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Biomedical subjects

J W Lewis

Publications and source records attributed to J W Lewis.

At least 145 records · Page 8Linked to original sources
PubMed1993

Hypothermic circulatory arrest and the management of giant and large cerebral aneurysms.

The surgical adjuncts of hypothermic circulatory arrest, exsanguination, and barbiturate cerebral protection were evaluated in nine cases of cerebral aneurysms felt unapproachable by conventional surgery. These techniques were used in seven posterior circulation aneurysms, two of which were giant and two giant anterior circulation aneurysms originating at the middle cerebral artery bifurcation. Four patients had excellent outcomes, two had a fair result, one had a poor result, and two died. The outcome of surgery reflected that of the management of patients with unruptured or ruptured aneurysms. Three of the four patients who did well had unruptured aneurysms, and all three of the cases in which death or a poor outcome resulted occurred in patients presenting with subarachnoid hemorrhage. The rationale for the use of hypothermic circulatory arrest is discussed, and the surgical indications, techniques, and anesthetic considerations are also reviewed.

Adolescent↗
PubMed1993

The prevalence and intensity of infection with helminth parasites in Mus spretus from the Setubal Peninsula of Portugal.

The results of a 5 year study of helminth parasites of Mus spretus, are reported. Six nematode and 5 cestode species were identified but no helminth showed 100% prevalence in M. spretus, the most commonly encountered nematode and cestode species being Syphacia obvelata (46.6%) and Taenia taeniaeformis (22.4%). Among the more unusual helminth species identified was Eucoleus bacillatus, a capillariid nematode inhabiting the stomach musculature. This species was identified in 3 of the 5 years of the study. The results are discussed in the broader context of previous studies and the epidemiology of rodent helminth infections in general.

Animals↗
PubMed1993

Epidemiology of Toxocara canis in red foxes (Vulpes vulpes) from urban areas of Bristol.

A descriptive epidemiological survey was undertaken of the ascarid nematode Toxocara canis in 521 red foxes (Vulpes vulpes) during the period January 1986 to July 1990. Age-prevalence and age-intensity profiles show that worm burdens are significantly higher in cubs than in subadult or adult foxes and higher in subadult than in adult foxes. Seasonal variations in worm burdens occur, with the highest prevalences and intensities being found during the spring, when cubs are born, and in the summer months. Prevalences and intensities then decrease during the autumn and winter months in both subadult and adult foxes, but, during this period, prevalences are significantly higher in male than in female foxes. Variations in worm burdens in the fox population are likely to be related to the reproductive cycle of the fox, with a high proportion of cubs becoming infected in utero. The role of the fox in the transmission of T. canis in the urban environment is discussed.

Age Factors↗
PubMed1992

Photointermediates of visual pigments.

Much progress has been made in recent years toward understanding the interactions between various proteins responsible for visual transduction which are initiated by an activated state of visual pigments. However, the changes which take place in the visual pigments themselves to convert them to the activated state are more poorly understood. Many spectroscopic techniques have been applied to this problem in recent years and considerable progress has been made. A major goal of these efforts is to understand at which stages protein change occurs and to characterize its structural features. In the visual system evidence is accumulating, for example, that chromophore independent protein change begins immediately prior to lumirhodopsin formation. Considerable insight has been gained recently into the early intermediates of visual transduction and the stage is set to achieve similar understanding of the later intermediates leading to rhodopsin's activated state.

Photolysis↗
PubMed1992

The utility of a double-lumen tube for one-lung ventilation in a variety of noncardiac thoracic surgical procedures.

To determine the utility of one-lung ventilation (OLV) in a variety of noncardiac thoracic surgical procedures, 200 patients were studied to document the ease of double-lumen tube (DLT) placement, associated complications, intraoperative respiratory changes, and methods for managing hypoxic events. Most tubes could be placed, repositioned when necessary, and secured within 12 minutes. By defining tube position with fiberoptic bronchoscopy, auscultatory assessment of placement was found to be incorrect in 38.0% of patients. The tip occluded the respective upper lobe orifice in 40.5% of this subgroup, the endobronchial cuff was at or above the carina in 38.7%, and in the wrong mainstem bronchus in 20.8%. During OLV, PaO2 initially fell to approximately 200 mmHg in most patients but gradually rose during the balance of the operation. Hypoxia (PaO2 less than 80 mmHg) during OLV developed in 28.5% of patients. Preoperative spirometry and arterial blood gases had no predictive value for this complication. Pulse oximetry values between 95% and 100% reliably reflected systemic arterial oxygen saturation. Hypoxia occurring during OLV was successfully reversed in 40.0% of instances by positive end-expiratory pressure (PEEP) to the ventilated lung. The addition of continuous positive airway pressure (CPAP) to the nonventilated lung reversed persistent hypoxia in virtually all cases. There was no difference in oxygenation, carbon dioxide elimination, airway pressures, or intraoperative complications noted between right and left double-lumen tubes. In conclusion, a DLT for OLV can expeditiously and safely be placed. Because auscultation for tube position is unreliable, bronchoscopic assessment of final position should be performed in every instance. Hypoxia during OLV can be detected reliably by pulse oximetry.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Sites of encystment by the metacercariae of Echinoparyphium recurvatum in Lymnaea peregra.

