Seven male college students, whose ages ranged from 18 to 24 years, were subjected to 8 weeks of interval training followed by 12 weeks of inactivity and intermittent exposure to 4,572 m (15,-000 ft). The data presented indicate that intermittent exposure to hypoxia may act in some degree as an antithesis to deconditioning. This is evidenced by the ability of hypoxia to maintain a lower pulmonary ventilation, lactic acid production, and heart rate during submaximal work following training. While the data are not conclusive they do lend some support to the use of hypoxia as an antideconditioning agent. If this is the case, one might suggest a wider application for the use of hypoxia.Abstract
The metabolic response of goats was assessed during a 1 hr exposure of 97%N2-3%0", 97% He-3% 02, or air at 7 atmospheres absolute (ata) and to 75% NzO-25% 0: at sea level. Physiologic and metabolic parameters measured included heart rate, EEG, visual evoked cortical response, ECG, body tem-peratures, oxygen consumption, COs production, the uptake and oxidation of COz of infused glucose-UL-14C, the blood levels of glucose, pyruvate, lactate, and free fatty acids. Hyperbaric nitrogen caused an increase in metabolic rate and a general decrease in blood constituent levels which was interpreted as reflecting a shift toward fatty acid metabolism at the expense of carbohydrate. A similar but more pronounced pattern was observed with hyperbaric helium. Breathing N20 at sea level resulted in a substantially depressed metabolic rate and an apparent shift toward greater carbohydrate catabolism. It is considered that the effects at raised pressure were primarily the result of stress whereas the effect of N.O was typical of a volatile anesthetic.Abstract
The cortical auditory evoked responses (AER), recorded at the skull vertex were studied in 56 experiments using 29 healthy subjects with normal breathing and during the following altered respiratory conditions: hyperventilation, hypoxia, asphyxia, and hypercapnia. All four conditions approached the limits of physiological tolerance. Since such conditions can occur in aircrew when exposed to malfunction of the aircraft oxygen regulation system or during other emergencies in flight, it was of interest to know, therefore, which of these conditions might impair hearing perception. Under the assumption that AER latency changes correlate with hearing impairment (or raise in auditory threshold), it can be concluded that only those respiratory changes, which include a raised end-tidal Pco2> are effective in this regard, for these conditions caused significant latency increase of all the auditory evoked response components (Px, N,, P2 and N2). These conditions involve asphyxia and hypercapnia. With hypercapnia, a positive significant correlation was found between the relative Pco2 increase and the relative latency increase. The possible implications of these findings to aircrew safety are apparent.Abstract
Experiments were performed to clarify the mechanisms by which hyperoxia suppresses erythropoiesis. Increased plasma erythropoietin levels induced in rats by phlebotomy or phenylhy-drazine were suppressed by a hyperoxic environment. The stimulation of erythropoiesis by testosterone propionate, presumably resulting from increased production of erythropoietin, was also suppressed by hyperoxia. No effect on the activity of erythro-poietin was found. The results suggest that decreased levels of circulating erythropoietin can be attributed to decreased production rather than increased clearance or reduction in the activity of erythropoietin.Abstract
Tetanic syndrome represents a neurovegative and neuromuscular hyperexcitation of diverse etiology. Clinical manifestations of tetany range from the characteristic tetanic episode with carpopedal spasms and acroparaesthesias as well as vegatative (cardiovascular, respiratory, gastrointestinal) to vestibular (vertigo), cerebral and psychic (depression) symptoms which may jeopardize flying safety to a high degree. Clinical and neurophysiological diagnostic possibilities to assess the tetanic disposition in the interval without clinical symptoms are presented including the following: Chvostek’s sign, Trousseau’s and Von Bonsdorffs signs and hyperventilation test, conventional electrical investigation (Erb’s sign), and electromyography. Electrodiagnosis and electromyography are the most reliable methods of examination to demonstrate a disposition to tetany. Standardized examination of neuromuscular hyperirritability is reported.Abstract
