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Biomedical subjects

A D Johnson

Publications and source records attributed to A D Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1977

Electrographic exercise stress testing and coronary arteriography. Correlation among 114 men with chest pain.

The electrocardiographic response to exercise stress testing (EST) was compared with coronary arteriographic findings in 114 men referred for evaluation of chest pain. The men were divided into two groups: group A (69 men) in whom the coronary arteriograms showed at least one major vessel with greater than 70 percent reduction in cross sectional area, and group B (45 men) in whom there was no evidence of coronary arterial narrowing. In both groups A and B the description of chest pain was judged to be at least consistent with the diagnosis of angina pectoris if not always representing classical angina pectoris. Only men with a positive finding to EST and those with a negative EST response after achieving at least 90 percent of predicted maximum heart rate were included in the calculations. Our results were strikingly similar to those obtained from an extensive review of the literature and showed the following: sensitivity, 80.4 percent; specificity, 88.6 percent; predictive value of a positive test result, 91.1 percent; predictive value of a negative test result, 75.6 percent, and efficiency of the test 83.7 percent. The maximal EST is a useful predictor of coronary artery disease when a male population is evaluated for chest pain. When a population is selected on some basis other than chest pain (such as elevated lipids or age), EST is a much less useful predictor of coronary artery disease.

Angina Pectoris↗
PubMed1976

An echocardiographic study of interventricular septal motion in the Wolff-Parkinson-White syndrome.

Echocardiographic studies of interventricular septal motion were performed in 26 consecutive patients with the Wolff-Parkinson-White (WPW) syndrome and in ten normal subjects. All patients with types A or B pre-excitation were subclassified into groups I to IV on the basis of their electrocardiogram utilizing the method of Boineau and associates. In all 14 patients with type A (Group III or IV) pre-excitation, the motion of the interventricular septum and posterior left ventricular wall motion were normal. However, in 11 patients with type B (Group I) WPW an abnormal septal movement was noted. This was characterized in ten patients by an early systolic posterior motion, a subsequent anterior movement in mid systole, and the usual posterior septal motion beginning in late systole. In eight patients, including the one without early systolic posterior movement of the septum, the late systolic posterior movement was interrupted by a prominent septal notch. On e patient with type B (Group II) WPW was studied and exhibited normal septal and posterior wall motion. In one patient with a spontaneous change in the QRS complex from normal to a type B (Group I) WPW pattern, the septal motion was initially normal and abruptly changed following the first WPW beat. The onset of abnormal interventricular septal motion with type B pre-excitation QRS complexes strongly suggests that abnormal septal movement may be related to an altered sequence of ventricular depolarization during right ventricular pre-excitation.

Action Potentials↗
PubMed1976

Assessment of left ventricular function in severe aortic regurgitation.

Echocardiographic (echo) measurements of left ventricular ejection phase indices--ejection fraction, percent shortening of the minor diameter (%deltaD), and velocity of circumferential fiber shortening (Vcf)--are said to be accurate reflections of their angiographic (angio) counterparts. Most studies correlating echo and angio left ventricular function parameters have included relatively few patients with aortic regurgitation. Echo and angio measurements of left ventricular ejection phase indices thus might not correlate in these patients in whom left ventricular geometry may have been altered due to the volume overload. To test this hypothesis, left ventricular ejection phase indices were determined by angiography and echocardiography and compared in 20 patients with isolated, symptomatic, severe aortic regurgitation. Ejection fraction, %deltaD, and Vcf by LAO cineangiograms and echo were uniformly higher than corresponding measurements from RAO angio, and were often normal in the presence of other indicators of significant left ventricular dysfunction. We conclude that the usual, linear echocardiographic measurement of left ventricular wall motion may not reflect significant myocardial dysfunction in patients with severe aortic regurgitation.

Adolescent↗
PubMed1975

Combined hyertrophic subaortic stenosis and calcific aortic valvular stenosis.

