with the unfavorable outcome.

CONCLUSIONS

Higher PaCO2 levels are associated with an unfavorable outcome in ventilated patients with TBI. These results underscore the importance of PaCO2 levels in patients with TBI and whether it should be adjusted for populations living at higher altitudes.

PaCO2 Association with Traumatic Brain Injury Patients Outcomes at High Altitude: A Prospective Single-Center Cohort Study

Background

partial pressure of carbon dioxide (PaCO2) is generally known to influence outcome in patients with traumatic brain injury (TBI) at normal altitudes. Less is known about specific relationships of PaCO2 levels and clinical outcomes at high altitudes.

Methods

This is a prospective single-center cohort of consecutive TBI patients admitted to a trauma center located at 2600 meter above sea level. An unfavorable outcome was defined as the Glasgow Outcome Scale-Extended (GOSE) < 4 at 6-month follow-up.

Results

81 patients with complete data, 80% (65/81) were men, and median (IQR) age was 36 (25-50) years). Median Glasgow Coma Scale (GCS) on admission was 9 (6-14), 49% (40/81) were severe (GCS: 3-8), 32% (26/81) moderate (GCS 12 - 9), and 18% (15/81) mild (GCS 13-15) TBI. The median (IQR) Abbreviated Injury Score of the Head (AISh) was 3 (2-4). Frequency of an unfavorable outcome (GOSE < 4) was 30% (25/81), median GOSE was 4 (2-5), and 6-month mortality was 24% (20/81). Comparison between patients with favorable and unfavorable outcomes revealed that those with unfavorable outcome were older, median [49 (30-72) vs. 29 (22-41), P < 0.01], had lower admission GCS [6 (4-8) vs. 13 (8-15), P < 0.01], higher AIS head [4 (4-4) vs. 3(2-4), p < 0.01], higher APACHE II score [17(15-23) vs 10 (6-14), < 0.01), higher Charlson score [0(0-2) vs. 0 (0-0), P < 0.01] and higher PaCO2 (mmHg), mean ± SD, 39 ± 9 vs. 32 ± 6, P < 0.01. In a multivariate analysis, age (OR 1.14 95% CI 1.1-1.30, P < 0.01), AISh (OR 4.7 95% CI 1.55-21.0, P < 0.05), and PaCO2 (OR 1.23 95% CI: 1.10-1.53, P < 0.05) were significantly associated with the unfavorable outcomes. When applying the same analysis to the subgroup on mechanical ventilation, AISh (OR 5.4 95% CI: 1.61-28.5, P = 0.017) and PaCO2 (OR 1.36 95% CI: 1.13-1.78, P = 0.015) remained significantly associated with the unfavorable outcome.

Conclusion

Higher PaCO2 levels are associated with an unfavorable outcome in ventilated TBI patients. These results underscore the importance of PaCO2 level in TBI patients and whether it should be adjusted for populations living at higher altitudes.

Low oxygen in inspired air causes severe cerebrocortical hypoxia and cell death in the cerebral cortex of awake rats

Type 1 respiratory failure (T1RF) is associated with secondary acute brain injury (sABI). The underlying mechanisms of sABI could include injury to brain cells mediated either by hypoxia or by lung injury-triggered inflammation. To elucidate to what extent T1RF causes hypoxia and a consequent hypoxic injury in the brain in the absence of lung injury, we exposed healthy, conscious Sprague-Dawley rats to 48 h long low partial pressure of O2 in inspired air (PiO2) (7.5-8 % O2 in N2, CO2 < 0.5 %, normal barometric pressure) and measured the partial pressure of oxygen in the premotor cortex (PtO2), cerebral blood flow (CBF), lactate concentrations, and cell death. Low PiO2 significantly affected PtO2, which was 52.3 (SD 2.1) mmHg when PiO2 was normal but declined to 6.4 (SD 3.8) mmHg when PiO2 was low for 1 h. This was accompanied by increased lactate concentrations in plasma, CSF, and premotor cortex. Low PiO2 elevated the number of dead cells in the cerebral cortex from 5.6 (SD 4.8) % (when PiO2 was normal) to 20.5 (SD 4.1) % and 32.37 (SD 6.5) % after 24 h and 48 h exposure to low PiO2, respectively. The Mann-Kendall test could not detect any monotonic increase or decrease in pial blood flow during the 48 h exposure to low PiO2. In summary, our findings suggest that exposure to low PiO2 caused a severe hypoxia in the cerebral cortex, which triggers a massive cell death. Since these conditions mimic T1RF, hypoxic injury could be an important underlying cause of T1RF-induced sABI.

