Superior canal dehiscence: mechanisms of pressure sensitivity in a chinchilla model.

BACKGROUND: Patients with superior canal dehiscence syndrome may experience vertigo and nystagmus when pressure changes occur in the external auditory canal, the middle ear, or the intracranial space. The cause is a defect in the bone of the superior canal. OBJECTIVE: To study the mechanisms of pressure sensitivity of the labyrinth in superior canal dehiscence syndrome and its surgical repair in a chinchilla model. METHODS: We investigated the changes in firing rates of vestibular nerve afferents in the chinchilla in response to changes in external auditory canal pressure before and after fenestration of the superior canal, and after repair of the fenestra. RESULTS: Before superior canal fenestration, external auditory canal pressure changes caused no responses in horizontal canal or otolith afferents, and only 1 of 9 superior canal afferents responded to pressure. After fenestration, all superior canal afferents were excited by positive pressure and inhibited by negative pressure. Half of 18 otolith and most (21 of 33) horizontal canal afferents were unaffected by pressure. The superior canal afferents had higher pressure gain than the horizontal canal afferents (P =.03). Pressure responses could be abolished only by applying a rigid seal to the fenestra. CONCLUSIONS: Fenestration of the superior canal rendered all superior canal afferents sensitive to pressure, whereas less than half of the other afferents became pressure sensitive. The direction of the superior canal afferent responses agreed with the predictions of our model of endolymph flow within the superior canal. A rigid seal applied to the fenestra abolished pressure sensitivity while maintaining physiologic rotational sensitivity.

Increased retinal image velocity after vestibular lesion.

The vestibulo-ocular reflex stabilizes gaze during head movements by producing compensatory eye movements. Retinal image velocity (RIV) is defined as the difference between the eye and head velocities. The RIV of 20 vestibular schwannoma (VS) patients and 17 healthy controls was measured with a head autorotation test. The head autorotation test had a sensitivity of 80% and a specificity of 88%. The mean RIV (degree/second) +/- 95% confidence intervals of the VS patients in the 5 frequency bands of 1 to 5 Hz was respectively 4.8 (4.2 to 5.5), 11.5 (8.6 to 14.4), 21.7 (15.5 to 27.9), 25.2 (17.1 to 33.4), and 26.1 (13.1 to 39.1). The RIV of the VS patients was asymmetrically larger on the operated side (P<0.05) in the frequency band of 1 Hz. The mean RIV was significantly (P<0.05) larger in the VS patients than in the controls in the frequency bands of 1 to 4 Hz. The vestibulo-ocular reflex is inaccurate after VS surgery; but the inaccuracy may not lead to the occurrence of any symptoms.

Vestibulo-ocular reflex function as measured with the head autorotation test.

The vestibulo-ocular reflex (VOR) of 125 healthy subjects was examined over the frequency range of 0.5-5 Hz with the head autorotation test (HART). During the HART the subjects fixated at a steady target while moving their heads horizontally from side to side with increasing frequencies according to auditory signals. The gain was determined as the ratio between the amplitude of the eye and head movements in five frequency bands between 0.5 and 5 Hz. The phase difference between the eye and head movements was determined in both degrees and milliseconds. The ability to reach high-frequency bands was evaluated. The mean gain was close to unity up 5 Hz, when it decreased to 0.91. The mean phase difference showed a lead of approximately 5 degrees at frequencies below 2 Hz, and at frequencies above 2 Hz there was no phase difference within the resolution of the test. The frequency band of 5 Hz was reached by 78% of the subjects, and that of 4 Hz was reached by 94% of the subjects. In summary, the HART is a new approach with which to study VOR function and determine accurately the VOR for healthy subjects. The normal upper frequency limit is 4 Hz in the HART.

Comparison of two head autorotation tests.

The head autorotation test is a novel method for studying the high-frequency vestibuloocular reflex without heavy machinery to generate whole-body rotation. Despite many studies with the test, the method is far from standardized, and no comparison has been made of different versions of the test. The objective of this study was to compare the vestibuloocular reflex of 100 healthy subjects measured simultaneously with two versions of the head autorotation test. Gain, phase, asymmetry, and the frequency bands reached were determined in the frequency bands of 1, 2, 3, 4, and 5 Hz. The gain measured with both tests was close to unity (range 0.95-1.04) from 1 to 4 Hz and about 0.9 at 5 Hz. In the test developed by Vorteq the phase lagged (-7 to -21 degrees) in all the frequency bands, and it differed significantly from the phase lead of 2 to 5 degrees that was measured by the other test. The asymmetry measured with the Vorteq test increased continuously from 1.5% (1 Hz) to 5.7% (5 Hz). The results of the tests showed intersubject variation, which was larger in the higher frequency bands. In conclusion, the high-frequency vestibuloocular reflex of healthy subjects can be quantified with active head oscillation. Both tests produced similar gain results, but the phase results differed systematically. Thus, the results of different head autorotation tests may not be directly comparable.

