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PubMed2003

Acute soft tissue neck injury from unexpected acceleration.

Recent evidence has identified a risk of neck injury resulting from exposure to high sustained G force during operation of fast jet military aircraft. This review considers the risk of acute soft tissue neck injury when exposure to acceleration is unexpected by the individual. In a military jet, this might occur to a back seat occupant such as an instructor or weapons operator/navigator, but unexpected forces may also be encountered by roller coaster riders and human centrifuge users under certain conditions. The mechanisms of injury in this situation are examined, the effect of acceleration axes (Gx, Gy, and Gz) are considered, and relevant experimental data are evaluated. These data are used to determine what influence the unexpected nature of the acceleration exposure has on the risk of neck injury. Injury below previously established 'tolerance' limits is possible, with some individuals being at risk from unexpected acceleration exposure above around +2 to .

Aerospace Medicine↗
PubMed2003

Changes of cardiac catecholamines in rats after repeated +Gz exposures and protective effects of low-G preconditioning and tea polyphenols.

OBJECTIVE: To observe whether repeated +Gz exposures could induce metabolic disorder of cardiac catecholamines in rats as well as the protective effects of low-G preconditioning and tea polyphenols (TP). METHOD: Thirty-two male Wistar rats were randomly divided into 4 groups (n=8): group A (control), only submitted to +1 Gz 5 min; group B (+10 Gz stress), exposed to +10 Gz 30 s, 5 times/d with +1 Gz 1 min interval, 3 d/wk, for 3 wk in total; group C (low G preconditioning), +Gz stress parameters were the same to that of group B, but the rats were submitted to +2 Gz 5 min 1 h prior to +10 Gz exposure; group D (TP protection), + Gz stress parameters were the same to that of group B, but TP was given orally to the rats at the dose of 200 mg/kg 1 h prior to +10 Gz exposure. These animals were decapitated on the next morning of the last centrifuge run, and the hearts were taken out and stored in liquid nitrogen immediately. The contents of noradrenaline (NA), adrenaline (AD), dopamine (DA) and serotonin (5-HT) in myocardial tissue were determined using HPLC with electrochemical detector. RESULT: Compared with group A, AD level in group B increased significantly (P < 0.01), but there were no significant differences of NA, DA and 5-HT contents between the two groups. Compared with group B, the myocardial contents of AD and 5-HT were decreased significantly in group C and D (P<0.01), while myocardial DA concentration in group D increased significantly (P<0.01). CONCLUSION: Repeated +10 Gz exposures could induce metabolic disorder of catecholamines in rat heart, especially the increase of AD level. Low-G preconditioning and natural antioxidant TP had significant protective effects.

Acceleration↗
PubMed2003

[Changes of dentin, dental pulp and periodontium tissue in tail-suspended rats].

OBJECTIVE: To investigate the metabolic changes of calcium and phosphorus in dentin, dental pulp and periodontium in tail-suspended rats, and the functions of TGF-beta 1, c-fos, collagen-I and collagen IV in dentin, dental pulp and periodontium. METHOD: Relative percentage contents of Ca, P in dentin, dental pulp and periodontium were measured with scanning electron microscope and energy spectrum analytical system in 3 groups of rats. The expression of TGF-beta 1, c-fos, collagen-I and collagen IV were also observed. RESULT: In the suspension group, the relative percentage content of Ca declined significantly, while P increased slightly. There were no significant differences of Ca, P in alveolar bone. The expressions of TGF-beta 1, c-fos and collagen-I declined, but the expression of collagen-IV in pulp vessel increased. There were no significant changes of expressions of TGF-beta 1, c-fos, collagen-I and collagen-IV in the vicinity of PDL. After adopting artificial countermeasures, the above expressions restored partly. CONCLUSION: Weightlessness might cause abnormal mineralization in dentin, and 1.5 G artificial countermeasures could eliminate the above changes of mineral metabolism. The poor mineralization of dentin might be associated with the reduced secretion of TGF-beta 1, c-fos and collagen-I in tail-suspended rats.

Animals↗
PubMed2003

Effects of gravitational loading on rat soleus muscle fibers following hindlimb suspension.

