Objective:To understand the current status of pubertal sexual characteristics development of girls aged 6-18 years in Tongzhou District of Beijing and to compare the differences in sexual characteristics development among girls characterized as thin, normal, overweight, and obese.Methods:A cross-sectional survey was conducted among 2 844 girls aged 6-18 years in Tongzhou District of Beijing from September 2022 to July 2023. The developmental stages of breast and pubic hair were assessed on site, and menarche status was inquired. Weight and height were measured. The girls were subsequently characterized into thin, normal, overweight and obese groups. Basic information (including family and personal history) was obtained through questionnaires. Probit probability unit regression was applied to calculate the age of each Tanner stage of sexual characteristics development and the age of menarche. The χ 2 test was applied to compare the counting data between two or multiple groups. Results:A total of 2 844 girls were surveyed and 2 704 girls met the inclusion criteria, resulting in a valid response rate of 95.1%. Among these girls, 1 105 (40.9%) were aged 6-9 years, 1 053 (38.9%) were aged 10-13 years, and 546 (20.2%) were aged 14-18 years. The of height-for-age Z-score (HAZ), weight-for-age Z-score (WAZ), and body mass index-for-age Z-score (BAZ) were 0.46(-0.23,1.16), 0.69(-0.16,1.67), and 0.67(-0.27,1.73) respectively. The prevalences of thin, overweight, and obesity were respectively 1.7% (45/2 704), 17.3% (467/2 704), and 19.9% (538/2 704), respectively. There were 45 girls in the thin group, 1 654 girls in the normal weight group, 1 005 girls in the overweight and obesity group. The age of Tanner stage breast 2 (B2), Tanner stage pubic hair 2 (P2), and menarche was 9.0 (95% CI 8.9-9.1), 10.5 (95% CI 10.4-10.6), and 11.4 (95% CI 11.3-1.5) years, respectively. The current status of breast and pubic hair maturity in girls with pubertal development shows that 64.6% (1 211/1 874) of these girls had breast development preceding pubic hair development, 32.4% (607/1 874) had concurrent breast and pubic hair development, and 3.0% (56/1 874) had pubic hairs development preceding breast development. The interval age between B2 and B5 was 4.7 (95% CI 4.6-4.8) years, between P2 and P5 was 4.5 (95% CI 4.4-4.6) years, and between B2 and menarche was 2.4 (95% CI 2.3-2.5) years. The ages of sexual characteristics development in overweight and obese groups were earlier than that in normal and thin groups. The ages of B2 in thin, normal, overweight, and obese groups were 10.0 (95% CI 9.5-10.6), 9.3 (95% CI 9.2-9.4), and 8.6 (95% CI 8.4-8.7) years, respectively. The age of menarche in thin, normal, overweight, and obese groups were 13.1 (95% CI 12.4-13.7), 11.6 (95% CI 11.4-11.7), and 11.1 (95% CI 11.0-11.2) years, respectively. The interval ages between B2 and B5 and between P2 and P5 was 4.5 and 4.1 years, respectively in the overweight and obese groups, and those in normal group and thin group was 4.7 and 4.5 years, 4.6 and 4.7 years, respectively. Conclusions:The ages of sexual characteristics development and menarche tend in Tongzhou District of Beijing to be earlier than that being reported of Beijing's survey 20 years ago. Girls characterized as overweight and obese not only start puberty at an earlier age than girls of normal weight, but also have a shorter developmental process.

Objective:To provide basis for preventing flight safety accidents caused by hypoxia by exploring the subjective and objective performance of pilots in hypobaric hypoxia environment.Methods:The relevant data of pilots′ high altitude physiological training were retrospectively analyzed and a symptom questionnaire upon the training were summarized. The pilots were divided into excellent group (time of useful consciousness >6 min), good group (3 min ≤time of useful consciousness <6 min) and qualified group (2 min ≤time of useful consciousness <3 min) according to the time of useful consciousness. The hypoxia symptoms and physiological parameters of pilots in each group were statistically analyzed.Results:A total of 919 pilots were included, in which 416 were in excellent group, 490 were in good group and 13 were in qualified group. Among the 25 hypoxia symptoms, there were significant differences in the components of numbness and difficulty in calculation among 3 groups ( χ2=6.04, 7.79, P=0.049, 0.020), but there were no significant differences in the components of the other 23 hypoxia symptoms (all P>0.05). The changes of blood oxygen saturation were significant in group main effect, time main effect and their interaction ( F=25.65, 1 039.77, 25.22, all P<0.001). The change of heart rate was statistically significant in the main effect of time ( F=66.41, P<0.001) but in time main effect and their interaction (both P>0.05). There was no significant difference in respiratory rate among group main effect, time main effect and their interaction (all P>0.05). The distribution and variation of blood oxygen saturation were statistically significant differences among the 3 groups in the ranges of 81%-90%, 71%-80% and 65%-70% ( H=125.93, 372.83, 13.10, all P≤0.001) unlike the range of 91%-100% ( H=2.48, P=0.289). Conclusions:The excellent group showed better blood oxygen saturation maintaining and useful consciousness time enduring capabilities, and those imply them in better performance and consciousness that enable the operation in hypoxic environment with more ease.

