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Biomedical subjects

R V Harrison

Publications and source records attributed to R V Harrison.

At least 73 records · Page 4Linked to original sources
PubMed1991

Correlation of cochlear pathology with auditory brainstem and cortical responses in cats with high frequency hearing loss.

Newborn kittens were treated with the aminoglycoside amikacin to produce a bilateral high frequency cochlear hearing loss. The degree and stability of hearing loss were confirmed by recording auditory brainstem evoked potentials (ABR audiograms). After maturation, cochleotopic frequency representation within primary auditory cortex (AI) was mapped using standard microelectrode recording techniques. The cochlear sensory epithelium was assessed with SEM and the pattern of damage compared with the ABR audiograms and cortical frequency maps. Amikacin treatment resulted in various patterns of haircell damage towards the base of the cochlea. A relatively abrupt transition between damaged and undamaged haircell regions resulted in an ABR audiogram with normal threshold to low frequencies and a high frequency elevation with a steep cut-off slope. In the cortical map, low frequency representation was normal, but anterior areas contained only neurons tuned to a common frequency which corresponded to the frequency-place position of the boundary of the haircell lesion and to the cut-off frequency of the audiogram. A large transitional zone of the cochlear lesion correlated with a gradual cut-off slope to the audiogram and again a remapping of the anterior and normally high frequency area to a common lower frequency. Haircell loss or damage (i.e. disarray of stereocilia) in lower frequency regions of the cochlea correlated with a significant reorganization of the lower frequency bands in the cortical map. We conclude from this study that the pattern of cochleotopic organization of the cortex is dependent on the pattern of activity in the ascending sensory pathway during early stages of development.

Amikacin↗
PubMed1991

Autoimmune inner ear disease: a review of basic mechanisms and clinical correlates.

Otolaryngologists have long sought to identify causes of sensorineural hearing loss that might be reversed by medical treatment. One such entity has become known as autoimmune inner ear disease. The potential improvement in auditory function in these patients subsequent to immunosuppressive therapy has created a desire in clinicians to better understand this disease. This paper begins by reviewing the basic concepts of autoimmunity. The experimental and clinical data concerning autoimmune inner ear disease are then described and analyzed. Finally, conclusions are drawn concerning our current state of understanding of this disease process.

Animals↗
PubMed1990

The association between community physician's attendance at a medical center's CME courses and their patient referrals to the medical center.

This study attempts to quantify an overall association between CME course attendance and referrals. Attendance at formal CME courses given by the University of Michigan Medical School and referrals to the University Hospitals were examined over a two-year period. Attendance and referrals were linked to physicians in Michigan identified through the Michigan Department of Licensing and Regulation and through the American Medical Association. For physicians who are office-based and likely to be in active practice (age less than 70), those who attended at least one of the University's CME courses referred more patients than those who did not attend one (means of 1.9 referrals per physician and 1.3 referrals per physician, p less than .001). The causal direction of the relationship is not clear, but probably operates in both directions. It is reasonable for medical center marketers to consider CME as an indirect method for marketing clinical services. It is also reasonable for CME directors to identify referring physicians as high-priority groups for marketing CME. Both marketing efforts may be significantly enhanced by linking data bases for referrals and for CME attendance. CME directors must also ensure that marketing efforts do not compromise the objectivity and integrity of the content of the institution's CME program.

Data Collection↗
PubMed1990

Influence of acoustic deprivation on recovery of hair cells after acoustic trauma.

The purpose of this study was to investigate how the recovery of the cochlea, after acoustic trauma, might be influenced by acoustic stimulation or deprivation. In anaesthetized adult chinchillas, both ears were simultaneously exposed to a traumatizing acoustic stimulus (2 kHz tone, at 117 dB SPL for 15 min). Probe microphones positioned in both bullae were used to ensure identical exposure to the two ears; this was important because the experiment relies on within-animal controls. Cochlear action potential thresholds across frequency (CAP audiograms) were used to verify the similarity of threshold shifts to the two ears. Immediately following, a unilateral ossiculectomy was performed which resulted in one cochlea being acoustically deprived during the recovery period, whilst the other was not. In groups of animals with recovery periods of 1, 3, 6, and 12 weeks, both the acoustically deprived and the normally stimulated cochleas were examined with scanning electron microscopy. To quantify hair cell damage, we used a damage scale based on stereociliar integrity; for each cochlea, a standard region 5.5-8.5 mm from the apex was studied in detail. We found that after acoustic trauma, hair cell damage to the cochlea which is deprived of sound during the recovery period, is significantly greater compared with that in the normally stimulated, contra-lateral cochlea. Our results suggest that mechanical activation of the inner ear acts to inhibit long-term degenerative processes, or influence repair of partially damaged hair cells.

Action Potentials↗
PubMed1989

Cochlear nerve action potentials during cerebellopontine angle surgery: relationship of latency, amplitude, and threshold measurements to hearing.

