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Biomedical subjects

A D Johnson

Publications and source records attributed to A D Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Swallowing-induced paroxysmal supraventricular tachycardia.

This report describes an unusual case of swallowing-induced paroxysmal supraventricular (atrial or junctional) tachycardia in a young man without evidence of organic cardiac or esophageal disease. The arrhythmia was apparently potentiated by excessive coffee ingestion. Unlike swallowing-induced brady-arrhythmias which are due to vago-vagal mechanisms, the supraventricular tachycardia in the present case may have been related to an adrenergic reflex.

Adult↗
PubMed1980

Mitogenic activity of staphylococcal exfoliative toxin.

Exfoliative toxin from Staphylococcus aureus was mitogenic for murine spleen cells. It was primarily active on T lymphocytes but also significantly stimulated B cells from the spleens of nude mice. The mitogenicity was not affected by simple sugar or alpha-methylpyranosides. N-acetylglucosamine and N-acetylgalactosamine inhibited its effect. Exfoliatin was as powerful a mitogen as the enterotoxins of S. aureus. Some significant differences between the mitogenic activity of the two toxins were demonstrated.

Animals↗
PubMed1979

Distribution and severity of coronary artery disease in 500 patients with angina pectoris.

The distribution and severity of coronary disease in 500 patients with angina pectoris and at least one area of 50% or greater reduction of luminal diameter in a major coronary artery were compared with respect to patients' age and coronary arterial pattern. The coronary arterial patterns were separated into right (360 patients), mixed (89 patients), and left (51 patients) systems, depending upon the blood supply to the inferior surface of the left ventricle. The following relationships were noted: 1) In patients with angina pectoris, the distribution and severity of coronary artery disease is similar from the third to eighth decade. 2) Coronary arterial stenoses of 50-70% of greater reduction of luminal diameter involve most frequently the proximal portion of the major vessels. Coronary artery disease is multivessel in nature in 80% of cases. In single vessel disease the left anterior descending artery is involved most frequently. 3) The left main coronary artery is moderately to severely obstructed less frequently in individuals with left (2%) as compared to right (8%) and mixed (10%) systems. Otherwise, the distribution of coronary artery disease is similar in right, mixed, and left systems. 4) Coronary artery disease is a diffuse rather than a focal process. As demonstrated by coronary arteriography, patients with coronary artery disease have smaller vessels throughout the arterial tree as compared with individuals free of evident coronary atherosclerosis.

Adult↗
PubMed1979

Transseptal and retrograde left ventricular catheterization in patients with the stent-mounted porcine xenograft valve prosthesis in the aortic position.

Cardiac catheterization techniques for measuring the systolic pressure gradient across the stent-mounted porcine xenograft in the aortic position and accomplishing left ventriculography are described. The transseptal technique is a rapid and predictable means of entering the left ventricle but requires a highly skilled operator. Retrograde left ventricular catheterization via the femoral artery is a technique familiar to all invasive cardiologists. Usually a pitfall catheter is used. In patients with the stent-mounted procine xenograft in the aortic position, we have found the A2 Multipurpose catheter to be the fastest and most predictable means of entering the left ventricle from the groin. Potential complications of retrograde left ventricular catheterization in patients with aortic valve prostheses are discussed.

Aortic Valve↗
PubMed1979

Interactions between DNA-bound repressors govern regulation by the lambda phage repressor.

The lambda phage repressor binds cooperatively to the three sites in the right operator (O(R)) according to the following pattern. If the DNA is wild type, O(R)1 and O(R)2 are filled coordinately because of interactions between repressor dimers bound to these two sites. Site O(R)3 is filled only at higher repressor concentrations. In contrast, if O(R)1 is mutant, O(R)2 and O(R)3 are filled coordinately because of interactions between repressors bound to these sites. In this case, the affinity of O(R)3 is increased and that of O(R)2 is decreased relative to the wild type. We infer that a repressor dimer bound to the middle site O(R)2 can interact either with another repressor dimer bound to O(R)1 (wild-type case) or, alternatively, with one bound to O(R)3 (mutant O(R)1 case). We argue that these repressor interactions are mediated by protein-protein contacts between adjacent repressor dimers, because the isolated amino-terminal domains of repressor bind to the operator sites noncooperatively. The cro protein of phage lambda, a second regulatory protein, which recognizes the same three sites in O(R) as does repressor, binds non-cooperatively. Experiments performed in vivo show that regulation of gene expression by repressor can be influenced critically by cooperative interactions. We demonstrate that the effect of repressor in a lysogen on the activity of the promoter P(RM) can be changed from activation to repression by deletion of O(R)1. We explain this effect in terms of the alternative cooperative interactions described above.

Bacteriophage lambda↗
PubMed1979

Purification and characterization of different types of exfoliative toxin from Staphylococcus aureus.

Exfoliative toxin was isolated from strain DI of Staphylococcus aureus using carboxymethyl cellulose and hydroxylapatite chromatography. This purified toxin was compared with that produced by strain TA. The specific biological activity of the two toxins was the same, but they were serologically distinct. These strains have different loci (plasmid or chromosomal) for toxin production; differences were seen in molecular weight and amino acid composition. N-terminal amino acid sequences from the two strains showed significant homology using a single unit alignment shift.

Amino Acid Sequence↗
PubMed1979

Instantaneous transmitral blood flow and anterior mitral leaflet motion in man.

Transmitral blood flow was measured in man by numerical differentiation of left ventricular volume as a function of time in 11 patients undergoing cardiac catheterization. Using this technique, transmitral blood flow may be studied in a variety of pathologic states without the need for surgically introduced flowmeters. Just before left ventriculography, echocardiography of the mitral valve was performed. The pattern of transmitral blood flow was strikingly similar to the diastolic movement of the anterior mitral leaflet. At any equivalent diastolic filling time, the percent of the integrated area beneath the curve inscribed by the diastolic anterior mirtal leaflet echoes closely approximated the percent of stroke volume which had entered the left ventricle. This observation supports the hypothesis that mitral leaflet motion accurately reflects transmitral flow. Consequently, at a given time during diastole, the relative velocity of transmitral flow and the percent of the stroke volume which has entered the left ventricle may be approximated noninvasively from the anterior mitral leaflet echogram.

Adult↗
PubMed1979

Measurement of left ventricular ejection fraction by mechanical cross-sectional echocardiography.

Cross-sectional echocardiography is a new noninvasive technique for imaging the heart. We developed a method for using mechanical cross-sectional echocardiograms (sector scans) to determine left ventricular volumes and ejection fraction. Using left ventricular cineangiography as a standard, sector scan ejection fraction correlated better (r = 0.93) than M-mode echocardiography by any of three established methods, and the sector scan regression line did not differ from the line of identity (p greater than 0.33). Interobserver variability for sector scan ejection fraction was 2.3 +/- 1.2% (mean +/- SD). Variation between two studies performed within 24 hours and analyzed by the same observer was 1.4 +/- 1.5%. However, the sector scans consistently underestimated left ventricular end-diastolic volume. We conclude that sector scan echocardiography is more reliable than conventional M-mode technique for estimating left ventricular ejection fraction, but estimation of left ventricular end-diastolic volume is unreliable with the methods currently available.

Blood Volume↗