The pathway enabling external sounds to reach and excite the fetal inner ear

The human fetus in utero is able to respond to sounds in the amniotic fluid enveloping the fetus after about 20 weeks gestation. The pathway by which sound reaches and activates the fetal inner ear is not entirely known. It has been suggested that in this total fluid environment, the tympanic membrane and the round window membrane become 'transparent' to the sound field, enabling the sounds to reach the inner ear directly through the tympanic membrane and the round window membrane. It is also possible that sounds reach the inner ear by means of tympanic membrane--ossicular chain--stapes footplate conduction (as in normal air conduction). There is also evidence that sounds reach the fetal inner ear by bone conduction. Several animal and human models of the fetus in utero were studied here in order to investigate the pathway enabling sounds to reach and activate the fetal inner ear. This included studying the auditory responses to sound stimuli of animals and humans under water. It was clearly shown in all the models that the dominant mechanism was bone conduction, with little if any contribution from the external and middle ears. Based on earlier experiments on the mechanism and pathway of bone conduction, the results of this study lead to the suggestion that the skull bone vibrations induced by the sound field in the amniotic fluid enveloping the fetus probably give rise to a sound field within the fetal cranial cavity (brain and CSF) which reaches the fetal inner ear through fluid communication channels connecting the cranial cavity and the inner ear.     

The latency of auditory nerve-brainstem responses in sensorineural hearing loss

Summary The use of auditory nerve-brainstem responses in differential diagnosis of hearing loss is based on several properties of these responses including response latency. The auditory nerve response latency has been shown to be prolonged in conductive hearing loss. The latency of the brainstem responses is also often prolonged in retrocochlear hearing loss. However, the effect of sensorineural hearing losses on auditory nerve response latency is not clear. Several authors report that response latency is prolonged in sensorineural loss, whereas others claim that it is unchanged.To study this, auditory nerve-brainstem responses to 75 dB HL clicks were recorded in normal-hearing subjects and in those with various degrees of high-frequency sensorineural hearing loss. In the more extreme hearing losses, the auditory nerve response could not be seen in the response trace, so the latency of the earlobe positive wave from the region of the inferior colliculus was considered as mirroring auditory nerve response latency, since the time interval between these two waves has been shown to be constant.The average latency of the more severe hearing loss group (more than 40 dB hearing loss at 4 kHz) was found to be only 0.35 ms longer than that of the normal-hearing group. This value is smaller than that seen in most conductive and retrocochlear hearing losses.This result warrants continued use of prolonged auditory nerve response latency (greater than 0.35 ms) as an indicator of conductive hearing loss. Possible explanations for smaller latency prolongation than expected of the auditory nerve response in sensorineural hearing loss are discussed based on the properties of single auditory nerve fibers.Part of a PhD thesis to be submitted by R. Kinarti to the Senate of the Tel-Aviv Universtity     

Team communication patterns in emergency resuscitation: a mixed methods qualitative analysis

Background

In order to enhance patient safety during resuscitation of critically ill patients, we need to optimize team communication and enhance team situational awareness but little is known about resuscitation team communication patterns. The objective of this study is to understand how teams communicate during resuscitation; specifically to assess for a shared mental model (organized understanding of a team’s relationships) and information needs.

Methods

We triangulated 3 methods to evaluate resuscitation team communication at a tertiary care academic trauma center: (1) interviews; (2) simulated resuscitation observations; (3) live resuscitation observations. We interviewed 18 resuscitation team members about shared mental models, roles and goals of team members and procedural expectations. We observed 30 simulated resuscitation video recordings and documented the timing, source and destination of communication and the information category. We observed 12 live resuscitations in the emergency department and recorded baseline characteristics of the type of resuscitations, nature of teams present and type and content of information exchanges. The data were analyzed using a qualitative communication analysis method.

Results

We found that resuscitation team members described a shared mental model. Respondents understood the roles and goals of each team member in order to provide rapid, efficient and life-saving care with an overall need for situational awareness. The information flow described in the interviews was reflected during the simulated and live resuscitations with the most responsible physician and charting nurse being central to team communication. We consolidated communicated information into six categories: (1) time; (2) patient status; (3) patient history; (4) interventions; (5) assistance and consultations; 6) team members present.

Conclusions

Resuscitation team members expressed a shared mental model and prioritized situational awareness. Our findings support a need for cognitive aids to enhance team communication during resuscitations.

     

Combined effects of salicylic acid and furosemide and noise on hearing

Background  

A major cause of the hearing loss following exposure to intense noise involves release of free radicals resulting from the elevated metabolism. The free radicals induce damage to several of the components of the cochlear amplifier including the outer hair cells and indirectly to the transduction currents. Salicylic acid induces a reversible hearing loss since it binds to the motor protein prestin in the outer hair cells, reducing electromotility. Furosemide also induces a reversible hearing loss since it reduces the endocochlear potential which is a major component of the cochlear transduction currents. On the other hand, each of these drugs also provides protection from a noise induced hearing loss if they are injected just before a noise exposure, probably as a result of the decreased metabolism induced in their presence, with release of lower levels of free radicals. In this study, both drugs were administered in order to assess whether their protective effects would be additive.     