Effects of 16 days of hindlimb suspension and 16 days of ambulation recovery at 1-G or 2-G environment on the characteristics of soleus muscle fibers were studied in male Wistar Hannover rats. The mean cross-sectional area and myonuclear number in isolated single fibers at the termination of suspension were approximately 30% and 25% of the controls, respectively. Satellite cells were distributed evenly throughout the fiber length in the control. However, the number of satellite cells distributed at the middle of the fiber was less in the unloaded rats immediately after the termination of suspension. Both the numbers of quiescent and mitotic active satellite cell per fiber were approximately 57% less immediately after the termination of suspension than controls. The number of satellite cells at the end of fibers was increased first during the early phase of reloading. Subsequently, the number at the middle was gradually increased. The myonuclear number per fiber was also less (approximately 25%) in the unloaded than the age-matched control at the termination of suspension, but was increased following the recovery. Although the mean in vivo sarcomere length of the soleus muscle was shortened in response to plantarflexion of ankle joint, the length at the certain ankle joint angle was increased after 16 days of suspension due to sarcomere remodeling. The length at the proximal and distal, rather than the middle, portion of the fiber was stretched in both reloaded and control rats in response to dorsiflexion of the ankle joint. But it was noted that the magnitude of stretch was greater in the unloaded rats. It is suggested that the fiber end is more stimulated rapidly than the middle portion by the load applied to the muscle during the ambulation recovery.

Animals↗
PubMed2003

Effects of high gravity on amphibian development.

In order to clarify the possible effects of high gravity environments on eggs and developing embryos, Rana rugosa and Xenopus laevis fertilized eggs and early embryos were raised in 2 G, 5 G, 7 G and 10 G up to the hatched tadpole stage. The results showed that: (1) High gravity significantly retarded the development of eggs and embryos beginning treatment before the blastula stage and induced various abnormalities, including two heads and microcephally suggesting that high gravity is apt to disrupt the animal-vegital axis. On the other hand, embryos beginning treatment after the gastrula stage showed a striking increase in the number of normal-appearing feeding tadpoles. (2) Autopsy revealed that brains, notochords and muscles were reduced in development and differentiation for embryos and tadpoles developed in high gravity. (3) It seems likely that the system for hydrogen peroxide detoxification develops abnormally in high gravity-treated embryos and tadpoles, which probably results in oxidative stress, leading to considerable cell damage.

Animals↗
PubMed2003

Effects of parabolic flight on abdominal arterial pressure in conscious rats.

Abdominal arterial pressure during parabolic flight was measured using a telemetry system to clarify the acute effect of microgravity on hemodynamics in conscious rats. The microgravity condition was elicited by three different levels of entry gravity, i.e. 2 G, 1.5 G and 1 G. On exposure to 2 G, mean aortic pressure (MBP) increased up to 118.7 mm Hg +/- 7.3 compared with the value at 1 G (107.0 +/- 6.3 mm Hg, n=6). The value at microgravity preceded by 2 G was 118.0 mmHg +/- 5.2 mm HG and it was still higher than at 1 G. When 1.5 G was elicited before microgravity exposure, MBP also increased (1.5 G: 114.9 +/- 5.3 vs 1 G: 105.8+/-5.0 mm Hg) and the value at microgravity was 117.3 + /- 5.3 mmHg. During pre-microgravity maneuver with 1 G, no changes were observed compared with the control level at 1 G (pre-microgravity: 105.0 +/- 5.0 vs 1G: 104.8 +/- 5.1 mm Hg ), whereas the MBP increased up to 117.0 +/- 6.5 mm Hg on exposure to microgravity. From these results, we found that in conscious rat MBP increase during acute microgravity exposure with either 1 G or hyper-G entry.

Animals↗
PubMed2003

Changes of bone morphology in response to hindlimb suspension of rats.

Effects of chronic hindlimb suspension or exposure to 2-G from postnatal day 4 to month 3 followed by ambulation recovery on the floor on the morphology of hindlimb bones were investigated in rats. The dorsi-flexion of the ankle was inhibited in the suspended group and such phenomena were not recovered at all. The mean weight and length of femur, tibia, and fibula were less than the cage controls at the end of suspension, but gradually increased during recovery. However, they were still less than those of the age-matched controls even after 3-month recovery. External bending of shaft and rotation of distal end of tibia were observed in the suspended group and these phenomena were not recovered at all. These morphological changes caused the inhibition of dorsi-flexion of ankle joints. The electromyogram activities of ankle plantar-flexors, soleus, plantaris, lateral gastrocnemius, were inhibited and those of dorsi-flexor, tibialis anterior, were increased during suspension. Typical changes in bone morphology were not induced by exposure to 2-G. It was suggested that gravitational unloading during developing period causes irreversible inhibition of normal bone growth. It was also indicated that the suspension-related changes in bone morphology may be caused by abnormal mechanical stress due to the altered mobilization of hindlimb muscles.

Animals↗
PubMed2002

Changes in left ventricular size during parabolic flights by two-dimensional echocardiography and level set method.

