The role of physical conditioning in tolerance to +Gz remains the subject of debate, particularly in relation to the relative merits of aerobic vs. anaerobic conditioning. The purpose of this study was to document the patterns of physical conditioning in Royal Australian Air Force (RAAF) fighter pilots and to relate these findings to the question of +Gz tolerance. A questionnaire was used to determine the physical conditioning activities of RAAF F/A-18 pilots. Aerobic fitness levels (Vo2max) were determined in a sample of eight pilots using a progressive cycle ergometer protocol. Of the 42 F/A-18 pilots who completed the questionnaire, 86% reported regular physical conditioning, mostly three times per week. Aerobic activities were the most common (83%), with running the most popular activity (55%). Anaerobic activities were reported by 26% of respondents. Most respondents reported doing more than one activity, with an average weekly training volume of 129 ± 77 min. The ergometer test results revealed a mean Vo2max of 50 ± 6 ml O2 · kg · min-1. The high rates of participation in regular physical activity suggest that physical fitness is perceived as important by the fighter pilot operating in the high +Gz environment. The fighter pilots in this study participated in aerobic activities at a much higher rate than anaerobic activities. The aerobic fitness levels measured suggest that the pilots have good but not exceptionally high levels of aerobic power that are unlikely to influence +Gz tolerance.Abstract
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Flying an aircraft requires a considerable degree of coordination, particularly during activities such as takeoff and landing. No studies have examined the magnitude and phasing of muscle activity required to fly an aircraft. The aim of this study was to examine the muscle activation patterns and control forces of novice and experienced pilots during simulated flight. Twelve experienced and nine novice pilots were tested on an Aermacchi flight simulator while performing a randomized set of take-off and landing maneuvers. Four different runaway trim settings were used to increase the difficulty of the landings (elevator-up, elevator-down, aileron-left, and aileron-right). Variables recorded included aircraft attitude, pilot applied forces, and electromyographic (EMG) activity. Discriminant function analysis was used to distinguish between novice and experienced pilots. Across all landings, wrist flexors and wrist extensors were the predominant muscles used, with EMG activity consistently around 20-30% maximum voluntary contraction (MVC). In respect to differences in EMG activity between novice and experienced pilots, novices had significantly more activity in wrist extensors during all landings. In contrast, experienced pilots had consistently more vastus lateralis activity for all landings than did novice pilots. Over all landings and take-off, 89.5% of pilots were correctly classified as novice or experienced. When the maneuvers were analyzed individually, normal, elevator-down, and aileron-left landings were the most accurate maneuvers for pilot prediction. EMG and force variables were more important than aircraft attitude in discriminating between novice and experienced pilots (83%, 79%, and 65%, respectively). The consistency of the finding that EMG activity and control forces are accurate discriminators of pilot experience is indicative of underlying differences in neuromuscular control strategies between novice and experienced pilots.Abstract
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To date, there is no standard jettison mechanism for doors, windows, or hatches in ditched helicopters. A new Universal Escape Exit (UEE−) has been invented and the performance has been compared with two current in-service systems in a helicopter underwater escape trainer. A total of 416 evacuations were conducted by 40 subjects in two experiments using the Survival Systems Limited's underwater escape trainer. The UEE− had a distinct 2-s advantage to escape; and, in the majority of cases, was preferred to a rotating lever or a straight push out system. Further work should continue with UEE− development for qualification in an operational helicopter.Abstract
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This study investigated the physiological correlates of motion sickness provoked by viewing an optokinetic rotating drum. A total of 52 subjects viewed an optokinetic rotating drum for 16 min. Subjective symptoms of motion sickness (SSMS) and ratings of over-all sickness were measured during the drum rotation. Electrogastrogram (EGG), electroencephalogram (EEG), electrocardiogram, and skin conductance were measured as physiological correlates of motion sickness. Analysis by Pearson's correlation showed that the subjects who had higher scores of SSMS during the drum rotation generated the following: a) a higher rating of over-all sickness (r = 0.76); b) a higher ratio of spectral power of EGG at 4-9 cycles per minute (cpm) between drum rotation and baseline periods (r = 0.63); c) a higher net percent increase of spectral power in the EEG frequency band 0.5-4 Hz between drum rotation and baseline periods on C3 (r = 0.29) and C4 (r = 0.31); d) a higher ratio of spectral power of EEG frequency band 0.5-4 Hz between drum rotation and baseline periods on C3 (r = 0.31 ); and e) a higher level of net increase in skin conductance from baseline to drum rotation (r = 0.30). The increase of EGG at 4-9 cpm activity, gastric tachyarrhythmia, is the most sensitive physiological index of the severity of symptoms of motion sickness.Abstract
