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Biomedical subjects

J I Simpson

Publications and source records attributed to J I Simpson.

At least 55 records · Page 3Linked to original sources
PubMed1988

Flammability of esophageal stethoscopes, nasogastric tubes, feeding tubes, and nasopharyngeal airways in oxygen- and nitrous oxide-enriched atmospheres.

This study determines the flammability of materials in the oral cavity and pharynx during anesthesia in an environment of potentially high oxygen (O2) and nitrous oxide (N2O) concentrations where an ignition source (cautery, laser) may be in close proximity. The materials tested included esophageal stethoscopes, Salem sump nasogastric tubes, enteric feeding tubes, and plastic and rubber nasopharyngeal airways. Flammability was determined using oxidant O2 and oxidant N2O indices of flammability. The oxidant O2 and oxidant N2O indices of flammability are defined as the minimum fraction of oxidant (O2 or N2O) in nitrogen diluent that supports a candle-like flame for a given fuel source. The oxidant O2 index of flammability for esophageal stethoscopes is 0.218, for Salem sump nasogastric tubes 0.229, for enteric feeding tubes 0.192, for plastic nasopharyngeal airways 0.196, and for rubber nasopharyngeal airways 0.172. The oxidant N2O index of flammability for esophageal stethoscopes is 0.430, for Salem sump nasogastric tubes 0.430, for enteric feeding tubes 0.375, for plastic nasopharyngeal airways 0.415, and for rubber nasopharyngeal airways 0.366. These indices are linearly additive.

Auscultation↗
PubMed1988

The pretectal nuclear complex and the accessory optic system.

A critical survey of the nomenclatures used for subdivisions of the pretectal nuclear complex is followed by a description of pretectal development and connectivity of individual nuclei. Some of these mediate the pupillary light reflex; part of another forms part of the accessory optic system, involved in processing visual signals for the generation of compensatory (optokinetic) eye movements. The anatomy, development, connections and function of the accessory optic system and its subdivisions are reviewed.

Afferent Pathways↗
PubMed1987

Pulse oximetry during pulmonary artery banding.

In children with a ventricular septal defect and congestive heart failure, banding of the pulmonary artery (PA) causes equalization of right and left ventricular pressures, reduces the volume of the left-to-right shunt, and diminishes the work of the left ventricle and the engorgement of the pulmonary vessels. However, banding the PA too tightly usually produces hypoxemia by reversing the left-to-right shunt and causes severe hemodynamic changes. A series of 14 infants is reported who underwent PA banding during which a pulse oximeter was used as an early indicator of excessively tight PA banding. Significant hemodynamic changes occurred in eight infants in whom the PA banding was too tight. This consisted of hypotension and bradycardia three to four minutes after the banding. The eight patients also showed significant desaturation of the blood after application of the band, with the arterial hemoglobin saturation (SaO2) dropping from a preband value of 98 +/- 6% to a postband value of 80 +/- 2%. The decrease in SaO2 preceded the hypotension and bradycardia by two to three minutes in all cases. When the band was removed, the hemodynamic and SaO2 changes returned toward baseline. Subsequently, a less tight band was applied; this was associated with a smaller decrease in SaO2, an elevation of blood pressure, and no bradycardia. This was considered to be acceptable banding. The right ventricle/PA pressure gradient significantly decreased after acceptable banding, and a gradient higher than 45 mmHg was usually associated with hypoxemia.

Blood Pressure↗
PubMed1987

Flammability of endotracheal tubes in oxygen and nitrous oxide enriched atmosphere.

Endotracheal tube (ETT) fire has been reported secondary to laser and electrocautery ignition. The flammability of polyvinylchloride (PVC), silicone (Si), and red rubber (RR) ETTs in oxygen (O2) and/or nitrous oxide (N2O) in nitrogen was determined and compared by means of the O2 and N2O indices of flammability. The O2 index of flammability is the minimum O2 fraction in nitrogen that will support candle-like flame using a standard ignition source. The O2 index of flammability for PVC ETTs is 0.263, for Si 0.189, and for RR 0.176. The N2O index of flammability is the minimum N2O fraction in N2 that will support candle-like flame using a standard ignition source. The N2O index of flammability for PVC ETTs is 0.456, for Si ETTs 0.414, and for RR ETTs 0.374. The indices are additive. Flammability is a valid method of comparing safety of various endotracheal tube materials. There is a need for new endotracheal tube material with a higher index of flammability. The significance of these findings and the clinical applications are discussed.

Anesthesia, Inhalation↗
PubMed1980

Retinal ganglion cells projecting to the rabbit accessory optic system.

