Study of the effectiveness of the "Centaur" anti-G suit [correction of suite] during exposure to +Gz accelerations after immersion

This paper describes a study of the effectiveness of the "Centaur" anti-G suit during exposure to +Gz accelerations before and after immersion. Results indicated that the subjects were better able to tolerate the acceleration using the "Centaur" suit than in control studies. Specific cardiovascular responses are presented. This suit has also been used successfully during space missions.     

Comparison of of techniques for measuring +Gz tolerance in man.

Two objective methods and one subjective method for measuring +Gz tolerance (inertial vector in a head-to-foot direction) were compared on the human centrifuge. Direct eye-level blood pressure (Pa), blood flow velocity in the superficial temporal artery (Qta), and subjective visual symptoms were used to determine tolerance to rapid onset acceleration (1 G/s) on the USAFSAM human centrifuge. Seven "relaxed" subjects with extensive centrifuge experience were exposed to gradually increasing +Gz plateaus until the subject reported 100% loss of peripheral centrifuge gondola lights (PLL) and 50% loss of central light (CLD); viz., blackout. Zero forward Qta occurred 6 s (range 4-9 s) before subjective blackout and when mean eye-level blood pressure had reached 20 +/- 1 mmHg (SE). The results of this study indicate that flow changes in the superficial temporal artery reflect flow changes in the retinal circulation during +Gz stress.     

Effect of increased acceleration on regional pleural pressure in dogs

The variation of pleural pressure was measured in anesthetized spontaneously breathing dogs subjected to increased acceleration (0-4 G) in a centrifuge. Two groups of animals were studied. In one group, the resultant acceleration was in a direction either ventral-to-dorsal (+Gx) or dorsal-to-ventral (-Gx), with a relatively small residual cranial-to-caudal acceleration. In the other group, the resultant acceleration was either cranial-to-caudal (+Gz) or caudal-to-cranial (-Gz), with a relatively small residual dorsal-to-ventral acceleration. Pleural liquid pressure (Ppl) was measured by two rib capsules that were separated by 7-9 cm and oriented either in the dorsal-to-ventral or cranial-to-caudal direction. At functional residual capacity, Ppl in the nondependent lung region became more negative when the acceleration was in the +Gx or +Gz direction. Thus the lung would be susceptible to damage that results from overexpansion in these acceleration directions. By contrast, acceleration in the -Gx or -Gz direction produced values of Ppl at functional residual capacity that were positive. Thus, in these acceleration directions, the respiratory muscles must provide greater force during inspiration to overcome lung compression before lung ventilation can occur. The Ppl gradients with respect to the acceleration directions increased approximately in proportion to acceleration in the +Gx, -Gx, and -Gz directions but remained relatively constant in the +Gz direction.     

Application of multivariate statistical analysis to estimate +Gz tolerance based on the changes of hemodynamic parameters during lower body negative pressure (LBNP)

The application of lower body negative pressure (LBNP) is very useful method for simulation of +Gz stress and for evaluation of orthostatic reaction. The different physiological changes that occur during LBNP test and +Gz acceleration test are similar. Lategola and Trent found that supine LBNP exposure at the level of -50 mmHg may be equivalent to +2Gz in producing the changes of heart rate (HR). Polese and coworkers compared hemodynamic changes occurring during upright and supine LBNP at the levels to -70 mmHg with identical measurements made during accelerations to +2Gz, +3Gz, and +4Gz in the same subjects. They noted for example that HR changes during upright LBNP exceeded HR supine levels. Peak values of HR during +3Gz and +4Gz significantly exceeded HR levels during both kinds of LBNP, but HR values at +2Gz were equivalent to those at -40 mmHg of upright and -70 mmHg of supine LBNP. So, the present study was undertaken to evaluate adaptating responses to LBNP stimulus at the level of -60 mmHg, regulatory mechanisms of the circulatory system (central and peripheral) and to look for the possibility of +Gz tolerance prediction based on the changes of some hemodynamic parameters during LBNP.     

Effect of oxygen and hypergravitation on alveolar surfactant

The effect of prolonged exposure (up to 66 hours) to pure oxygen breathing and to short (5-minute) oxygen breathing combined with acceleration (+5Gz) on the surface tension and surface potential of the alveolar washout of the albino rat lungs was determined. Both experimental conditions produced atelectasis and a decrease of the surfactant surface activity. Possible mechanisms of shifts of the surfactant activity under hyperoxia only, and hyperoxia with accelerations are discussed.     

