Hypoxic Test Research Articles

Assessing air travel safety in neuromuscular disease: standard versus prolonged hypoxic challenge tests.

The hypoxic challenge test (HCT) is used to evaluate safety for air travel in individuals with respiratory disease by breathing in 15% oxygen for 20min. Our aim was to determine if a prolonged HCT, lasting 120min, identified more individuals with neuromuscular disease at potential risk than the standard HCT lasting 20min. This was a cross-sectional study. All of the clinical testing took place at SickKids, Toronto, Canada. Patients were included in the study if they had a diagnosis of NMD, greater than 6years of age, resting oxygen saturation ≥ 94%, and partial pressure of carbon dioxide (pCO2) ≤ 45mmHg. Notable exclusion criteria were left ventricular ejection fraction < 30%, presence of a tracheostomy, and use of non-invasive ventilation for more than 12h daily. Participants underwent a standard HCT as well as the prolonged HCT on the same day. Twenty-three patients consented to the study. One patient was withdrawn because he was unable to follow the study procedures. The 22 study participants had a mean age of 14.9years (standard deviation (SD) of 5years). Seventeen (77%) participants were male. Two participants were withdrawn on the day of testing due to hypercapnia. Twenty participants completed the standard and prolonged HCTs. None of the participants had a positive standard or prolonged HCT. Our results suggest that performing a standard or prolonged HCT may, in fact, not be of clinical utility in individuals with less severe NMD.

Feasibility of a Hypoxic Challenge Test Under Noninvasive Ventilation Versus Oxygen in Neuromuscular Patients with Chronic Respiratory Insufficiency.

Ribeiro Baptista, Bruno, Morgane Faure, Gimbada Benny Mwenge, Capucine Morelot-Panzini, Christian Straus, Thomas Similowski, and Jésus Gonzalez-Bermejo. Feasibility of a hypoxic challenge test under noninvasive ventilation versus oxygen in neuromuscular patients with chronic respiratory insufficiency. High Alt Med Biol. 22:346-350, 2021. Background: The British Thoracic Society recommendations suggest that all patients with an oxygen saturation (SpO2) <85% during a hypoxic challenge test (HCT) should receive supplemental oxygen during air travel. However, neuromuscular patients already using ventilatory support are a specific population and noninvasive ventilation (NIV) during a flight could be an alternative to oxygen for hypoxemia correction, through the augmentation of ventilation. Methods: We conducted a comparative, observational study of neuromuscular patients with chronic respiratory failure, requiring nocturnal mechanical ventilation, who were planning to take a flight. HCT was performed with a ventilated canopy placed over the patient's head or the patient's home ventilator. The positive threshold value chosen for the HCT was <90% SpO2. Results: HCTs were performed on 13 adults with neuromuscular diseases using their home ventilator. Among them, 11 had a positive HCT. For all patients with a positive test, hypoxemia was corrected (SpO2 to >90%) by oxygen therapy (+9 [6-12]%, p = 0.0029). Patient's home ventilator also significantly increased the SpO2 by 8 [7-12]% (p = 0.016). Correction of SpO2 during the HCT was not different between oxygen and NIV. NIV was associated with a significant decrease in pressure, end tidal, carbon dioxide (PetCO2) (-10 [-16 to -7.5] mmHg, p = 0.04). Conclusions: The performance of an adapted HCT in home-ventilated patients with a neuromuscular pathology may be useful in a personalized treatment plan for air travel. NIV can be a new alternative to oxygen therapy for neuromuscular patients planning to take a flight.

Features of hypoxic resistance in children with bronchial asthma who have undergone a new coronavirus infection

Aim. To study the characteristics of resistance/sensitivity to normobaric hypoxia in 50 children with bronchial asthma (BA) from 9 to 12 years old, 24 of them after a previous coronavirus infection СOVID-19.&#x0D; Materials and methods. A normobaric hypoxic test (HT) was carried out by creating hypoxemia (threshold level SpO2 80%) during mask inhalation of a gas mixture with 1011% O2 by a child using a ReOxy Cardio apparatus (Ai Mediq S.A., Luxembourg). The data obtained were compared with the results in a group of healthy children the same age.&#x0D; Results. It was found that the integral level of hypoxic resistance of children with BA was generally lower in comparison with the group of healthy children, which was manifested in lower values of the hypoxic index (3.11.4, in the group of healthy children 4.92.8, p=0.005), a significantly increased level of tachycardia and a hypotonic response to dosed hypoxia.&#x0D; Conclusion. When typing reactions to HT, it was found that in children with BA, the type of low resistance to hypoxia is more common (to a greater extent in children with BA after a coronavirus infection), which confirms the need to involve such children in comprehensive rehabilitation programs.

