不同压力制度抗荷正压呼吸的+Gz防护作用
作者：耿喜臣 詹长录 颜桂定 初旭 陆霞
单位：耿喜臣.航空医学研究所，北京 100036
关键词：加速度应激(生理)；加速度防护；加压呼吸；抗荷服；对抗措施
航天医学与医学工程000303The Protection against +Gz Afforded by Pressure Breathing with Different Pressure Schedules
GENG Xi-chen,ZHAN Chang-lu, YAN Gui-ding, CHU Xu, LU Xia
(Institute of Aviation Medicine,Air Force of China,Beijing 100036)
, 百拇医药
Abstract: Objective System of pressure breathing for +Gz (PBG) has been incorporated into service in the high performance fighter aircraft,but there were significant differences among PBG pressure schedules used in different countries.The purpose of this study was to define an optimal pressure schedule in PBG system.Method Five male subjects wearing GZ-2 anti-G suit and medium-sized bladder vest,plus PBG with 1.6,2.4,and 3.2 kPa/G pressure schedules,respectively,were exposed to rapid onset (3.0 G/s) centrifuge +Gz runs.+Gz protection of PBG with each of the three pressure schedules were measured and the subjective ratings were collected.Result The +Gz protection afforded by PBG with 1.60,2.40,and 3.20 kPa/G pressure schedules were 2.00±0.31,2.54±0.32,and 2.44±0.31 G,respectively.Subjective ratings showed that the PBG with 2.40 kPa/G pressure schedule was better than the other two.Conclusion Our data suggest that a PBG pressure schedule of 2.4 kPa/G in PBG system is optimal.It not only assures the anti-G performance of PBG,but also reduces its side effects.
, 百拇医药
Key words:acceleration-stress(physiology);acceleration protection;pressure breathing；anti-G suits;countermeasure
摘要： 目的 探讨抗荷正压呼吸(PBG)系统中最佳的PBG压力制度。 方法 5名被试者穿GZ-2抗荷服及中囊代偿背心，在快增长率(3.0 G/s)离心机+Gz暴露时分别进行了1.6、2.4及 3.2 kPa/G 3种压力制度PBG实验。分别测定了3种压力制度PBG的抗荷性能，并对主观感觉进行评分。结果 1.6、2.4及 3.2 kPa/G 3种压力制度PBG的抗荷性能分别为2.00±0.31、2.54±0.32及2.44±0.31G；主观感觉评分表明，2.4 kPa/G压力制度PBG优于其它两者。 结论 PBG系统的压力制度以采用2.4 kPa/G为最佳。这样，既可保证PBG的抗荷性能，又可减轻PBG的副作用。
中图分类号：R852.21 文献标识码：A 文章编号：1002-0837(2000)03-0166-05
, http://www.100md.com
During the last two decades,measures to enhance +Gz tolerance of the pilots and to prevent the occurrence of G-induced loss of consciousness(G-LOC) were actively explored in some countries,like U.S.,U.K.,Sweden,France,Canada and Russia.These efforts were mainly concentrated in the following two aspects.Firstly,from the point of enhancing the +Gz tolerance of pilots by themselves,problems like pilots selection,anti-G training and physical training,etc.,for high performance fighter aircraft pilots have been extensively studied and advanced protocols and measures have been developed and employed in practice with positive resul ts.Secondarily,from the point of improving the +Gz protection effectiveness of anti-G equipment,a series of research and developmental works on anti-G valve,anti-G suit,pressure breathing for +Gz (PBG),etc.,have been made,and several advanced bladder anti-G systems (such as Combined Advanced Technology Enhanced Design G-Ensemble,COMBAT EDGE/CE),including of high flow anti-G valve,extended coverage anti-G suit (ECGS),and assisted PBG,have been developed.The combined equipment of PBG and ECGS has been shown to substantially increase +Gz tolerance and reduce fatigue.However,there remain many problems to be solved,like the prominent thermal stress with ECGS,and significant differences present among PBG pressure schedules in different countries[1～4].The purpose of this study is to define an optimal pressure schedule in PBG system，so that it can afford higher +Gz protection with lower side effects.
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Method
Subjects The test subjects were five trained,healthy volunteers from the centrifuge panel at the Institute of Aviation Medicine,Beijing,China.Their mean (±SD) age,height,and weight were 19±0.7 year,172±1.4 cm,65±3.4 kg,respectively. All subjects gave their informed,written consent in accordance with current regulations pertaining to human experimentation.
Centrifuge The centrifuge (5.0 m radius) located at the Institute of Aviation Medicine,Beijing was used for the experiments.The seat back angle is 13° from the vertical.Two peripheral lights and a central red light in the gondola were used to assess visual light loss.
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Anti-G equipment The anti-G equipments used for the experiments include ECGS (GZ-2),KT-2 valve,counterpressure vest,oxygen regulator,TK-2 helmet and YM-6505 mask.
