Three-dimensional analysis of caloric nystagmus in the rhesus monkey.

The aim of this study was to investigate whether caloric nystagmus contains response components that can be attributed to a stimulation of the vertical semicircular canals. Three dimensional eye movement recordings with a dual search coil technique revealed important horizontal, vertical and torsional nystagmus components following irrigation of the external ear canal with cold water in various head positions relative to gravity. Horizontal nystagmus components, i.e. lateral semicircular canal vectors, followed a cosine function of both the pitch and yaw angle of the head relative to gravity, confirming a mainly thermovective mechanism for stimulation of the horizontal canals. Vertical and torsional nystagmus components behaved differently following left and right ear irrigations. Right-left symmetrical vectors emerged only when the vertical and torsional components were transposed into vectors of single semicircular canal directions. The intensity of these vertical semicircular canal vectors as a function of the position of the corresponding canal relative to gravity, however, excludes important thermovective mechanisms acting at the vertical canals. It remains an open question whether these vertical canal vectors represent a non-thermovective caloric stimulation of vertical canal afferents.     

Use of the loud sound stimulation test in diagnosis of semicircular canal dehiscence syndrome

Semicircular canal dehiscence (SCD) syndrome is rare, and its diagnosis is a significant challenge in clinical practice. Our aim was to explore application of the loud sound stimulation test for diagnosing SCD syndrome. Eight cases of superior semicircular canal dehiscence (SSCD), among them two patients had bilateral dehiscences and one case of lateral semicircular canal dehiscence (LSCD). A total of 11 dehiscences were studied retrospectively. Loud sounds (pure tones, 100 dB, 110 dB nHL) at frequencies of 500, 1,000, and 2,000 Hz were used to stimulate both ears for 5 s. A temporal bone computed tomography (CT) scan with semicircular canal reconstruction was performed in all patients. Vertigo was present in seven of nine cases following loud sound stimulation. In addition, the patient with LSCD demonstrated horizontal eye movement following loud sound stimulation, whereas six patients with SSCD showed rotational eye movement. Among them, two patients with bilateral superior canal dehiscence showed a positive response to the loud sound stimulation in only one ear. The diagnoses of all patients were confirmed with a high-resolution temporal bone CT with corresponding multi-planar reconstruction of the affected semicircular canals with various size dehiscences. We conclude that the characteristic eye movement following loud sound stimulation is valuable for diagnosing SCD syndrome. In addition, the loud sound stimulation test has unique advantages, especially for confirming the affected ear and the corresponding semicircular canal.     

垂直平面摆动试验检测垂直半规管功能及其正常值的研究

目的 利用垂直平面摆动试验检测垂直半规管功能并探讨中青年垂直半规管功能正常值.方法 运用自主研制的SRM-Ⅳ全自动前庭功能诊治系统,采用垂直平面180°正弦非阻尼摆动方法对100名18 ～59岁的健康受试者诱发垂直眼震,记录眼震视频和眼震曲线,采集眼震个数、持续时间、慢相速度等参数.将100名健康受试者以45岁为界分为青年组(68例)和中年组(32例)进行比较.试验中以右前半规管和左后半规管为一对(right anterior semicircular canal and left posterior semicircular canal,RALP),以左前半规管和右后半规管为一对(left anterior semicircular canal and right posterior semicircular canal,LARP),计算出两对垂直半规管垂直眼震平均慢相速度两侧不对称比( canal paresis,CP),采用SPSS 13.0软件进行统计学分析.结果 青年组和中年组平均慢相速度CP值差异无统计学意义(P＞0.05),总体CP值,RALP为10.2％±7.1％,LARP为10.4％±6.2％.健康中青年人群垂直半规管垂直眼震平均慢相速度CP值95％参考值范围,RALP为低于23.7％,LARP为低于22.9％;CP正常范围:≤20％为理想值,20％～ 25％为正常偏高.结论 垂直平面180°摆动试验可有效检测垂直半规管功能,此方法有望在临床得到应用.     