Analytical techniques were developed to measure oxygen uptake of divers breathing from semi-closed circuit underwater breathing apparatus. A series of trials was carried out under pressure in which the oxygen uptake of clearance divers was measured when fin swimming at maximum sustained effort. The divers, breathing an oxygen-nitrogen mixture from CDBA, swam against a trapeze in a wet chamber for periods of 10 in ins at depths of 6 ft, 78 ft and 176 ft. The mean maximum sustained oxygen consumption was calculated to be 2.6 litres/min NTP, and individual values of up to 3.4 litres/min were recorded. On the basis of the results, some problems regarding the design, safety and efficiency of semi-closed circuit underwater breathing apparatus are discussed.Abstract
In these preliminary investigations there was no evidence of systemic dehydration as opposed to local dehydration of areas like the lining of the upper respiratory tract and con* junctivae as a result of exposure to the cockpit environment. A diuresis occurring after a flight is a constant phenomena. Its cause is not established though it is almost certainly associated with the cockpit environment. Theoretically it could be caused by over-stimulation of ADH production consequent on loss of fluid from the mucous membranes of the pharynx and the conjunctivae, but no experimental proof of this was attempted. Whilst it is not considered that this phenomena is likely to be harmful, it may well contribute to bodily fatigue in aircrew.Abstract
This study was conducted to assess realistically the degree of physiologic protection afforded by fire fighters’ clothing. Eight subjects, each wearing standard and prototype proximity fire fighters’ clothing assemblies, were exposed to intense radiant sources in both laboratory and field environments. In the laboratory studies the subjects were exposed to radiant loads of 1.45 cal/cm" sec in a heat pulse facility to anticipate problems that might be encountered in field tests. In the field, 16 “fire ex-posures” were conducted involving 40 subject exposures to a 600 gallon JP-5 fuel fire. In each test, three subjects stood at rest 1.2 meters from the flame front for 10 mins or until tolerance was reached. Clothing design included bilateral construction of two materials (harlequin design) and various weights of 3M aluminized asbestos, nomex, polyvinyl chloride and kynol materials. Water-cooled calorimeters determined the energy flux at the surface of the garments. Clothing temperatures were monitored. Test results indicated the maximum energy flux at the clothing surface varied from 0.50 to 2.71 cal/cm2 sec. Physiologic data showed maximum heart rates of 160 beats/min. Rectal temperatures showed no change. Surface skin temperatures were critical in the hand and foot regions and routinely reached pain threshold levels of 46-50°C. Node weight losses varied from 200 to 400 grams. Based on these data, recommendations for improving clothing design are being incorporated into a new prototype garment.Abstract
Rewarming was studied in three lightly clothed divers who had swum submerged in water of 5°, 10°, and 15°C for 45 to 60 minutes, reaching the limit of subjective tolerance to cold. Heat for rewarming the men after the dive came from warm water being circulated through a water cooling garment, plus their own metabolic heat. Both of these heat quantities were measured, and it was found that an average of 210 kcals (range 165-292 kcals) was needed to replace the heat lost during the dives. The completion of rewarming was signalled by: the release of body heat when previously it had been conserved by the cold subject; a rise in heart rate and the return of cutaneous vasomotor control of body heat loss; and a restoration of the normal balance between heat produced and heat lost. Over-warming led to sweating. None of the following body temperatures reliably indicated completion of rewarming: rectal, ear canal, esophageal, skin (mean or any of 8 sites), calf or chest subcutaneous temperature, or calculated mean body temperatureAbstract
Eight young males were exposed for 30 days to hypobaric hyperoxia (100% Oa at 258 mm Hg.). The response of the following red blood cell (RBC) variables to hypobaric hyperoxia with time were measured: RBC density distribution, reduced glutathione, glutathione peroxidase, cholinesterase, catalase, gIyceraIdehyde-3-phosphate dehydrogenase, and glucose-6-phosphate dehydrogenase. In the studies reported, hypobaric hyperoxia resulted in slightly increasing percentages of more dense red cells. Further hypobaric hyperoxia showed a decrease in RBC glutathione peroxidase levels but without attendant statistically significant decreases in either reduced glutathione or gIucose-6-phosphate dehydrogenase. There were no gross effects of hyperoxia upon RBC catalase, another major cellular defense against the oxidation of hemoglobin. Finally, no effects of oxygen were noticed upon either RBC cholinesterase or upon RBC glyceraldehyde-3-phosphate dehydrogenase, a key enzyme in the Embden-Myerhoff pathway.Abstract