Steady-state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide

Ventilatory acclimatization (VA) is important to maintain adequate oxygenation with ascent to high altitude (HA). Transient hypoxic ventilatory response tests lack feasibility and fail to capture the integrated steady-state responses to chronic hypoxic exposure in HA fieldwork. We recently characterized a novel index of steady-state respiratory chemoreflex drive (SSCD), accounting for integrated contributions from central and peripheral respiratory chemoreceptors during steady-state breathing at prevailing chemostimuli. Acetazolamide is often utilized during ascent for prevention or treatment of altitude-related illnesses, eliciting metabolic acidosis and stimulating respiratory chemoreceptors. To determine if SSCD reflects VA during ascent to HA, we characterized SSCD in 25 lowlanders during incremental ascent to 4240 m over 7 days. We subsequently compared two separate subgroups: no acetazolamide (NAz; n = 14) and those taking an oral prophylactic dose of acetazolamide (Az; 125 mg BID; n = 11). At 1130/1400 m (day zero) and 4240 m (day seven), steady-state measurements of resting ventilation (V̇_I ; L/min), pressure of end-tidal (P_ET )CO₂ (Torr), and peripheral oxygen saturation (SpO₂ ; %) were measured. A stimulus index (SI; P_ET CO₂ /SpO₂ ) was calculated, and SSCD was calculated by indexing V̇_I against SI. We found that (a) both V̇_I and SSCD increased with ascent to 4240 m (day seven; V̇_I : +39%, p < 0.0001, Hedges' g = 1.52; SSCD: +56.%, p < 0.0001, Hedges' g = 1.65), (b) and these responses were larger in the Az versus NAz subgroup (V̇_I : p = 0.02, Hedges' g = 1.04; SSCD: p = 0.02, Hedges' g = 1.05). The SSCD metric may have utility in assessing VA during prolonged stays at altitude, providing a feasible alternative to transient chemoreflex tests.

On the use and misuse of cerebral hemodynamics terminology using Transcranial Doppler ultrasound: a call for standardization

Cerebral hemodynamics (e.g., cerebral blood flow) can be measured and quantified using many different methods, with Transcranial Doppler ultrasound (TCD) being one of the most commonly utilized approaches. In human physiology, the terminology used to describe metrics of cerebral hemodynamics are inconsistent, and in some instances technically inaccurate; this is especially true when evaluating, reporting, and interpreting measures from TCD. Therefore, this perspectives article presents recommended terminology when reporting cerebral hemodynamic data. We discuss the current use and misuse of the terminology in the context of using TCD to measure and quantify cerebral hemodynamics and present our rationale and consensus on the terminology that we recommend moving forward. For example, one recommendation is to discontinue use of the term "cerebral blood flow velocity" in favor of "cerebral blood velocity" with precise indication of the vessel of interest. We also recommend clarity when differentiating between discrete cerebrovascular regulatory mechanisms, namely cerebral autoregulation, neurovascular coupling, and cerebrovascular reactivity. This will be a useful guide for investigators in the field of cerebral hemodynamics research.

