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Biomedical subjects

L B Minor

Publications and source records attributed to L B Minor.

At least 37 records · Page 2Linked to original sources
PubMed1999

Relationship of the utriculus and sacculus to the stapes footplate: anatomic implications for sound-and/or pressure-induced otolith activation.

One hundred thirty human temporal bones that were sectioned in the vertical plane were examined to evaluate the relationship between the stapes footplate and the otolith organs. The shortest distance between the footplate and the utriculus was 0.58+/-0.10 mm in the posterior third of the oval window, 1.04+/-0.20 mm in the middle third, and 1.51+/-0.20 mm in the anterior third. The distance from the sacculus to the footplate was 1.33+/-0.20 mm in the middle third of the oval window and 1.31+/-0.18 mm in the anterior third. Membranous connections extending between the utriculus and the footplate were found in 26% of temporal bones. These membranous connections in coexistence with additional anatomic factors such as stapes hypermobility and/or dehiscence of bone within labyrinthine structures may predispose patients to sound- and/or pressure-induced otolith activation. The findings may have implications for different causes of the Tullio phenomenon.

Acoustic Stimulation↗
PubMed1999

Intratympanic gentamicin for control of vertigo in Meniere's disease: vestibular signs that specify completion of therapy.

OBJECTIVE: To determine if a protocol of weekly intratympanic gentamicin injections administered until development of signs of unilateral vestibular hypofunction can alleviate vertigo while preserving hearing in patients with intractable vertigo caused by unilateral Meniere's disease. STUDY DESIGN: The study design was a prospective investigational protocol. SETTING: The study was performed in outpatients at a tertiary referral center. PATIENTS: Entry criteria included a diagnosis of "definite" Meniere's disease according to the 1995 report of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), intractable vertigo despite optimal medical therapy, no symptoms suggestive of Meniere's disease in the contralateral ear and serviceable hearing in the contralateral ear. The outcomes of the first 34 patients who entered the protocol are reported. INTERVENTION: A buffered gentamicin solution was injected into the middle ear at weekly intervals until development of spontaneous nystagmus, head-shaking-induced nystagmus, or head-thrust sign indicative of vestibular hypofunction in the treated ear. MAIN OUTCOME MEASURE: The 1995 AAO-HNS criteria for reporting treatment outcome in Meniere's disease were used. The effects of treatment were assessed in terms of control of vertigo, disability status, hearing level, and quantitative measurement of vestibular function with caloric and rotatory chair tests. RESULTS: Vertigo was controlled in 91% of the patients. Profound hearing loss occurred as a result of gentamicin injection in one patient (3%). Intratympanic gentamicin was significantly less effective in controlling vertigo in patients who had previous otologic surgery on the affected ear. Recurrence of vertigo > or = 6 months after initially complete control was noted in seven patients (22%). Vertigo in six of these patients was eliminated by additional intratympanic gentamicin injections. CONCLUSIONS: Ending weekly intratympanic gentamicin injections when clinical signs of unilateral vestibular hypofunction appear can control vertigo in most patients. Hearing loss directly attributable to gentamicin is uncommon. Treatment outcome is best in patients who have not had previous otologic surgery.

Adult↗
PubMed1998

Sound- and/or pressure-induced vertigo due to bone dehiscence of the superior semicircular canal.