Peculiarities of breath holding tests in school age children

Objective of the study was to examine the performance of breath-holding and Ruffier tests, relationship between them and other factors in healthy school age children.Material and methods. The cross-sectional descriptive study with 45 healthy participants in age 7-13 years (22 boys and 23 girls) was performed. The study included assessment of nutrition, physical activity habits, family and socioeconomic data, resting anthropometric and blood pressure measurements, pulse oximetry, tests for the functional status of the cardiorespiratory system and readiness of child organism for physical loading (Ruffier and volitional breath-holding hypoxic tests). Results. The Rufier index in most children was average and amounted to 8.75±0.32 units. Test with breath-holding on inspiration was at the level of 37.0±1.84 sec, on exhalation - 22.2±1.3 sec. In children with low tolerance to exercise during respiratory tests execution there were a decrease in blood saturation and changes in heart rate. The tests are based on different physiological processes in the human body that create physical load tolerance: heart tolerance and cardiorespiratory oxygen supply to tissues.Conclusions. All selected tests could be executed anywhere and in a short period of time. They are easy to perform and do not cause emotional reactions in children and could be used for tolerance for physical loading assessment. The results obtained are complementary and can be recommended for use in the complex when examining the health and tolerance for physical loading in children during different screening types.

Endotheliumprotectiv and antihypoxic properties of quercetin in elderly patients with metabolic syndrome

Aim: To investigate the effectiveness of course quercetin in improving functional state of the microvascular endothelium and to determine the possibility of using quercetin to increase body resistance to hypoxia in the elderly. Materials and methods. The effectiveness of quercetin in improving the functional state of the endothelium and increasing body resistance to hypoxia was studied in 110 elderly patients with metabolic syndrome, who were divided equally into the main and control groups. Patients in the main group received quercetin at a daily dose of 240 mg for 3 months, and patients in the control group received placebo for the same period. Before and after treatment, the microvascular endothelial function was studied by laser Doppler flowmetry using the post-occlusive hyperemia test. Acute hypoxic test was performed under isocapnicnormobaric hypoxia, during which the followings were recorded: blood saturation (SpO2), heart rate and diastolic blood pressure (BP). Results. In the group of patients receiving quercetin, there was an improvement in blood flow to the skin, as evidenced by a statistically significant increase in the maximum volumetric rate of cutaneous blood flow and the duration of the recovery period of OSHSK to baseline in the post-occlusive hyperaemia. The course of quercetin also led to a less significant decrease in SpO2 during hypoxic test and to a decrease in the absolute values of systolic and diastolic blood pressure, while reducing an increase of the systolic blood pressure on the 20th min of the hypoxic test. Conclusions. In elderly patients with metabolic syndrome (within a 3 month course) the use of quercetin has improved the microvascular endothelium functional status and increased the resistance to hypoxia.

Опыт применения метода гипоксического кондиционирования в комплексной реабилитации детей с бронхиальной астмой, перенесших коронавирусную инфекцию

Objective. To evaluate the efficacy and safety controlled hypoxic stimulation in children after coronavirus infection, including those with BA. Patients and methods. This study included 72 children aged 9–12 years who had had COVID-19 at least 1.5–2 months before the enrollment; of them, 24 patients had mild to moderate BA. Study participants were randomized into two groups: ‘intermittent hypoxic training’ (IHT, n = 31) and ‘intermittent hypoxic-hyperoxic training’ (IHHT, n = 41). Before the procedures, we assessed hypoxic resistance of children using a hypoxic test. The following parameters were measured before and after the course, which included 10 procedures: hypoxic resistance (hypoxic index, time to desaturation, and reoxygenation time), spirometry parameters (forced expiratory volume in 1 second, peak expiratory flow, and airway resistance), changes in systolic/diastolic pressure, heart rate variability, tolerability of procedures (using a visual analog scale), and anxiety level (CMAS test). Results. We found no significant differences between BA and non-BA children in their spirometry parameters and hypoxic resistance. We observed good tolerability of the procedures in children from different groups. After the course of IHT/IHHT, patients demonstrated a significant increase in their resistance to hypoxic stimulation. IHHT procedures were more effective and safer than IHT according to spirometry parameters (RINTexp), tolerability, and anxiety level. Conclusion. Hypoxic conditioning procedures can be recommended as a part of comprehensive rehabilitation in BA children who had had COVID-19. Key words: intermittent hypoxic training, new coronavirus infection, bronchial asthma, children, rehabilitation

