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Biomedical subjects

R A Johnson

Publications and source records attributed to R A Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1984

Detection of left ventricular wall motion abnormalities for the diagnosis of coronary artery disease: a comparison of exercise radionuclide and pacing intravenous digital ventriculography.

Intravenous digital ventriculography before and after pacing was compared with equilibrium gated nuclear ventriculography at rest and after exercise. Specifically, the relative abilities of the 2 techniques to detect resting and stress-related wall motion abnormalities were tested. Twelve normal patients and 28 patients with coronary artery disease (CAD) were tested. Neither technique produced a new wall motion abnormality in a patient with normal coronary arteries. Six patients with CAD had a history of a myocardial infarction (MI); an abnormality at rest was present in all 6 by both techniques. Of the 22 patients with CAD and a normal baseline ventriculogram, a wall motion abnormality developed in 18 during digital ventriculography with pacing; a wall motion abnormality developed in 15 with exercise nuclear ventriculography. Wall motion abnormalities by nuclear ventriculography (performed in the left anterior oblique projection) tended to be apical; digital ventriculography (performed in the right anterior oblique projection) more often produced an abnormality of the anterior or inferior wall, which could be predictive of coronary anatomy. Thus, the 2 techniques are substantially equivalent for the detection of wall motion abnormalities in CAD.

Adult↗
PubMed1984

Heparin-induced thrombocytopenia: a prospective study.

Thrombocytopenia is a well-described complication of heparin therapy. Few studies describe the incidence of thrombocytopenia when low-dose heparin (10,000-15,000 units/day) is used for prophylaxis of deep venous thrombosis. In our study, ten of 66 courses (15%) of heparin prophylaxis in coronary care unit patients were accompanied by a mild thrombocytopenia with platelet counts below 150 X 10(3)/mm3. In all cases the platelet count returned to normal despite continued heparin therapy. Patients who became thrombocytopenic had significantly lower initial platelet counts. No cases of severe thrombocytopenia were seen (platelet count below 100 X 10(3)/mm3). No patient developed thrombosis, bleeding or elevated fibrin split products. Mild thrombocytopenia occurring after 2-5 days of low-dose heparin is common, but clinically insignificant.

Adult↗
PubMed1984

Elution of enteric viruses from Mississippi estuarine sediments with lecithin-supplemented eluents.

Isoelectric casein supplemented with lecithin was tested for its ability to recover enteric viruses from estuarine sediments of varied sand, silt, and clay composition. Recoveries were higher when lecithin was incorporated into an eluent as compared with trials with only the casein solution. Semipurified soybean lecithin (3%) allowed the highest overall recovery of virus from all sediments tested; crude soybean lecithin produced the lowest recovery. A difference in the percentage of virus able to be recovered from a sediment was related to the percentage of clay in the sample. Correlational statistics indicated a trend toward lower virus recovery as the clay composition of a sediment increased. Virus adsorption to the four sediments tested revealed differences between poliovirus, coxsackievirus, and echovirus adsorption that could not be explained on the basis of the clay content of a sediment.

Aluminum Silicates↗
PubMed1984

Elevated plasma tricyclic levels with therapeutic doses of imipramine.

Nine (15%) of 59 patients treated with imipramine at doses of 150 to 300 mg/day had steady-state plasma levels greater than 500 ng/ml. Low capacity for hydroxylation was found in all six patients for whom hydroxy metabolites were measured. Maximum tricyclic levels in the nine study patients were comparable to levels found in tricyclic antidepressant overdoses (651-2439 ng/ml). No study patient experienced any adverse effects: QRS durations were all less than 100 msec, and a mildly dry mouth was the most commonly reported side effect (five of nine patients). Depressive symptoms recurred in three patients when their imipramine dose was decreased.

Adult↗
PubMed1984

Tuberculosis screening.

In view of the decreasing prevalence of tuberculosis, it is important to be aware of the factors influencing the sensitivity, specificity and predictive value of tuberculin testing. The small predictive value of tuberculin testing in a low-risk population makes it an ineffective means for screening. Even in high-risk populations, factors such as geographic location, reaction size, previous skin testing and BCG vaccination significantly influence interpretation of the skin test.

BCG Vaccine↗
PubMed1984

Continued assessment of flexible sigmoidoscopy in a family practice residency.

