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Biomedical subjects

C Sagan

Publications and source records attributed to C Sagan.

At least 55 records · Page 3Linked to original sources
PubMed1994

[Coarctation of the subrenal abdominal aorta revealed by aortic thrombosis].

The authors report the case of a 44 year-old female patient with no particular history who presented with a suddenly occurring severe ischemia of the lower limbs during exercise which revealed a total thrombosis of the subrenal abdominal aorta. Angiography confirmed the diagnosis and demonstrated a partial compensation of the lesion by an important collateral network developed from the parietal and mesenteric arteries. Ultrasonography and computerized tomography showed an extensive coarctation of the abdominal aorta. The main visceral (particularly renal) arterial branches were not involved. The pathologic subrenal aortic segment was surgically resected, and a prosthetic aortobifemoral bypass provided. The further course was marked by several occlusions of the low anastomoses by fibrous hyperplasia. Coarctation of the abdominal aorta is briefly reviewed. This disorder is infrequent, and its infrarenal form can be compatible with a normal life. It can be revealed late, particularly when a thrombotic complication occurs.

Aorta, Abdominal↗
PubMed1994

[Reproducibility of histological criteria of dysplasia in Barrett mucosa].

Barrett's mucosa is a precancerous condition. The goal of endoscopic surveillance for patients with Barrett's esophagus is to grade dysplasia. The diagnosis of dysplasia is difficult. The aim of this study was to determine the observer variation in diagnosis of dysplasia. Thirty-seven biopsies selected from Barrett's mucosa reported as having dysplasia between 1987 and 1988 were reviewed by 4 pathologists. The biopsies were classified according to the method of Riddell, as no dysplasia, indefinite for dysplasia, low-grade dysplasia and high-grade dysplasia. Each pathologist reviewed the biopsies alone and then together. There was a total agreement between the 4 pathologists in 20 out of 37 biopsies (54%). The pair-wise agreement varied between 65 and 84%. It was 84% when the pathologists belonged to the same institution. Of 222 double reviews made by 6 pairs of pathologists (37 biopsies x 6 pairs of pathologists), there were 58 disagreements: 19 low grade/high grade dysplasia, 2 high grade/indefinite for dysplasia, 1 high grade/no dysplasia, 18 low grade/indefinite for dysplasia, 2 low grade/no dysplasia, 16 indefinite for dysplasia/no dysplasia. At the second review when the pathologists evaluated the biopsies together, the agreement was 92%; there were 3 biopsies on which there was total disagreement: twice between high grade and low grade dysplasia, once between low grade dysplasia, indefinite for dysplasia and no dysplasia. This retrospective study has shown that disagreement between pathologists was rarely found on the biopsies diagnosed as having high grade dysplasia, more often on those diagnosed as having low grade dysplasia or indefinite for dysplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Barrett Esophagus↗
PubMed1993

A search for life on Earth from the Galileo spacecraft.

In its December 1990 fly-by of Earth, the Galileo spacecraft found evidence of abundant gaseous oxygen, a widely distributed surface pigment with a sharp absorption edge in the red part of the visible spectrum, and atmospheric methane in extreme thermodynamic disequilibrium; together, these are strongly suggestive of life on Earth. Moreover, the presence of narrow-band, pulsed, amplitude-modulated radio transmission seems uniquely attributable to intelligence. These observations constitute a control experiment for the serach for extraterrestrial life by modern interplanetary spacecraft.

Atmosphere↗
PubMed1993

Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter.