ОСОБЛИВОСТІ СТІЙКОСТІ ДО ГІПОКСІЇ У ХВОРИХ ПОХИЛОГО ВІКУ З ХРОНІЧНИМ ОБСТРУКТИВНИМ ЗАХВОРЮВАННЯМ ЛЕГЕНЬ

FEATURES OF RESISTANCE TO HYPOXIA IN ELDERLY PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY DISEASE E. O. Asanov, Yu. I. Golubova, I. A. Dyba, S. O. Asanova Abstract Aim: to study the features of resistance to hypoxia in elderly patients with COPD. Material and methods. We examined 46 elderly patients with COPD and 18 apparently healthy elderly people. Hypoxia resistance was determined by performing a hypoxic test with inhalation of 12 % O2 for 20 minutes. The state of ventilation and blood saturation were assessed. Results. Hypoxia caused the reduction of SpO2 and the development of arterial hypoxemia in elderly patients with COPD, which were more significant than in healthy elderly people. It was found that among elderly patients with COPD and healthy elderly subjects there were people with preserved and reduced resistance to hypoxia. However, reduced resistance to hypoxia was much more common in elderly patients with COPD. Decreased resistance to hypoxia in elderly patients with COPD was associated with the degree of bronchial obstruction: deterioration of bronchial passability led to reduced resistance to hypoxia. Elderly patients with COPD with reduced resistance to hypoxia had a decrease in the ΔVE/ ΔSpO2 ratio and a slow ventilation response to hypoxic exposure. Conclusions. Among healthy elderly people and elderly patients with COPD there were subjects with reduced and preserved resistance to hypoxia. Decreased resistance to hypoxia was much more common in elderly patients with COPD. Decreased resistance to hypoxia was more common in patients with moderate than mild bronchial obstruction. Elderly patients with COPD with reduced resistance to hypoxia had reduced ventilation response to hypoxia and chemoreflex sensitivity. Key words: COPD, older age, resistance to hypoxia, ventilation, saturation. Ukr. Pulmonol. J. 2021;29(3):36–40:

ИСПОЛЬЗОВАНИЕ ЗАДЕРЖКИ ДЫХАНИЯ В СПОРТИВНОЙ ТРЕНИРОВКЕ ДЕТЕЙ 10–12 ЛЕТ КАК СПОСОБ ПОВЫШЕНИЯ ИХ ФУНКЦИОНАЛЬНОЙ ВЫНОСЛИВОСТИ

Statement of the problem. The article describes an alternative and affordable method of hypoxic training through holding the breath on inhalation and exhalation, as a tool for developing endurance. The relevance of the topic is in the absence of a method that develops endurance and hypoxic characteristics with a sparing effect on heart rate (HR) and availability in use. Research methodology (materials and methods). Using hypoxic tests of Stange and Genchi (holding the breath on the inhale and exhale by the stopwatch), as markers that determine the development of endurance, we arranged the experiment. We divided 24 young men of volleyball players aged 10–12 into two groups, experimental and control, 12 people in each group with a uniform level of sports fitness. The arithmetic mean of indices in the introductory Stange samples in the control group and in the Genchi samples showed 1 minute 8 seconds and 31 seconds, respectively. In the experimental group, there were 48 seconds in the Barbell samples and 25 seconds in the Genchi samples, confirming the uniformity of training in the development of endurance. The experiment lasted three months, during which time the experimental group underwent breathing exercises on inhalation and exhalation, regulated by the time of 20 and 7 seconds, maximum in the corridor of execution, and the control group trained in the normal mode. At the end of the experiment, samples were taken, similar to the introductory ones. The average result of the breath holding time in the control group changed by 4 seconds in the Genchi and Stange samples, in relation to their own results, and the results of the experimental group in relation to their own results increased by 1 minute 13 seconds in the Stange sample and by 23 seconds in the Genchi sample. The values of the samples are detailed in Table. Research results. As a result of the study, the experimental group exceeded the control group in the samples with breath-holding during inhalation (Stange) by 47 seconds and breath-holding during exhalation (Genchi) by 31 seconds. This practically confirms the significance of hypoxic training with regulated breath holding to develop endurance. Conclusion. The experiment proves the effectiveness of alternative hypoxic training with regulated breath holding during inhalation and exhalation and contributes to the further study of the tool, which is available for material and technical use.

