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Biomedical subjects

D A Robinson

Publications and source records attributed to D A Robinson.

At least 91 records · Page 5Linked to original sources
PubMed1984

Alexander's law: its behavior and origin in the human vestibulo-ocular reflex.

Alexander's law refers to the phenomenon in which the spontaneous nystagmus of a patient with a vestibular lesion is more intense when the patient looks in the quick-phase than in the slow-phase direction. Alexander's law was investigated in normal subjects as well as patients with vestibular lesions. During sinusoidal rotations of normal subjects, there was no trace of this phenomenon when subjects looked 25 degrees left and right in the dark. The phenomenon of Alexander's law is therefore created centrally and is not due to any mechanical properties of the orbit. During rotation at constant velocity in the dark, normal subjects did weakly demonstrate Alexander's law because of a mild gaze-evoked nystagmus present in normal subjects in the dark. Gaze-evoked nystagmus from a cerebellar lesion involved a pronounced demonstration of Alexander's law during rotatory nystagmus. In patients with a vestibular lesion and a mild spontaneous nystagmus in the dark that obeyed Alexander's law, the nystagmus reversed upon far gaze in the slow-phase direction. We propose that in patients with a vestibular lesion, the phenomenon of Alexander's law is created by the sum of vestibular nystagmus and an abnormally large gaze-evoked nystagmus that is consequent to the vestibular lesion. This conclusion has a number of neurological implications concerning the ways in which the nervous system attempts to compensate for vestibular lesions.

Adult↗
PubMed1984

A model of the mechanics of binocular alignment.

A computer model (SQUINT) of the static mechanics of human eyes is developed and applied to the diagnosis and treatment of defects of binocular alignment (strabismus). Brief discussions of ocular anatomy, binocular vision, strabismus and its surgical correction, and early strabismus modeling are provided for nonspecialists in these areas. Models of muscle force, muscle path, globe translation, and binocularity are developed. To illustrate the use of the model in clinical cases, it is applied to the diagnosis and surgical treatment of a case of superior oblique palsy. The model's implementation under the UNIX operating system is described.

Biomechanical Phenomena↗
PubMed1984

Pleural surgery in patients with cystic fibrosis. A review of anaesthetic management.

Eighteen patients with advanced cystic fibrosis complicated by pneumothorax required either pleurectomy or abrasion pleurodesis. Anaesthesia with nitrous oxide and oxygen was combined with controlled ventilation to both lungs, usually through a double lumen endobronchial tube. Spontaneous ventilation was restored at the end of operation in all but a minority of cases. Ten of 25 procedures were uncomplicated and a further five were followed by non-respiratory events. Respiratory complications developed after the remaining ten procedures which were carried out on six patients, of whom only one survived for more than 6 months. All five fatal cases suffered a recurrence of pneumothorax within 6 months whereas three patients requiring re-operation 2-6 years later survived. The principles of management are discussed and it is concluded that the operative and anaesthetic hazards of thoracic surgery in this group of high-risk cases can be avoided successfully, except when re-operation is required within 6 months.

Adolescent↗
PubMed1984

Signals in vestibular nucleus mediating vertical eye movements in the monkey.

The action potentials of single neurons were recorded extracellularly throughout the rostral vestibular nuclei and subadjacent reticular formation in three alert, juvenile, rhesus monkeys. Neuronal responses were tested during a) sinusoidal pitch oscillations in darkness, b) cancellation of the vestibuloocular reflex (VOR) during similar oscillations by fixation of a target moving with the head, c) sinusoidal vertical smooth pursuit, d) vertical saccades, and e) fixation with the head stationary. Eye movements were measured using the magnetic field-search coil technique. Of the 527 neurons isolated, 318 responded to pitch oscillation and/or vertical eye movements. The latter cells could be classified into six categories. Of this group, 273 cells were recorded from for sufficient time to allow them to be fully tested and form the basis of this report. Cells were classified as follows: pure-vestibular cells with firing rates modulated only by head velocity (15%), vestibular-pause cells that were similar to the pure-vestibular cells but paused for saccades in all directions (10%), gaze-velocity cells that modulated their rates in proportion to vertical eye velocity in space (7%), position cells with rates modulated by changes in eye position in the head but that did not burst or pause during saccades (33%), position-burst cells that also carried an eye-position signal but did burst during saccades in one direction and paused in the opposite direction (15%), and position-vestibular-pause cells that carried signals proportional to eye position in the head and head velocity and paused during all saccades (20%). Most cells that carried an eye-position signal also carried an eye-velocity signal during pursuit. Position and position-burst cells could be divided into two subcategories. Position cells that also reported head velocity represented 20% of the total sample, while those without head-velocity signals made up the remaining 13%. Position-burst cells were divided into two subcategories based on their behavior during pitch oscillation in darkness. Both carried eye-velocity signals during pursuit, but only one type (8% of the total sample) also carried an eye-velocity signal during vestibular eye movements in the dark, while the other (7%) did not. Some cells in all six categories except the pure-vestibular cells responded antidromically to stimulation of the medial longitudinal fasciculus (MLF). Only the position-vestibular-pause, position-burst, and gaze-velocity cells, however, were judged to be commonly antidromically activated, suggesting that these three cell types are the major contributors to the MLF from the rostral vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1983