Polycyclic aromatic hydrocarbons (PAHs) are important components of the interstellar medium and carbonaceous chondrites, but have never been identified in the reducing atmospheres of the outer solar system. Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze. Titan tholin and a tholin generated in a crude simulation of the atmosphere of Jupiter are examined by two-step laser desorption/multiphoton ionization mass spectrometry. A range of two- to four-ring PAHs, some with one to four alkylation sites are identified, with net abundance approximately 10(-4) g g-1 (grams per gram) of tholins produced. Synchronous fluorescence techniques confirm this detection. Titan tholins have proportionately more one- and two-ring PAHs than do Jupiter tholins, which in turn have more four-ring and larger PAHs. The four-ringed PAH chrysene, prominent in some discussions of interstellar grains, is found in Jupiter tholins. Solid state 13C NMR spectroscopy suggests approximately equal to 25% of the total C in both tholins is tied up in aromatic and/or aliphatic alkenes. IR spectra indicate an upper limit in both tholins of approximately equal to 6% by mass in benzenes, heterocyclics, and PAHs with more than four rings. Condensed PAHs may contribute at most approximately 10% to the observed detached limb haze layers on Titan. As with interstellar PAHs, the synthesis route of planetary PAHs is likely to be via acetylene addition reactions.

Ammonia↗
PubMed1993

[Arterial embolic manifestations in the legs revealing isolated aorto-iliac Takayasu's disease].

The authors report the case of a 30-year-old woman with Takayasu's disease revealed by acute leg ischemia and complicated by abortion during the fourth month of pregnancy. Clinically suspect lesions were confirmed by angiography showing a severe stenosis at the aorto-iliac bifurcation complicated by overlying mild ectasic lesions and a large thrombus. A total occlusion of embolic origin was noted in the right popliteal artery. An attempt to open up the thrombosis at the bifurcation led unfortunately to massive rethrombosis requiring implantation of an aorto-iliac prosthesis. Histopathological examination of the aortic surgical specimen indicated Takayasu's disease; the placenta showed multiple infarcts. The complete angiographic study revealed no arterial involvement in any other region. Five months after the initial operation, rapid development of claudication in both lower limbs suggested stenosis at the prosthesis implantation sites which was confirmed by angiography. Initiation of general corticosteroid therapy led to partial remission in less than two weeks. The unusual feature in this case was the revelation of the affection by distal arterial embolic manifestations, which have been reported only exceptionally in the literature. Moreover, isolated involvement of the aorto-iliac bifurcation constitutes a rare form of Takayasu's disease. With respect to therapy, the implantation of a prosthesis was complicated by severe stenoses of the junction zones, which is unfortunately an event in the course of this affection. The normality of biologic inflammation studies did not suggest an initial need for corticosteroid therapy, especially in the case of an isolated arterial manifestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Abortion, Spontaneous↗
PubMed1993

[Diffuse sclerosing papillary carcinoma of the thyroid. Report of a case].

The authors report the case of a 12-year-old girl presenting with a diffuse sclerosing papillary carcinoma of the thyroid. The diagnosis was made on a total thyroidectomy specimen three months after thyroid enlargement was detected. This child had previously been treated medically for thyroiditis because of an enlarged thyroid gland with serum antithyroid autoantibodies. A few cases have been described in the literature. Six morphologic findings define this variant of papillary carcinoma: a diffuse growth pattern involving one or both lobes of the thyroid, prominent fibrosis, heavy lymphocytic infiltration with germinal centers, large numbers of psammoma bodies, squamous metaplasia and papillae within cleft-like tissue spaces. Some authors stated that this variant has a poorer prognosis than the usual papillary carcinoma of the thyroid. However, in some series a few patients survive without local recurrence or distant metastasis at a mean follow-up period of more than 10 years. Immunohistochemical studies have shown high accumulation of S-100 protein positive dendritic cells. Such an infiltration has been correlated with a better prognosis.

Carcinoma, Papillary↗
PubMed1993

[An unusual secondary localization of bronchial adenocarcinoma].

The authors report a rare case of metastatic carcinoma of the large bowel, secondary to a primary bronchogenic adenocarcinoma. Abdominal pain developed in a 44-year old man 5 months after lobectomy for lung adenocarcinoma. The diagnosis of a large caecal extraluminal mass was established by means of sonography, scanner and laparoscopy. Palliative resection (brain metastases) was performed. Postoperative histological examination revealed the resected tumor to be identical to the lung adenocarcinoma. The patient eventually died 4 months after resection (complication of intracranial hypertension). Diagnosis and therapeutic features of metastatic extra-thoracic lung carcinoma are discussed.