Measuring Peripheral Chemoreflex Hypersensitivity in Heart Failure.

Heart failure with reduced ejection fraction (HFrEF) induces chronic sympathetic activation. This disturbance is a consequence of both compensatory reflex disinhibition in response to lower cardiac output and patient-specific activation of one or more excitatory stimuli. The result is the net adrenergic output that exceeds homeostatic need, which compromises cardiac, renal, and vascular function and foreshortens lifespan. One such sympatho-excitatory mechanism, evident in ~40–45% of those with HFrEF, is the augmentation of carotid (peripheral) chemoreflex ventilatory and sympathetic responsiveness to reductions in arterial oxygen tension and acidosis. Recognition of the contribution of increased chemoreflex gain to the pathophysiology of HFrEF and to patients’ prognosis has focused attention on targeting the carotid body to attenuate sympathetic drive, alleviate heart failure symptoms, and prolong life. The current challenge is to identify those patients most likely to benefit from such interventions. Two assumptions underlying contemporary test protocols are that the ventilatory response to acute hypoxic exposure quantifies accurately peripheral chemoreflex sensitivity and that the unmeasured sympathetic response mirrors the determined ventilatory response. This Perspective questions both assumptions, illustrates the limitations of conventional transient hypoxic tests for assessing peripheral chemoreflex sensitivity and demonstrates how a modified rebreathing test capable of comprehensively quantifying both the ventilatory and sympathoneural efferent responses to peripheral chemoreflex perturbation, including their sensitivities and recruitment thresholds, can better identify individuals most likely to benefit from carotid body intervention.

Global REACH 2018: Regional differences in cerebral blood velocity control during normoxic and hypoxic cold pressor tests.

The impact of oxygen on the cerebral response to the cold pressor test (CPT) remains unknown. In 13 participants, blood pressure, middle and posterior cerebral artery blood velocity (MCAv and PCAv, respectively) were measured during an isocapnic normoxic and hypoxic (SpO2=85%) CPT. The main findings were: 1) the MCAv response to the CPT was greater compared to the PCAv in both normoxic and hypoxic conditions (P=0.003 and P=0.002, respectively); and, 2) hypoxia did not alter the cerebral response to the CPT (P=0.141 and P=0.150, respectively). These data highlight that regional differences in cerebrovascular control exist during the CPT.

Bronchial obstruction and resistance to hypoxia in elderly patients with COPD

Background. Age-related morphofunctional changes in the body lead to the development of arterial hypoxemia, tissue hypoxia and hypoxic changes. All this causes a decrease in the body’s resistance to hypoxia and contributes to the development of lung diseases, in particular, chronic obstructive pulmonary disease (COPD) in the elderly. With the development of COPD in the elderly due to bronchial obstruction and disorders of pulmonary gas exchange, age-related hypoxic shifts, arterial hypoxemia, tissue hypoxia and resistance to hypoxia are further reduced. However, the relationship between bronchial obstruction and resistance to hypoxia in elderly patients with COPD has not been studied.&#x0D; Objective. To identify the relationship between bronchial patency and resistance to hypoxia in elderly patients with COPD.&#x0D; Materials and methods. The study included 30 patients with COPD in the elderly (60-74 years), I-II stage, without exacerbation, with a disease duration of 7 to 26 years, risk groups A and B. The type and severity of pulmonary ventilation were assessed indicators of spirometry and the curve “flow/volume” of forced exhalation on the device Spirobank (Mir, Italy). To determine the body’s resistance to hypoxia, a hypoxic test with 12 % oxygen content was performed for 12 min with monitoring of blood saturation using the automated software and hardware complex Hypotron (Ukraine).&#x0D; Results. Researches have shown that under hypoxic exposure, blood saturation in elderly patients with COPD is reduced, on average, by 18.23±0.26 %. This decrease in blood saturation can be regarded as severe arterial hypoxemia. At the same time, in elderly patients with COPD with an increase in bronchial patency disorders, the saturation shifts in hypoxia, on average, also increase. There was a significant correlation (r=0.50; p=0.006) of blood saturation shifts in hypoxia with bronchial obstruction.&#x0D; Conclusions. In elderly patients with COPD, resistance to hypoxia is determined by bronchial obstruction.

