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Biomedical subjects

M Lawrence

Publications and source records attributed to M Lawrence.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Effects of noise and quinine on the vessels of the stria vascularis: an image analysis study.

Surface preparations of the stria vascularis from guinea pigs exposed to wide-band noise or intoxicated with quinine monohydrochloride dihydrate were studied by light microscopy and computerized image analysis in order to evaluate quantitatively the effects of these agents on two characteristics of the strial vasculature: vascular density and erythrocyte distribution. An image analyzer was used to measure the area of strial vessel lumen and erythrocyte distribution as a fraction of the total area of strial tissue under observation. The results demonstrate that changes in the strial vessels do occur in guinea pigs exposed to noise or given large doses of quinine. Localized vessel narrowings caused by swollen endothelial cells and possibly by contraction of pericytes were found in both experimental groups, but there was no apparent tonotopical relationship between these effects and the reduction in cochlear potentials. A significant reduction in the number of erythrocytes was found in all turns of the cochlea in both experimental groups. Although a significant difference in vascular density was found among turns of the cochlea in both experimental and control animals, there was no widespread change in vascular density as a result of either noise exposure or quinine treatment.

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Auditing audits: use and development of the Oxfordshire Medical Audit Advisory Group rating system.

OBJECTIVES: To assess the value of the Oxfordshire Medical Audit Advisory Group rating system in monitoring and stimulating audit activity, and to implement a development of the system. DESIGN: Use of the rating system for assessment of practice audits on three annual visits in Oxfordshire; development and use of an "audit grid" as a refinement of the system; questionnaire to all medical audit advisory groups in England and Wales. SETTING: All 85 general practices in Oxfordshire; all 95 medical audit advisory groups in England and Wales. MAIN OUTCOME MEASURES: Level of practices' audit activity as measured by rating scale and grid. Use of scale nationally together with perceptions of strengths and weaknesses as perceived by chairs of medical audit advisory groups. RESULTS: After one year Oxfordshire practices more than attained the target standards set in 1991, with 72% doing audit involving setting target standards or implementing change; by 1993 this had risen to 78%. Most audits were confined to chronic disease management, preventive care, and appointments. 38 of 92 medical audit advisory groups used the Oxfordshire group's rating scale. Its main weaknesses were insensitivity in assessing the quality of audits and failure to measure team involvement. CONCLUSIONS: The rating system is effective educationally in helping practices improve and summatively for providing feedback to family health service authorities. The grid showed up weakness in the breadth of audit topics studied. IMPLICATIONS AND ACTION: Oxfordshire practices achieved targets set for 1991-2 but need to broaden the scope of their audits and the topics studied. The advisory group's targets for 1994-5 are for 50% of practices to achieve an audit in each of the areas of clinical care, access, communication, and professional values and for 80% of audits to include setting targets or implementing change.

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Cochlear potentials and oxygen associated with hypoxia.

In the guinea pig, during general hypoxia produced by shutoff of respiratory air, oxygen-sensitive microelectrodes detect a decrease in oxygen concentration in the fluids of the tunnel of Corti before detecting a decrease in scala media oxygen concentration. The present experiments were designed to measure the cochlear microphonic (CM) potential generated by the organ of Corti when vibrated by a microprobe on the basilar membrane along with the oxygen decline in both tunnel and scala media to see upon which source of oxygen CM is dependent. Because oxygen concentration in both areas can decrease considerably before CM is affected, the recovery following a brief period of hypoxia is a more accurate measure. Because CM starts a recovery before scala media oxygen, the positive endolymphatic potential (EP) was also measured to determine its role in the generation of CM. Our interpretation of the course of events is that CM is partially dependent upon oxygen supplied to the extracellular spaces of the organ of Corti by the spiral vessels and upon EP that, itself, is dependent upon several factors. The data indicate that EP plays a more complex role than that of providing a current flow for modulation by a resistance varying with vibration.

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Attachment of the tectorial membrane revealed by scanning electron microscope.