Vestibular adaptation studied with a prosthetic semicircular canal

We have developed and tested a prosthetic semicircular canal that senses angular head velocity and uses this information to modulate the rate of current pulses applied to the vestibular nerve via a stimulating electrode. In one squirrel monkey, the lateral canals were plugged bilaterally and the prosthesis was secured to the animal's head with the angular velocity sensor parallel to the axis of the lateral canals. In the first experiment, the stimulating electrode was placed near the ampullary nerve of one lateral canal. Over a period of two weeks, the gain of the horizontal VOR during yaw axis rotation gradually increased, although the response magnitude remained relatively small. In the second experiment, the stimulating electrode was placed near the ampullary nerve of the posterior canal, but the orientation of the velocity sensor remained parallel to the axis of the lateral canals. Over a one-week period, the axis of the VOR response gradually shifted towards alignment with the (yaw) axis of head rotation. Chronic patterned stimulation of the eighth nerve can therefore provide adequate information to the brain to generate a measurable VOR response, and this can occur even if the prosthetic yaw rotation cue is provided via a branch of the VIIIth nerve that doesn't normally carry yaw rotational cues. The results provided by this pilot study suggest that it may be feasible to study central adaptation by chronically modifying the afferent vestibular cue with a prosthetic semicircular canal.     

Time constant of nystagmus slow-phase velocity to yaw-axis rotation as a function of the severity of unilateral caloric paresis.

OBJECTIVE: Complete unilateral loss of vestibular function results in a phase advance (reduced time constant) of the horizontal slow-phase nystagmus response to yaw-axis rotation. The objective of this study was to determine whether partial losses of lateral semicircular canal function would result in proportional reductions in the time constant. SETTING AND STUDY DESIGN: This was a retrospective study of consecutive patients' records at two tertiary referral centers for vestibular disorders. PATIENTS: Four hundred fifty-four patients who presented for evaluation of vertigo or imbalance or both and who were found to have partial or complete unilateral canal paresis on caloric testing. MAIN OUTCOME MEASURES: In 372 patients, the gain and time constant of the horizontal nystagmus response was measured using a 5-second velocity ramp of constant yaw-axis acceleration. Caloric responses to standard bithermal irrigations at 30 degrees and 44 degrees were obtained using an open-loop irrigation system. In a second group of 82 patients, the gain and time constant of the horizontal vestibulo-ocular reflex were measured using a sum-of-sines (pseudorandom) yaw-axis acceleration. The caloric response was measured using a closed-loop system. Results: In both groups, the peak gain of the nystagmus response was independent of the level of the canal paresis. However, the time constant of the response both toward and away from the lesioned side decreased proportionally with increasing canal paresis. CONCLUSION: This result supports the hypothesis that bilateral symmetrical peripheral vestibular input is a necessary condition for the mechanisms or processes underlying normal horizontal slow-phase velocity storage.     

Subjective Visual Horizontal Determination During Otolith Stimulation by Eccentric Rotation in Conservatively Treated Meniere's Disease

Peripheral vestibular equilibrium disorders may originate in various parts of the labyrinth or of the vestibular nerve. Traditionally, the function of the lateral semicircular canals has been assessed by caloric irrigation and has been interpreted (sometimes falsely) as demonstrating a vestibular nerve lesion. The vertical semicircular canals are not assessed easily. Caloric testing with the head in various positions is not very helpful, but the canals may be tested in pairs using specific rotational techniques. Often, the otolith organs, detecting linear acceleration forces, are forgotten as a source of vertigo and dizziness. The extent of otolith involvement in Meniere's disease is not well understood. The tested subject is seated eccentrically in a rotatory chair and faces the direction of rotation. Thus, the otolith organs are stimulated in steady-state rotation. The subject experiences a lateral tilt and, in darkness, is instructed to point a short light bar in the position that he or she thinks a water surface would have (identical to the perceived tilt). Patients with conservatively treated unilateral Meniere's disease were tested. In the eccentric rotation test, the patients with unilateral Meniere's disease showed highly variable, sometimes even paradoxical, responses. No correlation was noted between the eccentric otolith test and pure-tone audiometry or the side difference of the caloric responses. Otolith and lateral semicircular canal functions may differ in patients with Meniere's disease, the nature of which remains to be elucidated in further studies.     