The objective of this study was to determine how much pull force a free-falling man could exert on the ripcord handle of a back-pack parachute. There were 41 free-fall parachute jump tests conducted using 11 USN and 11 USAF test parachutists in order to ascertain the maximum forces which can be exerted on manual ripcords. Subjects exited an aircraft at 10,000 ft (MSL) 110 knots (IAS), went into unstable free-fall attitude and then, in accordance with approved Navy or Air Force procedure, exerted maximum force against a dummy ripcord handle (containing a strain gage), which was anchored to the parachute harness. Other physiological and force parameters were acquired through 9-channel FM/FM bio-telemeters. Under the conditions of this study, 22 military parachutists generated average ripcord pull forces of 115 pounds during 41 actual aircraft bail-outs with observed values ranging from 40 to 210 pounds. Larger subjects generated significantly greater ripcord forces than lighter subjects. For the USAF assemblies, the actual force required to withdraw the pins from the cones averaged 42 poundsAbstract
Two young men are presented who demonstrated significant and disturbing ventricular arrhythmias in association with the mid-systolic click/late-systolic murmursyndrome. In both cases, the arrhythmias were most prominently displayed during in-flight maneuvers involving high +GZ stress. Based on our experiencewith these two individuals, it is recommended that individuals with this auscultatory syndrome be evaluated for arrhythmias not only with ECG monitoring post-exercise but also during and after Valsalva maneuver performed in the standing position. In addition, when aviation personnel are involved, monitoring during high +GZ conditions should be considered if there has been any suggestion of arrhythmias by history or from the previously mentioned maneuvers.Abstract
Right ventricular hypertrophy is a frequent but not an invariable fin ding in long-term residents of high altitude (native or otherwise), be they human or animal species. It is secondary to the development of chronic pulmonary hypertension of a mild or moderate degree which is caused by hypoxic pulmonary vaso-constriction, poorly defined structural changes in pulmonary resistance vessels, increased blood viscosity due to polycythemia, and possible occlusive effects of increased blood coagulability at high altitude. Hypertrophy is believed to be the result of an increase in the aerobic energy production of the myocardium per beat per unit mass of tissue. The left ventricle is mostly unaffected because the systemic microvessels dilate and capillaries open up in response to chronic hypobaric hypoxia thus offsetting the effect of increased blood viscosity (and coagulability?) on peripheral vascular resistance. Hence, systemic arterial pressure is normal or below normal. Heart rate in man is usually unchanged and thus plays no role in altering the stroke energy production and the induction of hypertrophy. The pulmonary arterial pressure and the cardiac changes are reversible if natives of high altitude descend to lower altitudes for permanent residence.Abstract
An epidemic of Group A beta-hemolytic streptococcal pharyn-gitis occurred on board the world’s largest warship. A captive population of 4,720 men were at risk. Epidemiologic investigation revealed that within 4 days of the outbreak, 680 asymptomatic cases were aboard. Appropriate antibiotic treatment for all hands aborted the outbreak. There were no cases of rheumatic fever or glomerulonephritis.Abstract
In this paper an attempt is made to put forth a consumer’s view of medical licensing standards for pilots. Some aspects of the International Civil Aviation Organization standard are considered directly, the use of drugs for hypertension therapy being one. The rationale behind medical standards is reviewed outlining the strength and weakness of some aspects thereof. An attempt is made to reflect the operational pilot’s view of certain facets of medical standards relative to flight safety. Comment is made on “flexibility” and some diagnostic procedures. The paper concludes with a few words of appreciation for the efforts being made by many practitioners of aeromedicine on behalf of pilots.Abstract