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Biomedical subjects

D W Jones

Publications and source records attributed to D W Jones.

At least 19 recordsLinked to original sources
PubMed1992

The usefulness of echocardiography in the surgical management of infants with congenital heart disease.

Between January 1988 and August 1991, at The Children's Heart Center, Atlanta, 83 infants with congenital heart defects were diagnosed by echocardiography and underwent surgery without cardiac catheterization. The diagnostic categories included 46 infants with left heart obstructive lesions, 19 infants with cyanotic heart lesions, and 18 infants with miscellaneous lesions. Forty-five infants (55%) underwent surgery under cardiopulmonary bypass. There were three errors in diagnosis, yielding a diagnostic accuracy of 95%. Many infants with congenital heart disease can be accurately and completely diagnosed by echocardiography and can safely undergo surgery without cardiac catheterization.

Aortic Coarctation↗
PubMed1992

A comparison of xenon-133 and xenon-127 for the determination of regional cerebral blood flow measured by dynamic SPECT.

Phantom studies and cerebral blood flow (CBF) measurements in 11 normal subjects at rest were performed by single photon emission tomography (SPECT) with Xe-133 (16 mm full-width at half-maximum [FWHM] collimation) and Xe-127 (16 mm, 12 mm, and 9 mm FWHM collimation). The phantom results clearly illustrated the feasibility of Xe-127 studies and the advantage of Xe-127 over Xe-133 for equivalent patient dose exposures. CBF values obtained with Xe-127 were comparable to those of Xe-133 for the 16 mm collimator, although higher flow values were found with the better resolution, probably because of reduced partial volume effects. The correlations between the various groups of examinations were high, except for the Xe-133 and Xe-127 16 mm collimator groups. Xe-127 allows a considerable increase in the resolution of the images, while exposing the patient to a lower radiation dose. Potential limitations because of higher energy penetrating photons from Xe-127 were not observed in this specially shielded equipment.

Adolescent↗
PubMed1992

Effect of phenylpropanolamine hydrochloride on blood pressure in Korean patients with hypertension controlled by hydrochlorothiazide.

The effect of 10 oral doses of phenylpropanolamine hydrochloride 25 mg four times a day on blood pressure and heart rate in Korean patients with hypertension controlled by hydrochlorothiazide was studied. A randomized, placebo-controlled, crossover, double-blind study design was used. Twenty Korean patients with mild hypertension controlled by hydrochlorothiazide were recruited from an ambulatory-care clinic. Blood pressure and heart rate were measured in triplicate before treatment, after a five-day washout period between phases of treatment, and two hours after the last dose in each phase of treatment. Eighteen patients completed both phases of treatment, and one patient completed only the placebo phase. Mean baseline values for systolic and diastolic blood pressures and heart rate before the placebo phase did not significantly differ from mean baseline values before the phenylpropanolamine phase. Comparison of mean baseline values for systolic and diastolic blood pressures and heart rate with mean after-treatment values showed no clinically relevant or statistically significant changes for the 19 patients who completed the placebo phase or the 18 patients who completed the phenylpropanolamine phase. There was no significant difference between the mean change in systolic blood pressure, diastolic blood pressure, or heart rate when the phenylpropanolamine phase was compared with the placebo phase. Phenylpropanolamine hydrochloride 25 mg p.o. four times a day (total, 10 doses) given to Korean patients with hypertension controlled by hydrochlorothiazide did not affect blood pressure or heart rate according to single-point outcome measurements.

Administration, Oral↗
PubMed1991

The distribution of cerebral muscarinic acetylcholine receptors in vivo in patients with dementia. A controlled study with 123IQNB and single photon emission computed tomography.

A high-affinity muscarinic receptor antagonist, 123IQNB (3-quinuclidinyl-4-iodobenzilate labeled with iodine 123), was used with single photon emission computed tomography to image muscarinic acetylcholine receptors in 14 patients with dementia and in 11 healthy controls. High-resolution single photon emission computed tomographic scanning was performed 21 hours after the intravenous administration of approximately 5 mCi of IQNB. In normal subjects, the images of retained ligand showed a consistent regional pattern that correlated with postmortem studies of the relative distribution of muscarinic receptors in the normal human brain, having high radioactivity counts in the basal ganglia, occipital cortex, and insular cortex, low counts in the thalamus, and virtually no counts in the cerebellum. Eight of 12 patients with a clinical diagnosis of Alzheimer's disease had obvious focal cortical defects in either frontal or posterior temporal cortex. Both patients with a clinical diagnosis of Pick's disease had obvious frontal and anterior temporal defects. A region of interest statistical analysis of relative regional activity revealed a significant reduction bilaterally in the posterior temporal cortex of the patients with Alzheimer's disease compared with controls. This study demonstrates the practicability of acetylcholine receptor imaging with 123IQNB and single photon emission computed tomography. The data suggest that focal abnormalities in muscarinic binding in vivo may characterize some patients with Alzheimer's disease and Pick's disease, but further studies are needed to address questions about partial volume artifacts and receptor quantification.