OBJECTIVES: To present symptoms, patterns of nystagmus, and computed tomographic scan identification of patients with sound- and/or pressure-induced vertigo due to dehiscence of bone overlying the superior semicircular canal. To describe anatomical findings and outcome in 2 patients undergoing plugging of the superior semicircular canal for treatment of these symptoms. DESIGN AND SETTING: Prospective study of a case series in a tertiary care referral center. PATIENTS AND RESULTS: Eight patients with vertigo, oscillopsia, and/or disequilibrium related to sound, changes in middle ear pressure, and/or changes in intracranial pressure were identified in a 2-year period. Seven of these patients also had vertical-torsional eye movements induced by these sound and/or pressure stimuli. The direction of the evoked eye movements could be explained by excitation or inhibition of the superior semicircular canal in the affected ear. Computed tomographic scans of the temporal bones identified dehiscence of bone overlying the affected superior semicircular canal in each case. Disabling disequilibrium in 2 patients prompted plugging of the dehiscent superior canal through a middle cranial fossa approach. Symptoms were improved in each case. One patient developed recurrent symptoms requiring an additional plugging procedure and developed sensorineural hearing loss several days after this second procedure. CONCLUSIONS: We have identified patients with a syndrome of vestibular symptoms induced by sound in an ear or by changes in middle ear or intracranial pressure. These patients can also experience chronic disequilibrium. Eye movements in the plane parallel to that of the superior semicircular canal were evoked by stimuli that have the potential to cause ampullofugal or ampullopetal deflection of this canal's cupula in the presence of a dehiscence of bone overlying the canal. The existence of such deshiscences was confirmed with computed tomographic scans of the temporal bones. Surgical plugging of the affected canal may be beneficial in patients with disabling symptoms.

Adult↗
PubMed1998

Physiological principles of vestibular function on earth and in space.

Physiological mechanisms underlying vestibular function have important implications for our ability to understand, predict, and modify balance processes during and after spaceflight. The microgravity environment of space provides many unique opportunities for studying the effects of changes in gravitoinertial force on structure and function of the vestibular system. Investigations of basic vestibular physiology and of changes in reflexes occurring as a consequence of exposure to microgravity have important implications for diagnosis and treatment of vestibular disorders in human beings. This report reviews physiological principles underlying control of vestibular processes on earth and in space. Information is presented from a functional perspective with emphasis on signals arising from labyrinthine receptors. Changes induced by microgravity in linear acceleration detected by the vestibulo-ocular reflexes. Alterations of the functional requirements for postural control in space are described. Areas of direct correlation between studies of vestibular reflexes in microgravity and vestibular disorders in human beings are discussed.

Acceleration↗
PubMed1996

Endolymphatic system shunting: a long-term profile of the Denver Inner Ear Shunt.

Endolymphatic system surgery for Meniere's disease, particularly endolymphatic shunting, remains controversial. In 1988, we presented our findings on the efficacy of the Denver Inner Ear Shunt in 100 patients. These data were accumulated in the short term. The purpose of this article is to review the long-term results of our endolymphatic shunt procedure, highlighting the population of Denver Inner Ear Shunt recipients. Results were analyzed according to both 1972 and 1985 AAO-HNS criteria. We seek corroboration or refutation of our preliminary conclusion that (a) endolymphatic shunt surgery has little efficacy and that (b) the Denver valve does not appear to offer any advantage in this regard.

Adolescent↗
PubMed1996

Trauma to the external auditory canal and temporal bone.

Sources of trauma to the external auditory canal range from impaction of small foreign bodies to severely comminuted temporal bone fractures sustained after blunt or penetrating forces. This article provides an overview of commonly encountered injuries. The proposed systematic approach to evaluation and management is meant to serve as a guide to individualizing patient care.

Ear, External↗
PubMed1995

Neuro-otology: hearing.

Selected topics relating to the diagnosis and management of disorders that affect hearing are reviewed, including updates on the outcome of attempted hearing preservation in the resection of acoustic neuromas. Newly defined indications and contraindications for surgical correction of stapes fixation are discussed. Reports of unilateral chemical ablation of vestibular function as treatment for intractable vertigo resulting from Meniére's disease, and the effects of this procedure on hearing are presented. Promising new insights into the etiology and treatment of autoimmune hearing loss are described. Emerging developments in measuring otoacoustic emissions and their potential clinical applications are discussed.

Hearing↗
PubMed1995

Physiological identification of morphologically distinct afferent classes innervating the cristae ampullares of the squirrel monkey.