Sources of averaged neural responses recorded in animal and human subjects during cochlear audiometry (Electro-Cochleogram)

Summary The five waves comprising the averaged neural response (cochlear audiometry or electrocochleogram) to click acoustic stimuli were recorded with pinna and scalp electrodes in both human and animal subjects. The latencies and waveform of the waves in the cat were similar to those recorded in human subjects. Recordings in the cat with pinna-scalp electrodes simultaneously with intracranial recordings from auditory nuclei in the same animal, lead to the following conclusions concerning the sources of these waves in cats and probably in man also: 1. the first response wave is generated by the first order cochlear nerve fibers; 2. the second wave is generated mainly in the cochlear nucleus; 3. the third wave is generated in the superior olivary complex; 4. the fourth and fifth waves are generated in the inferior colliculus. Thus, this recording system provides a convenient means of measuring the neural activity of the cochlea, the brain stem auditory nuclei and the cerebral cortex in human subjects.

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Zusammenfassung Ableitungen der gemittelten neuralen Potentiale der menschlichen Cochlea auf Klick-Reizung mit Elektroden am Ohrläppchen und Vertex (Electro-Cochleogram oder Cochleare Audiometrie) ergeben einen Wellenkomplex aus 5 Komponenten.Mit der gleichen Elektrodenanordnung konnte auch bei der Katze eine ebenfalls 5wellige Antwort auf Klick-Reizung erhalten werden.Dieselbe Elektrodenanordnung ermöglicht auch die Erfassung der Hirnrinden-Antwort auf akustische Reize (Evoked Response Audiometry).Registriert man die extracraniale Antwort simultan mit der elektrischen Antwort aus intracraniell eingepflanzten Elektroden der Cochlea, von der Fenestra rotunda, so erscheint die erste Welle des Antwortkomplexes gleichzeitig mit dem Aktionspotential der Cochlea (N ₁), die zweite gleichzeitig mit derjenigen bei direkter Ableitung vom Nucleus cochlearis. Der dritten Welle im Komplex entspricht eine Antwort, die vom Nucleus olivarius superior abzuleiten ist. Gleichzeitig mit der vierten and fünften Welle des Antwortkomplexes erscheint eine Antwort, die wir vom Colliculus inferior ableiten konnten.

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This study serves as partial fulfillment of the requirements of the Hebrew University-Hadassah Medical School, in Jerusalem toward the M.D. degree of A.L.

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This study was supported in part by a grant from the Joint Research Fund of the Hebrew University-Hadassah Medical School.     

Auditory nerve-brain stem evoked potentials in cats during manipulation of the cerebral perfusion pressure

In order to study the effects of various degrees of cerebral ischemia on the auditory nerve-brain stem evoked potentials (BAEP), the cerebral perfusion pressure (CPP), defined as the difference between mean arterial blood pressure (MAP) and intracranial pressure (ICP), was systemically manipulated in anesthetized, paralyzed and ventilated cats. The CPP was varied by decreasing MAP, either by hemorrhage or by the infusion of a vasodilating drug, and elevating ICP by infusion of mock CSF into the cisterna magna, or by MAP depression and ICP elevation simultaneously. Even though the lower limit of adequate CPP is considered to be 40 mm Hg, the EEG became isoelectric at an average CPP of 24 mm Hg and the BAEP became isoelectric at an average CPP of 7 mm Hg. These extremely low CPP values of 7-24 mm Hg are far below the range of autoregulation of cerebral blood flow (CBF) so that the brain stem auditory pathway is still capable of generating its electrical response (BAEP) at very low CBF. This is paradoxical since these same regions of the brain have been shown to have the highest levels or regional metabolism as shown by their very high local cerebral blood flow and local glucose utilization.     

Auditory brain-stem (ABP) and somatosensory evoked potentials (SEP) in an animal model of a synaptic lesion: elevated plasma barbiturate levels

Experiments were conducted to determine whether a consistent pattern of auditory nerve brain-stem evoked synaptic lesion model in cats (elevated levels of the lesion model in cats (elevated levels of the barbiturate thiopental). The ABP in response to low (10/sec) and high (80/sec) stimulus rates was recorded. In order to differentiate between the effects of the elevated drug levels on axonal propagation and on synaptic transmission, the early components of the somatosensory evoked potential (SEP) were also recorded, with particular attention to the first SEP wave, which is solely an axonal event without any intervening synapse. Calculations showed that the effect on synapses was 3.0-9.5 times greater than the effect of the drug on axonal propagation. As the level of barbiturates increased (representing a more severe synaptic lesion), the interpeak latencies of the ABP and the SEP became progressively prolonged, more so than the dependence of the first waves of both the ABP and the SEP on drug level. In general, amplitudes were not affected. At progressively elevated drug levels, higher stimulus repetition rates did not have an increasingly greater effect than lower rates on evoked response latencies and amplitudes so that this study also shows that the use of elevated stimulus rates does not hold much promise in the diagnosis of synaptic lesions.     

Somatosensory functioning in children with attention deficit hyperactivity disorder

In older to test the hypothesis that attention deficit hyperactivity disorder (ADHD) is related to deficits in somatosensory processing, 49 ADHD male children and 49 matched controls were tested on a wide range of tactile tasks, and somatosensory evoked potentials (SEP) were also recorded. In addition, parents' and teachers' ratings on the children's typical responses to tactile stimuli were obtained. The results show that the ADHD children were less skilled on suprathreshold, but not on threshold tasks than were the controls. Further, a larger percentage of ADHD children were 'tactile defensive'. Finally, the ADHD children showed Iarger-than-normal amplitudes of late, but not early components of the SEP. These data suggest that some aspects of somatosensory processing by ADHD children are deficient.