Augmentation of the push-pull effect by terminal aortic occlusion during head-down tilt.

Tolerance to positive vertical acceleration (Gz) gravitational stress is reduced when positive Gz stress is preceded by exposure to hypogravity, which is called the "push-pull effect." The purpose of this study was to test the hypothesis that baroreceptor reflexes contribute to the push-pull effect by augmenting the magnitude of simulated hypogravity and thereby augmenting the stimulus to the baroreceptors. We used eye-level blood pressure as a measure of the effectiveness of the blood pressure regulatory systems. The approach was to augment the magnitude of the carotid hypertension (and the hindbody hypotension) when hypogravity was simulated by head-down tilt by mechanically occluding the terminal aorta and the inferior vena cava. Sixteen anesthetized Sprague-Dawley rats were instrumented with a carotid artery catheter and a pneumatic vascular occluder cuff surrounding the terminal aorta and inferior vena cava. Animals were restrained and subjected to a control gravitational (G) profile that consisted of rotation from 0 Gz to 90 degrees head-up tilt (+1 Gz) for 10 s and a push-pull G profile consisting of rotation from 0 Gz to 90 degrees head-down tilt (-1 Gz) for 2 s immediately preceding 10 s of +1 Gz stress. An augmented push-pull G profile consisted of terminal aortic vascular occlusion during 2 s of head-down tilt followed by 10 s of +1 Gz stress. After the onset of head-up tilt, the magnitude of the fall in eye-level blood pressure from baseline was -20 +/- 1.3, -23 +/- 0.7, and -28 +/- 1.6 mmHg for the control, push-pull, and augmented push-pull conditions, respectively, with all three pairwise comparisons achieving statistically significant differences (P < 0.01). Thus augmentation of negative Gz stress with vascular occlusion increased the magnitude of the push-pull effect in anesthetized rats subjected to tilting.     

A new evaluation method for +Gz tolerance with loratadine by using a near-infrared spectroscopy

Background

Loratadine (Claritin^®), an over the counter antihistamine in U.S. and UK, is acceptable for use without adverse side effects by aircrew with mild or moderate allergic or other situations requiring an antihistamine. Although +Gz (head to foot direction) tolerance testing for aircrew with loratadine has not been documented in the published literature, it is commonly accepted that loratadine dose not effect +Gz tolerance. The purpose of this study was to offer and validate a new evaluation method for +Gz tolerance testing with loratadine by using a near-infrared spectroscopy (NIRS).

Methods

A double-blind, placebo-controlled, randomized, crossover protocol was used to administer 10 mg of loratadine or placebo in nine healthy subjects. The subjects didn't wear anti-G suit. The +Gz exposure profiles consisted of, in series, a gradual onset ran (0.1 G·sec^-1) to the subject's visual end-point (peripheral light loss) or loss of consciousness (GLOC), and rapid onset run (1.0 G·sec^-1) to the subject's same end-point. In this study, G-level tolerance was defined as the +Gz level at visual end-point and/or at GLOC. As a subject's G-duration tolerance, we measured the total time (seconds) during rapid onset run. Otherwise, to confirm the effect of loratadine on +Gz tolerance, we measured the cerebral NIRS variables (hemoglobin concentration changes and tissue oxygenation index) as a new quantitative method for +Gz tolerance during a centrifuge experiments.

Results

No significant differences were observed in +Gz tolerance (+Gz level, duration time and NIRS variables) between subjects taking loratadine and placebo.

Conclusion

Our results demonstrate that loratadine has no detectable effect on +Gz tolerance by using a new method with cerebral NIRS variables and the traditional method with +Gz level and duration time. This study represents the first use of a quantitative parameter such as cerebral NIRS variables to assess the effects of a drug on acceleration tolerance.

     

Disruption of Spatial Task Performance in Anorexia Nervosa

In anorexia nervosa (AN), body distortions have been associated with parietal cortex (PC) dysfunction. The PC is the anatomical substrate for a supramodal reference framework involved in spatial orientation constancy. Here, we sought to evaluate spatial orientation constancy and the perception of body orientation in AN patients. In the present study, we investigated the effect of passive lateral body inclination on the visual and tactile subjective vertical (SV) and body Z-axis in 25 AN patients and 25 healthy controls. Subjects performed visual- and tactile-spatial judgments of axis orientations in an upright position and tilted 90° clockwise or counterclockwise. We observed a significant deviation of the tactile and visual SV towards the body (an A-effect) under tilted conditions, suggesting a multisensory impairment in spatial orientation. Deviation of the Z-axis in the direction of the tilt was also observed in the AN group. The greater A-effect in AN patients may reflect reduced interoceptive awareness and thus inadequate consideration of gravitational inflow. Furthermore, marked body weight loss could decrease the somatosensory inputs required for spatial orientation. Our study results suggest that spatial references are impaired in AN. This may be due to particular integration of visual, tactile and gravitational information (e.g. vestibular and proprioceptive cues) in the PC.     