Functional optical coherence tomography at altitude: retinal microvascular perfusion and retinal thickness at 3,800 meters

Cerebral hypoxia is a serious consequence of several cardiorespiratory illnesses. Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into cerebral hypoxia in critical illness. Additionally, while sex-specific differences in cardiovascular diseases are strongly supported, few have focused on differences in ocular blood flow. We evaluated the retinal microvasculature in males (n=11) and females (n=7) using functional optical coherence tomography at baseline (1,130m) (Day 0), following rapid ascent (Day 2) and prolonged exposure (Day 9) to high altitude (3,800m). Retinal vascular perfusion density (rVPD; an index of total blood supply), retinal thickness (RT; reflecting vascular and neural tissue volume) and arterial blood were acquired. As a group, rVPD increased on Day 2 vs. Day 0 (p<0.001) and was inversely related to PaO₂ (R²=0.45; p=0.006). By Day 9, rVPD recovered to baseline, but was significantly lower in males vs. females (p=0.007). RT was not different on Day 2 vs. Day 0 (p>0.99) but was reduced by Day 9 relative to Day 0 and Day 2 (p<0.001). RT changes relative to Day 0 were inversely related to changes in PaO₂ on Day 2 (R²=0.6; p=0.001) and Day 9 (R²=0.4; p=0.02). RT did not differ between sexes. These data suggest differential time course and regulation of the retina during rapid ascent and prolonged exposure to high altitude and are the first to demonstrate sex-specific differences in rVPD at high altitude. The ability to assess intact microvasculature contiguous with the brain has widespread research and clinical applications.

Posterior reversible encephalopathy syndrome secondary to acute post-streptococcal glomerulonephritis in a child: a case report from the Tibetan plateau

Background

Posterior reversible encephalopathy syndrome (PRES) is a disorder of reversible vasogenic brain oedema with acute neurologic symptoms. It is a rare but serious disease that affects the central nervous system. PRES is a rare complication of acute post-streptococcal glomerulonephritis (APSGN). High altitude can accelerate vasogenic brain oedema by increasing cerebral blood flow (CBF), impairing cerebral autoregulation and promoting vascular inflammation. We report a case of PRES induced by acute post-streptococcal glomerulonephritis in a high-altitude environment.

Case presentation

A fourteen-year-old Tibetan girl presented with progressive headache with haematuria, facial swelling, dizziness and vomiting for 2 weeks as well as multiple episodes of tonic–clonic seizures for 14 h. She was diagnosed with APSGN based on laboratory tests and clinical symptoms. Brain magnetic resonance imaging (MRI) and computed tomography (CT) revealed bilateral frontal, parietal and occipital lesions that were compatible with the radiological diagnosis of PRES. The treatments included an antibiotic (penicillin), an antiepileptic drug, and hyperbaric oxygen (HBO) therapy. Follow-up MRI obtained 1 week after admission and CT obtained 4 weeks and 6 weeks after admission demonstrated complete resolution of the brain lesions.

Conclusions

The case illustrates a rare occurrence of PRES following APSGN in a 14-year-old child in the Tibetan Plateau. The hypoxic conditions of a high-altitude setting might lower the cerebral autoregulation threshold and amplify the endothelial inflammatory reaction, thus inducing PRES in patients with APSGN. It is important to recognize the clinical and radiologic features of PRES, and adjuvant HBO therapy can promote rapid recovery from this condition in high-altitude areas.

Dynamic cerebral blood flow changes with FOXOs stimulation are involved in neuronal damage associated with high-altitude cerebral edema in mice