190例特发性良性阵发性位置性眩晕患者半规管功能分析

目的 分析特发性良性阵发性位置性眩晕(benign paroxysmal position vertigo,BPPV)患者半规管功能的特征,为患者的治疗提供进一步帮助.方法 选择本院2019年8月至2020年2月收治的单侧特发性BPPV患者190例,包括后半规管BPPV患者162例,水平半规管BPPV患者28例.行冷热...     

A new rotational test for vertical semicircular canal function

OBJECTIVE: We developed a new rotating chair in order to assess the function of the vertical semicircular canal (VSCC) by analyzing VSCC-induced post-rotatory nystagmus (PRN). METHODS: We examined 14 healthy subjects, wearing goggles equipped with an infrared CCD camera, and sitting on a chair which was designed to stimulate a pair of the VSCCs by tilting the head 60 degrees backward with a 45 degrees rotation to the left or right side from the sagital plane. The time constant (TC) or maximal slow phase eye velocity (MSPEV) of the vertical component of four kinds of PRN were analyzed in four corresponding rotatory conditions, and used as functional index of the corresponding VSCC. RESULTS: The mean values of MSPEV in both anterior semicircular canal (ASCC) and posterior semicircular canal (PSCC)-induced PRN tended to be lower (P<0.10) than those induced by the lateral semicircular canal (LSCC). The result suggests that the threshold to the angular velocity in the VSCC is lower than that in the LSCC. The mean values of TC in both ASCC and PSCC-induced PRN were significantly lower (P<0.05) than those induced by the LSCC. CONCLUSION: The significant reduction of TC in VSCC-induced PRN compared with LSCC-induced PRN indicates that VSCC function is less affected by velocity storage mechanisms than LSCC function. The rotational test with respect to the VSCC can be used as a tool for assessing vertical canal function.     

Mechanism of posterior semicircular canal stimulation in patients with benign paroxysmal positional vertigo

A quantitative study of the stimuli and vestibulo-ocular response associated with benign paroxysmal positional vertigo (BPPV) was made to test and further develop the canalithiasis theory of BPPV. The angular velocities of the head in the planes of the semicircular canals during the Dix-Hallpike test were measured in four healthy subjects using electromagnetic sensors to record the position of the head in a six degrees of freedom paradigm. Next, the nystagmus reactions in seven patients diagnosed with idiopathic BPPV were recorded with video-oculography. The characteristics of the vestibulo-ocular reflex (VOR) response were analyzed using three-dimensional vector techniques. The angular velocity of the head was primarily, but not exclusively, in the plane of the posterior semicircular canal (PSC) in question. Both the anterior and horizontal canals were also stimulated by a lesser degree. The duration of the motion stimulus in the PSC was < 1.3 s with peak angular velocities of 150 deg/s. The eye response in BPPV patients began 4 s after the test and had a duration of 15-20 s. Peak slow-component eye velocities of about 42 deg/s were reached 3-5 s after onset of nystagmus. The motion of the eye, as predicted by the cupulolithiasis theory, is disconjugated and has torsional, vertical, and horizontal components. In the eye ipsilateral to the tested ear it is primarily torsional (0.80, 0.54, 0.16) and in the contralateral eye it is mainly vertical (0.57, 0.73, 0.08). These results suggest that particles, initially resting on the floor of the cupula dome in the PSC, are perturbed by the Dix-Hallpike test and disperse freely into the endolymph where they are propelled by gravity into the canal lumen. This creates abnormal pressure on the cupula and the specific VOR activation of the ipsilateral superior oblique and the contralateral inferior rectus muscles, whose force vectors are indistinguishable from the measured eye motion vectors. The estimated pressure exerted on the crista is approximately 10(-2) dyn/cm2.     

Symposium: new data for noise standards. V. Current status of labyrinthine cryosurgery

