Search PubMed⌕ Search

Biomedical subjects

K R Davis

Publications and source records attributed to K R Davis.

At least 55 records · Page 3Linked to original sources
PubMed1987

Comparison of magnetic resonance and roentgen ray computed tomography in dementia.

To compare the merits of magnetic resonance imaging (MRI) and roentgen ray computed tomography (CT) in assessing patients with dementia, we examined pairs of MR and CT brain images obtained from 26 patients with Alzheimer's disease (AD), eight patients with vascular or mixed dementia, and two patients with Parkinson's disease plus dementia. Magnetic resonance and CT images were independently rated on a qualitative scale of 0 (normal) to 3 (severely abnormal) in 39 separate brain regions. Ratios of anterolateral and third ventricular linear spans to linear skull spans were measured. Abnormalities in subcortical white matter and in hippocampus, enlargement of basal and sylvian cisterns, and ventriculomegaly were more evident on MR than CT scans, but qualitative ratings in all other brain regions were similar. Linear ventricular span ratios based on MR images did not differ significantly from those measured on CT. White matter abnormalities on MR were high signal foci on T2-weighted images whose pathologic substrate was uncertain; in a single case studied pathologically, no abnormalities were detected in brain regions that contained high signal foci. Dementia severity correlated with periventricular white matter abnormalities on both MR and CT images.

Aged↗
PubMed1987

Induction of defense responses in cultured parsley cells by plant cell wall fragments.

Cell suspension cultures of parsley (Petroselinum crispum) accumulated coumarin phytoalexins and exhibited increased beta-1,3-glucanase activity when treated with either a purified alpha-1,4-d-endopolygalacturonic acid lyase from Erwinia carotovora or oligogalacturonides solubilized from parsley cell walls by endopolygalacturonic acid lyase. Coumarin accumulation induced by the plant cell wall elicitor was preceded by increases in the activities of phenylalanine ammonia lyase (PAL), 4-coumarate:CoA ligase (4CL) and S-adenosyl-l-methionine:xanthotoxol O-methyltransferase (XMT). The time courses for the changes in these three enzyme activities were similar to those observed in cell cultures treated with a fungal glucan elicitor. The plant cell wall elicitor was found to act synergistically with the fungal glucan elicitor in the induction of coumarin phytoalexins. As much as a 10-fold stimulation in coumarin accumulation above the calculated additive response was observed in cell cultures treated with combinations of plant and fungal elicitors. The synergistic effect was also observed for the induction of PAL, 4CL, and XMT activities. These results demonstrate that plant cell wall elicitors induce at least two distinct biochemical responses in parsley cells and further support the role of oligogalacturonides as important regulators of plant defense.

Journal Article↗
PubMed1987

Embolization of epistaxis and juvenile nasopharyngeal angiofibromas.

This article reviews arterial embolization of epistaxis and juvenile nasopharyngeal angiofibromas. A protocol for the complete and rapid exploration of epistaxis is suggested that is based upon which arteries providing blood to the nasal fossa may be responsible for the bleeding and the most optimal way for their demonstration and evaluation. The relevant anatomy of the major arteries, their branches, and important anastomoses are described. The goals of embolization are to control severe or recurrent epistaxis, prevent recurrence if possible, and avoid occlusion of any vessels not responsible for the hemorrhage. The most appropriate embolic material is chosen, realizing that recurrence can be caused by the use of resorbable embolic material or by a very proximal or too complete embolization. Embolization may be used for specific causes of epistaxis including idiopathic, hereditary hemorraghic telangiectasia, hemorrhagic tumors, vascular malformations, trauma, disorders of hemostasis, and postsurgical problems. Juvenile nasopharyngeal angiofibromas are discussed with respect to their clinical presentation, classification, computed tomographic, MR imaging, and angiographic evaluation, treatment, future trends in treatment, and precautions and complications.

Adolescent↗
PubMed1986

Threatened carotid artery rupture: a complication of radical neck surgery.

Carotid artery rupture is an infrequent but highly dangerous postoperative complication of radical head and neck surgery. The principal predisposing factors are radiation therapy, infection, tissue necrosis, vessel exposure, and pharyngeal fistula formation. Actual or threatened carotid artery rupture has been most commonly managed by ligation of the involved vessel. We present a patient who showed signs of impending carotid artery rupture after both irradiation and radical neck surgery. Balloon embolization was employed in preference to traditional carotid artery ligation. The patient's risk factors for carotid artery rupture are analyzed and the application of balloon embolization is discussed.