The UCLA Family Practice Residency continues to use 60-cm flexible sigmoidoscopy in the care of patients. Between July 1980 and June 1983, 450 patients received an examination with the 60-cm flexible sigmoidoscope. One or more adenomatous polyps were detected in 21 patients. Adenocarcinoma was found in five patients. Four patients were found to have a villous adenoma, and four patients were determined to have inflammatory bowel disease. Of the 34 discrete lesions, 32 percent, 41 percent, and 27 percent were located between 0 and 20 cm, 21 and 35 cm, and 36 and 60 cm, respectively, from the anus. No complications were encountered. Sixty-four percent of the examinations were done by a family practice resident supervised by a full-time faculty member. The remaining 36 percent of the examinations were performed by full-time faculty. The overall detection rate for significant pathology was 8.0 percent. Most pathology by far was found in symptomatic patients. These results validate the safety and viability of 60-cm flexible sigmoidoscopy when performed by properly trained family physicians and family practice residents-in-training.

Adenocarcinoma↗
PubMed1984

Comparative analysis: effects of positive and negative lateral acceleration on isometric fatigue in the forearm.

UNLABELLED: The purpose of this investigation was to determine the difference, if any, produced by +/- Gy acceleration on forearm fatigue. The Dynamic Environment Simulator (DES) at the USAF Aerospace Medical Research Laboratory was used to create a lateral acceleration environment. The experiment was designed to measure the forearm strength, endurance, recovery from fatigue, and surface electrical activity of six subjects during +/- 2 Gy acceleration. THE RESULTS: isometric performance was degraded during -2 Gy acceleration compared to + 2 Gy acceleration. The percentage drop in center frequency of the EMG signal was determined to be unreliable as a fatigue index during lateral acceleration. When head and shoulder restraints were used during lateral maneuvers, they were a factor in pilot performance, with + 2 Gy being superior to -2 Gy. This study suggested a way of analyzing the EMG signals that may permit quantification of isometric fatigue during lateral acceleration.

Acceleration↗
PubMed1983

Activation of human platelet adenylate cyclase by a bovine sperm component.

The interaction of bovine sperm particles and human platelet membranes was studied with regard to adenylate cyclase activity. When sperm and platelet membrane preparations were combined, greater than additive adenylate cyclase activity was measured. Data obtained after inactivation of the sperm enzyme indicated that the observed increase in adenylate cyclase activity was not due to an activation of the sperm cyclase but that a sperm component, which could be extracted from the sperm particles, activated the platelet adenylate cyclase. Platelet cyclase activation by the sperm particles was a saturable and time-dependent process. The extent of activation was particularly high (up to 10-fold) in the presence of a stable GTP analog. Under this condition, the apparent affinity of the platelet enzyme for Mg2+ was increased by about one order of magnitude, whereas with Mn2+ only a minor effect of the sperm particles was observed. Platelet adenylate cyclase stimulation by prostaglandin E1 (up to 20-fold) was more than doubled by the sperm particles, whereas the inhibition of the platelet enzyme by epinephrine was abolished. The sperm factor was trypsin-sensitive and was inactivated by boiling. The data indicate that bovine sperm particles contain an extractable protein, which activates platelet adenylate cyclase probably by inactivating an inhibitory site.

Adenylyl Cyclases↗
PubMed1983

Detergent-induced distinctions between fluoride- and vanadate-stimulated adenylate cyclases and their responses to guanine nucleotides.

The influence of detergents on fluoride- and vanadate-stimulated adenylate cyclases was investigated with enzyme from liver and adipocyte plasma membranes. Stimulation of the adipocyte cyclase by Na3VO4 was maximal (sixfold) at 3 mM, was not additive with fluoride stimulation, and was readily reversed by washing of the membranes. Vanadate stimulation of the hepatic cyclase was specifically blocked by catechol, which had no effect on basal activity or on fluoride- or glucagon-stimulated activities. The hepatic enzyme, stimulated by fluoride ion, guanyl-5'-yl-(beta,gamma-imino)diphosphate (GPP(NH)P), or GPP(NH)P and glucagon, was inhibited by vanadate with 50% inhibition seen with 2 to 6 mM vanadate. The fluoride-activated adipocyte adenylate cyclase was inhibited by guanosine 5'-O-(3-thio-triphosphate) (GTP gamma S) more potently than by GPP(NH)P, with 50% inhibition being seen with 10 nM GTP gamma S or 100 nM GPP(NH)P. These nucleotides also inhibited the vanadate-stimulated enzyme, but with one-third the potency seen with the fluoride-activated cyclase. Dispersion of the adipocyte cyclase by Lubrol-PX into a 30,000g supernatant fraction caused no change in activation of the enzyme by fluoride, but reduced vanadate-stimulated activity 80%. By comparison, this treatment enhanced stimulation by GPP(NH)P twofold and by GTP gamma S threefold. More importantly, perhaps, the treatment with detergent blocked inhibition of the basal enzyme by GTP, blocked inhibition of fluoride- and vanadate-stimulated cyclases by GTP, GPP(NH)P, or GTP gamma S, and rendered vanadate-stimulated activity sensitive to enhancement by guanine nucleotides. The data indicate differences in the actions of vanadate and fluoride, made evident by the influence of guanine nucleotides and detergent treatment. The observations would be consistent with the idea that the effects of vandate may be due to the formation of GDP X V on the enzyme. The data strongly suggest that treatment of adenylate cyclase with Lubrol-PX causes a functional blockade in the guanine nucleotide-dependent inhibitory regulation (mediated by Ni), thereby allowing activation by the stimulatory guanine nucleotide-dependent regulatory component (Ns).