Loss of consciousness as criterion of +Gz tolerance at Institute of Aviation Medicine MMA during +Gz acceleration selective test

+Gz induced loss of consciousness (G-LOC) is one of the most serious threats to aircrews flying high performance fighter aircraft. From the early beginning of use of our Centrifuge, use in selection was primary task. As a functional "endpoints" we use criteria: loss of peripheral vision, extreme pulse rate (above 180 b.p.m.), arrhythmias and loss of consciousness. The key-method in selection the candidate who tolerates +Gz stress on the best way is selection by common selective centrifuge "Test of linear increasing of acceleration" (TOLIA). We used gradual onset rate (GOR--0.1 G/s) and maximum/peak value: +5.5 Gz, +6.0 Gz and 7.0 Gz. Applied peak value depends on the goal of the test. The lowest peak value is for candidates planned for Air Academy, higher peak value is for those pilots planned for training to supersonic combat aircrafts and the highest peak value is for pilots who are planned to fly High performance combat aircrafts. We examined 2192 candidates in the last 20 years. Eleven subjects experienced G-LOC episodes. All episodes of G-LOC had occurred occasionally and without warning symptoms (loss of peripheral vision, gray out, blackout). The percentage of subjects having G-LOC episodes was 0.50%. Nine subjects experienced G-LOC during primary selection (+5.5 Gz), one G-LOC were observed at secondary selection (+6.0 Gz) and one G-LOC was observed during tertiary selection (+7 Gz). G-LOC is the only "endpoint" in the centrifuge selection which disqualifies the candidate at once and forever for planned flying duties. The other "endpoints" (loss of peripheral vision, heart rate above 180 b.p.m., arrhythmias) allow one more testing, not less than seven days later.     

正加速度重复暴露后大鼠心室肌缝隙连接蛋白43表达及分布的改变

本文旨在探讨不同水平的一周重复多次正加速度( Gz)暴露后大鼠心室肌缝隙连接蛋白43(connexin 43, Cx43)表达及分布的改变.36只雄性Sprague-Dawley大鼠随机分为对照组、 6Gz组和 10Gz组,每组12只. Gz组大鼠分别暴露于 6Gz和 10Gz各3min,1次/d,共1周,分别于末次暴露后即刻、1d、3d、7d(各3只)取心室肌作免疫组织化学染色和Western blot分析,检测Cx43的表达和分布.免疫组织化学结果显示, Gz重复暴露可引起大鼠心室肌Cx43分布方式明显紊乱,Cx43在心肌细胞侧-侧连接处的表达明显增加,在心肌细胞端-端连接处的表达减少.Western Blot结果显示, 6Gz组与 10Gz组的Cx43蛋白表达量于末次暴露后即刻、1d、3d、7d与对照组相应时刻相比均明显减少(P<0.001),以暴露后即刻减少最为明显,且随着 Gz暴露时间的延长,表达逐渐恢复,但在暴露后7d,两组的Cx43表达量仍未恢复至对照组水平.Cx43蛋白表达的上述改变在 10Gz组比 6Gz组更为显著.以上结果提示 Gz重复暴露可引起大鼠心室肌Cx43表达量的一过性减少,分布方式明显紊乱,这种改变很可能是 Gz致心律失常发生的重要原因之一.     

Tolerance of snakes to hypergravity

Sensitivity of carotid blood flow to increased gravitational force acting in the head-to-tail direction(+Gz) was studied in diverse species of snakes hypothesized to show adaptive variation of response. Tolerance to increased gravity was measured red as the maximum graded acceleration force at which carotid blood flow ceased and was shown to vary according to gravitational adaptation of species defined by their ecology and behavior. Multiple regression analysis showed that gravitational habitat, but not body length, had a significant effect on Gz tolerance. At the extremes, carotid blood flow decreased in response to increasing G force and approached zero near +1 Gz in aquatic and ground-dwelling species, whereas in climbing species carotid flow was maintained at forces in excess of +2 Gz. Tolerant (arboreal) species were able to withstand hypergravic forces of +2 to +3 Gz for periods up to 1 h without cessation of carotid blood flow or loss of body movement and tongue flicking. Data suggest that the relatively tight skin characteristic of tolerant species provides a natural antigravity suit and is of prime importance in counteracting Gz stress on blood circulation.     