Carotid Arteries↗
PubMed1986

Host-Pathogen Interactions : XXIX. Oligogalacturonides Released from Sodium Polypectate by Endopolygalacturonic Acid Lyase Are Elicitors of Phytoalexins in Soybean.

Recent studies have demonstrated that an apparently homogeneous preparation of an alpha-1,4-d-endopolygalacturonic acid lyase (EC 4.2.2.2) isolated from the phytopathogenic bacterium Erwinia carotovora induced phytoalexin accumulation in cotyledons of soybean (Glycine max [L.] Merr. cv Wayne) and that this pectin-degrading enzyme released heat-stable elicitors of phytoalexins from soybean cell walls, citrus pectin, and sodium polypectate (KR Davis et al. 1984 Plant Physiol 74: 52-60). The present paper reports the purification, by anion-exchange chromatography on QAE-Sephadex columns followed by gel-permeation chromatography on a Bio-Gel P-6 column, of the two fractions with highest specific elicitor activity present in a crude elicitor-preparation obtained by lyase treatment of sodium polypectate. Structural analysis of the fraction with highest specific elicitor activity indicated that the major, if not only, component was a decasaccharide of alpha-1,4-d-galactosyluronic acid that contained the expected product of lyase cleavage, 4-deoxy-beta-l-5-threohexopyranos-4-enyluronic acid (4,5-unsaturated galactosyluronic acid), at the nonreducing terminus. This modified decagalacturonide fraction exhibited half-maximum and maximum elicitor activity at 1 microgram/cotyledon (6 micromolar) and 5 micrograms/cotyledon (32 micromolar) galactosyluronic acid equivalents, respectively. Reducing 90 to 95% of the carboxyl groups of the galactosyluronic acid residues abolished the elicitor activity of the decagalacturonide fraction. The second most elicitor-active fraction contained mostly undeca-alpha-1,4-d-galactosyluronic acid that contained 4,5-unsaturated galactosyluronic acid at the nonreducing termini. This fraction exhibited half-maximum and maximum elicitor activity at approximately 3 micrograms/cotyledon (17 micromolar) and 6 micrograms/cotyledon (34 micromolar) galactosyluronic acid equivalents, respectively. These results confirm and extend previous observations that oligogalacturonides derived from the pectic polysaccharides of plant cell walls can serve as regulatory molecules that induce phytoalexin accumulation in soybean. These results are consistent with the hypothesis that oligogalacturonides play a role in disease resistance in plants.

Journal Article↗
PubMed1986

Multiphasic MR imaging: a new method for direct imaging of pulsatile CSF flow.

A new technique is described that allows for the creation of pure pulsatile flow magnetic resonance (MR) images in a single acquisition. Five to 16 electrocardiographically gated images spanning the entire cardiac cycle are obtained with use of a gradient-echo pulse sequence. The section can be varied from 4 mm thick to full thickness projection. Taken singly, each image provides direct assessment of flow direction and velocity. Subtraction of image pairs eliminates signal detected from stationary protons, producing images of pulsatile flow. In this study the technique was used to image the flow of cerebrospinal fluid (CSF) in healthy subjects and in one patient with syringohydromyelia. The data suggest that multiphasic MR imaging provides a powerful means for the noninvasive assessment of CSF pulsatile flow dynamics and may have potential clinical application for the investigation of a variety of abnormalities such as normal pressure hydrocephalus, syrinx, and spinal block.

Cerebrospinal Fluid↗
PubMed1986

Assessment of ventricular shunt patency by sonography: a new noninvasive test.

This report describes a new test of patency of the ventricular component of a ventriculoperitoneal shunt that precludes injection into the shunt reservoir. Preliminary clinical experience confirms that digital compression of the ventricular shunt reservoir (Cordis standard and pediatric reservoir), while occluding the shunt distal to the reservoir, generates microbubbles that increase the echogenicity of the catheter, demonstrating shunt patency. In vitro, the extrusion of microbubbles from catheter side holes can be imaged during digital compression of the reservoir, but so far this has not been imaged in patients as a direct sign of shunt patency. A sonographic means of assessing shunt function offers the advantage of simultaneously imaging the ventricular catheter, determining its location, and assessing the etiology of shunt failure. Its usefulness is limited to pediatric cases in which an adequate transfontanelle cranial sonographic study can be obtained and to individuals with large craniotomy defects.

