Abstract
Method:
Vertical optokinetic nystagmus (VOKN) and after-responses were detected in nine subjects using the corneo-retinal potential (CRP) technique and an infrared video camera detection apparatus (ISCAN) simultaneously. The ISCAN method produced a much smaller inter-subject variability, a higher linear regression coefficient (0.94) when vertical eye position was regressed against vertical target position (±30°, 5° increments). Detected by ISCAN, VOKN responses were measured at 3 angles of pitch head (and body) tilt: upright (0° supine (90° and declined 45° below horizontal (135° Two stripe velocities (40° · s−1 and 60° ·−1) were used.
Results:
In six of the nine subjects (67%) and in 40/54 conditions (74%) for all subjects, upward (slow phase velocity up) VOKN gain was greater than downward VOKN gain for both stripe velocities at all tilt angles. The gain for both upward and downward VOKN decreased as stripe velocity increased from 40-60° s−1, which suggests that both upward and downward VOKN systems were starting to saturate. Across subjects, a mean up-down asymmetry index, I, increased monotonically as the subjects declined. The slope of the monotonic function was greater for 60° · s−1 stripe velocity than for 40° · s−1 stripe velocity. The mean of all subjects' individual asymmetry ratios (ASYM) also increased as tilt increased but the slope of the best fitted regression line was not statistically significantly different from zero (p > 0.05).
Conclusion:
Optokinetic after-responses observed in the present study were of two types: 1) resetting of the eye by a drift, with nystagmus superimposed, from a beating field (eye position) that occurred during optokinetic stimulation; and 2) resetting of the eye without nystagmus superimposed. Upward VOKN produced the greatest number of after-responses. The beating field of VOKN was not correlated with pitch tilt.
Abstract
Background:
Altitude convulsion is a rather specific form of experimental convulsion which is induced by acute exposure to a hypobaric hypoxic condition. Several neurotransmitters have been shown to be involved in the mechanisms of altitude convulsions. However, their roles and interaction were not clear.
Hypothesis:
The novel neurotransmitter nitric oxide (NO) may be involved in the mechanisms of altitude convulsion through its neuronal signalling roles in relation to the NMDA receptor.
Methods:
There were 177 mice intraperitoneally administrated (i.p.) with several drugs. The altitude convulsion threshold (ACT) was used as an index to evaluate the acute hypoxic tolerance.
Results:
NO synthesis precursor, L-arginine (20, 40, 200, 800 mg/kg), resulted in a dose-dependent decrease in the ACT in mice, while the NO synthase (NOS) inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME, 1.25, 2.50, 5.00 mg/kg, i.p.) increased the ACT. Pretreatment with L-NAME (5.0 mg/kg) prior to L-arginine (200 mg/kg) administration prevented the effect of decreasing ACT caused by L-arginine. Similarly, N-methyI-D-aspartate (NMDA, 2.5, 10.0, 20.0 mg/kg, i.p.) yielded a decrease in the ACT in mice and this decrease in hypoxic tolerance caused by NMDA can be prevented by pretreatment with either NMDA receptor antagonist 2-amino-5-phosphovalerate (AP-5, 20.0 mg/kg, i.p.) or NOS inhibitor L-NAME (5.0 mg/kg, i.p.).
Conclusions:
These findings suggest an important signalling role for nitric oxide and NMDA in the development of altitude convulsion and further support the hypothesized relationship between NMDA-receptor mediated neurotoxicity and nitric oxide.