A head autorotation test for patients with Menière's disease.

OBJECTIVE: We compared the vestibulo-ocular reflex (VOR) of healthy volunteers and of two groups (group A, conservatively treated; and group B, with gentamicin or surgically treated) of Menière's disease (MD) patients to determine whether the head autorotation test (HART) can reveal abnormality of the VOR and whether the HART can be applied in evaluation of MD. METHODS: The gain, phase, asymmetry, and the highest frequency band reached was evaluated with the HART in the frequency range of 1-5 Hz. The caloric responses and posturography results were also determined. RESULTS: The mean gain was lower for the both groups of MD patients than for the controls. In the MD patients the phase difference was shorter and the asymmetry was greater than in the controls. Only 58% (group A) and 36% (group B) of the MD patients reached the frequency band of 4 Hz, and 33% (group A) and 19% (group B) reached 5 Hz. The respective percentages for the controls were 97 and 77%. Of the 25 MD patients (group B) 72% had abnormal HART results. Among the group A of MD patients the HART (50%) was more sensitive to VOR abnormality than the caloric test (10%) was. For aggressively treated MD patients a decrease in gain at 2 and 3 Hz in the HART correlated with abnormal caloric test results. Increased body sway in posturography correlated with the pathological results in the HART. CONCLUSION: The HART is a complementary method for evaluating the natural frequency range of the VOR, and evaluation of MD patients may benefit from combined results of the caloric test and HART.

Decreased vestibulo-ocular reflex gain of vestibular schwannoma patients.

OBJECTIVE: The vestibulo-ocular reflex (VOR) stabilizes gaze during head movements by producing compensatory eye movements. Gain of the VOR can be defined as the difference between the eye and corresponding head movement amplitudes. The objective of the study was to compare the gain of postoperative vestibular schwannoma (VS) patients with that of healthy controls. METHODS: The gain of 19 vestibular schwannoma (VS) patients and 100 healthy controls was measured with a head autorotation test (HART) in the five frequency bands of 1-5 Hz. It was computed as the ratio of the amplitude of the eye position signal to the amplitude of the head position signal. The mean gain was compared between the VS patients and healthy subjects in each frequency band by using an analysis of variance with statistical significance pre-defined as P < 0.05. RESULTS: The HART was abnormal in 58% of the VS patients, whose mean gains in the five frequency bands of 1-5 Hz were 0.85, 0.79, 0.72, 0.64 and 0.60, respectively. The mean gains of the VS patients were significantly (P < 0.05) smaller than those of the controls in all the frequency bands. CONCLUSIONS: The deficit of the VOR gain seems to prevail in more than a half of postoperative VS patients, although this inaccuracy of compensatory eye movements may not lead to the occurrence of any symptoms. However, in these patients a potential threat to gaze stability exists.

Preoperative postural control of patients with vestibular schwannoma assessed by visual feedback posturography.

BACKGROUND: The need for an objective method to describe the functional postural control of patients with vestibular schwannoma in agreement with their subjective sensation of balance. OBJECTIVES: The objective was to compare the postural control of 49 patients with unilateral vestibular schwannoma (VS) with that of healthy subjects by using visual feedback posturography (VFP). We aimed to find out if preoperative postural control of the patients correlates with their subjective sensation of balance. METHODS: In the VFP, while standing on the platform, patients were instructed to move their center of gravity (COG) marker to the targets as fast and accurately as possible. Hit delay (HD) to the targets, hold percentage (HP) within the targets, COG marker velocity (CMV) to the targets, and balance index (BI) were calculated. We rated intensity of balance disturbance using a 5-point qualitative scale. RESULTS: Twenty-two (45%) patients had at least one abnormal VFP parameter, and 49% of patients were simultaneously symptomatic. Mean hit delay (HD), hold percentage (HP), and balance index (BI) were significantly worsened in patients with VS (p < 0.05). Increased HD and BI correlated significantly with subjective sensation of imbalance (p = 0.02). CONCLUSIONS: The overall deficit in preoperative postural control of the VS patients was not severe, and this finding agreed well with their subjective sensations.

Is small-fenestra stapedotomy a safer outpatient procedure than total stapedectomy?

