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  • 1975-1979  (8)
  • 1
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1435-1803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of anaesthetic agents and propranolol pretreatment on the adequacy of cardiovascular adjustment to progressive normovolaemic hemodilution and to the combination of anaemia and blood loss was studied in a total of 18 dogs which were divided into 3 groups of 6 dogs each. One group received neuroleptanalgesia, the second group was anaesthetized with halothane (1%), group three received halothane (1%) and was pretreated with propranolol (0.5 mg/kg). Acute isovolaemic anaemia was produced by a stepwise exchange of blood with 6% dextran. The total exchange volume was 70 ml/kg which was associated with a decrease of mean hematocrit values from about 45% to 16%. Cardiac output rose continuously with progressive hemodilution, the maximum percentage increases were 39% in the neuroleptanalgesia-group, 59% in the halothane-group and in the animals with halothane anaesthesia and propranolol pretreatment. These changes were due to increases in both heart rate and stroke volume, the greatest percent rise in stroke index (36%) and the least change in heart rate (+18%) being observed in the propranolol-treated dogs. Apart from a small overshoot of the systemic oxygen availability during the initial stages of exchange transfusion in the neuroleptanalgesia- and halothane-group, the reduced arterial oxygen content was not compensated by the increase in cardiac output. Consequently, there was a continuous reduction of the systemic oxygen transport capacity with a maximum decrease of about 40% in either group. Systemic oxygen uptake was maintained over a wide range of hematocrits by an increased extraction of oxygen from blood. Mean arterial pressure essentially remained unaffected in each of the groups, the changes in total peripheral resistance were inverse to that of cardiac output and showed little differences between the three groups in response to exchange transfusions. Left ventricular dP/dt values, left ventricular volumes and ejection fractions indicated an improved ventricular performance and a participation of the Frank-Starling mechanism in the response of the heart to isovolaemic hemodilution. The combination of hemodilution and limited blood loss (15 ml/kg) led to a significant reduction in arterial pressure and cardiac output, but all dogs tolerated this amount of hemorrhage and there was no indication of critical impairment of cardiac performance in any of the 3 groups. No major changes of the acid-base status were observed throughout the study. Thus, the adjustment of the normal cardiovascular system to acute normo- and hypovolaemic hemodilution appeared to be largely independent of the type of anaesthesia and of the presence or absence of betareceptor blockade.
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  • 5
    ISSN: 1435-1803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The adequacy of myocardial oxygen supply was studied during acute progressive isovolaemic hemodilution and during the combination of anaemia and blood loss under three different anaesthetic conditions: neuroleptanalgesia (6 dogs), halothane anaesthesia (1%, 6 dogs) and halothane anaesthesia (1%) plus propranolol (0.5 mg/kg) pretreatment (6 dogs). Acute isovolaemic anaemia was produced by a stepwise exchange of blood with 6% dextran leading to a decrease of the mean hematocrit values from about 45% to about 16%. Myocardial blood flow increased by 224% in the neuroleptanalgesia-group, by 179% in the halothane-group and by 143% in the halothane plus propranolol-group. The changes in MBF were accompanied by a corresponding fall in coronary vascular resistance. Coronary sinus oxygen saturations slightly decreased but remained within the physiological range in each of the three groups. Left ventricular oxygen consumption continuously rose in the dogs with neuroleptanalgesia, the maximum increase was 32%. Only small changes of the myocardial O2-consumption were observed in the halothane-group during moderate degrees of anaemia. LV $$\dot VO_2 $$ in this group significantly increased only when the hematocrit was 20% or less. No significant changes of the left ventricular oxygen consumption occurred in the animals which had received halothane anaesthesia and were pretreated with propranolol. Myocardial lactate extraction decreased but never reached critically low values. The coronary dilatory capacity was shown not to be exhausted under any anaesthetic condition. About 30–40% of this capacity remained at hematocrit values between 10 and 15%. The combination of hemodilution and limited blood loss (15 ml/kg) led to a significant fall in myocardial blood flow and oxygen consumption, coronary vascular resistance tended to increase. Coronary sinus oxygen saturation and myocardial lactate extraction changed little in response to the combination of hemodilution and blood loss, indicating that aerobic metabolism was maintained under any anaesthetic condition used in this study.
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  • 6
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Diels-Alder Reactions. VII. The Isomerization of 2-Vinylbicyclo[2,2,1]hept-5-eneThe isomerization of exo/endo-2-vinylbicyclo[2,2,1]-hept-5-ene in the presence of Na/Al2O3 rapidly gives the thermodynamic equilibrium between exo- and endo-2-vinylbicyclo-[2,2,1]hept-5-ene and cis- and trans-2-ethylidenbicyclo[2,2,1]-hept-5-ene. Far more slowly vinylnortricyclene is formed, which enriches to an equilibrium concentration of about 75% at 60°C. The dependence of equilibrium constants of isomerization on temperature allows the calculation of enthalpies and entropies of isomerization.