Abstract
Pulmonary air embolism occurs in diving and aviation during acute pressure reductions and in clinical complications. Undoubtedly physical obstructions play a role, but bubbles in blood can produce a number of indirect effects leading to tissue injury. In the present study, we investigated the involvement of the complement system and polymorphonu-clear leukocytes (PMN) in altering segmental vascular resistance, lung weight gain, and filtration coefficient (Kf), by using isolated and perfused rat lungs. After establishing ventilation with air and 5% CO2, the lung was removed en bloc and suspended in a humidified chamber at 37° Lung weight and arterial and venous pressures were monitored continuously. The buffered salt perfusate contains 4% Ficoll for osmotic balance. We used four series of perfusates containing 20% of: a) normal plasma; b) decomplemented plasma (from donor rats pretreated with a cobra venom factor); c) normal plasma and PMN at 2 × 106·ml−1; and d) decomplemented plasma and PMN at 2 × 106·ml−1. Pulmonary air embolism, air bubbles introduced through the pulmonary artery, increased pulmonary arterial resistance and pulmonary arterial blood pressure. The lung weight and lung water content were greater than those in the control groups. Air embolism increased vascular permeability, which was shown by an elevated Kf after air infusion. After air embolism, Kf was 0.63 ± 0.05 g· min−1 · cm H20−1 · 100 g−1 in lungs perfused with both PMN and plasma, which was significantly greater than those in lungs perfused with either plasma (0.49 ± 0.04), decomplemented plasma (0.44 ± 0.03), or PMN and decomplemented plasma (0.47 ± 0.03). These results demonstrated that air embolism increases vascular permeability of the lung by pulmonary hypertension, activation of the complement, and activation of PMN.
Abstract
Purpose:
The present study investigated the effects of differential spatial frequencies of a vertically striped, horizontally rotating drum on the observer's frequency of eye nystagmus, perceived velocity of self-motion, and symptoms of motion sickness.
Methods and Results:
Two experiments were conducted. In Experiment 1, each of 10 subjects viewed 1 min of an optokinetic rotating drum at the speed of 10 rpm covered with 6, 12, 24, 48, and 96 pairs of black and white stripes, presented in counterbalanced order. The results indicated that subjects perceived significantly stronger circular vection (p < 0.05) and generated significantly higher frequencies of eye nystagmus (p < 0.05) when they were viewing 24 pairs of black and white stripes than when they were viewing any of the other combinations of 6, 12, 48, or 96 black and white stripes. In Experiment 2, 100 highly susceptible subjects viewed 16 rain of an optokinetic rotating drum covered with one of the five different numbers of black and white stripe pairs: 6, 12, 24, 48, and 96. The results indicated that subjects in the group viewing 24 moving contrasts perceived significantly stronger circular vection (p < 0.001 ), reported significantly more severe symptoms of motion sickness (p < 0.001), and showed significantly greater ratios of EGG 4-9 cycles per minute spectral intensity between drum rotation and baseline periods (p < 0.004) than those in the groups of viewing 6, or 96 moving contrasts.
Conclusion:
These results demonstrated that the severity of vection-induced motion sickness is affected by differential spatial frequencies of the stripes of the rotating drum and may be affected by number of horizontal eye movements.
Pilot Performance of the Anti-G Straining Maneuver: Respiratory Demands and Breathing System Effects
Abstract
Introduction:
The anti-G straining maneuver (AGSM) is still an important part of pilot protection for G-induced loss of consciousness. The specific requirements for and the effects of breathing systems on the performance of the AGSM are essential elements to designing compatible breathing systems.
Methods:
Subject pools of 27 and 34 naval aviators were recruited and used to measure the inhalatory and exhalatory flow requirements for the AGSM and the breathing system effects of mask cavity pressure during AGSM performance on the Naval Air Warfare Center Dynamic Flight Simulator at acceleration levels up to 8 Gz.
Results:
The mean peak inhalatory flow was 125.5 L · min−1 (n = 135, SD = 42.1) with a maximum value of 274 L · min−1. The mean peak exhalatory flow was 154.4 L · min−1 (n = 135, SD = 49.6) with a maximum value of 308 L · min−1. For the effects of the breathing system on AGSM performance, inhalatory mask cavity pressures were not above 30 mmHg with the majority less than 10 mmHg. Exhalatory mask cavity pressures did not exceed 60 mmHg but predominated in the 20-30 mmHg range. In comparison to accepted guidelines, 67-77% of inhala-tory mask cavity pressures were below and 91% of the exhalatory mask cavity pressures were above the Air Standardization and Coordination Committee (ASCC) limit of ± mmHg.
