G protection: interaction of straining maneuvers and positive pressure breathing

INTRODUCTION: G protection in the 39 Gripen aircraft is provided by a full coverage anti-G suit, a pressure-breathing system, and anti-G straining maneuvers (AGSM). The purpose was to study (1) the interaction of pressure breathing and AGSM while wearing an anti-G suit; and (2) the G-protective properties of the anti-G suit alone and in combination with the pressure-breathing system. METHODS: During rapid onset rate G-time profiles (< or =9 G), 10 subjects were investigated in 5 conditions: (I) sitting relaxed, without any G-protective garment; (II) sitting relaxed and wearing an anti-G suit; (III) sitting relaxed, wearing an anti-G suit, and pressure breathing; IV) wearing an anti-G suit and performing AGSM; and V) wearing an anti-G suit, pressure breathing, and performing AGSM. In supplementary experiments (n=9), the share of the anti-G suit protection afforded by the abdominal bladder was investigated. RESULTS: G tolerance was 3.4 Gz (range: 2.8-4.3) in condition I, > or = 6.5 Gz (4.5-9.0) in II, > or = 8.0 Gz (6.5-9.0) in III, > or = 8.9 Gz (8.5-9.0) in IV and > or = 9.0 Gz (8.5-9.0) in V. In the supplementary experiments, the anti-G suit afforded a 2.8-G protection, a third of which was contributed by the abdominal bladder. In the relaxed state, pressure applied to the airways was transmitted undistorted to the intrathoracic space. During AGSM, intrathoracic pressure rose to 10-14 kPa, regardless of whether AGSM was performed with or without pressure breathing. DISCUSSION: AND CONCLUSIONS: The anti-G suit and the pressure breathing system provide G protection of > or = 4.6 G, of which the anti-G suit contributes about 3.0 G. The C-protective properties of the anti-G suit and those of pressure breathing appears to be additive, whereas the G protection afforded by pressure breathing does not add to that provided by AGSM.     

The effect of straining maneuvers on G-protection during assisted pressure breathing

INTRODUCTION: Pilots flying high-performance aircraft increase their acceleration tolerance by using straining maneuvers and anti-G suits. Recently, assisted positive pressure breathing has been added in some aircraft systems. This study assessed the effect of anti-G straining maneuvers on the G-protective properties of one such system, the AGE-39 anti-G ensemble used in the Swedish JAS 39 Gripen aircraft. METHODS: Ten subjects were studied in a centrifuge using each of the following: 1) the AGE-39 in combination with anti-G straining maneuvers (AGSM) throughout each high-G exposure (full maneuver; FM); 2) the AGE-39 in combination with AGSM only during the initial part of each high-G exposure (reduced maneuver; RM). G-tolerance was established during exposures to rapid onset rate (ROR) G profiles with plateau levels ranging from 6.5 to 9.0 G. RESULTS: Mean G-tolerance was > or = 8.8 G (range: 8.5 to > or = 9.0 G) in the RM condition and > or = 9.0 G in all subjects in the FM condition. Mean arterial pressure was 30-50 mm Hg higher (p < 0.001) in the FM than in the RM condition at any given ROR G-load. CONCLUSIONS: AGE-39 in combination with a brief period of straining provide efficient G-protection as illustrated by the finding that all subjects could tolerate 8.5 G while performing AGSM during the initial part of the high-G exposures. However, at 9.0 G, 40% of the subjects had to perform AGSM throughout the duration of the G-exposure. That arterial pressure was only 30-50 mm Hg higher in the FM than RM condition suggests that in the presence of straining maneuvers, pressure breathing makes only a minute contribution to the arterial-pressure response.     

Evaluation of assisted positive pressure breathing on +Gz tolerance.

The effect of both assisted and unassisted positive pressure (PPB) breathing on +Gz tolerance was evaluated. A GOR (gradual onset rate = 0.1 G/s) acceleration profile was used to evaluate five different experimental conditions: 1) G-suit-only, 2) G suit + unassisted PPB, 3) G suit + PPB assisted by the English jerkin, 4) G suit + PPB assisted by the Canadian waistcoat, and 5) the Swedish counterpressure garment G suit combination. Acceleration tolerances for these experimental conditions (excluding the Swedish garment) with the subjects performing M-1 maneuvers were measured using an exhaustive ACM (Aerial Combat Maneuvers) acceleration profile. GOR tolerances were similar for both assisted and unassisted PPB with the pressure breathing experimental conditions providing a significant GOR tolerance increase over the G suit only condition. Assisted PPB increased ACM tolerances over both unassisted PPB and G suit only conditions. It appears that assisted PPB may offer a practical method for reducing the fatigue associated with exposure to high G.     