The KT-2 anti-G valve was used for inflation of GZ-2. Its outlet pressure started at +1.75 Gz with ready pressure of 1.4 kPa and linearly increased to 86.3±2.7 kPa at +10 Gz with a schedules of 10.0 kPa/G.
The oxygen regulators,namely 3 prototypes of oxygen regulator A,B,and C,provide three pressure schedules of 1.6,2.4,and 3.2 kPa/G,respectively, for PBG. All breathing and vest pressure provided by A,B,and C regulators start at +4 Gz and linearly increase to 8.0 kPa at +9 Gz,9.6 kPa at +8 Gz,and 9.6 kPa at +7 Gz,respectively,with their pressure schedules.
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Experimental procedures On separation days,with at least 7 d interval,the subjects wore GZ-2,vest,helmet and mask et al,using one of the three different pressure schedules (oxygen regulators A,B,and C) in a balanced random order.The following +Gz exposure sets were used for all subjects: A series of 15 sec duration rapid onset runs (ROR at 3 G/s) beginning at +2.5 Gz and progressing at 0.25～1.0 G increments until terminating light-loss criteria were reached. First,G tolerances of subjects with the GZ-2 anti-G suit were determined. After a 3～5 min rest,G tolerances with GZ-2 plus PBG were determined,without anti-G straining maneuver.Criteria used for terminating the +Gz exposure were 100% loss of peripheral lights (PLL),50% dimming of central lights (CLD) or fatigue,whichever came first.Additional criteria for terminating an exposure were pain,discomfort,technical problems,high heart rate (HR) or serious rhythm disturbances (i.e.,HR above 200 bpm or numerous or coupled dysrhythmias).
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The following variables were recordedduring each centrifuge run: +Gz level,inflation pressure of the anti-G suit (PS),pressure in the mask (PM),electrocardiogram (ECG),heart rate and ear opacity pulse.Subjective assessment was made by the subject indicating his evaluation on 10 unit line scales (see Table 1).This assessment was performed after the completion of each centrifuge run.Medical and physiological variables were collected and analysed with a computer.Paired t-tests were used to evaluate the statistical differences.
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Table 1 Questionnaire used for subjective assessment scores subjective sense
subjective assessment scores
perceived level of
0
1
2 3
4
5
6
7 8
9
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10
+Gz protection
terrible
below
average
good
excellent
average
mask pressure
0
1
2 3
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4
5
6
7 8
9
10
extremely
below
average
above
extremely
low
average
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average
high
respiratory effort
0
1
2 3
4
5
6
7 8
9
10
none
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slight
average
moderate
extreme
fatigue
0
1
2 3
4
5
6
7 8
9
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10
much
less
same
worse
much
less
worse
arm pain
0
1
2 3
4
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5
6
7 8
9
10
much
less
same
worse
much
less
worse
overall comfort
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0
1
2 3
4
5
6
7 8
9
10
terrible
below
average
good
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excellent
average
Result
+Gz protections by PBG with different pressure schedules of oxygen regulators A,B,and C All subjects completed all sessions of the experiment.The PBG with pressure schedules of 1.6,2.4,or 3.2 kPa/G significantly improved +Gz protections by 2.00±0.31,2.54±0.32,and 2.44±0.31 G (P<0.01),respectively (Table 2).The +Gz protections by PBG with pressure schedules of 2.4 and 3.2 kPa/G were higher than that by 1.6 kPa/G (P<0.01),however,there was no significant difference between the former two pressure schedules (P>0.05).
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Changes of heart rate (HR) During centrifuge +Gz exposures with PBG,the mean HR (MHR) and maximum HR (HRmax) of subjects with pressure schedules of 2.4 and 3.2kPa/G were lower than those with pressure schedule of 1.6 kPa/G during +5 Gz (P<0.05),but no significant differences were formed among various groups at +6 Gz (P>0.05).The MHR and HRmax values with B and C were lower than those with A,but not significant at +7 and 8 Gz (P>0.05).There was no significant difference of MHR and HRmax among pressure schedules of 2.4 and 3.2kPa/G at +8.5 Gz (P>0.05) and their values were close to that of pressure schedule of 1.6 kPa/G at +8 Gz (Table 3).
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Subjective assessment After each +Gz exposure with PBG,subjective ratings for various feelings were made by the subjects.The scores of mask pressure and respiratory effort increased with a sequence with pressure schedules of 1.6,2.4,or 3.2 kPa/G during +Gz exposure (Table 4).The scores of overall comfort with pressure schedule of 1.6 kPa/G were lower than that with pressure schedules of 2.4 and 3.2 kPa/G during +5～7 Gz exposures,and the scores of overall comfort with pressure schedule of 3.2 kPa/G were lower than that with pressure schedule of 2.4 kPa/G during +7～8.5 Gz (Table 4).The subjects said that the oxygen supply was insufficient,and the mask pressure was on the low side,when breathing rapidly during +5～7 Gzwith pressure schedule of 1.6 kPa/G.The subjects said that the mask pressure was on the high side during +7～8.5 Gz with pressure schedule of 3.2 kPa/G.
