Abstract

An aircraft accident investigation program correlates injuries to occupants with the severity of impacts and structural changes in the crash. Findings brought to the attention of aircraft manufacturers have led to specific aircraft being made more crashworthy. The finding of a failure in a shoulder harness attachment led to the strengthening of the attachment brace. The way a shoulder harness was joined to a lapbelt was modified following a noted failure. The finding of fractures of lapbelt and shoulder harness cable tiedowns led to the use of stronger cables and modification of the installation. Other findings resulted in a shoulder strap guide being placed on an inertia reel and a sidemounted seat being modified. Described also are three seat-related features which, although meeting FAA standards, during the dynamics of a crash may lack desirable energy attenuation. These findings illustrate the value of aircraft crash injury correlations.

Abstract

The failure to achieve positive identification of aircrew following an aircraft accident need not prevent a full autopsy and toxicological examination to ascertain possible medical factors involved in the accident. Energy-dispersive electron microprobe analysis provides morphological, qualitative, and accurate quantitative analysis of the composition of dental amalgam. Wet chemical analysis can be used to determine the elemental composition of crowns, bridges and partial dentures. Unfilled resin can be analyzed by infrared spectroscopy. Detailed analysis of filled composite restorative resins has not yet been achieved in the “as-set” condition to permit discrimination between manufacturers’ products. Future work will involve filler studies and pyrolysis of the composite resins by thermogravimetric analysis to determine percentage weight loss when the sample examined is subjected to a controlled heating regime. With these available techniques, corroborative evidence achieved from the scientific study of materials can augment standard forensic dental results to obtain a positive identification.

Abstract

The drug screen as used in Aviation Pathology is unique in toxicological analysis in that it seeks to identify the whole range of clinical drugs at or below therapeutic levels.

Recently the introduction of proteolytic enzymes has enabled more efficient extraction of drugs from tissues. The measurement of the Gas Chromatographic Retention Index can provide an important parameter in the identification of drug substances.

Abstract

G_z loads in A-10 aircraft were recorded on nine sorties during JAWS II exercises, and the pilots completed questionnaires on the effects of G stress in the A-10. Analysis of the recordings provided, among other statistics, the following means: maneuvering time, 28 min; peak +G_Z load, +6.2; peak –G_z load, –0.1; G-time integral above 4 G, 85 G-s; G onsets ≥ 6 G/s, 13. The questionnaires and follow-up interviews generated little evidence of G intolerance; the pilots did report significant task saturation, however. To compare the physiologic effects of G stress in the A-10 with those of G stress in the F-4, eight volunteer subjects were exposed to simulated A-10 and F-4 missions on the USAFSAM centrifuge. Although the two G-stress profiles were equally difficult and fatiguing, the subjects experienced less visual loss and had lower maximum heart rates during the A-10 profile.

Abstract

The daily fluctuations in the levels of some physiological and performance parameters have been assessed in three young subjects. The assessment was carried out before and after exposing them to the combined effect of two stressors, reduced barometric pressure and hypoxia. The exposure was effectuated by a simulated flight in a low pressure chamber for 30 min. The measured altitude in the chamber was 25000 ft (7620 m). During the simulated flight, each of the individuals experienced 2-3 min of hypoxia. The examined parameters (oral temperature, peak expiratory flow, grip strength, 2 and 6 digits recognition test, addition, counting backward, and odd-even addition test) exhibited circadian rhythms whose acrophases shifted significantly after exposure to the combined effect of the two stressors. The phases continued to shift for 4 d in a concordantly synchronized pattern. On the fourth day, they exhibited a tendency to resume their original phase.

Abstract

Intravenous (10 μg/kg) or intracisternal (1 μg/kg) Clonidine inhibited the diuretic response to negative pressure breathing (NPB) and left atrial distension (LAD) in chloralose anesthetized dogs. The drug reduced the induced tachycardia, but not the increase in respiratory rate caused by NPB, and did not change the blood pressure. Propranolol (1 mg/kg i.v.) did not change the NPB-induced diuresis. Intravenous yohimbine (1 mg/kg i.v.) opposed the effects of intravenous or intracisternal Clonidine, whereas prazosin (0.05 mg/kg i.v.) had no effect. These results show that the adrenergic receptor implicated in the volumetric control of vasopressin secretion could be of the alpha₂ subtype. This alpha₂adrenoreceptor could be centrally located. Clonidine might therefore be proposed to combat the dehydration observed after long-term weightlessness.