Eye movements induced by linear acceleration in humans.

The otolith-function study is remarkably behind the semicanal-function study. In the present paper, we introduced briefly our on-going studies on eye movements including nystagmic elicitation during lateral (Gy) linear acceleration with step and sinusoidal modes using a sled-type accelerator. The eye movements were recorded by EOGs (DC) from subjects who looked at an imaginary target of their straight ahead in darkness during G-loading up to 0.5 G. Corresponding to the +Gy and -Gy segments, nystagmus and/or deviation in eye position were frequently induced in some subjects, but none or slightly in the other. The nystagmus changed the beating direction dependently on the Gy direction, while the eye-deviation could be either direction of compensatory or anticompensatory. In half of subjects, nystagmus elicitation was absent or low at 0.3 G, while it tended to increase above 0.3 G. The nystagmic elicitation was similar to each other between the both modes of acceleration, and directional preponderance (DP) was observed in some subjects. There was no correlation between the DP and the nystagmic slow-phase velocity. Functional meanings of these findings were discussed.     

Central venous pressure in humans during short periods of weightlessness

Central venous pressure (CVP) was measured in 14 males during 23.3 +/- 0.6 s (mean +/- SE) of weightlessness (0.00 +/- 0.05 G) achieved in a Gulfstream-3 jet aircraft performing parabolic flight maneuvers and during either 60 or 120 s of +2 Gz (2.0 +/- 0.1 Gz). CVP was obtained using central venous catheters and strain-gauge pressure transducers. Heart rate (HR) was measured simultaneously in seven of the subjects. Measurements were compared with values obtained inflight at 1 G with the subjects in the supine (+1 Gx) and upright sitting (+1 Gz) positions, respectively. CVP was 2.6 +/- 1.5 mmHg during upright sitting and 5.0 +/- 0.7 mmHg in the supine position. During weightlessness, CVP increased significantly to 6.8 +/- 0.8 mmHg (P less than 0.005 compared with both upright sitting and supine inflight). During +2 Gz, CVP was 2.8 +/- 1.4 mmHg and only significantly lower than CVP during weightlessness (P less than 0.05). HR increased from 65 +/- 7 beats/min at supine and 70 +/- 5 beats/min during upright sitting to 79 +/- 7 beats/min (P less than 0.01 compared with supine) during weightlessness and to 80 +/- 6 beats/min (P less than 0.01 compared with upright sitting and P less than 0.001 compared with supine) during +2 Gz. We conclude that the immediate onset of weightlessness induces a significant increase in CVP, not only compared with the upright sitting position but also compared with the supine position at 1 G.     

Relations between the errors of targeted movements and inexactitude of visual perception of space

Errors of targeted movements of the arm to the places of presentation of light targets (in darkness) were studied in healthy subjects kept in a vertical position or laying on their backs. An error along theY axis (corresponding to the longitudinal body axis) changed its sign depending on the body orientation with respect to the gravitation vector. In the vertical position, the arm shifted to the feet at the movement’s termination, while in the laying position it shifted to the head. AnX error showed no dependence on the position of the body in space. The errors reached their maxima in the absence of visual control, but became two-three times smaller when the tested subject could observe the position of an indicator (light diodes) fixed on the end of the index finger (or of a pointer rod). When the spatial positions of targets were reconstructed according to verbal “indications”, the amplitudes ofX andY errors appeared similar to those at real movements (indication under visual control). In this case, the sign ofY errors also depended on the body orientation, but their direction was opposite. We suppose that systematicY errors at the targeted arm movements are determined not only by an antigravitation component of the motor program, but also by shifting of a sensory visual estimations of the spatial target position.     

