Although the sickle cell trait (SCT) is usually a benign and innocuous carrier state or condition rather than a disease, those with the trait are capable of developing any and all types of vascular occlusive lesions that have been observed in patients with sickle cell anemia. Obstructive vascular lesions in individuals with SCT occur infrequently, but when they do occur they are disabling and may be life-threatening. Disabilities attributed to in vivo sickling have the potential of seriously impeding the success of military missions. When selecting recruits to be trained and assigned to special operations, consideration should be given to hyposthenuria, the possibility of hematuria and to exercise-induced syndromes. Exertion to the point of exhaustion in previously healthy individuals with SCT may cause sudden death, rhabdomyolysis, and acute tubular necrosis. In vivo sickling of erythrocytes is a superimposed and late contributory and complicating factor of exertional syndromes.Abstract
This study was designed to assess the effects of hypohydration (−5% body weight) and heat acclimation on plasma cortisol (PC) and growth hormone (GH) responses to exercise (1.34 m·s−1) in a hot-wet (35°C, 79% rh) or hot-dry (49°C, 20% rh) environment. Preacclirnation, hypohydration in both the hot-wet and hot-dry environments resulted in significant (p<0.05) increments in PC levels during the fourth exercise interval. Acclimation had no effects on PC levels in the euhydrated condition, but in the hotwet environment there did occur an attenuation of the PC response when hypohydrated. Preacclimation exercise in either the hot-wet or hot-dry environment resulted in significant (p<0.05) increments in GH when euhydrated. While the effects of acclimation were inconsistent, hypohydration generally resulted in elevated levels of GH compared to euhydration. We concluded from these studies that hypohydration to −5% of body weight generally elicited elevations in circulating levels of stress hormones, and that acclimation did not effect consistent decrements in these responses.Abstract
To test the hypothesis that arginine vasopressin (AVP) in the cerebral spinal fluid (CSF) influences CSF dynamics at simulated altitudes, cannulae were bilaterally implanted into the lateral ventricles of rabbits and rats. Recordings of CSF pressures at ambient and at various reduced barometric pressures identifed on increase in CSF pressure in animals at simulated altitudes. Samples of CSF collected before and immediately after altitude exposures and assayed for AVP did not show a significant change in AVP concentration. Brain water content did not change after 6–8 h of reduced barometric pressure. Intraarterial injections of acetazalamide reduced CSF pressures, whereas intraventricular injection had no effect. Intraventricular angiotensin II (All) elevated CSF pressures both at ambient (744–755 mm Hg) and reduced barometric pressures. When All was preceded by saralasin, an All blocker, the rise in CSF pressure with All injection was prevented. Indeed, saralasin given alone, reduced or prevented the rise in CSF pressure seen at simulated altitudes. Intraventricular AVP did not influence CSF pressures nor did prostaglandins E2 and F1α and norepinephrine. In AVPdeficient (Brattleboro) rats, response to intraventriculor AVP depended on barometric pressure; i.e. CSF pressure rose when the rat was exposed to reduced barometric pressures and fell when the rat was exposed to ambient pressure. We suggest that hypobaric stress could cause an increase in All content of the central nervous system which, in turn, would lead to an increase in CSF pressure. The exact mechanism of CSF pressure increase after All increase remains to be investigated.Abstract
Bilirubin metabolism was studied in rats injected with unconjugated bilirubin (0, 0.5, 1.5, 3.0, or 4.5 mg·100g−1) after 2 and 6 weeks continuous exposure to 4,600 m (15,000 ft) simulated altitude. Exogenous loads of bilirubin were used to exceed any effect of polycythemla, thereby allowing assessment of defects in conjugation and excretion due to the exposure to high altitude. Rats given no exogenous bilirubin shewed polycythemia when exposed to high altitude which may have contributed to the small but significant elevations in their serum bilirubin levels. Compared to sea-level controls, mean serum concentrations of total and unconjugated bilirubin were significantly elevated in altitude-exposed rats given exogenous bilirubin. Mean serum conjugated bilirubin levels did not rise at any dose. Thus, bilirubin uptake and/or conjugation rather than excretion are impaired in rats at high altitude. We conclude that while polycythemia may contribute to high altitude-induced bilirubinemia, an impairment in uptake and/or conjugation also exists.Abstract