We compared two stapedoplasty techniques to evaluate whether one technique is safer than the other as an outpatient procedure and to demonstrate possible reasons for outpatient failures. We performed a retrospective study of patient records of 94 operated adult patients who were all initially scheduled for outpatient surgery for otosclerosis (47 total stapedectomies and 47 small-fenestra stapedotomies). Six patients (13%) with stapedectomy and 1 patient (2%) with stapedotomy had to stay overnight at the hospital due to postoperative vertigo and nausea. The number of outpatient failures was statistically significantly different between the stapedoplasty techniques (p = 0.05). Five patients (11%) with stapedectomy and 2 patients (4%) with stapedotomy had a drop in bone conduction threshold between 5 and 8 dB pre- to postoperatively (n.s.). The short-term hearing improvement did not differ statistically significantly between the techniques when compared to the preoperative values. Small-fenestra stapedotomy is the safer procedure to be performed as outpatient setting than total stapedectomy.

Endoscopic CO(2) laser surgery for large internal laryngocele.

The laryngocele is a benign air-filled dilatation of the saccule of the laryngeal ventricle. Its appearance may be related to increased intralaryngeal pressure due to chronic straining. The internal laryngocele is confined to the false vocal cord, and it does not pass through the thyrohyoid membrane. The most common symptoms for internal laryngocele are hoarseness and dysphagia. Large internal laryngoceles may also cause airway compromise, especially when complicated with infection. Endoscopic laser surgery is an acceptable mode of treatment even for large internal laryngoceles as in the present case.

Phase difference of vestibulo-ocular reflex in head autorotation test.

In the head autorotation test (HART) gain is commonly used to determine the vestibulo-ocular reflex (VOR). The purpose of this work was to evaluate the relevance of phase (the phase difference between the eye and corresponding head movement) in describing the VOR. The phase was determined in 5 frequency bands in both degrees and milliseconds (ms) in 4 groups: 30 healthy adults, 15 elderly subjects, 37 vestibular schwannoma (VS) patients, and 35 Meniere's disease (MD) patients. In healthy adults and in MD patients the phase was close to nil in the frequency bands of 3 and 4 Hz. In elderly subjects phase lead was between 5.0 and 15.5 ms in each frequency band. Patients with VS showed a phase lag of -4.2 to -7.6 ms. The mean phase of the elderly in the frequency band of 3 Hz differed statistically significantly from that of MD and VS patients, and in the frequency band of 4 Hz from that of healthy adults and VS patients. In summary, the elderly had phase lead and VS patients showed increased phase lag in the frequency bands higher than 2 Hz. The phase is useful parameter together with gain in evaluating VOR and it seems to change in aged subjects and in patients with permanent vestibular lesion.

Stability limits for visual feedback posturography in vestibular rehabilitation.

Vestibular rehabilitation therapy (VRT) is used to enhance compensation after peripheral vestibular lesion. In visual feedback posturography (VFP) a patient can practice postural control actively on a force platform and progress in the VRT can be objectively measured. The aim of the study was to determine normative values for stability limits (SL) in the VFP. Eleven healthy subjects were measured with force platform in visual feedback condition. Subjects were instructed to move their center of gravity (COG) marker to given targets, which were displayed on a computer screen in front of them. Target distance from the center of the platform was increased step by step to determine the SL in 8 directions. Hit delays (HD) to the targets and hold percentages (HP) within the targets were measured to quantify the difficulty of the individual targets as a function of subject's shoe size. With fixed feet position the SL in anterior direction increased 1.2 times the absolute increase in shoe length. An almost similar increase was found in anterolateral direction. The knowledge of the mechanical SL is important, because targets near SL should be avoided for safety reasons.

Intratympanic and systemic dexamethasone for Ménière's disease.

Intratympanic and systemic dexamethasone treatment of Ménière's disease (MD) was evaluated in a prospective study. Seventeen patients (6 men and 11 women) with MD (5 right-sided, 11 left-sided and 1 bilateral) were treated with three 0.2- to 0.4-ml injections of intratympanic dexamethasone hyaluronate (16 mg/ml) during a week and with an initial intramuscular dexamethasone injection of 15 mg. Most of patients were in stage 3, and the mean duration of MD was 5. 3 years. Pure-tone and speech audiometry and the symptom scale of the patients were followed up for 1 year after the treatment. Symptoms of aural fullness, hearing loss, tinnitus and vertigo did not improve significantly. However, sufficient control of vertigo was achieved in 76% of the patients. In conclusion, no definite treatment effect has yet been shown for intratympanic and systemic dexamethasone treatment. Therefore, the clinical use of dexamethasone in MD needs further investigation.

Delays in thrombolytic therapy for acute myocardial infarction in Finland. Results of a national thrombolytic therapy delay study. Finnish Hospitals' Thrombolysis Survey Group.

