Two vaccination programmes for infectious bursal disease (IBD) were compared in broiler chickens with maternal immunity, placed on two farms. A turkey herpes virus (HVT)-IBD vector vaccine was administered by the subcutaneous route, at the hatchery, into the chicks of farm A at the age of 1 day. On farm B, an attenuated intermediate live IBD vaccine was given orally at the ages of 17 and 24 days. The vaccine uptake was monitored via serology and bursa/body weight ratio evolution, as well as PCR-based viral IBDV detection in the bursa of Fabricius at various time points. It was also verified by an experimental very virulent IBDV challenge performed at the age of 30 days in birds transferred from the farms with appropriate control groups in a laboratory. An immunity gap was observed in birds from farm B between the decay of the passive and the rise of the active immunity based upon serological data. The level of protection against challenge is not possible to establish in this farm as the reduction of the bursa/body weight ratio observed could be due to the residual pathogenicity of the vaccine strain or the challenge as well. This immunity gap was not present on farm A showing higher serological titres at the ages of 26 and 45 days via a suitable ELISA test and 93% protection against the very virulent challenge at the age of 30 days was observed. The maternal immunity interfering with the live IBDV vaccine replication had no detectable effect on the vector vaccine take.

: ELECTRONIC FILE CHARACTERISTICS: 70 files; Adobe Acrobat (.PDF) and HTML. PHYSICAL DESCRIPTION: 1 CD-ROM; 4 3/4 in.; 234 MB. SYSTEMS DETAIL NOTE: Adobe Acrobat Reader is included on disc. ABSTRACT: Participants from eight nations reviewed (1) technical challenges for more effective protection of human hearing in adverse military environments, (2) efforts to optimize the portrayal of auditory information via helmets and headphones, and (3) research to improve speech intelligibility, especially via channels that encode and transmit multiple speech and data signals. This report summarizes progress and recommends seven areas for future research concentration.

Abstract : Continuous and/or impulse noises produced by modern weapon systems constitute a threat for the health of the soldier and impede his operational ability. Moreover, their levels often exceed the statutory exposure limits as well for the users (unprotected and protected ears) as for the nearby community. The noise of the modern weapon systems is a limiting factor for their use either because no present hearing protection is able to protect the ear or because unsuited regulation will make their use impossible.

In order to measure the Insertion Loss (IL) of hearing protectors in high levels of steady-state or impulse noise, the acoustic isolation of an Acoustical Test Fixture (ATF) has to exceed the Insertion Loss of the hearing protectors. As the acoustic isolation of commercially available artificial heads does not meet this requirement, a new device has been designed and built. The artificial head, made of hard polyurethane, is designed to fit the Head Acoustics(R) external ear and circumaural region. An ear simulator from Bruel & Kjaer is used to simulate the acoustic impedance of the human ear. The isolation of this ATF is better than 70 dB in a large frequency range (even when exposed to shock waves). The transfer function of the open ear is in close agreement with the experimental data published by Shaw and is linear up to 190 dB (peak pressure). This ATF allows the evaluation of all kinds of hearing protectors from the lowest to the highest (190 dB) levels.

Direct intracochlear acoustic pressure recordings (from 20 to 20,000 Hz) are used to measure the middle-ear transfer functions (forward and reverse) and to better understand the cochlear mechanics in the guinea pig. In the forward direction, the middle-ear transfer function is strongly dependent on the frequency and presents a maximum of +30 dB at 1,000 Hz (bulla open). In the reverse direction, the middle-ear transfer function looks like an ideal reverse middle-ear pressure transformer with –35 dB gain and 0° phase lag from 20 to 8,000 Hz (bulla open, closed ear canal). Passive cochlear mechanics is studied with the help of intracochlear pressure measurements and differential cochlear microphonic potential recordings in the different turns.