This study aims to evaluate changes on cardiac chambers size, induced by gravitational stresses. During parabolic flight, seven subjects underwent 2-D transthoracic echocardiography at three different gravity phases (1 Gz, 1.8 Gz, and 0 Gz). LV endocardial borders were detected applying a semi-automatic segmentation procedure based on level set methods. LV cavity area was computed frame-by-frame for a whole cardiac cycle during each gravity phase. Expected modifications in LV area with different gravity were found: at 1.8 Gz, end-diastolic (ED) and end-systolic (ES) areas were significantly (p<0.05) reduced of 10.7 +/- 5.4% and 21.6 +/- 11.1% respectively, compared to 1 Gz values, while they were increased of 11.2 +/- 5.4% and 11.1 +/- 6% during 0 Gz. Fractional area change was augmented of 20.9 +/- 29.1% at 1.8 Gz, while it remained unchanged at 0 Gz, compared with 1 Gz values. Furthermore, LV filling due to atrial contraction was increased at 0 Gz of 39 +/- 35.6%.

Adult↗
PubMed2003

[Injuries caused by in-flight ejection].

The localization, causes and severity of 214 "ejection-associated" injuries occurred in 160 pilots are discussed. Spine, upper and lower extremities are affected most frequently. The severe injures prevail (57.8%). The main causes of severe injuries are the impact + Gz accelerations of ejection and the impact + Gz accelerations of landing.

Accidents, Aviation↗
PubMed2004

Acceleration in other axes affects +Gz tolerance: dynamic centrifuge simulation of agile flight.

BACKGROUND: Modern, thrust-vectored jet aircraft have the capability of developing multi-axis accelerations, especially during the performance of "supermaneuvers." These "agile" aircraft are capable of unconventional flight. The human consequences of this agile flight environment are unknown. METHODS: This multi-axis acceleration environment was studied on the Dynamic Environment Simulator gimbaled centrifuge. There were nine relaxed, unprotected subjects who were exposed to either lateral (+/- 1, +/- 2 Gy), transverse chest-to-back (+1, 2.5, or 4 Gx), or back-to-chest (-1 Gx) sustained acceleration. Positive C (+Gz) acceleration was then added beginning at 1.0 Gz by gradual onset (0.1 Gz x s(-1)) until the subjects lost nearly all of their vision. Baseline +Gz-only relaxed tolerances were measured before and after all combined Gy/Gz and Gx/Gz exposures. Heart rate, percent cerebral oxygen saturation, and cerebral blood volumes were collected during each exposure. RESULTS: Adding moderate transverse (+Gx) acceleration significantly reduced +Gz tolerance. Relaxed, unprotected +Gz tolerance was reduced approximately 0.25 G when 1.0 or 2.5 Gx was added to the increasing +Gz exposure. Adding moderate lateral Gy significantly increased +Gz tolerance. Relaxed, unprotected +Gz tolerance was increased approximately 0.5 G when +2 Gy or -2 Gy was added to the -Gz exposure. The decrease in cerebral blood volume was significantly less when +Gz was added to -1 Gx compared with the addition of +Gz to +Gx. CONCLUSIONS: Multi-axis sustained accelerations, such as those experienced during thrust-vectored aircraft maneuvers, can either enhance or reduce the +Gz tolerance of the pilot depending on the direction of the net gravitoinertial force. Gy acceleration in conjunction with Gz acceleration can enhance G tolerance. Gx acceleration in addition to Gz acceleration can reduce G tolerance.

Acceleration↗
PubMed2004

Neck muscle strength and endurance in fighter pilots: effects of a supervised training program.

INTRODUCTION: Cervical discomfort is common among pilots of high performance aircraft. An exercise program was introduced to increase the strength and endurance of the neck muscles. The purpose of this study was to analyze whether coaching or reinforcement strategies by a physical therapist was associated with improvement in neck muscle strength, endurance, and neck complaints in two cohorts of fighter pilots performing regular neck muscle exercises. METHODS: A reinforced group (RG) of 20 pilots (24-40 yr) at an Air Force base received weekly encouragement to perform their standardized exercise program three times per week. A non-reinforced reference group (NRG) of 20 pilots (23-37 yr) from another Air Force base carried out the same program without any supervision. Both groups performed the training program for 6-8 mo. Before and after the training period, isometric measurements of the neck flexors and neck extensors were performed in both groups. RESULTS: After the completion of the 6-8 mo training period, the RG pilots significantly increased their neck muscle strength (flexors: M = 3.9 nm, p = 0.000 and extensors: M = 5.0 nm, p = 0.001) as well as endurance in their neck extensors (M = 53 s, p = 0.000). The NRG pilots significantly decreased both strength (M = 11.5 nm, p = 0.0001) and endurance (M = 33 s, p = 0.003) of their neck extensors. Furthermore, the NRG pilots did not show any significant change of their neck flexor strength. No significant changes in the frequency of neck complaints were reported in either group throughout the entire study period. CONCLUSION: The reinforced training program increased the strength and endurance of the appropriate muscle groups. In order to draw any further conclusions concerning reducing neck complaints, a longer observation period with a larger group of pilots might be needed. However, it is likely that there is an individual correlation between strength and endurance of the neck muscles and neck pain, which means that any rehabilitation program should be tailored for each individual.