Adolescent↗
PubMed1986

MR and CT of occult vascular malformations of the brain.

The need for improved specificity in the diagnosis of "occult" vascular malformations led to the use of MR in suspected cases in order to determine MR's potential for improved diagnostic accuracy. Six patients with six lesions histologically diagnosed as vascular malformation after partial (1) or complete (5) microsurgical excision were studied by CT, MR, and selective magnification subtraction angiography. In all cases, the cerebral lesions were apparently solitary and were visible as focal lesions on both CT and MR. Since angiography failed to reveal the pathologic blood vessels of the lesions, and no arteriovenous shunting was evident, these lesions were termed vascular malformations occult to angiography (VMOTA). Angiography revealed a mass effect in only two cases. MR did not reveal additional vascular malformations missed by CT. In each case, MR, which was performed in an attempt to support the diagnosis suggested by CT, did in fact do so by revealing signal abnormalities indicative of nonacute hemorrhage within the lesion on T1- and T2-weighted pulse sequences. Although, as on CT, MR features of these lesions were found to be nonspecific, the MR criteria reinforced the probable diagnosis of VMOTA in an additional 30 cases that had shown similar nonspecific CT features. In this second group, excluded from this study, in which histologic verification was not obtained because of perceived hazards of surgery, the increased assurance regarding the diagnosis led to proton-beam therapy without histologic verification in 18 cases. It is concluded that MR can provide significant improvement in the accuracy of diagnosing VMOTA beyond that obtainable just by plain and contrast-enhanced CT.

Adult↗
PubMed1985

High-resolution surface-coil imaging of lumbar disk disease.

Seventeen patients with lumbar disk disease were studied using a prototype magnetic resonance (MR) surface coil. The high signal-to-noise ratio achieved with the surface coil permitted increases in spatial resolution to 0.9 X 0.9 mm in-plane resolution with 5 mm slice thickness. The surface coil was also compatible with multiplanar, multiecho imaging techniques. The spatial resolution achieved in this study was nearly equivalent to that achieved by state-of-the-art computed tomographic (CT) scanners, and MR showed a superior range of soft-tissue contrast. One significant limitation of MR was its inability to demonstrate small calcifications. Nevertheless, MR imaging provided diagnostic information comparable to CT or myelography in a completely noninvasive manner. With further technical advances, MR is likely to become the initial procedure of choice for evaluating patients with suspected lumbar disk disease.

Humans↗
PubMed1985

Cervical diastematomyelia presenting in adulthood. Case report.

A case of cervical diastematomyelia in an adult is reported. The patient first noted sensory and motor symptoms at 34 years of age after two episodes of cervical trauma. Metrizamide computerized tomography myelography of the cervical spine and cord showed the region of diastematomyelia and revealed a spur containing both bone and fat tissue projecting into the spinal canal and cord. The spur arose from the laminae and spinous processes of C-2 and C-3, and was successfully excised. Postoperatively, the patient's deficits gradually improved. The literature concerning adult cervical diastematomyelia is reviewed.

Adult↗
PubMed1984

Nuclear magnetic resonance imaging in evaluation of clinical stroke syndromes.

Proton nuclear magnetic resonance (NMR) imaging was performed on normal volunteers and patients with various types of clinical strokes. True three-dimensional volumetric data were obtained for subsequent reconstruction of images at various orientations, including transverse, coronal, and sagittal, and for specific matching to x-ray computed tomographic planes. A variety of radiofrequency pulse sequences was used to generate images weighted by the NMR parameters spin density (p) and spin-lattice (T1) and spin-spin (T2) relaxation times. Quantitative T1 data and qualitative T2 information were obtained from appropriate sequences. Proton NMR images embodying T1 information provided adequate delineation of normal intracranial anatomical structure and a high level of gray matter-white matter contrast; high lesion detection sensitivity in various clinical forms of stroke was seen in images providing both T1 and T2 information. T1 and T2 relaxation times were prolonged in embolic, thrombotic, and watershed infarctions as well as in lacunae; shortening of T1 and T2 was found in hematomas. Serpiginous vessels in an arteriovenous malformation were seen that had particular pulse sequences.