The application of positive pressure breathing for improving +Gz acceleration tolerance

Investigations on +Gz acceleration tolerance were carried out in pilots using various values of positive pressure breathing (PPB) during centrifugation. The greatest improvement of +Gz tolerance--2.2 +Gz--was achieved while applying PPB=45 mm Hg and using a counterpressure suit. PPB prolonged the time at +5Gz from 2 min 35 s under control conditions to 6 min 53 s at PPB=45 mm Hg. The author discusses the mechanism of the increase in acceleration tolerance at PPB, stressing its protective effect on the circulatory system.     

抗荷正压呼吸训练效果的评价

为有效地提高飞行员抗荷能力 ,笔者以抗荷正压呼吸训练方法为依据 ,对高性能战斗机飞行员进行训练前后的 G值比较 ,旨在为航卫保障提供客观依据。一、对象和方法1.对象 :来院疗养的高性能战斗机飞行员 4 0名 ,男性 ,2 5～ 34岁 ,飞行时间 110 0～ 2 30 0 h,平均飞行时间 132 0h。体检合格 ,平日坚持体育训练 ,能正确掌握抗荷正压呼吸训练动作要领。训练前受训者身体状况良好。2 .训练设备与抗荷装备 :采用地面加压供氧锻炼器、加压供氧面罩、代偿背心、飞行头盔和抗荷服 ,按医用氧标准用99.5 %的医用纯氧 ,氧气压力不低于2 .2× 10 4 mm Hg…     

新的抗荷动作:HP与PHP动作抗荷效果的评价

目的：检验新的抗荷动作－－HP与PHP动作的抗荷效果。方法：HP动作由两部分构成,第1部分为全身肌肉根据＋Gz大小进行用力收缩;第2部分为2．5s 1个周期的呼吸部分,即在0．5s内以口快吸气,同时发出汉语拼音“H”,再通过半闭的双唇用力进行慢呼气2．0s,同时发出汉语拼音“P”。PHP是在抗荷正压呼吸条件下做的HP动作。测试对象为20名飞行员和10名志愿者。在离心机上测定10名飞行员采用KH－7抗荷服与HP动作的抗荷耐力,另外10名飞行员采用KH－7抗荷服与L－1动作时的抗荷耐力作对照。在离心机上测定10名志愿者采用KH－5抗荷服、抗荷正压呼吸装备和做PHP动作时的＋Gz耐力。结果：分别采用HP动作、L－1动作的两组飞行员的抗荷耐力均可达到8G10s,但采用HP动作时心率、呼吸率显著低于L－1动作（P＜0．05）。志愿者采用装备做PHP动作的抗荷耐力均达到了9G10s,且完成得比较轻松。结论：HP、PHP动作具有良好的抗荷效果,心脏负荷较小,而且飞行员易于理解、掌握,易于抗荷正压呼吸结合。     

Endurance and performance during multiple intense high +Gz exposures with effective anti-G protection

BACKGROUND: In many high-intensity wartime scenarios, pilots may be required to fly multiple, strenuous missions during the same day. HYpothesis: New anti-G protection allows fighter pilots to endure multiple high +G, exposures during several sorties in a limited time interval. METHODS: Nine well-trained centrifuge subjects were exposed to tactical aerial combat maneuvers using balanced pressure breathing during G (PBG) and an extended coverage anti-G suit. The centrifuge exposures consisted of five simulated sorties during a 4-h period, each consisting of four engagements with rapid onset cycles (6 G x s(-1)) varying between +4 G, and -9 GC. The subjects executed a tracking task before, during, and after each engagement and verbally indicated their effort level. Neck muscle strength was measured before and after the test. RESULTS: Seven of the nine subjects could endure all five sorties during the 4-h period. On a scale from 0 (no effort) to 11 (maximum possible effort), highest effort level during runs varied from 5.5 to 11 units (mean 8.7). Maximal heart rate varied from 140-173 bpm (mean 159) and minimum finger oxygen saturation from 75-93% (mean 88). Maximal peripheral and central light-loss varied from 0 to 100% (mean 71 and 40, respeclively). Three G-LOCs (two in the same subject) and four cases of near loss of consciousness occurred. The general fatigue recovery time varied from 9 to 48 h (mean 21). The tracking tests showed that performance deteriorated significantly during all G exposures; the neck muscle contraction was impaired by 12% (p = 0.035) after the C exposures. CONCLUSION: It is possible to train subjects to withstand five simulated flight sorties during a 4-h period with a total of up to 80 peaks to +9 Gz and 80 peaks to +8 Gz using PBCG and an extended coverage anti-G suit.     

