For example, a 70-kg pilot executing a 9-G turn would experience the effects equivalent to a weight of 630 kg, resulting in pooling of blood volume in capacitance vasculature of the lower extremities, which reduces the ability of the cardiovascular system to ensure cerebral perfusion. This effect becomes quantified in multiples of the normal acceleration due to gravitational force, expressed as G. Importantly, the mechanics of rotational acceleration about various flight axes produce an effective increase in the force of gravity sustained by aircrew in the physiologic vertical axis (cephalad to foot). Īcceleration is typically a factor during flights involving aggressive maneuvering. Carotid baroreceptors perceive a hypervolemic state and enact a compensatory diuresis and reduce peripheral vascular resistance, resulting in orthostatic dysfunction sustained upon reentry and return to the normal gravity environment baroreceptor reflex must again reset to normal gravitation force. Reduced gravity also affects the cardiovascular system due to a decrease in hydrostatic pressure, which leads to a fluid shift from extravascular to intravascular spaces, as well as the cephalad movement of intravascular fluid. Negative sequelae include reduced strength, increased fracture risk, and potential renal calculi formation due to aberration in calcium metabolism. Primary musculoskeletal effects include loss of bone mineral density and deconditioning of skeletal muscle. Microgravity refers to an environment in which gravitational force is less than that experienced at the surface of Earth, including weightlessness. Additionally, limits to cumulative radiation exposure are enforced. Humans in space are unavoidably exposed to further increased amounts of cosmic radiation, and spacecraft employ radiation protection material to mitigate this risk. Aircrew and space crew may also sustain increased radiation exposure from vehicle systems (e.g., radar systems), which are specific to the aircraft, although there is only limited research regarding this factor. Further research is warranted to ascertain the extent to which exposure to cosmic radiation affects subsequent long-term pathology. Although anecdotal evidence suggests that aircrews are at an increased risk for malignancy, studies have reported conflicting results. Chronic exposure has been shown to increase the risk of nuclear cataracts in pilots compared with non-pilots. This exposure may be a factor for space crew, as well as long-haul commercial pilots or transport aircrew who experience exposure to increased cosmic and ultraviolet radiation at the typical cruising altitudes of modern aircraft (i.e., 10000 to 13000 m). Of additional concern is chronic exposure to low-dose cosmic radiation. Symptoms occur as a spectrum, dependent on the type, route, and dose of exposure, and typically lead to hematopoietic, gastrointestinal, neurovascular, and cutaneous manifestations. One concern is that an unpredicted solar particle event (e.g., solar flares) may expose space crew to unacceptably high radiation levels and cause acute radiation syndrome, which typically manifests following whole-body or partial-body exposure greater than 0.5 Gy. Humans in the aerospace environment are exposed to an increased ionizing radiation index, leading to genetic and cytogenetic changes. As opposed to the majority of medical disciplines in which pathophysiology gets addressed in a eubaric environment, here effects on normal physiology get addressed in an abnormal environment, which presents a myriad of challenges regarding environmental exposures and physiologic function. Aerospace medicine involves investigating and optimizing human physiology in esoteric environments such as undersea, flight, mountain, and space.
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