Objective:To provide scientific basis for pilots′ hypoxia training by comparing and analyzing the effects of hypoxia training under normobaric and hypobaric environments.Methods:Forty-two healthy subjects were selected. The pilot reduced oxygen breathing device and hypobaric chamber were used to simulate 7 500 m hypoxia training, and blood oxygen saturation, heart rate, respiratory rate and hypoxia endurance time were monitored and recorded. The hypoxia symptom questionnaire was filled out by the subjects after 2 training sessions. The hypoxia endurance time and hypoxia tolerance grade of normobaric and hypobaric hypoxia training were analyzed, and the differences of blood oxygen saturation and hypoxia symptoms were compared between 2 hypoxia trainings.Results:Forty-two subjects completed the normobaric and hypobaric hypoxia trainings. The survival curve analysis of hypoxia endurance time showed that the median hypoxia endurance time of normobaric and hypobaric hypoxia training was [3.17(2.70, 3.64)] min and [3.67(3.46, 3.88)] min respectively, with no significant difference ( P>0.05). There was no significant difference in the grade distribution of hypoxia tolerance between 2 hypoxia trainings ( P>0.05). The blood oxygen saturation curves of 2 hypoxia trainings were basically consistent. There was no significant difference between 2 hypoxia trainings on blood oxygen saturation, heart rate and respiratory rate (all P>0.05). There were significant differences in difficulty in calculation, difficulty in concentration and with palpitation ( χ2=4.81, 3.97, 3.98, P=0.028, 0.046, 0.046). Conclusions:The analysis showed that most physiological responses and subjective symptoms of pilots are quite similar in the normobaric and hypobaric hypoxia training at simulated 7 500 m. Both normobaric and hypobaric exposures show the similar hypoxia training effect.

Objective:To provide basis for preventing flight safety accidents caused by hypoxia by exploring the subjective and objective performance of pilots in hypobaric hypoxia environment.Methods:The relevant data of pilots′ high altitude physiological training were retrospectively analyzed and a symptom questionnaire upon the training were summarized. The pilots were divided into excellent group (time of useful consciousness >6 min), good group (3 min ≤time of useful consciousness <6 min) and qualified group (2 min ≤time of useful consciousness <3 min) according to the time of useful consciousness. The hypoxia symptoms and physiological parameters of pilots in each group were statistically analyzed.Results:A total of 919 pilots were included, in which 416 were in excellent group, 490 were in good group and 13 were in qualified group. Among the 25 hypoxia symptoms, there were significant differences in the components of numbness and difficulty in calculation among 3 groups ( χ2=6.04, 7.79, P=0.049, 0.020), but there were no significant differences in the components of the other 23 hypoxia symptoms (all P>0.05). The changes of blood oxygen saturation were significant in group main effect, time main effect and their interaction ( F=25.65, 1 039.77, 25.22, all P<0.001). The change of heart rate was statistically significant in the main effect of time ( F=66.41, P<0.001) but in time main effect and their interaction (both P>0.05). There was no significant difference in respiratory rate among group main effect, time main effect and their interaction (all P>0.05). The distribution and variation of blood oxygen saturation were statistically significant differences among the 3 groups in the ranges of 81%-90%, 71%-80% and 65%-70% ( H=125.93, 372.83, 13.10, all P≤0.001) unlike the range of 91%-100% ( H=2.48, P=0.289). Conclusions:The excellent group showed better blood oxygen saturation maintaining and useful consciousness time enduring capabilities, and those imply them in better performance and consciousness that enable the operation in hypoxic environment with more ease.