Adenocarcinoma↗
PubMed1992

Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life.

Sources of organic molecules on the early Earth divide into three categories: delivery by extraterrestrial objects; organic synthesis driven by impact shocks; and organic synthesis by other energy sources (such as ultraviolet light or electrical discharges). Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources. Which sources of prebiotic organics were quantitatively dominant depends strongly on the composition of the early terrestrial atmosphere. In the event of an early strongly reducing atmosphere, production by atmospheric shocks seems to have dominated that due to electrical discharges. Organic synthesis by ultraviolet light may, in turn, have dominated shock production, but only if a long-wavelength absorber such as H2S were supplied to the atmosphere at a rate sufficient for synthesis to have been limited by ultraviolet flux, rather than by reactant abundance. In the apparently more likely case of an early terrestrial atmosphere of intermediate oxidation state, atmospheric shocks were probably of little importance for direct organic production. For [H2]/[CO2] ratios of approximately 0.1, net organic production was some three orders of magnitude lower than for reducing atmospheres, with delivery of intact exogenous organics in interplanetary dust particles (IDPs) and ultraviolet production being the most important sources. At still lower [H2]/[CO2] ratios, IDPs may have been the dominant source of prebiotic organics on the early Earth. Endogenous, exogenous and impact-shock sources of organics could each have made a significant contribution to the origins of life.

Atmosphere↗
PubMed1992

Behçet's disease revealed by double peripheral arterial involvement.

We report the case of a 62-year-old man with Behçet's disease revealed by double aneurysmal involvement of the posterior tibial and popliteal arteries. The diagnosis was suggested because of repeated phlebitis, buccal aphthous ulcerations, and results of human leukocyte antigen gene typing. The different arguments leading to the diagnosis of Behçet's disease and appropriate treatment are presented.

Aneurysm↗
PubMed1992

Radiation chemistry in the Jovian stratosphere: laboratory simulations.

Low-pressure continuous-flow laboratory simulations of plasma induced chemistry in H2/He/CH4/NH3 atmospheres show radiation yields of hydrocarbons and nitrogen-containing organic compounds that increase with decreasing pressure in the range 2-200 mbar. Major products of these experiments that have been observed in the Jovian atmosphere are acetylene (C2H2), ethylene (C2H4), ethane (C2H6), hydrogen cyanide (HCN), propane (C3H8), and propyne (C3H4). Major products that have not yet been observed on Jupiter include acetonitrile (CH3CN), methylamine (CH3NH2), propene (C3H6), butane (C4H10), and butene (C4H8). Various other saturated and unsaturated hydrocarbons, as well as other amines and nitriles, are present in these experiments as minor products. We place upper limits of 10(6)-10(9) molecules cm-2 sec-1 on production rates of the major species from auroral chemistry in the Jovian stratosphere, and calculate stratospheric mole fraction contributions. This work shows that auroral processes may account for 10-100% of the total abundances of most observed organic species in the polar regions. Our experiments are consistent with models of Jovian polar stratospheric aerosol haze formation from polymerization of acetylene by secondary ultraviolet processing.

Ammonia↗
PubMed1992

Titan: a laboratory for prebiological organic chemistry.

