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Impedance cardiography (IC) is an inexpensive, reliable and noninvasive technique for determining stroke volume (SV) and cardiac output (CO). It relies on the measurement of phasic changes in transthoracic electrical resistivity, related to ejection of blood into the ascending aorta with each heart beat. Because of its non-invasive nature, IC is becoming increasingly used in clinical settings, as well as in many areas of physiological research. This paper discusses IC in terms of its theoretical basis, the components of the impedance signal and how impedance data is mathematically processed. One of the major controversies surrounding IC concerns how well it compares with conventional methods of determining SV and CO, such as thermodilution. A literature review of such comparative studies demonstrated that the controversy is far from settled, but that IC is generally agreed to be capable of accurately monitoring trends in cardiovascular dynamics. The question of accuracy of IC in terms of absolute values of SV and CO remains to be determined. The methodological limitations, accuracy, reliability and reproducibility of IC are examined, as are some of the methods developed to improve these aspects of the technique. The application and utility of IC in aerospace medicine research is also addressed.

Abstract

Despite remarkable advances in detection and therapy, coccidioidomycosis remains a persistent threat to military troops deployed in endemic areas. Pregnant women, immunocompromised hosts, and dark-skinned persons, particularly those of Filipino, African, Hispanic or Asian ancestry, are at greatest risk for disseminated coccidioidomycosis. The ethnically diverse military forces have susceptible active duty and reserve members stationed at or temporarily trained on bases located in endemic areas for Coccidioides immitis. Although the vast majority of infections with this organism are subclinical, unusual patterns of dissemination pose a diagnostic challenge. The military physician may be tasked with recognizing acute non-specific symptoms as well as bizarre, occult manifestations of coccidioidomycosis. We present a case of disseminated coccidioidomycosis in an active duty Caucasian male who presented with a right shoulder mass. Our patient is atypical in that he had disseminated disease although immunocompetent and Caucasian. Another unusual feature is that the mass was not preceded or accompanied by any other symptoms. We could find only two other reported cases of coccidioidomycosis presenting as a soft tissue mass, both in African-American patients. The epidemiology and history of coccidioidomycosis will be reviewed, with an emphasis on military populations. The insidious nature of coccidioidomycosis, the importance of early detection and treatment in decreasing morbidity and mortality, and the presence of large numbers of military members in the endemic areas make the lessons of this case particularly relevant for all flight surgeons.

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In aviation, it is essential that all aircrew members remain alert and contribute, by their observations and actions, to flight safety. Especially in helicopter operations, crewmembers riding in the rear of the aircraft play an integral role in many aspects of flight, such as take-offs, landings, turns, formation flights, hazard avoidance, situational awareness, military operations, and crew coordination. We present the case of a helicopter crew chief with idiopathic hypersomnia, briefly review the disorder, and give the recent U.S. military aviation experience with sleep disorders. Flight surgeons and aeromedical examiners should be active in considering and diagnosing sleep-related disorders as the aviator or crewmember may not be aware of the disease or may not volunteer the history. A directed history is important in making the diagnosis, as are reports from family and other aircrew members. Referral to a sleep specialist is required in performing objective sleep studies, establishing the diagnosis, recommending treatment, and providing a prognosis. Many sleep disorders are treatable and aeromedically waiverable.

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Tuberculosis in commercial aircraft has been a concern since a 1995 incident of possible transmission from an active case of tuberculosis to passengers in the cabin of a 747. Subsequently, commercial air carriers have been vigilant in cooperating with public health authorities in tracking all known exposures to tuberculosis. In 1998, a pilot of a commercial airliner was diagnosed with active tuberculosis. Company records demonstrated that in the previous 6 mo, the pilot had flown with 48 other pilots. Every exposed pilot was contacted and evaluated by skin testing (IPPD) or chest x-ray if previously positive. There were no skin test conversions and no changes on x-rays. This study demonstrates that transmission of tuberculosis in the aircraft cabin environment, even under close and continuous exposure to an active case, is a rare event.

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From 1929-1957, Harry Armstrong, M.D., rose from first lieutenant in the U.S. Army to the rank of major general in the U.S. Air Force. He founded the aeromedical research laboratory at Wright Field, Dayton, OH, founded the Central Medical Establishment, England, became command flight surgeon, U.S. 8th Air Force, England, and founded the Department of Space Medicine (1947), Randolph Field, TX, and served as Surgeon General, USAF (1949-54). Armstrong worked throughout his career on the most advanced aeromedical problems and personally directed breakthrough programs for which he received the highest national and international awards. Applying Armstrong-like projections, one can forecast faster, larger aircraft for the coming decades as well as 21st century habitations on the moon and Mars.