Objective:To provide scientific basis for pilots′ hypoxia training by comparing and analyzing the effects of hypoxia training under normobaric and hypobaric environments.Methods:Forty-two healthy subjects were selected. The pilot reduced oxygen breathing device and hypobaric chamber were used to simulate 7 500 m hypoxia training, and blood oxygen saturation, heart rate, respiratory rate and hypoxia endurance time were monitored and recorded. The hypoxia symptom questionnaire was filled out by the subjects after 2 training sessions. The hypoxia endurance time and hypoxia tolerance grade of normobaric and hypobaric hypoxia training were analyzed, and the differences of blood oxygen saturation and hypoxia symptoms were compared between 2 hypoxia trainings.Results:Forty-two subjects completed the normobaric and hypobaric hypoxia trainings. The survival curve analysis of hypoxia endurance time showed that the median hypoxia endurance time of normobaric and hypobaric hypoxia training was [3.17(2.70, 3.64)] min and [3.67(3.46, 3.88)] min respectively, with no significant difference ( P>0.05). There was no significant difference in the grade distribution of hypoxia tolerance between 2 hypoxia trainings ( P>0.05). The blood oxygen saturation curves of 2 hypoxia trainings were basically consistent. There was no significant difference between 2 hypoxia trainings on blood oxygen saturation, heart rate and respiratory rate (all P>0.05). There were significant differences in difficulty in calculation, difficulty in concentration and with palpitation ( χ2=4.81, 3.97, 3.98, P=0.028, 0.046, 0.046). Conclusions:The analysis showed that most physiological responses and subjective symptoms of pilots are quite similar in the normobaric and hypobaric hypoxia training at simulated 7 500 m. Both normobaric and hypobaric exposures show the similar hypoxia training effect.

Objective:To evaluate the protection performance of military transport aircraft oxygen system for aircrew and provide the physiological tests basis for product design finalization.Methods:Four dummies and 4 healthy volunteers who were equipped with individual protection equipment and military transport aircraft oxygen system completed 4 tests in altitude chamber including the oxygen supply performance physical test of oxygen system, the rapid decompression physical test of oxygen system, the physiological tests of oxygen continuously supplying for 6 h and oxygen supply performance test in rapid decompression at 12.0 km. Oxygen concentration, respiratory resistance, safety pressure, peak value, peak duration and steady pressure of mask under rapid decompression were tested. Electrocardiograph and oxygen saturation of volunteers were monitored.Results:The oxygen partial pressure provided by military transport aircraft oxygen system under 12.0 km was ≥19.1 kPa corresponding to the respiration ventilation volume of 20 L/min of dummy. The expiratory resistance was no higher than 441.3 Pa and the inspiration resistance was no higher than 490.3 Pa before the safety pressure connected. The peak pressure value in rapid decompression with 1.0 L lung volume of dummy was no higher than 5.8 kPa. The oxygen partial pressure provided by military transport aircraft oxygen system for volunteers was over 21.9 kPa in the 6 h cruising flight. All 4 volunteers successfully completed the rapid decompression physiological tests at 12.0 km with good subjective and objective responses.Conclusions:The protection performance of military transport aircraft oxygen system for aircrew can provide enough protection against the hypoxia up to 12.0 km

Objective:To study the simplified oxygen supply protection scheme below 15.0 km, and to evaluate its protection performance through tests.Methods:The parameter of YX-5 oxygen system was modified, by reducing its total oxygen supply pressure and closing a large number of oxygen supply mechanisms, and compensatory suit was cancelled. A dummy and 4 volunteers with helmet and oxygen mask using modified YX-5 oxygen system underwent 5 tests in hypobaric chamber, included ① normal oxygen supply performance test at 0-10.0 km; ② pure oxygen supply performance test at 0-10.0 km; ③ positive pressure supplying oxygen performance test at 13.0, 15.0, 16.0 km; ④ impact test of pressured oxygen supply; ⑤ pressured oxygen supplying performance physiological test at 15.0 km.Results:Under the normal oxygen supply, the oxygen pressure of modified YX-5 oxygen system below 12.0 km was >21.0 kPa. When high-altitude pressurized oxygen supply was used, the oxygen pressure was >15.8 kPa at 12.0-15.0 km. Inspiration resistance of modified YX-5 oxygen system was <0.34 kPa when the dummy′s respiration ventilation rate was 20 L/min. The impact pressure of mask was 1.25 kPa when pressured oxygen supply switched on but without compensatory suit connected to modified YX-5 oxygen system. Four volunteers completed the human physiological test up to 15.0 km high-altitude pressurized oxygen supply to verify the protective performance of the scheme, and they had no adverse physiological reactions after the test.Conclusions:The simplified protection scheme can provide protection against hypoxia for pilots at 0-15.0 km altitude.

