Behavioural responses have been elicited to acoustic stimuli in hereditarily deaf white mink (Hedlund). This revealed onset of auditory function at an average age of 31 days. The period of hearing lasted on the average only 7 days. Similar observations have been reported in other hereditarily deaf animals (cat, mouse, guinea pig). It is suggested that the onset of auditory function follows a progressive pattern which corresponds to the circulation of blood in the cochlea. Moreover, it is suggested that the subsequent deterioration of hearing follows a regression of this vascular pattern and thus a vascular pathogenesis may be responsible for this type of genetic deafness.

Acoustic Impedance Tests↗

PubMedDate not supplied

Cochlear hearing loss and viral infection.

A group of about 100 consecutive patients admitted to an otorhinolaryngological outpatient department for treatment of cranial nerve affections underwent detailed neurological, audiological and laboratory examinations. Of 34 patients with hearing loss, objective signs of viral infection were found in 12. The hearing loss was sensorineural of the cochlear type, in 7 cases of the high-frequency type, in 5 cases of the low-frequency (Menière) type. Within one year after the onset of the disease the hearing loss had disappeared in all but 2 cases. Reversible dysfunction of two or more cranial nerves was found in 7 of 8 cases examined. In the cerebrospinal fluid the cell count and the total protein and gamma-globulin values were increased in most patients. Our findings indicate a reversible sensorineural hearing loss to be part of a viral-induced meningoencephalitis and cranial polyneuropathy. The mechanism of the reversible low- and high-frequency hearing loss is discussed.

Adult↗

PubMedDate not supplied

Impedance changes elicited by electrocutaneous stimulation.

Electrical stimulation of the skin in the cavum conchae is followed by bilateral changes in the acoustic impedance of the ear due to reflex contraction of the stapedius muscle. A stimulator and a special surface electrode for electrical stimulation of the skin have been developed. The apparatus produces square-wave constant-current pulses independent of the electrical impedance of the electrode and the skin, and its hazard-proof. The effect of five independently variable stimulus parameters upon the elicited impedance changes has been examined in order to find a stimulus producing a large and reproducible impedance change without causing discomfort to the subject. Although a pronounced habituation phenomenon tends to mask the cause to effect relation of the various parameters, the results indicate that an appropriate stimulus is a pulse train of 0.5 s duration, consisting of individual pulses of a frequency of 200 Hz and 1 ms duration. The stimulus is applied at 10-second intervals.

Acoustic Stimulation↗

PubMedDate not supplied

Improving audiometric thresholds by changing the headphone position at the ear.

A 10-year noise project, consisting of annual hearing measurement, temporary threshold shift (TTS) measurements and examination of noise exposure in 250-300 employees, involved a study of the improvement in measured hearing threshold by changing the position of the headphone at the ear. Threshold measurements were performed at 11 frequencies ranging from 125 to 8,000 Hz, and consisted of 2,708 audiograms in the hearing control program and 551 audiograms in the TTS program. A new threshold determination at frequencies above 3,000 Hz was carried out after moving the earphone to a new position in 870 (32%) of the cases in the hearing measurement program and 248 (45%) of those in the TTS program. The indication for moving the phone is discussed. Improved thresholds in the range of 5-40 dB at 6,000 and 8,000 Hz were observed in 58-68% of the cases, depending upon frequency and program (measurement of hearing and TTS). Consequences for standard threshold values and for diagnostic purposes are discussed.

Audiometry, Pure-Tone↗