Acute hypobaric hypoxia (AHH) exposure causes altitude mountain sickness (AMS) and life-threatening high altitude cerebral edema (HACE). Despite decades of research, the role of cerebral blood flow (CBF) changes in the pathophysiology of severe AMS remains unclear. The current study evaluated spatiotemporal responses of CBF associated with HACE in mice during the early stages of ascent to high altitudes. First, mice were exposed to AHH to test their tolerance to increasing altitudes (3000-8000 m). Because of its significant influence on both locomotor activity and rotarod behavior tests in mice, further observations were initiated at an altitude of 6000 m to investigate the specific pathophysiology of AMS. Compared with controls, laser speckle contrast imaging (LSCI) revealed a significant decrease in CBF during the early stage (0.5-24 h) at an altitude of 6000 m that was accompanied by a significant increase in brain water content (BWC). Moreover, observations of brain lipid oxidative damage and oxidative stress during the early stage of AHH exposure revealed DNA and cellular damage in cortical and hippocampal regions. Transcriptome profiling of the hippocampus revealed upregulation of forkhead box transcription factors. Similarly, western blot assays revealed upregulation of FOXO1a, FOXO3a, caspase-3 and Bax, and downregulation of Bcl-2, indicating a temporal influence of AHH on mitochondrial function and neuronal apoptosis. Thus, we found that the pathophysiology of HACE occurred with dynamic CBF changes, which triggered oxidative stress and neuronal damage in the mouse brain after AHH exposure. Our findings provide potential strategies for treatment of AHH in the future.

Research progress on the mechanism of cerebral blood flow regulation in hypoxia environment at plateau

The plateau is a special environment with low air pressure and low oxygen content. The average altitude of Qinghai-Tibet is 3,500 m, and the atmospheric oxygen partial pressure in most areas is lower than 60% of that at sea level. In order to adapt to the plateau low-oxygen environment, the human body has developed corresponding physiological structure and functions adjust. In the present review, the regulation mechanism of cerebral blood flow (CBF) under high-altitude environments was elaborated in eight aspects: the arterial blood gas, endogenous substances in the nerve and blood, the cerebral neovascularization, the hematocrit, cerebral auto-regulation mechanism, cerebrovascular reactivity, pulmonary vasoconstriction, and sympathetic automatic regulation, aiming to further explore the characteristics of changes in brain tissue and cerebral blood flow in a hypoxic environment.

Neuropsychological and Neuroimaging Correlates of High-Altitude Hypoxia Trekking During the "Gokyo Khumbu/Ama Dablam" Expedition

Committeri Giorgia, Danilo Bondi, Carlo Sestieri, Ginevra Di Matteo, Claudia Piervincenzi, Christian Doria, Roberto Ruffini, Antonello Baldassarre, Tiziana Pietrangelo, Rosamaria Sepe, Riccardo Navarra, Piero Chiacchiaretta, Antonio Ferretti, and Vittore Verratti. Neuropsychological and neuroimaging correlates of high-altitude hypoxia trekking during the "Gokyo Khumbu/Ama Dablam" expedition. High Alt Med Biol 00:000-000, 2021. Background: Altitude hypoxia exposure may produce cognitive detrimental adaptations and damage to the brain. We aimed at investigating the effects of trekking and hypoxia on neuropsychological and neuroimaging measures. Methods: We recruited two balanced groups of healthy adults, trekkers (n = 12, 6 F and 6 M, trekking in altitude hypoxia) and controls (gender- and age-matched), who were tested before (baseline), during (5,000 m, after 9 days of trekking), and after the expedition for state anxiety, depression, verbal fluency, verbal short-term memory, and working memory. Personality and trait anxiety were also assessed at a baseline level. Neuroimaging measures of cerebral perfusion (arterial spin labeling), white-matter microstructural integrity (diffusion tensor imaging), and resting-state functional connectivity (functional magnetic resonance imaging) were assessed before and after the expedition in the group of trekkers. Results: At baseline, the trekkers showed lower trait anxiety (p = 0.003) and conscientiousness (p = 0.03) than the control group. State anxiety was lower in the trekkers throughout the study (p < 0.001), and state anxiety and depression decreased at the end of the study in both groups (p = 0.043 and p = 0.007, respectively). Verbal fluency increased at the end of the study in both groups (p < 0.001), whereas verbal short-term memory and working memory performance did not change. No significant differences between before and after the expedition were found for neuroimaging measures. Conclusions: We argue that the observed differences in the neuropsychological measures mainly reflect aspecific familiarity and learning effects due to the repeated execution of the same questionnaires and task. The present results thus suggest that detrimental effects on neuropsychological and neuroimaging measures do not necessarily occur as a consequence of short-term exposure to altitude hypoxia up to 5,000 m, especially in the absence of altitude sickness.

