J. Thoma

Experimental Investigations on the Suitability of the Carbon Dioxide Laser for Stapedotomy

Surgery of the footplate may cause a number of possible complications such as cochlear hearing defects or even complete loss of hearing. This has made it necessary to look for improved techniques. When a laser is used for stapedotomy, the energy transmitted to the cochlea must be reduced to the lowest possible level. We thus investigated the carbon dioxide laser to determine whether it would prove to be more advantageous than the argon laser. Animal experiments showed that CO2 laser irradiation is well tolerated. Tests performed on isolated petrous bone resulted in the development of a new surgical instrument suitable for stapedotomy using the CO2 laser. Temperature and pressure measurements were carried out on a simplified model of the human cochlea. Our findings indicated that, with both types of laser, the irradiation required to perforate the otosclerotically thickened footplate adversely affects temperature and pressure development in the cochlea.

A long-term study of hearing in children following neonatal hyperbilirubinemia

SummaryWe conducted a long-term study of 85 children with known transient neonatal hyperbilirubinemia to determine if their hearing had been affected. None of the children had neural symptoms such as kernicterus. The children ranged in age from birth to 9 months and were studied by means of brainstem evoked response audiometry (BERA). Thirty-four of the children were studied sequentially between 15 and 80 months after the initial examination. Our results showed that there was no significant correlation between serum bilirubin concentrations and BERA thresholds or latencies. These findings indicate that, unlike manifest cases of kernicterus, neonatal hyperbilirubinemia does not affect neonatal hearing when treated promptly.

Auditory Brain Stem Response Monitoring during Middle Ear Surgery

Conductive hearing loss can be determined in the course of middle ear surgery by sound probe stimulation and simultaneous recording of auditory brain stem responses. Mechanical properties of the ossicular chain, usually judged subjectively by the surgeons visual and tactile senses, can be quantified objectively. Thus, disarticulation of ossicles can be localized precisely, and fixation of the head of the malleus can be differentiated from stapes fixation. Moreover, the function of the reconstructed ossicular chain or prosthesis may be ascertained.

Klinische Sprachaudiometrie durch Registrierung von Erwartungs-Potentialen

SummaryThe expectancy potential or CNV, found by Walter et al. 1964, was checked for clinical application. For good comparison mono-syllable words from standard speech audiometry were used: 50 different “living beings” and 50 “things” were delivered via ear phones at random order and a set of their DC electric responses averaged seperately (Fig. 1). A flash series following only “living beings” after about 2 s had to be finished by the patient pressing a key as fast as possible. A punishing noise was applied when the key had been pressed at the wrong time or not at all. This measure stabilizes the patients attention, one of the important psychological factors influencing CNV-amplitudes. A ramp-shaped CNV develops only after successfull discrimination of a “living being” and is finished by the visually evoked response. Though varying extremely, amplitudes can be judged independent of sound intensity down to a steep break-off at a level where only about 50% are understood. This result was found in 20 cases of inner ear damage. Control of the threshold area of speech audiograms is one of the applications of expectancy potentials. Far above threshold subjective discrimination and CNV amplitude curves are not corresponding. A decrease in the speech audiogram was only found in few cases, may be due to lack of motivation at discomfort sound intensity.In cases of cerebral disturbances like suspected acoustic agnosia CNV could be a valuable diagnostical tool. But many of these patients are not able to cooperate properly. On the other hand, one CNV-measurement on a 57 year old patient with motoric aphasia proved his ability of word significance discrimination. Expectancy potentials, as the upmost stage of ERA, will probably be applicated only in a few problematic cases.

Ableitung von Hirnstammpotentialen während des Verlaufs von Mittelohroperationen bei Anwendung einer Körperschallsonde

SummaryUsing a special mechanical vibrating system we have applied brainstem audiometry in various types of tympanoplasty since 1980. The intraoperative measurement of sound transmission to the inner ear was carried out by brainstem potentials being evoked by stimulation with a piezo-electric transducer. Thus within certain limits the degree of postoperative sound transmission may be estimated.So it is for example possible to objectively examine interruptions of the ossicular chain or the acoustic transmission across a soft tissue scar within the chain. From this conclusions regarding the surgical procedure may be drawn.