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At least 1,099 records · Page 61Linked to original sources
PubMed2004

[Effects of combined stress of high +Gz and noise on learning and memory in rats].

OBJECTIVE: To study the effect of combined stress of noise and + Gz on learning and memory in rats. METHOD: Thirty-two male SD rats were randomly divided into 4 groups: control group, +10 Gz/3 min group, 90 dB(A)/30 min noise group, combined stress group (+10 Gz/3 min and 90 dB(A)/30 min), 8 rats in each group. Changes of learning and memory after stresses were measured by means of Y-maze test, open field test and step-through test. RESULT: As compared with control group and noise group, the number of correct reactions decreased significantly (P<0.01) and the reaction time increased significantly (P<0.01) in combined stress group at all time after stress; time stay in center grille (TSCG) increased significantly immediately after stress (P<0.01). When compared with control group, total time (TT) and number of error (NE) increased significantly (P<0.01) while latent time (LT) decreased significantly immediately and 6 d after stress (P<0.01). As compared with +10 Gz group, number of correct reactions in combined stress group decreased significantly (P<0.05) and reaction time increased significantly (P<0.01) immediately after stress. CONCLUSION: It is suggested that combined stress of noise and +Gz may impair learning and memory of rats, and +Gz seems to contribute more to the combined effects.

Acceleration↗
PubMed2003

[Effects of low-G preconditioning on contractive ability of left ventricle and contents of endothelin and prostacycline in myocardium of rats after repeated +10 Gz stress].

OBJECTIVE: To further test the protective effect of low-G pre-conditioning on +Gz stress induced cardiac damage. METHOD: Forty-two male Wistar rats were randomly divided into 3 groups (n=14 for each group): group A (+1 Gz group), group B (+10 Gz group) and group C (low-G pre-conditioning group). The rats in group B were exposed to five +10 Gz plateaus of 30 s with 1 min intervals at +1 Gz, 3 times a week, for 3 weeks; while group A were only submitted to +1 Gz for 5 min. The rats in group C were exposed to +2 Gz for 5 min about 1 h prior to +10 Gz stress. All the animals were decapitated in the next day after the last centrifuge run and function of the isolated working hearts and contents of endothelin and prostacycline in the myocardium were observed. RESULT: Compared with the control, a significant decrease of left ventricular systolic pressure (LVSP) and increase of myocardial contents of endothelin in rats were observed after repeated +10 Gz exposure; but low-G pre-conditioning could remarkably elevate the LVSP and reduce the myocardial endothelin level in rats after repeated +10 Gz stress. CONCLUSION: Low-G pre-conditioning has a significant protective effect on contractive ability of the left ventricle and secretion function of the vascular endothelium in rat heart after high G stress.

Acceleration↗
PubMed2003

[Development of a software for realtime display of physiological informations in human centrifuge training equipment].

OBJECTIVE: To develop a software for realtime display of physiological informations during human centrifuge training. METHOD: A software composed of CParaSetDlg, CRevMsg, CSndMsg, CWaveDsp and other classes was designed in Visual C + +6.0 environment, with object_oriented ideology. Some technical problems such as displaying the scrolled curves in realtime way, synchronous display of the waves with different sampling rates, acceleration and deceleration of the scroll were solved. RESULT: The software can display and store multiplex channels of wave signals and digital messages in realtime, synchronous way according to user's choices, with high reliability and friendly man-machine interface. CONCLUSION: This software fulfils the requirements for medical monitoring and data evaluation in human centrifuge training.

Centrifugation↗
PubMed2004

Changes in cervical spine bone mineral density in response to flight training.

