Fresh Temporal Bones Research Articles

Measurement of sound transmitted through the body while drilling and grinding isolated petrous temporal bone (author's transl)

Measurements of the effect of rotating drills and grinders on isolated fresh temporal bone on the sound transmitted through the body have not previously been made known. In contrast to measurement of air-conducted sound, they include the portion of sound which effects the hearing apparatus of the patient through the bone during the process of drilling the temporal bobe. Measurements were made with a calibrated acceleration pick-up in conjunction with a precision sound level meter (test amplifier with sound frequency analyser). The recording was made continuously between 20 Hz and 20 000 Hz. The range between 250 Hz and 8000 Hz was examined mathematically. Above 8000 Hz the curves dropped markedly, apart from a few exceptions. The level of the sound depends largely on the size of the drill bit, and consequently on the breadth and depth of the rotating cutting edges. The smaller drill heads produce a considerably smaller quantity of sound. The highest level of sound comes from the burrs and wing-cutters. The diamond head lies lower in the scale, but almost equals the effect of the steel drills. The speed of rotation of the drill head plays only a subordinate role. Between 16 000 and 80 000 r.p.m. the values are the same. In the region of 10 000 r.p.m. the sound level is frequently reduced, even if a few loud peaks may still occur here. The type of drilling machine, the handpiece or transmission handpiece used have no effect. Altogether, the rotary drill produces less sound transmitted to the inner ear through the body than through the air.

A Study of the Topographic Anatomy of the Human Vestibular Aqueduct

Taking consideration of its surgical importance the anatomy of the distal endolymphatic system, especially, dimensions of the vestibular aqueduct were investigated. Twenty-five adult human dry temporal bones were dissected for the study on dimensions and relationships of lumen of the common crus and the internal aperture of the vestibular aqueduct. And sixteen adult human fresh temporal bones were examined by osmic acid staining method on the measurement of whole course of the vestibular aqueduct. As the results, numerical data of the vestibular aqueduct were presented with particular reference to its shape, dimensions, and relationships of its internal aperture. The course and relationships of a para-vestibular canaliculus housing the blood supply of the endolymphatic sac was described.

The clinical significance of epitympanic mucosal folds.

The epitympanic mucosal folds were studied in 250 randomly selected fresh temporal bones and were found to be only rudimentary structures in normal ears, but had significant variations in abnormal ears. Pathological changes of the mucosal folds are a part of attic disease. In combination with tympanic membrane retraction, mucosal fold pathology seems to cause obstruction of the tympanic isthmus. Recognition of an air diffusion disturbance within the middle ear cleft pneumatic system at the area of the tympanic isthmus produced by these folds is important in the understanding of various middle ear diseases.

Acoustic input impedance of the human ear.

An objective method of measuring the vibrations of the tympanic membrane by means of an improved capacitive-probe system is described. The device has a dynamic range up to 7500 A over the whole audiofrequency range. A new probe tip was developed, serving for conduction of the modulated H.F. signal as well as for the sound transmission. The acoustic input impedance of the ear of 15 fresh temporal bone preparations was evaluated over the whole audio frequency range, and comparisons between the unloaded and the ear loaded by the inner ear were made. Characteristics of the ear were obtained from these data.

Observations on the Effect of High Intensity Sounds in the Ear

The middle ear of rabbits was photographed during exposure to high intensity sounds. Extreme amplitudes of the eardrum were observed and measured. Rupture of the eardrum occurred when the signal was increased further (motion picture film). The protective devices of the ear against intense signals are discussed. The reflex of the middle ear muscles is demonstrated. Tetanic contractions of both muscles dampen the movements of the ossicles. Another mechanism which most likely acts as protection for the vulnerable inner ear is the change of axis of the stapes at high intensity signals. The stapes movements were studied in fresh temporal bones. A small mirror was attached to the vestibular side of the footplate. Acoustic stimulation was carried out through the outer ear canal. The responses are asymmetrical. The negative amplitude is greater than the positive or sometimes negative only. Signals increasing in intensity produce a gradual change of the axis of vibrations. It was also observed that the stapes may suddenly change the axis of vibration as described previously by v. Békésy. The change of axis is interpreted as a protective device. Other features of the ear which act as protection against overstimulation are discussed.