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Hypothesis: This study tested the hypothesis that respiratory muscle fatigue occurs during a simulated air combat maneuver (SACM) centrifuge profile. Methods:Six subjects (four males, two females) were exposed to a SACM consisting of alternating +4 Gz to +7 Gz plateaus until volitional fatigue. Electrical activities of the diaphragm, scalene, intercostal and external oblique muscles were monitored along with esophageal pressure and ventilation. Results:SACM times averaged 358 ± 115 s. The mean frequency of the electromyographic signal of the diaphragm and scalenes during inspiration, and the intercostals during the static expiratory portion of the anti-G straining maneuver (AGSM), decreased significantly (p < 0.05) over the course of the SACM by about 9%, 10% and 4%, respectively, indicating muscle fatigue. Esophageal pressure (PES) during the straining portion of the AGSM decreased significantly from 72 ± 20 to 66 + 21 mmHg (mean ± SD). Ventilation increased significantly both at +4 Gz and +7 Gz (32 ± 16 L.min 1 to 56 - 19 L.min − at +4 Gz and 27 · 5 to 35 + 9 L.min -− at +7 Gz) over time. PES during a maximal AGSM at +1.4 Gz (baseline) was decreased post- vs. pre-SACM (p = 0.0575). PES exerted during a maximal static inspiratory maneuver at residual lung volume was not changed after the SACM. Inspiratory work increased significantly during the SACM. The elastance of the respiratory system did not change during the SACM, but itwas significantly increased when tested after the SACM. Conclusion: Increased inspiratory work, decreased pressure generation during a maximal AGSM and EMG frequency shifts suggest respiratory muscle fatigue coincides with the termination of SACM.

Abstract

The physiological responses of a group of nine subjects exercising at a metabolic rate of 510 W in a new low burden chemical protective ensemble, the Chemical/Biological Combat Suit (CBCS), have been determined under a warm, humid climatic condition, 30− and 60% relative humidity. The CBCS was significantly superior to a current NBC overgarment (MK4) in terms of induced physiological strain. Furthermore, there was no statistically significant difference between the normal combat uniform (DPCU) and the CBCS worn as a combat uniform (CS), without hood, mask and gloves, in terms of increase in rectal temperature and increase in heart rate. The major limitation on performance in the fully encapsulated CBCS was imposed by the combination of mask, permeable hood and impermeable gloves. It was concluded that there would be a mgnificant improvement in soldier performance in the CBCS rather than in the current MK4 overgarment and that there would be no detriment to soldier performance when wearing the CS uniform in times of chemical threat.

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Operational fighter squadrons frequently find themselves deployed to semi-isolated stations in the Arctic. This paper discusses the major issues necessary for fhght surgeon consideration. In particular, the areas of pre-deployment planning, preparing for the worst, routine operations, and post deployment actions are discussed. A recent month-long deployment of a 12-ship squadron of F18s with support elements from Bagotvdle, Canada, to Evenes, Norway, is examined. A proposed kit list to support a similar deployment to a semi-isolated station is provided.

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The effect of hyperbaric hyperoxia on the pharmacokinetics of caffeine was investigated in human volunteers. Some 600 ml of coffee were administered to 2 volunteers and blood samples were serially collected for 24 h. The volunteers entered a hyperbaric chamber 2.5 h following coffee ingestion for a total period of 110 min (0.25 MPa, alternating 100% O₂-breathing for 20 min and air breathing for 5 min). The concentrations of caffeine in serum was determined by high pressure liquid chromatography. The caffeine amount ingested was determined by analyzing an aliquot of the coffee beverage. Data were analyzed assuming hnear kinetics and an open one-compartment model. Effects of hyper-baric hyperoxia on caffeine disposition were investigated using a runs test. Moreover, a one-population t-test was applied to residuals, separately for data from the matial normobaric period, the hyperbaric period and the terminal normobaric period. Pharmacokinetic parameters were similar to established literature data on caffeine [Volunteer 1 : maximal concentration (C_max: 6.13 mg. L^-1 at T_max: 55 min, half-time of elimination (T_1/2:180 min, total clearance (CI): 3.41 ml·min^-1·kg^-1; volume of distribution (Vd: 0.88 L·kg^-1; Volunteer 2: C_max: 6.23 mg·L^-1, T_max: 94 min, T_1/2: 283 min, CI: 1.90 ml·min^-1·kg^-1, Vd: 0.77 L·kg^-1]. The runs test as well as the analysis of residuals gave no evidence for alterations of caffeine disposition by hyperoxia (p > 0.05). The pharmacokinetics of caffeine do not seem to be influenced in a clinically relevant way in humans during a stay for 110 min at 0.25 MPa, alternating 100% O₂ and air breathing.

Abstract

Muscular diseases including the dystrophies and myopathies are often incompatible with a variety of occupations including aviation and military duty. Many of these diseases present early in life, are readily diagnosable, and are therefore rare in the aviation community because of pre-screening and selection. Some forms, however, may not present until adulthood during an established aviation career. Furthermore, although initial presentations may be subtle and insidious, the potential occupational and aeromedical ramifications of these diseases can be profound.

The following report describes the case of a subjectively a symptomatic career military aviation officer who presented with an unusual gait, and was subsequently determined to have one of the late-presenting muscle disease variants: Anterior Compartment Distal Myopathy. The patient's presentation and progression, diagnostic evaluation, prognosis, aero-medical risk and disposition, and issues of occupational and aeromedical significance are discussed.

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Pilot studies are presently being carried out to determine the efficacy of raising the oxygen concentration in the room air of commercial and scientific facilities at altitudes of 4000-5500 m. This is a remarkably effective way of relieving hypoxia. For example, oxygen enrichment by only 5% (i.e., raising the oxygen concentration from 21 to 26%) reduces the equivalent altitude by 1500 m. However, concern has been expressed about the possibility of fire hazard. In this article, existing data from various sources have been analyzed to determine the burning rate of materials such as paper and cotton clothing at various altitudes when the Po2 in the air is increased to 110 mmHg to give an equivalent altitude of 3000 m. The analysis shows that in spite of the.increase in oxygen concentration, the burning rate is much less than at sea level, primarily because the Po2 is so much lower even with oxygen enrichment.