Adenylyl Cyclases↗
PubMed1983

Inhibition of platelet thromboxane A2 synthase activity by sodium 5-(3'-pyridinylmethyl)benzofuran-2-carboxylate.

This report outlines the activity of a new thromboxane synthase inhibitor sodium, 5-(3-pyridinylmethyl)-2-benzofurancarboxylate, (U-63557A). U-63557A is a potent inhibitor of the thromboxane synthase in human platelets in vitro, as well as in rhesus monkey platelets ex vivo. A single oral dose of 3.0 mg/kg U-63557A inhibits the platelet thromboxane synthase in rhesus monkeys approximately 80% for at least 12 hrs. U-63557A has been administered to monkeys twice a day, (10 mg/kg) for 14 days, without evidence of drug tachyphylaxis or rebound. U-63557A does not inhibit thrombin-stimulated PGI2 biosynthesis in human endothelial cells, the 5-lipoxygenase in human neutrophils, or the cyclo-oxygenase in a variety of test systems. In anesthetized dogs, U-63557A injected i.v. at 0.1 to 5 mg/kg prevented the blockage of stenosed coronary arteries caused platelet aggregation. Similar effects were obtained by oral administration of 1-5 mg/kg. The thromboxane synthase inhibitor was more efficacious than cyclooxygenase inhibitors and equal to PGI2 in efficacy. Under appropriate conditions the protective effects of U-63557A could be reversed by i.v. cyclooxygenase inhibitors suggesting that its efficacy depended in part on endogenous PGI2 formation. Due to its specificity, oral activity, and extended duration of action, U-63557A is a promising compound for the evaluation of the role of thromboxane synthase in a variety of pathophysiological states.

Animals↗
PubMed1983

Use of an MMPI scale to predict antidepressant response to lithium.

Previous research has indicated that a subset of Minnesota Multiphasic Personality Inventory (MMPI) items may be able to predict antidepressant treatment response to lithium. Twenty-one patients with major depressive disorder were assigned to treatment with lithium based on this MMPI lithium response scale. Twenty lithium-assigned patients completed the 4-week trial. Sixty percent of these patients showed a 50% reduction in Hamilton depression scores. This response rate is similar to results obtained in studies using no selection criteria in the treatment of depression with lithium.

Adult↗
PubMed1983

Intravenous digital left ventriculography at rest and with atrial pacing as a screening procedure for coronary artery disease.

Digital subtraction left ventriculography using intravenous contrast injection was evaluated as a screening diagnostic method for coronary heart disease. Intravenous ventriculography was performed in 61 patients with 35 cc of contrast medium injected into a central vein (usually the inferior vena cava). Recognition of regional wall motion abnormalities by this technique was shown to be comparable with direct left ventriculography in 40 patients who underwent both imaging modalities at rest. If the rest digital ventriculogram was normal, it was repeated after incremental atrial pacing to the onset of chest pain or to a maximal heart rate of 150 beats/min. Forty-four of the 61 patients had significant coronary artery disease, of whom 10 had a wall motion abnormality at rest on intravenous ventriculography. With pacing, 28 of the 34 remaining patients developed a new wall motion abnormality. Thus, 38 (86%) of 44 patients with coronary heart disease were identified by wall motion abnormalities. One of the 17 patients without coronary artery disease had an abnormal rest study and was incorrectly assigned a diagnosis of coronary disease. Intravenous digital ventriculograms approximate those obtained by direct ventriculography. When combined with atrial pacing they are a sensitive and specific means of detecting coronary artery disease.

Adult↗
PubMed1983

Elution of viruses from coastal sediments.

Enteric viruses were eluted from estuarine sediments by using four organic mixtures; these solutions, with or without various supplements, were compared by determining their abilities to desorb virus from sediments taken from shellfish-harvesting sites. The least effective eluents consisted of glycine buffer, milk preparations, and beef extract paste. When virus type and sediment composition were taken into consideration, higher percentages of virus recovery were achieved with isoelectric casein, powdered beef extract, and nutrient broth mixtures. In addition to the type of eluent used, variations in virus recovery were due to the pH of the eluent, the composition of the sediment, and the type of virus being extracted. No clear distinction between the values of protein and inorganic ion supplements could be made.

Adsorption↗