Our present-day descriptions of the causes of many forms of sensorineural deafness are based on what is known about the morphology of the organ of Corti. Unfortunately, this information is still woefully inadequate for a complete interpretation of normal events within this structure. Nevertheless there has been no shortage of theories based, in part at least, on assumptins of what the unknown morphology might be. One of the least understood structures is the tectorial membrane, for which the extent and position have had many descriptions. A review of these reveals that the observations vary with the techniques used, and different techniques have various effects on the sticky gel of the tectorial membrane which is reported to be 90% water. Here is described a technique whereby the bulk frozen-hydrated tectorial membrane is viewed by scanning microscopy. In its natural living state the tectorial membrane is sealed to the Hensen's cells, protecting the reticular lamina from endolymph.

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Communication disorders: investigator training and support needs.

There are very few "simple problems" left in the area of communication disorders, but that does not mean that there are unsolvable problems. However, in pursuit of these, present day research often requires extensive technical procedures which require teams of investigators trained in different areas. Among these should be the otolaryngologist, but, in this country, there are few involved and there is a paucity of disease-oriented research. In the 1950s and 1960s the NIH training grant provided funds for bringing doctor of philosophy researchers into clinical departments to set up laboratories and work intimately with the medical doctor. Basic research training is still essential during residency and the number of postresidency fellowships ought to be increased. The familiarity with clinical problems introduced into the research effort should improve the possibility for the conduction of disease-oriented research in addition to the present day emphasis on basic research.

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Recent advances in cochlear blood flow measurements.

Changes in blood flow to the inner ear have been thought to influence or underlie a number of cochlear diseases, including some forms of noise-induced hearing loss, sudden hearing loss, and Meniere's disease. Recently, important advances have been made in two technologies for the study of cochlear blood flow. The first is in the area of vital microscopic studies of cochlear microcirculation, and the second is based on the introduction of laser technology in the form of laser Doppler flowmetry. In this report, measurements are given of changes in cochlear circulation caused by carbon dioxide breathing, intravenous phenylephrine injection, systemic hemodilution, positive end expiratory pressure, and direct electrical stimulation of the cochlea. From these changes, we observe that cochlear blood circulation responds to systemic blood pressure alterations and is subject to local flow control mechanisms. Linearity and speed of response of the laser Doppler instrumentation also are shown. These advances show promise for contributing to our knowledge of control mechanisms of inner ear blood flow and for revealing the influence of various pharmacologic agents of potential clinical value.

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Resting potentials in the inner sulcus and tunnel of corti.

Under constant visual guidance and closed-circuit television monitoring, electrodes are inserted into the fluid spaces of the organ of Corti. The resting electrical potentials are determined with respect to the neutral voltage of the guinea pig and related to other potentials of the auditory labyrinth. The resting potential of the subtectorial space, inner sulcus, tunnel and other spaces of Corti's organ are found to be the same as, or slightly more negative than the potential of perilymph. The tectorial membrane isolates the reticular lamina from endolymph which fact, when considered along with other evidence, indicates a more biophysical than mechanical role for the membrane. A motion picture is presented showing the cells and spaces of the organ of Corti and the placement of electrodes.

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Oxygen reserve and autoregulation in the cochlea.

Endolymphatic O2-concentration was measured in the guinea pig cochlea with a microelectrode inserted through the zona pectinata of the basilar membrane and the cells of Claudius, so as not to interfere with the blood supply to the organ of Corti. The O2-level and the amplitude of the cochlear potentials were followed during hypoxia produced by lowering the pO2 of the inspired air. Persistence of a normal endolymphatic O2-level following the fall in arterial pO2 indicated an O2-reserve and au autoregulation of the cochlear circulation.

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PubMedDate not supplied

Effects of perilymphatic perfusion with neomycin on the cochlear microphonic potential in the guinea pig.

The effects of three concentrations of neomycin, administered by a method of acute perilymphatic perfusion of the guinea pig cochlea, on the cochlear microphonic potential (CM) at 4 kHz and 500 Hz are described. A concentration-dependent reduction in CM occured during the 60 minute perfusion period. Neomycin at 10-4 M did not change the CM magnitude, while at 10-3 and 102 M it caused 4 kHz (and 500 Hz) CM reductions which began within 24 (for both frequencies) minutes and 10 (and 12) minutes of drug application respectively. CM reduction proceeded at a higher rate for greater neomycin concentration. The perfusion technique, the implication of the frequency indifference, and the potential of the perfusion technique for inner ear biochemical analysis are discussed.

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