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Biomedical subjects

S L Dawson

Publications and source records attributed to S L Dawson.

71 records · Page 4Linked to original sources
PubMed1985

Percutaneous drainage of pyogenic liver abscesses.

This report summarizes the results of percutaneous catheter drainage in 23 cases of primary or secondary pyogenic liver abscess. The overall success rate was 76%. Only three (60%) of five cases of secondary abscess (infected hematoma or infected tumor) were cured with catheter drainage, but 11 (91%) of the last 12 primary pyogenic abscesses were drained successfully. Six patients with abscesses of less than 4 cm in diameter required catheter drainage for less than 72 hr. Although six abscesses in the series appeared septated or multiloculated, only one required more than a single catheter for curative drainage. Diagnostic and technical considerations for successful drainage of hepatic abscesses are discussed. The differential diagnosis includes echinococcal disease and hepatic amebiasis. Therapeutically, specific measures should be taken to ensure proper catheter position to prevent contamination of the subphrenic, perihepatic, and pleural spaces. Percutaneous catheter drainage should be attempted as a first choice of treatment in all pyogenic hepatic abscesses.

Diagnosis, Differential↗
PubMed1985

Regional changes in EEG power and coherence during cognition: intensive study of two individuals.

Two men underwent weekly electroencephalogram (EEG) recordings while living for several months in a controlled laboratory environment. Data collected from an eight-channel EEG during a resting period and during performance of two cognitive tasks (word fluency and mental imagery) were subjected to spectral analysis. Statistical analyses on power and coherence were conducted for each subject separately, to determine whether that individual showed a characteristic pattern of EEG activity for a given cognitive task which was stable over time. Although substantial individual differences were observed, particularly for the theta band, both subjects showed changes in the spectral information over the anterior left hemisphere during the word fluency task.

Cerebral Cortex↗
PubMed1984

Asymmetric EEG changes as method actors generated emotions.

Nine method actors recalled personal experiences to create emotional states of sexual arousal or depression. Electroencephalographic (EEG) data recorded from left and right frontal, central, parietal and occipital locations were spectrally analyzed for power in each major frequency band and for coherence among all pairs of channels. Contrasts between the emotion conditions showed less alpha power (greater activation) over the right hemisphere for sexual arousal than for depression. Analysis of coherence topography showed higher coherence in right central and posterior regions during the sexual arousal condition. These data are consistent with previous evidence of right hemisphere contribution to sexual arousal and suggest further that asymmetric patterns of brain activity may be associated with specific emotional states.

Adult↗
PubMed1984

Iron status and brain function: serum ferritin levels associated with asymmetries of cortical electrophysiology and cognitive performance.

Levels of serum ferritin and iron were examined in relation to cognitive performance and quantitative EEG measures in 69 normal university students. Higher levels of serum ferritin were associated with greater activation of the left hemisphere relative to the right, indicated by less power in the EEG spectra from left hemisphere electrodes. Iron status was significantly related to cognitive performance on two of the cognitive tasks, and these relationships were consistent with the EEG asymmetries: higher ferritin predicted greater verbal fluency but poorer nonverbal auditory task performance. These results suggest that body iron stores are relevant to specific neurophysiological processes supporting attention.

Cognition↗
PubMed1984

Serious complications following transgression of the pleural space in drainage procedures.

Transgression of the parietal pleura may occur during placement of interventional drainage catheters into the liver and upper abdomen, and occasionally results in lethal complications. In a review of nearly 2,000 such procedures, four deaths were found to be related directly to pleural transgression from biliary drainage. Therefore, the anatomy of the pleura pertinent to abdominal needle or catheter insertion was analyzed. In 14 cadavers examined after intercostal needle insertion into the liver, needles inserted through the 9th intercostal space or higher punctured the pleura in all but one cadaver. Radiologic studies of 15 clinical cases revealed that elderly patients rarely depressed the diaphragm below the 9th intercostal space, which increases the risk of unsuspected puncture of the pleura. Review of clinical material revealed that diagnostic needle puncture through the parietal pleura carries far less risk than placement of a long-term drainage catheter. Methods to avoid puncture of the pleura, as well as the technical problems involved in such maneuvers, are given.

Catheterization↗
PubMed1984

Severe esophageal strictures: indications for balloon catheter dilatation.

Bougienage of esophageal strictures is a traditional method of therapy for patients who present with a stricture sufficiently large to permit passage of a mercury-weighted rubber bougie. However, when the residual lumen is smaller than 12 mm diameter, bougie dilatation acquires a prohibitively high risk of esophageal perforation. Twenty patients who had severe esophageal strictures have undergone surgical repair or Eder-Puestow dilatation assisted by guidewire. Fluoroscopic balloon catheter dilatation obviated surgery and allowed subsequent standard bougienage both in hospital and at home performed by the patient. We discuss indications, technique, results, and complications.

Angioplasty, Balloon↗
PubMed1984

Abscess-fistula association: radiologic recognition and percutaneous management.

