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Biomedical subjects

R A Baker

Publications and source records attributed to R A Baker.

At least 109 records · Page 6Linked to original sources
PubMed1977

Myelography with metrizamide in infants and children.

Myelography with metrizamide (Amipaque) was performed in 46 infants and children. The contrast medium was rated as excellent. The examinations demonstrated more anatomic detail than is available from either myelography with oily contrast media or gas alone. The adverse reactions were at acceptable clinical levels.

Adolescent↗
PubMed1977

Ventriculography with metrizamide in children.

Experiences from 24 ventriculographies with metrizamide (Amipaque) in children are reported. The dose used was 3 to 6 ml 200 mg I/ml in most cases. Ventriculography with metrizamide has been most useful for evaluating obstructive lesions related to the aqueduct or within the third ventricle. The large volume may be required in cases with great ventricular dilatation. Polytomography is a useful addition in many cases but it is not a constant requirement.

Adolescent↗
PubMed1977

Gas myelography.

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Adolescent↗
PubMed1976

Light-driven proton translocations in Halobacterium halobium.

The purple membrane of Halobacterium halobium acts as a light-driven proton pump, ejecting protons from the cell interior into the medium and generating electrochemical proton gradient across the cell membrane. However, the type response of cells to light as measured with a pH electrode in the medium consists of an initial net inflow of protons which subsides and is then replaced by a net outflow which exponentially approaches a new lower steady state pH level. When the light turned off a small transient acidification occurs before the pH returns to the original dark level. We present experiments suggesting that the initial inflow of protons is triggered by the beginning ejection of protons through the purple membrane and that the initial inflow rate is larger than the continuing light-driven outflow. When the initial inflow has decreased exponentially to a small value, the outflow dominates and causes the net acidification of the medium. The initial inflow is apparently driven by a pre-existing electrochemical gradient across the membrane, which the cells can maintain for extended times in the absence of light and oxygen. Treatments which collapse this gradient such as addition of small concentrations of uncouplers abolish the initial inflow. The triggered inflow occurs through the ATPase and is accompanied by ATP synthesis. Inhibitors of the ATPase such as N,N'-dicyclohexylcarbodiimide (DCCD) inhibit ATP synthesis and abolish the inflow. They also abolish the transient light-off acidification, which is apparently caused by a short burst of ATP hydrolysis before the enzyme is blocked by its endogenous inhibitor. Similar transient inflows and outflows of protons are also observed when anaerobic cells are exposed to short oxygen pulses.

Bacteriorhodopsins↗
PubMed1976

Energy coupling in the active transport of amino acids by bacteriohodopsin-containing cells of Halobacterium holobium.

Growth of Halobacterium halobium under illumination with limiting aeration induces bacteriorhodopsin formation and renders the cells capable of photophosphorylation. Cells depleted of endogenous reserves by a starvation treatment were used to investigate the means by which energy is coupled to the active transport of [14C]proline, -leucine, and -histidine. Proline was readily accumulated by irradiated cells under anaerobiosis even when the photophosphorylation was abolished by the adenosine triphosphatase inhibitor N,N'-dicyclohexylcarbodimiide (DCCD). The uptake of proline in the dark was limited except when the cells were allowed to accumulate adenosine 5'-triphosphate (ATP) by prior light exposure or by the oxidation of glycerol. DCCD inhibited this dark uptake. These findings essentially support Mitchell's chemiosmotic theory of active transport. The driving force is apparently the proton-motive force developed when protons are extruded from irradiated bacteriorhodopsin or by the dydrolysis of ATP by membrane adenosine triphosphatase. Carbonylcyanide m-chlorophenylhydrazone (CCCP), a proton permeant known to abolish membrane potential, was a strong inhibitor of proline uptake. Leucine transport was also apparently driven by proton-motive force, although its kinetic properties differed from the proline system. Histidine transport is apparently not a chemiosmotic system. Dark- or light-exposed cells show comparable initial rats of histidine uptake, and these processes were only partially inhibited by DCCD or CCCP. The histidine system apparently does not utilize ATP per se since comparable rates of uptake were exhibited by cells of differing intracellular ATP levels. Irradiated cells did effect a greater total accumulation of histidine than dark-exposed cells. These findings suggest that ATP is needed for sustained transport.

Adenosine Triphosphatases↗
PubMed1976

Medullary arteries in cerebral neoplasms.

In cerebral neoplasms, the visibility of long segments of the medullary arteries indicates white matter involvement by infiltrative or compressive disturbances. Relating the mass effect to the position of the medullary arteries should allow for differentiating a primary from a secondary avascular neoplasm. When the neoplasm is vascular, the presence of neovascularity with the medullary arteries is likely to signify a high degree of anaplasia.

Brain Neoplasms↗
PubMed1976

Xeroradiography. Its value in gas myelography.

Electrostatic imaging with its capacity for enhancing borders improves radiographic demonstration of gas-soft tissue interfaces in gas myelography. Its wide recording latitude also provides satisfactory delineation through areas of widely varying photon absorption. Xeroradiogrphy surmounts the paradox wherein contrast and latitude are inversely related so that the combination of both high contrast and broad latitude are simultaneously used to advantage. The xerogram, especially in the thoracic region, may be sufficiently diagnostic so that tomography is not necessary. Where additional information is required, tomographic xeroradiography can provide diagnostic information not perceptible on film tomograms.

Adenocarcinoma↗
PubMed1975

Xerographic applications in neuroradiology. A comparison with conventional film imaging.

The capacity of electrostatic imaging for edge enhancement and wide latitude recording can improve visualization in neuroradiologic studies using low differential absorption contrast agents. Gas myelography and pneumoencephalography show the most satisfactory improvement in visualization. Tomography combined with xerography enhances definition further, but with gas myelography, especially in the thoracic region, plain xeroradiographic definition is frequently diagnostic.

Cerebral Ventriculography↗
PubMed1975

Lateral projections with inclined head for angiography of basal cerebral aneurysms.

Inclined lateral projections prove useful in defining aneurysms situated about the circle of Willis. For these projections, the x-ray tube and film changer are positioned as for a true lateral projection. The MCA lateral projection (patient's head inclined away from the side of injection) is valuable in investigating aneurysms of the internal carotid artery, posterior communicating artery and middle cerebral artery trifurcation. The ACA lateral projection (head inclined toward the side of injection) may be used to define aneurysms in the region of the anterior communicating artery.

Carotid Artery Diseases↗
PubMed1975

Segmental intervertebral anastomosis in subclavian steal.

Segmental intervertebral arterial connections originate from normal vascular channels which are commonly seen on selective vertebral arteriography. In subclavian steal, these vessels can hypertrophy and form important collateral pathways. The significance of their haemodynamic contributions may be assessed by their multiplicity and calibre. Lateral or oblique projections in addition to frontal visualization may be required to differentiate the various transcervical channels which lie either anterior or posterior to the vertebral bodies.

Adult↗
PubMed1967

Acropetal movement of auxin: dependence on temperature.

The amounts of radioactive indole-3-acetic acid that moved, both basipetally and acropetally, through short sections of bean epicotyl were measured at 15 degrees and 25 degrees C in the presence and absence of 2,3,5-triiodobenzoic acid. Low temperature and this second compound each inhibited acropetal efflux of indole 3-acetic acid more than they did the influx. Results are interpreted as supporting a metabolically dependent component of the acropetal movement of auxin in bean epicotyls.

Benzoates↗