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Biomedical subjects

R Baker

Publications and source records attributed to R Baker.

At least 451 records · Page 25Linked to original sources
PubMed1985

A nursing home/university exchange program: an alternative model for teaching nursing homes.

The nursing home/university exchange program is a long way from the ideal teaching nursing home model, but it can meet many of the same objectives of providing high-quality care for the elderly. The utilization of an interdisciplinary exchange can encourage cohesiveness throughout the nursing home and provide for increased opportunities for university affiliation. The nursing home can serve as an educational bridge for educators. Likewise, the university can provide practitioners an environment in which to grow and keep current in the field. This model can be adapted by any nursing home and university committed to improving the quality of life of older persons, regardless of whether they have the resources to develop the ideal teaching nursing home. This type of exchange program will benefit academicians, administrators, students, service providers, and, ultimately, the older individual.

Academic Medical Centers↗
PubMed1985

Comparison of standards in training and non-training practices.

The in-practice component of vocational training should take place in practices working to high clinical and teaching standards. By means of a survey of its members, the Severn Faculty of the Royal College of General Practitioners was able to compare training practices with the criteria of the Joint Committee on Postgraduate Training for General Practice, and with non-training practices. The training practices fell short of the criteria in a few areas, but the differences between the training and non-training practices were extensive. Progress towards achieving the standards set by the criteria should be monitored, and the criteria themselves should be made more precise.

Education, Medical, Graduate↗
PubMed1984

Tachycardia-termination algorithm: a valuable feature for interruption of pacemaker-mediated tachycardia.

A 45-year-old man who had been implanted with a VVI pacemaker for sinus arrest complained of syncope, dizziness and throbbing in the neck. His pacemaker function was normal, but during ventricular pacing, retrograde V-A conduction was observed. This pacer was replaced by a DVI unit which caused periodic abdominal muscular contractions. We replaced this unit with an Intermedics Cosmos DDD-M pacemaker. This type of pacemaker in a patient with V-A conduction may cause pacemaker-mediated tachycardia (PMT). However, the Cosmos has a tachycardia-termination algorithm which detects continued pacing at the ventricular tracking rate, allows it to proceed for 15 consecutive pace events, and inhibits the 16th ventricular output pulse, thus breaking the reentry loop. The Cosmos pacer has a number of features to prevent initiation of PMT, and is also able to terminate the tachycardia when it occurs because of the tachycardia-termination algorithm. This feature is valuable in DDD-M pacemakers implanted in patients with V-A conduction. Whether this algorithm will be effective in all cases remains to be determined.

Abdominal Muscles↗
PubMed1984

Blinking and associated eye movements in humans, guinea pigs, and rabbits.

Recordings of upper eyelid movements in humans, guinea pigs, and rabbits demonstrated that all three species displayed qualitatively similar patterns of eyelid movement. The relation between amplitude, duration, and maximum velocity in rabbits and humans was nearly identical. Guinea pig blinks were faster than those of rabbit and man. Electromyographic (EMG) recordings in humans demonstrated that the orbicularis oculis muscle participated in downward movement of the upper eyelid during blinks and eyelid closure but did not participate actively in the downward lid movement occurring with gaze changes. When looking straight ahead, the estimated stiffness and viscosity of the upper eyelid were 10 g/mm and 0.38 g X s X mm-1 for humans and 1.17 g/mm and 0.062 g X s X mm-1 for rabbits. Upward and abducting rotations of the eye accompanied blinks in rabbits and guinea pigs. Simultaneously, the eyeball retracted (translational movement) into the orbit. These translational and rotational eye movements resulted from contraction of the retractor bulbi muscle and cocontraction of antagonistic extraocular muscles. The data suggested that humans also retracted the eye during voluntary blinks. The retraction produced a rotation of the eye toward a "primary position" rather than a rotation in one specific direction. The relationship between the maximum velocity, duration, and amplitude of the down phase of a blink may be expressed as a single equation, maximum velocity = c X average velocity, where c is a constant. The same relationship, with a similar value for c, also describes saccadic eye movements and rapid skeletal movements. This implies that all three movements employ comparable neural mechanisms.

