Published papers

High potassium concentration in the cochlear endolymph electrically drives hair cell activity. Sodium potassium ATPase (Na+/K+-ATPase) is an essential pump for ion homeostasis in the cochlea. Most of our knowledge regarding Na+/K+-ATPase has been obtained from rodent models, and knowledge of its distribution in primates, including humans, is limited. This study investigated the distribution of Na+/K+-ATPase in a common marmoset primate model. We investigated expression patterns of Na+/K+-ATPase α1 (ATP1A1), Na+/K+-ATPase α2 (ATP1A2), Na+/K+-ATPase α3 (ATP1A3), Na+/K+-ATPase β1 (ATP1B1), Na+/K+-ATPase β2 (ATP1B2), and Na+/K+-ATPase β3 (ATP1B3) in the cochlea of the neonates and the embryos of the common marmoset. We have described the distributions of specific pairs of Na+/K+-ATPase α and β subunits in each cochlear part, including spiral ganglion neurons, stria vascularis, and the organ of Corti. We also described developmental changes in Na+/K+-ATPases in common marmosets. The distribution of Na+/K+-ATPases in the common marmoset is similar to that in humans and is suitable for furthering our understanding of human cochlear development. The distribution established in this report will aid the study of primate-specific ion homeostasis in the inner ear.

The combination of directional microphones (DIR) and spectral noise reduction (NR) is a common technique in hearing aid signal processing, for improving speech intelligibility in spatial acoustic scenarios. The benefit from DIR + NR varies considerably across individuals, which impedes prescribing the optimal strength of such processing during hearing aid fitting. The goal of this study was to investigate the correlation of four audiological factors with the benefit of speech reception thresholds (SRTs) from DIR + NR: the closedness of the acoustic coupling in the ear canal, audible contrast thresholds test (ACT™), the audiogram, and age. As part of a larger field study, 123 experienced hearing aid users in two centers in Germany and Japan were fitted bilaterally with the same hearing aids. SRTs were obtained with and without strong DIR + NR in a spatial speech-in-noise scenario before and after the field trials. Closedness of acoustic coupling was found to have the strongest correlation with SRT benefit from DIR + NR (most likely dominated by DIR rather than NR processing), followed by audible contrast thresholds (ACT) and the audiogram, both with the same significantly weaker correlation. Age was not correlated with the benefit from DIR + NR. The results suggest fitting hearing aid users irrespective of age with as-closed-as-possible acoustic coupling to maximize the benefit of DIR + NR. Furthermore, the closedness of acoustic coupling in combination with ACT or the audiogram may serve audiologists in predicting individual speech intelligibility benefits from strong DIR + NR for better guidance to set its strength during hearing aid fitting.

Intralabyrinthine hemorrhage (ILH) is a rare differential diagnosis of sudden sensorineural hearing loss. Investigations using magnetic resonance imaging (MRI) in the early phase from the onset are inevitable to diagnose ILH. However, MRI is not usually performed during the early phases of sudden sensorineural hearing loss. Hence, ILH is rarely diagnosed, and the hearing prognosis and vestibular function in patients have been poorly understood. In the present study, we report the detailed course of ILH with relatively good hearing recovery. Additionally, vestibular function recovery was quantitatively examined using a video head impulse test. A 75-year-old man presented at our clinic with a chief complaint of dizziness, sudden hearing loss, left sensorineural hearing loss, and nystagmus. MRI 18 days after onset showed a left ILH. Following treatment with prednisone, the patient's hearing level partially recovered and nystagmus disappeared. Our experience emphasizes that MRI in the early phase is crucial for diagnosing ILH. Furthermore, MRI in the early phase should be considered in cases of sudden sensorineural hearing loss or dizziness and is beneficial for investigating ILH as a subpopulation of sudden sensorineural hearing loss.

聴覚過敏は、日常的な音に対して過敏性や不快感を示す状態で、外界からの音によらない耳鳴や、自分の声のみが強く聞こえる自声強聴とは異なった病態を表すと考えられている。しかし、過敏症状には「響く」、「大きく(強く)聞こえる」など多彩な表現が存在するにもかかわらず、各表現を分類して意義を検討している報告はない。そこで、過敏症状を訴えた168名を対象に、過敏症状の自覚的表現と疾患との関連や、これらの表現の臨床的意義について検討した。疾患の内訳は、約3分の2が急性感音難聴で、次いで加齢性難聴であり、聴力検査上異常を認めない症例も1割程度含まれていた。「響く」が最も多く、「響く」か否かを問診することは過敏症状のスクリーニングに役立ち、「割れる」や「二重に聞こえる」は感音難聴の存在を疑い、「大きく(強く)聞こえる」は極めて軽微な内耳障害や、聴覚中枢を含めた病態の関与を考える必要がある表現と考えられた。(著者抄録)