Evidence for a common anatomical and physiological substrate for the generation of the background EEG and the vertex-evoked response led to the hypothesis that the EEG can be interpreted as the ...output from a time varying filter driven by (a) a noise generator responsible for the background activity, and (b) a pulse generator creating the evoked response. The characteristics of the filter can be estimated by autoregression. The application of such a model results in considerable theoretical and practical improvements in the detection of evoked responses. Selected averaging on EEGs classified according to the filter characteristics shows improved S/N ratios and considerable diversity between classes. Investigations of an estimate of the input signal to the filter, derived by deconvolution, reveal a sound-evoked potential which is less variable than the response in the EEG. The study concludes that the proposed model and methods have a sufficient applicability and physiological relevance to support further developments.
By using average technique, cochlear micrc-phonics were recorded from an electrode in the ear canal, in response to 1 kHz-tone bursts, delivered via a μ-metal, magnetically shielded TDH 39 earphone ...in a closed acoustic system. No measurable artifacts could be recognized, either in normal ears or in deaf ears. The amplitude function is described from 65 dB to 120 dB p.e. SPL and appears to be similar to the established pattern in animals. The phase of the cochlear microphonic was compared with the phase of the stimuli in the ear canal, and the influence of the stapedius muscle contraction on amplitude and phase of the cochlear microphonic is briefly described. Besides the cochlear microphonics and the action potentials, a summating potential in response to 4 kHz-tone bursts was recorded. Cochlear microphonics in a few pathological ears are outlined. Approximately at a latency of 14 msec a multiphasic component was often present. The results are discussed.
Among 149 children (median age 23 months, range 2-123 months) examined by ECochG, a comparison was made between pure-tone and ECochG thresholds in 53 patients. By using linear regression analysis a ...high correlation was found (correlation coefficient 0.92, p< 0.0005) proving that ECochG gives valid estimates of the hearing thresholds, also in small children. A comparison between behavioral observation audiometry (BOA) and ECochG thresholds was performed in 62 children. It was concluded that BOA exhibits poor sensitivity in the assessment of hearing losses and underestimates their degree of severity. Furthermore, when BOA diagnoses normal hearing, there is a 9% risk of depriving a 'deaf child of suitable treatment'.
Parmi 149 enfants, ayant entre 2 et 123 mois (âge moyen: 23 mois), que nous avons examines entre 1969 et 1979, nous avons pu effectuer chez 53 une comparaison des seuils en son pur et en ECochG. Par analyse de régression linéaire, nous avons trouvé une haute corrélation (coefficient de corrélation 0,92; p < 0,0005) ce qui nous amène à penser que l'ECochG est une méthode valable pour l'estimation des seuils auditifs chez les petits enfants.
Chez 62 enfants, nous avons comparé l'audiométrie de comportement (AC) et les seuils estimés en ECochG. Nous avons pu observer que l'AC présente une faible sensibilité dans l'évaluation de la perte auditive; elle sous-estime tout particulierement les pertes d'audition graves; ce qui nous conduit à établir à 9% le risque de priver un enfant sourd d'un traitement convenable lorsque l'AC fait apparaiˇtre une audition normale.
Abstract only
Enhanced platelet reactivity is critical to the pathophysiology of occlusive arterial thrombotic disease. Despite the strong clinical associations between hyperlipidemia, a major risk ...factor for atherosclerosis, and a pro-thrombotic phenotype, the mechanisms responsible for enhanced platelet reactivity during hyperlipidemia remain unknown. Pro-atherosclerotic lipid abnormalities such as hypercholesterolemia are associated with both enhanced oxidant stress and generation of biologically active oxidized lipids, including potential ligands for the scavenger receptor CD36, a major platelet surface glycoprotein. Using multiple murine in vivo thrombosis models we now demonstrate that hyperlipidemic atherosclerosis prone mice (apolipoprotein E-deficient or LDL receptor-deficient) form occlusive intravascular thrombi faster than wildtype mice, and that genetic deletion of CD36 protects mice from hyperlipidemia-associated enhanced platelet reactivity and accompanying pro-thrombotic phenotype. Structurally defined oxidized choline glycerophospholipid molecular species that serve as endogenous high affinity ligands for CD36 are shown to :
be markedly increased in plasma of hyperlipidemic mice;
be elevated in plasma of subjects with low HDL levels; and
to promote platelet activation and alpha-granule release via CD36 at pathophysiological levels.
These studies thus demonstrate that platelet CD36 interactions with specific endogenous oxidized lipids play a heretofore unrecognized role in the well-known clinical associations between hyperlipidemia, oxidant stress and a prothrombotic phenotype.
Isoprostanes are prostaglandin-like compounds produced by non-enzymatic peroxidation of arachidonic acid. The cyclooxygenase-derived
endoperoxide, prostaglandin H 2 , can undergo rearrangement to ...highly reactive γ-ketoaldehyde secoprostanoids (levuglandin E 2 and D 2 ). We explored whether isoprostane endoperoxide intermediates also rearrange to levuglandin-like compounds (isolevuglandins).
Formation of a series of isolevuglandins during oxidation of arachidonic acid in vitro was established utilizing a number of mass spectrometric analyses. However, these compounds could not be detected in free
form in protein-containing biological systems, which we hypothesized was due to extremely rapid adduction to amines. This
was supported by the finding that >60% of levuglandin E 2 adducted to albumin within 20 s, whereas â¼50% of 4-hydroxynonenal still remained unadducted after 1 h. By utilizing electrospray
tandem mass spectrometry, we established that these compounds form oxidized pyrrole adducts (lactams and hydroxylactams) with
lysine. Formation of isolevuglandin-lysine adducts on apolipoprotein B was readily detected during oxidation of low density
lipoprotein following enzymatic digestion of the protein to single amino acids. These studies identify a novel series of extremely
reactive products of the isoprostane pathway that rapidly form covalent adducts with lysine residues on proteins. This provides
the basis to explore the formation of isolevuglandins in vivo to investigate the potential biological ramifications of their formation in settings of oxidant injury.
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