Aerospace Medicine

Aerospace medicine is a branch of preventive medicine, or occupational medicine, concerned with the health and safety of aircrew and passengers exposed to the aerospace environment. Practitioners and researchers apply principles of atmospheric physics and environmental physiology in assessing an individual's fitness for flight, and develop aviation hardware to maximize aircrew and passenger safety.

The aerospace environment may involve abrupt or prolonged exposure to altered atmospheric pressure, enhanced or reduced gravitational forces (g-forces, or Gz), or extreme low temperatures. Any of these, in addition to human factors, may pose serious threats to astronauts, pilots, aircrew, passengers, or patients during aero-medical transport.

With increasing altitude, atmospheric pressure and temperature lose compatibility with normal homeostasis. Although the fraction of atmospheric oxygen does not change with altitude, its partial pressure (PO2) decreases in proportion to the overall decline in barometric pressure (Dalton's Law). In the event [Page 28]of a sudden loss of cabin pressure aircrew and passengers are exposed to rapid decompression, which constitutes a medical emergency. At higher cruising altitudes (≥$30,000 feet), such a hypobaric environment renders the venous PO2 greater than the ambient PO2 and oxygen diffusion in the lungs is reversed. This serious hypoxic environment calls for the use of oxygen masks by aircrew and passengers and a rapid descent to lower altitudes.

When decompression does not necessarily involve a severe hypoxic environment, patients and/or aircrew may experience decompression sickness (DCS) during a transition to a lower atmospheric pressure. DCS is caused by soluble nitrogen trapped in the tissues that expands into bubbles as atmospheric pressure is decreased. Stiff, painful joints are diagnostic of DCS (referred to as the bends), while vascular and nervous tissue may also be affected. Commonly understood among SCUBA divers, DCS is also encountered in the aerospace environment.

Astronauts and pilots of high performance aircraft experience varied gravitational forces that may have adverse medical consequences. Positively enhanced gravitational forces are experienced by high-perfor-mance pilots during rapid acceleration and tend to cause pooling of blood in the lower extremities. Such blood shifting can lead to diminished cerebral perfusion and cerebral hypoxia at higher positive forces. This often results in episodes of syncope referred to as gravitationally induced loss of consciousness (GLOC). In contrast to these effects of enhanced gravitational forces, astronauts experience prolonged exposure to microgravity. Such prolonged exposure leads to changes in autonomic cardiovascular regulation, as well as altered skeletal muscle metabolism. Return to Earth's +1 Gz field may result in orthostatic symptoms such as postural tachycardia, and general orthostatic intolerance, while skeletal muscle is atrophied.

Civilian aerospace practitioners are referred to as aviation medical examiners (AME), while military practitioners are called flight surgeons. Both civilian and military practitioners perform aeromedical examinations to evaluate aircrew safety. AMEs are designated by the Federal Aviation Administration (FAA) and are tasked with screening aircrew for medical conditions that may compromise in-flight safety. The examination involves screening for conditions such as risk for myocardial infarction, epilepsy, color blindness, diabetes, and any other possible source of incapacitation. Upon assurance of safety, AMEs issue Airman Medical Certificates.

Despite the fact that aerospace medicine is considered its own boarded medical specialty, familiarity with medical problems in relation to the aerospace environment is essential to the practicing emergency physician. Emergency physicians are required to evaluate a patient's fitness for aeromedical transport, as well as to prepare them safely for flight.

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