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Biomedical subjects

H Atlan

Publications and source records attributed to H Atlan.

At least 55 records · Page 3Linked to original sources
PubMed1983

Probabilistic automata as a model for epigenesis of cellular networks.

Probabilistic automata are compared with deterministic ones in simulations of growing networks made of dividing interconnected cells. On examples of chains, wheels and tree-like structures made of large numbers of cells it is shown that the number of necessary states in the initial generating cell automaton is reduced drastically when the automaton is probabilistic rather than deterministic. Since the price being paid is a decrease in the accuracy of the generated network, conditions under which reasonable compromises can be achieved are studied. They depend on the degree of redundancy of the final network (defined from the complexity of a deterministic automaton capable of generating it with maximum accuracy), on the "entropy" of the generating probabilistic automaton, and on the effects of different inputs on its transition probabilities (as measured by its "'capacity" in the sense of Shannon's information theory). The results are used to discuss and make more precise the notion of biological specificity. It is suggested that the weak metaphor of a genetic program, classically used to account for the role of DNA in specific genetic determinations, is replaced by that of inputs to biochemical probabilistic automata.

Biological Evolution↗
PubMed1983

Atrial pacing thallium scintigraphy in the evaluation of coronary artery disease.

A study was undertaken to examine the value of rapid atrial pacing and thallium-201 scintigraphy in the evaluation of ischemic heart disease. Ten subjects with angiographically normal coronary arteries and 31 patients with coronary artery disease were studied. Six of these patients were studied after coronary artery bypass surgery. Coronary ischemia or infarction could be diagnosed from the ECG alone (rest and atrial pacing) in 87% of the patients with a greater than or equal to 50% narrowing of a coronary artery. The ECG and scintiscan (at rest and pacing) together had a sensitivity of 100%. The ECG could not identify the site of stress-induced ischemia. Rapid atrial pacing with scintigraphy identified 91% of those patients with a right coronary artery narrowing (greater than 50%), 85% with a narrowing of the left anterior descending coronary artery, but only 33% with a narrowing of the circumflex coronary artery. The scintiscan correctly identified 40% of arteries with a 50 to 89% narrowing, 75% with a 90 to 99% narrowing and 88% with a complete obstruction. The scintiscan predicted single- and double-vessel disease, but underestimated the number of vessels involved in patients with triple-vessel disease. This technique was also useful in assessing the patency of implanted coronary artery bypass grafts. Rapid atrial pacing is a simple and safe method of inducing ischemia, while thallium scintigraphy shows the site, extent and severity of coronary artery disease.

Adult↗
PubMed1983

Nuclear left ventriculography at rest and during atrial pacing in the evaluation of coronary artery disease.

This study was undertaken to examine the value of rapid atrial pacing (RAP) combined with left-ventricular nuclear (LVN) angiography in the diagnosis of ischemic heart disease. It included 32 patients: 12 normal subjects and 20 with clinical coronary artery disease (CAD) and greater than 50% narrowing of a coronary artery (significant CAD). The ECG and an LVN angiogram (LVNA) were recorded at rest and during graded RAP. In the normal subjects, left-ventricular wall motion was normal at rest and during atrial pacing, but a wall motion abnormality (WMA) appeared in one subject. Left-ventricular ejection fraction (EF) did not change significantly. In the 20 patients with significant CAD, the diagnostic sensitivity of the ECG during RAP was 100% and 90% for the nuclear angiogram (presence or appearance of WMA at rest and during RAP). The mean EF in this group decreased from 0.38 to 0.31. WMA on the LVNA was present in 79% of patients with significant left-anterior descending, in 44% of those with right, and in 33% of those with circumflex coronary artery disease. WMA (at rest or on pacing) occurred in 17% of patients with 50 to 89% narrowing of an artery, in 50% with 90 to 99% narrowing and in 68% with total obstructions. The LVNA (rest and/or RAP) identified patients with significant single-vessel disease, but underestimated the extent of double-and triple-vessel disease. The LVNA at rest and during atrial pacing was an excellent method of evaluating significant coronary artery disease.

Adult↗
PubMed1982

Differentiation between serum stimulation of ouabain-resistant and sensitive Rb influx in quiescent NIH 3T3 cells.

The addition of serum to quiescent NIH 3T3 mouse cell cultures resulted in a 10- to 20-fold increase of Rb influx which was resistant to ouabain, and only a three- to fourfold activation of ouabain-sensitive Rb influx. Stimulation of the ouabain-resistant Rb influx following serum addition reached its maximum within 2 min. The stimulation of ouabain-resistant Rb influx was a result of Vm increase while the Km for Rb was unchanged. Ouabain-resistant Rb influx, after serum addition, was resistant to amiloride and sensitive to ethacrynic acid. Replacing chloride in the medium by NO3-, CO3- and CH3COO- resulted in a drastic decrease in the ouabain-resistant Rb influx. It appeared, therefore, that the ouabain-resistant Rb influx in NIH 3T3 cells was Cl--dependent.

Animals↗
PubMed1981

The use of thallium 201 myocardial imaging to exclude myocardial infarction after dissection in congenital coarctation of the aorta.