A well documented case of combined hypertrophic subaortic stenosis and calcific aortic stenosis is reported. Detection of multilevel involvement in cases of left ventricular outflow obstruction requires a high index of suspicion and precise hemodynamic and angiographic documentation. Careful analysis of the total data base is necessary for proper management of the patient. The pathogenesis of this combined lesion is unclear: Asymmetrical septal hypertrophy may occur as a consequence of the valvular stenosis, or it may be that abnormal leaflet motion in patients with hypertrophic obstruction produces leaflet thickening, calcification, deformity and stenosis.

Aged↗
PubMed1975

Intrinsic and chemically produced microheterogeneity of Staphylococcus aureus enterotoxin type C.

Staphylococcus aureus enterotoxins C1 (SEC1) and C2 (SEC2) produced from 50-liter quantities of crude culture supernatants were purified chromatographically in a neutral or acid milieu. Microheterogenity of SEC1 was markedly increased by treatment of the purified toxin with alkali, and new more acidic charged species appeared. SEC2 was more heterogenous than any of the other S. aureus enterotoxins and was affected only slightly by treatment with alkali. Prolonged incubation of the organism during production of the SEC2 produced changes in charged species that may be related to a bacterial deamidase, since similar changes were not seen with alkaline treatment of the purified toxin. Although SEC1 and SEC2 showed complete identity immunologically, they are separate, distinct toxins, and alkali treatment of SEC1 did not produce SEC2.

Alkalies↗
PubMed1975

Production, purification, and chemical characterization of Staphylococcus aureus exfoliative toxin.

Methods for the production and isolation of exfoliative toxin are described. Fermentation conditions were established under which large quantities of the crude material can be produced. Column chromatography methods, including carboxymethyl cellulose and hydroxyapatite, were utilized to purify the toxic protein. The pure toxin had a molecular weight of 26,000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The pure toxin is a simple protein composed of 17 amino acids. Tests for carbohydrate and for alpha- and beta-hemolysin were negative. The mean effective dose of the purified toxin was 0.5 mug per newborn mouse.

Amino Acids↗
PubMed1975

Nontraumatic determination of left ventricular ejection fraction by radionuclide angiocardiography.

Previous reports have suggested that left ventricular ejection fraction can be assessed by recording the passage of peripherally administered radioactive bolus through the heart. The accuracy and validity of this technique were examined in 20 patients undergoing diagnostic cardiac catheterization. 99m-Tc-human serum albumin was injected via a central venous catheter into the superior vena cava and precordial activity recorded with a gamma scintillation camera interfaced to a small digital computer. A computer program was designed to generate time-activity curves from the left ventricular blood pool and to calculate left ventricular ejection fractions from the cyclic fluctuations of the left ventricular time-activity curve which correspond to left ventricular volume changes during each cardiac cycle. The results correlated well with those obtained by biplane cineangiocardiography (r equals 0.94) and indicated that the technique should allow accurate and reproducible determination of left ventricular ejection fraction. The findings, however, demonstrated that the time-activity curve must be generated from a region-of-interest which fits the left ventricular blood pool precisely and must be corrected for contributions arising from noncardiac background structures. This nontraumatic and potentially noninvasive technique appears particularly useful for serial evaluation of the acutely ill patient and for follow-up studies in nonhospitalized patients.

Adult↗
PubMed1975

Hypertrophic subaortic stenosis complicated by high degree heart block: successful treatment with an atrial synchronous ventricular pacemaker.

The development of high degree atrioventricular block in a patient with hypertrophic subaortic stenosis underscores the importance of a properly timed atrial contraction in this disorder. Atrial synchronous ventricular pacing therapy, by providing, reliably timed atrial systole and increased left ventricular end-diastolic volume, has an important role in this patient and in similar cases.

Aged↗
PubMed1975

Epididymal carbohydrate metabolism. III. Metabolism of the caput and cauda epididymidis after separation from the testis in the rat.