Increased gravitational stress does not alter maximum expiratory flow

We measured maximum expiratory flow-volume (MEFV) curves in six seated subjects during normal (+1 Gz) and increased (+2 and +3 Gz) gravitational stress. Full MEFV curves, initiated at total lung capacity, were recorded, as were partial MEFV curves, initiated at approximately 60% of the vital capacity. Data were acquired in all subjects breathing air at +1 and +2 Gz; results were available for three subjects breathing 80% He-20% O2 at +1 and +2 Gz, and in two subjects, results were obtained at +3 Gz. Changes in gravitational stress were not associated with changes of either full or partial MEFV curves. The known increase in differences of regional lung volume and recoil caused by increased gravitational stress did not influence maximum expiratory flow. Though increased gravitational stress probably changed regional emptying sequences little during full MEFV maneuvers, substantial changes of emptying sequence were expected during partial maneuvers. It is possible that such changes in emptying sequence occurred but were not associated with changes in maximum flow because the latter was determined by choking in central airways common to all regions.     

Brief exposure to -2 Gz reduces cerebral blood flow velocity during subsequent +2 Gz acceleration

In order to determine the implication of the cerebral vasoconstriction occurring under -Gz acceleration in the mechanism of the push-pull effect, four healthy male non-pilots were submitted to a control centrifugation at +2 Gz, and then to an experimental run with identical +2 Gz plateau, but preceded by -2 Gz exposure. Cerebral blood flow velocity (CBFV), pulsatility index, and resistance index (RI) were continually measured with a transcranial Doppler instrument. The decrease in blood pressure and in CBFV was more important during the experimental run, when the change in RI was not different. We concluded that the cerebral vasoconstriction occurring under -2 Gz exposure seems not to be a major contributor in the mechanism of the push-pull effect appearing during subsequent +2 Gz acceleration.     

大鼠正加速度高耐力相关基因的分离

 为从基因水平上揭示正加速度 (+Gz)高耐力产生机理及寻找 +Gz高耐力相关功能性蛋白 ,利用抑制消减杂交技术分离 +Gz高耐力相关基因 .雄性SD大鼠在离心机上处理后 ,选取耐受终点在高、低两个极端的动物 ,立即取全脑 ,分离mRNA .以高耐力者为Tester ,低耐力者为Driver,利用抑制消减杂交技术进行 +Gz耐力处于高、低两个极端动物脑组织间基因表达差异显示 ,获得 +Gz高耐力大鼠脑组织相关cDNA .以高、低耐力大鼠脑组织mRNA来源的cDNA为探针 ,对获得的cDNA克隆进行斑点杂交 .分别以杂交筛选出的阳性克隆为探针 ,对高、低耐力大鼠脑组织总RNA进行Northern杂交分析 .两次杂交结果均选择高耐力组杂交信号是低耐力组 3倍以上的cDNA克隆 .经过斑点杂交筛选 ,从大鼠脑组织中获得了 6 7个在 +Gz高耐力大鼠脑组织中上调表达的cDNA克隆 .Northern杂交分析发现 ,钙离子 钙调蛋白依赖性蛋白激酶Ⅱβ亚基 (Camk2b)和一未知基因在 +Gz高耐力大鼠脑组织中的表达量增加 .结果提示 ,+Gz耐力处于高、低两个极端的大鼠脑组织基因表达有明显差异 ,这些差异表达的基因很可能与 +Gz高耐力的产生有关 ,且钙离子 钙调蛋白依赖性蛋白激酶Ⅱβ亚基和一未知基因是初步获得的与 +Gz高耐力的产生特异相关的基因     

Angular acceleration,compensatory head movements and the halteres of flies (Lucilia serricata)

Summary Tethered flies were subjected to accelerations about their vertical axes while flying or walking. These accelerations were applied either suddenly to stationary animals or continuously by oscillating the animal from side to side. Head and wing movements resulting from the imposed angular accelerations were photographed with a camera and a stroboscopic flash.Analysis of the photographs shows that the wing movements act to counter the imposed angular accelerations and that during sinusoidal oscillations about the vertical axis, head turns are in antiphase with angular acceleration.Head turns do not occur when the halteres are absent or present and not oscillating. When oscillating, the halteres detect high values of angular acceleration, outside the known capabilities of the visual movement detection system.     

Reactions of dace to linear accelerations

It is demonstrated that the rheophilic fish dace ( Leuciscus leuciscus ) is able to detect the direction of its movements in a water flow by perceiving and analysing positive and negative accelerations from 15 up to 50 cm s⁻², by the use of labyrinth organs. Tests were conducted on fish with 'switched off' mechanoreceptors and labyrinth organs, under conditions which eliminated the use of visual orientation. It was also demonstrated that the values of linear accelerations which stimulated dace compensatory movements against water currents were comparable with the values of accelerations which could arise in river flows as a result of pulsation in current velocity. The results support the hypothesis that rheophilic fish are able to use inertial stimuli for their spatial orientation.