When we examine the atmospheres of the Jovian planets (Jupiter, Saturn, Uranus, and Neptune), the satellites in the outer solar system, comets, and even--through microwave and infrared spectroscopy--the cold dilute gas and grains between the stars, we find a rich organic chemistry, presumably abiological, not only in most of the solar system but throughout the Milky Way galaxy. In part because the composition and surface pressure of the Earth's atmosphere 4 x 10(9) years ago are unknown, laboratory experiments on prebiological organic chemistry are at best suggestive; but we can test our understanding by looking more closely at the observed extraterrestrial organic chemistry. The present Account is restricted to atmospheric organic chemistry, primarily on the large moon of Saturn. Titan is a test of our understanding of the organic chemistry of planetary atmospheres. Its atmospheric bulk composition (N2/CH4) is intermediate between the highly reducing (H2/He/CH4/NH3/H2O) atmospheres of the Jovian planets and the more oxidized (N2/CO2/H2O) atmospheres of the terrestrial planets Mars and Venus. It has long been recognized that Titan's organic chemistry may have some relevance to the events that led to the origin of life on Earth. But with Titan surface temperatures approximately equal to 94 K and pressures approximately equal to 1.6 bar, the oceans of the early Earth have no ready analogue on Titan. Nevertheless, tectonic events in the water ice-rich interior or impact melting and slow re-freezing may lead to an episodic availability of liquid water. Indeed, the latter process is the equivalent of a approximately 10(3)-year-duration shallow aqueous sea over the entire surface of Titan.

Amino Acids↗
PubMed1992

[Primary colonic linitis plastica. Apropos of 3 new cases].

Primary linitis plastica of the colon is unfrequent. Since Laufmann and Saphir's first cases in 1951, less than 50 cases have been described, to which our three new cases now add. The intramural origin with late involvement of the mucosa delays the onset of clinical signs, and accounts for the rarity of overt bleeding and for the frequent failure of biopsy. The radiological appearance is that a tubular colic narrowing without ulceration or intraluminal process. Endoscopy shows regular, centered stenosis with few modifications of the mucosa. The clinicopathological diagnosis is primarily microscopic: presence of isolate mucosecretory neoplastic cells infiltrating the whole wall of the colon without destroying it. Because of its potential for local invasion and of its centripetal extension, linits is often detected only at the equivalent of stage C (Astler-Coller). The prognosis is poor, with survival averaging 1 year after the onset of the first clinical signs.

Adult↗
PubMed1992

[Multiple granular cell tumor of the colon].

With reference to a case of multiple colorectal granular cell tumors, the authors briefly review the literature concerning this unusual tumor localization. This case demonstrates the most common appendicular, caecal and rectal forms among the localizations of colonic granular cell tumors: as well as the possible proliferation of many other tumors especially in caecal localizations. However the course of the disease is slow, and at the present time only one case report of malignant colonic TCG has been published.

Adult↗
PubMed1991

Electrical energy sources for organic synthesis on the early Earth.

In 1959, Miller and Urey (Science 130, 245) published their classic compilation of energy sources for indigenous prebiotic organic synthesis on the early Earth. Much contemporary origins of life research continues to employ their original estimates for terrestrial energy dissipation by lightning and coronal discharges, 2 x 10(19) J yr-1 and 6 x 10(19) J yr-1, respectively. However, more recent work in terrestrial lightning and point discharge research suggests that these values are overestimates by factors of about 20 and 120, respectively. Calculated concentrations of amino acids (or other prebiotic organic products) in the early terrestrial oceans due to electrical discharge sources may therefore have been equally overestimated. A review of efficiencies for those experiments that provide good analogues to naturally-occurring lightning and coronal discharges suggests that lightning energy yields for organic synthesis (nmole J-1) are about one order of magnitude higher than those for coronal discharge. Therefore organic production by lightning may be expected to have dominated that due to coronae on early Earth. Limited data available for production of nitric oxide in clouds suggests that coronal emission within clouds, a source of energy heretofore too uncertain to be included in the total coronal energy inventory, is insufficient to change this conclusion. Our recommended values for lightning and coronal discharge dissipation rates on the early Earth are, respectively, 1 x 10(18) J yr-1 and 5 x 10(17) J yr-1.

Earth, Planet↗
PubMed1991

Plasma discharge in N2 + CH4 at low pressures: experimental results and applications to Titan.