Different time constants for optokinetic and vestibular nystagmus with a single velocity-storage element.

Models have been proposed for the combined optokinetic system and vestibulo-ocular reflex that share a single, common, velocity-storage element that generates both optokinetic after-nystagmus and prolongs post-rotatory nystagmus. It has been thought by many that such a model requires the time course of these two types of nystagmus to be similar. The demonstration that vestibular or optokinetic habituation can selectively and significantly reduce the duration of each type of nystagmus without affecting that of the other has been taken to imply that the concept of shared velocity storage is incorrect. This need not be the case because post-rotatory nystagmus is described by two time constants, not one. Changes in the model's parameters can create time courses of this nystagmus that, when fit by single exponentials, have apparent time constants quite different from that of optokinetic after-nystagmus. Consequently, a common velocity-storage mechanism is still a tenable hypothesis for optokinetic and vestibular eye movements.

Animals↗
PubMed1983

A proposed neural network for the integrator of the oculomotor system.

Single-unit recordings, stimulation studies, and eye movement measurements all indicate that the firing patterns of many oculomotor neurons in the brain stem encode eye-velocity commands in premotor circuits while the firing patterns of extraocular motoneurons contain both eye-velocity and eye-position components. It is necessary to propose that the eye-position component is generated from the eye-velocity signal by a leaky hold element or temporal integrator. Prior models of this integrator suffer from two important problems. Since cells appear to have a steady, background signal when eye position and velocity are zero, how does the integrator avoid integrating this background rate? Most models employ some form of lumped, positive feedback the gain of which must be kept within totally unreasonable limits for proper operation. We propose a lateral inhibitory network of homogeneous neurons as a model for the neural integrator that solves both problems. Parameter sensitivity studies and lesion simulations are presented to demonstrate robustness of the model with respect to both the choice of parameter values and the consequences of pathological changes in a portion of the neural integrator pool.

Animals↗
PubMed1982

The use of matrices in analyzing the three-dimensional behavior of the vestibulo-ocular reflex.

The vestibulo-ocular reflex rotates the eye about the axis of a head rotation at the same speed but in the opposite direction to make the visual axes in space independent of head motion. This reflex works in all three degrees of freedom: roll, pitch, and yaw. The rotations may be described by vectors and the reflex by a transformation in the form of a matrix. The reflex consists of three parts: sensory, central, and motor. The transduction of head rotation into three neural signals, which may also be described by a vector, is described by a canal matrix. The neural, motor-command vector is transformed to an eye rotation by a muscle matrix. Since these two matrices are known, one can solve for the central matrix which gives the strength of the connections between all the vestibular neurons and all the eye-muscle motoneurons. The role of the metric tensor in these transformations is described. This method of analysis is used in three applications. A lesion may be simulated by altering the elements in any or all of the three component matrices. By matrix multiplication, the resulting abnormal behavior of the reflex can be described quantitatively in all degrees of freedom. The method is also used to directly compare the differences in brain-stem connections between humans and rabbits that accommodate the altered actions of the muscles of the two species. Finally the method allows a quantitative assessment of the changes that take place in the brain-stem connections when plastic changes are induced by artificially dissociating head movements from apparent motion of the visual environment.

