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Biomedical subjects

E B Darden

Publications and source records attributed to E B Darden.

13 recordsLinked to original sources
PubMed2000

Radiation exposure during air travel: guidance provided by the Federal Aviation Administration for air carrier crews.

Air carrier crews are occupationally exposed to ionizing radiation, principally from galactic cosmic radiation. To promote radiation safety in aviation the Federal Aviation Administration has: issued educational material on the nature of the radiation received during air travel; recommended radiation exposure limits for pregnant and nonpregnant aircrew members; developed computer programs that estimate for a given flight profile the amount of galactic radiation received on a current flight or on one flown at any time back to January 1958; published tables that enable aircrew members to estimate possible health risks associated with their occupational exposure to radiation; and conducted research on effects of radiation during pregnancy. References for this material are given in the article. In addition, graphic and tabular data in the article show how galactic radiation levels and the composition of the galactic radiation has changed between 1958 and 1999. Also given are estimates of effective doses received by air travelers on a wide variety of air carrier flights.

Aircraft↗
PubMed1998

Prenatal survival of mouse embryos irradiated in utero with fission neutrons or 250 kV X-rays during the two-cell stage of development.

PURPOSE: To investigate the relationship between radiation dose at the two-cell stage and prenatal survival. MATERIALS AND METHODS: Pregnant mice were irradiated with fast neutrons (0.53-1.94 Gy) or X-rays (1.50-5.00 Gy), or sham irradiated. At selected times up to gestation day 16, the mice were killed and the uterine contents examined. RESULTS: At doses up to 0.82 Gy of neutrons and 2.50 Gy of X-rays, all or virtually all the radiation-induced deaths occurred during the period from the time of implantation to gestation day 10. At higher doses an appreciable proportion of the deaths occurred after day 10. Many neutron-induced deaths in the period from implantation to day 10 occurred before day 7. A mathematical model was developed for estimating survival to gestation day 16 as a function of neutron dose. CONCLUSIONS: The mortality pattern, in which low radiation doses led to early deaths and high doses to both late and early deaths, suggests the existence of two lethal processes. The relationship between neutron dose and survival to gestation day 7 has been interpreted as indicating that the early deaths involved predominantly a two-event inactivation mechanism. An individual cell of a two-cell embryo was found to be less sensitive to lethal radiation injury than a pronuclear zygote.

Animals↗
PubMed1989

Galactic cosmic radiation exposure and associated health risks for air carrier crewmembers.

The dose equivalent to air carrier crewmembers from galactic cosmic radiation was estimated for each of 32 nonstop flights on a variety of routes to and from, or within, the contiguous United States. Flying times were from 0.4 to 13 hours. The annual dose equivalents received on the flights ranged from 0.2 to 9.1 mSv (20 to 910 mrem), or 0.4 to 18% of the recommended annual limit for occupational exposure of an adult. We reviewed some of the characteristics of galactic and solar cosmic radiation and provided example calculations for estimating radiation-induced risks of fatal cancer, genetic defects and harm to an embryo or fetus. The estimated increased risk of dying from cancer because of galactic radiation exposure received during 20 years of flying ranged from 0.1 to 5 in 1,000. For the adult U.S. population the risk of dying from cancer is about 220 in 1,000.

Abnormalities, Radiation-Induced↗
PubMed1987

Dose-incidence relationships for exencephalia, anophthalmia and prenatal mortality in mouse embryos irradiated with fission neutrons or 250 kV X-rays.

Groups of pregnant mice were irradiated at selected times between 10.00 hours on gestation day 7 and 16.00 hours on day 8. Each group received 0.39 Gy of neutrons or 1.60 Gy of X-rays, or was sham irradiated. We identified a period of high susceptibility of the embryos to radiation-induced exencephalia, anophthalmia and prenatal mortality early in gestation day 8. Dose-incidence relationships in this period were investigated with 0.19-0.48 Gy of neutrons and with 0.40-2.00 Gy of X-rays. With increasing neutron dose, incidence of exencephalia in live embryos rose and then declined. This response suggests that embryos with neutron injury of the type that leads to exencephalia are at a greater risk of dying in utero than are similarly irradiated embryos not so injured, and that this risk increases with dose. A model is proposed that accounts for the shape of the neutron dose-incidence curve. X-ray-induced exencephalia showed only an increase with dose. In X-irradiated litters, almost invariably, the incidence of anophthalmia was higher in exencephalic than in nonexencephalic embryos and the ratio of these incidences (relative risk) decreased toward 1 with increasing dose. A model is proposed that accounts for these observations. The incidence of bilateral anophthalmia in X-irradiated embryos was higher than would be expected if the bilateral form resulted solely from independent injury at each of two equally susceptible sites.

Abnormalities, Radiation-Induced↗