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Biomedical subjects

A Böhmer

Publications and source records attributed to A Böhmer.

At least 19 recordsLinked to original sources
PubMed2001

Caloric and search-coil head-impulse testing in patients after vestibular neuritis.

The objective of this study was to compare results of quantitative head-impulse testing using search coils with eye-movement responses to caloric irrigation in patients with unilateral vestibular hypofunction after vestibular neuritis. The study population consisted of an acute group (<3 days; N = 10; 5 male, 5 female; 26-89 years old) and a chronic group (>2 months; N = 14; 8 male, 6 female; 26-78 years old) of patients with unilateral vestibular hypofunction after vestibular neuritis. The testing battery included: (1) simultaneous measurement of eye and head rotations with search coils in a magnetic coil frame during passive Halmagyi-Curthoys head-impulse testing and (2) electronystagmography during bilateral monaural 44 degrees C-warm and 30 degrees C-cold caloric irrigation. The main outcome measures were (1) the gain of the horizontal vestibulo-ocular reflex during search-coil head-impulse testing and (2) the amount of canal paresis during caloric irrigation. All acute and chronic patients had a unilateral gain reduction during search-coil head-impulse testing. A pathological canal paresis factor was present in 100% of the acute patients but in only 64% of the chronic patients. The clinically suspected unilateral vestibular hypofunction resulting from vestibular neuritis was validated in all acute patients by both search-coil head-impulse and caloric testing. Hence, either of these tests is sufficient for diagnosis in the acute phase of vestibular neuritis. Chronic patients, however, were reliably identified only by search-coil head-impulse testing, which suggests that the low-frequency function of the labyrinths often becomes symmetrical, leading to a normal canal paresis factor.

Acute Disease↗
PubMed2000

Auditory threshold and inner ear pressure: measurements in experimental endolymphatic hydrops.

HYPOTHESIS: Experimental endolymphatic hydrops leads to an endolymph-perilymph pressure imbalance that is responsible for the loss of auditory sensitivity in the ear. BACKGROUND: This study investigates whether intralabyrinthine pressure is a factor in the auditory dysfunction of experimental endolymphatic hydrops. METHODS: Auditory function was investigated in 10 guinea pigs 90 to 120 days after endolymphatic sac ablation by measuring compound action potentials in response to acoustic stimuli including alternating clicks and tone bursts of 0.5, 1, 2, 4, and 8 kHz. After auditory thresholds to the various stimuli were established, endolymphatic and perilymphatic pressures were measured with a no-flow micropressure measuring system. The cause of the hearing loss in Meniere's disease, especially in the early phases of this condition, remains an enigma. Histologic temporal bone preparations show a disproportion in the volume of endolymph to perilymph with an expanded and distorted membranous labyrinth. Speculation as to whether an endolymph-perilymph fluid pressure imbalance is responsible for these morphologic changes were raised by Hallpike and Cairns (1) in their initial report of the histopathology of Meniere's disease. Further speculation has questioned whether this pressure imbalance may be responsible for the symptoms and physical finding of this condition, including hearing loss. The ability to produce experimental endolymphatic hydrops in the guinea pig secondary to surgical occlusion of the endolymphatic sac and duct has been useful in studying various aspects of Meniere's disease (2). Investigators have been able to demonstrate auditory threshold shifts with hydrops. Elevated endolymph-perilymph pressure gradients have also been demonstrated (3). This RESULTS: Increased auditory thresholds were noted in the hydrops ears at all tested parameters (p < 0.03). A relative increase in endolymph over perilymph pressure was found in hydrops ears as previously reported. The increase in endolymph-perilymph pressure of hydrops could not be correlated directly to the elevated auditory threshold shift. CONCLUSION: Endolymphatic hydrops is a complex pathologic state with multiple inner ear alterations including abnormal intralabyrinthine pressure. Factors other than or in addition to pressure contribute to the auditory threshold shift of hydrops.

Animals↗
PubMed1999

Assessing otolith function by the subjective visual vertical.