Indicators of individual hypoxia resistance — a way to optimize hypoxic training for children

Objective. To develop a protocol for a normobaric hypoxic test and criteria of resistance assessment — normobaric hypoxia sensitivity in children. Characteristics of children and research methods . 56 healthy children aged from 8 to 12 years underwent a hypoxic test inhaling gas mixture with 10—11% of O 2 through mask to create hypoxemia conditions (SpO 2 = 80%). The authors used a normobaric hypoxic device (certified in the Russian Federation) to produce hypoxic and hyperoxic gas mixtures — ReOxy Cardio (S.A. Aimediq, Luxembourg) with an integrated pulse oximetry sensor (Masimo Rad-5, USA). During hypoxic test they monitored the arterial blood oxygen saturation (SpO 2 ) and heart rate (HR, bpm), and there were automatically recorded the individual minimum values of SpO 2 level (SpO 2 min) and maximum heart rate (HR max). A “hypoxic phase” was terminated in case of decrease in SpO2 to 80% or lower, or breathing with a hypoxic gas mixture during 9 minutes. An additional criterion for termination was an increase in HR by 30% and higher over the initial level. After reaching one of the described criteria, the teenagers began to breathe ambient air and the authors determined the recovery time of SpO 2 to 97%. In addition, the authors calculated the hypoxic index as desaturation/reoxygenation time ratio. Results. The authors developed a protocol for conductance and assessment of hypoxic resistance in children and adolescents. There were determined three types (phenotypes) of response to dosed normobaric hypoxia in adolescents: low, medium and high levels of dosed hypoxic stimulus resistance. Conclusion . The proposed hypoxic test protocol reflects the individual hypoxia tolerance and can be used to individualize hypoxic therapy courses, as well as additional diagnostic tool in assessing the adaptive capabilities and non-specific reactivity in children.

Study of the Cardiorespirator System Response to Normobaric Hypoxia

Research into cardiorespiratory responses to prolonged hypoxia (more than 60 minutes) is of particular interest in terms of elucidating adaptive mechanisms under the conditions of oxygen deficiency. Aim: to identify the parameters of the cardiorespiratory system under relative rest most sensitive to hypoxia and to determine the most optimal time interval for a hypoxic test. Experiments were carried out in a normobaric hypoxic complex, in which hypoxic respiratory gas conditions were created corresponding to the partial oxygen pressure at altitudes of 3500 and 4500 m. Cardiorespiratory responses were evaluated using a MetaLyzer 3B ergospirometric system (Cortex, Germany). Indicators sensitive to moderate normobaric hypoxia under relative rest include hemoglobin oxygen saturation (the most sensitive indicator), oxygen and carbon dioxide ventilation efficiency (VE/VO 2 and VE/VCO 2 ), respiratory rate and respiratory coefficient (VCO 2 / VO 2 ). A significant change in the indicators of the cardiorespiratory system at an altitude of 4500 m was noted within 5 minutes following hypoxic exposure; therefore, normobaric hypoxic tests should be carried out at this height under the hypoxic exposure of 30 minutes.

Whole blood viscosity and red blood cell adhesion: Potential biomarkers for targeted and curative therapies in sickle cell disease.