Accidents, Occupational↗
PubMed2004

High-risk head and neck movements at high G and interventions to reduce associated neck injury.

BACKGROUND: Neck injuries are a significant concern for aviators of high performance aircraft. A recent comprehensive technical report on cervical spinal injury associated with exposure to sustained acceleration, from NATO's Research and Technology Organization, recommended delineating the neck muscles used by aviators in this flying environment and developing improved neck muscle strengthening programs in an attempt to reduce such injuries. METHODS: A review of current literature was conducted in the fields of biomechanics, ergonomics, orthopedics, neurology, neurosurgery, rehabilitative medicine, and aerospace medicine. An objective description is provided of the muscles involved in specific head and neck movements, and those movements that are associated with a greater risk of injury during high-G sorties. The intensity and duration of force exposures common to high performance aircraft sorties, the effects of seat-back angle on these exposures, and the types and mechanisms of neck injury reported in this environment are also described. RESULTS: Primary, secondary, and tertiary preventive interventions are introduced with the goal of providing unit-level flight surgeons an approach to reducing neck injury and promoting prompt, safe return to flying of aviators with identified neck injury. A central component of these interventions is a "specific" and "intensive" neck muscle training regimen, as described in the medical literature. CONCLUSION: Increased axial compressive force and unique biomechanics combine to make neck injury likely in high performance aviators. The application of some proposed intervention strategies may reduce the occurrence of these injuries.

Acceleration↗
PubMed2004

Preventing G-induced loss of consciousness: 20 years of operational experience.

INTRODUCTION: Although anecdotal reports of G-induced loss of consciousness (G-LOC) in military aviation date back to before 1920, regular reporting did not begin until 1982. The effectiveness in the operational setting of G-LOC preventive measures, such as positive pressure breathing for G protection (PBG), has not been studied. METHODS: We use the term "crash" to represent an event where the aircraft was destroyed and "incident" to define those events where the crew reported a G-LOC episode and the aircraft was not damaged. Data on G-LOC crashes, incidents, and aircraft sorties (number of take-offs) were obtained from the USAF Safety Center database for FY 82-01. RESULTS: During FY 82-01, there were 29 G-LOC crashes while those aircraft at risk of G-LOC crashes flew a total of 13,959,816 sorties. Poisson regression showed a non-significant decrease in crashes with an incidence rate ratio (IRR) of 0.096 (CI 0.89-1.03) (4% per yr). G-LOC crashes decreased from 4.4 per million flight sorties (PMFS) to 1.6 after the implementation of anti-G-LOC training programs beginning in 1985. However, G-LOC crashes remained unchanged after implementation of PBG in 1995. In contrast, incidents showed an IRR of 1.04 (CI 1.02-1.06) for G-LOC incidents, an estimated increase of 5% per yr. DISCUSSION: The physical/mechanical limitations of PBG, risk homeostasis, and the possibility that G-LOC rates have reached their asymptotic minimum are all discussed as possible explanations for the failure of PBG to decrease G-LOC crashes.

Accidents, Aviation↗
PubMed2004

An electromyographic assessment of the anti-G straining maneuver.

BACKGROUND: The anti-G straining maneuver (AGSM), used by aircrew to enhance their +Gz tolerance and to reduce the potential risk of G-induced loss of consciousness, has been recognized as an effective technique. The purpose of this study was to establish an objective tool to evaluate the effectiveness of an aircrew member's AGSM. METHODS: There were 20 healthy subjects who participated in the study, including 8 senior aviation physiological trainers and 12 trainees. The former were familiar with the anti-G maneuver and had experienced high +Gz exposure, the latter had never been exposed to any high +Gz stress before the study. The analytic method of electromyography (EMG) was used to investigate the physical characteristics of the L-1 AGSM. RESULTS: Comparison of the EMG data from the two groups indicated that the mean duration of a breathing cycle of the trainer group was significantly longer than that of the trainee group (p < 0.001). The buccinator was the muscle that had the most rapid firing rate in both groups (p < 0.001). The trainer group had a significantly faster firing rate of the buccinator than the trainee group (p = 0.03). In addition, the trainee group performed the AGSM with a firing sequence of muscles that was different from that of the trainer group. CONCLUSIONS: An automated and quantitative system based on EMG can be used during AGSM training to augment or replace the current subjective evaluation of the trainee's performance.