The present state of passive (linear and non-linear) and active techniques for hearing protection in the military environment is reviewed. Solutions which allow to protect the ear from large continuous and high-level impulse noises while preserving the operational abilities of the personnel (detection, localisation, communication.) are emphasised.

The aim of this study is to determine the actual efficiency of the present medical treatments of acoustic trauma. Untreated and treated groups of guinea pigs are exposed to a traumatic noise exposure, inducing up to 60-dB threshold shift. The recovery is followed for up to 14 days. The first results indicate that in some animals the recovery of the threshold shifts are complete despite the fact that significant areas of hair cells are damaged.The most widely used medical treatments of acoustic trauma (oxygenotherapy, carbogen, hyperbaric oxygen, vasoactive agents, and corticotherapy) have been tested. Preliminary results indicate that pure oxygen and carbogen seem ineffective, hyperbaric oxygen used alone is dangerous, and corticoids and combined corticoid/hyperbaric oxygen seem to improve functional and morphological recovery. This study will be taken as a reference to look for new treatments that will be applied directly to the cochlea by means of an implanted osmotic micropump.

The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non‐linear, hence combination tones are generated inside the cochlea when a pair of low‐level pure tones with neighbouring frequencies f1 and f2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non‐invasive measurement of the combination tone at 2f1–f2, called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea‐pig cochlea. Cubic difference tones at

In military life, noise has unusual characteristics and constitutes a serious hazard for hearing. Hearing impairments due to the exposure to weapon noises represent an important prejudice for the health of many soldiers. A special attention is given to (i) the "critical level", (ii) the frequency localization of the threshold shifts, (iii) the actual influence of the protective reflexes of the ear, (iv) the existence of delayed threshold shifts following impulse noise exposures, and (v) the interest of the medical treatment of the acoustic trauma. Damage risk criteria for weapon noises are compared: criteria using the (A-weighted) isoenergy principle represent the best present solution (LAeq = 85 dB). Specific problems related to the use of hearing protection are also discussed.

Otoacoustic emissions are increasingly useful for determining cochlear function noninvasively. It is widely agreed that these acoustic signals reflect micromechanical processes in the cochlea. However, their quantitative interpretation requires knowledge of the ways in which vibrations travelling back to the ear canal from the cochlea are shaped by the middle ear. An intracochlear source is needed to derive the reverse middle-ear transfer function (rMETF) by comparing pressure in the external ear canal to the corresponding pressure in scala vestibuli. In the present study, the rMETF was obtained in vivo in the guinea pig using as intracochlear sound source the cubic difference tones (CDTs) generated by a pair of external pure tones. With a closed ear canal and open bulla, the rMETF was found to be flat (-35 dB) over a broad frequency range (1.5-8 kHz). The differences between forward and reverse METF could be explained by different loads acting on the middle ear network, which depends on the direction of signal transmission. With knowledge of the rMETF, it becomes possible to quantify CDTs within the cochlea by measuring them noninvasively in the ear canal.

We describe the main biomechanical characteristics of the middle ear in man and in animals. Physical principles of functionment, tympano-ossicular displacements, acoustic reflex, adaptation of impedance, transfer function of the middle ear, middle ear as an acoustic power transformer... are presented. Practical consequences for the hearing sensitivity, the susceptibility to noise and some clinical applications are discussed.

Permissible exposure conditions to various weapon noises have been compared according to: (i) the Pfander criterion (Germany), (ii) the Smoorenburg criterion (the Netherlands) and, (iii) the DTAT recommendation (France) which is based on A-weighted L(eq8) measurements. The L(Aeq8) method allows the assessment of the hearing hazard for all weapon noises according to the well-recognized procedure used for occupational exposure (ISO R-1999). With a 85 dB limit this method does not lead to overprotection of the soldiers, as it is the case for the criteria of Pfander and Smoorenburg with respect to large-calibre weapon noises and it allows for the evaluation of the actual hearing protection afforded by earplugs or earmuffs from classical Insertion-Loss data obtained by Real-Ear-At-Threshold or Acoustical-Test-Fixture measurements. Moreover, the L(Aeq8) method is able to cope with exposure conditions which are difficult to evaluate on the basis of the former criteria (weapon noises in enclosures, combined exposures for example).