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This study compared the retention of adaptation to motion sickness eliciting stimulation after 1 mo and 1 yr. A total of 34 subjects who developed nausea to an optokinetic rotating drum in a preliminary session repeatedly viewed the same rotation with an interval of 48 h between sessions until they had no feelings of nausea. For each session, subjects’ electrogastrograms (EGGs) at 4-9 cycles per minute (cpm) were also recorded as a physiological index of the severity of motion sickness. Subjects were re-exposed to the optokinetic drum either after 1 mo or 1 yr. The mean ratings of nausea for the subjects who were re-exposed to the optokinetic drum after 1 mo were 9.23 for the initial exposure and 0.94 for the re-exposure session. EGG indicators of motion sickness were 6.65 for the initial exposure and 1.03 for the re-exposure session. The mean ratings of nausea for the subjects who were re-exposed to the optokinetic drum after 1 yr were 8.94 for the initial exposure and 6.88 for the re-exposure session. EGG indicators of motion sickness were 5.97 for the initial exposure and 4.05 for the re-exposure session. These results indicated that adaptation to the motion sickness eliciting stimulation of optokinetic rotation is almost completely retained for 1 mo and partially retained for 1 yr.Abstract
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The disposition of drugs may be influenced by hyperbaric conditions, in particular by changes of liver perfusion. The effect of hyperbaric hyperoxia on the pharmacokinetics of lidocaine, a drug eliminated in the liver with a perfusion-limited clearance, was investigated in human volunteers in a crossover trial. A single dose lidocaine i.v. bolus (0.69 or 0.75 mg · kg-1) was administered to two volunteers under normobaric conditions (NB: 1 bar or 0.1 MPa, air) and under hyperbaric/hyperoxic conditions (HBO: 2.5 bar or 0.25 MPa, alternating 100% O2-breathing for 20 min and air breathing for 5 min). Blood samples were serially collected for 5 h (NB) or 75 min (HBO), and lidocaine concentration in serum was measured by immunoassay. Data were analyzed assuming linear kinetics and an open two-compartment model. At 1 bar or 0.1 MPa, lidocaine injection caused only slight dizziness and buzzing in the ear. Heart rate and blood pressure were not influenced. Under HBO, lidocaine injection caused marked dizziness and buzzing in the ears, sweating, tremor and coordination disturbances, even though maximal lidocaine concentrations (0.63 mg · L-1 and 0.70 mg · L-1) were far below therapeutic serum concentrations (1.5-5.0 mg · L-l). Pharmacokinetic parameters of lidocaine were similar to those published earlier (T1/2β: 110 ± 16 min; CI: 12.6 ± 2.9 ml · min-1; Vss: 1.73 ± 0.18 L · kg-1). There was no indication for effects of HBO on the disposition of lidocaine (p > 0.05). The pharmacokinetics of lidocaine do not seem to be influenced in a clinically relevant way in humans by a single HBO-exposure under usual therapeutic conditions. Side effects of lidocaine at 2.5 bar or 0.25 MPa may be caused by pharmacodynamic interactions between lidocaine and hyperbaric/hyperoxic conditions.Abstract
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Orthostatic intolerance is a common complication associated with spaceflight, It has been speculated that this is due to changes in blood volume and alterations in cardiovascular reflexes. The objective of the current study was to develop a model that would allow us to study the cardiovascular system and the regulation of blood volume during short-term microgravity exposure in the primate with the intent of eventually being able to elucidate those factors responsible for the orthostatic intolerance. Head-out water immersion in the conscious non-human primate simulates the cardiovascular and volume regulatory responses observed in astronauts during exposure to microgravity. Four monkeys were chronically instrumented for measuring BP and heart rate and then conditioned to the primate restraint chair. They were then subjected to 72 h of head-out water immersion (two immersions in three monkeys and one immersion in the fourth) in order to simulate the cardiovascular and renal effects of the microgravity environment. During the immersion, there was an increase in arterial BP (ABP) and central venous pressure (CVP) and a reflex decrease in heart rate (HR). Urine flow (UV) increased and water intake decreased, producing a negative water balance. This was not associated with an alteration in food intake. CVP and UV decreased following de-immersion. There was also resetting of the arterial baroreflex control of HR. Significant tachycardia occurred after the immersion that was associated with a decrease in ABP. These results are similar to those observed in astronauts during and after spaceflight, suggesting that head-out water immersion of the non-human primate provides a good model for studying cardiovascular and renal adaptations to spaceflight.Abstract