Animals↗
PubMed1982

Plasticity in the oculomotor system.

The oculomotor system, responsible for the control of eye movement, is capable of a number of kinds of plasticity. The demonstration of such plasticity has been aided by several factors, including the present delineation of the system's major subsystems and their purposes; the relatively simple relationships between the system and the mechanical apparatus on which it acts, the eyeball and its muscles; and the development of techniques for studying central nervous system (CNS) activity in awake, behaving animals. Plasticity has been demonstrated by using noninvasive techniques to disturb the normal relationship between vision and eye movements, thereby creating a need for adjustment by the oculomotor system. Current studies are concerned with the location and identity of the responsible modifiable synapses. The cerebellum and the olivocerebellar pathways are definitely involved in several forms of oculomotor plasticity. However, it remains to be determined whether the responsible changes reside within these structures or are located elsewhere in the CNS.

Accommodation, Ocular↗
PubMed1981

The behavior of the vestibulo-ocular reflex at high velocities of head rotation.

The behavior of the vestibulo-ocular reflex (VOR) during both passive and active, high-velocity head movements was recorded in three normal subjects. We found that the VOR is compensatory for head velocities up to at least 350 deg . s-1, during both active and passive head rotation provided there is an attempt to visualize a real (or imagined) stationary object in space. Slow phase velocities, however, could reach values as high as 500 deg . s-1. Furthermore, during passive rotation at high velocities, the quick phase trajectory is modified--indicating an interaction between the slow phase and quick phase eye velocity commands.

Adult↗
PubMed1981

Milk-borne campylobacter infection.

The common factor in 13 recent outbreaks of Campylobacter jejuni enteritis was the consumption of unpasteurised or incompletely pasteurised milk. C jejuni is a common commensal in the alimentary tract of milking cows, but it is not clear how the milk becomes contaminated with the organism. Pasteurisation will readily eliminate the organism from milk. In England and Wales 3% of milk retailed is still unpasteurised, and in the light of these findings it is suggested that only pasteurised milk should be sold to the public.

Adolescent↗
PubMed1981

Campylobacter enteritis associated with the consumption of free school milk.

A large outbreak of campylobacter enteritis associated with the consumption of free school milk is described. The outbreak had an abrupt onset, and lasted for about 3 weeks; it involved mainly school children in the 2-4 and 5-7 year old age groups. During this period it was established from epidemiological and microbiological data that some 2500 children were infected. The source of the epidemic was almost certainly contaminated milk, although bacteriological proof could not be obtained. Biotyping of isolates was of considerable epidemiological value and showed the involvement of two distinct strains, one of which was dominant. Epidemiological evidence of limited person to person transmission of the infection was obtained; febrile convulsions as a prodromal sign of the illness was recognized for the first time. Strains of Campylobacter jejuni, and samples of patients' serum collected during this outbreak have enabled subsequent studies to be initiated on the serotyping of the responsible organism, on the serological response of patients infected with the organism, and on experimental infection of the bovine udder which demonstrated its potential as a source of C. jejuni in raw milk. A careful search of the literature suggests that this is the largest documented outbreak of campylobacter enteritis.

Animals↗
PubMed1981

Serological studies in two outbreaks of Campylobacter jejuni infection.

Two outbreaks of campylobacter enteritis in residential student populations are described. In the first outbreak, 34 of 240 students in one hall of residence became ill over the course of 4 or 5 days. A single serotype of C. jejuni was isolated from sample of faeces. Sera collected demonstrated that the students had little pre-existing antibody and antibody responses were demonstrated in those who were infected. About 30% of students with serological evidence for infection with C. jejuni did not have gastro-intestinal symptoms. In the second outbreak, 77 of 300 agricultural students developed symptoms over a period of 3 weeks. Unpasteurized milk was the source of infection. Two serotypes of C. jejuni were isolated from faeces. Antibody responses were detected to both these serotypes and to another serotype, suggesting the presence of at least 3 serotypes in the milk. Bactericidal antibody consistent with recent infection was found in all students with symptoms and in 63% of students in the absence of symptoms, indicating the possible development of immunity. The high prevalence of antibody in these students was correlated with the habitual consumption of unpasteurized milk.

Adult↗