Ultrasonic selective irradiation of the ear windows, as a new treatment of vertigo and tinnitus

Biological effects of ultrasound: development of safety guidelines. Part II: general review

In the 1920s, the availability of piezoelectric materials and electronic devices made it possible to produce ultrasound (US) in water at high amplitudes, so that it could be detected after propagation through large distances. Laboratory experiments with this new mechanical form of radiation showed that it was capable of producing an astonishing variety of physical, chemical and biologic effects. In this review, the early findings on bioeffects are discussed, especially those from experiments done in the first few decades, as well as the concepts employed in explaining them. Some recent findings are discussed also, noting how the old and the new are related. In the first few decades, bioeffects research was motivated partly by curiosity, and partly by the wish to increase the effectiveness and ensure the safety of therapeutic US. Beginning in the 1970s, the motivation has come also from the need for safety guidelines relevant to diagnostic US. Instrumentation was developed for measuring acoustic pressure in the fields of pulsed and focused US employed, and standards were established for specifying the fields of commercial equipment. Critical levels of US quantities were determined from laboratory experiments, together with biophysical analysis, for bioeffects produced by thermal and nonthermal mechanisms. These are the basis for safety advice and guidelines recommended or being considered by national, international, professional and governmental organizations.

Vestibular effects of chronic perilymph fistula in the cat

Chronic, unilateral perilymph fistulae were created in cats by removal of the round window membrane and placement of a tympanostomy tube into the round window. Rotary chair, fistula, caloric, and vestibulospinal tests were performed before and after fistulization, and periodically for 2 weeks. At 2 weeks, patency of the fistula was documented by fluorescein injection into the spinal fluid and visualization of leakage into the middle ear bulla via the fistula. All the cats had a patent fistula at 2 weeks, but one of the three cats had a greater perilymph leak than the others. The cat with the more active leak had a spontaneous nystagmus toward the side of the fistula on the first postoperative day; this changed to nystagmus toward the opposite side by the third postoperative day. The other cats had a spontaneous nystagmus toward the opposite side from the first postoperative day. Most abnormal test results returned to normal in the first week after fistulization. Histologic study of the temporal bones revealed that the cat with the greater leak had a wider cochlear aqueduct than the other cats.

Ultrasonic irradiation through the round window. Functional and morphological findings in sound-conditioned cats

Ultrasound was presented though the round window in 9 sound-conditioned cats at levels approximating clinical usage. Threshold shifts were mild to moderate and confined to 4 kHz and higher. There was total loss of function at 16 kHz in 2 animals. Threshold shifts correlated with cochlear histological findings as shown by reconstruction. There were three main types of lesions: abnormalities of supporting structures, hair cell loss, and lesion of Reissner's membrane. Supporting structure damage was the most frequent. The cristae of the semicircular canals did not show any lesions, though some saccular damage was noted. These changes were not observed in 4 control animals. Some conductive damage was noted as a result of probe placement. High frequency loss can be expected with the round window approach at irradiation levels of 52 mW for 20 min, or stronger.

Dimethyl sulfoxide therapy in subjective tinnitus of unknown origin

In fifteen patients affected by essential nonvibratory tinnitus, local applications in the external auditive canal of 2 ml medicated DMSO spray were made. The spray solution contained DMSO integrated with anti-inflammatory and vasodilatory substances. This application was repeated every four days for a month. At the same time each patient was administered a daily intramuscular injection of a preparation that contained DMSO and a vasodilatory component. The therapeutic effect was evaluated through the subjective modification of the symptom and functional tests of the auditory system. Of the fifteen patients treated, the tinnitus symptom completely disappeared in nine, and did not return during a one-year observation period. The patient's symptoms diminished in two cases, and in four cases the permanent tinnitus became occasional, triggered principally by environmental cold. It is important to note that among the concomitant signs, the five patients with vertigo noted improvement. Hypacusis diminished in three of the six patients affected. Insomnia disappeared in eight and diminished in seven cases. The rise in the average tympanic membrane temperature from 36.8 degrees C before to 37.9 degrees C after treatment was noteworthy. This could indicate an improvement of the blood flow in the inner ear.