Hind-limb hypokinesia was induced in rats by the Morey method to characterize the response of the gastrocnemius muscle. A comparison of rats suspended for 2 weeks with weight, sex, and litter-matched control rats indicate no difference in gastrocnemius wet weight, contraction, or one-half relaxation times, but less contractile function as indicated by lowered dP/dt. Myosin ATPase staining identified uniform Type I (slowtwitch) and II (fast-twitch) atrophy in the muscles from 4 of 10 rats suspended for 2 weeks and 1 of 12 rats suspended for 4 weeks; muscles from three other rats of the 4-week group displayed greater Type I atrophy. Other histochemical changes were characteristic of a neuropathy. These data together with recently acquired soleus data (29) indicate the Morey model, llke space flight, evokes greater changes in the Type I or slow twitch fibers of the gastrocnemius and soleus muscles.Abstract
A psychophyslcal matching experiment was conducted to compare the perceived intensity of Y-axis and Y-plus-roll vibrations. Seated subjects matched their perceptions of the intensity of single-axis stimulus vibrations in the Y-axis, or combined-axis stimulus vibrations made up of Y-axis and roll motions, by adjusting the intensity of a sinusoidal, 5 Hz, Z-axis response vibration. Stimulus vibrations were sinusoidal at 3.15, 4, 5, 6.3, and 8 Hz. For each frequency, both types of stimulus vibrations were presented at three acceleration levels related to three axis-to-seat distances for the roll vibrations. The results showed that as frequency increased the acceleration of the Z-axis matching response decreased for both types of stimuli. In addition, as stimulus acceleration (axis-to-seat distance) increased, response acceleration showed substantial increases at every frequency. However, the matching responses showed only minor differences due to vibration type, indicating that the effects of roll vibrations can be accounted for in terms of the Yaxis translational vibrations produced at the subject's seat.Abstract
Weight, height, and other anthropometric measurements were obtained on a cohort of 194 U.S. Navy divers 20–42 years old. Percent body fat was computed for each man using an established prediction equation derived from a population of U.S. Marine Corps personnel whose age, height, and weight characteristics were comparable to those of the divers. Among the divers, weight, weight-height indices, and percent body fat increased across age strata. The body mass index (W/H2) was the best predictor of adiposity, as it had the highest correlation with percent body fat and the lowest correlation with height. Regression analysis quantified this relationship. The relative obesity of the divers (18.2% body fat) and the implications for using the body mass index as a measure of adiposity in the medical examination of divers are discussed.Abstract
The diagnosis of decompression sickness is made largely by history; there are few physical findings and no radiographic or laboratory tests to support the diagnosis. We present three cases of factitious decompression sickness in which patients fabricated an appropriate history and underwent compression therapy. Due to the potential severity of decompression sickness and the relative safety of compression therapy, the initiation of therapy must not be delayed in a case of decompression sickness. Once therapy is begun, investigation into the particulars of a suspicious case can be made.Abstract
The extremely heterogeneous nature of the various peoples and states of today's world makes the development of a sarisfactory set of medical standards for the certification of civil aircrew extremely difficult. This difficulty is compounded by the varying roles aviation plays in different parts of the world. Essential to the understanding of this difficulty is a comprehension of the concept of the sovereignty of nations. Emphasis on aviation medical standards is affected by the variation in health care priorities seen amongst the worldwide community of nations. Annex I to the Convention an International Civil Aviation sets regulations and recommendations for aircrew licensure. The capability of the International Civil Aviation Organization (ICAO) to enforce regulations is restricted by the same factors which restrict the power of any supernational organization. Nonetheless ICAO remains the most effective means available for achieving the diplomatic consensus so essential to the development of international standards.Abstract
An expandable surgical chamber of transparent polyvinyl has been designed to provide a sterile environment for minor surgical procedures performed in conditions of weightlessness. Contamination of the cabin with blood and other debris is prevented while performing surgery. The patient's extremity is inserted through a cuff into the surgical chamber. The cuff may be inflated for rapid hemostasis. All instruments and suture material are stored within the chamber.Abstract