Sickle cell disease (SCD) is a recessive genetic blood disorder exhibiting abnormal blood rheology. Polymerization of sickle hemoglobin, due to a point mutation in the β‐globin gene of hemoglobin, results in aberrantly adhesive and stiff red blood cells (RBCs). Hemolysis, abnormal RBC adhesion, and abnormal blood rheology together impair endothelial health in people with SCD, which leads to cumulative systemic complications. Here, we describe a microfluidic assay combined with a micro particle image velocimetry technique for the integrated in vitro assessment of whole blood viscosity (WBV) and RBC adhesion. We examined WBV and RBC adhesion to laminin (LN) in microscale flow in whole blood samples from 53 individuals with no hemoglobinopathies (HbAA, N = 10), hemoglobin SC disease (HbSC, N = 14), or homozygous SCD (HbSS, N = 29) with mean WBV of 4.50 cP, 4.08 cP, and 3.73 cP, respectively. We found that WBV correlated with RBC count and hematocrit in subjects with HbSC or HbSS. There was a significant inverse association between WBV and RBC adhesion under both normoxic and physiologically hypoxic (SpO2 of 83%) tests, in which lower WBV associated with higher RBC adhesion to LN in subjects with HbSS. Low WBV has been found by others to associate with endothelial activation. Altered WBV and abnormal RBC adhesion may synergistically contribute to the endothelial damage and cumulative pathophysiology of SCD. These findings suggest that WBV and RBC adhesion may serve as clinically relevant biomarkers and endpoints in assessing emerging targeted and curative therapies in SCD.

Mechanism and effects of fructose diphosphate on anti-hypoxia fatigue and learning memory ability.

This study aims to investigate the mechanisms through which fructose diphosphate (FDP) causes anti-hypoxia and anti-fatigue effects and improves learning and memory. Mice were divided into three groups: low-dose FDP (FDP-L), high-dose FDP (FDP-H), and a control group. Acute toxic hypoxia induced by carbon monoxide, sodium nitrite, and potassium cyanide and acute cerebral ischemic hypoxia were used to investigate the anti-hypoxia ability of FDP. The tests of rod-rotating, mouse tail suspension, and swimming endurance were used to explore the anti-fatigue effects of FDP. The Morris water maze experiment was used to determine the impact of FDP on learning and memory ability. Poisoning-induced hypoxic tests showed that mouse survival time was significantly prolonged in the FDP-L and FDP-H groups compared with the control group (p < 0.05). In the exhaustive swimming test, FDP significantly shortened struggling time and prolonged the time of mass-loaded swimming; the rod-rotating test showed that endurance time was significantly prolonged by using FDP (p < 0.05). FDP significantly decreased lactate and urea nitrogen levels and increased hepatic and muscle glycogen and glucose transporter-4 and Na+-K+-ATPase (p < 0.05). To conclude, FDP enhances hypoxia tolerance and fatigue resistance and improves learning and memory ability through regulating glucose and energy metabolism.

Angiotensin II-Type I Receptor Antagonism Does Not Influence the Chemoreceptor Reflex or Hypoxia-Induced Central Sleep Apnea in Men.

Components of the renin-angiotensin system (RAS) situated within the carotid body or central nervous system may promote hypoxia-induced chemoreceptor reflex sensitization or central sleep apnea (CSA). We determined if losartan, an angiotensin-II type-I receptor (AT1R) antagonist, would attenuate chemoreceptor reflex sensitivity before or after 8 h of nocturnal hypoxia, and consequently CSA severity. In a double-blind, randomized, placebo-controlled, crossover protocol, 14 men (age: 25 ± 2 years; BMI: 24.6 ± 1.1 kg/m2; means ± SEM) ingested 3 doses of either losartan (50 mg) or placebo every 8 h. Chemoreceptor reflex sensitivity was assessed during hypoxic and hyperoxic hypercapnic ventilatory response (HCVR) tests and during six-20s hypoxic apneas before and after 8 h of sleep in normobaric hypoxia (FIO2 = 0.135). Loop gain was assessed from a ventilatory control model fitted to the ventilatory pattern of CSA recorded during polysomnography. Prior to nocturnal hypoxia, losartan had no effect on either the hyperoxic (losartan: 3.6 ± 1.1, placebo: 4.0 ± 0.6 l/min/mmHg; P = 0.9) or hypoxic HCVR (losartan: 5.3 ± 1.4, placebo: 5.7 ± 0.68 l/min/mmHg; P = 1.0). Likewise, losartan did not influence either the hyperoxic (losartan: 4.2 ± 1.3, placebo: 3.8 ± 1.1 l/min/mmHg; P = 0.5) or hypoxic HCVR (losartan: 6.6 ± 1.8, placebo: 6.3 ± 1.5 l/min/mmHg; P = 0.9) after nocturnal hypoxia. Cardiorespiratory responses to apnea and participants’ apnea hypopnea indexes during placebo and losartan were similar (73 ± 15 vs. 75 ± 14 events/h; P = 0.9). Loop gain, which correlated with CSA severity (r = 0.94, P < 0.001), was similar between treatments. In summary, in young healthy men, hypoxia-induced CSA severity is strongly associated with loop gain, but the AT1R does not modulate chemoreceptor reflex sensitivity before or after 8 h of nocturnal hypoxia.