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Impedance cardiography (IC) is an inexpensive, reliable and noninvasive technique for determining stroke volume (SV) and cardiac output (CO). It relies on the measurement of phasic changes in transthoracic electrical resistivity, related to ejection of blood into the ascending aorta with each heart beat. Because of its non-invasive nature, IC is becoming increasingly used in clinical settings, as well as in many areas of physiological research. This paper discusses IC in terms of its theoretical basis, the components of the impedance signal and how impedance data is mathematically processed. One of the major controversies surrounding IC concerns how well it compares with conventional methods of determining SV and CO, such as thermodilution. A literature review of such comparative studies demonstrated that the controversy is far from settled, but that IC is generally agreed to be capable of accurately monitoring trends in cardiovascular dynamics. The question of accuracy of IC in terms of absolute values of SV and CO remains to be determined. The methodological limitations, accuracy, reliability and reproducibility of IC are examined, as are some of the methods developed to improve these aspects of the technique. The application and utility of IC in aerospace medicine research is also addressed.Abstract
Despite remarkable advances in detection and therapy, coccidioidomycosis remains a persistent threat to military troops deployed in endemic areas. Pregnant women, immunocompromised hosts, and dark-skinned persons, particularly those of Filipino, African, Hispanic or Asian ancestry, are at greatest risk for disseminated coccidioidomycosis. The ethnically diverse military forces have susceptible active duty and reserve members stationed at or temporarily trained on bases located in endemic areas for Coccidioides immitis. Although the vast majority of infections with this organism are subclinical, unusual patterns of dissemination pose a diagnostic challenge. The military physician may be tasked with recognizing acute non-specific symptoms as well as bizarre, occult manifestations of coccidioidomycosis. We present a case of disseminated coccidioidomycosis in an active duty Caucasian male who presented with a right shoulder mass. Our patient is atypical in that he had disseminated disease although immunocompetent and Caucasian. Another unusual feature is that the mass was not preceded or accompanied by any other symptoms. We could find only two other reported cases of coccidioidomycosis presenting as a soft tissue mass, both in African-American patients. The epidemiology and history of coccidioidomycosis will be reviewed, with an emphasis on military populations. The insidious nature of coccidioidomycosis, the importance of early detection and treatment in decreasing morbidity and mortality, and the presence of large numbers of military members in the endemic areas make the lessons of this case particularly relevant for all flight surgeons.Abstract
In aviation, it is essential that all aircrew members remain alert and contribute, by their observations and actions, to flight safety. Especially in helicopter operations, crewmembers riding in the rear of the aircraft play an integral role in many aspects of flight, such as take-offs, landings, turns, formation flights, hazard avoidance, situational awareness, military operations, and crew coordination. We present the case of a helicopter crew chief with idiopathic hypersomnia, briefly review the disorder, and give the recent U.S. military aviation experience with sleep disorders. Flight surgeons and aeromedical examiners should be active in considering and diagnosing sleep-related disorders as the aviator or crewmember may not be aware of the disease or may not volunteer the history. A directed history is important in making the diagnosis, as are reports from family and other aircrew members. Referral to a sleep specialist is required in performing objective sleep studies, establishing the diagnosis, recommending treatment, and providing a prognosis. Many sleep disorders are treatable and aeromedically waiverable.Abstract