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Table 2 +Gz protections afforded by PBG with 1.6,2.4,3.2 kPa/G pressure schedules(
±s,n=5) Pressure schedule
(kPa/G)
+Gz tolerance(G)
+Gz protection
afforded by PBG (G)
using GZ-2
using GZ-2 plus PBG
1.6
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6.10±0.42
8.10±0.14**
2.00±0.31
2.4
6.00±0.35
8.54±0.05**☆☆
2.54±0.32☆☆
3.2
6.13±0.25
8.56±0.13**☆☆
2.44±0.31☆☆
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**P<0.01,as compared with using GZ-2;☆☆P<0.01,as compared with group ATable 3 MHR and HRmax with PBG of different pressure schedules during centrifuge +Gz exposures(b/min,±s,n=5) pressure schedules
(kPa/G)
+Gz level
5
6
7
8
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8.5
MHR
1.6
108.6±8.6
104.0±7.8
113.0±6.6
119.4±10.6
—
2.4
99.6±8.4*
105.2±7.0
108.4±9.3
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116.4±8.2
119.4±9.9
3.2
98.0±8.8*
103.0±7.7
109.5±8.5
113.5±13.4
119.5±15.3
HRmax
1.6
115.4±9.24
113.4±11.1
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125.2±7.6
135.6±17.0
—
2.4
106.8±9.6*
113.4±9.5
117.4±12.1
128.8±9.5
132.6±11.4
3.2
105.5±6.6*
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121.7±5.3
126.5±13.4
134.0±16.7
*P<0.05，as compared with group 1.6 kPa/GTable 4 Ratings of mask pressure,respiratory effort,and overall comfort with different pressure schedules PBG during centrifuge +Gz exposures(±s,n=5) pressure schedule
(kPa/G)
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+Gz level
5
6
7
8
8.5
ratings of mask pressure
1.6
2.9±0.8
3.6±0.6
4.9±0.3
5.8±0.6
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2.4
3.9±0.2
4.9±0.1
5.3±0.2
6.5±0.3
6.2±0.3
3.2
5.1±0.1
5.5±0.0
6.4±0.4
6.6±0.5
6.6±0.3
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ratings of respiratory effort
1.6
3.4±0.4
4.8±0.7
5.7±0.3
6.3±0.7
—
2.4
4.1±0.8
5.0±0.5
5.5±0.3
6.1±0.1
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6.3±0.3
3.2
4.5±0.7
5.7±0.2
6.7±0.4
6.8±0.3
6.8±0.3
ratings of overall comfort
1.6
5.3±1.1
5.5±0.4
6.1±0.7
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6.6±0.4
—
2.4
6.1±0.4
6.6±0.4
7.0±0.3
7.5±0.3
7.7±0.3
3.2
6.3±0.4
6.7±0.3
6.6±0.4
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6.5±0.4
Discusion
The +Gz protection of PBG with pressure schedule of 1.6 kPa/G in this study was similar with that reported by Domaszuk[5],and those with pressure schedule of 2.4 and 3.2 kPa/G were similar with those reported by Clere et al[6,7].PBG enhancement of G tolerance depends upon following factors: mask pressure,anti-G suit pressure and lower body coverage of the suit.Raising the PBG mask pressure tends to increase +Gz protection for any given level of +Gz acceleration[4].In this study,the pressure schedule of anti-G valve and lower body coverage of anti-G suit were similar in various test groups,so the difference of +Gz protection is mostly dependent upon the PBG mask pressure.The PBG mask pressure with pressure schedules of 2.4 and 3.2 kPa/G were higher than that of 1.6 kPa/G,so that the +Gz protections of the former two pressure schedules were higher than that of the latter.The PBG mask pressure of the former two pressure schedules was consistent,were both 9.6 kPa,during +8～9 Gz,so their +Gz protections were similar.Our result showed that the +Gz protections of PBG with various pressure schedules mostly depend upon the level of raised intrathoracic pressure.Certainly,the circulatory support provided by GZ-2 anti-G suit,with markedly larger lower body bladder coverage than that of standard anti-G suit,was the basis of +Gz protection afforded by the various pressure schedules.