Objective:To evaluate the protection performance of military transport aircraft oxygen system for aircrew and provide the physiological tests basis for product design finalization.Methods:Four dummies and 4 healthy volunteers who were equipped with individual protection equipment and military transport aircraft oxygen system completed 4 tests in altitude chamber including the oxygen supply performance physical test of oxygen system, the rapid decompression physical test of oxygen system, the physiological tests of oxygen continuously supplying for 6 h and oxygen supply performance test in rapid decompression at 12.0 km. Oxygen concentration, respiratory resistance, safety pressure, peak value, peak duration and steady pressure of mask under rapid decompression were tested. Electrocardiograph and oxygen saturation of volunteers were monitored.Results:The oxygen partial pressure provided by military transport aircraft oxygen system under 12.0 km was ≥19.1 kPa corresponding to the respiration ventilation volume of 20 L/min of dummy. The expiratory resistance was no higher than 441.3 Pa and the inspiration resistance was no higher than 490.3 Pa before the safety pressure connected. The peak pressure value in rapid decompression with 1.0 L lung volume of dummy was no higher than 5.8 kPa. The oxygen partial pressure provided by military transport aircraft oxygen system for volunteers was over 21.9 kPa in the 6 h cruising flight. All 4 volunteers successfully completed the rapid decompression physiological tests at 12.0 km with good subjective and objective responses.Conclusions:The protection performance of military transport aircraft oxygen system for aircrew can provide enough protection against the hypoxia up to 12.0 km

Objective:To study the simplified oxygen supply protection scheme below 15.0 km, and to evaluate its protection performance through tests.Methods:The parameter of YX-5 oxygen system was modified, by reducing its total oxygen supply pressure and closing a large number of oxygen supply mechanisms, and compensatory suit was cancelled. A dummy and 4 volunteers with helmet and oxygen mask using modified YX-5 oxygen system underwent 5 tests in hypobaric chamber, included ① normal oxygen supply performance test at 0-10.0 km; ② pure oxygen supply performance test at 0-10.0 km; ③ positive pressure supplying oxygen performance test at 13.0, 15.0, 16.0 km; ④ impact test of pressured oxygen supply; ⑤ pressured oxygen supplying performance physiological test at 15.0 km.Results:Under the normal oxygen supply, the oxygen pressure of modified YX-5 oxygen system below 12.0 km was >21.0 kPa. When high-altitude pressurized oxygen supply was used, the oxygen pressure was >15.8 kPa at 12.0-15.0 km. Inspiration resistance of modified YX-5 oxygen system was <0.34 kPa when the dummy′s respiration ventilation rate was 20 L/min. The impact pressure of mask was 1.25 kPa when pressured oxygen supply switched on but without compensatory suit connected to modified YX-5 oxygen system. Four volunteers completed the human physiological test up to 15.0 km high-altitude pressurized oxygen supply to verify the protective performance of the scheme, and they had no adverse physiological reactions after the test.Conclusions:The simplified protection scheme can provide protection against hypoxia for pilots at 0-15.0 km altitude.

Objective To develop a kind of rapid decompression equipment replacing the toughened glass simulating the state of aircraft cabin glass bursting on the fly.Methods The metallic membrane was used to isolate both chambers with different air pressures.The areas of decompression membrane and path were determined by calculating on the basis of aircraft decompression altitude,cabin pressure differential and decompression time.The structural strength was determined according to enduring force of the metallic membrane.The membrane was ejected by high pressure air using the ejection launch technology of aircraft missile.The result of simulating aircraft cabin glass bursting on the fly was achieved.Results The rapid decompression equipment ejected by air pressure in low-pressure chamber could achieve the state of simulating aircraft cabin glass bursting on the fly,and the best decompression time was 0.16 s.Conclusion The rapid decompression equipment ejected by air pressure accomplishes the decompression preparative in short time with easy operation,and can satisfy the desired requirements for the performance and precision.