OBJECTIVE: To determine lengths and causes of pre- and in-hospital delays in thrombolytic treatment. DESIGN: A prospective national survey covering 48 of the 51 Finnish university, central and general hospitals to obtain basic data before the start of a public campaign to shorten patient-related delay in acute myocardial infarction. SUBJECTS: One thousand and twelve consecutive patients with acute myocardial infarction who received thrombolytic therapy over 3 months in 1995 and who represent 40% of all patients with confirmed acute myocardial infarction. RESULTS: The median interval between onset of infarction symptoms and initiation of thrombolytic therapy was 160 min (30-647). Only 13% of the patients received thrombolysis within 60 min and 38% within 120 min. The median time from the onset of symptoms to the call for help was 60 min (5-491), and no difference was found in patients with or without a history of previous myocardial infarction (60 and 64 min, respectively). Only 52% of the patients called to the dispatch centre. The median delay from calling for help to hospital arrival was 40 min (10-170). The median in-hospital door-to-needle thrombolysis delay was 40 min (12-196). In 13% of hospitals the median delay was more than 60 min. The emergency physician encountered difficulties in decision making in 33% of cases. CONCLUSIONS: Only 38% of the patient received thrombolysis within 2 h of onset of symptoms. Patient-related delay before they sought help accounted for the major portion of the total treatment delay. Thus the findings emphasize the importance of prompt action when people are confronted with an acute heart attack. Reorganizing the emergency medical service and emergency department routines is also a necessary target to shorten thrombolysis delays. The delay attributable to transporting patients could be shortened by initiating thrombolytic treatment in the pre-hospital setting. In Finnish hospitals, door-to-needle delay was acceptable in cases with clear indications for thrombolysis. However, emergency physicians often had diagnostic difficulties, which led to remarkably longer in-hospital delays.

Changes in vestibulo-ocular reflex of elderly people.

Dizziness is a common symptom in elderly people. Head autorotation test (HART) has earlier shown no significant vestibulo-ocular reflex (VOR) disturbances in healthy elderly subjects. We used our recently developed HART to determine VOR in 14 elderly volunteers without otoneurological diseases and sedative medications. Gain and phase were determined in 5 frequency bands from 0.5 to 5 Hz. The gain of the elderly was significantly increased to 1.11-1.27 in the frequency range of 3-5 Hz compared with the controls. The phase lead of 7-8 degrees in the frequency bands of 2 and 4 Hz differed significantly from normative values of the controls. The percentage of the elderly to reach high-frequency head movements was diminished to 50% in the frequency band of 3 Hz and to 36% in the frequency band of 4 Hz (controls 100% and 95%, respectively). The individual HART results were abnormal in 86% of the elderly. The high-frequency VOR of the elderly was inaccurate in magnitude and timing. More than half of aged subjects were not able to generate voluntary fast head movements. These findings may explain the high prevalence of dizziness and falls in elderly subjects.

Changes in the vestibulo-ocular reflex: a study of elderly day hospital patients.

The vestibulo-ocular reflex (VOR) of 50 elderly day hospital patients (mean age of 82 years) was studied with the head autorotation test. Amplitude gain, phase and the highest frequency band reached were determined in the five frequency bands of 1, 2, 3, 4, and 5 Hz. Of the 50 patients, 81% had abnormal results. The gain of the elderly was significantly increased to 1.06-1.24 in the frequency bands of 3, 4, and 5 Hz in comparison with that of a control group. The elderly showed constantly a phase lead of 8-19 degrees in the frequency range of 1-4 hz and in this range differed significantly from the control group. The percentage of the elderly who reached high frequencies of head movements was reduced to 55% in the frequency band of 3 Hz and to 30% in the frequency band of 4 Hz. These findings may lead to oscillopsia and explain the high prevalence of dizziness and falls among the elderly.

Three-dimensional respiratory-gated coronary MR angiography with reference to X-ray coronary angiography.

PURPOSE: To assess the clinical value of three-dimensional coronary MR angiography (CMRA) in the detection of significant coronary artery stenosis using conventional X-ray angiography as the standard reference. MATERIAL AND METHODS: Sixty-nine patients underwent X-ray coronary angiography and CMRA because of suspected or previously diagnosed coronary artery disease. MRI was performed with a 1.5-T whole body imaging system using ECG-triggered 3D gradient echo sequence with retrospective navigator echo respiratory gating and fat suppression. RESULTS: A total of 276 coronary artery segments were analyzed. The X-ray coronary angiography was normal in 22 patients. Significant proximal stenoses (exceeding 50%) or occlusions were present in 102 coronary artery segments. In all, 120 stenoses or occlusions were identified in CMRA. Sixteen percent of the coronary artery segments had to be excluded because of poor image quality. The overall sensitivity and specificity for MRA for identification of significant stenosis were 75% and 62%, respectively. CMRA correctly detected 89% of patients with at least one vessel disease, but 6 patients with coronary artery disease would have been missed. CONCLUSIONS: Because of the high data exclusion and false- negative case rate, CMRA with retrospective navigator echo triggering is at present not suitable as a clinical screening method in coronary artery disease.