Determination of a pressure breathing schedule for improving +Gz tolerance.

A base of empirical data for developing optimal pressure breathing during +Gz (PBG) schedules is lacking. Relaxed +Gz-intensity tolerance with PBG was measured during gradual +Gz-onset rate centrifuge profiles using standard lightbar criteria. Constant PBG levels ranging from 18-73 mm Hg were randomly assigned. G-suit pressure followed the standard or an increased inflation schedule. Nine subjects wore a jerkin, CSU-15/P G-suit, and TLSS helmet and mask. With mean mask cavity pressures of 0, 18, 38, 60, and 73 mm Hg, corresponding +Gz-tolerances (mean +/- S.E.M.) were: 5.3 +/- 0.2, 5.8 +/- 0.1, 6.6 +/- 0.2, 7.3 +/- 0.3, and 7.5 +/- 0.3 Gz (linear correlation, r = 0.994). Increased G-suit pressure did not change the +Gz-tolerance improvement with PBG. The inverse of individual subject regression slopes ranged from 22.6 to 58.1 mm Hg/+Gz. Considering additional factors and adequate +Gz protection for all subjects while relaxed, the proposed schedule would apply 42 mm Hg PBG/+Gz beginning at +3.3 Gz with a maximum pressure of at least 73 mm Hg.     

抗荷正压呼吸训练效果的观察

为适应新机型的特点，我军高性能战斗机飞行员于1998年开始实施地面抗荷正压呼吸(prssure breathing for G，PBG)训练，现对训练效果评价如下。     

使用大覆盖面抗荷服+Gz作用下中心血液动力学变化的仿真研究

目的　为阐明囊式抗荷系统是否会给心脏及大血管带来不良影响 ,对使用由不同大覆盖面积囊式抗荷服 (ECGS)与抗荷正压呼吸 (PBG)组成的抗荷系统在 8Gz 时的中心血液动力学变化进行数字仿真研究 ,以评价其对心脏的影响与防护作用。　方法　利用所建立的可仿真 Gz 与抗荷系统综合影响的多元非线性循环呼吸模型 ,对由两种ECGS(囊覆盖面积分别为 6 5 %和 90 % )与两种PBG(压力制度分别为 1 6kPa/G与 2 4kPa/G , 4Gz 启动 )组成的抗荷系统的抗荷效果及中心循环重要生理参数的变化进行仿真。　结果　仿真G耐力结果与国内外报道的人体离心机实验数据基本相符 ,验证了仿真模型的有效性。仿真结果表明 ,ECGS的抗荷性能虽随着囊覆盖面积的扩大及压力制度的提高而增加 ,但每搏输出量略有降低 ,心脏、大血管及其瓣膜受到损伤的可能性亦增大。PBG引起的高胸内压虽可使呼吸困难程度增加 ,却能在不增加心脏做功的情况下提高心水平的动脉压 ,增强防护效果 ,并可使心脏、大动脉血管及其瓣膜的跨壁压 /跨膜压幅度减小 ,从而使人体在高G防护下受损的可能性降低。　结论　由于PBG对 Gz 作用下中心血液动力学的改变具有正面影响 ,因而在抗荷装备中具有特殊应用价值。     

Hemodynamic reactions to positive intrathoracic pressure in + Gz overload

Eight male test subjects, aged 20-28, were exposed to acceleration +Gz and positive breathing pressure (PBP) of 30 mm Hg to study their hemodynamics under these conditions. The calculated and experimental decrease of blood pressure at the eye level during increasing acceleration and voluntary myorelaxation was comparable. The exposure to PBP helped tolerate higher (by 1.1 +/- 0.2 G) acceleration values without visual disorders. The exposure to 7.0 G and PBP caused a lower increase in heart rate and breathing frequency (by 6% and 12%, respectively), a smaller reduction of blood pressure at the eye level (by 20%), and a decreased muscular tension (by 18%).     

Electromyographic activity while performing the anti-G straining maneuver during high sustained acceleration.