Adult↗
PubMed1991

Clinical implications of resilient denture lining material research. Part II: Gelation and flow properties of tissue conditioners.

The clinical effectiveness of tissue conditioners and functional impression materials is influenced by their gelation and flow properties. Laboratory tests were previously conducted that simulated the conditions of clinical use to the extent possible on six commercial intraoral-gelling resilient denture liners. The liners were found to vary significantly in their gelation times and to flow throughout the 7-day study. Their initial flow after mixing was influenced most by the time of loading. While extrapolations to the clinical environment require caution, the results of this study imply that the dentist should (1) adapt clinical techniques to the gelation times of particular materials, (2) reduce the initial flow of some materials by delaying denture placement on the supporting mucosa, and (3) expect the materials to be effective tissue conditioners for at least 7 days.

Acrylic Resins↗
PubMed1991

In vivo fungal presence and growth on two resilient denture liners.

To determine whether two intraoral-setting resilient denture liners supported the in vivo presence or growth of oral commensal fungi, the liners were randomly placed in the mandibular complete dentures of 14 patients. Cytologic smears were made from the liner surfaces at 1 hour and 1, 2, 7, 14 and 30 days after intraoral placement. Yeast forms were observed in six patient trials of material A and in two trials of material B. Hyphae were observed in only one patient trial of material A and in two trials of material B. When yeast forms and hyphae findings were combined and were considered as indicative of fungal presence or growth, the prevalence up to 30 days was seven for material A and four for material B. Statistical analysis revealed no significant difference in the prevalence of fungal presence or growth between the two resilient denture liners tested.

Acrylic Resins↗
PubMed1991

Gel strength and rate of gelation of soft polymers.

A rheometer was used to characterize the gelation rate of six commercial short- to medium-term (chairside intra-oral gelation) denture soft-lining materials. Shear puncture force was measured from one to 60 days for six short- to medium-term materials as well as for three heat-cured (polymerizable) materials. The observed increase in puncture force with age of the specimen was considered to be a function of increased polymer chain entanglement and/or loss of plasticizer. Reduction in puncture force with age occurred for some materials as a result of hydration of the polymer gel. Rheometer setting time (gelation rate) and puncture force values for the intra-oral gelation materials were influenced by the quantity of ethyl alcohol present in the mixing liquid. In general, the higher the level of ethyl alcohol, the shorter the gelation time and the stronger the gel. The characterization of the properties may help develop improved prosthodontic treatment procedures, and allow better management of soft-tissue recovery following trauma.

Denture Liners↗
PubMed1991

Detection of protein C deficiency during oral anticoagulant therapy--use of the protein C:factor VII ratio.

Laboratory diagnosis of protein C deficiency is complicated by the fact that many patients referred for investigation are already being treated with oral anticoagulants. Protein C and factor VII have similar half lives and by using the protein C:factor VII ratio we hoped to be able to detect protein C deficiency in patients receiving oral anticoagulants. We have studied activity levels of protein C and factor VII to produce protein C:factor VII activity ratios in 105 patients receiving oral anticoagulants, 42 normal subjects, and nine patients with known inherited protein C deficiency. The mean ratios for these groups were 1.38, 1.12 and 0.63 respectively. In patients receiving oral anticoagulants, the protein C level showed a poor correlation with the international normalized ratio (INR) value. Reference ranges for protein C at different levels of anticoagulation were therefore considered unsuitable for the identification of inherited protein C deficiency. Five patients with inherited protein C deficiency were studied with and without oral anticoagulation; their protein C:factor VII ratios remained relatively unchanged, despite alterations in the level of the individual proteins. These results suggest that measurement of the protein C:factor VII ratio may help to identify patients with inherited protein C deficiency whilst on oral anticoagulants.

Adolescent↗
PubMed1991

An in vivo and in vitro study of the loss of plasticizer from soft polymer-gel materials.