The effects of peripheral vestibular diseases on the subjective visual vertical (SVV) are resumed and provide the basis for some insights into the otolith pathophysiology. With a normal range of 0 +/- 2 deg (when measured in an upright body position), the SVV was shifted by 11 +/- 6 deg toward the ipsilateral ear in 40 patients following an acute unilateral vestibular deafferentiation (UVD), but in the opposite direction in 9 of 52 patients after stapes surgery. These opposite effects suggest a push-pull mechanism of the pairs of otolith organs with respect to the SVV. The dissociation between the SVV and the perception of body position indicates influences by unconscious reflexive mechanisms such as ocular cyclotorsion on the SVV. In chronic UVD patients, lateral shifts of the subjects during constant angular velocity rotation into various eccentric positions (+/- 16 cm) revealed a shift of the "center of graviception" close to the remaining intact contralateral inner ear. To date, this seems to be the most consistent test for clinical identification of a chronic compensated unilateral loss of otolith function. The findings regarding asymmetries in otolithic sensitivity to medially and laterally directed roll-tilts remain controversial, probably mainly because of influences of extravestibular cues.

Afferent Pathways↗
PubMed1999

Vestibulo-ocular responses during static head roll and three-dimensional head impulses after vestibular neuritis.

This study aimed to investigate whether unilateral vestibular neuritis (VN) causes the same deficits of ocular counter-roll during static head roll (OCR(S)) and dynamic vestibulo-ocular reflex gains during head impulses (VOR(HI)) as unilateral vestibular deafferentation (VD). Ten patients with acute and 14 patients with chronic vestibular paralysis after VN were examined. The testing battery included fundus photography of both eyes with the head upright (binocular cyclorotation) and dual search coil recordings in a three-field magnetic frame. With one dual search coil on the right eye and the other on the forehead, the following stimuli were given: i) Halmagyi-Curthoys head impulses about the vertical, horizontal and torsional axes. ii) Static roll positions of the head up to 20 degrees right- and left-ear-down by movement of the neck. The comparison group consisted of 19 healthy subjects. Compared with the VD-patients, as reported in the literature, acute VN-patients showed the same pattern of OCR(S) gain reduction and binocular cyclorotation (CRb). The main feature that distinguished chronic VN-patients from chronic VD-patients was the normalization of the torsional VOR(HI) gain to the affected side, whereas the VOR(HI) gains in the horizontal and vertical directions did not show recovery (as in the patients with chronic VD). Chronic VN-patients differed from acute VN-patients by: i) symmetrical OCR(S) gains, ii) a less pronounced CRb toward the affected side, and iii) a normal torsional VOR(HI) gain toward the affected side. Since the ipsilesional torsional VOR(HI) gain did not recover in VD-patients, the normalization of this gain in our VN-patients can only be explained by a (partial) recovery of otolith function on the side of the lesion after the neuritis.

Acute Disease↗
PubMed1999

Persistent bilateral hearing loss after shunt placement for hydrocephalus. Case report.

Transient hearing decrease following loss of cerebrospinal fluid (CSF) has been reported in patients undergoing lumbar puncture, spinal anesthesia, myelography, and/or different neurosurgical interventions. The authors present the first well-documented case of a patient with persistent bilateral low-frequency sensorineural hearing loss after shunt placement for hydrocephalus and discuss the possible pathophysiological mechanisms including the role of the cochlear aqueduct. These findings challenge the opinion that hearing decreases after loss of CSF are always transient. The authors provide a suggestion for treatment.

Audiometry, Pure-Tone↗
PubMed1999

Chronic unilateral loss of otolith function revealed by the subjective visual vertical during off center yaw rotation.

Assessing the subjective visual vertical, SVV, in a static upright position is an easy clinical test in which a deviation of some 10 degrees from true vertical indicates an acute loss of unilateral (otolithic) vestibular function on the side to which the SVV is tilted. Because this deviation of the SVV is compensated during the following months, patients with chronic unilateral vestibular loss do no longer differ from normal subjects. This study presents an experimental set-up that allows for clear detection of compensated chronic loss of unilateral otolithic function by testing the SVV. 21 normals and 17 unilaterally vestibular deafferentiated (UVD) patients (vestibular neurectomies) were first rotated on a human centrifuge about an earth vertical yaw axis through the midsagittal plane of the head (240 degrees/s). This induced tilts of the gravito-inertial force (GIF) vectors, which differed at the two inner ears by 8 degrees. During constant velocity rotation, the subjects were moved in pseudo-randomized steps laterally up to 16 cm apart from the rotation axis, inducing roll tilts of the GIF vectors up to 16 degrees. Normal subjects set their SVV to pre-centrifugation values at positions with the midsagittal plane of their head close to the rotation axis, while chronic UVD patients indicated pre-centrifugation values during positions with the rotation axis 5.9 +/- 2.5 cm paramedian on the side of the intact ear. Tilts of the GIF vectors shifted the SVV with a gain of 0.70 in normals and only 0.32 in UVD patients. Roll gains for laterally directed GIF vectors relative to the intact inner ear did not differ from medially directed roll gains in the UVD patients. The roll gains observed in this experimental set-up were lower than those observed with static body tilts or during eccentric rotation with a larger radius, which might be at least partially due to conflicting stimulation between otolithic and extra-vestibular cues.