1. Semicircular-canal afferents in the squirrel monkey were characterized by their resting discharge, discharge regularity, sensitivity to galvanic currents delivered to the ear (beta *), the gain (g2Hz), and phase lead (phi 2Hz) of their response to 2-Hz sinusoidal head rotations, and their antidromic conduction velocity. Discharge regularity was measured by a normalized coefficient of variation (CV*); the higher the CV*, the more irregular the discharge. g2Hz and phi 2Hz were expressed relative to angular head velocity. 2. These physiological measures were used in an attempt to discern the discharge properties of the three morphological classes of afferents innervating the crista. Presumed bouton (B) fibers were identified as slowly conducting afferents. Presumed calyx (C) fibers were recognized by their irregular discharge and low rotational gains. The remaining fibers were considered to be dimorphic (D) units. Single letters (B, C, and D) are used to emphasize that the classification is based on circumstantial evidence and may be wrong for individual fibers. Of the 125 identified fibers, 13 (10%) were B units, 36 (29%) were C units, and 76 (61%) were D units. 3. B units were regularly discharging D units ranged from regularly to irregularly discharging. C units were the most irregularly discharging afferents encountered. The mean resting discharge for the entire sample was 74 spikes/s. Resting rates were similar for regularly discharging B and D units and higher than those for irregularly discharging C and D units. 4. Except for their lower conduction velocities, the discharge properties of B units are indistinguishable from those of regularly discharging D units. Many of the discharge properties of B and D units vary with discharge regularity. There is a strong, positive relation when beta *, g2Hz, or phi 2Hz is plotted against CV*. For beta * or phi 2Hz, C units conform to the relation for B and D units. In contrast, values of g2Hz for C units are three to four times lower than predicted from the relation for the other two classes. 5. Internal (axon) diameters (dp) of peripheral vestibular-nerve fibers were estimated from central antidromic conduction velocities. Thick fibers (dp > or = 49 microns) were irregularly discharging, mostly C units. Medium-sized fibers (dp = 1.5-4 microns) included regular, intermediate, and irregular D units, as well as C units. Thin fibers (dp < or = 1.5 microns) were defined as B units.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1994

The natural history of untreated acoustic neuromas.

The emergence of magnetic resonance imaging with gadolinium has dramatically enhanced our ability to accurately detect the presence of acoustic tumors as small as 2 mm in diameter. Early diagnosis and improved surgical techniques continue to reduce the morbidity associated with surgical removal of these lesions. There exists, however, a select group of patients in whom no treatment may be the most appropriate management. Since 1979, a total of 51 patients with radiographic evidence of an acoustic neuroma have been prospectively followed for tumor growth and progression of symptoms. Patients were chosen for this conservative approach on the basis of age, medical condition, tumor size, audiometric data, and patient preference. This study reveals that a significant number of patients with acoustic tumors can be safely followed with regular imaging studies and may never require treatment. Discussed are tumor growth rates, epidemiology, and the impact of these factors on patient management.

Adult↗
PubMed1994

Facial nerve neuromas presenting as acoustic tumors.

Facial nerve tumors can present as masses in the internal auditory canal or cerebellopontine angle and may mimic an acoustic neuroma. These tumors can occur in any segment of the nerve from the brain stem to the neuromuscular junction. Prior to the advent of computed tomography and magnetic resonance imaging with gadolinium, facial nerve tumors were often difficult to diagnose. Even with these modalities it may be difficult to distinguish preoperatively between an acoustic neuroma and a facial schwannoma. Particular signs and symptoms associated with facial nerve tumors (in the spasms, and a facial tic. These symptoms, combined with modem radiologic studies, should allow for more accurate diagnosis, patient counseling, and treatment. This report presents a series of 32 facial nerve tumors diagnosed and treated at The Otology Group from 1975 to 1992. Of these lesions, 12 (38%) were thought to be acoustic neuromas. Eighteen tumors were correctly identified preoperatively as facial nerve tumors. Two facial nerve tumors were found incidentally.

Adult↗
PubMed1993

Preservation of hearing in surgery for acoustic neuromas.