BACKGROUND: High magnitude loads and unusual loading regimes are two important determinants for increasing bone mass. Past research demonstrated that positive Gz-induced loading, providing high loads in an unaccustomed manner, had an osteogenic effect on bone. Another determinant of bone mass is that the bone response to loading is site specific. This study sought to further investigate the site specific bone response to loading, examining the cervical spine response, the site suspected of experiencing the greatest loading, to high performance flight. METHODS: Bone mineral density (BMD) and bone mineral content (BMC) was monitored in 9 RAAF trainee fighter pilots completing an 8-mo flight training course on a PC-9 and 10 age-height-weight-matched controls. RESULTS: At completion of the course, the pilots had a significant increase in cervical spine BMD and total body BMC. No significant changes were found for the control group. CONCLUSIONS: This study demonstrated that the physical environment associated with flight training may have contributed to a significant increase in cervical spine bone mass in the trainee PC-9 pilots. The increase in bone mass was possibly a response to the strain generated by the daily wearing of helmet and mask assembly under the influence of positive sustained accelerative forces.

Absorptiometry, Photon↗
PubMed2004

Renal artery dissection associated with Gz acceleration.

A 55-yr-old male presented with flank pain and nausea minutes after intensive aerobatic flight maneuvers. An initial diagnosis of acute appendicitis was made. Computed axial tomography and renal arteriography showed a right kidney with two renal arteries, a right upper pole infarction, and a dissection in the upper renal artery which had a more vertical trajectory than the usual main renal artery. No signs of diseases known to be associated with renal artery dissection were present. The patient recovered without residual hypertension. Heavy positive G loads may have potential to cause renal arterial injury, particularly when renal vascular anatomical variations exist. The postulated mechanism is similar to fall injuries in which the subjects landed on their feet, with inertia causing caudal renal dislodgement and stretch of the renal vessels.

Aerospace Medicine↗
PubMed2004

Speed and accuracy of head- and eye-based aiming systems at high vertical acceleration.

BACKGROUND: The benefits of using a head tracker in a fast jet to aim weapons and control sensor direction have been amply demonstrated, but head direction is difficult to control at high G. An experiment was conducted to assess whether aiming using the eye, rather than the head, might be advantageous. METHODS: A centrifuge provided sustained accelerations of up to 8 Gz. Participating aircrew were asked to point at static targets using head- or eye-aiming, maintain the acquisition while the target was lit, and then transfer to the next target as quickly as possible. A helmet-mounted scene camera recorded the subject's view of the target board. A laser mounted by the scene camera was used for head-aiming and to determine head direction. The eye tracker camera and illuminator were also helmet-mounted. The eye and scene images were recorded and analyzed off-line. RESULTS: Eye-aiming acquisition times and accuracy were affected only slightly by Gz; however, both head-aiming speed and accuracy deteriorated as Gz increased. Eye-aiming was substantially faster than head-aiming at all Gz levels, but head-aiming was more accurate under these experimental conditions. Subjective ratings supported the objective data. A majority of subjects preferred eye to head as an aiming mechanism. CONCLUSIONS: Eye-aiming was faster and easier to use than head-aiming at all Gz levels, and particularly at high Gz.

Acceleration↗
PubMed2004

Centrifuge braking effects on cardiac arrhythmias occurring at high +Gz acceleration.

Abrupt onset and offset of acceleration induces hemodynamic changes that activate a number of reflex cardiovascular responses. At high +Gz on a centrifuge, apparently healthy subjects occasionally develop a serious cardiac arrhythmia such as supraventricular tachycardia or asystole. We report on four such cases and examine the effect of rapid centrifuge braking (1 G x s(-1)) on the arrhythmia. It appears that the hemodynamic consequences and reflex responses produced by rapid deceleration may have a positive effect on paroxysmal supraventricular tachycardia, slowing the heart rate or terminating the arrhythmia. On the other hand, deceleration tends to intensify sinus bradycardia. If further study confirms these findings, medical monitors and centrifuge operators may want to consider using gradual braking in cases of bradycardia.

Acceleration↗
PubMed2004

Arrhythmias observed during high-G training: proposed training safety criterion.

