The purpose of this study was to examine the effects of scopolamine on the physiological patterns occurring prior to and during motion sickness stimulation. In addition, the use of physiological profiles in the prediction of motion sickness was evaluatecl. Sixty subjects ingested either 0.6 mg scopolamine, 2.5 mg methscopolamine, or a placebo. Heart rate (HR), respiratory sinus arrhythmia (an index of vagal tone), and electrogastrograms were measured prior to and during the exposure to a rotating optokinetic drum. Compared to the other groups, the scopolamine group reported fewer motion sickness symptoms, and displayed lower HR, higher vagal tone, enhanced normal gastric myoelectric activity, and depressed gastric dysrhythmias before and during motion sickness induction. Distinct physiological profiles prior to drum rotation could reliably differentiate individuals who would develop gastric discomfort from those who would not. Symptom-free subjects were characterized by high levels of vagal tone and low HR across conditions, and by maintaining normal (3 cpm) electrogastrogrophic activity during drum rotation. It was concluded that scopolamine offered motion sickness protection by initiating a pattern of increased vagal tone and gastric myoelectric stability.Abstract
The hazard potential of ejection with canopy fragmentation was evaluated by horizontal sled tests. A series of 14 ejections of tandem seats with 1st or 95th porcentiie anthropometric dum-mies were performed at sled speeds of 0, 150, 350, and 600 knots. Canopy-mounted miniature detonating cords (MDC) were fired in nine and not fired in five ejections. Maximal impact leads on each dummy's neck, knees, and shoulders were measured, and noise levels inside and outside the helmet recorded. The acceleration waveform for each dummy was recorded and used to calculate a dynamic response index (DRI) to assess the risk of spinal injury. Impacts with canopy fragments during ejections resulted in minor visible damages to the dummies and their equipment regardless of MDC firing. It was noted that MDC firing significantly attenuated the mean neck load (231 ± 63 kg, unfired, to 108 ± 20 kg, fired, p < 0.05). Noise levels with MDC firing averaged 162 dB. The mean DRI of dummy Gz for the small dummies was significantly greater than for large dummies (20.8 ± 0.44 and 18.05 ± 0.98, respectively, p < 0.05). We conclude that superficial injuries to ejecting pilots and their equipment is not a hazard with the canopy fragmentation system; however, spinal injury may occur at rates of 5 to 50% depending on the size of the pilot.Abstract
The role of stereopsis (i.e., the use of binocular cues for depth perception) in military aviation is undetermined. Pilots possessing adequate near stereopsis but having deficient distant stereopsis are thought to have microtropias. Historical reviews of microtrepia and research concerning the role of depth perception in military aviation are described. A historical prospective study of student pilots entering U.S. Air Force Undergraduate Pilot Training (UPT) from Oct 1990 through Sep 1991 (FY 90–91) compares UPT attrition rates according to their preseloction stereoscopic status (microtropia vs. normal). Univariate and multiple logistic regression analyses do not show significant differences in attrition rates between the two groups, implying that distant stereopsis is not critical to successful completion of UPT. The U.S. Air Force decided in Oct 91 to eliminate near stereoscopic vision screening while retaining distant stereoacuity testing as a criterion for candidates to qualify medically for UPT. Valid rationale for this decision includes simplified and uniform administration of stereoacuity testing, minimizing spurious results, the continued validity of stereopsis testing as a cross-check of other areas of visual function, the uncertain role of stereopsis in critical areas of flight operations, and the large applicant poo1 competing for a limited number of pilot training positions.Abstract
An anonymous and voluntary questionnaire was completed by 461 (73.4%) Coast Guard aviators at 26 participating Air Stations. Most (92%) pilots felt that helicopters had more dangerous missions and were less safe than fixed wing aircraft (FXAC). Two thirds (204) of helicopter and 19.3% (29) of FXAC pilots stated a desire to change to a different aircraft category. Only 1 (3.6%) of the FXAC pilots but 81 (39.8%) of the helicopter pilots stated their wish for aircraft change was influenced by a desire to operate aircraft they perceived as safer. Pilots who desired change in aircraft category were more senior, more experienced, and felt they were currently engaging in dangerous flight operations. In conclusion this study found that: 1) Coast Guard pilots consider helicopters less safe than FXAC; 2) a substantial proportion of helicopter pilots would like to change to FXAC; 3) safety concerns can be a common factor in pilots' desires to change aircraft.Abstract