Preservation of hearing was attempted in 161 cases of histologically confirmed acoustic neuroma removed by the senior author between January 1, 1970, and September 30, 1991. There were 136 patients with unilateral tumors; 22 patients had bilateral tumors (neurofibromatosis 2) and underwent a total of 25 procedures. Hearing was initially preserved in 35% of patients with unilateral tumors and in 44% of those with bilateral tumors. Results are reported in terms of pre- and postoperative pure tone average and speech discrimination scores. Surgical access to the tumor was obtained via middle cranial fossa and suboccipital approaches. The latter has been used more often over the past 5 years because of a lower associated incidence of transient facial paresis. Persistent postoperative headaches have been the most common complication following the suboccipital approach. The results of preoperative brain-stem auditory evoked response (BAER) studies were useful in predicting the outcome of hearing preservation attempts. Patients with intact BAER waveform morphology and normal or delayed latencies had a higher probability of hearing preservation in comparison to those with abnormal preoperative BAER morphology.

Adolescent↗
PubMed1993

Malignant neoplasms of the scalp. Etiology, resection, and reconstruction.

Malignant scalp neoplasms initially spread by radial extension with deep invasion occurring relatively late in the course of disease. Basal cell carcinomas have the highest incidence followed by squamous cell carcinomas and melanomas. Surgical excision provides the best chance of cure in the majority of cases. Tumor histology influences decisions about margins of resection and regional lymph node dissection. Primary closure usually can be obtained for scalp defects measuring up to 3 cm in diameter. Larger defects can be reconstructed with skin grafts, local flaps, musculocutaneous flaps, free flaps, or transposition flaps following tissue expansion.

Humans↗
PubMed1991

Vestibular-nerve inputs to the vestibulo-ocular reflex: a functional-ablation study in the squirrel monkey.

Advantage was taken of differences in the electrical excitability of vestibular-nerve fibers to characterize the afferent input to the canal-related vestibulo-ocular reflex. Large anodal (inhibitory) currents, when delivered to both ears, result in a selective, reversible ablation of irregular afferents. Their background discharge and responses to head rotations are temporarily abolished. The same currents have less effect on the background discharge and no effect on the rotational sensitivity of regular afferents. Eye movements were evoked by head rotations in alert monkeys. The ablating currents did not alter the ocular responses to sinusoidal head rotations in yaw or pitch planes. Responses to rapid changes in head velocity were similarly unaffected. It is concluded that irregular afferents do not make a net contribution to the reflex. Slow-phase eye movements evoked by unilateral galvanic currents are consistent with this conclusion. The results are incorporated into a systems model of the reflex. There are three conclusions from the model: (1) the signal to motoneurons consists of the sum of three components related, respectively, to head velocity, eye position, and filtered eye velocity; (2) regular afferents provide the best match to the dynamic requirements of the reflex; and (3) the central pathways responsible for all three signal components receive regular inputs.

Afferent Pathways↗
PubMed1990

Influence of static head position on the horizontal nystagmus evoked by caloric, rotational and optokinetic stimulation in the squirrel monkey.

We studied the influence of static head position on the horizontal nystagmus produced by caloric, rotational and optokinetic stimulation in alert squirrel monkeys. Caloric nystagmus is stronger for nose up (NU) than for nose down (ND) pitches; so, for example, slow-phase eye velocity is four times larger in supine than in prone positions. A similarly directed asymmetry occurs in the horizontal vestibulo-ocular (HVOR) responses to long-duration, constant angular-head accelerations, but not to midband (0.1 Hz) sinusoidal head rotations. Consistent with a first-order model of the HVOR, the low-frequency or acceleration gain of the reflex (GA) is equal to the product of the midband velocity gain (GV) and a time constant (TVOR). GV is proportional to the cosine of the angle between the horizontal-canal plane and the plane of rotation, from which it is concluded that signals from the horizontal, but not from the vertical canals contribute to the HVOR. TVOR can be as much as twice as large in NU than in ND positions. GA is proportional to TVOR and it, too, shows a NU-ND asymmetry. The time constant of optokinetic after nystagmus (TOKAN) was also studied. Since TVOR and TOKAN are modified in similar ways by static tilts, it is concluded that head position affects the time constants by way of velocity-storage mechanisms. Evidence is presented that the position-dependent modification of velocity storage is otolith-mediated. The results are used to analyze the mechanisms of caloric nystagmus. The caloric response consists of a convective component (CC), as originally envisioned by Bárány (1906), and a nonconvective component (NC). CC accounts for 75% of the caloric response in the conventional supine testing position. Both components can be affected by the position-dependent modification of TVOR or, equivalently, of GA. It has been suggested that two mechanisms might contribute to NC: 1) a direct thermal effect on hair cells or afferents; or 2) a thermal expansion of labyrinthine fluids that results in a cupular displacement. Both theoretical and experimental evidence indicates that only the first of these mechanisms could result in the steady-state caloric response that is observed in the absence of convection (e.g., in spaceflight and after canal plugging) and that contributes to the prone-supine asymmetry seen in caloric testing.