Laboratory investigations on the squirrel monkey demonstrated that cryosurgery of the labyrinth was able to attenuate consistently the sensitivity of the vestibular end organ to caloric stimulation. The post surgical rate of decline in semicircular canal function was found to be directly related to the temperature and exposure time employed. For a given exposure time, decreasing cryosurgical temperatures provided loss of function in fewer days. When temperature was held constant, increases in duration of cryosurgical application produced a more rapid decline in semicircular canal function. Examination of the temporal bone of these animals showed that morphological alterations were restricted to the place of contact of the cryosurgical probe on the horizontal semicircular canal. These changes appeared in the form of fibrosis and bony obliteration in the perilymphatic space. Although this blockage could conceivably inhibit the movement of endolymph within the horizontal canal, the posterior and superior canals should remain functional. The absence of nystagmus in response to either caloric or rotational stimuli suggested that cryosurgery did more than just produce an obstruction of the horizontal canal. A series of experiments were then performed on the vestibular end organ of the pigeon, in an attempt to study further the effects of cryosurgery of the labyrinth. In order to eliminate the tissue reaction observed in the monkey, the site of cryosurgical application was moved from the thinned horizontal canal to the bony crista ampullaris, and the cryoprobe temperature adjusted to produce the same intralabyrinthine temperature that had eliminated semicircular canal function in the earlier studies. Using this new technique, a normal rotatory reaction was observed after the horizontal crista was cooled to -30d? and -40d? C for nine minutes. The animals exposed to -70d? and -90d? C for nine minutes demonstrated marked reduction in rotatory reaction three weeks after the cryosurgery. Rotatory responses were abolished in those animals which were exposed to -120d? and -190d? C for nine minutes. Pigeons exposed to -30d? and -40d? C for nine minutes failed to show any structural changes in the horizontal crista, and surrounding area. Pigeons exposed to -70d? C showed the presence of exudate in the endolymphatic space and shrinkage of cupula. Cooling the horizontal crista to -90d? C produced partial degeneration of the specialized cells and the sensori-epithelia. The membranous wall of the horizontal canal was ruptured (one of four animals) and the cupula detached. Pigeons exposed to -120d? and -190d? C demonstrated severe degeneration of the sensori-neural and specialized cells. Ruptures of the membranous wall were present in every specimen. The cupula was not present and exudate was commonly found in the endolymphatic space. A definite correlation seems to exist between histologic and functional changes of the semicircular canals following cryosurgery. It appears that the critical threshold dosage necessary to alter the morphology and function of the semicircular canal system is approximately -70d? C for nine minutes (intralabyrinthine temperature +18d? C) in the experimental animal. Temperature measurements were performed on two patients with Ménière's disease prior to performing a total labyrinthectomy. The cryosurgical probe was positioned on the thinned bony wall of the horizontal canal at a temperature of -160d? C. The temperature of the horizontal crista ampullaris in both patients ranged from +17d? to +20d? C. These intralabyrinthine temperature measurements correlate well with the experimental data. The clinical use of labyrinthine cryosurgery began in May of 1965. The surgical technique has been described in previously published reports. Using a temperature of -160d? C, a cryogenic application is made to the thin bony wall of the horizontal semicircular canal for a total of six minutes (three applications of two minutes each). Since cryosurgery has a dual objective of relieving vertigo and preserving hearing, a case is considered successful only if both objectives have been accomplished. There are 134 cases in which an adequate follow-up has been maintained for one year or more. The results indicate that 100 operations (75 percent) were successful, and seven patients (5 percent) were considered as being improved. Twenty-seven procedures (20 percent) were considered surgical failures, due to inadequate relief of the vertigo attacks. Since experimental animals were rendered unresponsive to caloric stimulation following cryosurgery, it seemed reasonable to assume that the successful clinical cases could be attributed to an attenuation of the sensitivity of the semicircular canal system. Although this change did occur in the majority of the operated cases, 36 percent of the successful cases demonstrated little or no change in the postoperative caloric tests. A change in the sensitivity of the semicircular canal system, therefore, could not completely explain the mechanism by which cryosurgery produces its effect. Based upon the more recent experimental observations, it is entirely possible that changes in the dark and light cells, or the creation of an otic-periotic shunt secondary to rupture of the membranous labyrinth may explain a successful clinical result when little or no change has occurred in the postoperative caloric test.     

Does unilateral utricular dysfunction cause horizontal spontaneous nystagmus?