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With regard to the pressure schedule of PBG,we adopted three types:1.6,2.4,and 3.2 kPa/G.The pressure schedule of 1.6 kPa/G was similar with that of COMBAT EDGE and ATLSS of USA[2].Since eye-level blood pressure decreases by approximately 2.93～3.33 kPa/G[8],this schedule corresponds only its half,so the pilots have to perform strong anti-G straining maneuver during PBG in order to protect against +9 Gz[2,9].In this study,the +Gz tolerance of subjects with this schedule reached +8.1 Gz,it verified the above viewpoint,i.e.pilots must perform strong anti-G straining maneuver during PBG for protection of +9 Gz.This result indicates that the pressure schedule of 1.6 kPa/G might be insufficient,and the subjective rating also supported it.The pressure schedule of 3.2 kPa/G is similar to that in Canadian STING system[3],and also similar to the eye-level blood pressure decrease during +Gz stress.But,the +Gz tolerance of subjects wearing GZ-2 already reached about +6 Gz[10],PBG pressure may reach 9.6 kPa at +7 Gz,which would certainly aggravate respiratory load on the pilot,yet its +Gz protection was only close to that of 2.4 kPa/G.This indicates that the pressure schedule of 3.2 kPa/G might be unnecessarily high.This point was also supported by the subjective rating.The PBG schedule in Canadian STING system reaches a maximum level of 9.33 kPa at +6.3 Gz,and its cut-in point of +3.5 Gz is comparatively low,while a pressure schedule of 3.33 kPa /G is comparatively high.Higher PBG pressure is easy to produce some side effects,such as respiratory fatigue,nasopharyngeal distention,press pain of ears,leak of mask,arm pain et al,and it may also affect communication.So,it can't be accepted by pilots.The pressure schedule of 2.4 kPa/G located between those of 1.6 and 3.2 kPa/G,and only slightly lower than that of eye-level blood pressure decrease,but the +Gz protection afforded is not lower than that with 3.2 kPa/G,because the PBG pressure with 2.4 kPa/G is lower only at +5～7 Gz and reaches the same level with that with 3.2 kPa/G at +8～9 Gz,and GZ-2 anti-G suit is still functioning at +5～6 Gz.The pressure schedule of 2.4 kPa/G avoids the draw back of both the lower PBG pressure with 1.6 kPa/G,and the higher PBG pressure with 3.2 kPa/G,and the scores of mask and overall comfort also supported it.The +Gz tolerance of subjects using PBG with 2.4 kPa/G already reached +8.54 Gz,and with moderate leg tensing they already can accomplish the protection at +9 Gz.Considering that the +Gz tolerance of subjects already reached about +6 Gz with ECGS[11],the cut-in point of PBG can be postponed from +4 Gz to +5 Gz,so the +Gz protection of PBG and that of anti-G suit can be linked together,and the PBG pressure can also reach 9.6 kPa at +9 Gz.
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According to the above results and analyses,we think that pressure schedule of 2.4 kPa/G is optimal,when PBG is used in combination with ECGS.PBG pressure should be started at +5 Gz and linearly increased by a schedule of 2.4 kPa/G until a maximum of 9.3 kPa at +9 Gz.The PBG with this schedule can assure good +Gz protection,and reduce the side effects of PBG as well as the effort made during AGSM.
Foundation item: supported by the Medical Research Foundation of PLA(96L005),China
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[References]
[1] Balldin UI,Krock LP,Danielsson CH et al.Centrifuge man-rating internal abdominal bladder restraint in an extended coverage anti-G suit[J].SAFE J,1996,26 (2): 42～46
[2] Burns JW,Hill RC.Comparative centrifuge evaluation of the Air Force advanced technology anti-G suit (ATAGS) and the Navy enhanced anti-G lower ensemble (EAGLE)[J].SAFE J,1994,24(1): 31～35
[3] Pecaric M,Buick F,Maloan I et al.STING: 3.Advanced +Gz protection in the Canadian F-18-a schedule for positive pressure breathing during +Gz(PBG) (Abstract)[J].Aviat Space Environ Med,1995,66(5): 477
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[4] Prior ARJ.The optimization of a positive pressure breathing system for enhanced G protection[R].AGARD,1991,CP 516: 1～11.