Abstract

The purpose of this study was to compare pulmonary ventilation and blood acid-base responses for upper and lower body exercise at a variety of metabolic intensities. Nine male subjects completed a progressive intensity, discontinuous test for arm crank (AC) and cycle (CY) ergometry. During submaximal exercise, oxygen uptake (VO₂), pulmonary ventilation (VE), VE/VO₂, alveolar ventilation (VA) and blood lactate (LA) values were found to increase, whereas arterial carbon dioxide partial pressure (Pco₂) and arterial pH values were found to decrease with increasing power output for both modes of ergometry. Generally, for a given submaximal power output level, VO₂, VE, VE/VO₂, VA, and LA values were higher, but, Peo₂ and pH values were lower for AC compared to CY exercise. During maximal exercise, VO₂, VE, VA, LA, and Pco₂ values were lower for AC than CY exercise. When VE, VA, LA, Pco₂ and pH were expressed in relation to percent of peak VO₂ (ergometer specific), nearly identical response patterns were found for both modes of exercise. These results indicate that pulmonary ventilation and blood acid-base responses are dependent upon relative exercise intensity rather than the muscle groups employed.

Abstract

The Eustachian tube function in 32 aviation trainees was comprehensively tested in simulated flights in a pressure chamber on three occasions during their training. Their mean flight experience between tests comprised 150 h in jet training planes and 260 h in jet fighters. Their capacity to clear the ears in descent did not improve convincingly between tests, but the pressure opening level in ascent was significantly lowered. The elasticity of the eardrum system was significantly increased. The results suggest that the first test, before the flight training, is reliable for selection purposes. Reasons for difficulties in finding good agreement between test results and results of actual flight training are discussed.

Abstract

The isometric strength and endurance of the neck muscles in man was measured in four male subjects during dorsal, ventral, and lateral flexion of the head in a helmet dynamometer. The purpose of these experiments was to quantify the maximum strength of the neck muscles in these directions and to examine the relationship between isometric strength and endurance for various submaximal isometric tensions. Isometric contractions were sustained to fatigue by these subjects at tensions of 25, 40, 55, 70, and 90% of the maximum isometric strength in each of the directions of movement. Generally, the endurance of the muscles involved in ventral flexion was less than that found in dorsal and lateral flexion of the head. However, the strength of the muscles involved was progressively greater for lateral, dorsal, and ventral flexion, respectively. The implication of these findings in helmet design and helmet loading are discussed.

Abstract

Paramecium tetraurelia was cultivated aboard the Soviet orbital station Salyut 6. Each culture included one cell, bacterized culture medium, and two small glass tubes filled with a fixative. Cultures were kept at a low temperature before Soyouz-Salyut docking. Cultures were maintained at 25° ± 0.1°C in orbit and were fixed every 12 h. The space flight resulted in an increase in cell growth rate and in cell volume. Measurements of cell dry weight and total protein content favour a higher cell water content. Respective roles of cosmic rays and microgravity are discussed. Cytos results are compared to those of previous space experiments.

Abstract

An ultrasonic Plethysmograph, which gives improved performance over the standard Whitney Strain Gauge, is described. This instrument monitors dimension changes in human limbs by measuring the transit times of acoustic pulses across two chords of the limb. In the case of a small uniform expansion, the percentage change in limb volume is shown to be proportional to twice the percentage change in either of the measured chords. Measurement of two chords allows correction for possible non-uniform expansion. In addition, measurement of two chords allows an estimate of the absolute cross-sectional area of the limb. The developed instrument incorporates a microprocessor, which performs necessary calculation and control functions. Use of the microprocessor allows the instrument to be self-calibrating. In addition, the device can be easily reprogrammed to incorporate improvements in operating features or computational schemes.

Abstract

During a 1-year period, the United States Air Force School of Aerospace Medicine reviewed routine exercise tests by 771 completely asymptomatic male flying personnel aged 35-54 years, who underwent the stress test as the sole screening procedure to detect latent coronary artery disease. All of the aviators had a normal baseline 12-lead electrocardiogram, which would not have required a stress test in accordance with current policies of the USAF Central Electrocardiographic Library. Of these 771 exercise tests, 153 were maximal treadmill tests without a previous Double Master’s Step test, and 618 were Double Master’s tests. Borderline abnormal or abnormal Double Master’s tests were followed by treadmill testing. Airmen with abnormal treadmill tests were offered coronary angiography for clarification of the aeromedical significance of the test result. The predictive value of a routine abnormal treadmill test in a population of aircrew members with a borderline abnormal or abnormal Double Master's test ranged from 17-55%. Thus, mass screening for coronary artery disease with exercise stress tests in apparently asymptomatic individuals is hampered by a low yield of true positive test in an unacceptably high proportion of false positive results.

