ECochG and psychoacoustic tests compared in identification of hearing loss in young children

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 less than 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.

Slow cortical responses and the diagnosis of central hearing loss in infants and young children

To evaluate the usefulness of slow cortical responses (ERA) for threshold estimation in infants and young children, 83 children were investigated with combinations of pure-tone audiometry, electrocochleography (ECochG) and ERA. The deviations between ECochG/ and ERA thresholds were correlated to brain function in order to diagnose central hearing losses. By comparing corresponding values of 2 kHz pure-tone and ERA thresholds, 32% (10/31) errors were found, mainly below 35 dB HL. In a group of patients with no sign of brain disorder, an overall error rate of 37% (20/53) was found. Below 35 dB HL, 72% (11/15) errors were found. In a group of patients with brain dysfunction, the overall rate was 70% (21/30), below 35 dB HL it was 84% (21/25). In the range below 35 dB HL, no significant difference (p greater than 0.05) in errors was found between the groups with and without brain disorders. It is concluded that ERA is unreliable for the estimation of moderate hearing losses and cannot per se detect a central hearing dysfunction. Elevated ERA thresholds may indicate a central hearing loss, but to establish this topical diagnosis, ECochG and neuropsychological examinations are necessary.

Middle components of the auditory evoked response in bilateral temporal lobe lesions. Report on a patient with auditory agnosia

An investigation of the middle components of the auditory evoked response (10--50 msec post-stimulus) in a patient with auditory agnosia is reported. Bilateral temporal lobe infarctions were proved by means of brain scintigraphy, CAT scanning, and regional cerebral blood flow measurements. The middle components were found to be normal regarding latency (pa approximately 30 msec) and configuration of the recordings, when evaluated relative to the peripheral hearing loss in the patient and to the corresponding normative template. Based upon the combined procedures, it is concluded that the middle components cannot be generated exclusively, if at all, in the primary auditory cortex, located in the temporal lobe. Furthermore, the responses are found to be of neurogenic origin according to the methodological procedure applied.

Conductive hearing loss evaluated by brief tone audiometry

Bone-conduction measurements are inaccurate and often troubled by masking problems. Determination of the temporal integration of acoustic energy by Brief Tone Audiometry permits an estimate of the cochlear threshold. In 71 patients with middle ear pathology, the conductive impairment was measured using both conventional audiometry and Brief Tone Audiometry. In 85% of the patients, the estimates coincided within 15 dB. Results from pre- and post-operative measurements are given, and it is demonstrated that Brief Tone Audiometry can be used as an alternative to bone-conduction audiometry to determine the degree of conductive loss with the same accuracy, but without the latter's limitations.

Temporal integration of acoustic energy

Perception of sound shows an increase in loudness related to the duration of the acoustic stimulus. This phenomenon has been studied at threshold (temporal integration) in normal and impaired ears. Normal ears showed an improved threshold with impulse durations up to 200 msec. In cochlear hearing loss, regardless of pathology, the threshold improvement was reduced. A method to evaluate these changes has been designed (Brief Tone Audiometry). When using this method, a quantitative comparison showed the same reduction in temporal integration in ears with hearing loss, regardless of pathology. By using a loudness balance test, the increase in loudness related to prolongation of the stimulus was investigated (Loudness Summation). Loudness growth was measured at various intensities and the results from normal and hearing-impaired ears were compared. At a given sound intensity both normal and hearing-impaired ears showed the same Loudness Summation, which in turn showed a simple relationship to Brief Tone Audiometry in impaired ears. Physiological and diagnostic aspects of these findings are discussed.

A new concept of vertex ERA and EEG analysis applying inverse filtering

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.

Correlations between Structure of Elastomers and the Mechanism of their Degradation by Ozone

Ozone cracking is treated as a special case of stress corrosion. The correlation between delayed fracturing, stress and strain is explained in terms of changing crack geometry. Structural relationships have been studied in the region of minimum, critical stress. Two groups of ozone sensitive polymers can be distinguished: in highly ozone sensitive materials cracks are initiated at very low values of stored elastic energy, while initiation in the more resistant butyl rubbers and EPT rubbers occurs only at much higher values of stored elastic energy. The rate of cracking in neoprene is shown to be much less stress sensitive than the corresponding rate in other polydiene rubbers. It is conjectured that this favorable property of neoprene depends on the rheological behaviour of the ozonized surface layer.

Infrared Analysis of Some Chlorinated Natural Rubbers

In an earlier paper spectra of polyisoprenes were discussed. In this communication effects due to the introduction of 1 to 4 chlorine atoms per C5H8 unit are reported. Since an unlimited number of polymers with such empirical compositions derived from isomeric monomer units is conceivable, it seems convenient first to compare some prototypes, then to report in more detail our experience, which is a continuation of earlier work in this field.