INTRODUCTION: Most arrhythmias during centrifuge training are physiological responses to high +Gz stress. However, potentially dangerous arrhythmias occasionally occur during centrifuge training. We reviewed all arrhythmias recorded during the Japan Air Self-Defense Force (JASDF) centrifuge training from April 2001 to March 2003, and developed a criterion for suspending G-training based on observed arrhythmias. METHOD: There were 195 male fighter pilots who received high-G centrifuge training monitored with electrocardiographs (ECGs). We evaluated types and occurrences of all arrhythmias during high-G training over a 24-mo period. RESULTS: Sinus arrhythmia (48.7%), single premature atrial contraction (32.3%), and single (58.5%) or paired (9.7%) premature ventricular contraction were commonly occurring arrhythmias during high-G training. We considered these arrhythmias as variant physiological responses to high-G training (category 1). In addition, we observed ventricular tachycardia (2.6%), paroxysmal supraventricular tachycardia (1.5%), and paroxysmal atrial fibrillation (0.5%). Further investigation of these trainees revealed a significant proportion with cardiac anomalies. As a result, the JASDF currently categorizes these arrhythmias as indicators to suspend G-training and initiate cardiac workup (category 3). Other arrhythmias, such as non-sustained ventricular tachycardia (VT) or Morbitz type I atrioventricular (AV) block, were considered borderline anomalies; whether training was allowed to continue depended on the decision of the physicians monitoring the training (category 2). CONCLUSION: Routine ECG monitoring during centrifuge training is recommended to catch the pathology underlying dangerous arrhythmias for flight safety. Our proposed criterion for stopping the centrifuge is intended to differentiate between serious arrhythmias and arrhythmias of physiologic response.

Adult↗
PubMed2004

Acceleration risk in student fighter pilots: preliminary analysis of a management program.

Despite advances in G-protection, F-16 student pilots continue to demonstrate G-performance inadequacies. The G-Risk Indicator Management (GRIM) Program was introduced at Luke Air Force Base in 2000 to facilitate early detection of G-related problems and to aid in the establishment of tailored ground training programs designed to enhance a student's performance under G. Assessment of anthropomorphic data, previous G-performance, anaerobic fitness, and centrifuge qualification scores comprise the initial assessment in the GRIM Program. Observations from these assessments are used to qualitatively determine the level of risk for the student. In the absence of any historical controls, no conclusions could be drawn with regards to the overall efficiency of the GRIM program. Significant differences were found between groups for anaerobic test scores, centrifuge scores, and gradebook comments. The results from this non-experimental study suggest the need for future studies to better determine the validity of G-risk indicators.

Adult↗
PubMed2004

Change of voice characteristics during +3 Gz acceleration.

BACKGROUND: This study was performed to test the feasibility of an experimental approach for assessing voice changes during exposure to increased +Gz acceleration. Such changes are probably due to mechanical alterations of the structures involved in voice production. This may be relevant to automatic speech analysis for flight control. Because voice control by means of auditory feedback may compensate for acceleration effects, the investigations included conditions with masked auditory feedback. METHOD: Four male subjects read standard speech test material while seated in a human centrifuge both during sustained +3 Gz acceleration and in a reference condition. Both test runs were repeated with masking of the auditory feedback by a white noise presented via headphones. Microphone and acceleration signals were recorded on a PC-based dynamic signal acquisition board. Long-time average spectra (LTAS), fundamental frequency (F0), and the frequency of the first, second, and third formant (F1, F2, F3) of the vowels /a/, /o/, and /i/ were extracted from the microphone signal for the different conditions. RESULTS: LTAS clearly differed between the masking conditions, but not between reference and +3 Gz conditions. F0 clearly rose with auditory masking and showed a small increase under +3 Gz acceleration. Several effects of +3 Gz acceleration on formant frequencies were found, all of rather small magnitude. Increased acceleration lowered F2 for the vowel /i/. A decrease of F3 was observed for vowels /i/ and /o/. CONCLUSION: This pilot study has shown the feasibility of an experimental approach to assessing voice changes during exposure to increased +Gz acceleration. Exposure to +3 Gz showed small effects on FO and several formant frequencies. A definitive forthcoming study should assess the significance of these effects by investigating a greater number of subjects during exposure to acceleration higher than +3 Gz.

Adult↗
PubMed2005

EEG correlates of G-induced loss of consciousness.

