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Biomedical subjects

E L Johnson

Publications and source records attributed to E L Johnson.

9 recordsLinked to original sources
PubMed1992

Measurement of volumetric coronary blood flow with a Doppler catheter: validation in an animal model.

Although Doppler catheter recordings are used to determine coronary flow velocity, their accuracy in the estimation of volumetric blood flow has not been validated. To address this issue, Doppler-derived coronary flow was measured in a canine model and compared with that obtained by means of an electromagnetic flowmeter. A carotid artery-to-circumflex coronary artery shunt was created in six dogs with tubing that incorporated an inline electromagnetic flow device. The circumflex artery was occlusively cannulated by means of a rigid metal stent of known internal diameter, which was placed 2 cm into the vessel, and flow was measured in the stent region by means of a 3F Doppler catheter. Analysis of Doppler shift signals was performed by means of a zero-crossing detector (ZCD) and an off-line fast-Fourier transformation (FFT) system. Flow derived from peak FFT velocities corresponded closely to electromagnetic flow (slope 1.09, r = 0.93), whereas mean FFT and ZCD velocities underestimated electromagnetic flow (with slopes of 0.47 and 0.46, respectively) despite a close correlation (r = 0.92, 0.94). Thus FFT analysis of the Doppler signal with determination of peak velocity gives the most accurate representation of flow, whereas measurements based on ZCD mean velocities may significantly underestimate coronary flow.

Animals↗
PubMed1992

Use of oral tolerance tests to investigate disaccharide digestion in neonatal foals.

Oral tolerance tests were performed on 13 neonatal foals to determine their ability to digest disaccharides on d 1, 3 and 5 postpartum. Foals were assigned randomly to treatments consisting of 20% (wt/vol) solutions of either maltose, lactose, or sucrose, dosed at 1 g/kg of BW, or glucose, dosed at .5 g/kg of BW. After a 2-h fast, an initial blood sample was collected via jugular catheter. Foals were administered the appropriate solution orally, and blood was collected every 15 min for 1 h and then every 30 min for 3 h. Plasma glucose increased after dosing with lactose or glucose but not with sucrose. Plasma glucose concentrations increased slightly on d 3 and 5 in foals dosed with maltose. These findings suggest that although lactose is well digested by neonatal foals, maltose is digested only slightly, and sucrose is not digested by d 5. Results of this experiment indicate that maltose and sucrose would not be suitable for inclusion in artificial diets for foals less than 1 wk old. Oral tolerance tests could be useful for determining the ability of premature or sick foals with lactose intolerance to digest alternate carbohydrate sources.

Animal Feed↗
PubMed1989

Disturbances of brain maturation and neurodevelopment during chronic renal failure in infancy.

Fifteen infants with moderate to severe congenital renal disease were prospectively studied by serial renal, neurodevelopmental, neurophysiologic, and anthropometric assessments. The observation period ranged from 3 to 25 months (mean = 10.9). Eight patients maintained a Mental Development Index (MDI) above the 16th percentile (greater than -1 SD) and comprised group 1. Of the remaining seven patients (group 2), three had an MDI less than 16th percentile when first studied and four had serial decreases of the MDI to less than 16th percentile. Although motor development was more delayed in group 2 at study entry, there were no significant changes of motor performance levels for either group during the study period. Group 2 patients had smaller length (p less than 0.05) and head circumference (p less than 0.05) standard deviation scores in comparison with group 1, and they had higher serum creatinine values (mean = 3.8 vs 1.3 mg/dl, respectively; p less than 0.01). By spectral electroencephalography, the expected progressive increase of the frequency of cerebral cortical background activity with age was demonstrated in group 1 but was not seen in group 2 (multivariate analysis of variance p less than 0.03). This increase of faster-frequency activity was primarily manifested in the left cerebral hemisphere of group 1 patients (p less than 0.01), a finding that was also absent in group 2. The frequent occurrence of neurodevelopmental abnormalities in infants with renal failure is possibly a consequence of impaired dominant hemispheric maturation in the first several years of life, which is clinically manifested as deterioration of cognitive function.

Cephalometry↗
PubMed1989

Assessment of severity of coronary stenoses using a Doppler catheter. Validation of a method based on the continuity equation.