The presence of spontaneous nystagmus in darkness with a strong horizontal component has been taken to indicate that there is asymmetrical function of the horizontal semicircular canals. If this horizontal spontaneous nystagmus can be suppressed by vision, then it is regarded as due to peripheral horizontal canal dysfunction. However, we report evidence from one patient (61-year-old male), who visited the MSA ENT Clinic, Cassino (FR) Italy, reporting acute, severe vertigo, postural unsteadiness, nausea and vomiting associated with right sudden hearing loss. The patient received instrumental audiovestibular testing to obtain objective measurements of his inner-ear receptors. At the time of the attack, the patient showed spontaneous nystagmus, mainly with horizontal and vertical components (3D infrared video-oculography). Video head-impulse tests of dynamic horizontal canal function showed that the functional status of both horizontal canals was within the normal range. Cervical VEMPs to 500 Hz bone-conducted vibration at Fz showed normal results; ocular VEMPs to the same stimulus showed a reduced n10 amplitude beneath the left eye, corresponding to the right ear. For this reason, the patient was diagnosed as having right unilateral selective utricular macula lesion due to labyrinthitis. There is considerable evidence of convergence of neural input from the otoliths onto horizontal canal neurons in the vestibular nuclei. The firing of such neurons could reflect either asymmetrical horizontal canal function or asymmetrical utricular function. The problem with this patient was not due to asymmetrical horizontal canal function, but only to asymmetrical utricular function, demonstrated by the results of the oVEMP test.     

Ecological Aspects of Auditory Rehabilitation

A quantitative study of the stimuli and vestibulo-ocular response associated with benign paroxysmal positional vertigo (BPPV) was made to test and further develop the canalithiasis theory of BPPV. The angular velocities of the head in the planes of the semicircular canals during the Dix-Hallpike test were measured in four healthy subjects using electromagnetic sensors to record the position of the head in a six degrees of freedom paradigm. Next, the nystagmus reactions in seven patients diagnosed with idiopathic BPPV were recorded with video-oculography. The characteristics of the vestibulo-ocular reflex (VOR) response were analyzed using three-dimensional vector techniques. The angular velocity of the head was primarily, but not exclusively, in the plane of the posterior semicircular canal (PSC) in question. Both the anterior and horizontal canals were also stimulated by a lesser degree. The duration of the motion stimulus in the PSC was &;lt;1.3 s with peak angular velocities of 150 deg/s. The eye response in BPPV patients began 4 s after the test and had a duration of 15-20 s. Peak slow-component eye velocities of about 42 deg/s were reached 3-5 s after onset of nystagmus. The motion of the eye, as predicted by the cupulolithiasis theory, is disconjugated and has torsional, vertical, and horizontal components. In the eye ipsilateral to the tested ear it is primarily torsional (0.80, 0.54, 0.16) and in the contralateral eye it is mainly vertical (0.57, 0.73, 0.08). These results suggest that particles, initially resting on the floor of the cupula dome in the PSC, are perturbed by the Dix-Hallpike test and disperse freely into the endolymph where they are propelled by gravity into the canal lumen. This creates abnormal pressure on the cupula and the specific VOR activation of the ipsilateral superior oblique and the contralateral inferior rectus muscles, whose force vectors are indistinguishable from the measured eye motion vectors. The estimated pressure exerted on the crista is approximately 10^-2 dyn/cm².     

The 2D modified head impulse test: a 2D technique for measuring function in all six semi-circular canals

The head impulse test can be used to measure peripheral vestibular function of all six semicircular canals. Traditionally, vertical canal function is measured by rotating the head from a starting neutral position (forward facing) about a diagonal plane that bisects the sagittal and coronal planes. These types of head rotations elicit eye movements with large vertical and torsional (about the line of sight) angular velocity components. Three-dimensional (3D: horizontal, vertical and torsional) eye measurement techniques are needed to measure these velocity components. We wanted to determine whether 2D measurements coupled to a modified head impulse test are sufficient to measure function of all six canals. In this study we measured individual canal function in patients (n=5) with peripheral unilateral hypofunction and control subjects (n=4) using the traditional head impulse test and the 'gold standard' 3D (dual-coil) scleral search coil technique. We compared these results with those from our 2D modified head impulse test using the 2D coil technique (single-coil). We show that both techniques detect similar levels of asymmetrical function in patients and are equally accurate in isolating canals with hypofunction. We conclude that 2D eye measurement techniques, such as video pupil-tracking, can be used to test all six canals.     