The cochlear nerve action potential (AP) was monitored during two types of hearing preservation surgery: (1) removal of small cerebellopontine angle tumors and (2) retrolabyrinthine vestibular nerve section. The purpose of this investigation was to study the relationship between changes in intraoperative AP latency, amplitude, and threshold, and changes in audiometric hearing subsequent to surgery. The presence or absence of a cochlear nerve AP toward the end of surgery accurately predicted the presence or absence of postoperative hearing (93%). Regression analyses were performed to explore the relationship between audiometric pre- and postoperative thresholds and intraoperative AP threshold changes. Statistically significant relationships were found for (1) pre-operative audiometric thresholds and initial AP click thresholds (p = 0.0068); (2) final AP click thresholds and postoperative audiometric thresholds (p = 0.0003); (3) AP click (p = 0.0001) and 1 kHz (p = 0.0006) threshold shifts and pre- to postoperative audiometric threshold shifts. No relationship was found between either AP latency or amplitude values and postoperative hearing. Intraoperative threshold measurements can be used as an indicator of hearing change. If amplitude or latency indices are also monitored it may be better to use stimulus levels close to the evoked potential threshold.

Action Potentials↗
PubMed1988

An immunohistochemical and electron microscopic study of extra-renal basement membranes in dogs with Samoyed hereditary glomerulopathy.

Samoyed hereditary glomerulopathy (SHG) in dogs has been employed as a model for human hereditary nephritis (HN), since affected dogs and patients show splitting of glomerular capillary basement membranes by electron microscopy (EM) and absent staining of glomerular capillaries for Goodpasture antigen (GPA) by immunofluorescence (IF). EM and IF were used to examine basement membranes (BM) in skin, lung, choroid plexus, lens, retina, and inner ear in SHG. By EM, BM in these tissues appeared similar in affected male, carrier female, and unaffected dogs. By IF, GPA could be detected only in lens capsule, internal limiting membrane of retina and basilar membrane of inner ear of unaffected and carrier female dogs, but not in affected male dogs. However, eye abnormalities and hearing loss were not present in any dogs, in contrast to their frequent occurrence in human HN. Our findings on extra-renal BM in SHG suggest that GPA is not required to maintain normal vision or hearing in affected male dogs and permit a greater understanding of the pathogenesis of human HN.

Animals↗
PubMed1988

Cochlear nerve monitoring during cerebellopontine angle operations.

The authors present their experience with intraoperative monitoring of cochlear nerve action potentials (AP) in 30 adult patients. Operative procedures were acoustic neuroma excision with attempted hearing preservation and selective vestibular neurectomy in patients with incapacitating Meniere's disease and serviceable hearing (SRT less than 50 db, discrimination greater than 60%). Loss of AP is detected rapidly and has been demonstrated after manipulation of the cochlear nerve and after coagulation of small arteries on the tumour capsule. Presence of an AP at the end of the procedure usually correlates with postoperative preservation of hearing. AP monitoring appears to be a reliable means of detecting potentially reversible changes in cochlear nerve function intraoperatively.

Action Potentials↗
PubMed1987

Psychosocial adjustment to and control of diabetes mellitus: differences by disease type and treatment.

The relationship of diabetic patients' psychosocial adjustment to disease type, treatment mode, and indexes of control was examined in a representative community population. The psychometric properties of the Diabetes Educational Profile (DEP) and its application to psychosocial research in diabetes were also investigated. Findings support the reliability and validity of the DEP. Various measures of psychosocial adjustment were related to diabetes control but the specific relationships depended on the particular aspect of adjustment, the specific measure of diabetes control, and the type of disease and treatment. The findings suggest that analyses that aggregate dissimilar patient groups are subject to misinterpretation due to ecological masking and supressor effects. The results indicate that clinicians and researchers must recognize that patients with different disease types and treatment modes have different norms for psychological adjustment and diabetes control. Further, the particular aspects of psychosocial adjustment associated with diabetes control differ across patient groups.

Adaptation, Psychological↗
PubMed1987

Scanning electron microscopic observations of the canine inner ear.

The sensory epithelia of the inner ear of the dog have been investigated using scanning electron microscopy (SEM). The surface appearance of the cristae ampullares of the semicircular canals and of the macula utriculi are very similar to other mammalian species. The crista ampullaris of the anterior vertical semicircular canal is divided by a non-sensory septum cruciatum, found in cats and rats but not, for example, in man. The vestibular sensory cells possess two distinct types of stereocilia, one is thick and rigid appearing, the other is thin and limp. Neither type of stereocilium is restricted to a particular hair cell type. From SEM views of the undersurface of the tectorial membrane of the cochlea we show evidence that some inner hair cell stereocilia may be attached to the tectorial membrane. This observation is made only in middle to upper cochlear regions (those subserving transduction of low frequencies of sound).

Animals↗
PubMed1987

Auditory science tutorial. III: The role of the ascending pathways.

