HBOP can improve the lower negative pressure endurance and acceleration endurance of pilots
The results showed a significant increase in the cumulative stress index after HBOP among the 30 pilots.A centrifuge review was performed, and the 4.0G10S pass rate reached 93.3%.The pilot who failed to pass the centrifuge test had a history of overheating shooting ten years ago. Although they are currently healthy, the acceleration is still not reaching the standard, and they will follow up with the training of the pilot's acceleration endurance.
Head foot to positive acceleration endurance namely + Gz endurance is one of the main factors affecting flight safety, this paper acceleration endurance refers to + Gz endurance [11].
Liu Hongjin team [10] in the "hyperbaric oxygen pretreatment to improve the pilot lower body negative pressure endurance application research" has confirmed that HBOP can improve the lower body negative pressure endurance of normal fighter pilots.As can be seen in this experiment, after HBOP, the lower body negative pressure endurance of the poor acceleration endurance pilots was significantly improved and verified by the centrifuge test. 93.3% of the poor acceleration endurance (+ Gz endurance <4.0G / 10s) pilots had reached the standard in the centrifuge test.The mechanism that HBOP can improve the negative pressure endurance and acceleration endurance is discussed from the following aspects.
Preliminary discussion on the mechanism of negative pressure endurance by HBOP
HBOP improves autonomic nervous function
This experiment found that HBOP improved the diastolic blood pressure of the pilots with poor acceleration endurance, slowed the heart rate, increased the blood oxygen saturation, made the pilot's autonomic nervous system more stable, and the sympathetic and parasympathetic nerves can better coordinate with each other, thus improving the lower negative pressure endurance [12].
Studies have been shown that hyperbaric oxygen (HBO) can increase arterial pressure and reduce heart rate [13].Increasing arterial pressure is due to: 1) the direct effect of HBO on peripheral arterial vessels, stimulating the synthesis and release of active chemicals such as endothelin-1 and thromboane in the body, causing rapid contraction of peripheral blood vessels, vascular resistance to greatly increase [14]; 2) HBO can reduce CO2 content in blood, thus reducing its dilating effect on [13]; 3) HBO also has a-adrenaline-like effect, which can directly make vaso constriction and increase hypertensive [15].It has been believed that [16-17], healthy people increase total vascular resistance by more than 50% under 3ATA oxygen pressure, can lead to increased diastolic blood pressure.The main factors affecting the diastolic blood pressure are the heart rate and the peripheral resistance, while the main factors affecting the systolic blood pressure are the cardiac output per beat and the elasticity of the arterial wall.Under HBO, the slowing heart rate decreases the cardiac output, the systolic blood pressure decreases while the diastolic blood pressure increases, and the pulse pressure difference decreases by [18].
HBO treatment can slow down heart rate probably because the chemoreceptors and pressure receptors of the carotid sinus and aortic arch are stimulated by high concentrations of blood oxygen and increased intracascular pressure, which reflex slows heart rate, which further causes insufficient blood oxygen supply [19] in all organs, especially the human brain; At the same time, during HBO treatment, the obvious decrease in nitric oxide concentration makes it directly act in sinus node disciplined cells, and also reduces heart rate [20].It has been shown that HBO exposure can increase the high-frequency power in the frequency domain index of heart rate variability, thus increasing the vagal nerve activity, slowing down the heart rate, reducing its load on the heart wall, and reducing the myocardial oxygen consumption by [21].
The amount of oxygen fed into the tissue by HBO treatment is increased, so the oxygen saturation levels in posterity after HBO exposure significantly increase [22].
HBOP can promote the heart to show signs of "functional saving", which can prolong the duration of physical load, enhance the body movement ability and thus improve the lower body negative pressure endurance [23].
HBOP enhances the human energy metabolism
In this experiment, it was found that BLA decreased significantly after HBOP compared with before, indicating that HBOP may be involved in the metabolic clearance of lactic acid in the body, which is beneficial to prolong the time of physical load and further improve the acceleration endurance.
Fatigue refers to the energy needed to fully release muscle strength and muscle contraction, due to the accumulation of lactic acid, hydrogen ions, inorganic phosphate and ammonia and other metabolites and inhibit muscle contraction, so, the accumulation of lactic acid will lead to fatigue, and the rapid elimination of fatigue will help to improve the exercise ability [24].According to the domestic military,[25], at an altitude of 3700m, five HBOP can effectively improve the oxygen radical metabolism of up to 8d and two HBOP of up to 5d.As HBOP can accelerate the clearance rate of BLA in the body at high altitude, the energy supply of the body is transformed from anaerobic glycolysis of sugar to aerobic oxidation of sugar, which not only rapidly reduces the production of BLA, but also facilitates the clearance of BLA and other acidic products due to the significant increase of oxygen tension in tissues, cells and body fluids [9].At the same time, short-term HBOP can significantly and effectively improve the blood glucose level after physical load, significantly reduce the activity of lactate dehydrogenase and Na + -K + -ATP enzyme, and accelerate the clearance of BLA invivo, which is very important to effectively reduce the occurrence of fatigue, reduce the fatigue severity and effectively improve the labor efficiency of [26].
HBOP used in pilots with poor acceleration endurance can increase the blood oxygen content of the body, further expand the effective area when the blood flows through each tissue, and then improve the cardiovascular function during the physical load, reduce the lactate concentration, reduce the fatigue degree, and improve the acceleration endurance [27].
HBOP affects the hypothalamic-pituitary-adrenocortical axis (HPA axis)?
Due to the detection of ACTH blood indicators involved in the experiment, there was a circadian rhythm of normal ACTH secretion, high in the morning and low in the afternoon and evening, and the blood draw time was uniformly set at 8:00 am to control the experimental variables.
After result analysis, the ACTH change after HBOP in this experiment was not statistically significant.In this study, the pilots were in a quiet state before and after HBOP, and showed no acute stress response, and failed to monitor the changes of HBOP in ACTH under stress.The HPA axis is the neuroendocrine system with sensitive to stress response in the body. In the environment of acute stress, people experience a corresponding response and gradually adapt to the new environmental [28].It has been shown that in [29], reacute high-altitude exposure after HBOP can continuously increase both central neurotransmitter and ACTH.The mechanism may be that HBOP keeps the body's HPA axis continuously excited during stress, which enables the human body to produce an enhanced stress response under high altitude, low oxygen, insufficient physical load oxygen supply and HBOP to adapt to the new environment faster.HBOP can effectively regulate the secretion of the HPA axis to a series of hormones such as noradrenaline and corticotrotrophin under stress.
The factors related to HBOP for stress experiments will be studied in the future.