The Dix-Hallpike test and the canalith repositioning maneuver

The Dix-Hallpike test and the canalith repositioning maneuver (CRM) are used to diagnose and treat benign positional vertigo (BPV). Dix-Hallpike is the standard procedure for diagnosis of BPV, but if the horizontal canal is not tested for BPV and the Dix-Hallpike is only carried out once, the condition may not be diagnosed and appropriately treated. We describe our method of testing for BPV and treating it with CRM. The Dix-Hallpike test involves rapidly moving the patient from a sitting position to "head hanging," where the patient's head is at least 10 degrees below horizontal. This is performed initially for the posterior semicircular canals. If these movements fail to elicit vertigo and nystagmus, tests of the horizontal semicircular canals are performed by laying the patient on each side. Importantly, if there is no vertigo or nystagmus elicited by testing the horizontal semi-circular canals, the posterior semicircular canals are tested again. It appears that being held in the head hanging positions and then left and right lateral positions will often allow the canaliths to collect such that the Dix-Hallpike test will become positive. Failure to repeat the tests of the posterior semicircular canals may result in a falsely negative test. Testing the horizontal canals and repeating the Dix-Hallpike test will reduce the likelihood of patients undergoing extra testing or other consequences of misdiagnosis. If, during any of this testing, a movement elicits vertigo or nystagmus, the appropriate CRM is then carried out.     

高分辨率CT多平面重组对半规管病变的诊断价值

目的:探讨高分辨率CT(HRCT)多平面重组对半规管病变的诊断价值,提高对半规管病变的认识。方法:对怀疑上半规管裂缺的患者3例(6耳),突发性聋患者30例(60耳),感音神经性聋患者30例(60耳)及同期进行体检无耳部疾患的患者20例(40耳)行HRCT扫描,对原始数据行多平面重组,观察正常耳各半规管的形态并与病变组相比较。结果:各半规管均表现为不同倾斜度的C形,正常耳上半规管全程斜矢状位表现为"∩",前端与前庭相通,后端与后半规管上半部形成总脚并与前庭相通;外半规管全程轴位呈""形,前后脚与前庭相通;后半规管全程斜矢状位表现为""形,下端与前庭相通,上端与上半规管形成总脚与前庭相通。半规管管腔平滑,骨质无缺损。发现上半规管裂1耳;突发性聋组前庭导水管与上半规管相通1耳,与后半规管相通2耳;感音神经性聋上半规管闭塞1耳,外半规管闭塞2耳,外半规管骨质不完整2耳,上半规管粗短2耳、外半规管与前庭融合4耳、后半规管短小2耳。结论:HRCT扫面多平面重组能全程观察各半规管,对诊断半规管病变具有重要价值,值得临床推广。     

半规管阻塞技术的初步临床应用

目的初步探讨临床应用半规管阻塞技术治疗位置性眩晕与梅尼埃病的安全性与有效性。方法回顾性分析1994-2000年间半规管阻塞技术临床应用的资料,其中,后半规管位置性眩晕2例,水平半规管位置性眩晕1例,内淋巴囊阻塞术后5年复发的梅尼埃病1例,男1例,女3例,年龄39-58岁。梅尼埃病患者行三半规管阻塞及内淋巴乳突腔分流术,位置性眩晕患者行相应的半规管阻塞术。结果位置性眩晕患者术后随访1.5-7年,全部患者位置性眩晕得到解除,术后纯音测听、中耳功能分析、听觉脑干电反应测试、耳声发射等听觉功能检查结果显示耳蜗功能与术前完全一致,水平半规管阻塞的患者双耳冷热试验结果显示手术消除了水平半规管的功能,后半规管阻塞的患者双耳冷热试验结果显示手术后以水平半规管为代表的其它前庭末梢器官的功能得到良好的保存。内淋巴囊阻塞术后5年复发的梅尼埃病患者术后随访2年,眩晕得到完全控制。结论半规管阻塞技术可有效控制位置性眩晕与梅尼埃病患者的眩晕,半规管阻塞对患者耳蜗功能及所阻塞半规管以外的其它前庭末梢器官功能没有影响,半规管阻塞技术可望成为位置性眩晕和梅尼埃病安全、有效的治疗手段,符合现代外科学对手术微创的要求。     

Selective resection of the semicircular canals of rabbits with preservation of hearing.