Recent evidence from extracellular recording studies indicates that the medial terminal nucleus (MTN) of the rabbit accessory optic system receives inputs from a particular functional class of retinal ganglion cells--specifically, the on-type direction-selective cells. These ganglion cells have been selectively labeled by the retrograde transport of horseradish peroxidase (HRP) injected into the MTN. The number of labeled cells, their distribution over the retina, and their soma areas were determined. In one animal in which the HRP injection completely filled the nucleus, two thousand ganglion cells were labeled. This number agrees with previous estimates of the number of retinal axons terminating in the MTN. Unlike results in avians, none of the ganglion cells was displaced--i.e., they were not Dogiel cells. The density of labeled cells was highest in the visual streak and, overall, the distribution of labeled cells corresponded to the physiologically determined distribution of on-type direction-selective cells. Cells labeled by the HRP injection were among the 20% largest cells in the retina. This result, in conjunction with conclusions from other studies, leads to the prediction that on-type direction-selective cells can be characterized morphologically as cells with large cell bodies and a very extensive dendritic spread in which the dendrites ramify in the vitreal sublamina of the inner plexiform layer.

Animals↗
PubMed1980

Effects of microlesions of dorsal cap of inferior olive of rabbits on optokinetic and vestibuloocular reflexes.

1. Discrete, unilateral, electrolytic lesions of the dorsal cap of the inferior olive were made in rabbits in an attempt to assess the effect on eye movements of removal of a visual climbing fiber input to the fluocculus. The position of the lesioning electrode within the dorsal cap was adjusted on the basis of the field potential evoked by flash stimulation of the contralateral eye. 2. Electrophysiological and anatomical evidence confirmed that the microlesions of the dorsal cap destroyed 10-80% of olivary cells, but cause only slight damage to the olivocerebellar pathway originating from the contralateral dorsal cap. 3. The immediate effect of the microlesions was a spontaneous, conjugate drift of the eyes to the side contralateral to the lesion. The effects of the microlesions on eye movements were further examined using reflexes evoked by vestibular and optokinetic stimulation. 4. Postoperatively, the vestibuloocular reflex (VOR) gain was not modified, but there was a marked VOR velocity bias to the contralateral side. This velocity bias was most pronounced at low stimulus frequencies (0.02-0.05 Hz, +/- 10 degrees) and was minimal at stimulus frequencies above 0.5 Hz. 5. Monocular, sinusoidal optokinetic stimulation with a large contrast-rich visual target evokes, in normal rabbits, a conjugate asymmetric following response with a higher eye velocity for target movement from posterior to anterior. Following damage to the dorsal cap, the asymmetry of this optokinetic reflex was reversed when the target was presented to the eye contralateral to the lesion. With monocular, constant-velocity optokinetic stimulation delivered to the contralateral eye, the optokinetic gain for movement in the posterior to anterior direction was decreased. 6. These data suggest that visual climbing fibers are part of a feedback loop that reduces retinal slip of low velocity. The relatively low discharge rate of climbing fibers would seem appropriate to ecode continuously retinal slip of low velocity and to influence low-velocity eye movements.

Animals↗
PubMed1976

Responses of Purkinje cells in rabbit nodulus and uvula to natural vestibular and visual stimuli.

1. The responses of Purkinje cells and presumed mossy fibers to natural stimulation of the horizontal semicircular canals were recorded in the nodulus and uvula of rabbit vestibulocerebellum. Units responding to vestibular stimulation were also studied with visual stimulation. 2. The responses of presumed mossy fibers were of the Type I and Type II varieties and were characterized by a low threshold for angular acceleration and high sensitivity. 3. Purkinje cell responses were divided into two groups: The first group showed only modulation of simple spike activity during rotation. According to the directionality of their responses to rotation, Purkinje cells of the first group could be further subdivided into Types I, II or III; Type II was the most frequently encountered. The second group showed modulation of both simple spike and climbing fiber activity. The simple spike response most frequently encountered was of Type II while the climbing fiber activity in the same Purkinje cells responded in the Type I mode. In another population of Purkinje cells of this group, simple spike activity was modulated by rotation in one direction only. All Purkinje cell responses had relatively high thresholds and low sensitivities. 4. Some Purkinje cells responding to rotation showed direction-selective modulation of climbing fiber discharge in response to slowly moving visual patterns.

Animals↗
PubMed1976

Nystagmic modulation of neuronal activity in rabbit cerebellar flocculus.

1. The responses of neuronal elements in the flocculus of the awake, restrained rabbit were recorded during horizontal vestibular nystagmus in the dark. 2. Purkinje cells showed both vestibular (Types I and II) and eye movement modulation of simple spike activity. Type I Purkinje cells most commonly were inhibited in association with the ipsilaterally directed fast phase of nystagmus and excited during contralaterally directed fast phases. Type II Purkinje cells had a similar modulation but in the opposite direction. Variations on this pattern included an increase in firing during fast phases in both directions. 3. Presumed mossy fibers and granule cells also exhibited both vestibular and nystagmic modulation in various combinations. The nystagmic modulation often began during the fast phase and continued into the early part of the slow phase. Mossy fibers showing both vestibular and nystagmic modulation probably arise from the vestibular nuclei and/or the perihypoglossal nuclei. 4. Floccular control of brain stem nuclei utilizes not only vestibular but also eye movement signals and probably all sensory and internal signals involved in the regulation of gaze.

Animals↗