Thirty-five patients with postoperative enteric and/or biliary fistulae were diagnosed and treated by percutaneous catheter drainage. All were initially considered to have postoperative abdominal abscesses, and the enteric or biliary communications were unrecognized before radiologic intervention. In addition, at the time of initial catheter insertion, only six of the 35 abscesses were recognized as being associated with an underlying fistula. In the other 29 patients the fistulae were found either by clinical follow-up or contrast sinogram after 24-72 hr of catheter drainage. Percutaneous catheter drainage was the definitive treatment in 28 (80%) of the 35 patients. The seven failures were either from inadequate catheter positioning or inability to treat the primary cause of the fistula (e.g., radiation enteritis, perforated cancer). These data suggest that even abscesses with underlying fistulae, traditionally an indication for surgical intervention, may be successfully managed by percutaneous methods.

Abscess↗
PubMed1980

The contrecoup phenomenon. Reappraisal of a classic problem.

We describe briefly and comment upon the salient strengths and limitations of the major published theories that purport to explain the mechanism of contrecoup cerebrocortical contusions. Through the application of mechanical principles, we then present a modification, clarification, and expansion of selected aspects of several theories. Our final formulation emphasizes the injurious potential of nonuniform compressive stress and the relationship between brain lag and rotationally induced injury. The resulting theory remains faithful to the laws of physics while explaining the location and distribution of cerebrocortical contusions opposite the site of a moving head impact.

Biomechanical Phenomena↗
PubMedDate not supplied

Peptide-derived self-assembled monolayers: adsorption of N-stearoyl L-cysteine methyl ester on gold.

The work reported herein concerns the assembly of N-stearoyl L-cysteine methyl ester [CH3(CH2)16COCysOMe, 1] on the surface of gold. This compound serves as a simple model of a related polypeptide, which has been designed to adopt a beta-sheet architecture on metallic and oxide surfaces. We describe the preparation of monolayers of 1, and characterization of these layers via ellipsometry, vibrational spectroscopy and X-ray photoelectron spectroscopy. The results are most consistent with a disordered array of the alkyl chains, in which close packing is frustrated by a mismatch in the cross-sectional areas of the cysteinyl ester head group and the stearoyl chains of the thiol. Despite the disorder, the alkyl chains form a hydrophobic surface layer, with an advancing contact angle for water comparable to that observed for octadecanethiol on gold.

Adsorption↗
PubMedDate not supplied

Transluminal radiofrequency tissue ablation with use of metallic stents.

PURPOSE: To determine if transluminal coagulative necrosis can be induced by applying radiofrequency (RF) energy to indwelling metallic stents. MATERIALS AND METHODS: RF energy was applied to metallic alloy stents (20-68 mm length, 5-16 mm diameter) in tissue phantom (n = 31), ex vivo bovine liver (n = 10), and in vivo porcine hepatic veins (n = 4). For ex vivo and in vivo liver experiments, RF was applied for 5-6 minutes, titrating generator output to produce 85 degrees-95 degrees C temperatures at the stent surface. Local and remote temperature sensing was performed. Imaging and pathologic studies documented the extent of coagulation necrosis. RESULTS: Phantom studies demonstrated uniform temperature distribution along the entire stent length for all Elgiloy stents powered for 2 minutes with a minimum of 120 watts. Shorter stents required less power or reduced time to achieve uniform temperature. In ex vivo liver, 25-mm stents (n = 5) showed 8-10 mm of uniform circumferential coagulation necrosis along the entire stent length. Fifty-millimeter stents showed less uniform coagulation necrosis. For the in vivo stents (20 mm), 8-10 mm of uniform circumferential coagulation necrosis surrounded the stent along its entire length. CONCLUSION: Metallic stents can be used to deliver transluminal RF energy from an external source, inducing heat deposition with resultant circumferential tissue coagulation. Clinical applications might include reduction of intimal proliferation in vascular diseases and/or treatment of periluminal tumors compressing the bile ducts, the urethra, or other luminal structures.

Animals↗
PubMedDate not supplied

Dynamic but not static cerebral autoregulation is impaired in acute ischaemic stroke.

It remains unclear as to whether dynamic and static cerebral autoregulation (CA) are impaired in acute ischaemic stroke, and whether these changes are related to stroke subtype. This could have important implications with regard to post-stroke prognosis and the management of blood pressure (BP) in the acute post-ictal period. Using transcranial Doppler ultrasonography and non-invasive manipulation of BP, we compared both mechanisms in 61 patients with ischaemic stroke within 96 h of ictus, and 54 age- and sex-matched controls. There was no difference in static and dynamic CA indices between the various stroke subtypes. Combining all stroke subtypes dynamic autoregulation, as measured using thigh cuff release, was significantly impaired in both the affected and non-affected stroke hemispheres compared to controls (mean autoregulation index 4.1 +/- 3.3, 4.8 +/- 3.1 and 6.2 +/- 2.3, respectively, p < 0.05). By comparison static autoregulation, assessed using isometric hand grip and thigh cuff inflation, was not significantly different. In conclusion, dynamic but not static CA appears to be globally impaired in acute ischaemic stroke. This deserves further study and may identify possibilities for therapeutic intervention.

Aged↗