Animals↗
PubMed1984

Some considerations arising from the treatment of a patient with necrophilic fantasies in late adolescence and young adulthood.

Some psychoanalytic theories relating to necrophilia are reviewed, supplemented by other relevant theoretical abstracts. A psychoanalytic case of a young man with necrophilic fantasies is described, emphasizing separation anxiety, sadism and anal masturbation, all compellingly manifest in the transference and rooted in infantile trauma. The material is compared with that of other analysts working with similar pathology, then discussed in relation to perversions generally. Finally, it is argued that if the prognosis depends on whether core fantasies are amenable to analysis in the transference, then there may be therapeutic justification for keeping adolescence open by blocking the developmental move forward, on the grounds that these fantasies would quickly be rendered inaccessible under the normal repressive processes of young adulthood.

Adolescent↗
PubMed1984

Virus-induced complement activation and neutrophil-mediated cytotoxicity against respiratory syncytial virus (RSV).

Complement-dependent neutrophil-mediated cytotoxicity (CDNC) was determined by specific release of 51-chromium (51Cr) from respiratory syncytial virus infected HEp2 cells in a microcytotoxicity assay. There was significant release of 51Cr from RSV infected cells as compared to uninfected cells in the presence of complement (C) and neutrophils (PMN). The degree of cytotoxicity was dependent upon the concentration of C used in the assay. Such cytotoxicity was effectively abolished after heat-inactivation of complement. Complement deficient in C4 did not induce cytotoxicity. Similarly, inhibitors of C1 or C3 blocked CDNC. The maximal CDNC was observed at 37 degrees C with little or no response at 4 degrees C. Lymphocytes and monocytes mediated complement-dependent cytotoxicity very poorly in comparison to PMN. Evidence of complement activation by infected cells was demonstrated by the detection of C3 fixed to RSV infected cells by indirect immunofluorescence. Treatment of C with EDTA or heat prevented subsequent attachment of C3 to the infected cells. These in vitro observations suggest an initial activation of complement by RSV infected cells and subsequent lysis by PMN. It is proposed that this process may play a role in the elimination of virus in the early phase of infection in the absence of specific antibody or sensitized lymphocytes.

Complement Activation↗
PubMed1983

Adaptive changes of the vestibulo-ocular reflex in flatfish are achieved by reorganization of central nervous pathways.

Flatfish provide a natural model for the study of adaptive changes in the vestibulo-ocular reflex system. During metamorphosis their vestibular and oculomotor coordinate systems undergo a 90 degree relative displacement. As a result, during swimming movements different types of compensatory eye movements are produced before and after metamorphosis by the same vestibular stimulation. Intracellular staining of central nervous connections in the flatfish with horseradish peroxidase revealed that in postmetamorphic fish secondary horizontal semicircular canal neurons contact vertical eye muscle motoneuron pools on both sides of the brain via pathways that are absent in all other vertebrates studied.

Adaptation, Physiological↗
PubMed1983

The locations of stapedius and tensor tympani motoneurons in the cat.

The numbers and locations of motoneurons to the stapedius and tensor tympani muscles were determined by retrograde transport of horseradish peroxidase. Stapedius motoneurons lay outside the traditionally recognized facial nucleus, in several distinct locations: (1) in the interface between the facial nucleus and the superior olive; (2) in a thin, scattered lamina of somewhat smaller cells spread dorsal to the facial nucleus; and (3) in a cluster located ventromedial to the rostral third of the facial nucleus. Some cells also lay dorsal to the superior olive or scattered in the reticular formation, just medial to the descending loop of the facial nerve. Tensor tympani motoneurons also lay outside the traditionally recognized trigeminal motor nucleus, in an area just ventral to it. Both motoneuron pools were large, producing innervation ratios that establish stapedius and tensor tympani among the most finely innervated muscles yet studied. The degree of intermingling of large and small cells in these pools may explain, in part, why it has been easier to identify slow muscle fibers physiologically in tensor tympani than in stapedius.