Abdomen↗
PubMed1995

Ballistocraft: a novel facility for microgravity research.

One of ESA's aims is to provide the microgravity research community with various microgravity exposure facilities. Those facilities include drop towers, sounding rockets, and parabolic flights on board aircraft, in addition to orbital spacecraft. Microgravity flights are usually achieved using large aircraft like the French 'Caravelle' that offer a large payload volume and where a person can be present to perform the experiments and to participate as a human test-subject. However, the microgravity community is also very interested in a flexible, complementary facility that would allow frequent and repetitive exposure to microgravity for a laboratory-type of payload. ESA has therefore undertaken a study of the potential of using a 'ballistocraft', a small unmanned aircraft, to provide a low-cost facility for short-duration (30-40 seconds) microgravity experimentation. Fokker Space & Systems performed the study under an ESA contract, supported by Dutch national funding. To assess the ballistocraft, a simple breadboard of the facility was built and flight tests were performed. The ability of the on-board controller to achieve automated parabolic flights was demonstrated, and the performance of the controller in one-g level flights, and in flights with both zero-g and partial-g setpoints, was evaluated. The partial-g flights are a unique and valuable feature of the facility.

Aircraft↗
PubMed2003

[Application of sensitivity analysis method in mode analysis of hypergravitation training facility].

OBJECTIVE: To increase the natural frequencies of hypergravitation training facility. METHOD: The natural frequencies of the hypergravitation training facility were modified by using sensitivity analysis method. RESULT: The natural frequencies of the hypergravitation training facility were improved by modification of physical and geometrical parameters of sensitive elements. CONCLUSION: The computational results indicates that sensitivity analysis method is feasible.

Astronomical Phenomena↗
PubMed2003

[Human-centered ergonomical study and applications in manned spacecraft project of China].

High G and weightlessness are two important environment factors that are unavoidable during spaceflight. They will bring key effects on astronauts' posture and working efficiency. In this paper, on the basis of experience of China first manned spacecraft project in the past 10 years, the concept of space ergonomics and its role in the project were reviewed. Ergonomic research items and corresponding methods were systematically analyzed with astronauts' working state, and ergonomic evaluation types and approaches were discussed with some given cases being used in the project. Finally, some suggestions were proposed on space man-machine system development according to recent ergonomic trend in space ergonomics and the basis of experience of first manned spacecraft project.

Aerospace Medicine↗
PubMed2004

[Effects of repeated lower g exposures on high-G induced memory and balance changes in rats].

OBJECTIVE: To study the protective effects of repeated +4 Gz/3 min exposures on memory and balance changes induced by +10 Gz/5 min exposure in rats. METHOD: 32 male SD rats were randomly divided into 4 groups: control group (C) ; +10 Gz/5 min group (10 Gz); 3 d training group (3 d) ; 5 d training (5 d) group (exposed to +4 Gz/3 min per day for 3 or 5 days before +10 Gz/5 min exposure). Changes of memory and balance in rats of all the 4 groups were observed after +10 Gz/5 min exposure. RESULT: In +10 Gz group, the percentage of correct reaction (CR) decreased significantly at all times after +10 Gz exposure (P<0.01), and the reaction time (RT) lengthened significantly at all times after +10 Gz exposure (P<0.01); as compared with control group. In 3 d training group, CR decreased significantly at 1 d, 2 d and 6 d after +10 Gz exposure (P<0.05), RT lengthened significantly at all times after +10 Gz exposure (P<0.05); as compared with control group. CR increased significantly at 2 d, 4 d and 6 d after +10 Gz exposure (P<0.01), RT shortened significantly at 1 d, 2 d, 4 d and 6 d after +10 Gz exposure (P<0.01) as compared with +10 Gz group. In 5 d training group, there were no apparent changes compared to control group; but CR increased significantly and RT shortened significantly at the time of 1 d, 2 d, 4 d and 6 d after +10 Gz exposure (P<0.01) as compared with +10 Gz group. Balancing function (BF) of +10 Gz group decreased significantly immediately and 2 d after +10 Gz exposure (P<0.01) as compared with control group. BF in 3 d and 5 d training group improved significantly immediately and 2 d after +10 Gz exposure as compared with +10 Gz group (P<0.01). CONCLUSION: It is suggested that repeated low +Gz exposures could provide protective effect on memory and balance changes induced by high +Gz exposure in rats.

Acceleration↗