Conclusions:
The difference in the peak inhalatory and exhalatory flows measured during this study and clinically can be attributed to different test conditions and performer techniques. The reduction in inhalatory flow with increasing G is consistent with the increase in breathing difficulty due to the G load and the inflation of the anti-G suit. However, exhalatory mechanics appear unaffected by the G load and the inflation of the anti-G suit. Since 23-33% of the inhalatory mask cavity pressures were above this ASCC limit, improvements in regulator performance are still needed. For exhalatory effects of the breathing system, the main contributor is the mask valve. While no pilot suffered unconsciousness or expressed complaints with the breathing systems used, these exposures were of short duration. The additional work of breathing during a combat engagement may further compromise the pilot's ability to retain consciousness with the AGSM.
Abstract
Background:
Numerous questions have been raised about the health consequences to veterans of the Gulf War but most particularly to issues concerning women, who were deployed in unprecedented numbers. Little is known about the health consequences to women of wartime stressors, in general, or the environmental and job-related exposures specific to the theater of the Gulf War.
Methods:
A stratified sample of 525 women participated in the study following the war and again in a follow-up study 2 yr later. The sampling frame was stratified on component of the U.S. Air Force (active, guard or reserve), deployment (in the theater or elsewhere), and parental status (parent or nonparent). Measures included items concerning general physical health, gender-specific health, the “Gulf War Syndrome,” and the emotional responses to war, including symptoms of post-traumatic stress disorder (PTSD).
Results:
Multiple statistical analyses were used to describe women's physical and emotional health at two time points following the war. Women deployed to the theater reported significantly more general as well as gender-specific health problems than did women deployed elsewhere. A cluster of common health problems included: skin rash, cough, depression, unintentional weight loss, insomnia, and memory problems. Women serving in the theater also reported a significant increase in several gender-specific problems compared to women deployed elsewhere.
Conclusions:
Findings suggest the need for follow-up of a cluster of specific health effects, including those concerning gynecologic and reproductive health.
Abstract
Initial high-G centrifuge training of USAF fast jet pilots was instituted in 1985. Also, since the mid-1980's, pilot awareness of G-induced loss of consciousness (G-LOC) has been enhanced by briefings, videotapes, and safety articles. Aircraft accidents caused by an improperly performed anti-G straining maneuver (AGSM), however, continue to occur. Deficiencies in the AGSM of pilots in flight have not been systematically studied. A test program to reinforce the proper performance of the AGSM in flight was initiated in the United States Air Forces Europe (USAFE) in 1993. Head-up display videotapes (HUD tapes) were recorded during flight and critiqued during debrief by flight leads for AGSM technique and continuity. Questionnaires were completed by F-16, F-15C, and F-15E pilots assigned to USAFE: 78 surveys were completed out of 110 distributed (71%). There were 57 pilots (73%) who reported one or more problems with their AGSM: 33 noted that the timing of their breathing was too quick (<2 s cycle), 11 that their breathing was too slow (>4 s), 9 that inhalation was too long, 18 occasionally did not “get the jump on the Gs,” and 34 frequently or occasionally talked during +Gz exposures. Of the 105 reported deficiencies, 67 (64%) were mostly or completely corrected: 30/33 (91%) if the timing of breathing was too quick, 8/11 (73%) if too slow, 5/9 (56%) if inhalation too long, 12/18 (67%) “jump on the Gs,” and 12/34 (35%) if they talked. This program was most successful in remediating timing problems with the AGSM.
Abstract
A retrospective study of scuba decompression illness (DCI) and fatalities in the U.S. military community on Okinawa Island, Japan, was performed for 1989-95. Some 94 cases of diving DCI, including 10 cases of cerebral air-gas embolism (CAGE), and 9 diving fatalities were reported, for an annual incidence of 13.4 DCI events and 1.3 fatalities per 100,000 dives. The overall estimated incidence of scuba DCI was estimated to be 1/7400 dives, with an annual incidence of undeserved DCI of 1/37,300, and a fatality rate of 1/76,900. A review of treatment dives revealed a 10% overdiagnosis rate in cases treated for presumed DCI. A bimodal distribution of DCI accidents was observed for depths deeper or shallower than 24.6m/80FSW (feet of sea water). Increased risk of DCI in diving deeper than 24.6m/80FSW was associated with violations of no-decompression limits (NDL), while other risk factors were associated with diving to less than 24.6m/80FSW. NDL violations accounted for only 24/94 (26%) of all DCI accidents. Treatment of divers with hyperbaric oxygen (HBOT) led to complete recovery in 91% of cases, but of those divers requiring retreatment with HBOT, 67% had chronic residua of DCI. Selected illustrative and interesting cases are discussed.