[5] Domaszuk J.The application of positive pressure breathing for improving +Gz acceleration tolerance[J].Aviat Space Environ Med,1983,54(3): 334～337
[6] Clere JM,Lejeune D,Tran-Cong-Chi D.Effect of different schedules of assisted positive pressure breathing on G-level tolerance[C].In: SAFE Association.ed.Proceedings of the 26th annual symposium,Las Vegas,Nevada,1988,Newhall: SAFE Association,1989: 76～79
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[7] Ossard G,Morgan TR,McKenzie I et al.Interest of low inflation schedules and extended coverage of anti-G suit associated with PBG (Abstract)[J],Aviat Space Environ Med,1994,65(5): 448
[8] Harding RM,Bormar JB.Positive pressure breathing for acceleration protection and its role in prevention inflight G-induced loss of consciousness[J],Aviat Space Environ Med,1990,61:845～849
[9] Pecaric M,Buik F.Determination of a pressure breathing schedule for improving +Gz tolerance[J].Aviat Space Environ Med,1992,63: 572～578
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[10] Xichen Geng,Changlu Zhan,Guiding Yan et al.Effect of different pressure schedule on +Gz protection afforded by an extended coverage anti-G suit[J].SAFE Journal,1999,29(2):59～64
[11] Xichen Geng,Changlu Zhan,Guiding Yan et al.An assessment of +Gz protection afforded by different extended bladder coverage anti-G suit[J].Space Medicine & Medical Engineering,1996,9(5):317～323
Received dtae:1990-09-16, 百拇医药
单位：耿喜臣.航空医学研究所，北京 100036
关键词：加速度应激(生理)；加速度防护；加压呼吸；抗荷服；对抗措施
航天医学与医学工程000303The Protection against +Gz Afforded by Pressure Breathing with Different Pressure Schedules
GENG Xi-chen,ZHAN Chang-lu, YAN Gui-ding, CHU Xu, LU Xia
(Institute of Aviation Medicine,Air Force of China,Beijing 100036)
, 百拇医药
Abstract: Objective System of pressure breathing for +Gz (PBG) has been incorporated into service in the high performance fighter aircraft,but there were significant differences among PBG pressure schedules used in different countries.The purpose of this study was to define an optimal pressure schedule in PBG system.Method Five male subjects wearing GZ-2 anti-G suit and medium-sized bladder vest,plus PBG with 1.6,2.4,and 3.2 kPa/G pressure schedules,respectively,were exposed to rapid onset (3.0 G/s) centrifuge +Gz runs.+Gz protection of PBG with each of the three pressure schedules were measured and the subjective ratings were collected.Result The +Gz protection afforded by PBG with 1.60,2.40,and 3.20 kPa/G pressure schedules were 2.00±0.31,2.54±0.32,and 2.44±0.31 G,respectively.Subjective ratings showed that the PBG with 2.40 kPa/G pressure schedule was better than the other two.Conclusion Our data suggest that a PBG pressure schedule of 2.4 kPa/G in PBG system is optimal.It not only assures the anti-G performance of PBG,but also reduces its side effects.
, 百拇医药
Key words:acceleration-stress(physiology);acceleration protection;pressure breathing；anti-G suits;countermeasure
摘要： 目的 探讨抗荷正压呼吸(PBG)系统中最佳的PBG压力制度。 方法 5名被试者穿GZ-2抗荷服及中囊代偿背心，在快增长率(3.0 G/s)离心机+Gz暴露时分别进行了1.6、2.4及 3.2 kPa/G 3种压力制度PBG实验。分别测定了3种压力制度PBG的抗荷性能，并对主观感觉进行评分。结果 1.6、2.4及 3.2 kPa/G 3种压力制度PBG的抗荷性能分别为2.00±0.31、2.54±0.32及2.44±0.31G；主观感觉评分表明，2.4 kPa/G压力制度PBG优于其它两者。 结论 PBG系统的压力制度以采用2.4 kPa/G为最佳。这样，既可保证PBG的抗荷性能，又可减轻PBG的副作用。
中图分类号：R852.21 文献标识码：A 文章编号：1002-0837(2000)03-0166-05
, http://www.100md.com
During the last two decades,measures to enhance +Gz tolerance of the pilots and to prevent the occurrence of G-induced loss of consciousness(G-LOC) were actively explored in some countries,like U.S.,U.K.,Sweden,France,Canada and Russia.These efforts were mainly concentrated in the following two aspects.Firstly,from the point of enhancing the +Gz tolerance of pilots by themselves,problems like pilots selection,anti-G training and physical training,etc.,for high performance fighter aircraft pilots have been extensively studied and advanced protocols and measures have been developed and employed in practice with positive resul ts.Secondarily,from the point of improving the +Gz protection effectiveness of anti-G equipment,a series of research and developmental works on anti-G valve,anti-G suit,pressure breathing for +Gz (PBG),etc.,have been made,and several advanced bladder anti-G systems (such as Combined Advanced Technology Enhanced Design G-Ensemble,COMBAT EDGE/CE),including of high flow anti-G valve,extended coverage anti-G suit (ECGS),and assisted PBG,have been developed.The combined equipment of PBG and ECGS has been shown to substantially increase +Gz tolerance and reduce fatigue.However,there remain many problems to be solved,like the prominent thermal stress with ECGS,and significant differences present among PBG pressure schedules in different countries[1～4].The purpose of this study is to define an optimal pressure schedule in PBG system，so that it can afford higher +Gz protection with lower side effects.
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Method
Subjects The test subjects were five trained,healthy volunteers from the centrifuge panel at the Institute of Aviation Medicine,Beijing,China.Their mean (±SD) age,height,and weight were 19±0.7 year,172±1.4 cm,65±3.4 kg,respectively. All subjects gave their informed,written consent in accordance with current regulations pertaining to human experimentation.
Centrifuge The centrifuge (5.0 m radius) located at the Institute of Aviation Medicine,Beijing was used for the experiments.The seat back angle is 13° from the vertical.Two peripheral lights and a central red light in the gondola were used to assess visual light loss.
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Anti-G equipment The anti-G equipments used for the experiments include ECGS (GZ-2),KT-2 valve,counterpressure vest,oxygen regulator,TK-2 helmet and YM-6505 mask.
The KT-2 anti-G valve was used for inflation of GZ-2. Its outlet pressure started at +1.75 Gz with ready pressure of 1.4 kPa and linearly increased to 86.3±2.7 kPa at +10 Gz with a schedules of 10.0 kPa/G.