Animals↗
PubMed1990

Dual projections of secondary vestibular axons in the medial longitudinal fasciculus to extraocular motor nuclei and the spinal cord of the squirrel monkey.

Recordings were made from secondary vestibular axons in the medial longitudinal fasciculus (MLF) of barbiturate-anesthetized squirrel monkeys. Antidromic stimulation techniques were used to identify the axons as belonging to one of three classes of neurons: vestibulo-oculo-collic (VOC) neurons project both to the extraocular motor nuclei and to the spinal cord; vestibulo-ocular (VO) neurons do not have a spinal projection; and vestibulocollic (VC) neurons do not have an oculo-motor projection. Galvanic stimulation was used to show that axons of all three classes received excitatory inputs from one labyrinth and inhibitory inputs from the other. VOC axons were confined to the MLF contralateral to the labyrinth from which they were excited. They made up more than half of the vestibular axons descending in the contralateral medial vestibulospinal tract (MVST), but less than one-quarter of those ascending in the contralateral MLF to the level of the oculomotor nucleus. Spinal projections were restricted to cervical segments with about half of the axons reaching segment C6. Conduction velocities, measured for C6-projecting axons, were similar for VOC and VC axons and were typically 25-50 m/s. Unlike the situation in the rabbit (Akaike et al. 1973) and cat (Akaike 1983), none of the MVST axons had conduction velocities greater than 75 m/s. The morphology of VOC neurons was studied by injection of horseradish peroxidase (HRP) into 60 physiologically identified axons in the MLF. Since individual axons were only stained for short distances, it was not possible to ascertain their complete branching patterns. Labeled fibers could be traced to an origin in and around the ventral lateral vestibular nucleus. This localization was confirmed by comparing the distributions within the vestibular nuclei of neurons retrogradely labeled from the upper cervical spinal cord (this study) and from the oculomotor nucleus (McCrea et al. 1987a; Highstein and McCrea 1988). VOC axons reached the contralateral MLF at the level of the abducens nucleus and immediately divided into an ascending and a descending, usually thicker, branch. Seven VOC axons could be traced to the extraocular motor nuclei; three terminated in the medial aspect of the oculomotor nucleus bilaterally and four terminated in the medial aspect of the contralateral abducens nucleus. The former axons may be part of a crossed, excitatory anterior-canal pathway; the latter, part of a similar horizontal-canal pathway. There were no terminations in the trochlear nucleus even though 12 labeled fibers passed close to it.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Staphylococcus epidermidis sepsis in surgical patients.

We examined 58 surgical patients with two or more blood cultures positive for Staphylococcus epidermidis to determine factors associated with risk, mortality, and invasive sepsis. Bacterial sepsis was associated with gastrointestinal (GI) operations, total parenteral nutrition, and a regimen of two or more parenteral antibiotics. Mortality was 46% overall and significantly increased with age greater than 50 years, GI operations, other gram-positive sepsis, recurrent sepsis (positive blood culture 24 hours or more after the first blood culture), and the presence of organisms sensitive to three or less antibiotics. Antibiotic therapy appropriate for more than 50% of the S epidermidis organisms cultured from each patient resulted in significant reduction in mortality. Staphylococcus epidermidis should be considered a significant pathogen in critically ill surgical patients. Invasive S epidermidis sepsis can be recognized and requires specific antibiotic therapy.

Adolescent↗