Experimental infection of Echinoparyphium recurvatum von Linstow (Digenea: Echinostomatidae) cercariae in the snail second intermediate host Lymnaea peregra Müller shows that metacercarial encystment takes place on the lining of the mantle cavity, pericardial cavity and kidney lumen, with the mantle cavity the most preferred site. All three sites are accessible via the body openings. The metacercariae appear to be more susceptible to encapsulation in the visceral mass than in the cavity of the mantle, pericardium and the lumen of the kidney.

Animals↗
PubMed1992

The laboratory maintenance of Sanguinicola inermis Plehn, 1905 (Digenea: Sanguinicolidae).

Methodology is described for the laboratory maintenance of the life-cycle of Sanguinicola inermis, using common carp (Cyprinus carpio) as the definitive host and Lymnaea peregra as the intermediate host. Lymnaea auricularia was also infected but is not considered to be a suitable laboratory host. Tench (Tinca tinca) were susceptible to infection at high cercarial doses but subsequent infection rates were low. Goldfish (Carassius auratus) and Lymnaea stagnalis were refractory to laboratory infection.

Animals↗
PubMed1992

Photolysis of rhodopsin results in deprotonation of its retinal Schiff's base prior to formation of metarhodopsin II.

Absorption changes following photolysis of bovine rhodopsin in mildly sonicated membrane suspensions are monitored at 25 degrees C. Difference spectra collected at 17 times between 1 microsecond and 75 ms following excitation are analyzed globally using singular value decomposition and non-linear least-squares fitting techniques. The results are not consistent with the simple scheme: Lumirhodopsin-->Metarhodopsin I<-->Metarhodopsin II, but indicate that an intermediate with a deprotonated Schiff's base is formed nearly simultaneously with metarhodopsin I upon the decay of Lumirhodopsin.

Animals↗
PubMed1992

Clocinnamox: a novel, systemically-active, irreversible opioid antagonist.

The warm water (55 degrees C) tail-withdrawal procedure was used to assess the analgesic effects of the prototypic mu opioid agonists, morphine and fentanyl, in mice. Both drugs produced full analgesic effects under these conditions, which were dose-dependently antagonized by naltrexone. The pA2 values for naltrexone with morphine and with fentanyl were not significantly different. Low doses (e.g., 0.32 mg/kg) of clocinnamox [C-CAM.14 beta-(p- chlorocinnamoylamino)-7,8-dihydro-N-cyclopropylmethylnormorphin one mesylate] produced rightward shifts in the dose-effect curves for each drug, whereas high doses (e.g., 32 mg/kg) depressed the maximal analgesic response. In addition, it was observed that higher doses of C-CAM were required to produce a shift down in the fentanyl dose-effect curve than were required to produce a shift down in the morphine dose-effect curve, which suggests that fentanyl is more efficacious than morphine. The highest dose of C-CAM (32 mg/kg) antagonized the analgesic effect of morphine for up to 8 days. In contrast, the antagonist activity of naltrexone (100 mg/kg) against morphine lasted for only 2 days. Finally, when naloxone was administered simultaneously with 32 mg/kg C-CAM 2 days before determination of the morphine dose-effect function, the antagonist effect of C-CAM was prevented in a dose-dependent manner. Taken together, these results suggest that C-CAM may be producing its antagonist action at opioid receptors through a nonequilibrium mechanism.

Analgesia↗
PubMed1992

Scanning electron microscope and histological studies of rare triradiate forms of Taenia pisiformis from dogs in Cairo.

Of 5,404 domestic dogs examined for normal and abnormal Taenia pisiformis in Cairo, Egypt, one dog contained 3 triradiate specimens while 3,569 harboured one or more normal cestodes. The study revealed a ratio of one triradiate to 5,620 normal adult worms in the parasite population and a prevalence of 0.02% for the triradiate forms. Polyradiate forms are far less common in this large survey than has been indicated in previous reports.

Animals↗
PubMed1991

Photolysis intermediates of human rhodopsin.