The oxygen regulators,namely 3 prototypes of oxygen regulator A,B,and C,provide three pressure schedules of 1.6,2.4,and 3.2 kPa/G,respectively, for PBG. All breathing and vest pressure provided by A,B,and C regulators start at +4 Gz and linearly increase to 8.0 kPa at +9 Gz,9.6 kPa at +8 Gz,and 9.6 kPa at +7 Gz,respectively,with their pressure schedules.
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Experimental procedures On separation days,with at least 7 d interval,the subjects wore GZ-2,vest,helmet and mask et al,using one of the three different pressure schedules (oxygen regulators A,B,and C) in a balanced random order.The following +Gz exposure sets were used for all subjects: A series of 15 sec duration rapid onset runs (ROR at 3 G/s) beginning at +2.5 Gz and progressing at 0.25～1.0 G increments until terminating light-loss criteria were reached. First,G tolerances of subjects with the GZ-2 anti-G suit were determined. After a 3～5 min rest,G tolerances with GZ-2 plus PBG were determined,without anti-G straining maneuver.Criteria used for terminating the +Gz exposure were 100% loss of peripheral lights (PLL),50% dimming of central lights (CLD) or fatigue,whichever came first.Additional criteria for terminating an exposure were pain,discomfort,technical problems,high heart rate (HR) or serious rhythm disturbances (i.e.,HR above 200 bpm or numerous or coupled dysrhythmias).
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The following variables were recordedduring each centrifuge run: +Gz level,inflation pressure of the anti-G suit (PS),pressure in the mask (PM),electrocardiogram (ECG),heart rate and ear opacity pulse.Subjective assessment was made by the subject indicating his evaluation on 10 unit line scales (see Table 1).This assessment was performed after the completion of each centrifuge run.Medical and physiological variables were collected and analysed with a computer.Paired t-tests were used to evaluate the statistical differences.
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Table 1 Questionnaire used for subjective assessment scores subjective sense
subjective assessment scores
perceived level of
0
1
2 3
4
5
6
7 8
9
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10
+Gz protection
terrible
below
average
good
excellent
average
mask pressure
0
1
2 3
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4
5
6
7 8
9
10
extremely
below
average
above
extremely
low
average
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average
high
respiratory effort
0
1
2 3
4
5
6
7 8
9
10
none
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slight
average
moderate
extreme
fatigue
0
1
2 3
4
5
6
7 8
9
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10
much
less
same
worse
much
less
worse
arm pain
0
1
2 3
4
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5
6
7 8
9
10
much
less
same
worse
much
less
worse
overall comfort
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0
1
2 3
4
5
6
7 8
9
10
terrible
below
average
good
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excellent
average
Result
+Gz protections by PBG with different pressure schedules of oxygen regulators A,B,and C All subjects completed all sessions of the experiment.The PBG with pressure schedules of 1.6,2.4,or 3.2 kPa/G significantly improved +Gz protections by 2.00±0.31,2.54±0.32,and 2.44±0.31 G (P<0.01),respectively (Table 2).The +Gz protections by PBG with pressure schedules of 2.4 and 3.2 kPa/G were higher than that by 1.6 kPa/G (P<0.01),however,there was no significant difference between the former two pressure schedules (P>0.05).
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Changes of heart rate (HR) During centrifuge +Gz exposures with PBG,the mean HR (MHR) and maximum HR (HRmax) of subjects with pressure schedules of 2.4 and 3.2kPa/G were lower than those with pressure schedule of 1.6 kPa/G during +5 Gz (P<0.05),but no significant differences were formed among various groups at +6 Gz (P>0.05).The MHR and HRmax values with B and C were lower than those with A,but not significant at +7 and 8 Gz (P>0.05).There was no significant difference of MHR and HRmax among pressure schedules of 2.4 and 3.2kPa/G at +8.5 Gz (P>0.05) and their values were close to that of pressure schedule of 1.6 kPa/G at +8 Gz (Table 3).
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Subjective assessment After each +Gz exposure with PBG,subjective ratings for various feelings were made by the subjects.The scores of mask pressure and respiratory effort increased with a sequence with pressure schedules of 1.6,2.4,or 3.2 kPa/G during +Gz exposure (Table 4).The scores of overall comfort with pressure schedule of 1.6 kPa/G were lower than that with pressure schedules of 2.4 and 3.2 kPa/G during +5～7 Gz exposures,and the scores of overall comfort with pressure schedule of 3.2 kPa/G were lower than that with pressure schedule of 2.4 kPa/G during +7～8.5 Gz (Table 4).The subjects said that the oxygen supply was insufficient,and the mask pressure was on the low side,when breathing rapidly during +5～7 Gzwith pressure schedule of 1.6 kPa/G.The subjects said that the mask pressure was on the high side during +7～8.5 Gz with pressure schedule of 3.2 kPa/G.