Effectiveness of the hypoxic exercise test to predict altitude illness and performance at moderate altitude in high-level swimmers.

PurposeThe hypoxic exercise test is used to predict the susceptibility to severe High Altitude Illness (SHAI). In the present study, we aimed to use this test to predict the changes in performance and the physiological responses to moderate altitude in elite swimmers.MethodsEighteen elite swimmers performed a hypoxic exercise test at sea level before a moderate 12‐day altitude training camp (1,850 m) to determine if they were susceptible or not to SHAI. A maximal swimming performance test was conducted before (at sea level), during (at 1,850 m), and after (at sea level) the intervention. Arterial oxygen saturation (pulse oximetry), Lake Louise score, and quality of sleep questionnaire were collected every morning. The participants were classified in two groups, those who had a moderate to high risk of SHAI (SHAIscore ≥ 3) and those who had a low risk of SHAI (SHAIscore < 3).ResultsSeven swimmers presented a high risk of SHAI including three of them with a SHAIscore > 5. Pearson correlations indicated that SHAIscore was strongly correlated with the decrease in swimming performance at altitude (r = .60, p < .01). Arterial oxygen saturation during the hypoxic exercise test was the physiological variable that was best related to performance decrease at altitude (r = .54, p < .05). No differences were observed for Lake Louise score and quality of sleep between swimmers who suffered from SHAI or not (p > .1).ConclusionIn a population of elite swimmers, the combination of clinical and physiological variables (SHAIscore, oxygen desaturation) estimated the performance decrease at moderate altitude. The hypoxic exercise test could allow coaches and scientists to better determine the individual response of their athletes and manage the altitude acclimatization.

Secondary Analysis of Premature Respiratory Outcomes Program (PROP) Clinical Trial to Identify Correlations of Risk Factors for Respiratory Morbidity and Mortality in Premature Infants

BackgroundThe Premature Respiratory Outcomes Program (PROP) was a collaborative, multi‐disciplinary clinical study that sought to analyze the factors that could predict future risk for respiratory morbidity and mortality for 835 premature infants with gestational ages 23 0/7 to 28 6/7 weeks. PROP investigators conducted physiologic challenges called Room Air Challenges (RAC) and Hypoxic Challenges Tests (HCT) to determine whether the premature infants could maintain their SpO2 in the target range of ≥90% and to assess pulmonary reserve in former premature infants without Bronchopulmonary Dysplasia(BPD) at 36 weeks’ premenstrual age (PMA). This project was funded by the National Institutes of Health (NIH) and the National Heart, Lung, and Blood Institute (NHLBI) for 5 years through a $18.5 million research initiative.ObjectiveWe are interested in understanding the relationship between brain imaging data and respiration outcomes, and infection or chorioamnionitis and respiration outcomes. In addition, the RAC and HCT provides the opportunity to analyze the outcomes of physiologic challenges in preterm infants compared to term infants undergoing the same challenges in studies that conducted preflight HCT.Statement of the methodsWe utilized machine learning tools such as random forest, support vector machines, gradient boosted machines, and logistic regression to generate predictive models of the aforementioned features.Summary of resultsPreliminary data analysis of key variables to be included in our future data analytics includes standard deviations for birth weight (gm) (235.98), the baby’s head circumference (cm) (83.05), APGAR for one minute (scored 1–10) (2.47), and APGAR 5 minutes (2.10).Statement of conclusionsThis PROP clinical study encapsulates an immense amount of multidisciplinary data from 835 premature infants, which is an extremely special population to include in research as approximately 1 out of every 9 births in the United States occurs prematurely.Support or Funding InformationR01HL132355

Comparison of Steady‐state and Rebreathing Methods for Measuring CO2 Chemoreflexes Under Hyperoxic and Hypoxic Conditions