This paper attempts a thumbnail sketch of what is currently known about processing in the early parts of the auditory pathway. The paper briefly reviews the morphology and physiology of the auditory nuclei up to the inferior colliculi of the midbrain and discusses their function in processing sound information. Particular attention is paid to the role of these nuclei in sound localization and in analysing complex signals such as speech. One aim of the tutorial is to dispel any ideas that the peripheral auditory pathways are mere relays to the thalamus and cortex and to emphasize their fundamentally important role in auditory processing. The review is not comprehensive (indeed it can only touch upon some aspects of auditory processing) but key references are provided for those with more than just a passing interest.

Animals↗
PubMed1987

The effects of hypoxia on sensory cells of the cochlea in chinchilla.

The effects of hypoxia on the sensory epithelium of the cochlea were investigated in the chinchilla. Systemic hypoxia was produced by increasing the dead space of the respiratory tidal volume. A disarrangement of hair-cell stereocilia, and cytoplasmic protrusions from sensory cells are the main findings in cochleas from hypoxic animals; these changes take place firstly at the inner hair-cells then, with the increase in degree of hypoxia, at the outer hair-cells. These degenerative changes of sensory cells correlate well with both respiratory suppression and with the elevation of auditory threshold to click stimulation as monitored using the compound action potential recording from the cochlear nerve. The latter measure appears to be a useful indicator of cochlear hypoxia. Our morphological findings are similar to other studies including those which have reported on post-mortem cochlear hair-cell degeneration. Our studies indicate the deleterious effects of long term hypoxia on cochlear mechanisms and point to the need for careful monitoring of cardiovascular and respiratory functions in animals under anaesthesia for physiological studies of the auditory system.

Action Potentials↗
PubMed1987

Technical development of an implantable cochlear prosthesis in Canada.

A new cochlear implant device is currently being developed by a group of research teams in Canada. This is an update on the progress of this development, including a brief description of the cochlear electrode array, the implantable stimulator, and the software development for the speech processor.

Cochlear Implants↗
PubMed1987

A study of the ototoxicity of deferoxamine in chinchilla.

Deferoxamine is a chelating agent used for the treatment of chronic iron overload in patients requiring long-term blood transfusions. Audiological testing of patients with B-thalassemia major and steroid-unresponsive Diamond-Blackfan anemia who were on long-term deferoxamine treatment indicated a possible ototoxic side-effect. In the present study we have investigated this potential toxicity to the cochlea of experimental animals by monitoring electrophysiological responses to sound and also by histological evaluation of the cochlea. In animals having chronic deferoxamine treatment, there were no significant changes in cochlear function or morphology. Data from acutely treated animals indicated an elevation of cochlear response thresholds together with morphological changes at the inner hair-cell level. However, these changes were highly correlated with the respiratory depression caused by an acute general toxicity, rather than a direct ototoxic effect of deferoxamine.

Animals↗
PubMed1986

Visual and auditory neurotoxicity in patients receiving subcutaneous deferoxamine infusions.

Of 89 patients receiving nightly subcutaneous deferoxamine for transfusion-dependent thalassemia major or Diamond-Blackfan anemia, 13 presented with visual loss or deafness of acute onset or both. Detailed ophthalmologic, audiologic, and evoked-potential studies uncovered abnormalities caused by neurotoxicity in 27 more. Four patients with visual loss had optic neuropathy, with a marked decrease in acuity, loss of color vision, and delayed visual evoked potentials. Five asymptomatic patients had changes in the pigment of the retinal epithelium. The hearing loss was characterized by a high-frequency sensorineural deficit, which necessitated hearing aids in six patients. When deferoxamine was stopped, recovery of vision was complete in 2 patients and partial in 2, and in 22 patients with abnormal audiograms, reversal of the hearing deficit was complete in 4 and partial in 1. An analysis of the clinical data showed that members of the affected group were younger, had lower serum ferritin values, and were self-administering higher doses of deferoxamine per kilogram of body weight. Significantly lower doses of deferoxamine were being taken by patients without abnormalities than by those with visual symptoms, abnormal audiograms, or prolonged evoked potentials (P less than 0.001, less than 0.006, and less than 0.04, respectively). The data implicate high-dose deferoxamine as a central factor in the pathogenesis of the neurotoxicity. We strongly recommend careful regulation of the deferoxamine dosage and serial audiovisual monitoring in all patients receiving the drug.

Adolescent↗
PubMed1986

Institutional subsidization of medical-school based continuing medical education.

The changing financial structure of health care is prompting review of medical school resources allocated to CME units. This study examined the types of subsidization provided to CME by medical schools and the methods of allocation of CME revenue within medical schools. Data are presented for 21 medical schools from different geographic areas of the United States. Medical schools often provide appreciable financial support to CME offices, particularly office space, faculty time, and space for CME meetings. However, the amount of support varies greatly from school to school. Revenue distribution arrangements also vary. Medical schools can use the description of arrangements at other schools in reviewing the appropriateness of their own current arrangements.

Data Collection↗