Animals↗
PubMed1983

Morphology of posterior canal related secondary vestibular neurons in rabbit and cat.

The morphology of secondary vertical vestibular neurons was investigated by injection of horseradish peroxidase (HRP) into cells connected to the posterior canal system in rabbits (lateral-eyed animals) and cats (frontal-eyed animals). Vestibular neurons were identified by stimulation with bipolar electrodes implanted into the ampullae of the anterior and posterior (PC) semicircular canals of pigmented rabbits; in the cat, these cells were identified by natural and electrical stimulation. Axons monosynaptically activated by PC stimulation were injected with HRP in the medial longitudinal fasciculus (MLF). These were later reconstructed by light microscopy after the brains had been processed with a DAB-CoCl2 method. In the rabbit the majority of the axons bifurcated after crossing the midline with one branch ascending and the other descending in the MLF. The ascending branches gave rise to collaterals that terminated in both the trochlear nucleus and the inferior rectus subdivision of the oculomotor nucleus. In addition some axons also sent collaterals into the paramedian pontine reticular formation, the periaqueductal grey and the interstitial nucleus of Cajal. The descending branches were followed to the caudal part of the medulla in the MLF and gave rise to collaterals terminating in the vestibular nuclei, the medullary reticular formation, the perihypoglossal nuclei, the abducens nucleus, and the facial nucleus. In another cell type axons crossed the midline without giving off any collaterals and proceeded caudally in the caudal MLF. The synaptic effects of the two types of cells were concluded to be excitatory and inhibitory, respectively. Cell bodies of contralaterally projecting neurons were located in either the medial or ventro-lateral vestibular nuclei. In the cat we observed two neuron classes, with contralaterally projecting axons, whose synaptic effects are presumably excitatory. Their cell somata were located in the medial vestibular nucleus. Termination patterns were similar to both the trochlear and oculomotor nuclei, but neither projected to the abducens nucleus. One class of neurons was almost identical to that found in the rabbit with the main axon bifurcating in the MLF. The second type lacked a descending branch in the MLF. Axon collaterals of the latter type crossed the midline within the oculomotor nucleus after terminating in the inferior rectus subdivision to reach a similar portion of the ipsilateral oculomotor nucleus. Collaterals of these axons also terminated bilaterally in the supraoculomotor region between trochlear and oculomotor nucleus, the interstitial nucleus of Cajal and prerubral loci (including the fields of Forel). In similarity to the rabbit, presumed inhibitory vestibular neurons were found with axons directed caudally in the MLF without brain stem collaterals.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Hydronephrosis: a new method to visualize vas afferens, efferens, and glomerular network.

We have developed a new preparation for in vivo visualization of the glomerular microcirculation, the vas afferens and the vas efferens. This preparation utilizes postischemic hydronephrosis (PIH) to destroy the renal tubular system while preserving a portion of the cortex. In this preparation, glomeruli and associated vasculature remained intact. Observations can be made with either incident light or transillumination. The inner diameter of the vas afferens, measured within 50 microns of the glomerular vascular pole, was 7.9 +/- 0.5 microns (N = 12; SEM) while that of the vas efferens was 7.7 +/- 0.5 microns (N = 12). Both vessels were narrower adjacent to the glomerulus; minimal diameters in this region were 4.5 +/- 0.5 microns (N = 10) and 4.3 +/- 0.5 microns (N = 11), respectively. A specialized round cell, which may act as a sphincter, was seen in the vas efferens. In a second series of experiments, blood velocity was measured in the vas afferens and efferens about 100 microns from the vascular pole. Mean control velocities at these sites were 5.9 +/- 0.9 (N = 14) and 4.6 +/- 1.3 (N = 9) mm X sec-1, respectively; diameters at these same sites were 10.3 +/- 0.6 microns and 11.2 +/- 0.7. During angiotensin II infusion (first series, 0.2 to 0.4 micrograms X min-1 X kg-1, i.v.) the vas efferens in the vicinity of the glomerulus constricted by 22% whereas the corresponding vas afferens showed no consistent response. During angiotensin II infusion, the filtration fraction (GFR/RPF) may, therefore, be elevated by an increased resistance in the vas efferens, particularly at the outflow point of the glomerulus. In the second series of experiments higher dosages of angiotensin II caused vasoconstriction of both vessels, especially at sites more distant from the glomerulus. Furthermore, the new approach is suitable for observing the flow direction within single capillaries of one third to one half of the glomerulus. Therefore, for the first time it is possible to determine the real flow direction in a three-dimensional way.