Regional differences in cerebrovascular reactivity in response to acute isocapnic hypoxia in healthy humans: Methodological considerations

The cerebrovasculature responds to blood gas challenges. Regional differences (anterior vs. posterior) in cerebrovascular responses to increases in CO₂ have been extensively studied. However, regional cerebrovascular reactivity (CVR) responses to low O₂ (hypoxia) are equivocal, likely due to differences in analysis. We assessed the effects of acute isocapnic hypoxia on regional CVR comparing absolute and relative (%-change) responses in the middle cerebral artery (MCA) and posterior cerebral artery (PCA). We instrumented 14 healthy participants with a transcranial Doppler ultrasound (cerebral blood velocity), finometer (beat-by-beat blood pressure), dual gas analyzer (end-tidal CO₂ and O₂), and utilized a dynamic end-tidal forcing system to elicit a single 5-min bout of isocapnic hypoxia (∼45 Torr P_ETO₂, ∼80 % SpO₂). During exposure to acute hypoxia, absolute responses were larger in the anterior compared to posterior cerebral circulation (P < 0.001), but were not different when comparing relative responses (P = 0.45). Consistent reporting of CVR to hypoxia will aid understanding normative responses, particularly in assessing populations with impaired cerebrovascular function.

The role of carbon dioxide in acute brain injury

Carbon dioxide is a common gas in the air which has been widely used in medical treatment. A carbon dioxide molecule consists of two oxygen atoms and one carbon atom through a covalent bond. In the body, carbon dioxide reacts with water to produce carbonic acid. In healthy people, carbon dioxide is maintained within a narrow range (35–45 mmHg) by physiological mechanisms. The role of hypocapnia (partial pressure of carbon dioxide < 35 mmHg) and hypercapnia (partial pressure of carbon dioxide > 45 mmHg) in the nervous system is intricate. Past researches mainly focus on the effect of hypocapnia to nerve protection. Nevertheless, Hypercapnia seems to play an important role in neuroprotection. The mechanisms of hypocapnia and hypercapnia in the nervous system deserve our attention. The purpose of this review is to summarize the effect of hypocapnia and hypercapnia in stroke and traumatic brain injury.

Bilateral regional extracranial blood flow regulation to hypoxia and unilateral duplex ultrasound measurement error

NEW FINDINGS

What is the central question of this study? Is blood flow regulation to hypoxia different between the internal carotid arteries (ICAs) and vertebral arteries (VAs), and what is the measurement error in unilateral extracranial artery assessments compared to bilateral? What is the main finding and its importance? ICA and VA blood flow regulation to hypoxia is comparable when factoring for vessel type and vessel side. Compared to bilateral assessment, vessels assessed unilaterally had individual measurement errors of up to 37%. Assessing the vessel with the larger resting blood flow, not the left or right vessel, reduces unilateral measurement error.

ABSTRACT

Whether blood flow regulation to hypoxia is similar between left and right internal carotid arteries (ICAs) and vertebral arteries (VAs) is unclear. Extracranial blood flow is regularly calculated by doubling a unilateral assessment; however, lateral artery differences may lead to measurement error. This study aimed to determine extracranial blood flow regulation to hypoxia when factoring for vessel type (ICAs or VAs) and vessel side (left or right) effects, and to investigate unilateral assessment measurement error compared to bilateral assessment. In a repeated-measures crossover design, extracranial arteries of 44 participants were assessed bilaterally by duplex ultrasound during 90 min of normoxic and poikilocapnic hypoxic (12.0% fraction of inspired oxygen) conditions. Linear mixed model analyses revealed no Condition × Vessel Type × Vessel Side interaction for blood flow, vessel diameter and flow velocity (all P > 0.05) indicating left and right ICA and VA blood flow regulation to hypoxia was similar. Bilateral hypoxic reactivity was comparable (ICAs, 1.4 (1.0) vs. VAs, 1.7 (1.1) Δ%·Δ S p O 2 ^-1 ; P = 0.12). Compared to bilateral assessment, unilateral mean measurement error of the relative blood flow response to hypoxia was up to 5%, but individual errors reached 37% and were greatest in ICAs and VAs with the smaller resting blood flow due to a ratio-scaling problem. In conclusion, left and right ICA and VA regulation to hypoxia is comparable when factoring for vessel type and vessel side. Assessing the ICA and VA vessels with the larger resting blood flow, not the left or right vessel, reduces unilateral measurement error.