Infrared Analysis of Isomerized, Vulcanized, and Oxidized Natural Rubber

This paper is a continuation of our study on the infrared spectra of natural rubber and its derivatives. It was found previously that, in certain reactions of rubber, the original double bond (I) is shifted to the side group (II) and that this leads to significant changes in the chemical and mechanical behavior of the polymer. Others have also reported the occurrence of groups (II) and (III) in rubber and certain rubber derivatives. Group (II) is also found in synthetic polyisoprenes as a result of 3,4-polymerization. We have now measured the intensities of the absorption bands of the rubber spectrum and changes produced by cyclization and isomerization. Certain statements on the formation of (II) and (III) during vulcanization were at variance with our experience, but a detailed investigation cleared up some misconceptions. Modifications brought about by oxidation are chemically related to those produced by sulfuration reactions. A classification of oxidation reactions, based on typical changes in the infrared spectrum, will be proposed in the discussion.

Kinetic Analysis of Organic Halides. IV. Analysis of Macromolecular Polyhalides

Chlorination products derived from natural rubber and some synthetic polymers have been subjected to kinetic analysis with aniline at 100° C and piperidine at 20° C. The influence of the chlorinating agent on the structure of the reaction products has been elucidated. It is shown that allylic chloride groups, the rubber dichloride, (see PDF for diagram) and rubber polychlorides can be identified and separated kinetically. By a combination of kinetic and infrared analysis the structure (see PDF for diagram) can be proved as the primary reaction product of direct chlorination.

Chlorination of Natural Rubber. I. Preparation and Properties of Chlorinated Rubber

The chlorination of rubber has been the subject of extensive investigations, the rubber being commonly treated in solution with gaseous chlorine at a given temperature and pressure. The properties of the products of rubber thus treated vary in close dependence on the chlorine content, which may be as much as 70 per cent. The drawback to a low chlorine content is that, as a rule, the chlorine is loosely bound, with the result that, when exposed to heat or light, it splits off as HC1, with formation of discolored and cyclized products and serious deterioration of the mechanical properties. But the higher the chlorine content, the more stable are these chlorinated rubbers. The stability of chlorinated products of natural rubber containing approximately 65 per cent of chlorine is such that they are used commercially as a component of anticorrosive paint. The instability of chlorinated rubber of low chlorine content is closely connected with its chemical constitution and the mechanism of reaction. The current opinion ten years ago was that chlorine first adds to the double bond of the rubber, and that this primary product, while splitting off HC1, enters into further reaction with chlorine ; but reexamination of this reaction in the laboratory of our affiliated English organization and independently in our own laboratory has led to very different views. It was realized that rubber dichloride (the addition product of chlorine and rubber) is far too stable to act as an unstable intermediate product during the chlorinating reaction. Bloomfield argued that, during the primary reaction, the chlorine is attached by substitution to an α-methylenic carbon atom of the rubber molecule and that there is a considerable amount of cyclization. It was not our sole concern to study the mechanism of reaction; we were also bent on following the chlorination of rubber under the most diverse conditions, starting from dry rubber, rubber in solution, and rubber in latex, and with highly diversified sources of chlorine such as from liquid chlorine, gaseous chlorine, hypochlorites, and sulfuryl chloride. The normal course of reaction, involving the formation of unstable intermediate products, is discussed in Part I of this series; methods of producing comparatively stable rubber chlorides by adding chlorine onto the double bond are considered in Part II.

Kinetic Analysis of Organic Halides. II. Analysis of Macromolecules Built up of Monohalide Units

A number of hydrochlorides of natural and synthetic rubbers and allied polymers have been prepared and subjected to kinetic analysis with organic bases. The hydrochlorides of natural rubber react at 100° C at a rate identical to that of low-molecular tertiary chlorides. At 50° C the reactivity of the polymer is, however, reduced by physical factors. The hydrochloride of GR-S (a synthetic rubber made from butadiene and styrene) has been prepared for the first time by heating the swollen polymer with HC1 under pressure. Kinetic analysis of this product revealed two fractions: the expected secondary chloride, and a small fraction of a very reactive (tertiary?) chloride. After elimination of experimental difficulties, we succeeded in the preparation and kinetic identification of the pure tertiary hydrobromide of natural rubber. Attempts to prepare the secondary bromide under peroxide conditions failed. Kinetic analysis of two types of Neoprene revealed the presence of a small quantity of allylic groups in the polymer, while 95 per cent of the chlorine in Neoprene has the expected stability of a vinyl chloride. This stability can be used for the identification of Neoprene.

Kinetic Analysis of Rubber Halides

A correlation is established between the structure of an organic halide and its rate of reaction with a number of organic bases. Analysis by reaction kinetics, based on this correlation, is applied to the following problems. (1) Estimation of the allylic fraction in the chlorination and bromination of natural rubber. (2) Differentiation between a dichloride and a polychloride from natural rubber. (3) Determination of an equilibrium between natural rubber and hydrochloric acid at 130° C in closed systems. (4) Identification of tertiary chlorides and bromides in natural rubber and allied polymers.