The purpose of this study was to measure the muscle activity during performance of the anti-G straining maneuver (AGSM) at high sustained acceleration stress (+Gz = head-to-foot inertial loading). Ten males were exposed on three separation occasions to a rapid onset rate of 6 + Gz. Subjects wore standard United States Air Force (USAF) anti-G trousers and performed the AGSM until perceived fatigue or until achieving light loss criteria. During each exposure, surface electromyography (EMG) was recorded from the erector spinae, external oblique, bicep femoris, vastus lateralis, and lateral gastrocnemius muscles. The normalized root-mean squares (RMS) and mean power frequency (MPF) for each muscle were calculated and tested for significant differences with an analysis of variance (ANOVA) procedure. The results of this study showed that mean amplitude decreased during the AGSM (35.40%) while MPF showed no significant change. The EMG amplitude of lower extremity muscles decreased (61.45%) while the amplitude of trunk muscles decreased slightly (3.45%). These results indicate that during the performance of the AGSM, motor unit recruitment in lower extremity muscles decrease without evidence of fatigue.     

扩大囊覆盖面积抗荷服＋Gz防护作用的计算机仿真研究

为检验所建立的心血管系统仿真模型，对扩大囊覆盖面积抗荷服的囊覆盖面积及压力制度地人体Ｇ耐力及心血管反应的影响进行了仿真实验，得到了与耿喜臣等离心机实验数据基本吻合的结果。     

带呼吸囊管式背心抗荷服的热负荷测定

测定5名志愿被试者在34－35℃环境中着用带呼吸囊管式背心抗荷服时的加权平均皮肤温度（TS）、囊下局部皮肤温度、口腔温度等指标。结果表明，与不带呼吸囊组比较，管式背心加呼吸囊后除局部皮肤温度略有升高（1．2±0．1℃）外，其他各项指标均无显著差别（P＞0．05）。初步认为，在环境热负荷强度不大时，该装备不会引起飞行员显著热应激。     

Protection against the physiological effects of positive pressure breathing.

The degree of protection afforded by three jerkin G-suit systems (British, Canadian and Swedish) using different pressures against the adverse physiological effects produced by high levels (50 mm Hg and 70 mm Hg) of positive pressure breathing (PPB) was investigated at ground level in 10 male subjects. The British and Canadian systems were evaluated with G-suit pressure equal to breathing pressure and 3.2 times breathing pressure, whereas the Swedish system was studied only with 3.2 times breathing pressure in the G suit. The experimental design was a 10 X 10 Latin swuare. PPB produced significant increases in heart rate, peripheral resistance, and systolic, diastolic and mean arterial blood pressures, and significant decreases in stroke volume and cardiac output. These effects were directly related to the level of PPB. Our results show that the British system provides the highestdegree of protection against PPB, followed by the Swedish and the Canadian systems. It was also found that a G-suit pressure of 3.2 times breathing pressure significantly increases the degree of protection afforded by the British and Canadian systems.     

G-endurance during heat stress and balanced pressure breathing.

The effect of heat stress and balanced pressure breathing during G (PBG) on G-endurance was investigated. Ten fighter pilots wearing anti-G-suits with increased bladder coverage were warmed to 38.2 degrees C and exposed to 15-s periods at 4.5 and 7 G in a heated human centrifuge gondola until exhaustion during PBG and normal breathing (NB). During both NB and PBG, the rectal temperature rose to a mean of 38.3 degrees C, and the dehydration was about 1.2 kg. With NB the endurance was a mean of 254 s, while it was 300 s with PBG (n.s.). Oxygen saturation and ratings of perceived exertion were mainly unchanged, while the maximum heart rate decreased by a mean of 13 bpm during PBG. In conclusion, the G-endurance was not deteriorated with PBG, in comparison with NB, during heat stress. In conjunction with experiences from other studies, however, it emphasizes the importance of avoiding heat stress and dehydration during G-loads, even with PBG.     

Concurrent loss of consciousness and sino-atrial block during +Gz stress.

Current USAF fighter aircraft easily exceed human physiologic limits with their rapid onset of head-to-foot acceleration forces (+Gz). Sudden in-flight incapacitation caused by these increased +Gz forces could be disastrous with loss of materiel and human life. The physiologic mechanisms responsible for loss of consciousness (LOC) secondary to high +Gz must be fully understood so that maximum protection against it can be provided. An interesting case of an episode of LOC with concurrent sino-atrial block occurring during a relaxed rapid onset (1 G/s) centrifuge run is presented. The patient was undergoing flight medical evaluation for an episode of syncope, etiology unknown. An unusual characteristic of the patient was his high level of endurance training. The possibility of an excessive increase in vagal tone, developed by endurance training, is discussed as a probable etiology for this patient's prolonged time of incapacitation evidenced after +Gz-induced loss of consciousness.