Abstract
The case history of a 38-yr-old military aviator qualified on a range of rotary and fixed wing aircraft is presented. A radiologically evident and clinically debilitating (initially) lumbar disc protrusion was the source of the aviator's temporary grounding from flying duties. A full clinical recovery was made and he returned to flying, eventually to ejection seat aircraft. It is proposed that: 1.) wherever possible, initial conservative non-invasive management of back problems is preferable; 2.) lumbar disc lesions may sometimes totally spontaneously resolve (retraction or autolysis?), and; 3.) development and diagnosis of a lumbar disc lesion should not always be an automatic permanent expulsion from rotary wing or ejection seat aircraft.
Abstract
During Operation Desert Storm, 21 United States and 2 Italian military personnel were held in Iraq as prisoners of war. Of these, 18 had ejected from fixed-wing, ejection seat-equipped, combat aircraft prior to their capture. Of the 18, 6 (33%) had sustained vertebral fractures; 4 of these were compression fractures. This fracture rate is comparable to that of previously studied groups. Fractures were noted to be at several different vertebral sites and after ejecting from a variety of aircraft. Apart from contusions and abrasions, vertebral fractures were the most common injuries discovered in this repatriated population. None of the vertebral fractures produced recognizable neurological disability. The development of vertebral fractures was neither associated with the use of any particular ejection system or aircraft nor did the development of vertebral fractures appear dependent on the age, height or length of service of the affected personnel. Ejected aircrew with low altitude mission profiles seemed more predisposed to vertebral fracture than those at high altitudes, but with a small sample population, this relationship was not statistically significant (p > 0.25). Reliable data were unavailable on aircrew positioning and preparation time for ejection.
Abstract
Following didactic instruction, most aircrew are able to experience some of the disorientating illusions and limitations of the orientational senses in a variety of ground-based devices. In order to reinforce instruction in spatial disorientation (SD) within the environment in which they operate, British Army Air Corps helicopter pilots also receive an airborne demonstration of the limitations of their orientation senses. Since 1982, a specific SD sortie has been programmed towards the end of the basic rotary-wing phase of flight training approximately 6 weeks after the aeromedical training module, and before students commence rotary-wing instrument flight training. Refresher sorties are flown every 4 years. The conduct of the SD sortie is described in detail. Analysis of helicopter accidents demonstrates that this training is operationally effective by contributing towards the reduction of SD-related mishaps. It is cost-effective and the addition of this type of in-flight demonstration to the aeromedical training syllabus is regarded as being of great value to British Army helicopter aircrew. Similar instruction could be readily adopted by other services.
Abstract
The human species is rapidly expanding. Barring global catastrophe and unnatural constraints, it will, in a brief time on the scale of natural history, fill the uttermost reaches of the solar system. The beachhead established by President Kennedy's lunar program will lead to lunar, Martian and free space settlements in the next century. In a single generation of those who call them home, the constant 9.81 m. · s−2 pull of Earth's gravity, which has influenced the evolution and development of terrestrial life forms for billions of years, will fade from common experience. Miogravity syndrome, a prognosticated complex arising in reduced gravity environments such as the surfaces of the Moon and Mars and principally encompassing muscle atrophy, cardiovascular deconditioning and bone demineralization, stands to replace physics and rock-etry as the fundamental challenge of interplanetary astronautics. Mirroring our past few million years of changing climate and resources, the mobility of humans between diverse gravitational environments on the high frontier will critically depend on our ability to adapt. Tomorrow, as ever, a mushrooming penchant for toolmaking will spearhead the human career.
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