We report the yields of gaseous hydrocarbons and nitriles produced in a continuous flow, low-dose, cold plasma discharge excited in a 10% CH4, 90% N2 atmosphere at 295 K and pressures p of 17 and 0.24 mbar, and use the results to compute expected abundances of minor constituents in Titan's atmosphere. These experiments are, by design, relevant to the atmospheric chemistry induced by cosmic rays in Titan's troposphere and (at the lower pressure) to chemistry initiated by Saturnian magnetospheric electrons and other charged particle sources which excite stratospheric aurorae. At p = 17 mbar, 59 gaseous species including 27 nitriles are detected in overall yield 4.0 (C + N) atoms incorporated into products per 100 eV (heV). At p = 0.24 mbar, 19 species are detected, including six nitriles and three other unidentified N-bearing compounds; the yield is 0.79 (C + N)/heV, a mild decrease with pressure. The types of molecules formed change more markedly, with high degrees of multiple bonding at 0.24 mbar prevailing over more H-saturated molecules at 17 mbar. The molecules and yields at 0.24 mbar bear a striking resemblance to the minor constituents found in Titan's atmosphere, all of which are abundant products in the laboratory experiment. Using the altitude-integrated flux of charged particle energy deposition at Titan, the laboratory yields at p = 0.24 mb, and a simple eddy mixing model, we compute absolute stratospheric column abundances and mole fractions. These are found to be in very good agreement with the Voyager IRIS observations. Except for the primarily photochemical products, C2H6 and C3H8, the match is much better than that obtained by photochemical-kinetic models, demonstrating that properly designed laboratory experiments are directly applicable to modeling radiation-chemical processes in planetary atmospheres. On the basis of this agreement we expect CH3-C triple bond N (ethanenitrile = acetonitrile) CH2=CH-CH=CH2 (1,3-butadiene), CH2=C=CH2 (1,2-propadiene = allene), and CH2=CH-C triple bond CH (1-buten-3-yne) to be present at mol fractions X > 10(-9), and CH2=CH-C triple bond N (propenenitrile), CH3-CH=CH2 (propene), and CH3-CH2-C triple bond N (propanenitrile) at X > 10(-10) in Titan's atmosphere.

Astronomical Phenomena↗
PubMed1991

CH4/NH3/H2O spark tholin: chemical analysis and interaction with Jovian aqueous clouds.

The organic solid (tholin) produced by spark discharge in a CH4 + NH3 + H2O atmosphere is investigated, along with the separable components of its water-soluble fraction. The chemistry of this material serves as a provisional model for the interaction of Jovian organic heteropolymers with the deep aqueous clouds of Jupiter. Intact (unhydrolyzed) tholin is resolved into four chemically distinct fractions by high-pressure liquid chromatography (HPLC). Gel filtration chromatography reveals abundant components at molecular weights approximately or equal to 600-700 and 200-300 Da. Gas chromatography/mass spectrometry of derivatized hydrolysis products of unfractionated tholin shows about 10% by mass protein and nonprotein amino acids, chiefly glycine, alanine, aspartic acid, beta-alanine, and beta-aminobutyric acid, and 12% by mass other organic acids and hydroxy acids. The stereospecificity of alanine is investigated and shown to be racemic. The four principal HPLC fractions yield distinctly different proportions of amino acids. Chemical tests show that small peptides or organic molecules containing multiple amino acid precursors are a possibility in the intact tholins, but substantial quantities of large peptides are not indicated. Candidate 700-Da molecules have a central unsaturated, hydrocarbon- and nitrile-rich core, linked by acid-labile (ester or amide) bonds to amino acid and carboxylic acid side groups. The core is probably not HCN "polymer." The concentration of amino acids from tholin hydrolysis in the lower aqueous clouds of Jupiter, about 0.1 micromole, is enough to maintain small populations of terrestrial microorganisms even if the amino acids must serve as the sole carbon source.

Amino Acids↗