Photochemical studies were conducted on human rhodopsin at 20 degrees C to characterize the intermediates which precede the formation of metarhodopsin II, the trigger for the enzyme cascade mechanism of visual transduction. Human rhodopsin was prepared from eyes which had previously been used for corneal donations. Time resolved absorption spectra collected from 10(-8) to 10(-6) s after photolysis of human rhodopsin in detergent suspensions displayed biexponential decay kinetics. The apparent lifetimes obtained from the data are 65 +/- 20 and 292 +/- 25 ns, almost a factor of 2 slower than the corresponding rates in bovine rhodopsin. The spectra can be fit well using a model in which human bathorhodopsin decays toward equilibrium with a blue-shifted intermediate (BSI) which then decays to lumirhodopsin. Spectra and kinetic rate constants were determined for all these intermediates using a global analysis which showed that the spectra of the human intermediates are remarkably similar to bovine intermediates. Microscopic rate constants derived from this model are 7.4 x 10(6) s-1 for bathorhodopsin decay and 7.5 x 10(6) s-1 and 4.6 x 10(6) s-1 for the forward and reverse reactions of BSI, respectively. Decay of lumirhodopsin to later intermediates was studied from 10(-6) to 10(-1) s after photolysis of rhodopsin in human disk membrane suspensions. The human metarhodopsin I in equilibrium metarhodopsin II equilibrium appears to be more forward shifted than in comparable bovine studies.

Humans↗
PubMed1991

Heligmosomoides polygyrus or Nematospiroides dubius?

The intestinal trichostrongylid nematode of mice, Heligmosomoides polygyrus bakeri, is often referred to as Nematospiroides dubius. Here, Jerzy Behnke, Anne Keymer and John Lewis ask the question: which is correct?

Journal Article↗
PubMed1991

Comparison of isolates and species of Toxocara and Toxascaris by biosynthetic labelling of somatic and ES proteins from infective larvae.

Infective-stage larvae of three different isolates of Toxocara canis were intrinsically ([35S]methionine) labelled in culture, to determine the presence of similarities or differences in the somatic and ES antigens expressed between larvae derived from different hosts and different geographical regions. Two other closely related ascaridids, Toxascaris leonina which infects cats and dogs, and Toxocara vitulorum (Neoascaris vitulorum) which infects cattle, were also compared to T. canis larvae by this method. Overall comparisons were made by 1- and 2-dimensional electrophoresis, while immunological cross-reactivities between the different species were analysed by radio-immunoprecipitation. Our results show that extensive physicochemical characteristics are shared between T. canis isolates, both from different hosts and different geographical locations. A substantial overlap was revealed when T. canis and T. vitulorum antigens were compared, whereas Toxascaris was found to produce a distinct antigen profile: this result was independent of whether methionine- or Iodogen-labelled products were being considered. Antigen recognition by polyclonal antibodies raised to all three species and to the cat ascaridid Toxocara cati, revealed considerable cross-reactivities. The cross-reactions were especially prominent between the Toxocara species, a fact further substantiated when reactivity of T. canis ES-specific monoclonal antibodies were tested against T. leonina and T. vitulorum antigens. The ES antigens of T. leonina were not recognized by the T. canis monoclonals, whereas the majority of these antibodies precipitated antigens of T. vitulorum. One which did not react with T. vitulorum was monoclonal antibody Tcn 2, indicating its species-specific reactivity and therefore its potential for the specific diagnosis of human toxocariasis.

Animals↗
PubMed1991

Rotational diffusion effects on absorbance measurements: limitations to the magic-angle approach.

Optical absorbance changes are commonly used to characterize intermediates which appear in the bleaching sequence of rhodopsin and in the photocycle of bacteriorhodopsin. Absorbance changes can be caused by an intermediate's rotational diffusion, and when this occurs it can distort absorbance changes due to the structural evolution of intermediates. Linear polarization of an optical probe source at 54.7 degrees (the magic angle) relative to the polarization direction of a linearly polarized actinic source has often been used to eliminate signals due to rotational diffusion. We used Jones calculus to investigate the validity of the magic-angle strategy. Taylor expansion of the result in powers of the absorbances of the bleached ground state and of the intermediates leads to a relatively simple expression which can be used to determine whether rotational contributions are likely under various experimental conditions. This expression shows that in first order no dichroism-dependent term appears in the absorbance measured at magic angle. In second order, however, linear dichroism contributes to signals. For the sequence of rhodopsin intermediates: rhodopsin hv----bathorhodopsin in equilibrium BSI----lumirhodopsin, where BSI is a recently discovered blue-shifted intermediate, we determined the magnitude of the dichroism signals to be, on average, less than 2% of the true absorbance change due to the intermediates themselves (and hence undetectable). Freedom from dichroism artifacts in this case results from the fact that the transition dipoles of these intermediates are similar to that of rhodopsin. Larger and certainly detectable dichroism signals are predicted to occur, even at the magic angle, for later intermediates which have transition dipole moments which differ significantly from that of rhodopsin.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriorhodopsins↗