The goal of this investigation was to develop a method of surgical removal of the semicircular canals of the rabbit without induction of auditory impairment. Four different surgical techniques were utilized: i) fenestration of the lateral semicircular canal; ii) fibrin glue perfusion of the canal following fenestration; iii) removal of the lateral semicircular canal by drilling after fenestration and fibrin glue perfusion, and iv) removal of all three canals after fenestration and fibrin gluing. Brainstem auditory potentials were recorded repeatedly for up to 3 months after operation and demonstrated preservation of hearing in all rabbits in the first group and in 78% of the second group. In the third group the potentials could be recorded in 67% of the animals and showed a 20 dB deterioration of hearing. After removal of all three semicircular canals residual hearing could be recorded in 50% of the rabbits. These animals regularly showed a 30-40 dB deterioration of hearing. A precise microsurgical technique using fibrin glue and bone chips for interruption of the peri- and endolymph flow proved crucial for hearing preservation.     

Effect on cochlear potentials of lateral semicircular canal destruction.

Recording of the cochlear potentials was successfully performed during experimental labyrinthectomy in the guinea pig and in three patients with acoustic neuromas during translabyrinthine removal of the tumors. In the guinea pig, complete interruption of the duct of the lateral semicircular canal including the endolymphatic canal caused little change in the endocochlear DC potential of the first cochlear turn and input-output function curve of the N1 component of the compound action potential elicited by 8-kHz tone bursts. Further drilling of the vestibular labyrinth in the guinea pig caused decline of these potentials when the vestibular was opened. In patients with acoustic neuromas, the interruption of the duct of the lateral semicircular canal hardly altered the N1 input-output function curve and N1 input-latency function curve during the 1-hour observation period. Consistent preservation of cochlear function even after interruption of lateral semicircular canals suggests the possibility of partial surgical labryrinthectomy with preservation of hearing for lesions involving semicircular canals.     

Cupulolithiasis of the horizontal semicircular canal

To clarify whether positional nystagmus of horizontal cupulolithiasis contains vertical and torsional components, and to quantify the asymmetry, we analyzed nystagmus in four positions (healthy-ear-down, affected-ear-down, supine, nose-down), using 3-dimensional video-oculography. Subjects were 20 patients with direction-changing apogeotropic positional nystagmus, 11 females and 9 males, with a mean age of 58.1 years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed 3-dimensional video-oculography and measured maximum slow-phase velocity (MSV) of three components. Positional nystagmus was not purely horizontal. Eleven (55%) patients revealed a vertical component, and 14 (70%) patients had a torsional component in the healthy-ear-down position. The mean value of MSV of the horizontal component in the healthy-ear-down position was 18°/s and that in the affected-ear-down position was 7.8°/s. For the horizontal component, MSV in the healthy-ear-down position was significantly greater than that in the affected-ear-down position (p < 0.01). These results suggest that vertical and torsional components occur from the horizontal semicircular canal, and the response to ampullopetal bending is more than two times as strong as that to ampullofugal bending.     

Geometry of the semicircular canals of the chinchilla (Chinchilla laniger)

The orientations of the semicircular canals determines the response of the canals to head rotations and, in turn, the brain's ability to interpret those motions. The geometry of chinchillas' semicircular canals has never been reported. Volumetric representations of three chinchilla skulls were generated using a microCT scanner. The centroids of each semicircular canal lumen were identified as they passed through the image slices and were regressed to a plane. Unit vectors normal to the plane representing canal orientations were used to calculate angles between canal pairs. Pitch and roll maneuvers required to bring any canal into the horizontal plane for physiologic investigation were calculated. The semicircular canals of the chinchilla were found to be relatively planar. The horizontal canal was found to be oriented 55.0 degrees anteriorly upward. Pairs of ipsilateral chinchilla canals were not orthogonal and contralateral synergistic pairs were not parallel. Despite this arrangement, the canal plane unit normal vectors were organized to respond with approximately equal overall sensitivity to rotations in any direction. The non-orthogonal chinchilla labyrinth may provide an opportunity to determine whether the frame of reference used by the central vestibular and oculomotor system is based on directions of afferent maximum sensitivity or prime directions.