INTRODUCTION: Electroencephalographic (EEG) correlates of Gz-induced loss of consciousness (G-LOC) were examined to better understand the mechanisms of G-LOC. METHODS: There were 10 subjects (4 women) who provided 35 G-LOC episodes during which 13 channels of EEG and eye activity were recorded. Subjects simultaneously performed tracking and mathematical tasks prior to and following G-LOC. The performance data and cerebral regional oxygen saturation (rSO2), as measured using near infrared spectroscopy, were correlated with the EEG changes. RESULTS: Across all subjects, seven EEG events were identified and measured. The two most significant were found over widespread scalp sites. They were a 1-2 Hz waveform just prior to G-LOC and a very large, approximately 1 Hz waveform just prior to regaining consciousness. These were associated with a drop of rSO2 levels to approximately 90% of the pre-G-LOC baseline levels. rSO2 levels returned to pre-G-LOC levels within approximately 15 s following G-LOC while EEG and performance measures took approximately 60 s. DISCUSSION: There were two unique EEG waveforms found, one preceding unconsciousness and the other preceding the return to consciousness during G-LOC episodes. Further, the supply of oxygen to the brain was rapidly restored, within approximately 15 s, while the EEG and performance data showed that approximately 60 s were required for the brain to regain functional integrity. The delay in performance and EEG recovery following G-LOC demonstrates that the recovery of brain activity to support cognitive function requires more than just the restoration of normal oxygen levels.

Adult↗
PubMed2005

[Effects of low gravity preconditioning on rat learning and memory impairment induced by high gravity exposure].

OBJECTIVE: To study the protective effects of low gravity preconditioning against learning and memory function impairment induced by high gravity exposure in rats. METHOD: Twenty-four male SD rats were randomized equally into control group, high gravity exposure group (+10 Gz/3 min) and low gravity preconditioning group (LGP group, preconditioned by a daily exposure to +4 Gz/3 min for 3 days before +10 Gz/3 min exposure). Both the learning and memory abilities of the rats in the 3 groups were examined after +10 Gz/3 min exposure. RESULTS: In open field test, the rats exposed to +10 Gz/3 min, in comparison with the control rats, exhibited significantly declined total square-crossing and rearing (SCR) on days 0 and 2 (P<0.05), with also significantly prolonged stay in the central square at 0 d(P<0.01). In the low gravity preconditioned rats, SCR declined and length of stay in the central square increased significantly on day 0 (P<0.01). Compared with the rats in +10 Gz/3 min group, the rats in the LGP group showed decreased length of stay in the central square on day 2, and such changes was statistically significant on day 6 (P<0.05), but there was no difference in SCR at all time points. In Y-maze test, the number of times of right reaction (RR) decreased and the reaction time (RT) increased significantly in +10 Gz/3min group compared with those of the control group (P<0.01), whereas no significant differences were found between the control group and LGP group. Compared with +10 Gz/3 min group, the RR was increased (P<0.01) and RT shortened significantly (P<0.01) in LGP group. In the step-through test, the latent time (LT) increased (P<0.05) on day 0 but was then shortened significantly on day 6 in + 10 Gz/3min group (P<0.01), and no difference was found between LGP group and the control group. LT on day 6 increased significantly (P<0.01) in LGP group as compared with the +10 Gz/3 min group. CONCLUSION: High gravity exposure-induced rat learning and memory impairment can be markedly improved by lower gravity preconditioning.

Acceleration↗
PubMed2005

[The heart and aerobatics].

Aerobatics is an aerial sport which has many physiological constraints, principally cardiovascular, with a risk if not adapted of sudden mid-air incapacity which could jeopardise aviation safety, and thus justifies the selection and surveillance of pilots. The aeronautical constraints during flight are multiple, related to the environment traversed, how the aircraft functions and its movements. Those which cause accelerations (+G in particular) pose the problem of haemodynamic tolerance because they can induce loss of consciousness due to cerebral hypoxia. Tolerance of acceleration varies among individuals; it can be improved with training, certain protective manoeuvres, and is reduced by hypoxia, certain medications, dehydration and heat. Moreover, in aerobatics certain tricks require manoeuvres which reduce this tolerance to +G accelerations. This is the "push-pull" effect (_G acceleration immediately followed by +G acceleration). This leads to a risk of sudden loss of consciousness with a load factor much lower than that which the pilot knows he is capable of tolerating. Besides the haemodynamic effects, the existence of an actual acceleration cardiomyopathy has been suggested but has not been proven in man. Finally, while changes in cardiac rhythm during accelerations are usual and relate to changes in vaso-sympathetic balance, ventricular and supra-ventricular rhythm disturbances are rare and are related to the intensity and duration of the acceleration.