Adult↗
PubMed1998

Pathomechanism of mammalian downbeat nystagmus due to cerebellar lesion: a simple hypothesis.

Most of the various hypotheses on the pathomechanism of the slight ocular upward drift in normal mammals and on the prominent downbeat nystagmus following cerebellar lesions assume an inherent vertical asymmetry in the central vestibulo-ocular pathways. In this paper we propose that this vertical asymmetry is simply based on the anatomical orientation of the six semicircular canals in the head which is right-left symmetrical but lacks symmetry in the cranio-caudal direction. Presuming that each semicircular canal elicits eye movements in a direction roughly in its anatomical plane, vectorial addition of the tonic resting activity of all six canals leads to a cancellation of horizontal and torsional eye movement components but leaves an important vertical (slow phase) upward component. This peripheral vestibular bias is centrally cancelled by floccular and parafloccular inhibitory pathways which are related to the smooth pursuit system, but becomes disinhibited in the presence of posterior cerebellar lesions.

Animals↗
PubMed1997

[Evaluating otolith function with subjective visual vertical discrimination].

This report summarizes our experiences with the subjective visual vertical (SVV) as a clinical neuro-otological tool. In the SVV test, patients have to orient a dim light bar in an otherwise dark surrounding earth-vertical, using a remote-control. Normal subjects in an upright position did not deviate more than 2 degrees from true vertical. After vestibular neurectomy, the SVV was consistently tilted by some 12 degrees toward the affected ear. Smaller tilts (approximately 7 degrees) of the SVV occurred in patients with spontaneous peripheral vestibular diseases. This shift in SVV disappeared within weeks to months, similar to the spontaneous nystagmus. After stapes surgery slight deviations of the SVV towards the unoperated ear were seen in about 20% of the patients, indicating a slight irritation of the otolith organs. Assessed in an upright position, the SVV thus may be regarded as reflecting tonic otolithic input differences between the two ears. Asymmetries in the shifts of the SVV induced by roll tilts of the gravito-inertial vector by eccentric rotations of the subject have been proposed as a test for otolithic sensitivity. In our studies such asymmetries in the shifts of the SVV could not be induced by 26 degrees or 90 degrees roll tilts of subjects towards the affected or healthy ears. A simple clinical test to reveal unilateral otolithic sensitivity (comparable to an otolithic "caloric test") thus still has to be found.

Dark Adaptation↗
PubMed1997

Three-dimensional analysis of spontaneous nystagmus in peripheral vestibular lesions.

The direction of spontaneous nystagmus was recorded in three dimensions with scleral dual search coils in three patients after vestibular neurectomy and in seven patients with vestibular neuritis. The rotation vectors of the spontaneous nystagmus clustered along the sensitivity vector of the lateral semicircular canal (SCC). The direction of the spontaneous nystagmus after resection of the whole eighth nerve was not different from that after resection of only the superior branch of the vestibular nerve. Deviations from this direction were observed only after resection of the inferior vestibular nerve and in one patient with vestibular neuritis. The absence of nystagmus components in direction of the vertical SCC reflects an anisotropy of oculomotor efferents of the vestibulo-ocular reflex are rather than a lesion limited to the lateral SCC afferents. Therefore, the three-dimensional analysis of spontaneous nystagmus does not permit accurate localization of a peripheral vestibular lesion.

Adult↗
PubMed1996

[Sudden vertigo--differential diagnosis and therapy in peripheral vestibular (inner ear-induced) forms].

The most important forms of inner ear disorders manifesting as sudden vertigo may be distinguished by the duration of the vertiginous spells: sudden vertigo, diminishing during days = acute peripheral vestibulopathy, recurrent spells lasting for hours = Ménière's disease, recurrent vertigo lasting for minutes = "vascular', recurrent positioning-induced vertigo lasting for seconds = benign paroxysmal positioning vertigo (BPPV). In the last years, major progress was made in the treatment of BPPV. Based on new ideas on the underlying pathomechanism, this most common form of vestibular vertigo now can be treated definitively in most patients within a few minutes by a simple maneuver (canalith reposition maneuver by Epley/Parnes). This procedure is presented in this paper.