Two techniques for measuring ventilatory chemoreflexes are the steady‐state (SS) and rebreathing (RB) methods. In SS tests, a constant inspired PO2 and end‐tidal PCO2 are maintained to allow gas pressure equilibration at the tissues over several minutes. Ventilation is measured at two or more set points to determine CO2 chemosensitivity at a constant PO2. Alternatively, RB methods allow PCO2 to increase gradually as a participant rebreathes from a bag while PO2 remains constant. RB studies reveal a dog‐leg response, where PCO2 must rise above a subject‐specific threshold before ventilation increases. It is argued that measurements made below this threshold with SS may artificially lower the gain. Furthermore, it is unclear how these methods compare when conducted in hypoxia. This study aimed to compare ventilatory responses to CO2 during sustained hyperoxia and hypoxia within the same individuals, to determine (1) whether the difference in gain between methods is due to an inability to detect the recruitment threshold in the SS test, and (2) to determine how these methods compare at multiple PO2 levels. We hypothesized that the SS method would produce lower CO2 sensitivity responses at both oxygen levels due, in part, to measurements taken below the recruitment threshold. Healthy participants (N = 9 men, 10 women) between 18 and 65 years of age completed SS and RB tests under similar environmental conditions on the same day in a randomized order with a &gt;30‐minute rest period between tests. The SS method targeted two stable end‐tidal PCO2 levels (45 and 55 mmHg) under inspired PO2 levels of 170–180 mmHg (hyperoxic) or 70 mmHg (hypoxic). We also conducted a modified Duffin’s RB method in 2 sessions with the same stable inspired PO2 levels. Data were analyzed with Friedman’s two‐way ANOVA with Bonferroni correction and data are presented as Median [Q1,Q3]. CO2 chemosensitivity measured with the SS method was lower than the RB method in both the hyperoxic (SS slope = 0.65 [0.48,0.94] L/min/mmHg CO2; RB slope = 1.70 [1.11,2.29]; p&lt;0.001) and hypoxic (SS slope = 1.16 [0.89,1.46] L/min/mmHg CO2; RB slope = 1.87 [1.17,2.79]; p=0.034) tests. Additionally, chemosensitivity was higher during hypoxia compared to hyperoxia in the SS method (p=0.034). However, although ventilation was higher at a given PCO2 during hypoxia versus hyperoxia in the RB method due to a lower recruitment threshold (hyperoxia RT = 47.4 [45.4,49.2]; hypoxia RT = 43.3 [41.6,44.5], p=0.005), the slope above the threshold was not different (p=1.000). While the longer exposure time during SS likely alters hemodynamics and therefore gas tensions at both the central and peripheral chemoreceptors, this data also supports the idea that, without verifying that measurements are made above the recruitment threshold, the SS method produces lower sensitivity during hyperoxia. Furthermore, the SS method may produce higher gains during hypoxia due to the inability to detect the left shift along the metabolic hyperbola that occurs during hypoxia.Support or Funding InformationThis work was supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health under awards to AM and FLP (R01HL081823).

Assessment of portable oxygen concentrators in infants undergoing hypoxic challenge testing. A randomised controlled crossover trial.

Due to reduced PaO2 , aircrafts at cruising altitudes are pressurised to a cabin altitude of 2438m, equivalent to breathing FiO2 0.15. Portable oxygen concentrators (POCs) are approved for onboard oxygen supply with lack of evidence, especially in infants. We assessed POCs (continuous-flow cPOC vs. pulsed-flow pPOC) under simulated altitude conditions performing Hypoxic Challenge Testing (HCT). In a randomised controlled crossover trial, we included patients <1year born prematurely. In incidents of hypoxia (SpO2 ≤85%), oxygen was administered through POC. In patients with a positive hypoxia reversal, HCT was repeated 24hours later. If hypoxia occurred during the second testing, oxygen was given using the alternative POC. We randomised 26 patients; 22 patients received allocated intervention (4 dropped out). Mean gestational age 30.4weeks, mean corrected age 38.2weeks. Both POCs achieved immediate hypoxia reversal in all cases (SpO2 cPOC/pPOC 98%/99.4% (95%CI -2.91, 0.01)) without any adverse events. No significant difference was observed in patients with BPD. Both POCs generated sufficient oxygen to reverse HCT induced hypoxia. Although pPOCs are not recommended in paediatric age, our data suggest their effectiveness even in neonates without any associated adverse events. Future research on pPOCs safety is required to establish recommendations for their use.