Aerospace Medicine↗
PubMed2005

Cerebral hypoperfusion precedes nausea during centrifugation.

INTRODUCTION: Nausea and motion sickness are important operational concerns for aviators and astronauts. Understanding the underlying mechanisms associated with motion sickness may lead to new treatments. The goal of this work was to determine if changes in cerebral blood flow precede the development of nausea in subjects susceptible to motion sickness. METHODS: Cerebral flow velocity in the middle cerebral artery (transcranial Doppler), BP, and end-tidal CO2 were measured while subjects were rotated on a centrifuge (250 degrees x s(-1)). Following 5 min of rotation, subjects were translated 51.5 cm off-center, creating a +1 Gx centripetal acceleration in the nasal-occipital plane. RESULTS: There were 10 subjects who completed the protocol without symptoms while 5 developed nausea (4 while off-center and 1 while rotating on-center). Prior to nausea, subjects had significant increases in BP (+13 +/- 3 mmHg, p < 0.05) and cerebrovascular resistance (+46 +/- 17%, p < 0.05) and decreases in cerebral flow velocity both in the second (-13 +/- 4%) and last minute (-22 +/- 5%) before symptoms (p < 0.05). In comparison, subjects resistant to motion sickness demonstrated no change in BP or cerebrovascular resistance in the last minute of off-center rotation and only a 7 +/- 2% decrease in cerebral flow velocity. All subjects had significant hypocapnia (-3.8 +/- 0.4 mmHg, p < 0.05); however, this hypocapnia could not fully explain the cerebral hypoperfusion associated with the development of nausea. CONCLUSIONS: These data indicate that reductions in cerebral blood flow precede the development of nausea. Further work is necessary to determine what role cerebral hypoperfusion plays in motion sickness and whether cerebral hypoperfusion can be used to predict the development of nausea in susceptible individuals.

Adult↗
PubMed2005

Localization of virtual sound at 4 Gz.

INTRODUCTION: Acceleration directed along the body's z-axis (Gz) leads to misperception of the elevation of visual objects (the "elevator illusion"), most probably as a result of errors in the transformation from eye-centered to head-centered coordinates. We have investigated whether the location of sound sources is misperceived under increased Gz. METHOD: Visually guided localization responses were made, using a remotely controlled laser pointer, to virtual auditory targets under conditions of 1 and 4 Gz induced in a human centrifuge. As these responses would be expected to be affected by the elevator illusion, we also measured the effect of Gz on the accuracy with which subjects could point to the horizon. RESULTS: Horizon judgments were lower at 4 Gz than at 1 Gz, so sound localization responses at 4 Gz were corrected for this error in the transformation from eye-centered to head-centered coordinates. We found that the accuracy and bias of sound localization are not significantly affected by increased Gz. CONCLUSION: The auditory modality is likely to provide a reliable means of conveying spatial information to operators in dynamic environments in which Gz can vary.

Acceleration↗
PubMed2005

Psychostimulants and G tolerance in rhesus monkeys: effects of oral modafinil and injected caffeine.