Hypoxla in aviation remains a major hazard. It may be caused by ascent while breathing air, failure of oxygen supply or loss of cabin pressurisation. Malfunction of equipment or its improper use accounted for the majority of hypexic incidents in one lO-year military study. Symptoms of hypexia depend on rote of ascent, temperature, and individual variation, as well as altitude. Dyspnoea, lack of coordination and reduction in capecity for skilled performance precede the gross changes which occur at altitudes of over 4572 m (15,000 ft) and lead ultimately to unconsciousness. Studies have shown a significant decrease in psychomotor task ability at altitudes as low as 2438 m (8000 ft). Developments in aircraft oxygen systems are discussed and the importance of adequate crew instruction on hypexia and their aircraft oxygen equipment is stressed.Abstract
Hyperventilation in flight may be caused by environmental, psychological, pharmacological, and pathological factors. The effects are discussed and two case histories are presented, illustrating the development and effect of hyperventilation in training or aircrew under stress. Investigation of in-fllght hyperventilation is technically very difficult, but positive acceleration, hypoglycaemia, and anxiety are important contributory factors. The incidence of hyperventilation must be reduced by educating aircrew in its aetiology, early recognition, and treatment.Abstract
The anatomy, physiology and functional assessment of small airways and their relevance to aviation is reviewed. Small airways normally contribute little to lung function, and they can become extensively and irreversibly damaged, or even closed, before clinical deterioration is evident. Small airways disease does, however, produce typical and reproducible changes in spirogram, flow volume, and closing volume measurements. Minor abnormalities of respiratory function, inconsequential at sea level, can substantially reduce arterial oxygen saturation at high altitude. Aircrew with pulmonary disease could also be severely affected by loss of pressure, causing significant hypoxia. Stress during flight may exacerbate airways obstruction, especially in asthmatics. The hypexia resulting from these situations could seriously compramiso in-flight performance. Peak flow, FEV I, and FVC measurements are recommended for civilian air crew prior to employment and at routine intervals thereafter.Abstract
Asthma is often incompatible with flying and it is Important that the natural history of the disorder is understood in relation to both pretraining enralment and inservice fitness checks. Studies of childhood asthma with prolonged follow-up have shown that as many as 70% experience some asthmatic symptoms in later life. Of asymptomatic adults with a history of childhood asthma, 60% have evidence of bronchial lability and therefore an ongoing asthmatic tendency. Asthma developing in adulthood may be intermittent or continuous, with a poorer prognosis. A history of childhood asthma should be disqualifying for entry into pilot training. If asthma develops after training, persistent asthma, intermittent asthma with frequent or severe attacks, and asthma requiring regular hota-agonist, theophyl-line or corticosteroid inhaler treatment should all preclude aircrew from further flying.Abstract
Greater awareness of the morbid condition in severe asthma attacks would decrease the still considerable number of deaths which occur in otherwise fit, young asthmatics. Failure to recognise serious attacks in time may be due to the presumption that the disorder is one of bronchoconstriction. More dangerous is the hyperaemia and exudation of plasma into the bronchial lumen where it mixes with mucus to form plugs. Bronchial epithelium damaged during an attack may take weeks to regenerate, increasing the risk from another attack. Patients should be instructed to consult a doctor when expected bronchodilator relief decreases in either degree or duration.Abstract
Allergic rhinitis is often trlvlalised but accurate diagnosis and institution of therapy greatly alleviate its symptoms. Diagnosis requires a careful history and nasal mucosal examination. Nasal smear eosinophil staining and skin tests can be helpful, but skin and nasal provocation testing should be controlled and related specifically to a patient's history. Recent advances in symptomatic treatment, particularly antihistamines and mast cell stobilising drugs, and immunotherapy are considered.Abstract
The nasal cavity and sinus system is extensive but its examination is limited. Listening to breathing and respiration can afford useful clues to underlying abnormality. Examination of the nasal cavity may reveal the pale swollen mucosa of allergic rhinitis or the overdeveloped lining seen in perennial rhinorrhoea and hypertropic rhinitis. Localised hypertrophy gives rise to the nasal polyp which usually forms in the region of the ethmold sinus. Atrophic rhinitis is a destructive condition of the nasal lining. Sinusitis may be open or closed, presenting with Iocalised pain and displacement of the eye in the case of frontal or ethmoidal abscess or mucocoele. Deformities of the external nose or nasal septum are often encountered during examination. Epistaxis may be caused by bleeding simply from Kiesselbach's vessels, or may be an early feature of telangiectasla or cardiovascular diseases. Tumors are rarely found but Include papillomata and the mucous membrane melanoma.Abstract