The coronary Doppler catheter has been used primarily in the measurement of coronary vasodilator reserve, most often as the ratio of peak to resting velocity in response to an intracoronary dose of papaverine. We have developed a new method based on the continuity equation using a Doppler catheter for the assessment of stenosis severity in the coronary circulation by means of quantitative velocity measurements obtained by complex spectral analysis of the Doppler signal. With this system we have been able to detect a high-velocity stenosis jet in a canine model of coronary stenosis of known cross-sectional area. Using the peak velocity obtained by complex spectral analysis, we found a strong correlation between cross-sectional areas determined by the continuity equation and known cross-sectional areas (r = 0.93, SEE = 0.23 mm2). We also found a strong correlation between the ratio of peak stenosis velocity to proximal vessel velocity and percent diameter and percent area stenosis (r = 0.91 and 0.92, respectively). When the velocity was determined with conventional zero-crossing methods for these parameters, there was no correlation between calculated and known values for cross-sectional area and percent diameter or area stenosis. Measurements of the vasodilator reserve in response to intracoronary papaverine before and after implantation of the stenosis did not correlate with any of the anatomic parameters of stenosis severity regardless of the method of signal analysis (zero-crossing or complex spectral analysis). The measurement of quantitative peak coronary velocity with a Doppler catheter using complex spectral analysis may provide an accurate method for determining the severity of a coronary stenosis.

Animals↗
PubMed1987

The protein-tyrosine kinase activity of the insulin receptor is necessary for insulin-mediated receptor down-regulation.

We have previously demonstrated that the human insulin receptor, mutated in the ATP-binding domain of the beta-subunit, is kinase-defective and fails to mediate multiple post-receptor actions of insulin in stably transfected Chinese hamster ovary cells (Chou, C.-K., Dull, T. J., Russell, D. S., Gherzi, R., Lebwohl, D., Ullrich, A., and Rosen, O. M. (1987) J. Biol. Chem. 262, 1842-1847). This study addresses the role of protein-tyrosine kinase activity in insulin-mediated receptor down-regulation. Although the mutant insulin proreceptor was properly processed and able to bind insulin like the wild-type human receptor, it differed from the latter in the following respects: 1) it failed to mediate internalization of surface-bound radiolabeled ligand; 2) it did not undergo short- or long-term down-regulation in response to 1 microM insulin; 3) it did not exhibit ligand-promoted receptor turnover; and 4) it was not phosphorylated on either tyrosine or serine residues in response to insulin. Although the cells transfected with the mutant receptor failed to respond to insulin-mediated insulin receptor down-regulation, they were able to down-regulate their insulin-like growth factor I receptors in response to insulin-like growth factor I or high concentrations of insulin and were sensitive to monoclonal antibody-induced down-regulation of their insulin receptors. Antibody-mediated receptor internalization alone, however, was unable to mimic at least one action of insulin, thymidine incorporation into DNA, and did not lead to any phosphorylation of the receptor. It is concluded that either the protein-tyrosine kinase activity of the insulin receptor or its phosphorylation state is essential for ligand-mediated receptor down-regulation.

Adenosine Triphosphate↗
PubMed1986

Keyboards for the handicapped. A new concept.

A keyboard has been designed and constructed for persons restricted to using a head or mouth stick. The keyboard is not a modification of existing keyboard technology but involves a completely new concept. The keyboard, called a 2DOF keyboard, requires only two degrees of freedom motion for actuation. The problems of simultaneous key requirements, accidental key strikes, and multiple strikes of the same key have been solved. The keyboard is transparent to the personal computer to which it is connected, allowing use of any available software.

Artificial Intelligence↗
PubMed1977

A computer-assisted, goal-oriented psychiatric progress note system.

The authors describe a computer system that develops a structured progress note for inclusion in the medical record. The progress note system reflects a goal-oriented patient treatment process and also provides for retrospective analysis of progress note information to accommodate research and review objectives. The system, which has met with a high degree of clinician acceptance, has resulted in improved case documentation, more timely and comprehensive notes, a higher level of objectivity, and a considerable reduction in the time required to organize and record progress note data.

Computers↗