INTRODUCTION: Caffeine and modafinil are psychostimulants that may be taken by fighter aircraft pilots to reduce fatigue. Fighter pilots are subjected to high positive G loads that reduce cerebral blood flow and consequently may induce G-LOC. The aim of the experiment was to determine whether these drugs may reduce tolerance to G stress. METHODS: Seven adult male rhesus monkeys participated in the experiment. Five were equipped with ECoG and ECG wires and underwent two G tests (A and B). Each experiment consisted of five centrifuge runs. Before the runs, the monkeys received no drug (control) or were given either 7.5 mg x kg(-1) caffeine IM or 64 mg x kg(-1) modafinil PO or the corresponding vehicles. The runs were performed up to +13 Gz with an onset rate of 0.1 G x s(-1) (test A) or 3 G x s(-1) (test B). The run was ended when the electrical activity of one ECoG channel had disappeared (i.e., G-LOC). RESULTS: In experiment A, drug administration had no significant effect. In experiment B, the injection of the caffeine-free solvent caused a delay in G-LOC compared with the control condition (no administration). Caffeine solvent also induced an increase in plasma osmolality. DISCUSSION: Modafinil administration has no significant effect on the G tolerance of rhesus monkeys. Regarding caffeine, the drug seems to have caused the reverse effect compared with the solvent. CONCLUSIONS: Caffeine and modafinil administration had no significant effect on the G-tolerance of rhesus monkeys when compared with controls. This result needs to be confirmed in humans.

Acceleration↗
PubMed2005

Isometric force production in high Gz: mechanical effects, proprioception, and central motor commands.

BACKGROUND: We have shown in the past that human subjects produce exaggerated isometric responses when exposed to high +Gz. The present study investigated the role played by different factors in this phenomenon. METHODS: There were 12 healthy non-pilot volunteers who were seated in the gondola of a centrifuge and were exposed to a +1, +1.5, and +3 Gz environment. During each exposure, they produced forces of prescribed magnitudes and directions in their frontal plane using an isometric joystick. From the registered data, we determined initial (100 ms after onset), peak, and end (70 ms before trial end) force. RESULTS: For a given target magnitude, initial, peak, and end force were each smallest in 1 G, higher in 1.5 G, and higher still in 3 G. This G-related exaggeration was most pronounced for initial, and less for peak and end force. We further found that responses in high G were biased downwards for end force, but not for initial and peak force. CONCLUSIONS: The G-related excesses of produced force are probably due to less appropriate central commands, since it manifests before proprioception becomes effective. The amelioration of this deficit for peak and end force is probably achieved by partial corrections based on proprioceptive feedback, or by direct mechanical effects. Our findings are relevant for the safe operation of high-performance aircraft during high-G maneuvers.

Adult↗
PubMed2005

G-induced loss of consciousness: case-control study of 78 G-Locs in the F-15, F-16, and A-10.

INTRODUCTION: This study determined the trends of reported G-induced loss of consciousness (G-LOC) mishaps from 1980--1999, and determined potential risk factors in pilot characteristics; specifically, 30/60/ 90-h and sortie history, total flight hours, total hours in the aircraft, age, height, weight, and BMI. METHODS: Using aircraft malfunction mishaps to reflect a cross-section of USAF pilots, potential risk factors were determined using a case-control method; cases were all G-LOC mishaps and controls were aircraft malfunction mishaps. The data consisted of 2002 mishap pilots in the history of the F-16, F-15, F-15E, and A-10 from 1980-1999. RESULTS: During this time, G-LOCs represented only 2.5% of all mishaps. The mean engagement number for G-LOC mishaps was three at an average of 8 Gs. A poor anti-G straining maneuver was cited in 72% of the mishaps, fatigue and G-suit malfunction in 19%, low G-tolerance at 14%, and 37% were student pilots. Within pilot characteristics, only two factors were found to be statistically significant: the time in the aircraft and pilot age. In the F-16, there was a 3.5 times greater chance of experiencing a G-LOC mishap if the pilot had less than 600 h in the aircraft [3.5 (1.7-7.2, 95%CI)], and a 9.5 times greater chance in the F-15 [9.5 (2.2-41.9, 95%CI)]. There was a 4.5 times greater chance of experiencing a G-LOC mishap if under the age of 30 in the F-16 [4.5 (2.3-8.5, 95% CI)] and a 3 times greater chance in the F-15 [2.8 (1.2-6.8, 95% CI)]. DISCUSSION: Though it is difficult to predict who will experience G-LOC, emphasis on prevention must be concentrated in training and in pilots new to the aircraft.

Aerospace Medicine↗