Preparation and Properties of Rubberlike High Polymers. VI. Polymerization and Dimerization of Isoprene

The inhibitor and initiator action of thirty-three compounds on the bulk polymerization of pure isoprene has been studied. Picric acid was found to be the most powerful inhibitor at 100° C. The conclusion reached in Part I that the initiator activity of diazoaminobenzene is superior to all other compounds has been found to be valid also between 100–150° C. The heat polymerization of isoprene between 100–150° C in the presence of picric acid leads only to the formation of dimers. Three of the four possible isomers have been separated. The solid complex compound of diprene (I) with silver nitrate has been used to separate it from dipentene (II) and the hydrocarbon of Lebedev (III, IV) has been identified as a monochloride. The relative yields (I) : (II) : (III = IV) of 16:1:2 are in agreement with the relative availability and localization of π-electrons in isoprene. Observations on the properties of polyisoprene are in agreement with the more extensive work by d'Ianni. Some remarks on polymers from bulk polymerization are added. Isoprene acts as a powerful inhibitor on the polymerization of vinylidene chloride. This effect is independent of the method of polymerization.

Influence of Structure on Polymer-Liquid Interaction. III. Swelling and Mechanical Properties of Some Partly Crystallized Polymers

We have shown in the first part of this work the influence of association on liquid-polymer equilibrium, while a study of nitrile copolymers revealed that mechanical properties are much more sensitive to certain changes in polymer structure (such as the introduction of methyl groups) than are swelling equilibria. In partly crystallized polymers, however, a close correlation between liquid-polymer interaction and mechanical properties exists, as is seen from the present paper.

Preparation and Properties of Rubberlike High Polymers. V. Influence of Nitrile Groups on the Properties of Copolymers

The introduction of methyl groups in butadiene leads to a decrease in 1,2- and 3,4-addition as well as to a reduction of cross-linking reactions. The same regularity can be observed in a series of copolymers, which will be discussed in the present paper. Apart from these interrelations between diene structure and pattern of the chain molecule, other physical properties such as the second order transition point and the closely related brittle point depend on the presence of methyl groups. Nitrile groups enhance these differences between the three series of diene polymers, as will be seen from the following results. A striking contrast between these widely diverging physical and mechanical properties is the similarity of swelling equilibria, which are obviously determined only by the number of nitrile groups per volume unit of polymer, as will be discussed in another communication.

Influence of Structure on Polymer-Liquid Interaction. II. Influence of Nitrile Groups

Swelling equilibria of a number of copolymers in various organic solvents have already been discussed. The influence of polarity and polarizable groups has been derived from the gradual changes of swelling equilibria. We shall deal with the same problem in the present paper, but, by considering only nitrile groups in the polymer, the resulting picture becomes less complex. The polymers under investigation are the three series of copolymers from acrylonitrile, with butadiene, isoprene, and dimethylbutadiene, respectively. In each series, the mechanical properties change with nitrile concentration, as indicated by a gradual increase in brittleness. The combination of nitrile and methyl groups leads to a further immobilization of the flow units; the copolymers from dimethylbutadiene are, therefore, plastics at room temperature—as has been discussed in another paper.

Preparation and Properties of Rubberlike High Polymers. IV. Correlation between Structure and Properties of Elastomers Derived from Dienes

The correlation between structure and properties of elastomers prepared from dienes, natural rubber, gutta-percha, as well as those of some significant derivatives of natural rubber, are discussed. The similar influence exerted by methyl groups on the brittle point, elastic recovery, and permeability to gases is demonstrated and separated from the effect caused by insertion of —CH2— CHR— groups in straight-chain polybutadiene, which takes place during co-polymerization or 1,2 addition. The preponderant influence of an unbranched-chain structure on tensile strength at elevated temperatures and in the swollen state is illustrated. Complex compounds with silver nitrate provide further evidence for the particular symmetry of the natural rubber chain: They are reinforcing agents for synthetic elastomers. The brittle points of hydrochlorides from natural rubber, gutta-percha, and polyisoprene are compared with those of polyvinyl compounds. Correlation between the structure of molecular units in a polymeric paraffin derivative and its elasticity is pointed out.

Influence of Structure on Polymer Liquid Interaction. I. Relative and Absolute Values of Swelling Equilibria

To reach a better understanding of the correlation between molecular structure and intermolecular attraction, a comparison was made of swelling equilibria. With this aim we studied the absolute value of the swelling equilibrium under the influence of polar and polarizable groups, which were introduced in solvents and polymers with different molecular structures. The influence of temperature, cross-linking, external pressure, and mechanical strain on the position of the equilibrium was also studied. Any general treatment of swelling is obviously limited by our present knowledge of the properties of liquid mixtures. Experimentally, however, the study of high polymeric solutions and gels offers several advantages over that of ordinary liquids. Our experiments, designed to elucidate the structure of polymers, also reveal properties of some organic liquids which could not be observed easily by other means. Results obtained with commercial rubbers will be given in this paper, while analogous measurements on a series of copolymers with increasing numbers of nitrile groups will be dealt with in a second paper.