Polymer-gel materials used as short-term denture soft linings are blended with plasticizers to lower the glass transition temperature (Tg). A lower Tg allows for greater polymer chain mobility, thus producing a more flexible material. The present work evaluated the loss of plasticizers due to leaching both in vivo and in vitro. Two commercial denture soft-lining materials (A and B) were tested. These were both poly(ethyl methacrylate) polymers, blended with alcohol and phthalate esters. A clinical study was conducted in which patients wore, sequentially, dentures bearing (on separate occasions) each of the two soft-polymer lining materials. The two materials A and B were randomly assigned for each of ten patients and were worn for 14 and 30 days, respectively. With one exception, patients wore dentures with both lining materials, for a total of 19 clinical evaluations. The plasticizer loss occurring during the clinical trial was determined by GC analysis from the initial and terminal day sampling of plasticizer content of the soft polymer-gel materials. The results of this analysis were compared with results obtained from an in vitro leachability study by use of sink conditions in water at 37 degrees C for the same two commercial soft polymers conducted over the same time periods of 14 and 30 days. The results indicated that a higher loss of plasticizer occurred in vivo, compared with the in vitro tests for 17 of the 19 clinical evaluations. The average plasticizer lost in vivo from material A at 14 days was 122 +/- 58 mg/g, and for material B at 30 days it was 33 +/- 27 mg/g.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1991

Chemical and molecular weight analyses of prosthodontic soft polymers.

A number of studies have been made investigating the properties of dental prosthodontic soft polymer materials. In such materials, which are used as short-term denture soft liners, the polymer component is complexed with one or more plasticizers. This lowers the glass transition temperature, Tg, of the polymer by allowing greater chain mobility and produces a more flexible material. Little information is available relating to the polymer components of such soft-lining materials. The chemical composition and molecular-weight distribution of a polymer help to determine its ability to form a plasticized soft polymer-gel. In the present work, both pyrolysis depolymerization/gas chromatography (GC) and size exclusion chromatography (SEC) have been used to characterize 11 commercial polymer powders. By use of SEC and polymer standards having a narrow molecular-weight range, it has been possible for accurate molecular-weight distributions to be determined for all 11 powders. The peak molecular weights were found to be between 1.79 x 10(5) and 3.28 x 10(5). These values are above the molecular weight at which chain entanglement occurs. The polydispersity ratios (Mw/Mn) were between 2.09 and 4.48. Methacrylate polymers can be readily decomposed thermally to their constituent monomers, which, once recovered, can be analyzed by gas chromatography. The simple pyrolysis apparatus used in the present study was easily assembled and was capable of producing both qualitative and quantitative results. None of the commercial polymers analyzed gave methacrylate decomposition products with pendant chains greater than ethyl (-CH2-CH3). All of the commercial polymers successfully studied by the pyrolysis test method proved to be poly(ethyl [100-79%]/methyl [0-21%] methacrylate) polymers or co-polymers.

Chromatography, Gas↗
PubMed1991

Hamster cheek-pouch testing of dental soft polymers.

The hamster cheek pouch provides a suitable model system for the mucous-membrane irritation testing of dental materials. Poor retention of materials or difficulties in histopathological interpretation caused by surgical artifacts have been reported in published techniques. We describe a new "pouch-in-pouch" technique for mucous membrane irritation tests. The retention rate of polymer discs was 97% and 87% at 14 and 35 days, respectively. Clear differentiation was obtained between the tissue reaction to the test materials and the surgical procedure. Polymer discs containing dibutyltin diacetate (DBTD) or dibutyl phthalate (DBP) as plasticizer resulted in epithelial changes, including epithelial atypia, early papillomas, and areas resembling dysplasia. The potentially pre-malignant nature of these changes requires further investigation.

Animals↗
PubMed1991

Crevice corrosion products of dental amalgam.

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD. Analysis showed the presence of three previously reported products [Sn4(OH)6Cl2, SnO, and Cu2O] and a new product, CuCl, which formed on high-copper, gamma 2-free amalgams. Thermodynamic considerations show that CuCl is stable for the reported in vivo potentials of amalgam restorations and the high acidity and high chloride ion concentration associated with crevice corrosion.

Copper↗
PubMed1991

Treatment of essential hypertension in Asians: enalapril as monotherapy versus combination therapy with hydrochlorothiazide.

This study compared enalapril maleate (Enaprin) as a single antihypertensive agent and enalapril plus hydrochlorothiazide in Korean patients to determine if one regimen is superior to the other in terms of efficacy and subjective adverse effects. After a 1-week washout period, 12 patients were randomized to receive enalapril 10 mg daily and 13 patients to receive enalapril 10 mg daily plus hydrochlorothiazide 25 mg daily. After 2 weeks, enalapril was increased to 20 mg daily if diastolic blood pressure was greater than 90 mm Hg. The study period was 12 weeks. The mean changes in diastolic blood pressure in mm Hg were enalapril alone -10.7 +/- 10.5 mm Hg and enalapril plus hydrochlorothiazide -25.1 +/- 12.1 mm Hg (difference between the two groups significant at p less than 0.01). Mean dose of enalapril required to achieve goal blood pressure was 18.8 mg for monotherapy and 13.0 mg for combination therapy (p less than 0.05). Adverse effects were comparable. We concluded that enalapril in combination with hydrochlorothiazide is more effective and safe, and allows for lower dosing of enalapril than the drug as monotherapy in Korean hypertensives.

Adult↗