Ten subjects participated in a laboratory experiment using cress-coupled angular stimulation to induce motion sickness symptoms. A 14-channel montage using subdermal electrodes was employed to record the electroencephalogram during a pre-Coriolis stimulation baseline through to imminent emesis. Spectrel analyses of the EEG were performed upon the recorded data and individual band energies were quantified to attempt to characterize the cortical electrical response to motion sickness. Power spectral analysis was performed upon the tempora-frontal signals through the entire period over the delta, theta, and alpha EEG bonds. The power in each of these bonds was integrated and the baseline periods compared with that during frank sickness. Mean power spectral energy in the delta bond during frank sickness increased by a factor of 13.7 over baseline. Mean theta bond energy increased by a factor of 2.2. Mean alpha bond energy was not significantly different. EEG power spectral levels in the delta and theta bonds increased along with the level of motion sickness symptoms. These changes, particularly those in the delta bond, suggest that intense low frequency oscillatory stimulation is being diffusely projected about the central nervous system. These EEG changes, similar to those sometimes seen in Partial seizures, and the similarity of the symptom/sign complex in the two disorders, provide evidence that the pathophysiology and electrephysiology of motion sickness may be a variant of seizure activity.Abstract
The N100, P200, N200 and P300 components of the auditory event-related potential were recorded from 10 male subjects at 0900, 1600, and 1830 hours at sea level and again following a rapid ascent to simulated 4300 m altitude. Amplitude and latency of components, ear oximetry, and concurrent performance measures {reaction time and counting errors) were assessed. Amplitude of P300 decreased, while P300 latency and reaction time increased, following ascent to altitude. However, the time course of altitude effects differed for amplitude versus latency. Components N100, P200, N200, and counting errors were unaffected by altitude. The results indicate that central measures of cognitire capacities are differentially sensitive to high altitude. The time course of altitude effects on P300 amplitude versus P300 latency suggests that the two measures reflect different aspects of a response to hypobaric hypoxia exposure.Abstract
Measurements in alveolar gas have suggested extreme hypocapnia and alkalosls on the summit of Mt. Everest. However, tensions in both expired gas and arterial blood have not been reported for the summit of Mt. Everest (Pio2 = 43 mm Hg). To approach the problem, we examined alveolar (and end-tidal) and arterial gas tensions in 6 healthy men who completed a 40-d chamber study to the simulated “summit,” with 20 d above 6,400 m and 9 d above 8,000 m. in 27 simultaneous samples of alveolar air and arterial blood for inspired oxygen tensions ranging from Pio2 of 55 mm Hg (7,380 m) to 43 mm Hg, the mean alveolar-arterial difference was negligible for Pio2 (-0.8 ± 2.4 {S.D.} mm Hg) and Pco2 (0.5 ± 1.4 mm Hg). For all 6 subjects at the summit, Paco2 was 12.0 ± 1.8 and Paco2 was 11.4 + 1.6 mm Hg, and for the two with the lowest values, alveolar and arterial Pco2, respectively, were 9.5 and 9.8 mm Hg. Arterial pH averaged 7.53 units. We conclude that while acclimatization to severe hypoxia results in extreme hypocapnia, alkalosis is more moderate than previously reported. Alveolar gas tensions reflect well the values obtained in arterial blood.Abstract
The introcardioc hemodynamic responses to short periods of 70° head-down and head-up tilts were studied in 12 normal male subjects, ages 19-24 years. Echo-Doppler techniques were used to measure the transmitral and transaortic flow velocities as well as cardiac index, and to evaluate the peripheral impedance. Head-down tilt (HDT) rapidly induced an increase (9.7%, p < 0.05) in the early passive fiUing of the left ventricle (Me peak of the transmitral flow velocity curve) and in transaortic flow velocity (8%, p < 0.05), as well as in cardiac output (6%, p < 0.05). In spite of a peripheral vasodilation, the blood pressure increased (7%, p < 0.05 for the systolic; 15%, p < 0.01 for the diastolic) and remained at a high level for the 5 min of the experiment. Head-up tilt (HUT) induced inverse responses; i.e., a large initial decrease in the transrnitral (-15%, p < 0.05) and transaortic (-16%, p < 0.001) flows. The shape of the arterial peripheral flow indicated an increased vascular impedance. After a short drop, the blood pressure rapidly recovered a level statistically close to that of the pretest. In both cases, tachycardia occurred. We conclude that, in man, the cardiac responses to the changes in posture appear to be related more to the passive changes in ventricuiar filling due to the blood shift than to the nervous regulation by the arterial baroreflexes, whereas these reflexes mainly act in the control of the vascular impedance.Abstract