Acute aerobic exercise impairs aspects of cognitive function at high altitude

Hypoxia-mediated cognitive dysfunction can be transiently mitigated by exercise in a laboratory-based setting. Whether this effect holds true in the context of high altitude hypoxia has not been determined. We investigated the effect of acute aerobic exercise on cognitive function (CF) at low (1400m) and high altitude (4240m). Fifteen volunteers (24.1±3.5yrs; 9 females) exercised for 20-min at 40-60% of their heart rate reserve at low and high altitude. CF was assessed before and 10-min after exercise using a tablet-based battery of executive function tests. A sea-level control group (n=13; 24.2±2.4 years; 9 females) performed time-matched CF tests to assess the contribution of a learning effects due to repeated testing. Measures of resting CF were unaffected by ascent to high altitude. Following high altitude exercise, performance significantly worsened on the digit symbol substitution task - a test of processing speed, working memory, and visuospatial attention (z=0.01 vs. -0.59, p=0.02, η²=0.35). No effect was found on other measures of CF following exercise. There was no association between changes in peripheral oxygen saturation and changes in CF following high altitude exercise (r=0.22, p=0.44), but higher hemoglobin concentration at high altitude was associated with a decline in CF following exercise at high altitude (r=-0.65, p=0.02). Acute aerobic exercise performed at high altitude impairs some aspects of CF, whereas other CF tests remain unchanged. The strong ecological validity of this study warrants attention and follow-up investigations are needed to better characterize selective impairment of CF with high altitude exercise.

Haemodynamic effects of hyperventilation on healthy men with different levels of autonomic tone

The topicality of the research is stipulated by insufficient study of the correlation between the functional state of the cardiorespiratory system and autonomic tone. The goal of the research was to analyze the changes of central haemodynamics with 10-minute regulated breathing at the rate of 30 cycles per minute and within 40 minutes of recovery after the test in healthy young men with different levels of autonomic tone. Records of the chest rheoplethysmogram were recorded on a rheograph KhAI-medica standard (KhAI-medica, Kharkiv, Ukraine), a capnogram - in a lateral flow on a infrared capnograph (Datex, Finland), and the duration of R-R intervals was determined by a Polar WIND Link in the program of Polar Protrainer 5.0 (Polar Electro OY, Finland). Systolic and diastolic blood pressure were measured by Korotkov’s auscultatory method by mercury tonometer (Riester, Germany). The indicator of the normalized power of the spectrum in the range of 0.15–0.40 Hz was evaluated by 5-minute records; three groups of persons were distinguished according to its distribution at rest by the method of signal deviation, namely, sympathicotonic, normotonic and parasympathicotonic. The initial level of autonomic tone was found to impact the dynamics of СО2 level in alveolar air during hyperventilation and during recovery thereafter. Thus, PetCО2 was higher (41.3 mm Hg) in parasympathicotonic than in sympathicotonic (39.3 mm Hg) and normotonic (39.5 mm Hg) persons. During the test, R-R interval duration decreased being more expressed in normotonic persons. At the same time, the heart index was found to increase in three groups, and general peripheral resistance – to decrease mostly in normo- and parasympathicotonic persons. In addition, the reliable increase of stroke index and heart index was found in these groups. In the recovery period after hyperventilation, the decrease of tension index and ejection speed was found in normo- and, particularly, parasympathicotonic compared with sympathicotonic men and the increase of tension phase and ejection phase duration.