    Notes: Die Isomerisierung von exo/endo-2-Vinylbicyclo[2,2,1]hepten-(5) in Gegenwart von Na/Al2O3 führt schnell zur Einstellung des thermodynamischen Gleichgewichtes zwischen exo- und endo-2-Vinylbicyclo[2,2,1]hepten-(5) und cis- und trans-2-Äthyliden-bicyclo[2,2,1]-hepten-(5). Wesentlich langsamer wird Vinylnortricyclen gebildet, das sich bis zu einer Gleichgewichts-konzentration von etwa 75% bei 60°C anreichert. Die Temperaturabhängigkeit der Isomerisierungs-gleichgewichtskonstanten gestattet die Berechnung der Isomerisierungsenthalpien und -entropien.
    Additional Material: 2 Tab.
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  • 7
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: DIELS-ALDER-Reactions. VI. Further Studies of the Reaction Products Formed by the Homodimerization of Acyclic 1,3-Diolefines with Five Carbon AtomsThe distribution of the products of homodimerization of isoprene, trans-piperylene and cis-piperylene in toluene as solvent was determined as a function of the reaction temperature; the products formed by concurrent reactions were obtained by extrapolating the conversion to zero. From the data obtained the rate constants and the activation parameters were calculated for the six-membered ring dimers formed as the only products of the thermal homodimerization of transpiperylene, and for the four membered, six-membered and eight-membered cyclic compounds formed from isoprene.As was already found in similar studies of 1,3-butadiene, also in the case of homodimerization of isoprene, the activation parameters of the symmetry-allowed six-membered ring formation and of the symmetry-forbidden formation of four-membered and eight-membered cyclic dimers do not differ much from each other.
    Notes: Es wurde die Produktverteilung der Homodimeren von Isopren, trans-Piperylen und cis-Piperylen in Abhängigkeit von der Reaktionstemperatur in Toluol als Lösungsmittel bestimmt, und durch Extrapolation auf den Umsatz null wurden die durch Konkurrenzreaktionen entstehenden Produkte ermittelt. Aus den erhaltenen Meßdaten wurden die Geschwindigkeitskonstanten und die Aktivierungsparameter für die Bildung der bei der thermischen Homodimerisierung des trans-Piperylens ausschließlich entstehenden Sechsringdimeren sowie für die aus Isopren gebildeten Vier-, Sechs- und Achtringprodukte berechnet.Wie bei analogen Untersuchungen des Butadiens bereits festgestellt wurde [3], liegen die Aktivierungsparameter der symmetrieerlaubten Sechsringbildung und der symmetrieverbotenen Bildung von Vier- u. Achtringdimeren auch bei der Homodimerisierung des Isoprens sehr nahe beieinander.
    Additional Material: 5 Tab.
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  • 8
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: About the Bond Isomerization of Acetylenic and Allenic Hydrocarbons. II. Kinetic Studies on the Isomerization of Propine and Allene with an Acidic Molecular Sieve Catalyst in the Gas PhaseThe gas phase isomerization of propine and allene (propadiene) was studied on a molecular sieve 13X, modified with Ni and Ca, in the temperature range of 108-173 °C with the aid of a close circulation apparatus. The bond isomerization may be considered as an example of a monomolecular, reversible, heterogeneous catalyzed reaction of the type A ⇌ B. For the studied isomerizations the rate equations of the Langmuir-Hinshelwood-type were derived by kinetic analysis of the experimentally obtained dependence of the mole fractions from the residence time. The rate and adsorption constants of the Langmuir-Hinshelwood equations were determined, their physical interpretation was possible.
    Notes: Die Gasphasen-Isomerisierung des Propins und Allens (Propadiens) wurde an einem mit Ni und Ca modifizierten Molekularsieb vom Typ 13 X im Temperaturbereich von 108 bis 173 °C in einer Zirkulationsapparatur mit geschlossenem Kreislauf kinetisch verfolgt. Für die als Prototyp einer monomolekularen, reversiblen, heterogen katalysierten Reaktion vom Typ A ⇌ B anzusehende Bindungsisomerisierung wurden vollständige Geschwindigkeitsausdrücke vom Langmuir-Hinshelwood-Typ abgeleitet und durch kinetische Analyse der experimentell bestimmten Molenbruch-Kontaktzeit-Verläufe die Geschwindigkeits- und Adsorptionsgleichgewichtskonstanten ermittelt. Sämtliche Konstanten sind physikalisch interpretierbar.
    Additional Material: 9 Ill.
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