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Table 2 +Gz protections afforded by PBG with 1.6,2.4,3.2 kPa/G pressure schedules(
±s,n=5) Pressure schedule(kPa/G)
+Gz tolerance(G)
+Gz protection
afforded by PBG (G)
using GZ-2
using GZ-2 plus PBG
1.6
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6.10±0.42
8.10±0.14**
2.00±0.31
2.4
6.00±0.35
8.54±0.05**☆☆
2.54±0.32☆☆
3.2
6.13±0.25
8.56±0.13**☆☆
2.44±0.31☆☆
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**P<0.01,as compared with using GZ-2;☆☆P<0.01,as compared with group ATable 3 MHR and HRmax with PBG of different pressure schedules during centrifuge +Gz exposures(b/min,
±s,n=5) pressure schedules(kPa/G)
+Gz level
5
6
7
8
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8.5
MHR
1.6
108.6±8.6
104.0±7.8
113.0±6.6
119.4±10.6
—
2.4
99.6±8.4*
105.2±7.0
108.4±9.3
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116.4±8.2
119.4±9.9
3.2
98.0±8.8*
103.0±7.7
109.5±8.5
113.5±13.4
119.5±15.3
HRmax
1.6
115.4±9.24
113.4±11.1
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125.2±7.6
135.6±17.0
—
2.4
106.8±9.6*
113.4±9.5
117.4±12.1
128.8±9.5
132.6±11.4
3.2
105.5±6.6*
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121.7±5.3
126.5±13.4
134.0±16.7
*P<0.05，as compared with group 1.6 kPa/GTable 4 Ratings of mask pressure,respiratory effort,and overall comfort with different pressure schedules PBG during centrifuge +Gz exposures(
±s,n=5) pressure schedule(kPa/G)
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+Gz level
5
6
7
8
8.5
ratings of mask pressure
1.6
2.9±0.8
3.6±0.6
4.9±0.3
5.8±0.6
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2.4
3.9±0.2
4.9±0.1
5.3±0.2
6.5±0.3
6.2±0.3
3.2
5.1±0.1
5.5±0.0
6.4±0.4
6.6±0.5
6.6±0.3
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ratings of respiratory effort
1.6
3.4±0.4
4.8±0.7
5.7±0.3
6.3±0.7
—
2.4
4.1±0.8
5.0±0.5
5.5±0.3
6.1±0.1
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6.3±0.3
3.2
4.5±0.7
5.7±0.2
6.7±0.4
6.8±0.3
6.8±0.3
ratings of overall comfort
1.6
5.3±1.1
5.5±0.4
6.1±0.7
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6.6±0.4
—
2.4
6.1±0.4
6.6±0.4
7.0±0.3
7.5±0.3
7.7±0.3
3.2
6.3±0.4
6.7±0.3
6.6±0.4
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6.5±0.4
Discusion
The +Gz protection of PBG with pressure schedule of 1.6 kPa/G in this study was similar with that reported by Domaszuk[5],and those with pressure schedule of 2.4 and 3.2 kPa/G were similar with those reported by Clere et al[6,7].PBG enhancement of G tolerance depends upon following factors: mask pressure,anti-G suit pressure and lower body coverage of the suit.Raising the PBG mask pressure tends to increase +Gz protection for any given level of +Gz acceleration[4].In this study,the pressure schedule of anti-G valve and lower body coverage of anti-G suit were similar in various test groups,so the difference of +Gz protection is mostly dependent upon the PBG mask pressure.The PBG mask pressure with pressure schedules of 2.4 and 3.2 kPa/G were higher than that of 1.6 kPa/G,so that the +Gz protections of the former two pressure schedules were higher than that of the latter.The PBG mask pressure of the former two pressure schedules was consistent,were both 9.6 kPa,during +8～9 Gz,so their +Gz protections were similar.Our result showed that the +Gz protections of PBG with various pressure schedules mostly depend upon the level of raised intrathoracic pressure.Certainly,the circulatory support provided by GZ-2 anti-G suit,with markedly larger lower body bladder coverage than that of standard anti-G suit,was the basis of +Gz protection afforded by the various pressure schedules.
