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Biomedical subjects

C Sagan

Publications and source records attributed to C Sagan.

88 records · Page 5Linked to original sources
PubMed1970

Shock synthesis of amino acids in simulated primitive environments.

A mixture of gases roughly simulating the primitive terrestrial atmosphere has been subjected to shock heating followed by a rapid thermal quench. Under strictly homogeneous conditions there is a very high efficiency of 5 x 10(10) molecules per erg of shock-injected energy for production of alpha-amino acids. Calculations suggest that rapid quenching bypasses the usual thermochemical barrier. The product of energy flux and efficiency implies the unexpected conclusion that shocks occurring on atmospheric entry of cometary meteors and micrometeorites and from thunder may have been the principal energy sources for pre-biological organic synthesis on the primitive earth.

Amino Acids↗
PubMed1964

Exobiology: a critical review.

The quest for life beyond the Earth can be implemented in three ways. First, we may study contemporary terrestrial biology and organic chemistry to approach the problem of the origin of life on Earth. If it appears relatively easy for life to have emerged in the primitive terrestrial environment, it may follow that the origin of life is a fairly general planetary phenomenon. Second, we can investigate the physical environments of the planets, and determine whether the conditions there are so severe that living processes are entirely excluded, even allowing for the adaptability of life. Third, the planets may be studied for direct evidence of indigenous life forms. All three approaches are beset with uncertainties, and it is important to state at the outset that no completely convincing evidence exists for extraterrestrial life. The problem often reduces to probability considerations, and to estimates of observational reliability. At convenient places in the marshalling of evidence, I shall try to pause and give brief expression to alternative interpretations. In almost all cases, an optimistic view can be found which holds that the evidence is strongly suggestive of, or at the worst, not inconsistent with, the existence of extraterrestrial life; and a pessimistic view can be found, which holds that the evidence adduced in favor of extraterrestrial life is unconvincing, irrelevant, or has an alternative, non-biological explanation. I leave it to the reader to pick his own way among the factions.

Atmosphere↗
PubMed1964

Biological contamination of Mars. I. Survival of terrestrial microorganisms in simulated Martian environments.

It has been postulated that the accidental introduction of terrestrial microorganisms to other planets during the course of space exploration might impede or bias the detection of organic matter and possible indigenous organisms, and thereby confuse subsequent studies of extraterrestrial life. To assess the likelihood of biological contamination of Mars, we have applied the principle of natural selection on a laboratory scale. Terrestrial microorganisms were collected from a variety of environments, including regions of high alkalinity, low mean daily temperature, and low annual rainfall. The air-dried soils were then subjected to a simulated Martian environment involving 12-hour freeze-thaw cycles from about -60 degrees C to about +20 degrees C; atmospheres of 95 per cent nitrogen, 5 percent carbon dioxide and low moisture content: < or = 0.1 atm pressure; and a total ultraviolet dose at 2537 angstrom of 10(9) erg cm-2. In some experiments, organic supplements were provided. Survivors were scored on supplemented agar. Preliminary results indicate a wide variety of survivors, even when no organic supplements were introduced. Survivors included obligate and facultative anaerobic spore-formers and non-spore-forming facultative anaerobic bacteria. Diurnal freezing and thawing was continued for six months. There was no significant loss of viability after the first freeze-thaw cycle. An extensive literature survey shows that survival of terrestrial microorganisms under individual simulated Martian conditions has been known for decades. The present investigation shows the absence of pronounced synergistic effects inhibiting survival. The probable existence of organic matter and moisture on Mars, at least in restricted locales and times, makes it especially likely that terrestrial microorganisms can also reproduce on Mars. The demonstration that all samples of terrestrial soil tested contain a population of microorganisms which survive in simulated Martian environments strongly underscores the need for scrupulous sterilization of all spacecraft intended for Mars landing.

Bacillus subtilis↗
PubMedDate not supplied

Plasma treatment effects on the tantalum Strecker stent implanted in femoral arteries of sheep.

PURPOSE: To evaluate the effects of plasma treatment, a cleaning process for removal of organic contaminants from the knit-wire surface of tantalum Strecker stents, on biocompatibility and thrombogenicity. METHODS: A treated or untreated stent was randomly implanted in both femoral arteries of 15 sheep studied for periods of 4 (group 1), 15 (group 2), or 42 (group 3) days. Patency, histological changes, and mechanical effects were compared by means of radiologic and pathologic controls. RESULTS: Plasma treatment did not influence overall patency (93.3% vs 86.7%), maximal neointimal hyperplasia in groups 2 and 3 (801 +/- 123 vs 733 +/- 179 microns), or media thinning in any group (254 +/- 92 vs 285 +/- 72 microns), but modified the elastic properties of the stents by limiting (p = 0.01) shortening at implantation. CONCLUSION: Plasma treatment does not affect the biocompatibility and thrombogenicity of Strecker stents implanted in normal femoral arteries of sheep but modifies their elastic properties. Further studies are needed to account for this effect.

Animals↗
PubMedDate not supplied

Giant cell arteritis presenting with aortic dissection: two cases and review of the literature.

Aortitis is the most serious location of the disease giant cell (temporal) arteritis (GCA). Aortic dissection or the rupture of an aortic aneurysm can be responsible for sudden death among patients with GCA. This report discusses two cases of GCA presenting with aortic dissection. One case had histologically proven giant cell aortitis. The second case was a fatal aortic dissection preceded by a stroke. We describe the main features of aortic dissection and aortitis during GCA, reviewing the existing literature on this subject, and focusing on the requirement of prospective aortic imaging studies to screen patients with this kind of location.

Aged↗
PubMedDate not supplied

Lymphoscintigraphy in the sentinel lymph node technique for breast tumor: value of early and late images for the learning curve.

As the performance of early (H+1 to H+4) and late (D1) lymphoscintigraphic images raises organizational problems in outpatient surgery for breast cancer, only early images are generally obtained. The present study evaluated whether two series of images are better than one and defined the advantages of both methodologies. One hundred and eighteen patients with infiltrating breast carcinoma (T(0), T(1) and T(2)) were included in the study: 87 in group A (early and late images) and 31 in group B (only early images). All patients received two peritumoral injections of (99m)Tc-sulfur colloid, 15-18 MBq (group A) and <15 MBq (group B). During the operation, the patent blue bye technique was associated with radioactivity detection. The two groups were comparable for histological type and tumor size and localization. Successful localization of sentinel nodes on early lymphoscintigraphic images was significantly greater for group B. The identification of a sentinel node focus on early lymphoscintigraphy increased by 10% during the study. Sentinel node detection by the isotopic method alone, or the two methods combined, was comparable for both groups. In radioactivity detection, the count rate for sentinel nodes versus background (contralateral breast) was similar for the two groups. During the learning phase, two series of images gave a definite advantage. Subsequently, lymphoscintigraphy performed at +2 h was sufficient (the results for the two groups became indistinguishable).

Adult↗