Acute Disease↗
PubMed1996

Candida maltosa NADPH-cytochrome P450 reductase: cloning of a full-length cDNA, heterologous expression in Saccharomyces cerevisiae and function of the N-terminal region for membrane anchoring and proliferation of the endoplasmic reticulum.

A full-length cDNA for NADPH-cytochrome P450 reductase from Candida maltosa was cloned and sequenced. The derived amino acid sequence showed a high similarity to the reductases from other eukaryotes. Expression in Saccharomyces cerevisiae under control of the GAL10 promoter resulted in an approximately 70-fold increase in NADPH-cytochrome c reductase activity in the microsomal fraction. The functional integrity of the heterologously expressed reductase as an electron transfer component for alkane hydroxylating cytochrome P450 from C. maltosa was shown in a reconstituted system containing both enzymes in a highly purified state. The signal-anchor sequence of the reductase was identified within the N-terminal region of the protein by means of constructing and expressing fusion proteins with the cytosolic form of yeast invertase. The first 33 amino acids turned out to be sufficient for stable membrane insertion, wild-type membrane orientation and retention in the endoplasmic reticulum. As shown by immunoelectron microscopy, the heterologously expressed reductase was integrated into the endoplasmic reticulum of the host organism. It triggered a strong proliferation of the membrane system. This membrane-inducing property of the reductase was transferable to the cytosolic reporter protein with the same N-terminal sequences that confer membrane insertion.

Amino Acid Sequence↗
PubMed1996

Can a unilateral loss of otolithic function be clinically detected by assessment of the subjective visual vertical?

Asymmetries in the settings of the subjective visual vertical after unilateral vestibular neurectomy during eccentric centrifugation [3] might provide a clinical test for unilateral otolithic function. This study investigates whether these asymmetries can also be revealed by a technically much easier practicable roll tilt of the subject relative to gravity instead of a roll tilt of the gravitational force on a human centrifuge. Twenty-seven normal subjects and 13 patients before surgery indicated verticality very accurately in the upright position. In 26 degrees roll positions (subjects seated on a slanted chair), they were only slightly more variable with no asymmetries larger than 5.3 and 7.8 degrees in normals and preoperative patients, respectively, between the roll positions toward the healthy and toward the affected ear. One week after surgical unilateral vestibular deafferentation, there was a consistent shift (mean 11.9 degrees) of the subjective vertical toward the affected ear in all patients and in all body positions. When the settings in the two roll tilt positions were referred to the setting in upright position, the group means of the patients were symmetrical although single subjects revealed asymmetries up to 22.4 degrees. Only one of four patients who were tested also during eccentric rotation revealed an important asymmetry with decreased sensitivity for tilts of the gravitational vector toward the affected ear. Measuring the subjective visual vertical assesses only asymmetrical tonic otolithic input, while a simple clinical test for unilateral otolithic sensitivity still has to be found.

Adolescent↗
PubMed1996

Contributions of single semicircular canals to caloric nystagmus as revealed by canal plugging in rhesus monkeys.

We demonstrated specific responses from the anterior and the posterior semicircular canal to irrigation of the outer ear canal with cold water in the Rhesus monkey. This required i) three-dimensional analysis of the evoked eye movements in the planes of the semicircular canals (canal plane vectors, CPV); ii) assessing these CPV responses in eight different head positions relative to gravity; iii) comparing the responses in 6 normal animals (12 ears) with responses after selective plugging of pairs of semicircular canals (all, both lateral, and right anterior + left posterior). The results showed: i) Irrigation of the outer ear canal with cold water induces thermoconvection also in the posterior and anterior semicircular canals. This can be inferred from the sinusoidal modulation of eye movement components with changes in position of the corresponding semicircular canal plane relative to gravity; ii) Specific vertical canal responses occur exclusively in the direction of the corresponding semicircular canal, though they are superimposed with response components of other origin, one probably related to endolymph shift in the lateral semicircular canal; iii) before possible clinical application, these different response components of vertical canals will need to be determined in humans.

Animals↗
PubMed1996

Correlation of MRI, clinical, and electroneuronographic findings in acute facial nerve palsy.