Angiotensin II↗
PubMed1983

Direct projections from vestibular nuclei to facial nucleus in cats.

Postsynaptic potentials were recorded from motoneurons in the facial nucleus in response to stimulation of the vestibular and trigeminal nerves. The motoneurons were identified by antidromic activation from their peripheral axons. Disynaptic excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) and mixed EPSP/IPSPs were recorded in response to vestibular nerve stimulation, ranging in latency from 0.9 to 2.1 ms, with most at 1.5 ms. Activity in secondary vestibular axons recorded within the facial nucleus occurred at a latency of 0.7-1.1 ms. The amplitudes of the vestibular postsynaptic potentials were small, generally less than a millivolt, but double shocks produced marked summation. The average time to peak of ipsilateral vestibular EPSPs, 1.1 ms, was faster than that of either ipsilateral IPSPs, 1.6 ms, or contralateral EPSPs, 1.4 ms. The double-spiked vestibular activity was detectable in double-peaked PSPs. Disynaptic EPSPs, ranging in latency from 2.0 to 3.0 ms, were recorded in response to trigeminal nerve stimulation. The average time to peak was 1.3 ms. The multiple-spiked activity of the trigeminal neurons was detectable in multipeaked EPSPs. Inhibitory ipsilateral effects (Vi IPSPs) were recorded twice as often as excitatory ipsilateral effects (Vi EPSPs), being found in 29% versus 15% of the motoneurons. Contralateral effects were found in 13% of the motoneurons studied, and almost all were excitatory. Analysis of synaptic potential shapes suggested that the excitatory and inhibitory vestibular synapses probably contact distal dendrites preferentially, with the excitatory connections being somewhat closer to the soma. The trigeminal inputs probably contact the facial motoneurons more extensively near the soma. Horseradish peroxidase was injected into the facial nucleus, and retrograde uptake by vestibular neurons was studied. The majority of filled vestibular neurons was ipsilateral to the injection site, especially in the medial vestibular nucleus, ventral y group, and supravestibular nucleus. On the contralateral side, filled vestibular cells were found almost exclusively in the medial nucleus. Filled cells were also noted in the trigeminal nucleus, predominantly ipsilaterally at all rostrocaudal levels. We have demonstrated monosynaptic projections to facial motoneurons from both vestibular and trigeminal nuclei. The trigeminal input is likely to be involved in facial reflexes, especially blinking and grimacing. The afferent vestibular population overlaps that going to the oculomotor and cervical motoneurons; these projections may be collaterals of single vestibular neurons.4+.

Animals↗
PubMed1983

Time course and variability of dark focus.

When the eye is deprived suddenly of visual stimulation, the accommodative system drifts from the previous state of accommodation to a state known as the dark focus. This condition also is known as night myopia. We measured the time course of this drift using a continuously recording infra-red optometer. The time course resembles an exponential decay function with a time constant of 1-3 seconds. The recovery of accommodation to the prior level after visual stimulation is restored suddenly has a time constant of 0.2-0.4 seconds. The state of accommodation in the dark depends on the state of accommodation prior to the onset of darkness. Our subjects showed a zone of accommodative inactivity rather than a single resting point of accommodation.

Accommodation, Ocular↗