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. 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. 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. 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.

Author Correction: Cardiac hypoxic resistance and decreasing lactate during maximum apnea in elite breath hold divers

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

CARDIORESPIRATORY SYSTEM AND ANTIHYPOXIC RESISTANCE STATE IN ELDER CORONARY HEART DISEASE PATIENTS

The aim of the study. Evaluation of cardiorespiratory system and microcirculation state in elder CHD patients with different resistance against hypoxia. Methods. The author has carried out a retrospective analysis of 103 CHD 60+-patients, their deaths have occurred due to cardiovascular events. Two patient groups have been formed including patients (68 persons) having kept their resistance to hypoxia (their blood SO2 level was never below 80 %) and patients (35 ones) with decreased resistance to hypoxia, their blood SO2 level having been dropped below 80 %. Results: The life span of patients with decreased hypoxia resistance is lower comparing to ones having kept such resistance. The patients with decreased hypoxia resistance demonstrate decreased ejection fraction, increased mass of left ventricle myocardium as well as increased left ventricle volumes. Such patients show also significant increase of mean daily values of systolic, diastolic, and mean arterial pressure. Generally, the micro-circulation state in patients with decreased anti-hypoxic resistance is lower comparing to persons having kept this resistance. Simultaneously, the endothelial function of persons with decreased anti-hypoxic resistance is significantly worse. The pulmonary ventilation system patency and bronchial patency in these persons are also lowered comparing to these indices in patients with kept anti-hypoxic resistance. Conclusions: The decrease of anti-hypoxic resistance leads to the shorter life span on elderly CHD patients. Such decreased resistance is accompanied by worsened potency of cardio-respiratory system, microcirculation, and endothelial system functioning.

PO-306 The effect of four weeks hypoxic resistance training on myostatin and follistatin expression in skeletal muscle of rats

Objective Loss of skeletal muscle weight is a common phenomenon in hypoxic environment. It has been recognized that resistance training can reduce hypoxia-induced skeletal muscle atrophy, but its molecular mechanism is still unclear. Myostatin is a major factor that inhibits muscle growth and differentiation, and Follistatin can inhibit Myostatin. Therefore, this study is to clarify the effect of 4-week hypoxic resistance exercise on Myostatin and Follistatin gene expression in skeletal muscle of rats. Methods Twenty four 8-week-old male SD rats were randomly divided into normoxic control group (group C: 6 rats), normoxic exercise group (group R: 6 rats), hypoxic control group (group H: 6 rats) and hypoxic exercise group (group HR: 6 rats). Rats in each hypoxic group were fed in a hypoxic chamber (atmospheric hypoxia) with oxygen concentration of 12.7% (simulated 4000m altitude). Rats in each exercise group were trained according to the rat's resistance training program developed in our laboratory. After all the intervention, DEXA was used to analyze the body composition. The soleus, extensor digitorum longus and biceps brachii muscles of rats were taken and the wet weight of individual muscles was measured. The data were processed by SPSS17.0 statistical software. The expression level of skeletal muscle mRNA was expressed as "median (25-75%)" and the data of body composition and muscle wet weight were expressed as"mean±standard deviation". The differences between the groups were evaluated using a one-way analysis of variance (ANOVA) test. The significance level for the study was less than 0.05. Results Body composition analysis after 4 weeks of hypoxic intervention showed that the body weight of rats in group H decreased significantly (p=0.012), and the muscle mass decreased more significantly (p<0.001). But resistance exercises obviously reduced the muscle atrophy (p<0.01) caused by hypoxia. After analyzing the changes of the wet weight of individual muscles, it was found that the wet weight of biceps brachii in HR group was significantly higher than that in H group (p=0.048). After 4 weeks of hypoxic intervention and hypoxic resistance exercise, the expression of Myostatin mRNA in individual muscles of each group changed differently. The expression of Myostatin mRNA in soleus muscle of H group was significantly higher than that of C group (371.2%) after 4 weeks of hypoxia intervention. Myostatin mRNA expression in soleus and biceps brachii of HR group was significantly lower than that of H group (591.1% and 478.4% respectively). However, there was no significant difference in the expression level of Myostatin mRNA in the extensor digitorum longus between each group (p=0.259). The change of Follistatin mRNA expression in different groups also showed a different trend. The expression of Follistatin mRNA in soleus muscle and biceps brachii muscle was significantly different among groups (p=0.003, p=0.004, respectively). However, there was no significant difference in the expression level of Follistatin mRNA in the extensor digitorum longus between each group (p=0.734). Myostatin mRNA/Follistatin mRNA ratio (M/F) showed a more significant difference. The M/F ratio of soleus muscle in group H was significantly lower than that in group C (p<0.001), but the M/F ratio in group HR was significantly higher than that in group H (p<0.001). The M/F ratio of biceps brachii in group H was significantly lower than that in group C (p<0.001), but the M/F ratio in group HR showed a higher trend than that in group H (p=0.051). Conclusions Hypoxic exposure results in an increase in Myostatin mRNA expression in skeletal muscle, but hypoxic resistance exercise reduces such an increase. On the contrary, the level of Follistatin mRNA expression in skeletal muscle decreased after hypoxic exposure, and hypoxic resistance exercise could slow down the decline. As a result, rat resistance exercise significantly slowed down hypoxia-induced muscle atrophy. In conclusion, the mutual restriction between Myostatin and Follistatin is one of the main links of resistance exercise to reduce hypoxia-induced skeletal muscle atrophy. However, the process of resistance training to reduce the hypoxia-induced skeletal muscle atrophy is very complex. There are many molecular signaling pathways involved, which need further study.

PL-012 Effect of hypoxic resistance training on the regulation of muscle mass and phenotype

Objective Hypoxia is a state of lowered oxygen tension in tissue that can be created by environmental or pathological conditions. Whatever the origin of hypoxia, different tissues will adapt acutely and/or chronically to deal with this reduction in oxygen availability. Hypoxia has recently emerged as a particularly efficient stimulus to stimulate muscle cell proliferation and accretion of muscle mass and hypoxic resistance training has become popular amongst athletes as it is thought to favor muscle accretion. However, the molecular mechanisms are largely unknown. Methods To determine those molecular mechanisms, 19 volunteers participated to 12 sessions of resistance training spread over 4 weeks whether in normoxia (n=9) or in hypoxia (n=10, FiO213.5% corresponding to 3500m altitude). Each session consisted in 6 sets of 10 repetitions of a one-leg extension exercise at 80% of one repetition maximum (1-RM). Blood and muscle samples in each leg were taken before and after the 4-week training period. Fiber types were determined by immunohistochemistry based on myosin heavy chain isotypes. Blood saturation (SpO2, pulsoximetry) and tissue saturation index (TSI, near-infrared spectroscopy) were monitored during the exercise sessions. Results Muscle thickness determined by ultrasound was increased by 7% in normoxia only (p=0.04). The 1-RM was increased in both groups but the increase was higher in hypoxia (+34%) than in normoxia (+24%) (p=0.02). In average, SpO2stayed around 98-99% in normoxia and around 93-94% in hypoxia during each set of contractions. No difference in TSI between normoxia and hypoxia was measured, which averaged 60% before starting muscle contractions and 40% during muscle contractions. A trend towards a shift in fiber type from type I to type IIa was observed in normoxia (p<0.09) but not in hypoxia. Fiber area was not modified by any condition. Conclusions In summary, 4 weeks of hypoxic resistance training induced a larger increase in 1-RM compared to normoxic resistance training, independently of muscle hypertrophy or any change in fiber type. Further investigation should determine whether metabolic or molecular changes may explain this potentiation of maximal muscle force by hypoxia.