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With regard to the pressure schedule of PBG,we adopted three types:1.6,2.4,and 3.2 kPa/G.The pressure schedule of 1.6 kPa/G was similar with that of COMBAT EDGE and ATLSS of USA[2].Since eye-level blood pressure decreases by approximately 2.93～3.33 kPa/G[8],this schedule corresponds only its half,so the pilots have to perform strong anti-G straining maneuver during PBG in order to protect against +9 Gz[2,9].In this study,the +Gz tolerance of subjects with this schedule reached +8.1 Gz,it verified the above viewpoint,i.e.pilots must perform strong anti-G straining maneuver during PBG for protection of +9 Gz.This result indicates that the pressure schedule of 1.6 kPa/G might be insufficient,and the subjective rating also supported it.The pressure schedule of 3.2 kPa/G is similar to that in Canadian STING system[3],and also similar to the eye-level blood pressure decrease during +Gz stress.But,the +Gz tolerance of subjects wearing GZ-2 already reached about +6 Gz[10],PBG pressure may reach 9.6 kPa at +7 Gz,which would certainly aggravate respiratory load on the pilot,yet its +Gz protection was only close to that of 2.4 kPa/G.This indicates that the pressure schedule of 3.2 kPa/G might be unnecessarily high.This point was also supported by the subjective rating.The PBG schedule in Canadian STING system reaches a maximum level of 9.33 kPa at +6.3 Gz,and its cut-in point of +3.5 Gz is comparatively low,while a pressure schedule of 3.33 kPa /G is comparatively high.Higher PBG pressure is easy to produce some side effects,such as respiratory fatigue,nasopharyngeal distention,press pain of ears,leak of mask,arm pain et al,and it may also affect communication.So,it can't be accepted by pilots.The pressure schedule of 2.4 kPa/G located between those of 1.6 and 3.2 kPa/G,and only slightly lower than that of eye-level blood pressure decrease,but the +Gz protection afforded is not lower than that with 3.2 kPa/G,because the PBG pressure with 2.4 kPa/G is lower only at +5～7 Gz and reaches the same level with that with 3.2 kPa/G at +8～9 Gz,and GZ-2 anti-G suit is still functioning at +5～6 Gz.The pressure schedule of 2.4 kPa/G avoids the draw back of both the lower PBG pressure with 1.6 kPa/G,and the higher PBG pressure with 3.2 kPa/G,and the scores of mask and overall comfort also supported it.The +Gz tolerance of subjects using PBG with 2.4 kPa/G already reached +8.54 Gz,and with moderate leg tensing they already can accomplish the protection at +9 Gz.Considering that the +Gz tolerance of subjects already reached about +6 Gz with ECGS[11],the cut-in point of PBG can be postponed from +4 Gz to +5 Gz,so the +Gz protection of PBG and that of anti-G suit can be linked together,and the PBG pressure can also reach 9.6 kPa at +9 Gz.
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According to the above results and analyses,we think that pressure schedule of 2.4 kPa/G is optimal,when PBG is used in combination with ECGS.PBG pressure should be started at +5 Gz and linearly increased by a schedule of 2.4 kPa/G until a maximum of 9.3 kPa at +9 Gz.The PBG with this schedule can assure good +Gz protection,and reduce the side effects of PBG as well as the effort made during AGSM.
Foundation item: supported by the Medical Research Foundation of PLA(96L005),China
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[References]
[1] Balldin UI,Krock LP,Danielsson CH et al.Centrifuge man-rating internal abdominal bladder restraint in an extended coverage anti-G suit[J].SAFE J,1996,26 (2): 42～46
[2] Burns JW,Hill RC.Comparative centrifuge evaluation of the Air Force advanced technology anti-G suit (ATAGS) and the Navy enhanced anti-G lower ensemble (EAGLE)[J].SAFE J,1994,24(1): 31～35
[3] Pecaric M,Buick F,Maloan I et al.STING: 3.Advanced +Gz protection in the Canadian F-18-a schedule for positive pressure breathing during +Gz(PBG) (Abstract)[J].Aviat Space Environ Med,1995,66(5): 477
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[4] Prior ARJ.The optimization of a positive pressure breathing system for enhanced G protection[R].AGARD,1991,CP 516: 1～11.
[5] Domaszuk J.The application of positive pressure breathing for improving +Gz acceleration tolerance[J].Aviat Space Environ Med,1983,54(3): 334～337
[6] Clere JM,Lejeune D,Tran-Cong-Chi D.Effect of different schedules of assisted positive pressure breathing on G-level tolerance[C].In: SAFE Association.ed.Proceedings of the 26th annual symposium,Las Vegas,Nevada,1988,Newhall: SAFE Association,1989: 76～79
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[7] Ossard G,Morgan TR,McKenzie I et al.Interest of low inflation schedules and extended coverage of anti-G suit associated with PBG (Abstract)[J],Aviat Space Environ Med,1994,65(5): 448
[8] Harding RM,Bormar JB.Positive pressure breathing for acceleration protection and its role in prevention inflight G-induced loss of consciousness[J],Aviat Space Environ Med,1990,61:845～849
[9] Pecaric M,Buik F.Determination of a pressure breathing schedule for improving +Gz tolerance[J].Aviat Space Environ Med,1992,63: 572～578
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[10] Xichen Geng,Changlu Zhan,Guiding Yan et al.Effect of different pressure schedule on +Gz protection afforded by an extended coverage anti-G suit[J].SAFE Journal,1999,29(2):59～64
[11] Xichen Geng,Changlu Zhan,Guiding Yan et al.An assessment of +Gz protection afforded by different extended bladder coverage anti-G suit[J].Space Medicine & Medical Engineering,1996,9(5):317～323
Received dtae:1990-09-16, 百拇医药