Blast injuries occur only on gas-containing structures: auditory system, upper respiratory tract, lung and gastro-intestinal tract. The severity of the injuries depends upon the physical characteristics of the shock waves: peak pressure, rise time and A-duration, and upon the number of exposures. We present results obtained on swine and sheep concerning tracheal, pulmonary, gastrointestinal injuries, and a survival estimate for man.

The effects of noise on the auditory transduction and the temporary and permanent threshold shifts (TTS and PTS) are reviewed in relation to the physiology, the morphology and the mechanics of the Corti's organ and especially of the outer hair cells. The modification of the mechanical characteristics of the stereocilia: decrease of stiffness, shortening of the rootlets, softening of the interciliary links...reduce the number of ionic channels which are opened during the mechanical excitation of the Corti's organ. This reduction modifies greatly the behavior of the "cochlear amplifier" which is located at the level of the outer hair cells and is responsible for the auditory sensitivity at threshold and the frequency selectivity. Permanent damages to the stereocilia of the hair cells following exposure to noise seem to be the main factor responsible for the apparition and the extent of the hearing losses. The influence cof several parameters: amplitude, duration, frequency..., on TTS and PTS are reviewed and the phenomenon of the half-octave shift is described.

A guinea pig temporal bone immersed in tissue culture medium is used for the study of the vibrations of the cochlear structures using laser interferometry. With the purpose of specifying the acoustic stimulation mode of this preparation, sound pressure measurements have been performed (i) in the vicinity of the cochlea in the temporal bone preparation, (ii) at different locations in scala vestibuli of living guinea pigs. In the temporal bone preparation, the tympanum is acoustically stimulated by air. The bulla as well as the apical portion of the cochlea are open and immersed in liquid The resulting data show that in this preparation: - the sound pressure field in the vicinity of the cochlea is essentially due to the direct transmission of the vibrations of the internal face of the tympanum through the liquid which fills the middle ear: - the vibrations of the intrachochlear apical structures constitute a second source which is almost masked by the first one: It has been shown that the transmission through the middle ear is the dominant stimulus that determines the measured responses of the intracochlear apical structures. The transmission characteristics are however modified because the bulla is fluid filled and the apex is open.

The mechanisms by which the organ of Corti is stimulated by acoustic stimuli are discussed on the basis of experimental observations. This discussion refers to the resonance theory as well as to the traveling wave (TW) theory. The measurement of the basilar membrane displacements, of the cochlear micro-phonic (CM) responses to pure tones and impulses, and the recording of the intracochlear acoustic pressure seem to indicate that, at least in the basal part of the cochlea and for frequencies up to the characteristic frequency of a given location, the cochlear responses do not exhibit large phase lags and long delays which characterize the one-dimensional long-wave models (in which a TW transports the energy along the cochlear partition). These experimental observations suggest that the cochlear partition is excited simultaneously as a whole, more or less like a bank of resonators, as proposed a long time ago by Helmholtz.

The mechanisms by which the organ of Corti is stimulated by acoustic stimuli are discussed on the basis of experimental observations. This discussion refers to the resonance theory as well as to the traveling wave (TW) theory. The measurement of the basilar membrane displacements, of the cochlear microphonic (CM) responses to pure tones and impulses, and the recording of the intracochlear acoustic pressure seem to indicate that, at least in the basal part of the cochlea and for frequencies up to the characteristic frequency of a given location, the cochlear responses do not exhibit large phase lags and long delays which characterize the one-dimensional long-wave models (in which a TW transports the energy along the cochlear partition). These experimental observations suggest that the cochlear partition is excited simultaneously as a whole, more or less like a bank of resonators, as proposed a long time ago by Helmholtz.