Cerebellar Diseases↗
PubMed1984

Computed tomography in experimental allergic encephalomyelitis--preliminary results.

Four dogs were immunized with a mixture of spinal cord homogenate and complete Freund's adjuvant. One of these dogs developed hyperacute allergic encephalomyelitis. Cranial computed tomography in this animal demonstrated a low absorption area in the internal capsule that corresponded to the pathologic lesion. Computed tomography scanning may be a useful tool in monitoring experimental allergic encephalomyelitis.

Animals↗
PubMed1984

Host-Pathogen Interactions : XXV. Endopolygalacturonic Acid Lyase from Erwinia carotovora Elicits Phytoalexin Accumulation by Releasing Plant Cell Wall Fragments.

Heat-labile elicitors of phytoalexin accumulation in soybeans (Glycine max L. Merr. cv Wayne) were detected in culture filtrates of Erwinia carotovora grown on a defined medium containing citrus pectin as the sole carbon source. The heat-labile elicitors were highly purified by cation-exchange chromatography on a CM-Sephadex (C-50) column, followed by agarose-affinity chromatography on a Bio-Gel A-0.5m gel filtration column. The heat-labile elicitor activity co-purified with two alpha-1,4-endopolygalacturonic acid lyases (EC 4.2.2.2). Endopolygalacturonic acid lyase activity appeared to be necessary for elicitor activity because heat-inactivated enzyme preparations did not elicit phytoalexins. The purified endopolygalacturonic acid lyases elicited pterocarpan phytoalexins at microbial-inhibitory concentrations in the soybean-cotyledon bioassay when applied at a concentration of 55 nanograms per milliliter (1 x 10(-9) molar). One of these lyases released heat-stable elicitors from soybean cell walls, citrus pectin, and sodium polypectate. The heat-stable elicitor-active material solubilized from soybean cell walls by the lyase was composed of at least 90% (w/v) uronosyl residues. These results demonstrate that endopolygalacturonic acid lyase elicits phytoalexin accumulation by releasing fragments from pectic polysaccharides in plant cell walls.

Journal Article↗
PubMed1984

Fat deposition in the cavernous sinus in Cushing disease.

Fat density in the cavernous sinus on computed tomography (CT) is described in 6 out of 16 (37.5%) patients with Cushing disease. This finding may aid in making a specific diagnosis in patients with a pituitary mass. It was not seen in 30 random CT studies of the sella; however, parasellar fat was incidentally noted in one patient with acromegaly.

Adipose Tissue↗
PubMed1984

Myocardial ischemia during intravenous DSA in patients with cardiac disease.

A prospective study was performed for 48 patients who had histories of angina and were referred for digital subtraction angiography (DSA). Cardiac disease was graded according to the American Heart Association (AHA) functional classification system. Each patient received 2-5 injections of 40-ml diatrizoate meglumine and diatrizoate sodium (Renografin-76, Angiovist-370, or MD-76) at 15 ml per second in the superior vena cava. Of the 28 patients in functional Classes I or II (no or slight limitation of activity), 11% had angina and 32% had definite ischemic ECG changes after the DSA injections. Of the 19 patients in functional Class III (marked limitation of activity), 63% had angina, and 58% had definite ischemic ECG changes after the injections. One patient in functional Class IV (total disability) developed ventricular fibrillation after the second injection. These observed cardiac effects following bolus injections of hypertonic ionic contrast media indicate that special precautions are necessary when performing intravenous DSA examinations on this group of high risk patients.

Aged↗
PubMed1984

Complications of intravenous DSA performed for carotid artery disease: a prospective study.

One hundred and two patients, who were being evaluated for carotid artery disease, were prospectively studied for complications occurring as a result of intravenous digital subtraction angiography (DSA). We recorded the type, number, and outcome of complications and reviewed the amount of contrast material used, along with the patient's age and medical history for possible correlation with increased complications. There were 55 total complications or side effects involving 37 patients. Central nervous system (CNS) complications included six major-transient and one major-permanent complication. Systemic complications included 20 major-transient and two major-permanent events. The patient's age and the amount of contrast material used did not appear to be significant risk factors. Complications in our series were significantly higher than previous DSA reports and published data on conventional angiography studies. Many of our patients were in a relatively high risk group, including 74 patients who had multisystem disease and 30 who had histories of angina.

Aged↗