The use of a mobile gamma camera with thallium 201 myocardial imaging is described to exclude myocardial infarction in a patient admitted to the coronary care unit in shock and with clinical, enzyme, and ECG changes consistent with infarction. The patient suffered from acute aortic dissection associated with congenital coarctation of the aorta. The myocardial scan excluded transmural myocardial injury.

Adult↗
PubMed1981

Diagnosis of coronary artery disease by multigated radionuclide angiography during right atrial pacing.

Right atrial pacing in conjunction with radionuclide angiography was used as a method to augment gradually myocardial oxygen demand in seven normal subjects and 11 patients with angiographically documented coronary artery disease (CAD). In five of the seven normal subjects the ECG during atrial pacing was normal and falsely pathologic in the two others; in all seven the ejection fraction (64 +/- 8 percent) did not change during the pacing. The atrial pacing was positive in seven of the eleven patients with CAD and falsely negative in four. In comparison, nine of these patients had more than 15 percent reduction in ejection fraction, while only two were regarded as negative. A maximal decrease of 31 percent in the average ejection fraction was observed in CAD patients at a pacing rate of 160/min. Wall motion pattern remained normal in all seven normal subjects, while new wall motion abnormalities developed during the atrial pacing in nine of the 11 CAD patients. We concluded that changes in ejection fraction induced by atrial pacing are sensitive indicators of myocardial ischemia. In patients with CAD, ejection fraction falls during pacing compared with normal subjects in whom ejection fraction remains unchanged.

Adult↗
PubMed1979

Carcinoma of the bronchus with atypical presentation: report of a case.

A 64-year-old man presented with dysphagia due to obstruction of lower third of the esophagus. Esophagoscopy showed narrowing of the esophagus with normal mucosa. Chest X rays were normal, but on lung scan there was no perfusion of the left lung. That patient died of aspiration and on post mortem a carcinoma of the bronchus with abscess formation and perforation into the esophagus was found.

Bronchial Neoplasms↗
PubMed1979

Radionuclide assessment of aortocoronary bypass surgery.

Rest and exercise thallium 201 myocardial scintigraphy and multiple gated radionuclide angiography were correlated with the results of clinical status, exercise electrocardiography, coronary arteriography, and contrast left ventriculography in a series of 12 prospectively studied consecutive patients before and after aortocoronary bypass operation. Patients were divided into two groups based on a comparison between preoperative and postoperative 201T1 scintigrams. Group 1 (6 patients) demonstrated improved or normal postoperative perfusion scintigrams and excellent correlation between the site of a patent graft and the improvement in myocardial perfusion on the postoperative exercise scintigrams. Regional wall motion remained normal in 3 patients and improved in 3. In Group 2 (6 patients) the postoperative 201T1 scintigrams were unchanged or worse. Each patient demonstrated graft occlusion, graft stenosis, distal disease, or a perioperative myocardial infarction. No improvement in regional wall motion occurred in 4 of these 6 patients. Neither the symptomatic response to aortocoronary bypass operation nor the response to exercise testing successfully predicted graft patency.

Adult↗
PubMed1979

[Study of muscle hemodynamics during exercise: Physiological and pathological variations in Xe 133 elimination: A new method of interpretation (author's transl)].

Muscle blood flow measurements are of physiological (and pathological) significance only during effort. For this reason, the authors used Xe 133, which has been known since 1964, to measure regional muscle blood flow after its injection into the muscle, to quantify results during effort (pedalling). Effort is controlled by two measurable parameters: the weight lifted by the pedal and the frequency of movements. Curves showing the reduction in intramuscular Xe 133 levels cannot be mathematically formulated. It is easy, however, to measure their areas and thus define a mean elimination time (Tm) between times T1 and T2, beginning and end of effort, corresponding to activities A1 and A2 such that: formula: (see text). Normal Tm value, measured in 58 normal subjects with variable frequencies and weights lifted is: Tm = 1.70 +/- 0.38 min. The values in 70 patients with arteritis were significantly longer and can be greater than 3.5 min. This objective test could be of value in quintifying the effects of so-called vasodilators, both in patients with arteritis and venous insufficiency.

Humans↗
PubMed1975

Interaction between membrane properties and proteins synthesis in reticulocytes - a two step inhibition of protein synthesis by valinomycin.

In this work we consider the differential effect of Valinomycin used at different concentrations both on the protein synthesis of reticulocytes and on 42K exchange. We demonstrate that there is a two step action of this antibiotic. At 10(-6)M and below the drug has no effect on the 42K exchange, but it stops, however reversibly, protein synthesis. At 10(-5)M the drug has a very sharp action on the 42K exchange and stops protein synthesis in an irreversible way. Ribosomal population checked by two ways, sucrose gradient and direct counting on E.M. sections shows that at low concentrations of Valinomycin (10(-8)M to 10(-6)M) there is no breakdown of the polysomes which can be detected by either one of these methods. On the contrary, after short incubation with 10(-5)M of Valinomycin the breakdown of ribosomes is very clear, as evidenced by sucrose gradient analysis. By direct ribosomes clusters counting on E.M. sections this breakdown is seen only after long incubation.

Animals↗