After unilateral separation of the rat epididymis from the testis, the metabolism of various substrates in vitro by tissue from the attached and separated caput and cauda epididymidis at 7 and 28 days after surgery was determined by radiorespirometry. Hourly collections of 14-CO2 were made during 5-hr incubations. The patterns of 14-CO2 evolution from glucose indicated that most of the metabolic activity followed the Embden-Meyerhof glycolytic and the Krebs cycle respiration pathways. The alteration of the rate of glycolysis was always greater than that of respiration. In all samples, the metabolism of (2-14C) glucose was approximately equal to that of (6-14C) glucose (G-6)and less than that of (1-14C) glucose (G-1). Pentose cycle activity was indicated in all tissues from the caput and cauda epididymidis by the preferential utilization of G-1 over G-6. At 7 and 28 days after surgery, respectively, the G-1:G-6 ratios of 14-CO2 evolution after incubation for 2 hr were 9.75 and 7.79 for the separated caput, 5.17 and 2.66 for the intact caput, 3.11 and 2.52 for the separated cauda and 3.73 and 2.84 for the attached cauda epididymidis. Although epididymal separation did not effect the metabolism of (U-14C) glucose or (U-14C) fructose, glucose appeared to be a more important epididymal substrate than fructose.

Acetates↗
PubMed1975

Effect of epididymal isolation on the protein component of bull eididymal tissue.

Four fractions of protein from intact and 'isolated' bull epididymides were extracted. The total extractable protein was increased by isolation mainly due to increases in the lipoprotein and DNA-protein fractions. Changes of lipoprotein may be associated with the increase of lipid which also occurs in isolated tissue. This may reflect the increase of pentose cycle activity and lipogenesis due to the absence of spermatozoa in the epididymal tubules. Changes of DNA-protein may indicate a change of protein metabolism. Electrophoresis of protein fractions showed that individual proteins may be changed by the zonal origin of the epididymal tissue and the presence or absence of spermatozoa in the epididymal tubules.

Animals↗
PubMed1975

Diazepam and paraldehyde for treatment of severe delirium tremens. A controlled trial.

Thirty-four patients with severe delirium tremens were allocated randomly to treatment with paraldehyde (10 ml rectally very 30 minutes) or diazepam (10 mg then 5 mg intravenously every 5 minutes) until they were calm but awake. Diazepam-treated patients became calm in one half the time needed to calm patients with paraldehyde. Half of the patients had delirium tremens in association with pneumonia, pancreatitis, or alcoholic hepatitis; these patients required twice as much paraldehyde or diazepam for initial calming as patients with delirium tremens alone. Maintenance of a calm state was accomplished easily with either diazepam, intramuscularly, or paraldehyde, rectally. Adverse reactions occurred in nine patients, all of whom had been treated with paraldehyde; these patients had greater degrees of fever, tachypnea, and tachycardia and required three times longer for initial calming than patients without adverse reactions. Diazepam given under this regimen is a safe and effective sedative for management of combative patients with severe delirium tremens.

Adult↗
PubMed1975

Functional evaluation of the porcine heterograft in the mitral position.

In vivo function of glutaraldehyde-fixed porcine heterografts used for mitral valve replacement was evaluated by cardiac catheterization in 14 of our first 33 patients who have undergone mitral valve replacement with this prosthesis. Diastolic gradients were present in each patient. Average mean diastolic gradient was 6.5 mm Hg for the group, and average end-diastolic gradient was 3.0 mm Hg. Calculated mitral valve orifice areas ranged from 0.92 cm2 to 3.39 cm2, the average being 2.15 cm2. With rapid pacing (heart rate approximately 140), average mean gradient increased by 6 mm Hg. No patient had mitral regurgitation. Two patients had calculated mitral valve areas of 1 cm2 or less; one of these was found at postmortem examination to have thrombus adherent to the ventricular aspect of 2 of the 3 valve leaflets, rendering them immobile.

Adult↗