Studies, to date, have not revealed the extent to which the heat strain of continuous heavy exercise while wearing NBC protective clothing can be reduced by providing liquid- or air-cooling and whether one system is more effective than the other in aiding heat transfer from the body and the clothing. It was of interest to know to what extent present-day cooling technologies can reduce the heat strain of light and heavy exercise in NBC clothing and to compare these reductions to other strategies that have employed changes in clothing design. It was hypothesized that there would be no difference between the liquid and air cooling systems and that sufficient cooling power would be delivered to the body to reduce the heat strain of heavy exercise to a level similar to that experienced with light exercise when no cooling was provided. Eight males performed 6 randomized exposures for a maximum of 3 h at 40°C and 30% relative humidity that involved either light (L) (walking at 3.5 km.h-1 or heavy (H) (walking at 4.8 km.h-1 and a 5% grade) exercise while wearing the NBC protective clothing ensemble with no cooling (N), liquid (L) or air (A) cooling. For L exercise, tolerance time was significantly increased from 100 min with N to the maximum of 3 h with either cooling system. There was no difference between L and A cooling in the extent of the changes in rectal temperature, heart rate and heat flow. For H exercise, tolerance time was significantly increased 150% from 57 min with N to 149 min with L and 140 min with A. These latter values for HL and HA were not different from each other but both were significantly greater than L exercise with N. Rectal temperature increased more quickly during HL compared with HA during the first 60 min of exposure but there were no differences between cooling trials for the remainder of the heat exposure. It was concluded that sufficient cooling power could be delivered to the body to effectively reduce the heat strain of wearing NBC protective clothing during heavy exercise in a hot environment to a level comparable to or slightly lower than that experienced with light exercise and no cooling.Abstract
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The introduction of advanced anti-G protection into agile fast fighter aircraft may result in the regular use of positive pressure breathing (PPB) for G protection by aircrew. Since PPB results in an external additional work of breathing (WoB), we compared the mechanical performance of the pneumatic and electronic O2 regulators designed for “Mirage 2000” and “Rafale” aircraft. Since mask pressure is regulated by the electronic device in relation to flow, mask pressure will remain constant throughout the respiratory cycle, so that PPB-related additional WoB will be less with the electronic regulator. In a bench dynamic study performed with a sinusoidal pump, we measured variations in mask pressure (ΔP) and calculated WoB at 0, 3 and 6 kPa of PPB (0, 30 and 60 cm H2O, respectively), for 0.5, 1 and 2 L of volume and for 10, 15 and 20 cycles per minute of respiratory rate. We found that, compared with the pneumatic device, inspiratory and expiratory WoB with the electronic device were respectively lower by ∼25% (p < 0.05) and by ∼10% (NS) at 3 and 6 kPa of PPB, for all respiratory conditions. Nevertheless, we also observed remaining variations in mask pressure with the electronic regulator, due to complex impedance of the inspiratory circuit, since the device uses the pressure measured into the regulator. We concluded that the electronic control of mask pressure is relatively efficient but that the device would be improved by placing the site of the pressure measurement into the mask.Abstract
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Tuberculosis in commercial aircraft has been a concern since a 1995 incident of possible transmission from an active case of tuberculosis to passengers in the cabin of a 747. Subsequently, commercial air carriers have been vigilant in cooperating with public health authorities in tracking all known exposures to tuberculosis. In 1998, a pilot of a commercial airliner was diagnosed with active tuberculosis. Company records demonstrated that in the previous 6 mo, the pilot had flown with 48 other pilots. Every exposed pilot was contacted and evaluated by skin testing (IPPD) or chest x-ray if previously positive. There were no skin test conversions and no changes on x-rays. This study demonstrates that transmission of tuberculosis in the aircraft cabin environment, even under close and continuous exposure to an active case, is a rare event.Abstract
From 1929-1957, Harry Armstrong, M.D., rose from first lieutenant in the U.S. Army to the rank of major general in the U.S. Air Force. He founded the aeromedical research laboratory at Wright Field, Dayton, OH, founded the Central Medical Establishment, England, became command flight surgeon, U.S. 8th Air Force, England, and founded the Department of Space Medicine (1947), Randolph Field, TX, and served as Surgeon General, USAF (1949-54). Armstrong worked throughout his career on the most advanced aeromedical problems and personally directed breakthrough programs for which he received the highest national and international awards. Applying Armstrong-like projections, one can forecast faster, larger aircraft for the coming decades as well as 21st century habitations on the moon and Mars.Abstract
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