The influence of simulated microgravity and reduced zeitgebets on the circadian system was examined in eight subjects. The 12-d study included a 3-d period for baseline measurements, 7 d of 6° head-down bed rest, and 2 d for recovery. The sleep-wake cycle was kept constant during the study. The state of the circadian system was assessed from continuous measurements of temperature and ECG, and collections of urine at 3-h intervals for the determination of hormone and electrolyte excretions. Results indicate that only minor changes occurred in rhythm acrophases, whereas daily means for several physiological functions and their circadian amplitudes were significantly altered during the bed-rest phase. These studies using head-down tilt confirm previous findings with horizontal bed rest and indicate that rhythm disturbances can occur without change in the sleep-wake cycle. To the degree that bed-rest studies simulate manned spaceflights, results indicate that variations in circadian cycles can occur even during short-term missions and must be taken into account when interpreting subsequently obtained physiological data.Abstract
The aim of this study was to investigate the effect of flight helmet weight on cervical erector spinae muscle strain under high +Gz forces. Two helmets of different weight were compared by recording infiight neck muscle activities with a portable surface-integrated EMG (IEMG) device. The obtained IEMG activities were normalized by comparing them with activities representing maximal voluntary contraction (MVC) of the muscles. Two test pilots carried out a total of 16 flights consisting of a series of different maneuvers. The results indicate that a lighter flight helmet may—at least in some pilots—cause less strain on neck structures than a heavier one. The effect of helmet weight was readily apparent only under high +Gz forces; changing from a heavier to a lighter helmet reduced the mean muscular strain from 9.5 to 8.8% and from 20.2 to 17.1% of the MVC under +4.0 and +7.0 Gz, respectively. Thus, some, but not all, acute inflight neck pain and related problems might be avoided by using lighter flight helmets.Abstract
The first surgical procedure in microgravity using an animal model is described. The investigation resulted in a realistic evaluation of prototype hardware and procedures that could be applied to a surgical support system on Space Station Freedom. This was especially true for the issue of the management of surgical bleeding, which was observed and studied in microgravity for the first time.Abstract
Pilots and frequent travelers on commuter aircraft are exposed to higher risks of death or injury than those on major air carriers. To provide a better understanding of the circumstances of crashes of scheduled commuter airplanes, National Transportation Safety Board data were analyzed for all cases of death, serious injury, or major damage involving commuter airplanes during 1983-88, when 172 people were killed and 207 injured in 118 events. Three-fourths of cases involved inadequate pilot performance, notably poor handling of emergencies and improper instrument flying procedures. Pilot errors occurred disproportionately in bad weather, which played a role in 30% of crashes. Aircraft malfunctions were involved in 42% of crashes. Certain airplanes were overinvolved in gear-up landings or in crashes due to fuel mismanagement. Greater priority should be given to applying known preventive measures to the problem of commuter crashes.Abstract
The physiological effects of wearing U.S. Army aviator nuclear-biological-chemical (NBC) individual protective equipment (IPE) were evaluated in the USAARL UH-60 research flight simulator. There were 16 male aviators who flew the simulator in 4 test conditions: standard flight suit and cool cockpit, standard flight suit and hot cockpit, NBr IPE and cool cockpit, NBC IPE and hot cockpit. The cool condition was a WBGT of 17.9°C the hot 30.60°C. Rectal temperature, mean skin temperature, and heart rate were monitored and showed significant increases for the NBC hot condition compared with the other three. Seven subjects failed to complete the sortie in the NBC hot condition, with a mean survival time of 298 min. All subjects flew for the target 6 h in the other conditions.Abstract
The aerospace medical research community needs to consider the individual as something other than a statistical entity. The cumulative effects of performance enhancers that are collectively ignored, secondary to statistical analysis of populations, can be significant for individuals. By considering the individual, all aspects of whatever makes humans unique need to be integrated into research. One suggested remedy to the problem of subordination of the individual to the population mean/standard deviation is the use of a “shopping beg” approach. In this approach, each individual may select those performance enhancers that work best for him or her (based on controlled studies). Acceleration protection devices are used as an example. The impact of this philosophy can be readily seen in human factor design strategy as well as in the interpretation of human research data.Abstract