Abstract

Correlational and contingency analytical techniques were used to investigate the relationship between subtest scores on the Minnesota Multiphasic Personality Inventory (MMPI) and coronary heart disease (CHD) risk factors in 1000 submariners. Groups of personality traits, both enhancing and protecting against risk of heart disease, were identified in these subjects. Personality trait patterns tending to be least associated with cardiovascular risk are tentatively identified by the three MMPI scales: psychasthenic, schizophrenia, and social introversion. On the other hand, the scales most strongly related to CHD risk in the submariner sample were denial of symptoms as measured by the K-scale, hypochondriasis, and hysteria. While the inherent inaccuracy in the prediction of CHD risk in young healthy individuals limits generalization from these findings, the potential utility of the MMPI to assist in risk detection is indicated. Comparisons of cigarette smoking, coffee drinking, and alcohol consumption with personality characteristics identified by the MMPI yielded trait clusters associated with each addictive habit. Cigarette smoking and alcohol consumption tended to correlate with traits positively associated with CHD risk. The correlations between those addictive habits and MMPI subtest scores were most significant for the F-scale, which measures inordinate tendencies to exaggerated emotional symptoms, and for the psychopathic deviate and hypomania scales. Significant negative correlations were found between the amount of coffee consumed and those personality traits negatively associated with CHD risk. These negative relationships were most significant for the MMPI scales schizophrenia and psychasthenic. Though the relationships were not necessarily construed to be causal, the contrasting modes through which these drug-associated habits appeared to relate to cardiovascular risk lend some support to the assumption that individuals with various specific sets of personality characteristics tend to incorporate these addictive behaviors into their behavior repertoire in very different ways.

Abstract

Chaotic atrial rhythm has traditionally been a dysrhythmia of the seriously ill elderly patient and commonly associated with pulmonary disease. It has been reported less frequently in young individuals with and without pulmonary disease. An apparently healthy asymptomatic centrifuge subject had reproducible episodes of chaotic atrial rhythm only in the recovery period after exhaustive +G_Z simulated aerial combat maneuvering. The underlying mechanism responsible for initiation of chaotic atrial rhythm is unknown, but may be related to distension of atrial tissue. In lung disease with attendant pulmonary hypertension or post +G_Z stress with the sudden increase in venous return, the necessary distension of the right atrium can be induced. The prognosis of individuals with chaotic atrial rhythm depends on the severity of the underlying illness and is probably benign in apparently healthy asymptomatic individuals with normal cardiovascular evaluation.

Abstract

This study was undertaken to explain the possible correlation between heterophoria and stereopsis because, in the literature, there are different opinions. The subjects were 806 recruits. They were trained as rangefinder men, of whom a perfect stereopsis is required. The permitted maximal limits of heterophoria were 1 prism diopter (PrD) vertically, of esophoria 5 PrD, and of exophoria 6 PrD. Soldiers with abnormal stereopsis, myopia, hyperopia more than 1.75, or astigmatism over 0.50 diopters, were omitted. The heterophoria was tested with Herschel's prism to 5 m distance. The stereoscopic vision was investigated using Pulfrich's device and the so-called three-needle test. No statistically significant correlation could be demonstrated between heterophoria and the degree of stereopsis. Surprisingly, it could be noticed that persons with esopheria finished Pulfrich's test more quickly than those with exophoria. This difference was statistically highly significant. In the three-needle test, the results had the same trend. This might have some importance to rangefinder men and to pilots if it can be confirmed in the military practice.

Abstract

The current economic crisis facing most major United States airlines has forced a close examination of airline-sponsored activities. The effectiveness of one airline's pilot preventive medicine program was estimated by comparing disability experience of its pilots against the experience of a larger population of airline pilots. The preventive medicine program at the studied airline was shown to reduce disability experience by one-third, while saving the airline better than $6 million annually. This program yielded the airline better than a 6-1 return on investment during the years studied.

Abstract

Beta adrenergic receptor blocking agents were used in the treatment of 1 5 hypertensive aircrew who had failed to respond to thiazide diuretics. Atenolol (Tenormin®) resulted in adequate control of blood pressure in all subjects. Side effects were minimal and insignificant. It is recommended that a cardio-selective, water-soluble beta blocker, such as atenolol, be made available to selected hypertensive aircrew.

Abstract

This feature is a self-assessment program consisting of 600 questions/answers/references covering all disciplines of aerospace medicine for your continuing medical education. Approximately 25 sets of questions/answers/references will be published each issue of the Journal, requiring 24 months to complete the entire set of 600. Questions each month will be randomly selected from different subject areas. This is a service brought to you by the Aerospace Medical Association. Take advantage of it.