Intratemporal enhancement of (Gd-DTPA) was investigated by an interleaved-overlapping magnetic resonance imaging (MRI) technique in 35 cases of acute facial palsy. In a reference group (normal facial function), enhancement was localized from the ganglion geniculi to the stylomastoid foramen. In cases of acute palsy, the facial nerve enhanced in the meatal fundus independent of etiology (idiopathic, herpetic, or traumatic). In 70% of those with Ramsay-Hunt syndrome, the vestibular and cochlear nerves, the labyrinth, and the sheets of the internal and external auditory canal additionally enhanced. No correlation was found between intensity, extension, and duration of the enhancement and the clinical, intraoperative, or electroneuronographic degree of the facial palsy. The pathogenesis of the Gd-DTPA enhancement of the facial nerve appears to be closely connected with the vascular supply of the fallopian canal and the permeability of the neural sheets.

Adolescent↗
PubMed1995

Use of selective tyrosine kinase blockers to monitor growth factor receptor dephosphorylation in intact cells.

A novel assay was developed which allows measuring the activity of protein tyrosine phosphatases (PTPases) downregulating the signaling activity of the receptors for platelet-derived growth factor (PDGF) or epidermal growth factor (EGF) in intact Swiss 3T3 cells and nerve growth factor (TrkA) in TrkA-overexpressing PC12 cells. The assay is based on the inhibition of the receptor tyrosine kinases by specific inhibitors which enter the cells rapidly and do not affect the activity of PTPases. Thereafter, the decay of phosphotyrosine in the autophosphorylated receptors is monitored by immunoblotting with anti-phosphotyrosine antibodies. The dephosphorylation kinetics of EGF receptors and PDGF receptors in Swiss 3T3 cells as measured with this assay were found to be strikingly different. EGF receptors are almost completely dephosphorylated after 2 min at room temperature, whereas PDGF receptors are dephosphorylated only by 50% after 5 min. These data agree with previous findings about receptor dephosphorylation kinetics in isolated Swiss 3T3 cell membranes employing conventional dephosphorylation assays. The novel assay will facilitate characterization of the hitherto not identified receptor-directed PTPases for PDGF receptors, EGF receptors, and TrkA. The assay principle is general and should be applicable to any PTPases and their substrates, provided specific inhibitors for the respective kinases are available. Furthermore, it can be applied to screen for regulator molecules of specific PTPases in their physiological environment.

3T3 Cells↗
PubMed1995

Clinical pathophysiology of vestibular neurectomy.

This study attempts to characterize the residual vestibular function remaining after incomplete supralabyrinthine vestibular neurectomy performed for disabling vertigo. Patients with bilateral vestibular neurectomy had preserved horizontal vestibulo-ocular reflexes in response to high angular accelerations with gain enhancement over time. A torsional down-beating spontaneous nystagmus and an important tilt of the subjective vertical were observed when the remaining eighth nerve was sectioned after homolateral incomplete supralabyrinthine vestibular neurectomy. These findings suggest that a reorganization of vestibular reflexes may occur after incomplete supralabyrinthine vestibular neurectomy if afferents of the inferior vestibular branch are partially spared. The vestibular function after incomplete supralabyrinthine vestibular neurectomy does not affect the postoperative control of vertiginous attacks and may have positive effects in case of deterioration of the contralateral inner ear.

Adult↗
PubMed1995

Are papillary adenomas endolymphatic sac tumors?

Papillary adenomas of the temporal bone have been considered as originating from the endolymphatic sac. The radiologic, surgical, and pathologic findings in a patient suffering from von Hippel-Lindau disease with bilateral papillary adenomas of the temporal bone cast some doubt on this site of origin. Radiologically, the center of tumor growth was at the top of the jugular bulb. Intraoperatively, the tumor was found to have reached the lateral wall of the endolymphatic sac, but the lumen was tumor-free. Both ciliated and nonciliated tumor cells were found in the resected tumor, resembling the ultrastructure of normal epithelial lining in the human mastoid. A strong positive immunohistochemical reaction for keratin and negative reactions for vimentin, glial fibrillary acidic protein, and S-100 protein in the tumor tissue of this patient are typical for middle ear mucosa. Therefore, the described papillary adenoma originated from the mucosa of the pneumatic spaces surrounding the jugular bulb, and the theory that the endolymphatic sac is the origin of all papillary-cystic tumors (adenocarcinomas) should be questioned.

Adenoma↗